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Sestepuiereion = : Bi atti. : et : oc een etietretth eersoe teat Ssctteet fisvee : * 5 He 3 - “ 2eteey Sonera - is ereierearty meeps trate Seen ene eee : BS mere gee ae BS Soe Seon Senet are ae as eae = < a= — ca a sox See = Ser - ; S a pers i 2 tee eee = * 5 ae. comets = Biren Set <= ie ae seer Spielmann pepe eee: Se eer lace Spereeemnien st Saha ipa ceeperarn bs Lier HARVARD UNIVERSITY LIBRARY OF THE Museum of Comparative Zoology MUS. COMP. ZOOL. LIBRARY act 261971 HARVARD UNIVERSITY. THE LIFE HISTORY AND ECOLOGY OF THE GRAY WHALE (ESCHRICHTIUS ROBUSTUS) SPECIAL PUBLICATIONS This series, published by the American Society of Mammalogists, has been established for papers of monographic scope concerned with some aspect of the biology of mammals. Correspondence concerning manuscripts to be submitted for publication in the series should be addressed to the Editor for Special Publications, James N. Layne (address below). Copies of special publications may be ordered from the Secretary- treasurer of the Society, Dr. Bryan P. Glass, Department of Zoology, Oklahoma State University, Stillwater, Oklahoma 74074. Price of this issue $5.00 COMMITTEE ON SPECIAL PUBLICATIONS James N. Layne, Editor Archbold Biological Station, Route 2, Box 380, Lake Placid, Florida 33852. J. Knox Jones, JRr., Managing Editor Museum of Natural History, University of Kansas, Lawrence, Kansas 66044. CONSULTING EDITORS FOR THIS ISSUE ROBERT T. ORR WILLIAM E. SCHEVILL Special Publication No. 3 was financed in part by contributions in memory of Paul Martin, Olympia, Washington il THE LIFE HISTORY AND ECOLOGY OF THE GRAY WHALE (ESCHRICHTIUS ROBUSTUS) By DALE W. RICE AND ALLEN A. WOLMAN U. S. FisH AND WILDLIFE SERVICE BUREAU OF COMMERCIAL FISHERIES MARINE MAMMAL BIOLOGICAL LABORATORY SEATTLE, WASHINGTON SPECIAL PUBLICATION NO. 3 THE AMERICAN SOCIETY OF MAMMALOGISTS PuBLisHED 30 Aprit 1971 ill MUS. COMP. ZOOL. LIBRARY oct 261971 HARVARD UNIVERSITY. Library of Congress Catalog Card No. 79-159963 © 1971 by The American Society of Mammalogists FOREWORD HALES long remained among the world’s least known mam- W mals because their large size and oceanic habitat make them difficult to observe and collect. Individual whales cannot be observed repeatedly, therefore knowledge of most aspects of their life history must be deduced from data provided by examining large series of specimens. In the early decades of this century the expansion of the modern whaling industry with its efficient catcher boats and its mechanized shore stations and floating factory ships finally provided biologists the opportunity to undertake large-scale studies of whales. Concern for the future of whale stocks provided an incentive for government support of whale research. As a result, we have now learned more about the biology of the rorquals and the sperm whale than of most other species of wild mammals. Gray whale populations, however, had been depleted before this oppor- tunity for research arose. Although field observations had provided a fairly detailed picture of the distribution, migration, and behavior of the gray whale, many important aspects of the species’ biology— such as age and growth, reproduction, parasites, pathology, and population dynamics—remained virtually unknown. Under the protection afforded by the 1946 International Con- vention for the Regulation of Whaling, the California gray whale stock has increased so much that a resumption of commercial exploitation has been considered. As the dearth of basic data on the biology of the species would handicap any efforts at rational regulation of the harvest, the Bureau of Commercial Fisheries in 1959 initiated a research program that included collecting small series of gray whales under Special Scientific Permits. Beginning in 1966, the number of animals taken annually was increased upon recommendation of the Scientific Committee of the International Whaling Commission, which has reviewed the work each year and provided much encouragement and advice. The data now available reveal the basic features of the ecology of the gray whale and provide a foundation for further studies on its population dynamics. This study would not have been possible without the cooperation of the Del Monte Fishing Company and the Golden Gate Fishing Company of Richmond, California. John Caito and Charles Caito of Del Monte, and Robert Casebeer of Golden Gate placed the Vv facilities and crews of their whaling stations and catcher boats at our disposal for collecting and examining specimens. Kenneth C. Balcomb III, James Ekberg, Bernard Lenheim, and ‘Toshio Kasuya (Ocean Research Institute, University of Tokyo), assisted in the examination of whales at the whaling stations. Margaret Anderson, Lawrence Dickson, Susan D’Vincent, Ekberg, James Houk, Hiroshi Kajimura, Lenheim, Donald Ramsey, Jeffrey Rochin, James Rote, Catherine Short, and Robert Strawn manned the counting stations. Lenheim, Ramsey, and Ancel M. Johnson conducted the transect cruises of the catcher-boat Allen Cody. Balcomb, Kasuya, Thomas J. McIntyre, Masaharu Nishiwaki (Ocean Research Institute), Daniel Lluch B., and Joaquin Arvizu M. (both with the Instituto Nacional de Investigaciones Biologico Pesqueras, Mexico) assisted in the whale-marking cruises. Ford Wilke, Johnson, and Lenheim assisted in the aerial surveys. Francis H. Fay, Arctic Health Research Laboratory, U. S. Public Health Service, provided a sample of the stomach contents of a gray whale killed near St. Lawrence Island, Alaska. Earl L. Bousfield, National Museum of Canada, identified the amphipods, provided information on the habits of benthic invertebrates, and made suggestions concerning the feeding behavior of gray whales. The following individuals identified other stomach contents or parasites: Martin W. Johnson and Margaret D. Knight, Scripps Institution of Oceanography (crab larvae); Josephine F. L. Hart, British Columbia Provincial Museum (cumaceans); Frank Bernard (ascidians and holothurians) and Cyril Berkeley (poly- chaetes and salps), Pacific Biological Station, Fisheries Research Board of Canada; Yuk-maan Leung and John L. Mohr, University of Southern California (cyamids); Kenneth M. Neiland, Alaska Department of Fish and Game (acanthocephalans and campulid trematodes); Robert L. Rausch, Arctic Health Research Laboratory (cestodes and notocotylid trematodes); John T. Davey, Common- wealth Bureau of Helminthology (nematodes). Daniel F. Cowan, Michigan State University, examined a pathological liver specimen. The late Gordon C. Pike, Arctic Biological Station, Fisheries Re- search Board of Canada, made the baleen tracings and allowed us to see his unpublished manuscript on gray whales taken off British Columbia. Unless otherwise noted, individuals mentioned above are present or former employees of the Marine Mammal Biological Laboratory, Bureau of Commercial Fisheries. vi CONTENTS ATED G1 LILY G Gri rot ss ee eS ah ] INomenclatunes | eee ee ie Be 5 Eieldgand laboratory Erocedures) ==" ee 7 @ollectionvol Specimens) a rela @ bsenvatioms) eee. ok es RT ee ee 9 Seasonal wMagmato tye Gy Cle ex =< ese ede ah 1] Gralla tert ae S60 Chk pe arr ie de i pot ail IESG EAM ay SE se a ee ee 19 AUNT GT Cas SLO CRS Sat on eo ee 20 Discussion and Conclusions _------- 21 VOD! GAG LLG UN OY aa a ee 23 SCOMACe GOmMte rs es ee 23 Seasonal Changes in Nutritive Condition —__.-----__- 27 Discussion and Conclusions ____------ 36 JANES INGE CARON Oy pr a 2 ea Ee eee ee 38 PNCCRDELEDIMIN ALO Me sees eee ee a ee 38 (CEO Wither eee CE WE ae NY Wane ene IR os 43 RUDeRtyeanGeSe xual Nia Cutty ees eee 46 physical Miatuidityie se oe ease ise Se ees 49 Discussionwanda Conclusions) = = eee ee 50 Hemale Reproductive Gy cle) esas sae ae eee 52 Ovamtamy' Gry Clejani 52 JE YECELESTO YE TOY Gh eh an Ske SSPE 2 CEE ee Os eee EEE 72 IL GCA nor iia Se Ses ee ee ee eee 86 PANGS (Yi UL'S fee aa eat Pn eee eae 90 Discussion and Conclusions ___.....-------------------- 90 Malemixeproductiver Cycle 222s sn et ne ee 92 WET G'S L1G Sparen ee es ice a sae AE Ee cath 92 JERE O US es Be Ie SI NN Se A el 94 Discussionsands= Conclusions; ee 95 APPT LANE YS eee es ec NR Sn 98 Rarasites and Ee piZOlteSee = es eee ee 100 Ecloparasites ang eB 1ZO1 esp =a ae 100 Endoparasites | 2.22. ee ee 104 IDiKEnKON eraxel (Comelnsions 108 Population: 225222 6t A0 see Oh 109 Present INuimibers! 22 8) ee 109 Population Mvends ¢22.- 2 eee. 2. 112 Density:and Biomass= see 114 RopulationgS tructures = 6. eee 115 ropulationt Dynamics 2.2 2 = ee 117 lDigenssiom srl Comeltieomne 2 118 Bq Oba G1 OMe eee eat Se ee 120 Aboriginal Whaling -...2 2) ee 120 Commercial Whaling 22 Se eee 121 SUMMING ee se 2 ee ee 127 Weiteratune Gite =~ = ae ee ae ie ee ee 132 irl exerts et Se i eh SS 141 Vill INTRODUCTION N February each year, pod after pod of gray whales departs from I the tropical mangrove-fringed lagoons bordering Bahia Mag- dalena, from Laguna Ojo de Liebre in the heart of the Vizcaino Desert, and from other lagoons on the west coast of Baja California. Swimming slowly but steadily, they move northward along the coast; four months later the same whales may be surfacing and blowing among the ice floes of the Chukchi Sea. This migration is the longest performed by any mammal. The gray whale, Eschrichtius robustus (Lilljeborg, 1861), is unique in other ways. It is the sole member of the family Eschrichtiidae and the most primitive surviving baleen whale. In structure it is remarkably similar to the extinct cetotheres, which were ancestral to all living baleen whales. The gray whale became extinct in the North Atlantic only a few centuries ago and is now a relict species confined to neritic waters of the North Pacific Ocean and adjacent waters of the Arctic Ocean (Fig. 1). Because gray whales swim slowly and congregate in near-shore waters, they were easy prey to whalers. By the turn of the century, the species was almost extinct. Since 1946, the eastern Pacific stock has increased under the legal protection afforded by the In- ternational Convention for the Regulation of Whaling to the point that commercial utilization may again be advocated. Gray whales are the only large whales that can regularly be observed in large numbers from shore. Their annual passage along the coast of California is one of the world’s outstanding wildlife spectacles. Public interest in gray whales is increasing, and they have become an important tourist attraction in southern California. More than a million people visit Cabrillo National Monument on Point Loma, San Diego, each year to watch the migrating whales, and several sport-fishing companies in San Diego and San Pedro profitably operate “whale watching” cruises (Rice, 1961). The abundance and accessibility of gray whales in their calving lagoons and along the coast is also attracting a growing number of experimental biologists, and there is cause for concern that, espe- cially on the calving grounds, repeated harassment of gray whales ] Z The Gray Whale PACIFIC: SUMMER GROUNDS AG MIGRATION ROUTE CALVING AREAS PRESENT FORMER re2>) ATLANTIC: SUBFOSSIL FINDS Fic. 1. Distribution of the gray whale. A few gray whales spend the summer in the migration area, especially along the coast of Washington and Oregon. by investigators using small boats or aircraft in attempts to implant telemetering and tracking devices or drug darts may deleteriously affect reproduction (Schevill et al., 1967; American Society of Mam- malogists, 1967). Another threat to the survival of the gray whale is increasing industrial development and boat and ship traffic in the remaining calving lagoons (Marx, 1966). The species has long since been driven from San Diego Bay. The gray whale is clearly an important species from the stand- point of basic scientific interest, esthetic appeal, and economic significance. If commercial exploitation is resumed it should be limited to the sustainable yield so that the scientific and esthetic values of the population may be preserved. A wise management program must be based on a sound knowledge of the biology of the species. Introduction 3 Beginning with Scammon’s (1874) classic account, the gray whale has been the subject of many field observations (for example, Gil- more, 1960a, 1960b; Hubbs, 1959; Hubbs and Hubbs, 1967; Pike, 1962a). As a result, certain facets of its life history and ecology, such as distribution, migrations, and behavior, are better known than for other baleen whales. Only five biologists have had the opportunity to examine series of gray whales. Andrews (1914) studied 23 specimens taken during southward migration and brought into the shore station at Ulsan, Korea, in January and February 1912. In his monograph he presented a historical review of earlier research on the species. Zenkovich (1934a, 1934b, 1937a, 1937b, 1937c) examined 104 gray whales aboard the Soviet floating factory Alewt during the summers of 1933 through 1936. Tomilin (1937) examined 54 specimens aboard the Aleut in August and September 1934. Unfortunately, neither Andrews, Zenkovich, nor Tomilin recorded reproductive information other than measurements of fetuses and condition of mammary glands. Pike (1962a and unpublished data) examined 10 northward migrating gray whales killed under a special scientific permit and brought into the shore station at Coal Harbour, British Columbia, during the first week of April 1953. Zimushko (1969a, 19696) reported on 63 gray whales collected off the Chukotsky Peninsula in the summer and autumn of 1965 and 1966. Few other original data based upon examination of dead gray whales have been published. Gilmore (1960a) and Eberhardt and Norris (1964) examined a number of dead calves at Laguna Ojo de Liebre, Baja California, and Maher (1960) reported on several whales killed by Eskimos at Barrow, Alaska. Statistical data from commercial catches of gray whales in Baja California and in the Bering Sea were analyzed by Risting (1928). Unfortunately, his data are unreliable, because body lengths were estimated rather than measured (see Mackintosh and Wheeler, 1929, p. 273), and therefore the conclusions concerning fetal growth and size at sexual maturity are not valid. Mizue (1951) presented statistical data from gray whale catches in Korea. The Bureau of Commercial Fisheries began a program of research on the species in 1952 under the leadership of Raymond M. Gilmore. During the first five years, the work consisted of field observations 4 The Gray Whale and censuses designed primarily to determine the extent of the calving grounds and to document fluctuations in population size (Gilmore, 1960a, 1960D). In 1958, responsibility for whale research was transferred to the Marine Mammal Biological Laboratory in Seattle, Washington, under the direction of the senior author. Beginning in 1959, small series of gray whales have been periodically collected to obtain basic data on all aspects of the life history and ecology of the species. Particular emphasis has been given to reproduction, growth, age, and population structure. As collections and observations had to be made incidentally to studies on rorquals and sperm whales, they have been mostly confined to the periods when the gray whales were on migration along the coast of California. ‘This report presents the results of the study from 1959 through February 1970. NOMENCLATURE HERE has long been a controversy over the correct scientific ch name of the gray whale. Eschrichtius robustus (Lilljeborg, 1861) is used here for the extinct Atlantic and the living Pacific populations of gray whales following Cederlund (1939). As the data and conclusions of this author have been mostly ignored by sub- sequent workers, none of whom has contributed new evidence to refute his conclusions, it seems desirable to briefly review the nomenclature of the gray whale. The generic name Eschrichtius Gray (1864) is now used by virtually all taxonomists. There are three available species-group names (Hershkovitz, 1966) that require consideration. ‘These are, in order of priority: (1) Balaena gibbosa Erxleben (1777), based on the New England “scrag whale’ described by Dudley (1725); (2) Balaenoptera robusta Lilljeborg (1861), based on subfossil skeletal remains from Gras6, Sweden; and (3) Agaphelus glawcus Cope (1868), based on gray whales from the coast of California. Two questions must be resolved: (1) which of the first two names should be used for the Atlantic population, and (2) is the Pacific population taxonomically distinct from the Atlantic population? The applicability of Erxleben’s name gibbosa to the gray whale depends upon the identity of Dudley's “scrag whale.” Dudley's (1725) brief description reads as follows: ‘The Scrag Whale is near a-kin to the Fin-back, but, instead of a Fin upon his Back, the Ridge of the Afterpart of his Back is scragged with half a Dozen Knobs or Nuckles; he is nearest the right Whale in Figure and for Quantity of Oil; his Bone is white, but won't split.” The lack of a dorsal fin, knobs on the back, and white baleen are diagnostic of the gray whale. It seems improbable that Dudley’s description of the scrag whale is inaccurate because all other large whales described by him are readily recognizable. On the other hand, there are minor discrepancies between Dudley’s description of the scrag whale and the gray whale. For one thing, the oil yield is too high; Scammon (1874) stated that right whales yielded an average of 60 barrels, but that gray whales produced only 20 with a maximum of 60 or 70. For another, the number of knobs on the back is too few; gray 5 6 The Gray Whale whales have nine to 14 knobs behind the dorsal hump, although the posterior knobs are weakly defined. These discrepancies might seem minor were it not for the fact that no other account of early whaling gives any indication of the occurrence of Eschrichtius in the North Atlantic (True, 1904) and the fact that the term “‘scrag” or “scragg’’ was applied to different kinds of whales, particularly small, lean, right whales (Allen, 1916; Eschricht and Reinhardt, 1866). As the identity of Dudley’s scrag whale can never be un- equivocally determined, we agree with Cederlund (1939) and Sche- vill (1952) that Lilljeborg’s specific name should be used for the Atlantic gray whales. The question of the taxonomic relationship of the Pacific and Atlantic gray whale stocks has been investigated by van Deinse and Junge (1937) and Cederlund (1939), who compared the sub- fossil skeletal material from the Atlantic with skeletons and pub- lished data and photographs of Pacific gray whales. These authors found no consistent differences between the Atlantic and Pacific specimens and concluded that these populations were conspecific. FIELD AND LABORATORY PROCEDURES Collection of Specimens total of 316 gray whales was examined. These were collected by the whale catcher boats of the Del Monte and the Golden Gate Fishing Companies, Richmond, California, under special scientific permits issued to the Marine Mammal Biological Labora- tory. The whales were taken along the coast of central California between Half Moon Bay (37°30’ N lat.) and Point Reyes (38°00’ N lat.). The collections were scheduled to provide representative samples for the periods of the southward (December to January) and north- ward (February to April) migrations. The total sample included 180 southbound migrants (85 males, 95 females) and 136 north- bound migrants (81 males, 55 females). Dates of collection, numbers of specimens (in parentheses), and persons who made the examina- tions and measurements are as follows: 23 to 26 February 1959 (two) Rice; 27 to 30 March 1962 (four) Rice; 14 to 25 March 1964 (20) Rice; 22 to 29 March 1966 (26) Rice, Wolman, Balcomb; 14 De- cember 1966 to 19 January 1967 (95) Rice, Wolman, Ekberg, Kasuya; 21 February to 9 March 1967 (30) Wolman, Ekberg; 14 to 25 January 1968 (35) Rice, Wolman; 26 February to 11 March 1968 (24) Wolman, Lenheim; 2 to 11 April 1968 (seven) Rice, Wolman; 20 December 1968 to 9 January 1969 (50) Rice, Lenheim; 2 to 16 March 1969 (23) Wolman, Lenheim. Whales were delivered to the shore stations of the Del Monte and Golden Gate Fishing Companies at Point San Pablo, Richmond, California, where the following data were recorded. MEASUREMENTS AND Counts.—Twenty-two standard external body measure- ments of the first 177 whales collected were made with a steel tape graduated in centimeters. A preliminary analysis revealed that many of these measurements were redundant, imprecise, or useless. Consequently, only nine measurements were made on the last 139 specimens. These were: total length (straight line from tip of snout to notch of flukes); head length (from tip of snout to occipital condyles); tail length (from notch of flukes to anus); maximum girth of body 7 8 The Gray Whale (determined by measuring from the mid-dorsal line to the mid-ventral line on the side of the whale that was uppermost as the animal lay on the flensing deck and multiplying by two); span of flukes; breadth of flukes (from notch to nearest point on leading edge); anterior length of flipper; posterior length of flipper; and maximum width of flipper. Sixteen skulls and one complete skeleton were collected for cranial measurements. Throat grooves, baleen plates, and knobs on the dorsal ridge of the caudal peduncle were counted on most specimens. Bopy WEIcHTs.—Weights of six whales were determined by summing the weight of the meat produced after it had been packaged in 50-pound (22.7 kilogram) bags and the weights of the blubber, viscera, and bones, which were determined by weighing each truckload of raw material on commercial truck scales. One near-term fetus was weighed in pieces. ECTopARASITES AND EpizoirEs.—Abundance, position, and sizes of ectoparasites and epizoites on the body surface and baleen plates were recorded, and a series of each species was collected for identification. Scars.—The nature and position of any scars and wounds were noted. BLUBBER ‘THICKNESS.—Thickness of the blubber was measured (to the nearest half centimeter) at a mid-lateral point on the body opposite the dorsal hump. MamMARy GLANps.—Development of the mammary glands and presence or absence of secretory activity was noted. Maximum thickness of the glands, as determined by inspection, was measured to the nearest half centimeter. A small portion of mammary gland tissue was fixed in 10 per cent formalin or FAA (10 parts formalin, 30 parts isopropanol, 5 parts acetic acid, 55 parts water), sectioned at 10 microns, and stained with hematoxylin and eosin. The develop- ment of glandular tissue subsequently was determined by projecting a randomly selected section about one-quarter of a square centimeter onto a sheet of paper on which 100 dots were arranged in a regular 10 by 10 grid; the number of dots falling within glandular areas was used as an index of the proportion of glandular tissue. Ovarigs.—The ovaries of each female were collected and fixed in 10 per cent formalin. The preserved ovaries were weighed to the nearest hundredth of a kilogram and serially sectioned at half a centimeter on a mechanical meat slicer. Each corpus luteum and corpus albicans revealed through sectioning was measured, to the nearest millimeter, across its greatest diameter and across its maximum diameter at right angles to the greatest diameter; and the two measurements were averaged. The maximum diameter of the largest Graafian follicle also was measured to the nearest millimeter. Urerus.—The diameter of each uterine horn at approximately the middle was measured to the nearest half a centimeter. A sample of the uterine wall was fixed in 10 per cent formalin or FAA, sectioned at 10 microns, and stained with hematoxylin and eosin for histological study. In specimens in which a corpus luteum or recently ovulated follicle was present in either ovary, but there was no obvious indication of pregnancy, the entire uterus was removed from the carcass, each uterine thorn slit open along its entire length, and the Field and Laboratory Procedures 9 surface of the endometrium carefully searched. Embryos and small fetuses were preserved in 10 per cent formalin and their length (crown to tip of tail, with body straightened) and sex recorded. Standard body measurements were made on near-term fetuses and the sex was noted. TEsTEs.—Each testis was weighed to the nearest tenth of a kilogram at the whaling station. A small sample (1 to 2 cubic centimeters) of the largest testis of each whale was taken for microscopic examination from the middle of the gonad about halfway between the surface and center and fixed in FAA, 10 per cent formalin, or Bouin’s solution. Specimens were sectioned at seven microns and stained with hematoxylin and eosin. Mean diameter of the semi- niferous tubules was calculated from measurements with an ocular micrometer of the greatest diameter and maximum diameter at right angles to the greatest diameter of 20 tubules cut in cross section. The presence or absence of fluid in the epididymides and deferent ducts was noted. PENIs.—The length of the extruded penis from the base on the ventral surface to the tip and the circumference at the base were measured to the nearest centimeter. —These measurements could not be made on some males, especially immature individuals, because the penis was not completely extruded. STOMACH CONTENTS.—The quantity of any food remains in the stomach was estimated and a sample preserved for identification. ENDOPARASITES.—The stomach, intestine, liver, kidneys, lungs, peribullary sinuses, and blubber were examined for endoparasites. The intestine was slit Open at three or more randomly selected points, and in the years 1967, 1968, and 1969 the rectum also was opened for inspection. The tips of the liver lobes were examined for evidence of cirrhosis and were sliced to reveal the bile ducts. The kidneys were slit to expose the main urinary duct. VERTEBRAL EpipHysres.—The degree of fusion of the epiphyses of the anterior thoracic vertebrae to their centra was determined by chopping into the ends of the vertebrae with a hatchet to a depth of several centimeters. Ear Piucs.—An attempt was made to collect at least one ear plug from each whale. In a few animals, however, the plug was so soft that it could not be successfully removed. Ear plugs were preserved in 10 per cent formalin. They were bisected longitudinally and gently polished on a whetstone, so that the growth layers could be counted. BALEEN PLATEs.—Several of the longest baleen plates were collected from each whale. Variations in thickness of the plates were recorded graphically by means of an apparatus similar to that used by Ruud (1940). Field Observations Observations on living gray whales were made from coastal look- out points, chartered whale catcher boats, and light aircraft. 10 The Gray Whale CoasTaL STATIONS.—During the southward migration in 1967-68, 1968-69, and 1969-70, coastal lookout stations were established to count migrating whales. One was on Point Loma at San Diego, California (32°40’ N lat.), 130 meters above sea level (Rice, 1961) and is the site where previous counts were made (Gilmore, 1960a, 1960b; Rice, 1961). This station was manned for 52 days (27 December to 16 February) in 1967-68 and for 57 days (20 December to 14 February) in 1968-69. The second station was 2 km. § Yankee Point, Monterey Co., California (36°29' N lat.), 23 meters above sea level and about 100 meters back from the shoreline. This was near the site where a partial count of migrating gray whales was made in 1966-67 (Adams, 1968). We manned this station for 49 days (18 December to 4 February) in 1967-68, 60 days (10 December to 7 February) in 1968-69, and 64 days (8 December to 9 February) in 1969-70. Observations were made continuously from 0700 to 1700 hours (essentially sunrise to sunset) each day. At each station, two observers each worked a 5-hour shift; morning and afternoon shifts were alternated between the two observers. The number of whales, time of passage, estimated distance from shore, and direction of travel were recorded for each group sighted. Wind direction and force, cloud cover, precipitation, and fog were logged throughout the day. VEssELS.—Between 25 January and 9 February 1968, we ran a series of transect cruises between Point Loma and a position west of Tanner and Cortez Banks. A similar transect was run off Yankee Point on 18 January 1968. While the vessel was underway, a constant watch for gray whales and other marine mam- mals was maintained on the bridge. All whales sighted were approached closely enough to ensure positive identification and the number of whales in each pod, the direction of travel, and the position and time of sighting recorded. Observations on gray whales also were made during many cruises conducted for marking rorquals (Balaenopteridae) and sperm whales (Physeter catodon). The area covered included the waters along the coast from Point Reyes, Cali- fornia (38° N lat.), south to Isla Clarion off Colima, Mexico (18° N lat.). The cruises, totaling 15 months, were made mostly between December and April from 1962 to 1969. The calving grounds in Laguna Ojo de Liebre, Laguna Guerrero Negro, Laguna San Ignacio, and Bahia Magdalena, Baja California, were briefly visited. Gray whales were sighted on 304 occasions, and a total of 1045 individuals was recorded. AIRCRAFT.—On 25 and 26 March 1969, an aerial survey was made in both directions along the entire coast beween San Francisco, California (38° N lat.), and Cape Flattery, Washington (48° N lat.). Two aircraft (a Cessna 177 and a Cessna 185) were used, each with two observers in addition to the pilot. The flight path was 0.3 to 2.0 kilometers offshore at an average altitude of 230 meters and air speed of 200 kilometers per hour. When pods of whales were sighted they were often circled at a lower altitude. Data were recorded on a tape recorder. Sighting conditions were optimum, with calm seas and clear skies, throughout the period of the survey. SEASONAL MIGRATORY CYCLE RAY Whales now occur only in the North Pacific Ocean and G adjacent waters of the Arctic Ocean. The species also existed in the North Atlantic until a few centuries ago. There are presently two geographically isolated stocks (Fig. 1): an eastern Pacific stock, which migrates between Baja California and the Bering and Chuk- chi seas, and a western Pacific stock, which migrates between South Korea and the Okhotsk Sea. These may be designated the California stock and the Korean stock, respectively, on the basis of their breed- ing grounds. California Stock SUMMER Grounps.—From late May through October, gray whales occupy the shallow waters of the northern and western Bering Sea, the Chukchi Sea, and the western Beaufort Sea. ‘They are common along the Koryak coast of Siberia from Cape Navarin to Glubokoi Inlet (Berzin and Rovnin, 1966). Farther to the southwest they are rare; a few have been seen as far as Kronotskiy Bay on the Kamchatka Peninsula (Tomilin, 1957) and the Kommandorskiye Islands (Barabash-Nikiforov, 1938; Grebnitskii, 1902). In the Gulf of Anadyr, these whales are abundant along the southwest shore from Cape Navarin to Tymna Lagoon; they have not been seen in the northwestern part of the gulf from the Anadyr Estuary to Cape Kresta (Berzin and Rovnin, 1966). Gray whales are also common along the northeastern shore of the Gulf of Anadyr, from Cape Retkon to Cape Chaplino (Berzin and Rovnin, 1966), around St. Lawrence Island (Ichihara, 1958), around the shores of the Chukotskiy Peninsula as far northwest as Cape Serdtse Kamen’ (Nikulin, 1946), in Kotzebue Sound (Wilke and Fiscus, 1961), and in the Chukchi Sea (north as far as 69° N lat.—Nasu, 1960). A few go westward along the coast as far as Tynkurginpil’gyn Lagoon (Berzin and Rovnin, 1966), and northwestward through the pack ice as far as Wrangel Island (Sleptsov, 1955). Along the Arctic coast of Alaska they are found regularly from Cape Thompson (Pike, 1962a) east to Point Barrow, and a few have Wt 120 The Gray Whale been reported by Eskimos along the shores of the Beaufort Sea as far east as Barter Island (Maher, 1960). To the southeast, there are few records of gray whales. One was found stranded at Scammon Bay, south of the Yukon Delta, in September (Fay, in Pike, 1962a). There is only one published record of gray whales from the Pribilof Islands (Gilmore, 19606), but several were seen around St. George Island in the summers of 1965 and 1968 by C. H. Fiscus, A. M. Johnson, and V. B. Scheffer (personal communication). Gray whale remains have been found on St. Matthew Island (Pike, 1962a), and C. H. Fiscus (personal communication) saw four gray whales in Sarichef Strait between St. Matthew Island and Hall Island on 3 August 1960. Not all gray whales migrate to the Arctic in the summer. A few remain scattered along the west coast of North America. Pike and MacAskie (1969) reported several near Langara, Queen Charlotte Islands, British Columbia, in late August and early September of 1959 and 1960, and a young male stranded near Ucluelet, Van- couver Island, on 16 August 1966. Some were seen near Lapush, Washington, in June and July 1961 by C. Munsen (personal com- munication) and in July 1967 by the junior author. A few were seen near Kalaloch, Washington, in July 1968, by A. M. Johnson (personal communication). Fiscus (personal communication) saw one near Cannon Beach, Oregon, in July 1969. Gilmore (1960a) reported that a few regularly spend the summer in the vicinity of St. George Reef and Pelican Bay in northern California and southern Oregon. Whalers working off San Francisco occasionally see gray whales during the summer. L. Newton (personal com- munication), captain of the catcher boat “Lynnann,” saw a few near the Farallon Islands, California, throughout the summer of 1964; they remained until late September or early October. K. C. Balcomb saw a small gray whale in Bahia Magdalena, Baja Cali- fornia, on 11 June 1965, during one of our whale marking cruises aboard the catcher boat “Sioux City.” The northern boundary of the known summer range of the gray whale corresponds closely with the southern edge of the zone of close pack ice during the period 1 to 15 September (U. S. Navy Hydrographic Office, 1958). Close pack ice may limit their move- ments. Scammon (1874) and Sleptsov (1955) have reported seeing Seasonal Migratory Cycle 13 gray whales in broken pack ice. Gray whales do not arrive at Point Hope or at Barrow, Alaska, until most of the ice has gone out, long after the bowhead whales have arrived. As few observers experienced in identifying whales enter the close pack ice in ships or fly over it in the summer, the extent to which gray whales penetrate the pack ice is unknown. In the western Bering Sea, gray whales are confined to coastal waters, their seaward range being delimited by the edge of the Continental Shelf. They have never been found in the deep waters of the southwestern Bering Sea. Their feeding habits (see section on food and feeding) ap- parently restrict them to shallow water. Although most of the eastern Bering Sea is shallow, the scarcity of gray whales there is believed to be the result of a low biomass of benthos, 55 grams per square meter, compared with 200 to 900 grams per square meter in the northwestern region (Berzin and Rovnin, 1966; Neiman, 1963). Micrations.—Pike (1962a) summarized all published’ informa- tion on the migration route of the California population and presented significant new data. There are few observations on ; southward-migrating whales in the northern part of their range. From October through January, they probably move down the eastern side of the Bering Sea, go through Unimak Pass, and then follow the coast to Baja California. A few go around Cabo San ' Lucas and cross to the eastern side of the Gulf of California. From late February to June, the northward migration of males and females without calves, which is much better documented, follows the reverse route. Our observations during whale marking cruises off California and Baja California show that the majority of gray whales migrate within a few kilometers of shore when passing points, headlands, and sectors of coastline where the Continental Shelf is narrow and _ there are no off-lying islands. Many tend to take the most direct route, however, when crossing bights and indentations of the coast- line. For example, many southbound whales, after passing Point Conception (34°27’ N lat.), head southeast through the Channel Islands, passing as much as 200 kilometers offshore from the main- land of southern California (Rice, 1965). Some gray whales make a similar offshore passage from about Punta Baja (29°57’ N lat.) 14 The Gray Whale to Isla Cedros (28°22’ N lat.), Baja California, thus avoiding the long journey around the shores of Bahia Sebastian Vizcaino. Quan- titative data on offshore migration are presented in the chapter on populations. The route taken by females with calves during the spring mi- gration is unknown. During this study, the catcher-boat crews saw only one female with a calf—near Point Reyes on 15 March 1969. From 1959 through 1967, we collected no gray whales later than 30 March, and during that time we thought females with calves moved north later in the season. Therefore, in 1968 we hunted gray whales until 25 April, 14 days after the last whale was taken, and had one boat searching exclusively for females with calves from 2 to 25 April. Each year from 1956 through 1968, the regular sperm whaling season opened on | April and the baleen whaling season opened on 1 May (1956-59) or 16 April (1960-68). During these years, the whalers never saw a gray whale accompanied by a calf. Shore-based whalers working from San Simeon, California, in the 1880’s likewise told Townsend (1887) that they never en- countered females with calves. On whale marking cruises in 1965, 1966, 1967, and 1969, we traveled north during late February, March, and early April, by which time most females with calves had already left the calving lagoons. We put in at many points along the coast between Cabo San Lucas (23° N lat.), Baja California, and San Francisco (38° N lat.), California, but never encountered a female accompanied by a calf, although we saw many northward-migrating gray whales. During the transect cruises, we saw two females with calves on 10 February 1968 (at 32°48’ N and 118°08’ W, heading west-northwest near San Clemente Island). During the aerial surveys between San Francisco, California, and Cape Flattery, Washington, on 25 and 26 March 1969, no females with calves were identified among 816 gray whales sighted. Morejohn (1968) reported a female with a calf at Moss Landing, northeast of Monterey, California, on 2 May 1967. Gray whales observed on migration are usually swimming steadily and continuously in a constant direction on a course parallel to the shore. They surface regularly about every 3 to 5 minutes to blow three to five times. When out of sight of land, Seasonal Migratory Cycle 15 they usually travel in a straight line. General observations indicate that the usual swimming speed is about 7 to 9 kilometers per hour (4 to 5 knots). Wyrick (1954) followed four separate gray whales migrating south past San Diego, California, for a total of more than 5 hours; their average speed was 8.5 kilometers per hour (4.6 knots). Cummings et al. (1968) tracked nine lone whales (some in daytime, others at night), over distances less than 1.7 kilometers and found the average speed to be 10.2 kilometers per hour (5.5 knots). There was no consistent hourly variation in the number of gray whales migrating south past the counting stations, contrary to the opinion of Ramsey (1968). This lack of variation indicates that gray whales, on the average, maintain a constant speed throughout daylight hours. There are few observations to show how fast gray whales travel at night. Unlike sperm whales, baleen whales are rarely, if ever, seen resting at the surface. Since they must rise to the surface regularly every few minutes to breathe, they must continue to swim at least slowly during hours of darkness. In polar regions during the summer when daylight is continuous, baleen whales appear to remain active continuously. Cummings et al. (1968) used an array of hydrophones mounted on the sea bottom off San Diego to track migrating gray whales. VY They reported the following: “Gray whales were soniferous day / and night. One hundred twenty-four signals were recorded from at least 61 whales between 1800 and 0600 h, compared with 107 signals recorded from at least 157 whales between 0600 and 1800 h. All whales seen or heard at night apparently were migrating south- ward, and there was no evidence of the popular notion that gray whales characteristically stopped migrating at night to rest or to sleep.7 The average speed of gray whales along their entire migration route, calculated from dates of peak passage at various points along the coast, is about 185 kilometers per day, or 7.7 kilometers per hour, on the southward migration and half as fast on the north- ward migration (Pike, 1962a). If their average speed during the 10 hours of daylight is 8.5 kilometers per hour, they cover 85 kilometers; to travel the remaining 100 kilometers during the 14 16 The Gray Whale SOUTHBOUND NORTHBOUND _ ll Lik ADULT 17 3] ae id ——_— > ADULT Oo SS SS SS SS SS SS SS SS FSS SSS S55 > aa LATE PREGNANT POST- PARTUM eae > RECENTLY OVULATED SSS EARLY PREGNANT RFS =_ a5 ANESTROUS IMMATURE go pa et eT SSS SS >> -->m _om sh SHH, Ff 8 Fic. 2. Collection dates of gray whales, according to sex, age, and reproductive status. Each square represents one animal. hours of darkness, they must average 7.1 kilometers per hour, or 92 per cent of their speed during daylight. During migration, there is a partial temporal segregation of gray whales according to sex, age, and reproductive status. This is evident from Fig. 2 in which the collection date of each whale is plotted according to sex, maturity, and reproductive status. ‘These data cannot be regarded as strictly representative, however, because the collecting effort was not the same throughout the season. It must be kept in mind also that the gunners doubtless tended to select the larger animals, even though we imposed no size limita- tions. ‘This tends to bias the sample in favor of mature animals and females, especially those in late pregnancy. The mean and extreme dates of passage for each class (Table 1), however, should be fairly reliable. In general, in both the southward and the northward migration, females migrate earlier than males and adults migrate earlier than sexually immature animals. The vanguard of the southward mi- gration from mid-December to the first of January is composed predominantly of females carrying near-term fetuses. The late- pregnant females are followed by adult females that have recently Seasonal Migratory Cycle 17 TABLE 1 MEAN PAssAGE DATES OF MIGRATING GRAY WHALES OFF CENTRAL CALIFORNIA (38° N Lat.) CLAssIFIED ACCORDING TO SEX, AGE, AND REPRODUCTIVE STATUS. Mean passage date Days Category Southbound Northbound elapsed Late pregnant (southbound); postpartum females (northbound) 31 December 26 March 85 Recently ovulated (southbound); early pregnant females (northbound) 5 January 28 February 54 Recently ovulated (southbound); metestrous and anestrous females (northbound) 5 January 14 March 68 Immature females 1] January 21 March 69 Adult males 9 January 12 March 62 Immature males 15 January 23 March 67 ovulated but have no macroscopically visible conceptus in the uterus; most of these females presumably weaned a calf a few months previously. “The number of females in this class that were collected was fewer than expected. This probably resulted from gunner selection, although there also is a possibility that such females travel farther offshore. Next to pass are the immature females and, at about the same time, the adult males. Last to pass are the immature males. During the northward migration, the first to pass are the newly pregnant females, which comprised the recently ovulated class of the preceding southward migration. Most of them pass within a - limited period of about 15 days. We took them only between 21 February and 7 March in 1967, and between 26 February and 10 March in 1968. None was taken in 1969, when collecting did not commence until 2 March. The peak passage of adult males occurs more than 2 weeks later than that of the pregnant females. Adult males are followed by a few anestrous females that have failed to conceive. Immature whales of both sexes are the last to pass. Only two postpartum females were collected, both in late March. Neither was lactating; obviously their calves were stillborn or were lost shortly after birth. Migrating gray whales travel singly or in pods of up to 16 individuals. In the course of the southward migration past Cali- 18 The Gray Whale YANKEE POINT POINT LOMA - 22-31 DEC —} Te 20 JAN 21-30 JAN = 31 JAN- 9 FEB 10-19 FEB 5 10 15 5 SRG Mae GROUP SIZE Fic. 3. Frequency distribution of group size of gray whales passing Yankee Point and Point Loma, by 10-day periods, during the southward migrations of 1967-68 and 1968-69. Solid bars indicate the number of groups, open bars the number of whales. fornia, there are marked changes in the sizes of the groups (Fig. 3). During the early part of the migration, single whales (presumably mostly females carrying near-term fetuses) predominate, and almost no whales are in groups of more than six. During the Seasonal Migratory Cycle 19 remainder of the migration, groups of two predominate. Most of the larger groups pass in the middle of the season, and towards the end of the season no groups contain more than five whales. WINTER Grounps.—In January and February most gray whales of the eastern Pacific population are in warm temperate or tropical waters on the west coast of Baja California and the southern Gulf of California. Our southernmost sighting was at Punta Mita, Bahia de Banderas, Jalisco (20°45’ N, 105°34’ W) on 17 February 1965. Gilmore (1960a) reported alleged sightings of gray whales at Isla Guadalupe and at Isla Clarion; we have seen none there nor anywhere else far off the coast of Mexico. Most calves, as far as is known, are born in certain shallow lagoons. The six known calving areas, charted in detail by Gilmore (1960a), are as follows: California and west coast of Baja California— San Diego Bay (no longer occupied), Laguna Ojo de Liebre (“Scam- mon’s Lagoon’) and the adjacent Laguna Guerrero Negro, Laguna San Ignacio, and Bahia Magdalena and adjacent waters (including Bahia Almejas, Canal San Carlos, Estero Soledad, Estero Santo Domingo, Estero Las Animas); eastern shore of Gulf of California— open coast south of Yavaros, Sonora (see Gilmore et al., 1967), and Bahia Reforma, Sinaloa. Korean Stock There is little information on the distribution of the Korean stock. No gray whales have been reported in recent years in either the Okhotsk Sea or the Sea of Japan, according to (personal com- munications) V. A. Arseniev and M. V. Ivashin of the All-Union Research Institute for Marine Fisheries and Oceanography, Mos- cow; H. Omura of the Whales Research Institute, Tokyo; and M. Nishiwaki of the Ocean Research Institute, Tokyo. SUMMER GrouNps.—Gray whales occupy, or at least formerly occupied, the northern Okhotsk Sea. They penetrated as far north as Penzhinskaya Bay (Krasheninnikov, 1755), and ranged southward as far as Akademii and Sakhalinskiy gulfs on the west (Sleptsov, 1955), and the mouth of the Kikhchik River on the east (Ditmar, 1890). 20 The Gray Whale Micrations.—The migration route of the Korean stock of gray whales lay along the mainland coast of eastern Asia from Tatarskiy Strait to South Korea. Southbound whales passed Ulsan, South Korea, from late November to late January, and northbound whales passed there from the middle of March to the middle of May (Andrews, 1914). All the whales apparently passed through Tatar- skiy Strait, as none was ever seen in La Perouse Strait between northern Hokkaido and southern Sakhalin (Mizue, 1951). WINTER GrRounDs.—The channels, inlets, and bays along the southern coast of South Korea are believed to have been the winter calving grounds of the western Pacific gray whales. According to Andrews (1914): “In November and December, when the females are taken, almost every individual will be found to be carrying young nearly ready for birth. As these would necessarily be de- livered within two or three weeks after passing Ulsan, the birth must occur in the bays among the numerous islands at the extreme southern end of the peninsula. Indeed Captain H. G. Melsom, who has hunted gray whales for 15 years along the Korea coast, has often observed them in this vicinity, but because of the abun- dance of other and more valuable species, they are not killed at this time by the Japanese.”’ Atlantic Stocks Subfossil gray whale bones have been found at five localities along the coast of northwestern Europe: Pentuan, Cornwall, and Torquay, Devonshire, England, on the English Channel; IJmuiden and Wieringermeer Polder in the Netherlands; and on the Island of Gras, Sweden, in the northern Baltic (van Deinse and Junge, 1937). The most recent bones are those from IJmuiden, which date from about A.D. 500. There are no historical records of gray whales in the eastern North Atlantic. The summer grounds of the eastern Atlantic gray whales probably were in the Baltic Sea, where Ampelisca macrocephala (the predominant food of the California stock in the Bering Sea) is abundant (Kanneworff, 1965). Their winter grounds were perhaps along the Atlantic or Mediterranean coasts of south- western Europe or northwestern Africa. Seasonal Migratory Cycle 21 Discussion and Conclusions In their annual migrations between summer feeding grounds in Arctic waters and winter breeding grounds in subtropical waters, gray whales may travel more than 18,000 kilometers each year, a distance exceeding that traveled by any other baleen whale. This extensive migration, spanning 50 degrees of latitude, exposes them to a broad range of environmental conditions. Sea surface tempera- tures on the summer grounds range from about 8° centigrade down to 0° or slighly less in the pack ice. On the winter grounds, temperatures range from about 18° centigrade at the latitude of Laguna Ojo de Liebre to 22° off Cabo San Lucas. In mid- summer most gray whales experience more than 22 hours of light each day, and those north of the Arctic Circle experience continuous daylight for several weeks. As the whales migrate southward, they are subjected to a rapidly decreasing photoperiod, which reaches a minimum of less than 8 hours in early December. Day length increases slowly during the remainder of the southward migration and while the whales are on the winter grounds, and then increases rapidly as the animals move north in the spring. The variable photoperiods to which the species is exposed may be an important proximate factor in regulating gonadal development. There is no evidence to suggest that gray whales slow down at night while migrating southward. The length of their migration route, and their relatively slow swimming speed, makes it necessary for them to travel almost continuously at night as well as day. The reasons for this long migration become apparent when the food habits of the gray whale are considered. In summer, the species requires areas of shallow water with an abundant benthos. In the North Pacific, large areas with such conditions are found only in parts of the Bering Sea and adjacent waters of the Arctic Ocean, and in the northern Okhotsk Sea. For almost half the year, the ice cover on these summer grounds cuts off the whales’ major food supply and forces them to migrate. Because they cannot feed much during the winter, it is necessary that they seek warmer waters to minimize energy requirements, particularly for the newborn calves. During the winter, the eastern North Pacific from California north is cold (less than 15° centigrade) and is subject to frequent storms with northwest winds that cause aD The Gray Whale heavy surf along the coast. The lagoons of Baja California are the nearest areas of warm, shallow, protected waters suitable for calving. Females ready to bear a calf arrive on the winter grounds earlier and spend more time there than females that have recently mated. Apparently, calves must remain in warm protected waters until they have grown sufficiently to face the rigors of the long north- ward migration. The movements of females with calves after they leave the breeding lagoons are unknown. Unlike the other members of the population, they must travel farther offshore. Pregnant females apparently are the first to arrive on the sum- mer feeding grounds and spend more time there than lactating females. This is also true of fin whales, Balaenoptera physalus (Mackintosh, 1965), and humpback whales, Megaptera novaeangliae (Dawbin, 1966), and is no doubt related to the need of pregnant females to acquire more fat reserves (see discussion beyond of sea- sonal changes in nutritive condition). FOOD AND FEEDING Stomach Contents UMMER.—Few data are available on the stomach contents of gray whales killed on the summer grounds. Zenkovich (1934a, 1934b, 1937c) and Tomilin (1937) examined 104 and 54 stomachs, respectively, of whales taken in the Bering and Chukchi Seas from August to October. They did not publish quantitative data, but reported finding mostly gammaridean amphipods, of which were listed the following forms: Family Ampeliscidae—Ampelisca macro- cephala; family Aoridae—Lembos arcticus; family Lysianassidae— Anonyx nugax and an unidentified species; family Haustoriidae— Pontoporeia femorata; family Eusiridae—Eusirus sp.; family Atylidae —Atylus sp.; family Gammaridae—unidentified species. Ampelisca macrocephala predominated in the stomachs of whales killed in the Chukchi Sea and northern Bering Sea, whereas a species of Atylidae, apparently Atylus carinatus, predominated in those from along the coast between Natal’inskiy Bay and Cape Navarin. In addition to amphipods, several stomachs contained a few bottom-dwelling isopods, mysids (Mysis oculata), mollusks (Buccinum sp.), polychaetes (Travisia forbesi), and hydroids (Ser- tulariidae). Pike (1962a) examined samples of the stomach contents of two gray whales killed by Eskimos off St. Lawrence Island in May and June. He found mostly the amphipods Ampelisca macrocephala and A. eschrichti, and a few Anonyx nugax; other items recorded were decapod crustaceans (including Chionoecetes bairdi, Hyas coarcticus, and Liocyma fluctuosa), cumaceans, polychaete (Pectinaria sp.) tubes, gastropods, and ascidians. We examined a sample (collected by F. H. Fay) of the stomach contents of an immature female gray whale killed by Eskimos about 9 kilometers southwest of the village of Gambell, St. Lawrence Island, Alaska, in water about 30 meters deep. ‘The sample of about 1 liter was a composite of random samples from several parts of the total contents of the stomach. More than 95 per cent of the sample consisted of gammaridean amphipods, ranging from less 23 2s The Gray Whale than 6 to more than 25 millimeters in length. A few other inverte- brates were present. Following is a complete list of the species identified. Classification of amphipods at the level of family and genus follows Barnard (1969). The numbers of each species of amphipod identified are given in parentheses, but they do not necessarily represent the proportion of each species in the total sample. Cass CRUSTACEA Order AMPHIPODA Family Lysianassidae Anonyx sp. (16) Hippomedon ?minusculus (1) Hippomedon cf. abyssi (4) Orchomene minuta (12) Family Phoxocephalidae Paraphoxus ?milleri (3) Family Ampeliscidae Ampelisca macrocephala (ca. 85) Ampelisca sp. (fragments) Family Pleustidae Pleustes sp. (2) Family Oedicerotidae Acanthostepheia malmgreni (6) Family Atylidae Atylus bruggeni (1) Family Isaeidae Protomedeia grandimana (1) Family Ischyroceridae Ischyrocerus latipes (1) Family Podoceridae Dulichia cf. knipowitschi (1) Order CUMACEA Diastylis bidentata CLAss POLYCHAETA Unidentified tube CLAss HOLOTHUROIDEA Unidentified holothurian CLAss ‘TUNICATA Order ASCIDIACEA ? Phallusia sp. Order THALIACEA ? Salps (attached to polychaete tube) Food and Feeding 25 All of the organisms found in the stomachs of gray whales killed on the Arctic summer grounds are typically infaunal benthic species, that is, they burrow or live buried in the bottom sediments. Ampelisca macrocephala, the species most commonly eaten, is a large amphipod about 25 millimeters long. A study of its life history has been published by Kanneworff (1965). In the Bering and Chukchi Seas, A. macrocephala occurs mainly on sandy bot- toms at depths of 5 to 300 meters (Gur’yanova, 1955). Most of the amphipods in our sample were adult females, which are rarely found above the substratum during the day, although they form an appreciable part of the planktonic population at night; males alone tend to be pelagic during the day (E. L. Bousfield, personal communication). In addition to food items, there was a considerable amount of fine gray sand or silt mixed with the stomach contents of the whale from St. Lawrence Island that we examined. Such extraneous material has also been recorded by other authors. Pike (1962a) found sand, silt, and bits of wood in the two samples he examined, and Zenkovich (1937a) found quantities of pebbles, as much as “2-3 pails,” in many stomachs. Tomilin (1937) also reported find- ing silt, pebbles, and a large cobblestone, in addition to kelp leaves. In northern California, Howell and Huey (1930) found a quantity of Euphausia pacifica in the baleen of a gray whale killed on 21 July 1926; they did not examine the stomach. This euphausiid is the chief food of rorquals in the waters off California. The occasional infestation of gray whales with parasites that probably require fishes as intermediate hosts (see discussion of parasites in a later chapter) suggests that they sometimes eat fish. Durinc Micration.—Our data confirm the reports by other authors (Andrews, 1914; Pike, 1962a; Scammon, 1874) that the stomachs of migrating gray whales are almost invariably empty. Stomachs of all 180 southbound migrants and those of 134 of the 136 northbound migrants examined contained no traces of food, and the intestines contained only small amounts of a thick green- ish fluid, apparently bile and mucosal secretions. One of the two specimens containing food was an anestrous female taken on 20 March 1964. Its stomach contained about 20 liters of the zoea stage larvae of the littoral crab Pachycheles rudis (Anomura, 26 The Gray Whale Porcellanidae) and a few brachyuran zoeae, probably of the genus Fabia (Brachyura, Pinnotheridae). The other animal was an im- mature female taken on 11 April 1968. Its stomach contained about 50 liters of the zoea stage larvae of a pinnotherid crab, probably the same species found in the preceding specimen, and a few scattered porcellanid zoeae, which were in too poor condition to identify further. Migrating whales sometimes have gravel and other miscellaneous items in their stomachs. We found almost a kilogram of gravel in the stomach of one southbound, recently-ovulated female; mixed with the gravel were numerous ascidian tunics, fragments of hydroid stems and polychaete worm tubes, a few gastropod opercula, one pelecypod shell, and two tiny fragments of waterlogged wood. A late pregnant female had several liters of hydroid stems and a few polychaete tubes in her stomach, but no gravel or sand. The stomachs of two immature males collected during the northward migration each contained about 10 kilograms of gravel. The stomach of an early pregnant female contained about 100 kilograms of gravel in which were a few polychaete tubes, hydroid stems, and a small bit of waterlogged wood. A northbound immature female contained about 50 kilograms of sand and silt. ‘The stomachs of several other animals contained traces of sand and gravel. Andrews (1914) found pebbles in the stomachs of two southbound migrants taken off Korea. Gravel and sand are probably ingested accidentally while the whale is feeding. WINTER.—Scammon (1874) appears to have been the only person to examine the stomachs of animals taken in the calving lagoons. He examined “several’’ and found no food—only a small quantity of vegetable matter that was no doubt accidentally ingested. According to Matthews (1932), Norwegian whalers found gray whales feeding on the “red crab,” Plewroncodes planipes (Anomura, Galatheidae), at Bahia Magdalena, Baja California, in 1926. He did not indicate whether this was ascertained by actual examination of stomachs. The red crab exists in both a benthic and pelagic phase (Boyd, 1967) and at times is extremely abundant off the western coast of central and southern Baja California. We found red crabs so abundant in Bahia Magdalena on the night of 6 February 1965 that they formed a continuous, tightly packed layer Food and Feeding ill on the surface, evidently attracted by the lights of our anchored vessel. On 1 March 1967, we passed through many dense shoals of these crabs, each a few meters wide and up to half a kilometer long or longer, just inside the 180-meter isobath about 45 km. SW Punta Abreojos. However, we never saw gray whales that appeared to be feeding on red crabs. Plewroncodes apparently does not occur in Laguna Ojo de Liebre. According to Matthews (1932), Nor- wegian whalers noticed that the blubber oil obtained from “sei” whales (Balaenoptera borealis or B. edeni) on the Mexican coast was yellowish; he suggested that this was due to their feeding on Pleuroncodes. We have found that the blubber of gray whales is often yellow or orange during both the southward and northward migrations. A similar variation in blubber color was noted by Andrews (1914) in northbound Korean whales and by Zenkovich (1934a) in summer-taken specimens from the Bering Sea. There is only one report on the stomach contents of gray whales on or near the wintering grounds in the western Pacific (Mizue, 1951). ‘Iwo individuals killed in the northern waters of the Yellow Sea in May 1922 contained Nephrops thomsoni, a small benthic anomuran decapod similar to Pleuwroncodes. ‘These whales were taken unusually late in the spring and probably somewhat outside the normal range. Seasonal Changes in Nutritive Condition During southward migration, gray whales are fat, whereas dur- ing northward migration they are much thinner. Quantitative information on nutritive condition is provided by body weight, blubber thickness, and oil yield. Bopy WEIGHT.—We calculated and compared body weights of gray whales on southward and northward migrations, and attempted to estimate metabolic rate to determine if the difference between the two periods is sufficient to account for energy requirements in winter. Weights and lengths of nine gray whales are given in Table 2. To calculate weights of other whales that could not be weighed, we used the formula W = aLG?, where W = weight in kilograms, L = length in meters, and G = maximum girth in meters. The 28 The Gray Whale IMMATURE = 68'I1 ia 060 LO 0'06 660 + LF'6 96:0 + PS IT G6 (que. 10d) pesderya (quo. sad) WN WS WN Avp sed sAvp jo SSO] SSOT JYSIOM awaqumu 7YBIOM (AS = uvout) 7q FO on[VA uvoyy Uva [ROL raquinn, (INN) winj1edysod (INS) Queusaid ae] (INN) shonsoue ‘S) parepnao ApTUIIay (WN) Jueusaid ATAva SINS) parepNAo ATIUWIIOY, (savulay) NPV (sayeuay) at eULwy (sojvm) Inpy (soyet) ange wUwUy snjejs aArjonporda.t puv ‘xes ‘asy ‘(NN) NOLLVUSI, (UVMHON GNV (JAS) NOLLVHDIP, @IVMHLNOG NAAMLAG SHIVH MA AVA) AO SSOTT LOTTA 6 ATAVL 34 The Gray Whale of tidal air may be estimated at 80 per cent, as Irving et al. (1941) found in Tursiops truncatus, giving an estimate of 560 liters per breath. Oxygen utilization may be estimated at 10 per cent of tidal volume, based on Tursiops (Irving et al., 1941), giving an estimate of 56 liters of oxygen per breath. As a gray whale breathes about once a minute, it uses an estimated 80,640 liters of oxygen per day, or 0.17 cubic centimeters per gram per hour. Since 1.99 liters of oxygen are required to oxidize 1 gram of fat (Bishop, 1950), 80,640 liters is sufficient to oxidize 41 kilograms or 0.20 per cent of the animal’s body weight per day. Oxidation of 1 gram of fat produces 9.54 kilocalories (Bishop, 1950), so the whale will produce about 3.8 by 10° kilocalories per day or 19 kilocalories per kilogram per day. ‘This estimate of the meta- bolic rate is lower, on the basis of kilocalories per kilogram of body weight, than that of smaller mammals, but lies above Benedict’s (1938) “mouse-to-elephant” curve. His curve gives a value of 70 times 20,000°-75, or about 1.2 times 10° kilocalories per day for a 20-ton animal. It should be noted, however, that our estimate cannot be considered a basal rate, because it is based on the respiration rate of an actively swimming animal. In some other mammals, the energy expended over a 24-hour period ranges between 1.3 and 4.0 times the basal rate, and for animals performing a moderate amount of work the average is approximately three times the basal rate (Brody, 1945). On this basis, the metabolic rates of large whales do not appear to be far above the “mouse-to-elephant” curve (see Kanwisher and Sundnes, 1966). BLUBBER THICKNESS.—The thickness of the blubber has long been about the only measurement that has been used as an indicator of the nutritive condition of large whales (Slijper, 1954). Blubber thickness of gray whales was not correlated with body length, so we have used absolute measurements in our analysis. All sex and age classes of gray whales showed a slight decrease in blubber thick- ness between the southward and northward migration (Table 4), but this decrease was not statistically significant (P > .05) for any class. Blubber thickness is less sensitive than girth as an indicator of the nutritive condition of gray whales. The reduction of girth reduces body surface area, and thus tends to make the blubber Food and Feeding 35 TABLE 4 COMPARISONS OF BLUBBER THICKNESS OF GRAY WHALES DURING MIGRATION PERIODS. Age, sex, and Blubber thickness (cm) reproductive ee status Number Mean + SE Range Immature males Southward : 17 12.8+ 0.3 10.5-15.0 Northward 25 12.6=0.3 9.5-16.0 Adult males Southward 66 13.5 = 0.2 9.5-17.5 Northward 44 12.8+0.2 10.5-16.0 Immature females Southward 11 14.4+04 12.5-16.5 Northward 23 128+0.4 8.0-17.0 Adult females Southward (recently ovulated) 27 15.7+0.4 10.5-20.0 Northward (early pregnant) 22 15.2+04 10.0-18.5 Northward (anestrous) 8 13.3 =1.1 9.5-19.0 Southward (late pregnant) 53 15.7+0.2 12.5-19.0 Northward (postpartum) 2 14.5 10.0—-19.0 thicker. It was apparent to us while examining the viscera of southbound and northbound migrants that weight loss is due more to utilization of body fat than to utilization of blubber. Om YreLtp.—The oil yield of the carcass is probably the most reliable indicator of nutritive condition, but such data are not available for individual gray whales. The mean estimated body weight and mean yields of oil, meal, and meat from southbound whales were two and one-half to three times those of northbound animals (TVable 5). The southbound sample consisted mostly of adult females carrying near-term fetuses; the northbound sample consisted mostly of males, and included many immature animals. The cubic mean length of the southbound whales was 12.62 meters, whereas that of the northbound animals was 11.23 meters. Quan- tities of each product were also affected by the relative amount of meat salvaged from each carcass. ‘The remainder of each carcass was rendered for oil and meal. The difference between calculated body weight and total weight of oil, meal, and meat may be at- tributed to water loss during rendering of the oil and drying of the meal. Inasmuch as the samples are heterogeneous as regards 36 The Gray Whale TABLE 5 MEAN WEIGHTs OF O1rL, MEAL, AND MEAT PRODUCED FROM GRAY WHALES TAKEN IN SOUTHWARD AND NORTHWARD MIGRATIONS. MEAN CALCULATED BoDY WEIGHT OF 26 SOUTHBOUND WHALES WAS 31,662 KILOGRAMS AND THAT OF THE 26 NORTH- BOUND WHALES WAS 12,861 KILOGRAMS. Southward migration Northward migration Products Kilograms Per cent Kilograms Per cent Oil 7,559 39.6 2,496 38.1 Meal 6,834 35.8 2,520 38.5 Meat 4,689 24.6 1,533 23.4 Total 19,082 100.0 6,549 100.0 sex, age, and reproductive status, they are not directly comparable, but they do show the great difference in body weight between south- bound and northbound migrants. The ratio of oil to meal also indicates a moderate decrease in relative oil yield between the southward and northward migrations. Discussion and Conclusions The predominance of gammaridean amphipods, especially Ampelisca macrocephala, among stomach contents indicates that gray whales, unlike other baleen whales, are primarily, if not exclusively, bottom feeders. The poor representation of polychaete worms and mollusks, which are usually dominant in the infauna, suggests that gray whales are selective feeders. Perhaps they stir up the bottom sediments with their snouts, then filter the turbid water immediately above the bottom from which the heavier mol- lusks have settled out. The worms presumably retreat deep into their tubes and burrows, whereas the amphipods, freely swimming, are trapped in the baleen plates. ‘The occurrence of sand, silt, and gravel in the stomachs provides further evidence that gray whales feed on the bottom. In the Chukchi Sea, several observers (Pike, 1962a; Scammon, 1874; Wilke and Fiscus, 1961) have reported seeing gray whales, presumably feeding, surfacing with muddy snouts. Greater wear of the baleen on the right side suggests that gray whales swim on their right side while feeding (Kasuya and Rice, 1970). Fin whales (Gunther, 1949), Bryde’s whales, Balaenop- tera edeni (Rice, field notes), and humpback whales (Andrews, 1909) Food and Feeding 37 swim on their sides when feeding near the surface. Swimming on their side permits whales to turn more easily in the horizontal plane. While migrating, gray whales apparently rarely attempt to feed, at least along the southern sector of their migration route. What little evidence is available also indicates that gray whales seldom, if ever, feed while on the winter grounds. A calculated weight loss of 0.21 to 0.37 per cent of body weight per day between the south- ward and northward migration past San Francisco exceeds the hypothetical value of 0.20 per cent per day based upon their esti- mated metabolic requirements. ‘Thus, there is no reason to assume that gray whales must feed while on the winter grounds. This conclusion, may not apply to females with calves, however, as we have no data for them. AGE AND GROWTH Age Determination o gray whales of known age have been studied. Age must be deduced from indirect evidence and by analogy with other species of baleen whales. Jonsgard (1969) reviewed methods of determining the ages of cetaceans. Three criteria appeared promis- ing for determination of age in gray whales. These are the number of growth layers in the ear plugs, corpora albicantia in the ovaries, and growth zones in the baleen plates. Ear Pxiucs.—In balaenopterid whales, the number of growth layers in the ear plug is generally considered to be the most useful indicator of age (Purves, 1955; Laws and Purves, 1956). Each layer consists of one light and one dark lamina. There has been con- troversy, however, over the correlation between number of growth layers and absolute age. Data on ear plugs collected from fin whales marked more than 25 years previously, and several independent lines of indirect evidence, support the hypothesis that only about one growth layer is formed each year, at least in sexually mature fin whales (Ohsumi, 1964a). Ichihara (1966) provided evidence suggesting that in immature fin whales the rate of accumulation of ear plug laminae is irregular, varying from one to two annually, with a mean of one and one-half. Roe (1967a, 1967b), however, on the basis of histological examination of the ear plugs of fin whales collected in all months of the year, concluded that one growth layer is produced each year in both immature and adult whales of both sexes. He found that the light laminae are formed in summer and the dark laminae in winter. He also noted that the ear plugs of immature whales usually have minor laminae similar to but much thinner than the normal laminae; their sig- nificance is obscure, but he concluded that they should not be included in lamina counts for age determination. Ear plugs of gray whales (Figs. 9-11) are soft, especially in the smaller animals, and difficult to remove without distortion or breakage. Some of the plugs have a fibrous, columnar, or amorphous 38 Age and Growth 39 Fic. 9. Ear plugs of immature gray whales bisected longitudinally. A, 9.8- meter male, estimated age one year (attached to the “glove finger” of the tympanic membrane); B, 8.6-meter female, estimated age one year (attached to “glove finger’); C, 10.1-meter male with three growth layers; D, 11.3-meter female with six growth layers. All plugs are to same scale. structure in which no laminae can be discerned. In the remaining plugs, laminae are vaguely to moderately well defined. Readable ear plugs were obtained from only 100 (60 per cent) of 166 males and 68 (45 per cent) of 150 females. On the better plugs, repeated counts of the laminae were consistent to within plus or minus 10 per cent of the total count. Males more often show regular laminae than do females, presumably because the annual physiologi- cal rhythm of females is modified by their longer and more irregular reproductive cycle. The ear plug laminae are broad and poorly defined in immature whales but narrow and more sharply defined in adults. In many plugs from mature gray whales, the laminae are clear in the basal portion but indistinct or absent in the distal portion. This dif- 40 The Gray Whale Fic. 10. Ear plugs of adult gray whales bisected longitudinally. A, 11.7-meter male with 11 growth layers; B, 11.4-meter female with 14 growth layers; C, 12.8-meter female with 18 growth layers; D, 12.3-meter male with 21 growth layers. All plugs are to same scale. ference in the two regions suggests that the laminae laid down during immaturity may disappear as the plug grows. Another possible explanation—that some animals do not begin to produce clear laminae until they attain sexual maturity—appears unlikely, because the proportion of readable plugs was higher in immature than in mature whales (65 compared to 59 per cent in males and 56 compared to 42 per cent in females). We found no ear plugs in several near-term fetuses that we dissected, and found no individuals with only one growth layer in the ear plugs. The smallest animals collected, 8.63 to 10.34 meters long, had two growth layers. We assumed that most of these animals were yearlings, and that the first layer forms during the nursing period and the second in late summer after weaning. As a working hypothesis, we assumed that each subsequent growth layer repre- sented one year of growth-in both immature and mature whales Age and Growth 4] Fic. 11. Ear plugs of adult gray whales. A, 11.7-meter male with 23 growth layers; B, 12.5-meter female with 24 growth layers; C, 12.5-meter male with 40 growth layers; D, 11.7-meter male with amorphous plug showing no growth layers. All plugs are to same scale. This interpretation is consistent with our estimate of the rate of accumulation of corpora albicantia in the ovaries (see discussion of reproductive cycle beyond). As it appears that two layers are formed the first year, the age of a whale in years should be one less than the number of growth layers in its ear plug. If, as suggested above, the earlier layers disappear in older animals, the count of growth layers provides only a minimum estimate of age. OvariEs.—As the ovulation rate appears to be regular at about 0.50 per year, and the corpora albicantia remain permanently visible in the ovaries, the number of corpora in the ovaries provides a reliable estimate of the number of years elapsed since a female attained puberty. The mean age at puberty appears to be about 8 years (see below). Therefore, the age of a recently ovulated or early pregnant female is about twice the number of corpora (including ae The Gray Whale 14 e BODY LENGTH (M) = 10 20 30 40 50 60 rae) NUMBER OF GROWTH LAYERS Fic. 12. Body length in relation to number of growth layers in ear plugs of female gray whales (open circles, immature females; solid circles, adult females; line, von Bertalanffy growth curve). the corpus luteum) in her ovaries plus 6 years, and that of a late pregnant or postpartum female twice the number of corpora plus 7 years. BALEEN PLaTEs.—Ruud (1940, 1945) found that the growth of baleen plates of blue (Balaenoptera musculus), sei (B. borealis), and fin whales is characterized by seasonal changes in thickness and that the pattern of variation in thickness can be used to esti- mate the age of the whales (see van Utrecht-Cock, 1965). Because of constant wear, there is rarely more than 5 or 6 years of growth present in a baleen plate. Thus this method is useful only for young whales. Baleen plates of most gray whales show moderately well-defined “steps,” or growth zones, each of which presumably represents one year of growth. None of the baleen plates we examined showed more than four growth zones, regardless of the age of the whale as estimated from the ear plugs. The number of growth zones in the baleen plates of most whales was less than the number of growth layers in the ear plug, and in no specimen was it greater. It thus appears that wear on the baleen plates of the gray whale is more rapid than in other baleen whales, probably because of greater abrasion resulting from bottom-feeding habits. Age and Growth 43 e e e 5 ve e S. a e °3 e = ae = SS = s7ieie ee ° 12 O.0AY a) Y . ~- e oem e e e 8 o} 3 e ce =x ee e e $ ee ° 2 Bas ke FF | ° orn ns a) 8 ‘co > roy ) ° 210 8 ° ° of 8 a Jo o SL a 1 SS ees 20 30 40 50 60 70 NUMBER OF GROWTH LAYERS Fic. 13. Body length in relation to number of growth layers in ear plugs of male gray whales (open circles, immature males; solid circles, adult males; line, von Bertalanffy growth curve). Growth The external morphology and osteology of the gray whale have been described in detail by Andrews (1914), Zenkovich (1934a), and Tomilin (1957). Further data on growth in length, ontogenetic changes in body proportions, and sexual dimorphism were obtained in this study. LreNncTH.—Body lengths of males and females one year old and older have been plotted against the number of growth layers in the ear plugs in Figs. 12 and 13. Growth curves for each sex were calculated by using the von Bertalanffy equation (von Bertalanffy, 1938; Beverton and Holt, 1957) as follows: 1, = L, [l—e* t+], where | = body length in meters, L,, = asymptotic body length, K = rate at which length approaches the asymptote, and t = time in years. The results are given below (mean and standard deviation). Females Males ee 297 OF ee 12-45 == 012 Ke 02467 e003 Ke ON ==10:021 Gy Sai aE 2 iy SS Sey Ss le! It should be emphasized that because of the small sample sizes and the difficulty of reading ear plugs these curves are not com- 44 The Gray Whale l4r to) ‘6 ° e ° 0 0 apy e e ° ore eee IB e On OO a ot I3b 5 a g e eer + o 5 (eelars gr © 55 Oe Uo giese Ot 0 5 pee : : Tien 5 OG ece eo ° e eo 0 e e oe . BODY LENGTH (M) I) T ee 10 20 30 NUMBER OF CORPORA IN OVARIES Fic. 14. Body length in relation to number of corpora albicantia and corpora lutea in ovaries of adult female gray whales. Crosses are running means of two; growth curve fitted by eye to mean values. pletely reliable. ‘The samples of the younger age groups are biased in favor of the larger individuals. Furthermore, possible disap- pearance of some ear plug laminae in older animals may have resulted in the estimated mean length at any given age being greater than the true mean. In Fig. 14, the body length of adult females has been plotted against the number of corpora in the ovaries and a curve fitted by eye to the running means of two. This curve is probably a more accurate representation of the growth characteristics of adult females than the von Bertalanffy curve. From a mean length at birth in January of about 4.9 meters, calves grow to a mean length of about 8.5 meters at weaning in August and to 9.3 meters by the following winter. With this first annual increment of 90 per cent of neonatal size, the females attain 66 per cent of their ultimate body length and the males 72 per cent. The growth rate drops to 7 per cent during the second year and continues to decline in subsequent years, but growth continues until at least about 30 years of age. Age and Growth 45 TABLE 6 Bopy PROPORTIONS (EXPRESSED AS PERCENTAGE OF TOTAL Bopy LENGTH) OF NEAR- TERM FETUSES AND POSTNATAL GRAY WHALES. SEE TEXT FOR DESCRIPTION OF MEASUREMENTS. Females Males Fetuses Postnatals Fetuses Postnatals Measurement N Mean+SD N Mean+=SD N- Mean+SD N Mean=+ SD Head lensth 17, 224==11 136 23-2210) 25 22 5251.3 Ibb 23:3 ==09 Mail Mlensth) 25 28: 4==2'4 147 30:3)-= 16) 30) 28:2 26 167 2977 103 Fluke span 25 228+18 120 24318 30 22618 138 249+1.46 Fluke breadth 25 76+£06 141 IB=0H BO TH=0G IBZ > 7206 miippermlenethe 25 L9G =— 10 147 ied =a ll 929) 19°92 (0:8 1665) 7-8 = 12 Flipper width 25 68+£05 144 65405 29 70+£04 166 67+0.6 PROPORTIONS.—We have analyzed the following six body measure- ments to determine if body proportions change with age: (1) head length, (2) tail length, (3) span of flukes, (4) breadth of flukes, (5) length of flippers, and (6) width of flippers. A comparison of these measurements (expressed as a percentage of body length) of near-term fetuses with those of postnatal whales (Table 6) shows that mean tail length increases from 28.2 to 29.7 per cent in males (P < .05) and from 28.4 to 30.3 per cent in females (P < .001). Relative flipper length decreases from 19.9 to 17.8 per cent (P < .001) in males and from 19.6 to 17.3 per cent (P < .001) in females. Fluke span increases from 22.6 to 24.9 per cent (P < .005) in males and from 22.8 to 24.3 per cent (P < .01) in females. Exam- ination of near-term fetuses suggests that the apparent increase in relative fluke span does not represent differential growth, but instead is simply the result of postnatal abduction of the flukes in the horizontal plane from the adducted and folded position in utero. ‘There are no significant age differences in relative head length, fluke breadth, or flipper width. The magnitude of changes in body proportions of gray whales from one year of age to physical maturity also was examined. All postnatal animals of each sex were grouped into one-meter length classes. Ihe mean and standard deviation of each measurement for each length class were calculated and the mean expressed as a percentage of total body length (Table 7). Only specimens for which 46 The Gray Whale all six measurements were available were included. For each series of measurements, we calculated the allometric equation Y = bX4, where X = body length and Y = measurement being compared with X. The constant of allometry, d, does not differ significantly (P > .05) from unity for any of the series of measurements for either sex, indicating that body proportions change little after one year of age. SEXUAL DimMorPHisM.—There was no significant difference be- tween the sexes in body length of near-term fetuses. As noted above, females grow more rapidly after birth and average larger than males at any given age, as is true for all other species of baleen whales. The data in Tables 6 and 7 reveal small but statistically sig- nificant postnatal differences between the sexes in some body proportions. Thus, males have longer flippers (P < .01) and shorter tails (P < .01) than females. There is no sexual dimorphism in number of throat grooves, baleen plates, or crenulations on the dorsal ridge of the caudal peduncle. Puberty and Sexual Maturity As ordinarily used by cetologists, puberty refers to the age at which gametes are first produced, and sexual maturity is the age at which the animal reaches its full reproductive power. For purposes of this study, any animal that had attained puberty is referred to as an adult. Puberty in the female is indicated by the presence of a corpus luteum or at least one corpus albicans in the ovaries. Females are considered to be sexually mature at the onset of the first pregnancy. Evidence of sexual maturity thus is pregnancy, lactation, or the presence of mature but involuted mammary glands and a parous type uterus. In the female gray whale, attainment of puberty and sexual maturity usually coincide, but in five of 15 nulliparous and primiparous females, the presence of a corpus albicans (in one case, three corpora), in addition to a corpus luteum or recently ovulated follicle, indicated that they had attained puberty but had not conceived at least a year before their most recent estrous cycle. Males are considered to be sexually mature when first capable of successfully impregnating females. It is impossible to make a distinction between puberty and sexual maturity in the male on 47 Age and Growth ee eeeeTNSFT 89 F0'0 = 980 F0'0 = #80 S00 = LL'0 G00 = IL°0 60°0 = 99°0 600 = 6§'0 60 40'0 = L8°0 F0'0 = 180 S00 = 9L'0 F0'0 = 89'0 600 = 69'0 60°0 = $90 60°0 = 660 O10 += 666 STO0= 816 910 = S06 61 0= I6T OV0O= TILT LO'0 = 66:0 09° 66.0 = S66 FLO+9TG IT0= 66T 610 = 08'T 610+ L9'T L0'0 = 9F T 80'0 = 66:0 69 S00 = 16:0 60°0 = 68°0 90'0 = £80 40'0 = 940 G00 = I4'0 600 = £50 [6:0 90'0 = $60 40'0 = 160 +00 = 880 90°0 = 9L'0 90°0 = OL'0 60'0 = 49'0 40'0 = 96°0 STOFLGE 08 910+ G06 08 6604 L8G 66 1G0+ 896 06 Ol0+ 8h I€ ITO+cOT 86 sa]D IN P66 06 PCOFOTE O06 6GOFLOE 06 slO+066 16 LEO+9FG IE 910+ 88S 6& IVO+66 6& 6TO0+80T 86 sajvwuiag L0°0 = 166 FLO + 99'§ S10 = Gs 610 + 066 61:0 = 90'S 610+ 641 06h S10 = 96'S 660 + 816 O10 += $96 S10 + 96'S S10 = 40'S 60'0 = LLG FLO= S61 6G 66 66 ¥6 66 16:0 = 066 60°0 = 866 610+ 16 610+ 196 80°0 = 966 400 = 60'T 036° § ITO = G0°¢ O10 = 066 O10 += S16 610 = SFG SlO+ 166 60°0 = 661 60°0 = SO'T 8911 6F OL 896 698 69°F 6 && 00'FI-10°&1 00°'S1-10'6I 00'GI-10' TI 00 LI-L0'01 0001-106 SOSNJIF WWI9}-1TPIN] 00°SI-10'F1 00'FI-10'§1 00'SI-10°6I 0061-10 TI 00 TI-10°01 00°0I-10°6 00°6 —10°8 LI Sosnjoy UW19}-1RaN ee eee quao QS = Uva jus. Gs =F Ura Jag yap soddipy Jag yysue] s19dd1,7 yuao. qs = Uva Jag wprerq oynpy a ee ee ee ee Eee ‘SHTVHM AVA AO SLAVE AGO SNOMIVA AO (HLONAT AGOG’ AO ANVLINAMAd SV) AZIG AALLVIAY ANV (suaLap NI) SLNAWANASVAI L ATAVL uvds ayn]J quso Qs = uvay jusd Jad Jad CS = uray quo Gg = uray yisugy [el Jog yu] prof tp Yojacs) | Apoq uvaj N yisue, Apoq jO osuet sse[D 48 The Gray Whale PERCENT MATURE 10 I 12 13 BODY LENGTH (M) Fic. 15. Percentage of adult gray whales according to body length (grouped by 0.3-meter length classes). Open circles and broken lines represent males; solid circles and unbroken lines represent females. the basis of our data. We determined the attainment of puberty by histological examination of the testes and regarded as adult all males whose testes showed evidence of spermatogenesis. Fig. 15 shows that 50 per cent of the females have attained puberty by the time they reach a length of about 11.7 meters. The two smallest females that had reached puberty were 10.92 meters and 11.20 meters long; both were nulliparous and had recently ovulated for the first time. The smallest parous female was 11.24 meters long, whereas the largest immature female was 12.92 meters in length. Fifty per cent of the males had attained puberty at a length of 11.1 meters (Fig. 15). The smallest male showing spermatogenic activity was 10.56 meters long, and the largest immature male was 11.75 meters long. The age at puberty was estimated by plotting the percentage of animals that had attained puberty against the number of growth layers in the ear plug (Fig. 16). The mean number of growth layers at puberty was nine, giving an estimated age of 8 years. In both males and females, the fewest growth layers found in the ear plug Age and Growth 49 iKeXe) 80 60 40 PERCENT MATURE 20 3) 6 7 8 9 10 I 12 13 14 NUMBER OF GROWTH LAYERS IN EAR PLUG Fic. 16. Percentage of adult gray whales in relation to number of growth layers in ear plugs. Open circles represent males and solid circles represent females; line connects running means of three for both sexes combined. of an adult animal was six, whereas the highest number in an immature animal was 11 (excepting one female with 13). On this basis, age at puberty is estimated to range from 5 to at least I] years. Because of the difficulty of counting growth layers in ear plugs of immature animals, these figures may not be entirely reliable. Physical Maturity We collected few physically mature animals, as determined by the complete fusion of the vertebral epiphyses with the centra. Only two of the females examined fell in this class. They were 13.98 and 14.20 meters long. The smaller had 35 corpora in the ovaries and about 41 growth layers in the ear plugs, whereas the larger had 22 corpora and 43 laminae in the ear plugs. Physically immature females had 20 or fewer corpora and as many as 40 growth layers. Except for one individual with unreadable ear plugs that was 14.05 meters long, physically immature females were 13.75 meters or less in length. 50 The Gray Whale Five males were regarded as physically mature. They ranged from 12.75 to 13.30 meters in length. The smallest had only 21 growth layers in the ear plug, whereas the others had 38 to 70 (the plugs of one were unreadable). Physically immature males did not exceed a length of 12.80 meters, except for one with 23 growth layers that was 13.23 meters long. The largest reliably measured gray whales on record are males 14.3 meters long and a female 15.0 meters in length (Zenkovich, 1937a). Discussion and Conclusions Growth layers in the ear plugs have limited use for age determina- tion in the gray whale because of uncertainty in counting them and because not all individuals have readable plugs. They provide a minimum estimate of age because laminae produced early in life may disappear in older whales. The number of corpora in the ovaries appears to be a more reliable method for age determina- tion in adult females. Growth zones in the baleen plates are of little use for age determination because of the rapid wear of the plates. Gray whales grow rapidly during their first year. Rapid initial growth is essential in large aquatic mammals that depend primarily on size for thermoregulation and protection from predators. Between late fetal life and one year of age, relative length of the flipper decreases slightly and relative length of the tail in- creases slightly. There are no appreciable changes in body pro- portions from one year to physical maturity. The latter conclusion is contrary to the findings for blue whales and fin whales (Mackin- tosh and Wheeler, 1929; Ohsumi, 1960), sei whales (Matthews, 1938), humpback whales (Matthews, 1937), right whales, Balaena glacialis (Omura et al., 1969), and bowhead whales, Balaena mysticetus (Eschricht and Reinhardt, 1866). In most of these species, as body length increases the head becomes relatively longer, the tail relatively shorter, and the flippers and flukes relatively shorter and narrower. Sexual maturity is attained in both sexes at a mean age of 8 years (range, 5 to 11), at a mean length of 11.1 meters in males and 11.7 meters in females. This estimate of age at sexual maturity is Age and Growth il in general agreement with estimates for fin whales (Nishiwaki e¢ al., 1958) and humpback whales (Chittleborough, 1959) that were based on counts of growth layers in the ear plugs. Physical maturity is attained at a mean length of about 13.0 meters in males and 14.1 meters in females, at a mean age of about 40 years. As in other baleen whales, females are larger than males. Sexual dimorphism in body proportions is slight, but males have slightly larger flippers and shorter tails than females. FEMALE REPRODUCTIVE CYCLE EPRODUCTION in cetaceans has been reviewed by Harrison (1969), Rice (1967), and Slijper (1956, 1963). Our collection of 116 adult females included animals in four stages of the reproductive cycle (sample sizes in parentheses): southbound females that had recently ovulated (28); northbound females in early pregnancy (22); southbound females in late pregnancy (56, including one recently aborted individual); and northbound postpartum females (two, neither of which was lactating, apparently having lost their calves). In addition, eight northbound metestrous and anestrous females, which had failed to conceive, were included in the sample. Some anestrous females would also be expected on the southward migra- tion, but none was collected in this study. Where appropriate, the data on the 15 females undergoing their first reproductive cycle were analyzed separately from the data on the 101 females that had previously experienced one or more cycles. We defined a female as nulliparous if she has never given birth (or aborted) and was not visibly pregnant (although she may contain a macroscopically undetectable conceptus), as primiparous if she was in her first pregnancy or had given birth (or aborted) only once, and as multiparous if she had given birth (or aborted) at least twice or had given birth (or aborted) only once and was currently pregnant; parous refers to any female that had conceived at least once (North Pacific Fur Seal Commission, 1963). Nulliparous females and primiparous females in early pregnancy were recognized by the condition of the mammary glands and uterus as described below. Females in late pregnancy and postpartum females with a single corpus luteum and no corpora albicantia were obviously primiparous, and those with at least one corpus albicans in addition to the corpus luteum were regarded as multiparous. Ovarian Cycle The ovaries of the gray whale are morphologically similar to those of the fin whale (Laws, 1961; Mackintosh and Wheeler, 1929; Ommanney, 1952), and the humpback whale (Dempsey and Wislocki, 52 Female Reproductive Cycle 53 Fic. 17. Ovaries of gray whales showing various stages of ovarian cycle. A, 8.6-meter immature female with no large Graafian follicles; B, 11.2-meter immature female with enlarged Graafian follicles; C, southbound female with recently ruptured Graafian follicle in right ovary and corpus luteum of ovula- tion in left ovary; D, southbound, recently ovulated female with developing corpus luteum in left ovary. All ovaries are to same scale. 1941). They are elongate, flattened, and oval, with the anterior end slightly larger than the posterior end. Some are exceptionally long and narrow, being almost strap-shaped. The larger Graafian follicles and corpora albicantia protrude from the surface. Ovaries 54 The Gray Whale Fic. 18. Transverse sections of ovaries shown in Fig. 17. Sections shown in C and D transect the most recent corpora. All sections are to same scale. representative of various stages of the reproductive cycle are shown in Figs. 17 to 20. Ovary WeEiIcHTs.—There is no marked or consistent difference in weight between left and right ovaries. ‘The mean weight of both ovaries of sexually immature females is plotted against body length in Fig. 21. In the smaller individuals, ovary weights range from 70 to 250 grams, with a mean of 136. At a body length of 11.2 to 11.4 meters, corresponding to an estimated age of about 5 years, Fic. 19. Ovaries of gray whales showing various stages of the ovarian cycle. northbound, early pregnant female (90-millimeter fetus) with corpus luteum in left ovary; B, southbound late pregnant female (4.86-meter fetus) with corpus luteum in right ovary; C, northbound postpartum female (that had lost her calf) with regressing corpus luteum in left ovary; D, northbound anestrous female with large corpus albicans derived from the most recent corpus luteum A ’ in right ovary. All ovaries are to same scale. ovarian weight increases abruptly to 250 to 550 grams (mean, 312), approximating that of younger sexually mature females. The weight of the ovaries of sexually mature females is greatly increased when a corpus luteum is present. As most mature females 56 The Gray Whale Fic. 20. ‘Transverse sections through the most recent corpus in each pair of ovaries shown in Fig. 19. All sections are to same scale. Female Reproductive Cycle 57 600 500 400 300 200 MEAN WEIGHT OF OVARIES (G) 100 8 9 10 I] l2 I3 BODY LENGTH (M) Fic. 21. Ovary weights of immature female gray whales plotted against body length. Line connects mean weights at one-meter length intervals. loooF a ° °o OVARY WEIGHT (G) .- L 4 n ae fe 4 1— L tt n 4 oe 6 7 8 9 10 I 12 13 14 15 16 17 18 19 20 «2i 22 35 NUMBER OF CORPORA IN OVARIES ab Fic. 22. Ovary weights of adult female gray whales plotted against number of corpora in ovaries. 58 The Gray Whale OJ fe) ie) (eo) DIAMETER OF LARGEST FOLLICLE (MM) 8 i) lO lI 12 13 BODY LENGTH (M) Fic. 23. Diameter of largest Graafian follicle versus body length of im- mature female gray whales. Solid circles indicate southbound migrants; open circles indicate northbound migrants. had a corpus luteum in one ovary, we have used only the weight of the other ovary in making comparisons. For females without a corpus luteum, we have used the mean weight of the two ovaries. In Fig. 22, these weights are plotted against the number of corpora in both ovaries. The weights of mature ovaries without a corpus luteum vary from 170 to 1270 grams. The regression of ovary weight on number of corpora is Y = 316 + 15X, where Y = ovary weight in grams and X = number of corpora. As the slope of this line differs significantly from zero (P < .001), ovarian weight apparently increases with age from a mean of 331 grams at puberty to 646 grams at an age of 50 years. FoiiicLes.—None of the follicles in the ovaries of immature females up to 9.6 meters long exceeded 7 millimeters in diameter; in all immature females longer than 10.2 meters, the largest follicle Female Reproductive Cycle 59 40 (MM ) 30 20 10 N fo) 10 20 ess) DIAMETER OF LARGEST FOLLICLE N S N S) N ANESTROUS REC. OVULATED] EARLY PREG. | LATE PREG. | POST-PARTUM Fic. 24. Frequency distribution of diameter of largest Graafian follicle in ovaries of adult female gray whales in different phases of the reproductive cycle (N, northbound migrants; S$, southbound migrants). in either ovary exceeded 14 millimeters (Fig. 23). In the latter animals the largest follicles ranged from 18 to 34 millimeters (mean, 27) in southbound animals and from 14 to 28 millimeters (mean, 21) in northbound animals. These data suggest that females first begin to undergo a seasonal cycle of follicle-stimulating hormone secretion when they reach a length of between 9.6 and 10.2 meters at an estimated age of 2 or 3 years. Laws (1961) found a seasonal follicular cycle in immature fin whales. It should be noted that the follicles in these older immature females are significantly larger than those of late pregnant or postpartum females and slightly larger than those of northbound anestrous females. It is probable that the southbound immature females with follicles about 30 millimeters in diameter or larger (see below) are destined to ovulate for the first time later in the same season. The size of the largest follicle in either ovary of adult females differs markedly in various phases of the reproductive cycle (Fig. 24). All southbound females not carrying near-term fetuses had recently ovulated. The largest follicle in these specimens ranged 60 The Gray Whale from 18 to 40 millimeters (mean, 28) in diameter (except for one nulliparous animal in which maximum follicle diameter was only 6 millimeters). Assuming that the largest follicle had ovulated, the biggest remaining follicle in these females would have been the second largest follicle just before ovulation. It thus appears that in gray whales the follicle exceeds 30 millimeters and may reach 40 before rupturing. Chittleborough (1954) found that the follicles of humpback whales exceed 30 millimeters before ovulation. In the northbound early-pregnant females, the diameter of the largest follicles average less than two months earlier, ranging from 16 to 33 millimeters, with a mean of 22. In strong contrast to females that had recently ovulated, south- bound pregnant females carrying near-term fetuses had no greatly enlarged follicles. The largest follicle varied from 3 to 16 milli- meters, with a mean of only 6. A female taken on 8 January that had apparently aborted recently likewise had no follicles larger than 6 millimeters. Such follicles are significantly smaller than those of anestrous females. The small size of follicles in late- pregnant females suggests that the progesterone secreted by the corpus luteum suppresses follicular maturation. Chittleborough (1954) found that the follicles of humpback whales in late pregnancy were smaller than those in anestrous animals. No such marked reduction has been found in blue whales and fin whales examined mostly during midpregnancy (Laws, 1961; Mackintosh and Wheeler, 1929; Nishiwaki and Oye, 1951). In the two northbound females examined that were nonlactating and postpartum, the largest follicles were 24 and 29 millimeters in diameter. Their size suggests a resumption of follicular maturation after regression of the corpus luteum. Northbound females that were neither pregnant nor postpartum had follicles ranging from | to 37 millimeters (mean, 18) in diameter. In three of these females that had recently ovulated, the largest follicles ranged from 14 to 37 millimeters, with a mean of 24. These approximate maximum follicle sizes of southbound females that had recently ovulated and were presumably pregnant. These three females probably should be regarded as being in metestrus. Five anestrous females that had not ovulated recently had follicles with maximum diameters of 1 te 25 millimeters, with a mean of 14. Female Reproductive Cycle 61 This size range is probably closest to that of follicles of fully anes- trous females. Nine pairs of ovaries contained one to several thin-walled, fluid- filled cysts up to about 8 centimeters in diameter. Presumably, these are cystic follicles. FREQUENCY OF OvULATION.—Nonpregnant adult females regularly ovulate in late November and early December (see discussion of gestation period and fetal growth beyond), while still north of central California on the southward migration. All of the adult females collected in southward migration that were not carrying near-term fetuses had recently ovulated, as revealed by the presence of recently ruptured follicles or developing copora lutea. The mean number of recent ovulations in these females was 1.14 for nulliparous animals and 1.10 for parous animals (Table 8). It is possible that some of these whales would have ovulated again later if their most recent ovulation did not result in conception. The mean number of recent ovulations in northbound females (excluding postpartum animals) was 1.33 in the nulliparous and the primiparous pregnant females and 0.85 in the parous non- pregnant and the multiparous pregnant females. The diameter of the largest corpus albicans in the ovaries of each metestrous and anestrous female suggests, however, that some of these may have been fairly recently formed corpora whose recent origin was no longer apparent. These corpora ranged from 24 to 39 millimeters in diameter, with a mean and standard error of 32.3 + 3.0, whereas the largest corpus albicans in each early pregnant female ranged from 18 to 42 millimeters, with a mean and standard error of 27.4 + 1.6. The latter presumably were the corpora lutea of the previous pregnancy that had regressed after the end of lactation several months earlier. The mean ovulation rate estimated for females during their regular biennial breeding season was 1.20 for nulliparous females, 0.96 for parous females, and 1.00 for all females (Table 8). For reasons stated above, these estimates may be slightly low. Each of two females taken on 16 and 18 January had both recently ruptured follicles and a corpus luteum of ovulation. This observa- tion suggests that about 40 days intervene between successive ovula- tions during one breeding season. 62 The Gray Whale TABLE 8 NUMBER OF RECENT OVULATIONS IN ADULT FEMALE GRAY WHALES, EXCLUDING LATE PREGNANT AND POSTPARTUM FEMALES. Number of Total Number recent ovulations1 recent Ovula- Direction of migration fo) —_—— — ovula- tion and reproductive status whales 0 1 2 3 tions rate Southbound Nulliparous 7 0 6 1 0 8 1.14 Parous 21 0 20 0 1 23 1.10 Total 28 0 26 1 1 31 1.11 Northbound Nulliparous or primiparous Nonpregnant 1 0 0 1 0 2 2.00 Pregnant 2 0 Z 0 0 2 1.00 Subtotal 3 0 i 1 0 4 1.33 Parous or multiparous Nonpregnant 7 5 2 0 0 2 0.29 Pregnant 20 0 19 1 0 21 1.05 Subtotal il 5 2) 1 0 23 0.85 Combined northbound sample Nonpregnant 8 5 2 1 0 4 0.50 Pregnant 22 0 21 1 0 23 1.05 Total 30 5 23 2 0 27 0.90 All specimens Nulliparous or primiparous 10 0 8 2 0 12 1.20 Parous or multiparous 48 5 4] 1 1 46 0.96 Grand total 58 5 49 3 1 58 1.00 1 Figures in body of table indicate the number of whales that had the number of recent ovulations shown at the top of each column. The only evidence for multiple (simultaneous) ovulation was one female with two recently ruptured follicles of the same size. The nature of the estrous cycle in baleen whales has been the sub- ject of controversy, because few specimens taken during the breeding season have been available for study, and conclusions have had to be drawn mostly from indirect evidence. Harvey (1963) reviewed the relevant literature and concluded that balaenopterid whales are monestrous. Chittleborough (1965), however, presented direct evidence that female humpback whales, although they usually con- ceive after ovulating only once, may undergo two or three estrous Female Reproductive Cycle 63 cycles if pregnancy does not intervene. Gambell’s (1968) data strongly suggest a similar condition in sei whales. Potential polyestry would be of considerable selective advantage in a species that can produce no more than one offspring every 2 years, that does not form permanent pair bonds, and that may be so widely dispersed that a male might not be available when the female first comes into estrus. As southbound female gray whales carrying near-term fetuses had no enlarged follicles, it may be concluded that there is usually no postpartum estrus in this species. However, postpartum estrus sometimes occurs in other whale species. A postpartum estrus resulting in pregnancy almost invariably occurs in the minke whale, Balaenoptera acutorostrata (Jonsgard, 1951; Omura and Sakiura, 1956). Postpartum estrus in a high proportion of Southern Hemisphere humpback whales also is indicated by the fact that eight (44 per cent) of 19 lactating animals examined in one study were simultaneously pregnant (Chittleborough, 1958). Likewise, 15 (12 per cent) of 129 lactating Southern Hemisphere fin whales also were pregnant (Laws, 1961). According to Gambell (1968) an esti- mated 1] per cent of female Southern Hemisphere sei whales experienced postpartum estrus. The two nonlactating postpartum females examined had not recently ovulated, but the fact that they had follicles (24 and 29 millimeters) much larger than any late pregnant female and larger than the average for anestrous females indicates a resumption of follicular maturation after the corpus luteum starts to regress and progesterone secretion is reduced. It is possible that such follicles may develop sufficiently to undergo ovulation. Chittleborough (1958) has shown that humpback whales usually recommence estrous cycles immediately after stillbirth or early loss of the calf. Ovulation following stillbirth or loss of a calf would be so infrequent that it would not significantly affect the mean ovulation rate. The possibility of postlactation ovulation, or ovulation by any nonpregnant females during the summer, remains to be considered. The southbound females that had recently ovulated, most of which presumably had ceased lactating about 5 months previously, gave no evidence of having ovulated more than once since that time. 64 The Gray Whale In each, the largest corpus albicans was 22 to 38 millimeters in diameter (mean, 29); this was no doubt the regressing corpus luteum of lactation. Only data from females collected on the summer grounds can provide direct evidence on this point. There is evidence that a considerable proportion of Southern Hemisphere fin whales experience a postlactation ovulation (Laws, 1961), and about 12.5 per cent of the female Southern Hemisphere sei whales ovulate in the summer (Gambell, 1968). These summer ovulations almost never result in pregnancy. In humpback whales, which lactate for approximately 10’2 months, an estrous cycle usually commences immediately following the end of lactation; this cycle corresponds with the normal winter breeding season and usually results in pregnancy (Chittleborough, 1958). The two oldest females studied, with 19 and 34 corpora albicantia, were pregnant, so there is no indication of cessation of breeding in old females. In summary, female gray whales normally experience one estrous cycle every 2 years, although rarely they may ovulate twice or per- haps three times during one breeding season. The mean ovulation rate for parous females is 0.96 per breeding season. A female that fails to conceive during one breeding season probably undergoes an estrous cycle again the following year. As the pregnancy rate is 0.46 (see below), the mean ovulation rate per year of parous females is 0.52 ({1.00 — 0.46] x 0.96). CorroraA LuTeA.—Our material included three ovaries with recently ruptured Graafian follicles that provided data on early development of the corpus luteum. In one case the rupture site was still open (Figs. 17 and 18), and in the other two the rupture sites were still obvious as dark spots, although no actual openings were visible. These follicles, 24, 25, and 25 millimeters in diameter, were smaller than mature unruptured follicles. Loss of fluid pre- sumably causes the follicle to collapse immediately after rupture. There is a marked infolding of the walls and a proliferation of luteal tissue from the membrana granulosa. The luteal tissue fills almost the entire antrum. One corpus contained a small amount of liquor folliculi in the central cavity. Subsequent development of the corpus luteum depends-upon whether or not pregnancy ensues. Female Reproductive Cycle 65 It is difficult to distinguish corpora lutea of ovulation from corpora lutea of pregnancy, because failure to find a visible con- ceptus in the uterus is not proof that an animal has not conceived. Only in the four females that had recently undergone more than one estrous cycle was it certain that corpora lutea of ovulation were present (Figs. 17 and 18). In these animals the penultimate corpora were 13, 15, 21, and 25 millimeters in diameter. Because of their small size, they did not greatly protrude from the surface of the ovaries. In cross section, the corpora were somewhat irregular or stellate in outline. The layer of luteal tissue was thin and greatly plicated, and no cavity remained. The luteal tissue was pale yellow, as in corpora lutea of pregnancy, in the larger two of the four corpora and more orange-yellow in the two smaller corpora. Three northbound females had corpora lutea 22, 81, and 102 millimeters in diameter but showed no macroscopic evidence of pregnancy. The two larger corpora in this series were indistinguish- able from corpora lutea of pregnancy. The above data indicate that corpora lutea of ovulation do not attain a size greater than about 25 millimeters and rapidly regress if the female comes into estrus again after a brief diestrous period. The fate of the corpus luteum when the female does not become pregnant or undergo another estrous cycle requires further study. Corpora lutea of pregnancy in the gray whale (Figs. 17 and 20) are similar to those of the fin whale (Laws, 1961) and humpback whale (Chittleborough, 1954). They protrude from the body of the ovary, from which they are separated by a constricted neck. In most of the southbound females that had recently ovulated but were not yet visibly pregnant, the corpora lutea ranged from 37 to 87 millimeters (mean, 56; standard deviation, 16). Females with small fetuses collected two months later during northward migration had corpora lutea ranging from 61 to 100 millimeters in diameter (mean, 82; standard deviation, 11). In these animals, the size of the corpus luteum was correlated with the length of the fetus. The female carrying the smallest fetus (25 millimeters long) had a corpus luteum only 63 millimeters in diameter. In females with fetuses 120 to 140 millimeters in length (estimated age 87 to 89 days), the average diameter of the corpus luteum was 84 millimeters, which is not significantly different from that in late pregnant females. 66 The Gray Whale Chittleborough (1954) has shown that it takes nearly three months for the corpus luteum of the humpback whale to reach maximum size. In southbound female gray whales with near-term fetuses, the corpora lutea varied from 61 to 115 millimeters in diameter (mean, 87; standard deviation, 12). No data were obtained on the condition of the corpora lutea in lactating females. Twenty-one per cent of the corpora lutea of pregnancy contained central vesicles filled with liquor folliculi. Thus, in this species the presence or absence of a central vesicle is of no use in distinguish- ing corpora lutea of ovulation from those of pregnancy. Laws (1961) has refuted the contention of some authors (for example, Robins, 1954) that the absence of a central vesicle is diagnostic of corpora lutea of ovulation in balaenopterid whales. The largest vesicle in our animals was 54 millimeters in diameter. A few were irregularly shaped or eccentrically located. Some corpora lutea had gel-filled cavities up to 24 millimeters in diameter located around their periphery or at the base (Fig. 20). Although these structures re- semble large, flattened follicles, their close association with the corpus luteum suggests that they are part of it. Only one whale, a primiparous late pregnant female, had an accessory corpus luteum (in the opposite ovary from the primary corpus luteum). It was 14 millimeters in diameter and lacked a stigma, suggesting that it must have developed from an unruptured follicle. Corpora ALBICANTIA.—The corpora albicantia (Fig. 20F) of gray whales are morphologically similar to those of balaenopterid whales, and the sequence of changes during regression is essentially the same as described by Laws (1961) and van Lennep (1950) for the fin whale. The earliest stages of regression were seen in the two postpartum females that had recently lost their calves (Figs. 19, 20). ‘The corpora lutea in these individuals were 53 and 60 millimeters in diameter. The connective tissue septa characteristic of corpora albicantia were already obvious, and the color of the luteal tissue was more orange than is typical of the corpus luteum of pregnancy. As the corpus albicans continues to shrink, it recedes below the surface of the ovary. The color changes to brown as collagen 67 Cycle Female Reproductive 9-LI I bE-66 LI I él I 16 81 I La I 06 Ol I 81 I al I 6l él I 81 I a I 8I él I 81 I SI I LI 61 I 81 I ST I 9I él I 81 I SI I cI FI-él Cel 6 81 I SI-6I OFT 6 al 6I-F1 LI=L41 6 81 I GI-él 60+ LEI 6 reat 61-41 YI+ 091 6 61-61 aici 6 91-61 90+ ¢6F1 v él 61-8 SlL+TPI L 61-61 09r 6 9I-FI 90+ 0ST v II 61-61 O1L+6FI 6 61-91 FLT 6 LI-él 60+ 091 g Ol SI I 06-61 90+ 691 él 61-41 GIT+=OLI 6& LI-&1 80+ FSI ij 6 OI I 66-01 LO+ 641 6l 06-F1 61+ L41 & 8I-S1 GO>+= 691 9 8 91 I 66-II 90+ 9ST 66 06-S1 GIT +081 6 06-S1 9O0=TLI 8 L 81 I bo-61 G0 + 891 GG 16-61 SI+ 941 9 16-61 SO= FOI II 9 06 I beF1 GO>+6L1 LG 66-¥1 60+ 081 II §6-6l 60+ LL1 él i) 66 I 86-01 FOF LEI I¢ 6<6-6l 60+P78I ST 96-91 LO+F6l La P 66 I 66-61 90 = $61 86 86-LI L0 += ¥'06 9I 96-F1 LO>+=L6I OT 6 G6¥6 GHG 6 66-F1 G0 = 906 6h O¢-LI LO+ 816 06 Is-F1 8'0 + 0°66 81 6 L6-96 G96 6 Gé-LI LO+=8 V6 0G 6b-81 DT + VLE 06 86-66 60 + 166 06 I asuvy uvayy N asury AS = uray N asuvy AS = uvoyy N asury AS = uvoypy N SEG umjaiedysog quvuseid o}eT yuvusoid Apieq poerepnao ApUID0y ae G28 “SSVID AZIS AO NOILVNVIdXY YO LXA], AAS ‘HIOAT) AALLONGOUdAY AHL AO SANVIG INAIAAAAIC, LV SHIVHAA AVUD AO SAIUVAOG NI VILNVOIATY VuOatorD AO (WW) YaIaWVIC 6 AWIAVL 68 The Gray Whale replaces the luteal cells, and the proportion of connective tissue increases. Some of the smaller corpora albicantia consist almost entirely of unpigmented connective tissue. The corpora albicantia persist throughout life in the ovaries of fin whales (Laws, 1961) and this probably applies to all large balaenopterids. This also occurs in sperm whales (Best, 1967), but not in at least some of the smaller odontocetes, such as the pilot whale, Globicephala melaena (Harrison, 1949; Sergeant, 1962). The corpora persist as permanently recognizable structures in the ovaries of gray whales. The corpora albicantia of each female (excluding nulliparous and primiparous ones) were classified accord- ing to relative size in the following manner: class 1, the largest corpus in each whale; class 2, the second largest, and so on. The mean, standard error, and range for each of these classes in females in each phase of the reproductive cycle are presented in Table 9. It is apparent from the size distribution that after an initial phase of rapid regression, there is little further decrease in size of the corpora albicantia. Few were less than 12 millimeters in diameter. In the discussion of time and frequency of ovulation, it was concluded that females usually ovulate only once every 2 years. If this is true, and the corpora albicantia persist for life, the rate of accumulation of corpora albicantia would be close to 0.5 per year. We examined two other lines of evidence bearing on this question: the size frequency distribution of the corpora albicantia and the correlation between number of corpora albicantia and number of growth layers in the ear plug. The means, standard errors, and ranges of the diameters of the corpora lutea and two largest corpora albicantia of females in each stage of the reproductive cycle are shown in Fig. 25. We assumed that each female ovulates only once every 2 years, and adjusted the horizontal time scale accordingly. The smooth line shows the presumed rate of regression in size of the corpus albicans during the first 4 years. If the smaller corpora albicantia (Table 9) were similarly plotted, the line would gradually approach the horizontal at about 14 millimeters beyond 20 years. It is apparent from Fig. 25 that a presumed accumulation rate of one corpus albicans every 2 years is consistent with the observed size-frequency distribution of Female Reproductive Cycle 69 120 100 80 DIAMETER (CM) g + b fe) oO fe) ee ee a 20 oy 10 << CORPUS LUTEUM——S|<-LARGEST CORPUS ALBICANS >| 2nd LARGEST CORPUS ALBICANS> RO EP LP PP RO EP LP PP RO EP LP PP YEARS Fic. 25. Diameter of corpus luteum and two largest corpora albicantia in ovaries of gray whales in different stages of the reproductive cycle. The hori- zontal scale represents the age of each corpus, assuming one ovulation every two years. RO, recently ovulated females; EP, early pregnant females; LP, late pregnant females; PP, postpartum females. The two postpartum females had lost their calves, thus their corpora lutea were smaller than in lactating animals. Horizontal dashes, mean; vertical bars, two standard errors on either side of mean; vertical lines, range. Curve fitted by eye to mean diameters of corpora. corpora. If the ovulation rate were significantly greater, the size- frequency data would not show such a regular decline. The data on ovulation further indicate that the rate cannot be less than about 0.5 per year. The relationship between number of corpora albicantia and the number of growth layers in the ear plug is presented in Fig. 26. The solid line (Y = 0.5X — 3.5) represents the expected correlation between number of corpora and number of growth layers under the assumptions that two growth layers are formed the first year 70 The Gray Whale i) et] fo) (o) NUMBER OF CORPORA IN OVARIES re) 40 50 10 20 30 NUMBER OF GROWTH LAYERS IN EAR PLUG Fic. 26. Number of corpora in the ovaries versus the number of growth layers in the ear plugs of adult female gray whales. The hypothetical correlation is represented by the unbroken line (mean) and the broken lines (range). and one each year thereafter, and that one corpus is formed every 2 years beginning at 8 years of age (mean age at sexual maturity). The two broken lines (Y = 0.5X — 2.0 and Y = 0.5X — 5.0) represent the lower and upper limits, respectively, of variation expected because of the variation in the age at sexual maturity of from 5 to 11 years. Deviations from the hypothetical mean number of growth layers are markedly skewed. The mode falls on the lower limit (-3); 41 per cent of the specimens fall within the expected limits (-3 to +3). Only one whale falls above the expected limits (+7); 57 per cent fall below the lower limit (—3 to —37), with 33 per cent falling between —3 and —7. These data are thus consistent with the conclusions that corpora accumulate at a rate of 0.5 per year and growth layers in the ear plug accumulate at a rate of one per year, although the earlier layers may not be discernible. The only corpora albicantia that are unquestionably derived from corpora lutea of ovulation are those in nulliparous and Female Reproductive Cycle 71 primiparous females. ‘These corpora do not differ in size or other respects from those representing corpora lutea of pregnancy. In three recently ovulated nulliparous females, the largest corpora albicantia were 23, 30, and 34 millimeters in diameter, and in two primiparous females in early pregnancy they were 13 and 29 milli- meters in diameter. All except the smallest of these were within the size range of the largest corpora albicantia in multiparous females in corresponding phases of the reproductive cycle (Table 9). In addition to normal corpora albicantia, the ovaries of 13 females each contained one to three small orange bodies 4 to 9 millimeters in diameter and which were either compressed and elongate, or stellate, in cross section. The total number of these structures in the 13 animals was 17, which was 2 per cent of the corpora albicantia present in all the females. They are similar to the corpora atretica described by Laws (1961) for the fin whale and presumably originate by atresia of follicles that have not ovulated. This assumption is supported by the finding of a few unruptured follicles with a partial lining of yellow-orange colored tissue. These corpora ap- parently do not represent ovulations and they were not included in counts of corpora albicantia. FUNCTIONAL SYMMETRY AND POLARITY OF OvarirEs.—Of the total of 756 corpora, 418 (55.3 per cent) were in the left ovary and 338 (44.7 per cent) in the right ovary. The probability of this ratio occurring in a random distribution is less than .05, suggesting that the observed dominance of the left ovary may be real. Laws (1961) found a slight but statistically insignificant dominance of the right ovary in fin and blue whales. In many odontocetes, most ovulations occur in the left ovary (Ohsumi, 19640). The position of each of 179 corpora in the anterior, second, third, or posterior quarter (measured linearly) of 52 mature ovaries was recorded. ‘There was a significant (P < .005) preponderance of corpora toward the anterior pole. The numbers of corpora in each quarter, from anterior to posterior, were: 61 (34 per cent), 48 (27 per cent), 45 (25 per cent), and 25 (14 per cent). A preponderance of ovulations from the anterior pole of the ovary was also found in fin and sei whales (Laws, 1957) and in the sperm whale (Best, 1968), but not in the pilot whale (Harrison, 1949; Sergeant, 1962) or false killer whale, Pseudorca crassidens (Comrie and Adam, 1938). 72 The Gray Whale Pregnancy PREGNANCY RatTe.—The pregnancy rate is difficult to determine directly because of bias introduced into the sample by the temporal and spatial differences in migration patterns between females in different phases of the reproductive cycle and by gunner selection for the larger animals. In the series of 84 southbound migrants examined, the ratio of late pregnant females to other mature females was two to one, whereas the actual ratio in the population must be less than one to one. The sample of northbound adult females consisted of 22 early pregnant females and eight anestrous females, but only two postpartum females. As it is logical to assume that the number of postpartum females in the spring population should be nearly equal to the number of pregnant females, the sample was obviously biased. Because the proportion of late pregnant and postpartum females in the samples was biased, these animals were excluded from cal- culations of the pregnancy rate and appropriate corrections made to determine the overall pregnancy rate in the adult female segment of the population. The pregnancy rate of females that had already undergone at least one pregnancy will be considered first. During the southward migration, all females that were not carrying near-term fetuses had a developing corpus luteum. If we assume that all of them had conceived, their pregnancy rate would be 1.00. As a few may not have conceived, this figure may be a slight overestimate. During northward migration, 20 of 27 females (exclusive of postpartum females) were pregnant, giving a pregnancy rate of 0.74. Two of the females that were not visibly pregnant each had a corpus luteum that we assumed to be a corpus luteum of ovulation. Although it is possible that they had recently conceived and were carrying a con- ceptus too small to detect, we think this is unlikely so late in the season. Considering both the northbound and southbound migrants, 41 of the 48 were pregnant or could reasonably be assumed to have already conceived. ‘This gives a pregnancy rate of 0.85 per breeding season. Considering females that had not undergone a previous preg- nancy, all seven taken onthe southward migration had recently Female Reproductive Cycle 73 ovulated. Each of five animals had a single corpus luteum 19 to 62 millimeters in diameter and were assumed to have already conceived. One with a recently ruptured follicle and a corpus luteum of ovulation (25 millimeters in diameter) possibly had done so. The last had what appeared to be a corpus luteum of ovulation (27 millimeters in diameter) and Graafian follicles up to 35 milli- meters in diameter, so it might have ovulated again later and then conceived. Of the three northbound animals examined, two were pregnant. The third had two fairly recent corpora lutea (22 and 13 millimeters in diameter) and was probably not pregnant. Thus, of 10 females that had not previously been pregnant, seven were pregnant, two were not pregnant but probably would have con- ceived later, and one probably would not have conceived that season. These data indicate a probable pregnancy rate of 0.90 per breeding season, but further data are needed to determine whether newly mature females are as fertile as older individuals. The combined pregnancy rate for nulliparous and parous fe- males, exclusive of late pregnant and postpartum animals, is 0.86. To determine the overall pregnancy rate for all adult females in the population, we made a correction for the biased representation of late pregnant and postpartum females in the sample. If the pregnancy rate remains constant from year to year, or if the sample was taken over a period of several years, the overall pregnancy rate may be calculated as 0.86/1.86, or 0.46 per year. Zenkovich (1937a) examined a large series of gray whales taken in the Bering Sea between August and October from 1933 to 1936. Assuming that all females 12.0 meters or more in length were sex- ually mature, there were 57 mature females in his sample. Of these, only 16 were pregnant, giving a calculated pregnancy rate of only 0.28. G. C. Pike (unpublished data) reported that only one of three adult females he examined off British Columbia in April was pregnant. Of the seven northbound adult females (exclusive of postpartum individuals) that were not pregnant, only three had recently ovulated, indicating that missed pregnancies may result from either failure to ovulate or failure to conceive following ovulation. BREEDING SEASON.—Almost all of the adult females (except those carrying near-term fetuses) taken during southward migration 74 The Gray Whale TABLE 10 Bopy LENGTH oF GRAY WHALE EMBRYOS AND EARLY FETUSES (CROWN-RUMP LENGTH OF EMBRYOS IN PARENTHESES). Length (mm) Date of collection Males Females 21 February 80 90 22 February 120 23 February 59 (40), 85 24 February 110 90, 110 26 February 80 28 February 85 90 1 March 75, 120 140 2 March 39 (16) 25 (10), 105 6 March 120, 120 7 March 110 8 March 135 10 March 120 probably had already conceived, although none was visibly preg- nant. The mean conception date calculated from the fetal growth curve (see below) is 5 December. We calculated the duration of the breeding season by estimating the ages of the 22 embryos and early fetuses collected. ‘The estimated ages were based on certain assumptions about early fetal growth discussed below. The cal- culated conception dates fall between 27 November and 13 De- cember, except for one on 22 December and one on 5 January. The female that conceived about 22 December was multiparous and showed evidence of two recent ovulations, indicating that she had failed to conceive following her first ovulation that season. The female that conceived about 5 January was primiparous; Laws (1961) found that newly mature female fin whales conceive, on the average, later than multiparous females. The duration of the breeding season also was estimated on the basis of length measurements for 16 fetuses collected in late summer by Zenkovich (1937a). ‘The estimated conception dates of 12 (75 per cent) of these fetuses fall between 23 November and 14 De- cember, and all fall between 13 November and 10 January. In- dividual variations in growth rate will give a spurious spread to the calculated range, so that the actual breeding season is doubtless even shorter than these data indicate. For the same reason, the Female Reproductive Cycle Fic. 27. Embryos and early fetuses of gray whales. A, 25-millimeter (10 millimeters crown-rump) female embryo, estimated age 55 days; B, 39-millimeter (16 millimeters crown-rump) male embryo, estimated age 70 days (note hind limb buds); C, 120-millimeter male fetus, estimated age 87 days (note size and position of penis); D, 110-millimeter female fetus, estimated age 86 days (note size and position of clitoris). 76 The Gray Whale data from near-term fetuses are even less useful for calculating conception dates. GESTATION PERIOD AND FETAL GrowTH.—Available measurements of fetuses are limited to the periods of early and late pregnancy. A total of 22 embryos and early fetuses was collected between 21 February and 10 March (Table 10, Fig. 27). Body length, measured from the crown to the tip of the straightened tail varied between 25 and 140 millimeters (mean, 96; standard error, 6). Additional data on fetal sizes in the gray whale are contained in a number of reports. Scammon (1874) examined five embryos taken on the California coast, but gave no measurements or dates. Andrews (1914) reported fetuses 180 and 250 millimeters long taken on 13 and 14 March 1912, on the coast of Korea. Pike (unpublished data) found a 250-millimeter fetus the first week of April from the coast of Vancouver Island, British Columbia. Zen- kovich (1937a) published data for 16 fetuses collected in the Bering Sea between 8 August and 24 September. Their lengths ranged from 1.70 to 2.64 meters, with a mean and standard error of 2.05 + 0.06. ‘Townsend (1887) examined four fetuses taken in December 1885 at San Simeon, California, and stated: ‘Their average length was about 12 feet [3.66 meters]; the longest .. . 17 feet [5.18 meters] long.” Andrews (1914) inconsistently reported one fetus taken at Ulsan, Korea, on 8 January 1912, as 4.35 and 4.76 meters long. We measured 55 near-term fetuses (30 males, 25 females) col- lected during a 38-day period from 14 December to 20 January. The length varied between 3.60 and 5.31 meters, with a mean and standard error of 4.62 + 0.05 (Table 11, Fig. 28). The average leneth of females (4.65 + 0.06 meters) was slightly greater than that of males (4.60 + 0.08), but the difference was not statistically sig- nificant (P > .10). If these measurements are grouped by shorter time periods, they show no change in mean length from mid- December until late January. This suggests that the timing of migration of a pregnant female depends upon how advanced her pregnancy is. The statistics for Norwegian factory ship operations near the calving grounds on the west coast of Baja California from 1924 to 1927 (published in part by Risting, 1928) list 20 fetuses taken from 29 December to 16 February with estimated (not actually Female Reproductive Cycle Ty TABLE 11 Bopy LENGTH OF NEAR-TERM FETUSES OF GRAY WHALES. Length (meters) Date of collection Males Females 14 December 4.86 15 December 4.58 16 December 4.53, 4.65, 4.67 18 December 4.50 19 December 4.15 20 December 4.07, 4.54, 4.84 4.55, 4.78, 5.12 21 December 3.85, 4.62, 4.63 5.08 22 December 4.62, 4.79 27 December 4.22, 4.89 3.60 28 December 4.52, 4.81 4.32 29 December 4.70 5.12, 5.12 30 December 5.24 2 January AZ 4.58 3 January 4.77, 5.31 4.42, 4.44, 4.93 4 January Aide, GeO 5 January 4.72 AO 7 January A Lie, as 4.43 8 January 4.11, 4.73 1] January 4.33, 5.11 12 January 4.59 13 January 4.41, 4.48 15 January 4.26 16 January 4.53 18 January 4.80 19 January 4.39 20 January 4.75 measured) lengths ranging from 6 to 18 Norwegian feet (1.90 to 4.71 meters). Measurements of six recently born calves found dead at Laguna Ojo de Liebre, Baja California, in late January and early February, are given by Eberhardt and Norris (1964). ‘These ranged from 3.95 to 5.40 meters (mean, 4.68; standard error, 0.245). Gilmore (1960a) also listed measurements of seven recently born calves found in the same lagoon. ‘The total lengths given for these calves (3.54 to 4.51 meters, mean, 4.05) are well below those presented by Eberhardt and Norris and even average less than our December fetuses. ‘There- fore, we can only conclude that Gilmore made his measurements differently or that the published figures are in error. 78 The Gray Whale Fic. 28. Near-term gray whale fetus 4.54 meters long. Note color pattern of whitish rings and blotches (the other marks are postmortem abrasions). Only three of the series of measurements presently available are large enough to provide statistically reliable data for use in con- structing a fetal growth curve for the gray whale. These include our series of early embryos and fetuses, Zenkovich’s series taken in late summer, and our series of near-term fetuses. ‘The means for these three sets of measurements have been plotted in Fig. 29. It is apparent that the points do not fall on a straight line. Laws (1959) found that in balaenopterid whales, excepting the earliest 5 EST. MEAN LENGTH AT BIRTH | N BODY LENGTH (M) EST. MEAN BIRTH DATE MONTH Fic. 29. Estimated prenatal growth curve based on measurements of 22 embryos and early fetuses collected in February and March, Zenkovich’s (1937a) 16 mid-term fetuses collected in August and September, and 55 near-term fetuses collected in December and January. Horizontal dashes indicate means; vertical bars represent two standard errors on either side of mean, and vertical lines represent the range. For estimation of t, see text. Female Reproductive Cycle 79 part of pregnancy, the length of the fetus increases linearly during the first half of pregnancy and logarithmically during the last half. A similar curve fits the present data (Fig. 29). From the slope of the lower portion of this curve, we estimated the “specific fetal growth velocity,” or a of Huggett and Widdas (1951), as 0.95. To determine the total gestation period, it is necessary to esti- mate the length of the gestation period before the beginning of the linear growth phase, termed t, by Huggett and Widdas (1951). J. G. Sinclair, who is studying the anatomy of two early fetuses (25 and 39 millimeters long from crown to tip of tail, and 10 and 16 millimeters in crown-rump length), has, on the basis of their stage of development, estimated their ages at about 55 and 70 days. According to Sinclair, the rapid linear growth phase starts when ossification begins, at a crown-rump length of about 35 milli- meters; this is equivalent to a length of about 55 from crown to tip of tail. Judging from the estimated ages of the two early em- bryos, this length would be reached at an age of at least 80 days, or perhaps slightly more. An estimate of t, will therefore be 80 — (5.5 x 0.95), or about 75 days. The growth curve, extrapolated back- wards, intercepts the abscissa on 18 February (Fig. 29). Adding to this the estimate of tj, the calculated mean conception date falls on 5 December. If the growth curve is projected forward, it intercepts the mean length of the six newborn calves observed by Eberhardt and Norris (1964) on 2 January, only 2 days later than the mean date of passage of pregnant females past San Francisco. Considering the speed of migration, it would take the whales at least 9 to 12 days to travel from San Francisco to the major calving grounds at Laguna Ojo de Liebre, Laguna San Ignacio, and Bahia Magdalena. Therefore, the mean birth date would be about 10 January, when the projected growth curve reaches 4.90 meters. This estimate of length at birth falls within one standard error of the mean of newly born calves, so the agreement is close. Based upon the calculated mean dates of conception and parturi- tion, the mean length of the gestation period is estimated to be slightly more than 13 months, or about 400 days. Applying Laws (1959) method of estimating t, for baleen whales to the data of this study yields values of only 31 days for t, and 80 The Gray Whale CORNUA DIAMETER (CM) IMMATURE ] N N s N s | N s Ni ees N REC. OV. | E. PREG.| L. PREG. P.- PART. a PREG. |L PREG. |P-PART. REC. ov.) |ANESTR, NULLI | PRIMIPAROUS |paRous MULTIPAROUS | PAROUS NULLI. Fic. 30. Diameter of the uterine cornua of gray whales in different stages of the reproductive cycle. For pregnant and postpartum females, measurements of the horn in which implantation occurred are plotted above the base line and those for the other horn below. Symbols are as follows: horizontal dashes, mean; vertical bars, one standard deviation on either side of the mean; vertical lines, range; S, southbound migrants; N, northbound migrants. no more than one year for total gestation period, which are not consistent with the actual data. The discrepancy results from the way in which Laws interpreted data for several species of terrestrial mammals given by Huggett and Widdas (1951) in estimating the length of ¢, for three species of odontocetes in which fetal growth is linear until the end of pregnancy. His estimates showed an inverse relationship between t, and length of gestation period (and also a). Huggett and Widdas’ data show, however, that “t, increases as gestation times lengthen but forms a decreasing fraction of total gestation time” (italics added). ‘There are no data to justify Laws’ conclusions; his error appears to be the result of using im- precise, arbitrary percentage values for t,. Laws then estimated the length of t, in the humpback whale as 38 days on the basis of published fetal length data and Chittleborough’s (1954, 1958) data on the mating and calving seasons. Chittleborough’s data suggest, however, a peak conception date in late July, not early August as stated by Laws, so Laws’ estimate of t, is doubtless too short. Since his four estimates of t,, for three species of odontocetes and one Female Reproductive Cycle 81 mysticete, showed an apparently consistent inverse relationship between ¢, and a, he extrapolated these results to other species of baleen whales. ‘This resulted in his inexplicable and anomalous conclusion that the larger species of balaenopterid whales have shorter gestation periods than the smaller ones. Any logical extrapolation of the data presented by Huggett and Widdas would result in an estimate of at least 50 or 60 days for the duration of t, in larger cetaceans. In any event, it is dangerous to extrapolate from small terrestrial mammals to large cetaceans. We suspect that when more direct evidence is available on early embryonic growth, most large mysticetes will be found to have a gestation period of about a year or somewhat longer. It is certainly approximately 13 months in the gray whale, and probably more than a year in the humpback whale. A gestation period longer than one year would not preclude an occasional pregnancy resulting from a postpartum ovulation, as has been reported in fin whales (Laws, 1961) and humpback whales (Chittleborough, 1958), but it does indicate that such pregnancies cannot occur regularly if a marked seasonality of breeding is to be maintained. CALVING SEASON.—The mean calving date, as indicated above, is estimated to be about 10 January. The duration of the calving season should be generally similar to that of the breeding season, but slightly more prolonged because of individual variation in the length of the gestation period. As noted above, the timing of the southward migration of pregnant females depends on the stage of gestation. Because late pregnant females pass San Francisco for at least 38 days, we may assume that the calving season lasts about that many days. Therefore, we estimate that calving occupies a period of 5 or 6 weeks from late December to early February. ‘This is corroborated by field observations of recently born calves (Eber- hardt and Norris, 1964; Gilmore, 1960a, 1960b; Gilmore and Ewing, 1954; Hubbs and Hubbs, 1967). Cyctic CHANGES IN THE UTERUS.—Gray whales have a bipartite uterus similar to that of other baleen whales (Mackintosh and Wheeler, 1929; Matthews, 1948). The placenta is of the diffuse, nondeciduate, epitheliochorial type. Measurements of the diameter of the uterine cornua of specimens examined in this study are presented in Fig. 30. Histological characteristics of the endometrium 82 The Gray Whale Fic. 31. Photomicrographs of sections of the endometrium of gray whales in different stages of the reproductive cycle. A, immature female; B, north- bound anestrous female; C, southbound recently ovulated female; D, north- bound early pregnant female (110-millimeter fetus); E, southbound late pregnant female (3.60-meter fetus); F, northbound postpartum female. All sections are to same scale. 83 Cycle Female Reproductive dsolD aso[D dsoly aso[D asolyD IsolD asolD Iso[D asoly 9PIM 9PIM suroeds 04-06 OF 08-02 = GO 0 ee V6l Fo-16 G66 6 OLI-06 GLI+86I OOFE-06I OOF +FCL OOI-GI GI+6E 16-0 LEFOK Sb-Cl GLFV FS s8h O8-Sh FOI+LG 006-46 GOEFESI ESHS COFFE 066 FE+E6 66-8 OG+PF8I