Biological Services Program FW5/0B3-3I/36 FWS/OBS- 81/36 September 1981 0 I DOCUMENT COLLECTION Pilot Study of the Marine Mammals, Birds and Turtles in OCS Areas of the Gulf of Mexico Bureau of Land Management Fish and Wildlife Service U.S. Department of the Interior The Biological Services Program was established within the U.S. Fish and Wildlife Service to supply scientific information and methodologies on key environmental issues that impact fish and wildlife resources and their supporting ecosystems. The mission of the program is as follows: t To strengthen the Fish and Wildlife Service in its role as a primary source of information on national fish and wild- life resources, particularly in respect to environmental impact assessment. t To gather, analyze, and present information that will aid decisionmakers in the identification and resolution of problems associated with major changes in land and water use. • To provide better ecological information and evaluation for Department of the Interior development programs, such as those relating to energy development. Information developed by the Biological Services Program is intended for use in the planning and decisionmaking process to prevent or minimize the impact of development on fish and wildlife. Research activities and technical assistance services are based on an analysis of the issues, a determination of the decisionmakers involved and their information needs, and an evaluation of the state of the art to identify information gaps and to determine priorities. This is a strategy that will ensure that the products produced and disseminated are timely and useful. Projects have been initiated in the following areas: coal extraction and conversion; power plants; geothermal , mineral and oil shale develop- ment; water resource analysis, including stream alterations and western water allocation, coastal ecosystems and Outer Continental Shelf develop- ment; and systems inventory, including National Wetland Inventory, habitat classification and analysis, and information transfer. The Biological Services Program consists of the Office of Biological Services in Washington, D.C., which is responsible for overall planning and management; National Teams, which provide the Program's central scientific — ■■ ■ ■ — i—a— .1 «^«»*uit_iiuLirMnna_jfflc rnntracting bioloqical services ^nd others; Regional level ; and staffs at iiho conduct in-house s, birds and lexico Reynolds , Biological 6) WHO I DOCUMENT O0U.ECT1ON ^m B~ n- ru =T I m m lj □ hi ^^^— o ^S2 m :e==e a =3 a 11 ■ FWS/OBS - 81/36 September 1981 PILOT STUDY OF THE MARINE MAMMALS, BIRDS AND TURTLES IN OCS AREAS OF THE GULF OF MEXICO W H 0 I DOCUMENT by V COLLECTION Thomas H. Fritts and Robert P. Reynolds U.S. Fish and Wildlife Service Denver Wildlife Research Center New Orleans Field Station Tulane University Museum of Natural History Belle Chasse, Louisiana 70037 Contract No. 14-16-009-79-951 Project Officers Cherry E. Keller David M. Smith National Coastal Ecosystems Team U.S. Fish and Wildlife Service This project was sponsored by the Bureau of Land Management Prepared for Coastal Ecosystems Project Office of Biological Services Fish and Wildlife Service U.S. Department of the Interior Washington, D.C. 20240 SUMMARY Aerial surveys of marine mammals, birds, and turtles were conducted at four subunits of the Gulf of Mexico from August to December 1979. This Pilot Study was designed to develop techniques and to collect preliminary data on the vertebrate faunas of outer continental shelf (OCS) waters. This information, once expanded to include an adequate sample size, will be important to evaluating effects of oil and gas development in offshore areas. Surveys were conducted at altitudes of 91 and 228 m. The 91-m surveys were superior for detecting and identifying birds and turtles, while more area could be surveyed for larger animals at 228 m. Waters within 111 km of shore were sampled at a 3:1 ratio in relation to waters 111 to 222 km offshore. Texas subunits extended beyond the continental shelf, but Florida subunits did not. Observations were made on 12 mammal, 35 bird, and 5 turtle taxa. Sperm whales were documented in waters off Texas. Marine turtles were common in the eastern Gulf but virtually absent from the western areas studied. Differences in dolphin faunas in the eastern and western subunits were noted and potential north-south movements in response to season were noted on both sides of the Gulf of Mexico. The maps and basic ecological data collected provided a unique view of faunal differences within OCS areas of the Gulf of Mexico. Because of the complexity of the Gulf of Mexico and its fauna, additional analyses will depend upon having data encompassing annual, seasonal, geographic, and bathymetric variation. Additional survey areas and more frequent samples emphasizing seasonal variation on successive years are required for making more accurate conclusions and effective management decisions relevant to OCS development. in CONTENTS Page SUMMARY iii FIGURES vi TABLES vii ACKNOWLEDGMENTS xi INTRODUCTION 1 STUDY AREA 5 METHODS 7 OBJECTIVE ONE: GENERAL SURVEY PROCEDURES 7 Survey Design 7 Data Collection 9 Environmental Parameters 9 OBJECTIVE TWO: DATA MANAGEMENT 12 Data Manipulation and Analysis 12 Population Enumerators 12 Mapping 13 OBJECTIVE THREE: THE PRELIMINARY SURVEY 13 Training Session 13 Survey Subunits 14 Survey Dates 14 Aircraft and Equipment 14 Oil and Oil Response Activities 17 RESULTS 18 IDENTIFICATION AND DETECTION 18 Mammals 18 Birds 19 Turtles 20 OCCURRENCE 21 Mammals 21 Birds 21 Turtles 28 SEASONAL VARIATION 28 Mammals in STEX 28 Mammals in NTEX 31 Mammals in NFLA 31 Mammals in SFLA 31 Birds in STEX 31 Birds in NTEX 34 IV CONTENTS Concluded Page Birds in NFLA 34 Birds in SFLA 34 Turtles in Texas and Florida 34 DAILY VARIATION 39 BATHYMETRY AND DISTANCE FROM SHORE 42 Mammals in STEX 43 Mammals in NTEX 43 Mammals in NFLA 44 Mammals in SFLA 44 Birds in STEX 44 Birds in NTEX 45 Birds in NFLA 46 Birds in SFLA 46 Turtles in Texas 47 Turtles in NFLA 47 Turtles in SFLA 47 GROUP SIZE 49 Mammals 49 Birds 49 ASSOCIATION OF MAMMALS AND BIRDS WITH VESSELS 56 MULTIPLE SPECIES ASSOCIATIONS 57 DENSITY ESTIMATES 58 SEA SURFACE TEMPERATURES 63 OBSERVER BIAS 63 ALTITUDINAL EFFECTS 65 BEAUFORT FORCE 71 GLARE 71 CONCLUSIONS 74 LITERATURE CITED 76 APPENDIX: MAPS 77 FIGURES Number Page 1 Overall study sequence for evaluating effects of OCS development on marine mammals, birds, and turtles 2 2 A hypothetical subunit depicting one day's flight path 8 3 Example of an aerial survey observation sheet used during the Pilot Study 10 4 Data flow for the field surveys 11 5 Deviation in percent of sightings by paired aerial observers 64 VI TABLES Number Page 1 Coordinates of the geographic limits of each survey subunit 15 2 Summary of dedicated aerial surveys conducted during the Pilot Study 16 3 Summary of all marine mammal species sighted in the four survey subunits during the August and November/December surveys 22 4 Summary of all bird species sighted in the four survey subunits during the August and November/December surveys 23 5 A primary list of sea birds occurring in waters of the Atlantic Ocean and Gulf of Mexico off the Southeastern United States 24 6 Summary of turtles observed during August and November/ December 1979 surveys 29 7 Seasonal variation in relative abundance of marine mammal sightings in the STEX survey subunit 30 8 Seasonal variation in relative abundance of marine mammal sightings in the NTEX survey subunit 30 9 Seasonal variation in relative abundance of marine mammal sightings in the NFLA survey subunit 32 10 Seasonal variation in relative abundance of marine mammal sightings in the SFLA survey subunit 32 11 Seasonal variation in relative abundance of bird sightings in the STEX survey subunit 33 vn TABLES Continued Number Page 12 Seasonal variation in relative abundance of bird sightings in the NTEX survey subunit 35 13 Seasonal variation in relative abundance of bird sightings in the NFLA survey subunit 36 14 Seasonal variation in relative abundance of bird sightings in the SFLA survey subunit 37 15 Sighting frequency of marine turtles in Texas and Florida 38 16 Seasonal occurrence of sightings for turtles in Florida 38 17 Daily variation in the number of sightings of groups of selected bird and mammal species in the NFLA survey subunit 40 18 Daily variation in the number of sightings of groups of selected bird and mammal species in the SFLA survey subunit 41 19 Depth and distance from shore comparisons for turtles sighted in Texas survey subunits 48 20 The distribution of loggerhead turtles sighted in Florida during August in relation to water depth 48 21 Summary of mean group sizes for mammals in STEX 50 22 Summary of mean group sizes for mammals in NTEX 50 23 Summary of mean group sizes for mammals in NFLA 51 24 Summary of mean group sizes for mammals in SFLA 51 Vlll TABLES Continued Number Page 25 Summary of mean group sizes for birds in STEX 52 26 Summary of mean group sizes for birds in NTEX 53 27 Summary of mean group sizes for birds in NFLA 54 28 Summary of mean group sizes for birds in SFLA 55 29 The number of surface vessels seen during aerial surveys 56 30 Density statistics for selected species in seasonal samples 60 31 Density statistics for selected species in the NFLA subunit 61 32 Density statistics for selected species in the SFLA subunit 62 33 The number of sightings made at low and high altitudes in STEX during August 66 34 The number of sightings made at low and high altitudes in NTEX during August 66 35 The number of sightings made at low and high altitudes in STEX during November 67 36 The number of sightings made at low and high altitudes in NTEX during November 67 37 The number of sightings made at low and high altitudes in NFLA during August 68 IX TABLES Concluded Number Page 38 The number of sightings made at low and high altitudes in SFLA during August 68 39 The number of sightings made at low and high altitudes in NFLA during November 69 40 The number of sightings made at low and high altitudes in SFLA during November 69 41 The number of groups seen in low flights expressed as a percentage of those seen in corresponding high flights 70 42 The number of unidentified bird sightings expressed as a percentage of total bird sightings made during low and high flights 70 43 Percentage of total observations made at each Beaufort sea state 72 44 Number of observations made from each side of the aircraft during surveys flown on east-west axes 72 45 Number of observations made from each side of the aircraft during surveys flown on northwest-southeast axes 73 46 Ratios of south/north (southwest/northeast for NTEX) observations for all groups 73 ACKNOWLEDGMENTS Field work was conducted by personnel of the Denver Wildlife Research Center and Texas A & M University. Larry Hobbs, Stephen Leatherwood, and Charles Gates contributed to the development of the study plan. Linda S. Dunn contributed technical assistance and Joan Randell typed the manuscript. XI INTRODUCTION The Marine Mammal Protection Act (MMPA) of 1972 (16 U. S. C. 1361-1407) recognized the importance of marine mammals and established a national policy designed to protect marine mammals and the habitats in which they occur. The Endangered Species Act of 1973 provided for the conservation of all plant and animal species that are determined to be endangered or threatened. Implementation of both acts has pointed out the complexity of biological systems and the need for information about organisms and their environments to provide a basis for management decisions relating to man's utilization of the environment. To make effective management decisions relative to oil and gas exploration and production on the Outer Continental Shelf (OCS), the Bureau of Land Management requires information on the distribution and abundance of organisms that are potentially affected or vulnerable to activities in the OCS area. Thirty-two species of marine mammals protected by the MMPA, including six endangered species, occur within the South Atlantic and Gulf of Mexico OCS area. However, even the most basic aspects of their biology within the area are poorly understood because of the lack of thorough studies involving systematic and modern sampling regimes. Similarly, five species of marine turtles are present, including four that are considered endangered within the area. Since the Gulf of Mexico and South Atlantic waters are the warmest waters coterminous with the United States, they contain the most significant sea turtle populations within national limits and border on all significant nesting beaches in the United States, with the exception of Hawaii and Puerto Rico. The birds of this area include several endangered species in coastal areas, but also include key pelagic species. The abundance of these important oceanic migrants reflects biological productivity and ecological relationships which are difficult and expensive to measure directly. Thus, oceanic birds are an important data source. In order to minimize the impact of the development of energy resources in OCS areas, baseline data are needed for birds, marine mammals, and turtles in marine and coastal areas. Once species composition and abundance are known and key biological areas are specified, more precise studies will be needed to address major data gaps, potential problems with OCS activities, and the management procedure necessary to minimize critical environmental alterations (Figure 1). These objectives are contingent upon a firmly based survey expanding our present knowledge of birds, mammals, and turtles within the study area. EXISTING KNOWLEDGE Data Collection Formulation of Needs Comprehensive Study Plan FIELD SURVEYS ->S ummar izat ion- Interpretation £- -^Analysis Data Collection- Continue to Monitor Formulation of Needs Study Plan for Specific Areas and Problems I Data Collection <- -> Summarization - Interpretation<- -> Summarization - Interpretation <- Formulation of Needs for Continued Work i Development of OCS Management Programs -> Analysis ->Analysis Figure 1. Overall study sequence for evaluating effects of OCS development on marine mammals, birds, and turtles. A pilot study of the seasonal distribution and abundance of marine mammals, birds, and turtles in the Gulf of Mexico was initiated in June 1979. This study encompassed the initial steps of a comprehensive study of OCS effects upon these taxa. A comprehensive study plan was developed, and a variety of preliminary activities was undertaken. These included summarization of existing knowledge, review of the literature, development of software, development of survey techniques, and collection of preliminary data. The objectives of the Comprehensive Study Plan were as follows: 1. To determine and confirm which species of marine mammals, birds, and turtles inhabit or migrate through the OCS areas of the South Atlantic and Gulf of Mexico; 2. To identify temporal and spatial distribution of these species and the patterns of movement associated with such distributions; 3. To identify, delineate, and describe any areas of special biological significance for feeding, migration, and maintenance of the populations encountered; 4. To provide a basis for estimating relative abundance of individual species within the study area; 5. To amplify the understanding of population structure and basic ecology of poorly known species or populations where possible; and, 6. To formulate specific questions and investigative lines for subsequent research relevant to effects of oil and gas development and other research priorities in OCS areas on mammal, bird, and turtle faunas. The objectives of the Pilot Study were as follows: 1. To develop and test methods suitable for simultaneously surveying marine mammals, birds, and turtles from aircraft. 2. To develop and test with real and simulated data, the computer software necessary for analysis and storage of survey data. 3. To collect preliminary data on the distribution and abundance of marine mammals, turtles, and birds in the study area. 4. To summarize existing knowledge and literature on the marine mammals of the Southeastern United States. 5. To survey manatee distribution in southwestern Florida. The present report presents the results of activities relative to objectives 1 through 3 of the Pilot Study. The methods section describes the survey techniques and analytical procedures developed. The results section provides detailed analyses of the preliminary data collected. Schmidly (1981) is publishing the review of marine mammal literature and data. The study of manatee distribution is contained in a separate report (Irvine et al. In press). Work was coordinated from the New Orleans Field Station of the Denver Wildlife Research Center (DWRC; formerly National Fish and Wildlife Laboratory, NFWL) on the Riverside Campus of Tulane University. Personnel and resources of DWRC laboratories in Gainesville, Florida., Washington, D. C, and Albuquerque, New Mexico, were also involved in the study. Arrangements were made with Texas A ic M University for participation of other scientists with expertise in marine mammals and for statistical analysis of animal abundance. STUDY AREA The Pilot Study aerial surveys were conducted entirely within the U.S. waters of the Gulf of Mexico. The Gulf of Mexico is a contiguous embayment of the north Atlantic Ocean encompassing some 1,640,000 km2. Bordered largely by the United States, Mexico, and Cuba; its two main avenues of water exchange are the Yucatan and Florida submarine channels. The continental shelf is variable in width but most of the coastline is characterized as having an extensive shelf. Widths vary from 185 km and 215 km off the West Florida and Yucatan coasts, respectively, narrowing to 25 km off the Rio Grande Outlet and 13 km near Vera Cruz, Mexico (Lynch 1954). The transition from a wide to narrow shelf is rather abrupt west of Campeche, Mexico, and southwest from approximately Galveston, Texas. The Desoto Canyon briefly interrupts the wide shelf off the panhandle region of Florida. Currents are complex in origin but the basic pattern is analogous to that of the North Atlantic (Sturges and Blaha 1976). External input is largely from the Caribbean via the Yucatan Channel. Output is largely through the Florida Channel which contributes to the Gulf Stream. The micro-tidal range and the dominance of diurnal components (Marmer 1954) result in an increased importance of meteorologic forces on water circulation. Two dominant meteorologic regimes characterize the region: the Bermuda High and mid latitude frontal passages. The Bermuda High dominates the area with wind speeds generally being the strongest during the summer months when the elimatologic equator reaches its northern limits. Surface water temperatures are typically uniform over the Gulf of Mexico at this time, averaging some 28° C over the continental shelf and slightly cooler over the central Gulf of Mexico (Leipper 1954). During winter, gradations of surface water temperatures are more conspicuous. Temperatures generally range from 18.5° C in the northern Gulf of Mexico to 25° C off the Yucatan Peninsula (Leipper 1954), reflecting the increasing influence of mid latitude frontal passages followed by cooler polar air. Tropical disturbances, of which hurricanes are the most intense, form a third weather regime. Although infrequent, these disturbances often result in dramatic environmental alterations. There is an appreciable difference in the extent of human activities along the Florida and Texas coasts. The offshore oil activities and associated tanker traffic, along with the shrimp industry, are more intense along the Texas coast than off Florida. In both Florida and Texas, the northern survey subunits described in this report occur in the vicinity of major shipping lanes and receive more commerical ship traffic h> than the southern subunits. Pleasure craft and sport fishing boats are common in both Florida and Texas waters. METHODS The methods utilized can be viewed in relation to the first three objectives of the Pilot Study. Objective one requires survey procedures generally applicable to the study of marine mammals, birds, and turtles. Objective two involves data management and analysis, and objective three requires methodological details specific to the preliminary surveys. OBJECTIVE ONE: GENERAL SURVEY PROCEDURES Survey Design The survey design was based on a replicate model allowing the collection of a hierarchical data set which could be analyzed in a variety of ways. It was developed for the Pilot Study in consultation with Mr. Stephen Leatherwood of Hubbs-Sea World Research Institute. The design reduces sampling bias and "dead time" (travel to and from sampling units) between transects while enhancing statistical reliability and identification of environmental correlates. It is also suited to a large and complex study area such as the OCS areas of the southern United States. Individual subunits with borders of approximately 111 km (60 nmi) on the shoreline and extending 222 km (120 nmi) perpendicular to the shoreline were sampled using transect legs 111 and 222 km long. Six legs were flown per day at intervals of 18 km (10 nmi) and parallel to the long axis of the subunit. Replicates were flown on two successive days resulting in a total of 18 transects (total survey length 2,664 km per subunit). Transects were randomized with regard to (1) sampling order, (2) subunit section (north or south boundary), (3) exact starting position, (4) flight altitude (91 and 228 m), and (5) observer position within the aircraft. Transect lengths of 111 and 222 km were used in a 2:1 ratio, but aircraft altitudes of 91 and 228 m were flown with equal frequency. A hypothetical subunit depicting the flight path for one day is shown in Figure 2. Aircraft ground speed was constant at 222 km per hour (120 kn). Flights began at approximately 0800 hrs. and were terminated if the sea state conditions reached a Beaufort 4 or higher. A minimum of 6 hours per day was required to complete six transects. Weather conditions posed a particularly difficult problem in marine censusing, and not all surveys could be conducted under optimum conditions. Solar glare and rough seas were two problems for which no suitable solutions have been advanced. At Beaufort 4 large waves and numerous whitecaps impaired visibility by creating a visual distraction. N Figure 2. A hypothetical subunit depicting one day's flight path. On this day, it was randomly determined that (1) sampling would start at the southern boundary, (2) sampling would begin at nautical mile number 2, (3) the first leg would be 222 km (120 nmi) in length, and (4) the first leg would be flown at an altitude of 228 m (750 ft). The starting point and beginning altitude for replicate days would also be randomly chosen, but the order of long and short transect legs would change systematically to insure that 222 km transects were conducted in all possible positions in the subunit. On all days, altitudinal coverage was amplified by flying at 91 m (300 ft) on one leg of each round trip and at 228 m (750 ft) on the other. The flight crew consisted of a pilot, data recorder, and two observers. Observers were positioned on each side of the rear of the aircraft, while the pilot and recorder manned the front seats. The data recorder also served as flight leader and was responsible for flight details. Observer position was switched after 222 km of transect flight. The following DWRC personnel participated as observers and/or recorders during the Pilot Study: John Caffin, Thomas H. Fritts, Larry Hobbs, Wayne Hoffman, A. Blair Irvine, and Robert P. Reynolds. Barbara Dorf and David Schmidly of Texas A & M University also participated as observer/recorders. The observer/recorder seating arrangement described was best for our purposes but should be adapted to the configuration of the plane. Data Collection While on transect, observers searched continuously. Upon making an observation, the observer relayed the information to the data recorder. The data recorded at each encounter included local time, distance from transect line (radial and perpendicular angles of observation using degrees marked on the wing struts and clinometers), species identification (to the lowest taxon possible), position of sighting (latitude and longitude from Loran C navigation system), group size, direction of movement, activity, and human activities. Flight characteristics and environmental data were recorded at the start of each flight and when changes occurred during the flight. Sea surface temperatures were measured with a radiometer and recorded. Data were recorded with both handwritten and verbal notes (cassette recorders). An example aerial survey observation sheet is shown in Figure 3. Data were reviewed and verified by the flight crew following each day's flight and subsequently transferred to computer compatible format for analysis. Figure 4 summarizes data flow for the field surveys. Generally, whenever mammals or turtles were sighted, the aircraft diverted to the sighting and circled for closer inspection. This was not practical for birds because of their mobility. In addition to marine mammals, birds, and turtles, sightings were recorded for fish, sharks, sargassum, oil, debris, oil platforms, and boats. When possible, vertical and oblique photographs were taken of observations and indexed to actual time and date of observation. Environmental Parameters Two important variables that potentially influence the distributions of animals in oceanic waters are water depth and distance from shore. These variables are correlated but obvious differences do occur within the subunits surveyed during the present study. Therefore, an attempt was made to separate the effect of depth and distance. Visual representations of bathymetric variation have been constructed on the same scales as maps. Diagrammatic representations of shoreline configurations were also compared to the distributional patterns observed. Surface water temperatures were measured using a Barnes PRT-5 radiometer onboard the aircraft at the time of the individual observations. These data are remarkably uniform. Analyses of surface water temperatures are presented in the results. 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KJ Eh U) 05 O Q. >> 3 +-> CO +-> o 0) -c +-> bD c C-i 3 •o 0) Q) B o >> a) > 3 QJ eo c co E CO X w CO 0) & 10 Data capture Review, labels, archived ID & Group size verified Basic data description Review-data operations Review-project director Feedback-field operations Observational effects AN OVA Contingency analysis Free format data sheet Voice recorder Chart recorder Photography J Verified by observer team Copied, original archived < Transcribed & coded-EDP format » Corrections — Review-data operations 4- _» Review-field operations Copied & archived Corrections -> EDP input, scratch file Copy archived f- Mapping 1 Data summary output Subfile merged in data base i Merge verified Data base copied I Transliteration, sort of subfiles 1 . Analyses by day, season, area & species Statistical analyses Environmental correlates Descriptive statistics Correlation/ regression I Bivariate plots & data display Figure 4. Data flow for the field surveys. Abundance LineTran Package Abundance estimates Confidence limits Data distribution Relative fit 11 The distribution of three types of nautical craft was considered in the study. These are sport (recreational) craft, fishing/shrimp boats, and ships (including all large vessels not engaged in fishing or sport activities). Two levels of association between different animal taxa were considered: (1) Incidental association resulting from sharing physical habitat such as inshore waters or perching sites, and (2) direct associations where interactions of various taxa are expected or where animals are responding to a shared resource such as krill, bait fish, and carrion. OBJECTIVE TWO: DATA MANAGEMENT Data Manipulation and Analysis The identification, development, and testing of software necessary to capture, analyze, and archive field data relevant to the study are important elements of the Pilot Study. The Statistical Package for the Social Sciences (SPSS), an information management system with adequate flexibility for input, modification, analysis, and storage of a large data source, was employed in this project. SPSS offers a powerful combination of data input and data modification subroutines with potential for entry into a spectrum of internal or external statistical programs. Data from all surveys were transcribed into a computer compatible format and entered into a data bank in the DEC-20 computer system at Tulane University, New Orleans, Louisiana. Transliteration was performed to standardize units of measure in the metric system and to facilitate data analysis. Latitude and longitude for each observation were stored as decimal equivalents of degrees in place of degrees and minutes as used on charts and maps. Species and other taxonomic groups were identified with a four letter alphanumeric code and a four digit numeric code which facilitated grouping and sorting of observations. The altitude of the aircraft, the group speed, and the water depth at the position were recorded in feet, knots, and fathoms, and subsequently converted to meters, kilometers per hour, and meters, respectively. Population Enumerators The investigation of marine animal abundance is fraught with numerous problems concerning the quantification of data due to the complexities of the living world. Although estimates of animal abundance are often imprecise, they provide a relative estimate of abundance that can answer a broad range of ecological and management questions to an acceptable level of approximation. In the present study a combination of strip and line transect population enumerators was used to analyze data. Because of the diversity of methods for estimating animal abundance using line and strip transect methods and the need to compare the results of varied methods, a computer program capable of calculating the various estimates using the basic data input was needed. Linetran, the computer program chosen for data analysis, was developed by Professor Charles E. Gates at Texas A & M University. As no single estimator is best under all conditions, Linetran uses up to 14 different estimators to compute abundance. Linetran is very flexible and will handle right angle (perpendicular) distance and radial (sighting) distance in any combination. This program can provide a variety of parametric or non-parametric estimates depending 12 on the normality of the data. This is an extremely important attribute as parametric estimates are highly dependent on underlying assumptions. Analysis of population abundance has been completed at the Texas A & M Computer Center and the results are presented later in this report. Mapping As a preliminary aid to interpretation of the distribution and frequency of sightings, schematic maps (presented in the Appendix) have been plotted for selected species in each of the survey subunits. In these maps latitude and longitude of individual sightings are plotted on the vertical and horizontal axes, respectively. Positions are expressed as decimal equivalents of degrees rather than the degrees and minutes normally used in nautical mapping: for example, 82°15' N is plotted as 82.25° N. In areas where two or more asterisks would potentially be plotted, the number of data points to be represented is used instead of the asterisks. Each diagrammatic map represents an area 111 x 222 km (60 x 120 nmi), and in some cases a slightly larger area including the survey subunit and adjacent areas necessary to form a rectangle with sides approximately parallel to lines of latitude and longitude. For the SFLA survey subunit, a rectangle 111 x 222 km with an area of 24,730 km2, the diagrammatic maps are accurate representations of the area surveyed. For NFLA and STEX, maps are approximate representations of areas 266 and 245 km in length which include a parallelogram with a length of 222 km and an altitude of 111 km equivalent to the survey subunit. Therefore, the NFLA maps include an area of approximately 2,550 km that is outside the actual survey subunit, and the STEX maps include 4,928 km2 not within the actual survey subunit. The actual area of maps used to depict the NTEX survey subunit encompasses 47,777 km, an area 23,047 km2 larger than the survey subunit. OBJECTIVE THREE: THE PRELIMINARY SURVEY Training Session An observer team was assembled and trained for aerial surveys in the Gulf of Mexico. Orientation flights and training sessions were conducted 20-23 July 1979 for testing of equipment, development of data recording sheets, standardization of observation techniques, and familiarization with the aircraft and navigational equipment. Personnel were subjected to an intensive training session using selected training aids with an emphasis on field identification. Color slides of the marine mammals, birds, and turtles in the study area were studied along with field guides. Color slides were taken under field conditions and allowed observers to study the type of sightings they were likely to encounter while on survey. An important aspect of preparation was training observers to make consistent estimates by having them estimate the number of animals in a series of color slides projected for brief intervals. Copies of slides and field guides were made available to all workers for maintaining observation proficiency. 13 Offshore training flights were conducted to familiarize observers with the plane, navigational equipment, and survey mechanics. Survey Subunits Four offshore survey subunits were established in the vicinity of the following locations: Brownsville, Texas (STEX); Corpus Christi, Texas (NTEX); Tampa Bay, Florida (NFLA); and Naples, Florida (SFLA). Map 1 shows the approximate locations of the subunits; the precise subunit boundaries are listed in Table 1. Subunit deliniation was not restricted to specific bathymetric limits because of the extreme mobility of marine organisms, and the paucity of existing information precluded determination of definite depth correlates for marine mammals, birds, and turtles. Provision was made, however, for surveying subunits to depths exceeding 200 m and, in some areas, to much greater depths. Subunits were positioned so as to provide coverage on the eastern and western extremes of the Gulf of Mexico. The total area encompassed by the four survey subunits was 98,568 km2. Survey Dates Dedicated aerial surveys were conducted from August to December 1979. Surveys were conducted during 5 to 10 August at the Florida subunits and in Texas from 20 to 25 August. No delays due to inclement weather were encountered in August. During the November/December flights, numerous cold fronts from the north created foul surveying conditions in the Gulf of Mexico, and flights were delayed considerably. During this period the Florida subunits were surveyed from 4 to 17 November, and the Texas subunits surveyed between 19 November and 4 December. Table 2 lists a detailed breakdown of survey dates. Personnel at the National Oceanic and Atmospheric Administration (NOAA) Weather Service at Corpus Christi International Airport, Texas, informed us that inclement weather we encountered in the Gulf of Mexico during November/December was typical of the winter months. Future surveys should be scheduled accordingly. Aircraft and Equipment Aero-Marine Survey, Inc., a company with experience in marine survey work, was contracted for the tenure of the Pilot Study. The Cessna 337 Skymaster, used to fly the surveys, was equipped with extended-range fuel tanks, STOL kit for slow flight, TDL 711 Loran C radio navigation, surface and weather radar, radar altimeter, and an infrared radiometer for monitoring sea surface temperatures. The additional fuel capacity enabled the plane to carry 2 hours of extra fuel for emergency use. A voice-actuated intercom system was used during the November surveys, but not in August. The use of this equipment greatly facilitated data transfer from observers to the recorder. Safety equipment aboard the plane consisted of a self-inflating life raft with attached radio beacon, Mae West style life preservers, and an emergency first aid kit. Vertical photographs were taken with a built-in Hasselblad MK-70 camera with 70-mm wide angle lens. A 35-mm SLR camera with 200-mm telephoto lens was used for oblique photos. 14 CO E cd ■v CD CO o o CO CM CM o o co cm O m o> co 02 en O t- o in to t- •"tf ITS CO 00 CM 00 G5 C3 CO 0 O m rr T-H in O O O 1* to CO 00 cm 00 -O ■o o o CO co CV cOcm s e O O O CO o «^ "3,5? .a •»-' 3 co co p ST* s a CO Cl J= * cj co CO ■"■ <~ 2 to 2 E ■J u CL . 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Oil and petroleum components were conspicuous in both STEX and NTEX survey subunits during August 1979 surveys. At that time oil containment devices were being utilized and tested for some of the coastal lagoons of Texas. Corpus Christi, Texas, was the oil spill response center for U.S. personnel, and as a result air and ship traffic was possibly above normal levels preceding and during some surveys. The actual effects of oil and oil spill activities on the results of the aerial surveys are unknown because pre-spiU baseline data are unavailable. The preliminary data gathered during the Pilot Study potentially establish such a baseline for evaluating oil effects in an indirect manner. All flights were conducted according to the previously developed study plan. Oiled and non-oiled areas were studied with identical intensities and techniques. When possible the location and appearance of presumed oil concentrations were recorded for possible analysis with animal sightings and other environmental data. Evidence of oil contamination of ocean waters was also noted in Florida survey subunits. In one case, the source of the oil was traced to a Liberian tanker flushing tanks in open water. A group of dolphins were seen swimming through the slick. Such observations were recorded whenever possible. 17 RESULTS IDENTIFICATION AND DETECTION The ability to identify the animal species sighted during aerial surveys was important to the results and quality of the Pilot Study. On occasion conditions were encountered which prevented positive identification of the species or exact composition of mixed groups. In such cases the most detailed identifications available were recorded and analyzed. In some cases identifications were possible at a later time due to increased sightings and incorporation of other data not available at the time of the sighting. On the basis of all data available, probabilistic identifications can be made and the sum of all observations considered in evaluating occurrence, abundance, and movements. For example, tentative groupings such as unidentified dark tern were not necessarily a single species but instead were those animals for which more specific data were unavailable. Dark terns were likely to be black terns, sooty terns, or bridled terns and the availability of tentative data allowed consideration of the total number of possible black, sooty, or bridled tern records. Mammals The identification of mammals from an airplane depended upon a number of factors. The behavior, size, and coloration of individual species were critical in making precise identifications. Most species can be readily identified if viewed from the proper angle or vantage point. Most of the animals popularly termed dolphins are similar in body shape and size but differ in head shape, behavior, and subtle aspects of coloration. Bottlenose dolphins were distinctive but not all dolphins were adequately observed to differentiate the bottlenose from other species. Dolphins of the genus Stenella were quite similar and consequently difficult to identify to species in all cases. However, because of the paucity of information on the ecology, movements, and behavior of this genus, all data were considered to be of potential value. Three Stenella species were identified: spotted dolphin, striped dolphin, and spinner dolphin; although the last species was identified tentatively and only once. Dolphin groups containing 20 to 150 animals were often sighted over large distances whereas individuals or small groups were seldom seen except near the transect line or immediately perpendicular to the plane's position. Because large groups presented more visual cues, most could be identified. In contrast, individuals and small groups were less likely to be viewed adequately for identification of species. Thus, the number of sightings of unidentified dolphin groups probably represented a small percentage of the total number of dolphins relative to the number of identified individuals and groups. 18 Pilot whales were sighted in association with fish schools and feeding flocks of birds. Such association allowed detection from greater distances than other solitary animals of comparable sizes. Large whales are more easily detected even over long distances. Identification was possible except when a whale was sighted from a distance and sounded prior to the approach of the aircraft. The effect of altitude on detection and identification of marine mammals was investigated using the data available. Birds Marine birds provide problems for aerial censusing which are very different from those of marine mammals and turtles. Birds are much smaller than most marine mammals and turtles. They are also more mobile and may fly to high altitudes above the ocean's surface. In general, conspicuousness is a function of size, color, and behavior. Large birds and white birds are more conspicuous than small and dark birds, and birds that stay near the water surface are less conspicuous than those that fly several meters higher. Identification is affected by these same variables but is mainly a function of taxonomic diversity. The rest of this section is a brief review of the conspicuousness and identification problems of the birds we encountered in the pilot project. Shearwaters are easily identified as such by their characteristic shape and manner of flight. The two species seen (Cory's and Audubon's) are easily distinguished from one another by their plumage patterns, but Audubon's may be impossible to distinguish from the air from the very rare Manx shearwater. The shearwaters are dark above and usually stay close to the water, so they are more difficult to detect than pale birds such as terns. Storm-petrels are very small, and most are dark colored. Most storm-petrels are probably missed in censuses conducted from 228-m altitude, and they may be missed at 91 m. The three species (Wilson's, Leach's, and Harcourt's) likely to occur in the Gulf of Mexico are very similar in plumage and we did not identify many individuals to species. Tropicbirds are fairly large and predominately white. They also typically fly at an altitude of at least several meters and are very conspicous. They can be confused only with the larger pale terns; however, their shape and wingbeat are distinctive. White and brown pelicans are among the largest and most conspicuous birds in the area and are probably the most easily identified. The boobies and gannets are also very conspicuous but masked (blue-faced) boobies can be confused with gannets, particularly as subadults. Cormorants are so distinctively shaped that they are easy to identify when on the water or flying, and tend to be conspicuous despite their dark color. In Texas we did not distinguish between the very similar olivaceous and double-crested cormorants. Frigatebirds tend to be very conspicuous because of their large size. They also have a unique profile which makes identification very easy. They have a habit of soaring 19 to great heights, and therefore we probably missed some that were above the altitude of the plane. Phalaropes are very small, but their pale coloration and flocking habits make them more conspicuous than the storm-petrels. From the air the three species in winter plumage are probably not separable. Laughing gulls are moderately conspicuous when alone, but their numbers are probably underestimated when they occur in flocks with the more conspicuous royal terns. The terns are the most abundant birds offshore and the group presents some identification problems. Royal terns are large, pale, and have relatively broad wings set in the middle of the body. They are very conspicuous, and with practice can be distinguished from the rest of the terns even from 228-m altitude. Sandwich terns are smaller and more slender than royal terns, but larger than common terns. They can occasionally be distinguished from the related species, but only after experience. We identified as "common tern group" the species Forster's, common, roseate, and Arctic terns. These four species are very similar and we consider them indistinguishable from the air. They are pale and rather conspicuous, and as a group can be separated rather easily from the other terns. Least terns are very small and normally occur close to shore. They can be confused with the common group, but have shorter tails, relatively broader wings, and "floppier" flight. "Pale terns" are unidentified royal, Sandwich, common group, or least terns. As our experience increases, this category should become limited to those seen at great distances or under other poor viewing conditions. "Dark terns" are unidentified sooty, bridled, and black terns. These species are distinguishable in the field, but many are seen too poorly for positive identification. As a group they are much less conspicuous than the pale terns, and the proportion sighted is likely to be lower. Turtles Turtles presented distinct identification and detection problems in relation to birds and mammals. They were usually sighted floating at the surface or swimming immediately below the water surface. Consequently, they presented a low or nonexistent profile except when viewed from above. Head width, carapace shape, body proportions, and color were all useful criteria but depended upon adequate light, sufficient observation time, and proper sighting angle. Turtles, like some birds, were rarely seen at a distance. 20 Leatherback turtles were conspicuously separated from other species on the basis of color, shape, size, and lack of a keratinized carapace. Green turtles, hawksbills, loggerheads, and ridley turtles were more difficult to positively identify. A percentage of the turtles seen was classed as unidentified turtles, the equivalent of a non- leatherback classification. Loggerheads were often identifiable on the basis of head and neck size, and red carapace coloration. OCCURRENCE Mammals The marine mammal faunas of the Texas and Florida survey subunits appeared quite different in our surveys (Table 3). Bottlenose dolphins were the only marine mammals found in all survey subunits. They were found only during November in STEX, but were present during both August and November in the other subunits. During August dolphins of the genus Stenella were common off Florida and Texas. Three species of Stenella were observed off Texas (spotted, striped, and spinner dolphins). All those identified to species off Florida were striped dolphins (a single Stenella in NFLA was called a possible spotted dolphin). During November striped dolphins and unidentified Stenella dolphins were reported in the Florida survey subunits, but no Stenella were reported off Texas. Saddleback dolphins were identified during August in NFLA and both Texas survey subunits. They were not seen in SFLA nor in any subunits during November. In the Texas survey subunits we had several sightings of whales. During August sperm whales were seen in both STEX and NTEX, and a group of beaked whales was seen in STEX. Short-finned pilot whales were observed in STEX during August and November, and an unidentified small whale was seen there in August. In contrast, we had only one whale sighting for Florida: an unidentified large whale in NFLA during August. Our only manatee sighting was in SFLA during November, where three animals were seen approximately 100 m from shore. Birds Table 4 summarizes bird species occurrence by area and season. Table 5 provides scientific names for all sea birds expected to occur in the study area. We identified 21 species of birds and recorded an additional 14 categories of birds not identified to species. Most of the recorded avifauna can be grouped into the following categories: migrating landbirds, summer migrant pelagics, summer residents, wintering marine species, and permanent residents. We identified four species of migrating landbirds: the great egret (Casmerodius albus), cattle egret (Bubulcus ibis), Cooper's hawk (Accipiter cooperii), and willet (Catoptrophorus semipalmatus). Several smaller landbirds were seen and not identified (these are included in Table 4 in the unidentified bird categories). 21 Table 3. Summary of all marine mammal species sighted in the four survey subunits during the August (A) and November/December (N) surveys. „ Survey subunit peCieS STEX NTEX NFLA SFLA Unidentified beaked whale A (Mesoplodon sp.) Sperm whale A A (Physeter catodon) Short-finned pilot whale AN (Globicephala macrorhynchus) Unidentified whale A (Small) N A Bottlenose dolphin N AN AN AN (Tursiops truncatus) Spinner dolphin A (Stenella longirostris) Spotted dolphin AAA ( S. plagiodon) Striped dolphin AAA AN ( S . coeruleoalba) Stenella sp. Saddleback dolphin (Delphinus delphis) Unidentified dolphin Caribbean manatee (Trichechus manatus) A A AN AN A A A \N AN AN AN N 22 Table 4. Summary of all bird species sighted in the four survey subunits during the August (A) and November/December (N) surveys. Species STEX Survey subunit NTEX NFLA SFLA Common loon Cory's shearwater Audubon's shearwater Unidentified shearwater Storm-petrel Tropicbird Brown pelican Masked booby Brown booby Unidentified booby Northern gannet Cormorant Magnificent frigatebird Unidentified duck Phalarope Herring gull Laughing gull Unidentified gull Common tern group Sooty tern Bridled tern Least tern Royal tern Sandwich tern Black tern Unidentified dark tern Unidentified pale tern Unidentified tern Great (common) egret Cattle egret Cooper's hawk WiUet Unidentified dark bird Unidentified white bird Unidentified bird A A A AN A N A A A N A N A AN A A AN A AN AN AN N AN AN A A A A A N AN N AN AN A A A AN A A N A AN N AN AN AN AN A AN AN N N AN AN AN A A A AN A N A AN N AN A AN AN N N AN AN AN A A A AN AN AN A AN AN N N AN AN 23 Table 5. A primary list of sea birds occurring in waters of the Atlantic Ocean and Gulf of Mexico off the Southeastern United States. Common name Scientific name Common loon Arctic loon Red-throated loon Red-necked grebe Horned grebe Eared grebe Least grebe Western grebe Pied-billed grebe Yellow-nosed albatross Black-browed albatross Northern fulmar Cory's shearwater Greater shearwater Sooty shearwater Manx shearwater Audubon's shearwater Black-capped petrel Leach's storm-petrel Harcourt's storm-petrel Wilson's storm-petrel White-tailed tropicbird American white pelican Brown pen can Masked booby (= blue-faced booby) Brown booby Gavia immer Gavia arctica Gavia stellata Podiceps grisegena Podiceps auritus Podiceps nigricollis Podiceps dominicus Aechmophorus occidentalis Podilymbus podiceps Diomedea chlororhynchos Diomedea melanophris Fulmarus glacialis Calonectris diomedea Puffinus gravis Puffinus griseus Puffinus puffinus Puffinus l'herminieri Pterodroma hasitata Oceanodroma leucorhoa Oceanodroma castro Qceanites oceanicus Phaethon lepturus Pelecanus erythrorhynchos Pelecanus occidentalis Sula dactylatra Sula leucogaster 24 Table 5. Continued. Common name Scientific name Northern gannet Great cormorant Double-crested cormorant Olivaceous cormorant Magnificent frigatebird Northern phalarope Red phalarope Pomarine jaeger Parasitic jaeger Long-tailed jaeger Great skua South Polar skua Glaucous gull Iceland gull Great black-backed gull Lesser black-backed gull Herring gull California gull Ring-billed gull Black-headed gull Laughing gull Franklin's gull Bonaparte's gull Black-legged kittiwake Sabine's gull Gull-billed tern Morus bassanus Phalacrocorax carbo Phalacrocorax auritus Phalacrocorax olivaceus Fregata magnificens Lobipes lobatus Phalaropus fulicarius Stercorarius pomarinus Stercorarius parasiticus Stercorarius longicaudus Catharacta skua Catharacta maccormicki Larus hyperboreus Larus glaucoides Larus marinus Larus fuscus Larus argentatus Larus californicus Larus delawarensis Larus ridibundus Larus atricilla Larus pipixcan Larus Philadelphia Rissa tridactyla Xema sabini Gelochelidon nilotica 25 Table 5. Concluded. Common name Scientific name Forster's tern Common tern Arctic tern Roseate tern Sooty tern Bridled tern Least tern Royal tern Sandwich tern Caspian tern Black tern Brown noddy Black noddy Black skimmer Razorbill Thick-billed murre Dovekie Sterna forsteri Sterna hirundo Sterna paradisaea Sterna dougallii Sterna fuscata Sterna anaethetus Sterna albifrons Sterna maxima Sterna sandvicensis Sterna caspia Chlidonias niger Anous stolidus Anous minutus Rynchops niger Alca torda Uria lorn via A lie alle 26 The summer migrant pelagic birds are those that breed elsewhere, but are present in the Gulf of Mexico mainly during summer. Shearwaters, storm-petrels, boobies, tropiebirds, phalaropes, bridled terns, and black terns are in this category. Cory's shearwaters are migrants from Mediterranean and eastern subtropical Atlantic breeding colonies and are common off the southern Atlantic coast and uncommon during summer in the Gulf of Mexico. Our August survey data constitute most of the Cory's shearwater sightings for Texas. Aubudon's shearwaters and bridled terns breed in scattered colonies throughout the Bahamas, elsewhere in the Caribbean, and widely elsewhere in tropical and subtropical oceans. Both are uncommon or rare visitors to the Gulf of Mexico during August. We sighted several storm-petrels in the Gulf of Mexico during August. These were probably Wilson's storm-petrels, but Wilson's, Leach's, and Harcourt's storm-petrels are all found in the Gulf of Mexico. There was one tropicbird sighting in STEX. Tropiebirds are rare warm weather visitors from the Caribbean. Black terns breed on inland lakes and marshes and migrate through the Gulf of Mexico during August and the following months. There were large numbers of black terns sighted during August (especially in Texas) and a few in SFLA during November. Phalaropes breed in marsh and tundra habitats and winter at sea. We recorded a few phalaropes in NTEX during August and November. The summer residents are sooty terns and least terns. Sooty terns breed in a huge colony on Bush Key, the Dry Tortugas, and in very small colonies in Louisiana and Texas. A few were seen in STEX and SFLA during August. Least terns breed in scattered colonies along the coast of the Gulf of Mexico and winter south of the United States. We saw a few nearshore in the NTEX and SFLA subunits. The wintering marine species include common loons, northern gannets, various ducks, and herring gulls. Loons winter nearshore along the coast of the Gulf of Mexico, while gannets winter farther offshore. Some subadult gannets may remain in the Gulf of Mexico through the summer. Herring gulls and several species of ducks migrate from their northern breeding grounds to winter in the coastal waters of the Gulf of Mexico; some ducks continue to South America. The resident species include brown pelicans, cormorants, laughing gulls, and royal terns. These all breed along the coast of the Gulf of Mexico and remain in the area throughout the year. We commonly recorded brown pelicans in both Florida survey subunits, but in Texas where they are now very rare, we recorded them only in STEX and only during November. The laughing gulls and royal terns breed at various localities around the Gulf of Mexico and also to the north. They were present in all survey subunits during both seasons. There was a major influx of royal terns into the Florida survey subunits during November. Magnificent frigatebirds, Sandwich terns, and members of the common tern group do not fit well into the aforementioned categories. Frigatebirds breed in one small colony in the Florida Keys, but most of the frigatebirds in the Gulf of Mexico are non-breeders from farther south in the Caribbean. This non-breeding population is much larger in summer than winter, but some remain, at least in South Florida, through the winter. During August we found them to be common in Florida and rare in NTEX. During November they were uncommon in Florida. 27 Sandwich terns breed in large colonies in the northern Gulf of Mexico and sparingly farther north. They winter in much smaller numbers on the Florida coast of the Gulf of Mexico: most of the population migrates south into the Caribbean. The common tern group does not fit a pattern, as it is composed of one species that is a rare summer resident, another that is an uncommon breeder and common wintering bird in the Gulf of Mexico, another that is an uncommon migrant and wintering bird, and a fourth that is an accidental migrant. Roseate terns breed in small numbers in the Florida Keys, while Forster's terns breed uncommonly in the northern Gulf of Mexico and winter commonly on the coast of the Gulf of Mexico. Common terns are uncommon migrants and wintering birds, and arctic terns are accidental in the Florida Keys and very rare as migrants off the east coast of Florida. Turtles Four taxa of turtles were encountered in aerial surveys (Table 6). Loggerheads were conspicuous in Florida survey subunits but were infrequently sighted in Texas. The endangered Kemp's ridley was sighted only in Texas, and there in low numbers. Leatherbacks were evident but in low numbers in Florida. Green turtles of various size classes can resemble members of all other sea turtle taxa except the leatherback, so many turtles could not be identified to species. The preponderance of turtles in Florida in relation to Texas possibly reflects two facts. First, Florida includes nesting beaches for three marine turtle species (loggerhead, green, and leatherback turtles). Second, the species of primary importance in the western Gulf of Mexico, Kemp's ridley, has been severely reduced over the last four decades. Although all species present in the Gulf of Mexico are historically known from the Texas coast, surveys over an annual cycle may be necessary to elucidate the degree of utilization of the area by marine turtles. SEASONAL VARIATION Mammals in STEX The frequency of sightings of mammals in the South Texas survey subunit declined by 33.3% from August to November (Table 7). Of the nine taxa seen in August, only three were noted in November. Bottlenose dolphins, which were not observed in August, accounted for 71.4% of the sightings in November. Short- finned pilot whales were noted during both STEX surveys. Dolphins of the genus Stenella were conspicuously absent from observations in November. The absence of records for bottlenose dolphins in STEX during August is paralleled by observations made in transit along the coast between Corpus Christi and Brownsville. Bottlenose dolphins were not observed during flights paralleling the Laguna Madre and adjacent onshore waters of the Gulf of Mexico even though these included the shallow depths near the coast that are frequented by bottlenose dolphins throughout the range of the species. 28 Table 6. Summary of turtles observed during August and November/December 1979 surveys. LHTU = Loggerhead (Caretta caretta); GRTU = Green (Chelonia mydas); LBTU = Leatherback (Dermochelys coriacea); KRTU = Kemp's Ridley (Lepidochelys kempi); and UNTU = Unidentified species. Date Survey subunit LHTU GRTU LBTU KRTU UNTU Total Aug. 5 SFLA Aug. 6 SFLA Aug. 7 SFLA Aug. 8 NFLA Aug. 9 NFLA Aug. 10 NFLA Aug. 20 STEX Aug. 21 STEX Aug. 22 STEX Aug. 23 NTEX Aug. 24 NTEX Aug. 25 NTEX Nov. 8 SFLA Nov. 9 SFLA Nov. 10 SFLA Nov. 15 NFLA Nov. 16 NFLA Nov. 18 NFLA Nov. 19 STEX Nov. 25 STEX Nov. 26 STEX Nov. 30 NTEX Dec. 1 NTEX Dec. 4 NTEX 17 4 0 0 12 33 23 0 2 0 15 40 12 0 0 0 7 19 13 0 0 0 3 16 23 0 1 0 1 25 31 0 0 0 13 44 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 2 0 2 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 1 13 0 0 0 4 17 11 0 0 0 0 11 12 0 0 0 2 14 12 0 0 0 1 13 10 0 0 0 1 11 10 0 1 0 1 12 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 29 Table 7. Seasonal variation in relative abundance of marine mammal sightings in the STEX survey subunit. Species August November No. % 1 4.8 1 4.8 0 0.0 1 4.8 1 4.8 1 4.8 2 9.5 5 23.8 1 4.8 8 38.1 21 100.0 No. % 0 0.0 0 0.0 10 71.4 0 0.0 1 7.1 0 0.0 0 0.0 0 0.0 0 0.0 3 14 21.4 100.0 Sperm whale Unidentified whale Bottlenose dolphin Beaked whale Short-finned pilot whale Striped dolphin Spotted dolphin Stenella sp. Saddleback dolphin Unidentified dolphin Totals Table 8. Seasonal variation in relative abundance of marine mammal sightings in the NTEX survey subunit. Species August November No. % 1 3.5 0 0.0 10 35.7 1 3.5 1 3.5 2 7.0 2 7.0 1 3.5 10 35.7 28 100.0 No. % 0 0.0 1 11.1 7 77.8 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 11.1 9 100.0 Sperm whale Unidentified whale Bottlenose dolphin Striped dolphin Spinner dolphin Spotted dolphin Stenella sp. Saddleback dolphin Unidentified dolphin Totals 30 Mammals in NTEX In NTEX eight taxa were sighted a total of 28 times during August (Table 8). In the same subunit during November surveys, only three taxa were encountered for a total of nine sightings. Sperm whales, striped dolphins, spinner dolphins, spotted dolphins, unidentified Stenella, and saddleback dolphins were sighted during August but not November. The only taxon sighted during November surveys of NTEX and not encountered during August was an unidentified whale sighted with a group of bottlenose dolphins. This individual was medium in size, but could not be identified more precisely. Dolphins composed 95.9% of the mammal fauna during August and 88.9% during November. Bottlenose dolphin groups composed 37.0% of the dolphin sightings in August and 87.5% of such sightings in November. Although the number of groups of bottlenose dolphins sighted declined from 10 to 7 from August to November, other dolphin species present in August were not encountered at all in November surveys. Mammals in NFLA The number of mammal groups sighted in NFLA was reduced by nearly 50% (45.2%) during November in relation to August (Table 9). Three taxa were recorded during November whereas seven were observed during August. Bottlenose dolphins composed 45.1% and 58.8% of the August and November group sightings, respectively. Although three groups of unidentified Stenella, (17.7%) were present in November, the congeneric species (spotted dolphin and striped dolphin) were not identified. Considering all species of the genus Stenella, November sightings were only 37.5% of those in August. Saddleback dolphins, which represented 9.7% of the sightings in August were not observed in November. Mammals in SFLA The number of sightings in SFLA (Table 10) was only slightly reduced, 14.7%, during November in relation to August. This change was primarily the result of differences in the number of sightings of pelagic dolphins of the genus Stenella: 11 (32.4% of the mammal fauna) during August and 5 (17.3%) during November. In contrast to dolphin populations in both northern subunits, bottlenose dolphins in SFLA were sighted more frequently in November than in August. The appearance of a single manatee in the coastal margin of SFLA in November may be related to the season or to local movements in response to other factors. Manatees were present during both months but were not commonly seen due to the inshore habits of this species (Irvine et al. In press). Of the four survey subunits, only in SFLA were all taxa that were encountered in August, also recorded in November. Other subunits showed more conspicuous reductions in the frequency and diversity of sightings. Both STEX and SFLA surveys during November resulted in increased sightings of bottlenose dolphins. The absence of records for sperm whales, saddleback dolphins, and Stenella species in Texas survey subunits during November is noteworthy. Less conspicuous but parallel reductions occurred in Florida. Birds in STEX Table 11 presents relative frequencies of birds in the STEX survey subunit. Bird sightings were more frequent during November than August (190 vs. 122 records). Terns 31 Table 9. Seasonal variation in relative abundance of marine mammal sightings in the NFLA survey subunit. August November SPecies NoT-^ % N£ 9 Unidentified whale Bottlenose dolphin Striped dolphin Spotted dolphin Stenella sp. Saddleback dolphin Unidentified dolphin Totals No. % 1 3.2 14 45.2 5 16.1 1 3.2 2 6.5 3 9.7 5 31 16.1 100.0 0 0.0 10 58.8 0 0.0 0 0.0 3 17.7 0 0.0 4 23.5 17 100.0 Table 10. Seasonal variation in relative abundance of marine mammal sightings in the SFLA survey subunit. Species ^- — ^^- No. % 5 14.7 9 26.5 2 5.9 0 0.0 18 52.9 34 100.0 N ovember No. % 10 34.5 2 6.9 3 10.4 1 3.4 13 44.8 29 100.0 Bottlenose dolphin Striped dolphin Stenella sp. Caribbean manatee Unidentified dolphin Totals 32 Table 11. Seasonal variation in relative abundance of bird sightings in the STEX survey subunit. Asterisk (*) indicates groupings of similar birds and those not identified to species. Percentages are computed on the total number of sightings. Species listed separately and in general groups are only counted once in the total number of sightings. August November ojjctira No. % Cory's shearwater 9 7.4 Audubon's shearwater 2 1.6 * All shearwaters 17 13.9 Storm-petrel 1 0.8 Tropicbird 1 0.8 Brown pelican 0 0.0 Masked booby 2 1.6 * All boobies 6 4.9 Cormorant 0 0.0 Phalarope 2 1.6 Herring gull 0 0.0 Laughing gull 5 4.1 All gulls* 7 5.7 Royal tern 14 11.5 All pale terns 52 42.6 Sooty tern 3 2.5 Bridled tern 1 0.8 Black tern 12 9.8 All dark terns 29 23.8 * All terns 81 66.4 Other unidentified birds _J_ 5.7 Total sightings 122 No. % 0 0.0 0 0.0 0 0.0 1 0.5 0 0.0 1 0.5 0 0.0 0 0.0 1 0.5 0 0.0 26 13.6 0 0.0 45 23.6 66 34.6 122 63.9 0 0.0 0 0.0 0 0.0 2 1.0 124 64.9 19 9.9 33 accounted for two-thirds of all bird sightings in the survey (66.4% in August and 64.9% in November), but the composition of tern species was markedly different. During August pale terns (all that were identified to species were royal terns) accounted for 42.6% of all bird sightings, while dark terns (mostly black terns but a few sooty and bridled tern sightings) accounted for 23.8%. In contrast, dark terns accounted for only 1.0% of November sightings and pale terns accounted for 63.9%. Gulls accounted for 23.6% of the November sightings and only 5.7% in August, reflecting the influx of herring gulls from the northern United States and Canada. The August survey found a variety of non- breeding summer visitors, including shearwaters, boobies, storm-petrels, and a tropicbird, which were not present in November. Birds in NTEX The frequencies of bird sightings in NTEX are presented in Table 12. Terns accounted for 75.8% of all sightings in August but for only 34.5% of the November sightings. Dark terns were rare in both surveys (3.4% in August, 1.1% in November); therefore, the decrease was primarily in the frequency of sightings of royal and unidentified pale terns. Herring gulls were absent in August but accounted for 43.7% of the November bird sightings. Shearwaters, storm-petrels, boobies, and magnificent frigatebirds were sighted during August but not November. One group of ducks was observed during November. Birds in NFLA The frequencies of bird sightings in NFLA are presented in Table 13. There was a conspicuous increase in the number of royal terns sighted during November (64.4% of the bird fauna) in relation to August (30.2%). The number of brown pelicans seen was stable between the two surveys, but in November brown pelicans composed 9.2% of the bird fauna as compared to 17.9% in August. Frigatebirds were seldom seen in November in relation to the August survey. Laughing gulls were more frequently sighted in November with all gull species accounting for 12.1% of the November sightings. Dark terns were not sighted in November whereas nine groups were recorded in August. Birds in SFLA Table 14 presents relative frequencies of birds in the SFLA survey subunit. Royal terns were more commonly sighted in November than in August: they accounted for 17.8% and 69.5% of the bird sightings in August and November, respectively. Brown pelicans and laughing gulls showed a similar but less pronounced increase in November. Common group, least, sooty, and bridled terns were present in August but were not sighted in November. Cory's shearwaters and Sandwich terns were seen in low numbers during both months. Turtles in Texas and Florida The frequency of sightings of marine turtles in Florida greatly exceeded that in Texas (Table 15). Of all turtle sightings 97.3% were in Florida survey subunits and 2.7% were in Texas. The total number of turtles seen in August (182) exceeds the total for November (80). Turtles were approximately equal in abundance in NFLA and SFLA, with reductions during November surveys of slightly under 50% in relation to August surveys (Table 16). Leatherback turtles were sighted in Florida during both August and 34 Table 12. Seasonal variation in relative abundance of bird sightings in the NTEX survey subunit. Asterisk (*) indicates groupings of similar birds and those not identified to species. Percentages are computed on the total number of sightings. Species listed separately and in general groups are only counted once in the total number of sightings. August November occults No. % Cory's shearwater 4 2.2 All shearwaters 5 2.8 Storm-petrel 1 0.6 Masked booby 4 2.2 All boobies 4 2.2 Magnificent frigatebird 3 1.7 Ducks 0 0.0 Phalarope 3 1.7 Herring gull 0 0.0 Laughing gull 21 11.8 All gulls* 27 15.2 Common tern group 2 1.1 Least tern 1 0.6 Royal tern 75 42.1 Sandwich tern 1 0.6 * All pale terns 129 72.5 Sooty tern 1 0.6 Black tern 5 2.8 * All dark terns 6 3.4 * All terns 135 75.8 Other birds _0 0.0 Total sightings 178 No. % 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 1.1 1 1.1 38 43.7 2 2.3 50 57.5 0 0.0 0 0.0 26 29.9 0 0.0 29 33.3 0 0.0 0 0.0 1 1.1 30 34.5 _5 5.7 87 35 Table 13. Seasonal variation in relative abundance of bird sightings in the NFL A survey subunit. Asterisk (*) indicates groupings of similar birds and those not identified to species. Percentages are computed on the total number of sightings. Species listed separately and in general groups are only counted once in the total number of sightings. August November 0[JCre detectable than bottlenose dolphins. Terns can be seen from greater distances, although at extreme distances they are often not identified to species. Thus, the area covered with respect to terns is significantly greater than the area covered for bottlenose dolphins. The percent aerial coverage for August-NFLA was: bottlenose dolphins, 4.5%; royal terns, 14%; and unidentified terns, 21.5%. A comparison of the total number of individuals, the maximum observation distance, and the estimated density for the example taxa in Table 30 suggests several relationships relevant to evaluating the data. First, the taxa for which the most sightings were made are not necessarily judged to be the most abundant. Density estimates necessarily compensate for the observability of the animal away from the transect line. Those animals which are viewed at large distances must be seen more often than those with short observation distances. For example, the larger number of royal terns (281) seen in STEX during November resulted in a density estimate of 0.36 birds/km , whereas the smaller number (31) seen during August yielded an estimate of 0.20 birds/km . The 186 royal terns seen in NTEX-August surveys resulted in a density estimate only twice as large as the density estimate resulting from the 31 royal terns sighted in NTEX during November. In the first case, the aggregation of birds during November allowed detection at greater distances, and thus facilitated the greater area to be surveyed. Part of the increase in the total number of birds sighted was a result of increased area and part was the result of increased abundance. It may be significant that the decrease in royal terns in NTEX during November was accompanied by an increase in the species in STEX. A similar increase is seen in the density of royal terns in SFLA during November (Table 31); the change in NFLA is less pronounced (Table 32). This possibly suggests that the new birds in SFLA during November were arriving from areas other than NFLA. Comparison of seasonal and geographic variation in other density estimates for Florida subunits (Tables 31 and 32) allows several trends to be defined. Laughing gulls were twice as abundant in SFLA as in NFLA during November. Loggerhead turtles were only slightly more abundant in SFLA than in NFLA during August. However, loggerhead density in NFLA during November was below the number needed for density calculations, whereas they were only slightly less abundant during November. The brown pelican, a bird without pronounced seasonal movements, had similar density estimates in NFLA during November and August. Density estimates for royal terns were similar during the two surveys in NFLA (Table 31). In SFLA, higher November concentrations of royal terns are suggested by both absolute numbers and density estimates (Table 32). The estimates of densities available from the Pilot Study remain to be confirmed by repeated measurements and increased sample sizes. Confidence limits for most estimates are wide; however, these limits will be narrower when estimates spanning an increased number of observations are available. As the ecological zonation of each species is defined it will be important to calculate densities in appropriate portions of the subunits rather than considering a generalized distribution throughout the study area. Future studies will also allow the determination of seasonal trends by allowing comparison of an entire sequence of estimates instead of merely two points in time. 59 CD t) C E c3 ■4-J 3 .W £ ■5 X be a c £ *j -c bD * E lO OS 0) o s-. 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Ifl OJ CD a u a, Cl c co D C O V 0) > CM E +j co '55 "3 C 3 0) "O Q> '■a c 35 E •*= 3 hD Z '55 CO 0) cy a co CO 3 hD 3 < CM OS OS cm "tf1 *tf ■t t- CD CO CO co CO o o CO o CM CO CM CM I CD i— I X CM O o o o o o CM o o CM CO o in CM oo in JS Q, c O c •o -w cy "9 P *-> cu a) ^-< Cl, ■ — < CO T3 >» C *-> CO CQ o OS +-> Li 3 co CD he hD o -J CU E > o Z Ol CO CO I— 1 T CO CM o CO CO CO in 00 o o CO C TJ a> -o c CO CD CD .c c Ci ^ 0) cy CO ■o ho >> hD o 'S o =S 13 J 62 Similarly, the larger geographic area and ability to sample intervening areas will facilitate identification of movement patterns and their relative significance in local and overall populations. SEA SURFACE TEMPERATURES The sea surface temperatures recorded during the Pilot Study are comparable to winter and summer patterns previously known for the Gulf of Mexico (Leipper 1954). During August sea surface temperatures were warmer nearshore, decreasing in a seaward direction, but overall they remained quite uniform. For example, the mean temperatures recorded for each species observed in STEX ranged from 28.0" to 29.2° C. The mean temperatures observed in NTEX were slightly lower (27.5° to 28.6° C), as would be expected moving from south to north in the western Gulf of Mexico. In both Texas subunits during August, certain birds only seasonally present (i.e., absent in November) were concentrated in the areas of lowest sea surface temperatures. These species included sooty terns and masked boobies. The latter species, a diving bird poorly known in Texas waters, was reported to be one of the most conspicuously effected bird species during the Ixtoc oil spill (NOAA news briefing 1979). During November temperatures were not only lower, but the temperature gradient from shore to seaward was reversed in relation to August. Temperature gradients were steepest off NTEX and NFLA, which may explain the absence or low numbers of marine mammals during November surveys in these subunits. Whether the scarcity of bottlenose dolphins in STEX during August and in NTEX during November represents seasonal movements in response to temperatures remains to be confirmed, but temperatures where these dolphins were observed in Florida during both seasons were comparable to those in Texas waters. Movements into and out of coastal lagoons also may account for the intermittent absence of bottlenose dolphins in Texas survey subunits (Schmidly and Shane 1978). OBSERVER BIAS The quantification of observations by independent observers on opposite sides of the aircraft depends upon the comparability of sighting frequencies. Visual scan patterns, observer confidence, and individual reaction times are all important factors, but their effects can be minimized by appropriate training. A matched pair of observers simultaneously flying over the same geographic area would be expected to record approximately equal numbers of sightings and similar faunal compositions. Some deviation from a 50% frequency would be explained by sampling error and random deviations. Figure 5 charts the deviation of the observer pairs from the expected 50% sighting frequency. Only in two sampling periods does the deviation reach 15%. The samples in Figure 5 are arranged in chronological order from left to right and a trend toward reduction of the deviation is apparent as the observer team gained experience and methods were improved. This trend is probably explained by added observer experience and the improvement of observer methods during the Pilot Study. No discernible differences 63 c o > O 40- 30- 20- 17% 15% 12% 10- 8 6% 5% 2% 0 - SFLA NFLA STEX SFLA NFLA NTEX STEX Augi J St r «Jov< smber Figure 5. Deviation in percent of sightings by paired aerial observers. 64 were noted in the species cited by individual observers of the matched pairs. All observers participated in training sessions involving ground and aerial identification methods. ALTITUDINAL EFFECTS Due to the great disparity in size, coloration, and location of various species, it is important to consider the effect of the elevation of the aircraft on the detection and identification of individuals and groups of organisms. Flights were conducted at 91 and 228 m in equal frequency in order to evaluate altitudinal effects and maximize data accuracy for all groups. The total number of groups sighted during low (91 m) and high (228 m) flights are compared by season in Tables 33 through 41. In three of the eight seasonal samples (37.5%) more terns were seen during low flights than during higher flights. The number of turtles seen in low flights exceeded that of higher flights in three of the eight samples, and approached that of higher flights by 95% in two others. More mammals were seen in four of the eight seasonal samples (50%) at low altitudes. Thus, in terms of total numbers of groups seen, flight altitude may have only a slight effect on detectability depending upon the group concerned. Because of the small size and fast movements of birds, it was hypothesized that low altitudes would be necessary to allow identification. When the number of birds not identified to exact species is compared to the total number of birds sighted in a high or low sample (Table 42) an increase in unidentified birds at high altitudes is evident in seven of the eight seasonal samples. Thus, even if detectability of birds remains the same at both survey altitudes, the identifiability may be reduced at higher altitudes. In part, differences in detectability and identification may be related to the visual scan techniques employed by the aerial observer. At higher elevations a broader field of view is available which requires more deliberate eye and head movement. In fact, this increase in area scanned affords less time for detection of animals in any one location. However, because of the relatively slower speed of the aircraft in relation to the ocean's surface, once an organism is detected it remains in view longer, giving the observer more time to identify it. Such a time interval is in part nullified by the greater distance (both horizontal and vertical increases are possible) from which the animal is viewed. In practice, identifications of turtles, mammals, and most birds are often made instantaneously, but deviation from the flight path to confirm identification is necessary more often during high flights than during low ones. At present the practice of employing an equal number of flights at 91- and 228-m altitude appears to be justified in providing opportunities to maximize detection and identification of organisms of diverse sizes, habits, and group composition. It is probable that alternating flights at low altitudes serve to reinforce indentifications at higher altitudes. This would increase data quality at both altitudes. Actual effect of altitude is complex, with increased sightings often accompanied by decreased identifiability. For example, in November-NFLA surveys only 10% of all birds sighted during flights at 91 m were not identified to species whereas 34% of those sighted in flights at 228 m were not identified to species. 65 Table 33. The number of sightings made at low (91 m) and high (228 m) altitudes in STEX during August. Species 91 m 228 m Shearwaters 5 6 Dark terns 9 17 Pale terns 20 13 Unidentified terns 10 10 Boobies, gannets, and tropicbirds 4 2 Gulls 4 3 Phalaropes and storm-petrels 4 2 Frigatebirds and pelicans 1 0 Total birds 60 60 Total turtles 3 0 Total mammals 12 8 Total unidentified birds 33 38 Table 34. The number of sightings made at low (91 m) and high (228 m) altitudes in NTEX during August. Species 91 m 228 m Shearwaters 2 3 Dark terns 6 1 Pale terns 41 62 Unidentified terns 7 14 Boobies, gannets, and tropicbirds 1 4 Gulls 9 12 Phalaropes and storm-petrels 4 1 Frigatebirds and pelicans 0 3 Total birds 72 107 Total turtles 1 1 Total mammals 5 15 Total unidentified birds 24 48 66 Table 35. The number of sightings made at low (91 m) and high (228 m) altitudes in STEX during November. Species 91 m 228 m Shearwaters 0 0 Dark terns 2 0 Pale terns 29 37 Unidentified terns 21 34 Boobies, gannets, and tropicbirds 1 0 Gulls 31 14 Phalaropes and storm-petrels 0 0 Frigate birds and pelicans 0 1 Total birds 97 92 Total turtles 0 1 Total mammals 7 5 Total unidentified birds 54 42 Table 36. The number of sightings made at low (91 m) and high (228 m) altitudes in NTEX during November. Species 91 m 228 m Shearwaters 0 0 Dark terns 1 1 Pale terns 17 9 Unidentified terns 0 1 Boobies, gannets, and tropicbirds 0 0 Gulls 21 29 Phalaropes and storm-petrels 0 1 Frigatebirds and pelicans 0 0 Total birds 41 42 Total turtles 1 1 Total mammals 3 5 Total unidentified birds 8 12 67 Table 37. The number of sightings made at low (91 m) and high (228 m) altitudes in NFLA during August. Species 91 m 228 m Shearwaters 0 0 Dark terns 3 0 Pale terns 48 30 Unidentified terns 12 50 Boobies, gannets, and tropicbirds 1 0 GuUs 2 0 Phalaropes and storm-petrels 0 0 Frigatebirds and pelicans 31 26 Total birds 99 111 Total turtles 41 43 Total mammals 9 17 Total unidentified birds 20 58 Table 38. The number of sightings made at low (91 m) and high (228 m) altitudes in SFLA during August. Species 91 m 228 m Shearwaters 1 0 Dark terns 1 6 Pale terns 19 8 Unidentified terns 5 7 Boobies, gannets, and tropicbirds 0 0 Gulls 2 2 Phalaropes and storm-petrels 2 1 Frigatebirds and pelicans 9 12 Total birds 45 40 Total turtles 35 53 Total mammals 8 24 Total unidentified birds 11 19 68 Table 39. The number of sightings made at low (91 m) and high (228 m) altitudes in NFLA during November. Species 91 m 228 m Shearwaters 0 0 Dark terns 0 0 Pale terns 162 122 Unidentified terns 19 27 Boobies, gannets, and tropicbirds 0 0 Gulls 48 6 Phalaropes and storm-petrels 2 0 Frigatebirds and pelicans 30 13 Total birds 269 174 Total turtles 16 18 Total mammals 9 5 Total unidentified birds 42 34 Table 40. The number of sightings made at low (91 m) and high (228 m) altitudes in SFLA during November. Species 91 m 228 m Shearwaters 1 0 Dark terns 0 3 Pale terns 240 203 Unidentified terns 17 102 Boobies, gannets, and tropicbirds 0 0 Gulls 17 2 Phalaropes and storm-petrels 0 0 Frigatebirds and pelicans 11 10 Total birds 301 333 Total turtles 18 19 Total mammals 9 9 Total unidentified birds 31 113 69 Table 41. The number of groups seen in low flights expressed as a percentage of those seen in corresponding high flights. Species August November STEX NTEX NFLA SFLA STEX NTEX NFLA SFLA Terns 98 70 78 119 73 163 121 84 All birds 100 67 89 112 105 98 154 90 Turtles — 100 95 70 0 100 89 95 Mammals 150 33 52 33 140 60 180 100 Unidentified birds 87 50 34 58 128 66 123 27 Table 42. The number of unidentified bird sightings expressed as a percentage of total bird sightings made during low (91 m) and high (228 m) flights. Survey August November subunit 91m 228 m 91 m 228 m STEX NTEX NFLA SFLA 55.0 33.3 20.2 24.4 63.3 44.9 52.3 47.5 55.7 19.5 15.6 10.3 45.7 28.6 19.5 33.9 70 BEAUFORT FORCE The ocean surface forms a vast background against which and occasionally through which observations are made. The sea surface can have an appreciable effect on the detectability and observability of organisms depending upon waves related to wind, rain, and depth, as well as other factors. Sea surface state was recorded using the Beaufort Force Index. Table 43 details the percentage of observations made under Beaufort states 1 through 4. Although flights were terminated any time sea states stabilized at or above 4, a few observations were made under these conditions in the vicinity of local thunderstorms. States 1 and 2 are characterized by a smooth water surface without waves breaking. State 3 includes conditions with scattered white caps which provide some visual noise for aerial observers and may reduce detectability of those organisms of small size, those with white coloration, and animals which have a low profile in the water. The percentage of observations made at sea states of 3 or 4, summarized in Table 43, clearly shows that sea states during November flights were higher than those during August except in STEX. The future collection of seasonal data over the entire annual cycle and at more frequent intervals is necessary to allow rigid analysis of the effect of sea state on quantitative estimation of occurrence and abundance. GLARE The amount of reflected sunlight from the ocean's surface has a significant effect on the observer's ability to detect and observe the organisms of interest. Glare can severely impair otherwise ideal conditions, even calm sea states. Since the location of the survey aircraft, the position of the sun, and the intensity of the sunlight are dynamic factors, the effect of glare is most easily determined by comparing simultaneous sighting records made from opposite sides of the aircraft. In the Cessna Skymaster used in the Pilot Study, observers utilized observation windows on opposite sides of the plane and glare, when present, was usually on one side of the aircraft or the other. Flight paths at three survey subunits (STEX, NFLA, and SFLA) were in an east-west direction and comparison of observations on the north and south sides of the aircraft allow glare to be considered independent of subjective estimates of the intensity of the glare present. In those subunits flown on east-west axes, observations made from the north and south sides of the aircraft were comparable during August, but November observations made from the south side of the aircraft were markedly lower than those made from the north (Table 44). In the NTEX subunit, which was surveyed on a northwest-southeast axis, seasonal differences are less obvious; but observation totals on the southwest side were consistently lower than comparable sightings on the opposite side (Table 45). In fact, both sides of transect line were affected by glare but it was more severe on the southwest side. Since these results span flights in both landward and seaward directions and include systematic rotation of observers and their positions, these factors cannot be used to explain differences observed. As suggested above, the percentage of observations recorded on the side of the aircraft with glare will be significantly lower in winter months than in summer. Table 46 summarizes the expected effects on glare vs. nonglare situations. Pending confirmation of these trends, it may be necessary to adjust abundance estimates to compensate for glare factors. 71 Table 43. Percentage of total observations made at each Beaufort sea state. Survey subunit Season Sea states 1 2 3 4 3 2.0 51.3 44.0 2.7 46.7 27.8 37.1 33.2 1.9 35.1 61.2 34.2 3.2 1.4 4.6 21.4 58.1 20.4 0.0 20.4 41.7 57.1 1.2 0.0 1.2 0.0 50.7 49.2 0.0 49.2 45.8 54.2 0.0 0.0 0.0 2.1 61.5 36.1 0.03 36.1 STEX STEX August November NTEX NTEX August November NFLA NFLA August November SFLA SFLA August November Table 44. Number of observations made from each side of the aircraft during surveys flown on east-west axes. Survey subunit Season Observation port N STEX STEX August November 34 28 37 65 NFLA NFLA August November 45 63 45 137 SFLA SFLA August November 36 89 40 147 72 Table 45. Number of observations made from each side of the aircraft during surveys flown on northwest-southeast axes. Survey Season Observation port subunit SW NE NTEX NTEX August November 43 26 64 38 Table 46. Ratios of south/north (southwest/northeast for NTEX) observations for all groups. Survey subunit Season Ratio STEX STEX August November 0.91 0.43 NTEX NTEX August November 0.68 0.67 NFLA NFLA August November 1.00 0.45 SFLA SFLA August November 0.90 0.61 73 CONCLUSIONS Aerial surveys in the Gulf of Mexico completed during the Pilot Study provided unique data on the distribution, relative abundance, and ecology of 13 mammal, 35 bird, and 5 turtle taxa, including several endangered and threatened species. Precise locational and environmental data on approximately 3,000 sightings allowed formation of a preliminary data base for multidimensional analyses. Once data cover an adequate time period, analyses of species composition, temporal and spatial distributions, movements, areas of special significance, and relative abundance will be possible. The combined effect of the small number of samples (2) and the interval between samples (3 months) precludes such analyses at present. Knowledge of OCS areas must be based on more frequent samples conducted over annual cycles. The results of the present study indicate that large voids in the knowledge of endangered and vulnerable animals in OCS areas can be filled by future studies. Preliminary maps of the distribution of taxa within the study area illustrate relationships and zonation within surveyed areas and adjacent waters. These maps, although based on observations over a short time, illustrate distributions on a more detailed scale than previously available. A greater number of mammal species, including several whales, were found off Texas than off western Florida. This may reflect the narrower continental shelf of Texas waters. The importance of the waters off of southern Texas as marine mammal habitats was illustrated by the frequency of sightings in this area. The discovery of the endangered sperm whale in both Texas survey subunits is remarkable in providing the first observations of living individuals of this species in the western Gulf of Mexico in several decades. Seasonal movements of terns, shearwaters, and several dolphin taxa are evident. Royal terns and other species were noted to extend further offshore over deeper waters in November than in August. Understanding of these patterns would be important in evaluating of oil and gas impacts on these and other migratory species. More turtle species and a higher density of turtles were observed in Florida than in Texas during both survey periods. Loggerhead turtles were exceptionally abundant in Florida waters. Some evidence exists for long-distance movements of loggerhead turtles from the western Florida coast to the lower Keys and Dry Tortugas. Magnificent frigatebirds and other birds appear to move along similar routes. Of the Stenella species encountered, spotted dolphins were most conspicuous in Texas waters. Striped dolphins were in Florida waters on a seasonal basis. 74 Although regular seasonal migrations are well documented for birds, data available from this study suggest that migration patterns for mammals and turtles are poorly understood. In all survey subunits, more mammals and turtles were observed in August than in November. Some taxa which were conspicuous in one season were not observed during the other. The geographic limits and seasonality of these movements are not known at present. Distinct patterns were noted for the spatial occurrence of birds, mammals, and turtles in relation to water depth and distance from shore. These data are particularly pertinent to consideration of OCS development. The results of the Pilot Study illustrate the dynamic complexity of marine vertebrate faunas. The study provided the basis for development, testing, and implementation of a study plan which encompasses the collection, analysis, and interpretation of data within OCS areas. The data base of ultimate utility must encompass seasonal, geographical, environmental, and annual variation to allow detailed analyses. Such information is critically important to the conservation and management of endangered and vulnerable marine animals and the OCS planning. Many trends and conclusions are apparent in the data presented herein. However, the limitations of the data set must be considered. Two comparable surveys were made on a three month cycle. In the absence of data collected on a more frequent schedule and encompassing the entire annual cycle, correlations with seasonal, geographic, and environmental factors are difficult to distinguish from superfluous associations. The present discussion of the Pilot Study results was prepared to show the depth and complexity of the investigation. It also serves to elucidate the value of data on important vertebrate species to OCS planning and development, and the need for long- term studies. Aerial surveys are dependent upon qualified observers and statistically documented data. The quality of the observers improves with experience and time, and consequently, so does the data. In part, informational gain is additive with all previous information relevant to the interpretations of current data. As a consequence, further studies in the Gulf of Mexico and Atlantic Ocean off of the southeastern United States promise to contribute significantly to the understanding of the animals studied and their ecology. Such an understanding is essential to planning and development if the effects of OCS activities are to be minimized. 75 LITERATURE CITED Gates, C. E. 1979. Line transect and related issues. In R. M. Cormack, G. P. Patil, and D. S. Robson, eds. Sampling biological populations. Satellite Program in Statistical Biology, International Cooperative Publishing House, Fairfield, Md. Irvine, A. Blair, J. E. Caffin, and H. I. Kochman. 1981. Aerial surveys for manatees and dolphins in western peninsular Florida with notes on sighting of sea turtles and crocodiles. U. S. Department of Interior, Fish and Wildlife Service, Biological Services Program. FWS/OBS-80/50. Leipper, D. F. 1954. Physical oceanography of the Gulf of Mexico. Pages 119-137 in P. S. Galtsoff, coord. Gulf of Mexico: its origin, waters, and marine life. U.S. Fish Wildl. Serv. Fish. Bull. 55(89). Lynch, S. A. 1954. Geology of the Gulf of Mexico. Pages 67-86 in P. S. Galtsoff, coord. Gulf of Mexico: its origin, waters, and marine life. U.S. Fish Wildl. Serv. Fish. Bull. 55(89). Marmer, H. A. 1954. Tides and sea level in the Gulf of Mexico. Pages 101-118 m P. S. Galtsoff, coord. Gulf of Mexico: its origin, waters, and marine life. U.S. Fish Wildl. Serv. Fish. Bull. 55(89). Nie, N. H., C. H. Hull, J. G. Jenkins, K. Steinbrenner, and D. H. Bent. 1975. Statistical package for the social sciences, 2nd ed. McGraw-Hill, New York. 675 pp. Schmidly, D. J. 1981. Marine mammals of the Southeastern United States coast and the Gulf of Mexico. U. S. Department of the Interior, Fish and Wildlife Service, Biological Services Program. FWS/OBS-80/41. Schmidly, D. J., and S. H. Shane. 1978. A biological assessment of the cetacean fauna of the Texas coast. National Technical Information Service, Springfield, Va. PB-281763. 38 pp. Sturges, W., and J. P. Blaha. 1976. A western boundary current in the Gulf of Mexico. Science 192:367-369. 76 APPENDIX: MAPS Number Page 1 Survey subunits sampled in the Pilot Study of marine mammals, birds, and turtles 82 2 Diagrammatic map of STEX survey subunit with bathymetric contours 83 3 Diagrammatic map of NTEX survey subunit with bathymetric contours 84 4 Diagrammatic map of NFLA survey subunit with bathymetric contours 85 5 Diagrammatic map of SFLA survey subunit with bathymetric contours 86 6 Sightings of mammals, birds, and turtles in NFLA during August 87 7 Sightings of mammals, birds, and turtles in SFLA during August 88 8 Groups of bottlenose dolphins sighted in STEX during November 89 9 Groups of Stenella sp. and unidentified dolphins sighted in STEX during August 90 10 Groups of unidentified dolphins sighted in STEX during November 91 11 Short-finned pilot whales seen in STEX during the Pilot Study 92 12 Groups of sperm whales, unidentified beaked whales, and unidentified whales sighted in STEX during August 93 13 Groups of bottlenose dolphins and sperm whales sighted in NTEX during August 94 77 APPENDIX: MAPS Continued Number Page 14 Groups of unidentified dolphins and Stenella sp. sighted in NTEX during August 95 15 Groups of saddleback, spinner, spotted, and striped dolphins sighted in NTEX during August 96 16 Groups of bottlenose dolphins, unidentified whales, and unidentified dolphins sighted in NTEX during November 97 17 Groups of unidentified whales, saddleback dolphins, and bottlenose dolphins sighted in NFLA during August 98 18 Groups of striped dolphins, spotted dolphins, and Stenella sp. sighted in NFLA during August 99 19 Groups of bottlenose dolphins and unidentified dolphins sighted in SFLA during August 100 20 Groups of Stenella sp. and striped dolphins sighted in SFLA during August 101 21 Groups of Cory's shearwaters sighted in STEX during August 102 22 Groups of Audubon's shearwaters, unidentified shearwaters, and storm-petrels sighted in STEX during August 103 23 Groups of bridled terns, sooty terns, and tropicbirds sighted in STEX during August 104 24 Groups of black terns sighted in STEX during August 105 25 Groups of unidentified dark terns sighted in STEX during August 106 26 Groups of royal terns sighted in STEX during August 107 78 APPENDIX: MAPS Continued Number Page 27 Groups of unidentified pale terns sighted in STEX during August 108 28 Groups of laughing gulls and unidentified gulls sighted in STEX during August 109 29 Groups of royal terns sighted in STEX during November 110 30 Groups of unidentified terns sighted in STEX during November Ill 31 Groups of herring gulls sighted in STEX during November 112 32 Groups of unidentified gulls sighted in STEX during November 113 33 Groups of Cory's shearwaters, unidentified shearwaters, and storm-petrels sighted in NTEX during August 114 34 Groups of sooty terns and royal terns sighted in NTEX during August 115 35 Groups of common group, least, and Sandwich terns sighted in NTEX during August 116 36 Groups of unidentified pale terns sighted in NTEX during August 117 37 Groups of laughing gulls sighted in NTEX during August 118 38 Groups of magnificent frigatebirds sighted in NTEX during August 119 39 Groups of black terns and masked boobies sighted in NTEX during August 120 79 APPENDIX: MAPS Continued Number Page 40 Groups of laughing gulls and royal terns sighted in NTEX during November 121 41 Groups of herring gulls sighted in NTEX during November 122 42 Groups of unidentified gulls sighted in NTEX during November 123 43 Groups of bridled terns, unidentified dark terns, and unidentified terns sighted in NFLA during August 124 44 Groups of Sandwich terns and royal terns sighted in NFLA during August 125 45 Groups of northern gannets and brown pelicans sighted in NFLA during August 126 46 Groups of magnificent frigatebirds sighted in NFLA during August 127 47 Groups of brown pelicans and royal terns sighted in SFLA during August 128 48 Groups of common group, least, and Sandwich terns sighted in SFLA during August 129 49 Groups of unidentified terns sighted in SFLA during August 130 50 Groups of magnificent frigatebirds sighted in SFLA during August 131 51 Groups of bridled terns, sooty terns, Cory's shearwaters, and storm-petrels sighted in SFLA during August 132 52 Sightings of turtles in STEX during the Pilot Study 133 80 APPENDIX: MAPS Concluded Number Page 53 Sightings of turtles in NTEX during the Pilot Study 134 54 Sightings of leatherback and loggerhead turtles in NFLA during August 135 55 Sightings of unidentified turtles in NFLA during August 136 56 Sightings of loggerhead turtles in SFLA during August 137 57 Sightings of unidentified turtles in SFLA during August 138 58 Sightings of green and leatherback turtles in SFLA during August 139 81 J ■>u '"Vv^^'-*"*""0*-,. ilrf o r/ i \ t CO a, E CO CO CO *■> c n 3 CO >. $ c- 3 CO CO 82 cm • CP ■v c ca tr— • in CO W to CD i c\j i a- i vn i cr> T3 O C/3 l -J Z o 3 O ^-» c o >, J= +-* cd n (.0 0) ,c c -»-^ 5 c -t-1 ai ■ — ■<: c o 3 Lri Q n - 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"FWS/OBS-81/36 4. Title and Subtitle Pilot Study of the Marine Mammals, Birds, Turtles in OCS areas of the Gulf of Mexico 7. Author(s) Thomas H. Fritts and Robert P. Reynolds 3. Recipient's Accession No. 5. Report Date September 1981 8. Performing Organization Rept. No. 9. Performing Organization Name and Address U.S. Fish & Wildlife Service Denver Wildlife Research Center New Orleans Field Station Tulane University Museum of Natural History Belle Chasse, LA 70037 10. Proiect/Task/Work Unit No. 11. Contract(C) or Grant(G) No. (o 14-16-009-79-951 (G) 12. Sponsoring Organization Name and Address 13. Type of Report & Period Covered Bureau of Land Management and the Office of Biological Services U.S. Fish & Wildlife service, Department of the Interior Washington, D.C. 20240 Survey 1979 14. 15. Supplementary Notes 16. Abstract (Limit: 200 words) The report discusses techniques for collecting data on marine animals in OCS areas. Aerial surveys of mammals, birds and turtles were conducted in 4 study sites in the Gulf of Mexico, at altitudes of 91 and 228 m, in August and December 1979. The aerial survey method is described. Weather and physical factors, altitude, distance, depth, observer bias, species, and species group size are analysed as sources of error in aerial surveys. Also discussed are seasonal and daily variations in abundance of species. Twelve mammal, 35 bird, and 5 turtle taxa were observed, and are listed in the report. The report also contains maps documenting the locations of the sightings. The study will be used as a base for future marine surveys in the gulf. 17. Document Analysis a. Descriptors Turtles, birds b. Identlfiers/OpenEnded Terms Aerial survey, outer continental shelf, Gulf of Mexico, sea turtles. e. COSATI Field/Group Marine mammals, marine birds 18. Availability Statement Unlimited 19. Security Class (This Report) Unclassified 20. Security Class (This Page) Unclassified 21. No. of Pages 150 22. Price (See ANSI-Z39.18) *US GOVERNMENT PRINTING OFFICE 1981 775 137 See Instructions on Reverse OPTIONAL FORM 272 (4-77) (Formerly NTIS-35) Department of Commerce 0-0 Headquarters - Office of Biological Services, Washington, D.C. National Coastal Ecosystems Team, Slidell. La. Regional Offices U.S. FISH AND WILDLIFE SERVICE REGIONAL OFFICES REGION 1 Regional Direeior U.S. Fish and Wildlife Service Lloyd Five Hundred Building. Suite 1692 500 N.F. Multnomah Street Portland, Oregon 97232 REGION 2 Regional Director U.S. Fish and Wildlife Service P.O.Box 1306 Albuquerque, New Mexico 87 1 03 REGION 3 Regional Director U.S. Fish and Wildlife Service Federal Building, Fort Snelling Twin Cities. Minnesota 55111 REGION 4 Regional Director U.S. Fish and Wildlife Service Richard B. Russell Building 75 Spring Street, S.W . Atlanta. Georgia 30303 REGION 5 Regional Director U.S. Fish and Wildlife Service One Gateway Center Newton Corner, Massachusetts 02 REGION 6 Regional Director U.S. Fish and Wildlife Service P.O. Box 25486 Denver Federal Center Denver. Colorado 80225 REGION 7 Regional Director U.S. Fish and Wildlife Service 1011 E.Tudor Road Anchorage, Alaska 99503 158 DEPARTMENT OF THE INTERIOR U.S. FISH AND WILDLIFE SERVICE As the Nation's principal conservation agency, the Department of the Interior has respon- sibility for most of our nationally owned public lands and natural resources. This includes fostering the wisest use of our land and water resources, protecting our fish and wildlife, preserving the. environmental and cultural values of our national parks and historical places, and providing for the enjoyment of life through outdoor recreation. The Department as- sesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also has a major responsibility for American Indian reservation communities and for people who live in island territories under U.S. administration.