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526

Synopsis on the Biology of the

Jack Mackerel (Trachurus symmetricus)

By John S. /WacGregor

SPECIAL SCIENTIFIC REPORT-FISHERIES Na 526

UNITED STATES DEPARTMENT OF THE INTERIOR

Stewart L. Udall, Secretary

John A. Carver, Jr., Under Secretary

Stanley A. Cain, Assistant Secretary for Fish and Wildlife and Parks

FISH AND WILDLIFE SERVICE, Clarence F. Pautzke, Commissioner

Bureau of Commercial Fisheries, Donald L. McKernan, Director

Synopsis on the Biology of the Jack Mackerel

(Trachurus symmetricus)

By JOHN S. MacGREGOR

FAO Species Synopsis No. 86

United States Fish and Wildlife Service Special Scientific Report- -Fisheries No. 526

Washington, D.C. April 1966

CONTENTS

Introduction.

Page 1

1 Identity 1

1.1 Nonnenclature . 1

1.2 Taxonomy 1

1.3 Morphology 3

2 Distribution 3

2.1 Total area 3

2.2 Differential distribution. . 5

2.3 Determinants of distribution changes 5

2.4 Hybridization 5

3 Bionomics and life history 5

3.1 Reproduction • 5

3.2 Pre-adult phase V

3.3 Adult phase 11

3.4 Nutrition and growth 11

3.5 Behavior 12

4 Population 12

4.1 Structure 12

4.2 Abundance and density (of population) 12

4.3 Natality and recruitment 12

4.4 Mortality and morbidity 12

4.5 Dynamics of population (as a whole) 12

4.6 The population in the community and the ecosystem 12

5 Exploitation. 13

5.1 Fishing equipment 13

5.2 Fishing areas 13

5.3 Fishing seasons 13

5.4 Fishing operations and results 13

6 Protection and management 13

6.1 Regulatory (legislative) measures 13

6.2 Control or alteration of physical features of the environment. 14

6.3 Control or alteration of chemical features of the environment. 14

6.4 Control or alteration of the biological features of the environ- ment 14

6.5 Artificial stocking 14

Synopsis on the Biology of the Jack Mackerel

By JOHN S. MACGREGOR, FISHERY BIOLOGIST (RESEARCH)

BUREAU OF COMMERCIAL FISHERIES TUNA RESOURCES LABORATORY, LA JOLLA, CALIF.

ABSTRACT

This synopsis brings together all extant knowledge of the jack mackerel. This knowledge covers nomenclature, taxonomy, morphology, distribution, ecology and life history, population, exploitation, and protection and management.

INTRODUCTION

The Fisheries Biology Branch of F.A.O.has formed a "Synopsis Association" composed of fishery agencies willing to contribute to the preparation of synopses on fishes and other aquatic organisms of commercial value. As of this time several organizations, including the Bureau of Commercial Fisheries, have agreed to collaborate with F^.O. in this undertaking. Some Bureau of Commercial Fisheries personnel have already prepared species synopses, issued by F.A.O. Fisheries Biology Branch, in connection with the world species meetings on sardine and tuna. Under the present agreement the Bureauhas assigned the preparation of synopses on various eco- nomically important species to a number of its laboratories. These synopses will be pub- lished in the Special Scientific Report--Fish- eries series, and will follow the format pre- sented in "Preparation of Synopses on the Biology of Species of Living Aquatic Orga- nisms" by H. Rosa Jr., Biology Branch, Fisheries Division, F.A.O.

The primary purpose of this series is to make existing information readily available to fishery scientists, according to a standard pattern, and by so doing also to draw attention to gaps in knowledge. It is hoped that synopses in this series will be useful to scientists ini- tiating investigations of the species concerned or of related ones; as a means of exchange of knowledge among those already working on the species, and as the basis for comparative study of fishery resources.

Trachurus symmetricus (Ayres) Gill, Proc. Acad. Nat. Sci. Phila. 1862: 261. (Cape San Lucas),

Caranx picturatus (Bowdich); Jordan and Gil- bert, Proc, U.S. Nat. Mus. 1882; 269. (Mon- terey, Santa Barbara, San Pedro, Cape San Lucas).

Trachurus picturatus (Bowdich)^ Jordan and Gilbert, Proc. U.S. Nat. Mus. 1882, 269. Proc. U.S. Nat, Mus. 1883: 191. (Monterey, Santa Barbara, San Pedro, Cape San Lucas).

Trachurus picturatus (Bowdich). Jordan and Everman, Bull. U.S. Nat. Mus., 47, 1896; 909. (San Francisco, Monterey, Santa Barbara, San Pedro, Cape San Lucas).

Decapterus polyaspis Walford and Myers, Copeia. 1944: 45. (Oregon, British Columbia).

Trachurus symmetricus (Ayres) Roedel and Fitch, Copeia. No. 1, 1952; 4. (Oregon, British Columbia; Oregon to San Juanico Bay, Baja Calif.).

1.2 Taxonomy

1.21 Affinities

Phylum Class Order Family

Chorda ta Teleostomi Perciformes Carangidae

1 IDENTITY

1.1 Nomenclature

1.11 Valid name

Trachurus symmetricus (Ayres), Proc. Cal. Acad, Nat. Sci. 1: 1855, 62.

1.12 Synonymy

Caranx symmetricus Ayres, Proc. Cal. Acad. Nat, Sci, 1, 1855: 62. (San Francisco).

TRACHURUS

Scomber Linnaeus, 1758, Systema naturae, Ed, X, vol, 1; 298, Scomber, trachurus Linnaeus after Scomber linealaterali aculeata of Artedi.

Trachurus Rafinesque,

1810: Caratteri di

Alcuni Nuovi Generi e Nuove Specie di Animale e Piante della Sicilia, p. 41, Type: Scomber trachurus Linnaeus = Trachurus saurus Rafinesque.

Figure 1. — Trachurus symmetrlcus (Ayres) (Drawing by George Mattson USFWS).

The genus Trachurus may be separated from the other genera of the subfamily Car- anginae by the lateral line scutes which are present along the entire lateral line in Trachurus and either absent or confined to the posterior part of the body in the other genera.

Roedel and Fitch (1952) gave the following diagnosis of Trachurus symmetricus based on 1,100 specimens ranging in standard length from 93 to 557 mm. and collected from Oregon to central Baja California: "On the basis of these 1,100 fish, we conclude that in T. symmetricus, the accessory lateral line usually extends to the insertion of the second dorsal fin. It may end as far forward as the fourth dorsal spine or as far posterior as the fifth dorsal soft ray. All scales in the lateral line are enlarged. The lateral line is curved abruptly downward about under the insertion of the second dorsal and becomes straight under the eighth to eleventh dorsal ray. The length of the chord of the curved portion is usually, but not always, greater than the length of the straight portion. Scales number 52(41-59) in the curved portion and 46 (40-55) in the straight; total scales are 99(87-111). Other counts are: gill rakers 15 (13-18) + 41 (37-45) = 56 (51-61); gill teeth 7 (5-9) + 27 (25-30) = 34 (31-39); first dorsal fin, VIII; second dorsal I, 33(28-38); analll-I, 29 (22-33). The last dorsal and the last anal rays become progressively more finletlike in structure as the fish grows and in large individuals appear to be detached finlets. However, a very fine membrane or its remnants can usually be detected in carefully handled individuals."

Most earlier authors tended to place the various geographic populations of Trachurus

into two species, T. trachurus (L.) and T. picturatus (Bowdich), with T^- symmetricus in the latter. In 1920 Nichols described the Peruvian fornn as T\ murphyi and included a key to the species of Trachurus. Hildebrand (1946) was unable to separate T. symmetricus and T\ nnurphyi using Nichol's key, but could distinguish them on the basis of gill rakers on the lower limb of the first arch and depth of scutes. Roedel and Fitch (1952) also used height of scutes and, in addition, relative p ectoral fin length to separate the two species.

Hildebrand found that seven specimens of murphyi 485 to 497 mnn. standard length had 45-48 gill rakers on the lower arch and six specimens of symmetricus of undetermined length had 40-42. Roedel and Fitch gave 37 to 45 as the range for 1,100 symmetricus 93 to 557 mm. long. No data are given for their two specimens of murphyi.

Roedel and Fitch found that pectoral length was contained 3.2 times in standard length in two murphyi 275 and 323 mm.and 3.6 to 4.5 times in 200 symmetricus 250 to 350 mm. Al- though not stated by Hildebrand, his pectoral- in-length measurements appear to be based on total length. On the basis of standard length his measurements would be approximately 3.0 to 3.5 for an unstated number of small murphyi 60-117 mm. and 4.3 to 4.6 for seven large specimens 485-497 mm. The data on pectoral- in-head given by Walford and Meyers (1944) for five large specimens of synnmetricus 380 to 510 mm. ranged from 4.2 to 4.9. Apparently as in other Carangids (Berry, 1959), the pec- toral length increases at a relatively greater rate with growth than does body length.

Hildebrand used height of highest scale in the curved portion of lateral line into head and height of highest scale in the straight portion of lateral line into head to separate the two

species. Roedel and Fitch expressed scale height as a percentage of head length. Data fronn both as percentage of head length are as follows:

T. murphyi (Peru)

T. symmetricus (Calif,)

Curved

Straight

Curved

Straight

Roedel and Fitch (1952)

18.3-19.8 15.9-20.0

18.3-20.0 15.9-21.3

9.5-14.1 10.5-11.9

12.2-16.9

Hildebrand (1946)

12,7-14.9

The greater range of Hildebrand' s Peru data and Roedel and Fitchs' California data reflect larger numbers of specimens. Otherwise it is apparent that the largest scales in both the curved and straight portions of the lateral line of murphyi are about equal size; they are about 60 percent larger than the largest scale in the curved portion of the lateral line of synnnnetricus and about 30 percent larger than the largest scale in the straight portion.

Roedel and Fitch, using all specimens of Trachurus in the collections of the California Academy of Science and Stanford University stated:

"On the basis of published descriptions and comparisons with the specimens avail- able to us, T. synnnnetricus appears to be readily distinguishable from all other spe- cies except the Atlantic T^. picturatus (Bowdich). A direct comparison of material will be necessary before the relationship of these two can be determined."

The differences between only symmetricus and murphyi are discussed in their paper.

1.22 Taxonomic status

See above.

1.23 Subspecies See above.

1.24 Standard common names, ver- nacular names.

The name sanctioned by the state of California for purposes of record keeping is jack mack- erel. Other names are: horse mackerel, Span- ish mackerel, jackfish, saurel, agii, jurel, macarella caballa.

1.3 Morphology

1.31 There seems to be very little individual variation among jack mackerel, and no geographic variation has been reported. Clothier (1950) found that of 816 jack mackerel

from Monterey Bay and Southern California, 813 (99.6 percent) had 24 vertebrae, one had 23, and two had 25. The species appears to consist of a single population.

As the fish increase in length it appear s that the relative lengths of the pectoral fins in- crease, and the last two rays in the dorsal and anal fins become more finletlike in ap- pearance.

1.32 Cytomorphology No data available.

1.33 Protein specificity No data.

2 DISTRIBUTION

2.1 Total area

The population appears to have its maximum density in California coastal waters (46.3) between Point Conception, California, and central Baja California. The range limits of the population have not been determined fully as noted below. Extensive egg and larva surveys along the U.S. and Baja California coasts indicate that the greatest amount of jack mackerel spawning takes place between Point Conception and Baja California between 80 to 240 miles offshore (Fig. 2). The seaward extension of spawning has not been delimited by the present surveys. Abundance of eggs and larvae decreases to the south, and none are taken off southern Baja California. Spawning also occurs at least as far northas Washington State, In August 1955, eggs and larvae were taken on a special cruise (NORPAC) at stations off the Oregon and Washington coasts to 150° west longitude (or about 1/4 of the distance from U.S. to Japan) which was as far as the cruise extended (Ahlstrom, 1956).

According to Fitch (1 956) adult jack mackerel have been taken more than 600 miles off the southern California coast and along the coast from British Columbia to Cape San Lucas, Baja California. Juveniles have been taken farther

130" 125° 120° 115° 1

0"

1 1 1 1 1 ftAPE BLANCO

1. ,

0% 1

1 1 JACK MACKEREL LARVAE

1 i 1952

** tCAPE MENDOCINO 1

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1?

• STATIONS OCCUPIED

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1 1 1 1 ,_

1

lis*

Figure 2. — Distribution of jack mackerel as indicated by larval distribution.

to the south, at the Revillagigedo Islands and reportedly at Acapulaco and in the Gulf of Tehauntepec, Mexico. The latter two records may be fish transported south in bait tanks of tuna boats.

The record of Clemens and Nowell (1963) of one specimen of T. symmetricus taken off Costa Rica at lat. 10° Ol'N., long, 85° 55' W. by dip net and night light in July 1957 has been found to be in error.

2.2 Differential distribution

The distribution of adult jack mackerel ap- pears to correspond closely to that of eggs and larvae. The adults are present off southern California throughout the year, and seasonal and annual variations in landings are caused by primarily economic factors acting upon the fishing industry.

2.3 Determinants of distribution changes

Jack mackerel eggs and larvae have been taken for the past 15 years at most California Cooperative Oceanic Fisheries Investigation (CalCOFI) stations off southern California and northern Baja California except for those closest to shore. The catch of adults also in- dicates that the population is more stable with respect to distribution and more offshore than the other three small pelagic species, the sardine, Sardinops caerulea (Girard), the Paci- fic mackerel, Pneumatophorus diego (Ayres), and the anchovy, Engraulis mordax Girard, taken by the purse seine fishery.

2.4 Hybridization

No evidence of hybridization. 3 BIONOMICS AND LIFE HISTORY 3.1 Reproduction

3.11 Sexuality

Jack mackerel are heterosexual and without apparent sexual dimorphism.

3.12 Maturity

According to Fitch (1956) 50 percent of fe- males are mature at 250 mm. fork length and age 2; 100 percent at 350 mm. and age 3.

3.13 Mating

No record of observation but probably promiscuous.

3.14 Fertilization

External.

3.15 Gonads

No data are available on the relation of number of eggs to age and body length and weight for the jack mackerel. Within nnost fish species the number of eggs produced at one time is approxinnately proportional to the weight and the cube of the length of the fish.

Fecundity data for a jack mackerel taken off central Baja California in July 1953 are as follows:

Standard length 215 mm.

Fork length 229 mm.

Total length 242 mm.

Weight 171 grams

Gonad weight (left 3.17) , ,,

(right 2.97) 6.14 grams

Eggs (0.40-0.58 mm. diameter ... 52,600

Eggs per gram of fish 308

The pelagic eggs of marine fishes of most species have diameters within a few tenths of 1 nnillimeter. The number of eggs per gram of fish, developed as one spawning batch, tends generally to be high for small species of fish (i.e. about 600 eggs per gram of fish for Vinciguerria lucetia (Garman) weighing less than 1 gram and having ripe- egg diameters of about 0.7 mm.) and low for large species of fish (i.e. less than 50 eggs per gram of fish for some of the large tunas weighing over 100 kg. and having ripe- egg diameters of about I mm.).

The 308 eggs per gram of fish and ripe-egg diameter of about 1 mm. for the jack nnackerel are typical for a fish of this size producing a pelagic egg. A scombrid, the Pacific mack- erel--which inhabits much of the same range as the jack mackerel, is of similar size and has many comparable habits- -spawns a pelagic egg about 1.1 mm. in diameter and produces 304 eggs per gram of fish (based on counts for six specimens).

3.16 Spawning

The percentage frequency distribution of diameters of eggs containing yolk found within the ovaries of the 215 mm. jack mackerel (see preceding section) are presented in Figure 3. Numerous eggs less than 0.20 mm. diameter and not containing yolk are not shown. The eggs that form a distinct nnode from 0.40 to 0.58 mm. diameter are considered to be the group destined to be spawned. A bimodal distribution of yolked eggs may indicate two spawnings. The ratio of eggs 0.20 to 0.38 mm. to eggs 0.40 to 0.58 mm. diameter

ESTIMATED NUMBERS OF EGGS

IN THOUSANDS O ro -tk o) 00 O

tV)

J

1 1 1 1 1 1 1 1 1 1

1

i

o

-

-

-

-

CM

o

m o

o

.40 DIAMETER {

—

S S

^_

1

^

-

o

-

0>

o

1

1 1

1

1

1

1

1 1 1

1

Figure 3. — Frequency distribution of diameters of eggs from a jack mackerel ovary.

6

is approximately 1 to 1 . Alternatively the eggs 0.20 to 0.38 mm. may be only an extension of the large mode of nonyolked eggs that is resorbed following spawning of the more advanced yolked eggs. The presence of a bimodal size distribution of yolked eggs in the developing ovaries of fish species that spawn pelagically seems to be a typical condition, but whether this bimodality means the fish

will necessarily spawn more than once is an unsettled question.

Plankton tows taken at monthly intervals at the CalCOFl stations off the coasts of Califor- nia and Baja California reveal the following seasonal occurrence for the 105,776 jack mackerel larvae taken in the 7-year period 1951-57:

Month

Total

number

of larvae

Percentage

of

total

Month

Total

number

of larvae

Percentage

of

total

January

February

March

April

May

36 2,457 13,014 19,441 26,800 31,799

0.03 2.3 12.3 18.4 25.3 30.1

July

10,726

986

320

183

14

0

10.1

August

.9

September

October

November

December

.3 .2 .01 .00

The average age of the above larvae is 6.6 days from spawning, and therefore the larval occurrences should adequately indicate the spawning season.

Farris (1961) deternnined the daily distribu- tion of spawning by plotting the relative abundance of precleavage eggs against time of collection. He found that about one- third of these newly spawned eggs were taken in the hour between 2330 and 0030, and almost two- thirds in the 4 hours between 2030 and 0030; spawning activity seemingly reaches a peak shortly before midnight.

On monthly survey cruises, 1950 through 1952, Ahlstrom and Ball (1954) took jack mackerel larvae at water temperatures (20- meter depth) of 10° to 19.5° C, but over 70 percent of the larger concentrations of larvae (50 or more larvae per standardized haul) occurred within a 2° range, 14° to 16° C. They also found that 80.1 percent of the larvae occurred offshore between Point Conception, California, (about lat. 35° N.) and San Quentin Bay, Baja California, (about lat. 30° N.); 10.7 percent of the larvae were taken north of this area and 9.2 percent south. The spawning area did not appear to extend south of the area surveyed, but there was probably some spawn- ing to the north outside the survey area.

Spawning as indicated by percentage occur- rence of larvae (adjusted to number of sta- tions) relative to distance offshore was as follows:

80 miles 9.9

160 do 32.7

240 do 39.9

320 do 15.0

400 do 2.5

Coast

to

81

to

161

to

241

to

321

to

Spawning probably also extended farther sea- ward than the survey area.

3.17 Spawn

On the basis of 538 eggs taken during April and May 1950 from various parts of the spawn- ing range, Ahlstrom and Ball (1954) described the jack mackerel egg as pelagic, nonadhesive, spherical, 0.98 mm. (range 0.90-1.08) in di- ameter, with a yolk 0.80 mm. (0.68- 0.88) in diameter, a single oil globule 0.26 mm. (0.18- 0.35) in diameter, and a perivitelline space 0.09 mm, wide (fig. 4). The eggshell is clear, tough and unsculptured. The irregularly seg- mented yolk mass appears yellow to amber in preserved material.

Ahlstrom (1959 table 7) showed that 97 per- cent of the jack mackerel eggs and 88 percent of the larvae are found in the upper 50 meters of water. Few eggs or larvae are found below 100 meters and none below 140 meters.

3,2 Pre-adult phase

3.21 Embryonic phase

Embryonic development of the jack mackerel is typical of most fish with pelagic eggs. One identification feature present throughout em- bryonic development is the segmentation of yolk naaterial which is usual in the eggs of iso- spondylid fishes, but unusual in those of percomorph fishes. Ahlstrom and Ball (1954) gave a detailed description of the embryonic development of the jack mackerel (Fig. 4),

According to data presented by Farris (1961), incubation tinne from spawning to the last stage before hatching follows the formula log Y_ = 3.257-0.088X in which Y = hours and X - temperature in degrees Centigrade. Thus incubation time would be 2 days at 17.9° C, 3 days at 15.9° C, and 4 days at 14.5° C.

jBdc-mackerel eggs Id varlom sUges of developmf nL a, b, and r. earl; embryoDlc period, 0 being the stage Immediatelj preceding blastopore closure; d, IntercDedlate period of embryoolc developmest : 0 and f, late-period egga wltb advanced embryos: e shows an egg as viewed from above; all other figures are lateral vlewB.

I^trra, 10.0 mm.

Figure 4. — Eggs and larvae of jack mackerel (figures 1 through 8 of Ahlstrom and Ball, 1954).

3.22 Larval phase

Ahlstrom and Ball (1954) gave a (detailed description of the development of jack mack- erel larvae (fig. 4). Jack mackerel hatch in a relatively undeveloped condition- -before the mouth is formed, before the eyes are pigmented, and before any fin formation. In preserved material the larvae average 2.07 mm. (range 1.91 to 2.38) at hatching. During the yolk-sac

stage the eyes may begin to develop pigment in larvae as small as 2.2 mm. The jaws develop rapidly and begin to ossify- -the upper jaw in larvae between 3 and 3.5 mm. long, and the lower, in larvae between 3.2 and 3.8 mm. The following table gives the approximate length at which the first spine or ray appears and the approximate length at which the full complement of spines or rays is attained for each fin.

Fin

Full connplement

Fish length

when first

ray or spine

appears

Fish length

when full

complement

is attained

Caudal:

Principal rays

17 18-20

22-24

3 28-31

8

1 30-35

1 5

Mm.

5-6

8

6

7 7

8 8 7

11 9

Mm. 8 16

14

9 14

12

Secondary rays

Pectoral rays

Anal spines

Anal rays

First dorsal spines

Second dorsal spine

Second dorsal rays

14

Ventral spine

Ventral rays

11

The very small jack mackerel feed pri- marily on minute crustaceans; the food particle size ingested by mackerel of about 3 mnn. length ranges from 0.04 to 0.18 mm. diameter and by mackerel of about 9.5 mm. length from 0.10 to 0.56 mm. (Anonymous, 1953).

The size of larvae (based on preserved material which may shrink as much as 20 percent) at the end of the yolk-sac stage is as follows (Ahlstrom and Ball, 1954):

Size group

Number examined

Number with yolk

Percentage with yolk

Mm.

2.00-2.49 2.50-2.99 3.00-3.49 3.50-3.99 4.00-4.59

8 18 16 15 15

8

11

4

1 0

100

61

25

7

0

Farris (1959) gave the following data on larval growth for live larvae that were not given any nourishment other than that in the yolk; the yolk sacs were absorbed by the sixth day.

Numbers

Days past

Average length

of larvae

hatching

(millimeters)

4

0

2.0

17

1

2.6

12

2

2.9

14

3

3.4

10

4

3.5

11

5

3.5

9

6

3.7

7

7

3.8

3

8

3.7

3

9

3.7

3

10

3.5

2

11

3.4

On the basis of the above and other data on larvae Farris (1959, 1960, 1961) ob- tained growth and survival curves for larval jack mackerel. His survival curves are based on the questionable growth curves obtained fronn measurements of starving larvae, and therefore any advantages of his curve of survival with age over the curve of survival with length are lost. The length frequency distributions of larvae taken in 1952 through 1957 (table 1) may be used as length- survival curves if the numbers of larvae in the 0.50 mm. intervals (2.00 to 5.00 mm.) are doubled. If the 6-year totals so adjusted are plotted on semilog paper it is apparent that the length intervals at 3.50 through 7.75 have an excellent straight-line relationship to numbers of larvae. That is, if Y_ = numbers of larvae, and X_ = length in mm, log X ~ a-0.36428X or X = antilog a (O.43224E.) or survival is 43 percent for each millimeter of length increase from 3.50 to 7.75 mm. The value of "a" nnay be adjusted so that a predetermined number of larvae at hatching (2.00 mm.) nnay be used as a starting point. In Figure 5 the observed numbers of larvae were multiplied by 9.5427 to obtain a computed value at 2.00 mm. of 1 million larvae. The relation between length and numbers of larvae is log Y 5.74889 - 0.364282^. The fact that larvae smaller than 3.5 mm. fall progressively farther below the extrapolated line is explained by the incomplete retention of very small larvae by the plankton nets. This selection bias is discussed in detail by Farris (1961). The data indicate that, unless the mortality of these very small larvae is different from that of the larger ones, the nets retain about 15 percent of 2.0-mm.larvae, 47 percent of 2.5-mm. larvae and 86 percent of 3. 0-mm. larvae.

Table l.--Jack mackerel larvae of different lengths caught in standard hauls 1952-57

Standard length

Year

Range

Midpoint

1952

1953

1954

1955

1956

1957

Total

Mm. 1.75- 2.25

Mm.

2.00

2.50

3.00

3.50

4.00

4.50

5.00

5.75

6.75

7.75

8.75

9.75

10.75

11.75

12.75

13.75

No.

1,714

3,512

4,896

4,143

3,018

1.949

1.355

1.184

343

141

53

37

15

9

3

7

No.

1.005

1.646

1,614

842

679

567

445

506

335

124

51

37

7

18

11

6

No.

1,603

4,126

3.690

2.040

1.184

672

685

524

271

91

26

12

6

0

2

0

No.

791

1.797

3.026

2,803

1.509

869

750

964

436

160

52

46

15

8

12

0

No.

333

805

1,662

1.486

1,225

962

560

601

211

97

19

18

9

15

0

0

No.

2,173

4,283

4,570

3,610

1,881

1,291

677

808

375

207

59

28

26

6

0

3

No. 7 619

2.25- 2.75

16 169

2.75- 3.25

19,458

14,924

9.426

6 310

3.25- 3.75

3.75- 4.25

4.25- 4.75

4.75- 5.25.....

4,472 4 587

5.25- 6.25

6.25- 7.25

1 971

7.25- 8.25

820

8.25- 9.25

260

9.25-10.25

178

10.25-11.25

78

11.25-12.25

56

12.25-13.25

28

13.25-14.25

16

o

o

ro-

ot (ji

"1 1 — I — I I I 1 1

o o

o

NUMBERS OF LARVAE

O

'o o

o

-1 1 — I — I I I I

"1 1 — I — I I III

o o o o o

m

2

H X

ro- Ci-

"T 1 1 — r

o ^ -

I

J I I I I I I

J I I I I I I I I

J I I L

Figure 5. — Survival (length frequency) curve for larval jack mackerel.

10

The numbers of larvae larger than 7.75 mm. taken by plankton nets are undoubtedly affected by "net dodging." Most other larval fish taken with jack mackerel in plankton nets show an increase in the ratio of night-caught to day- caught larvae with increasing size of larvae. Farris found that the ratio of night-caught to day-caught larval jack mackerel remained approximately 1:1 for larvae 2 to 12 mm. He concluded that jack mackerel do not evade the net. A second interpretation is that they avoid the net equally well both by day and night.

The principal rays of the dorsal fin first appear at 5 to 6 mm.and a full complement is attained by 8 mm. The remaining fins begin to form at 6 to 8 mm. The resulting increased motility could decrease the capture of larvae by the net from a probable 100 percent (over the length range 3.50 to 7.75 mm.) of the larvae available to the net to considerably less.

Survival also appears to increase at this point. If the initial survival rate continued to 18.5 mm,, only 1 larva of the original 1 million would survive and the adult stock could not replace itself. The first reduction in mortality appears to take place at about 8 mm. when the larvae become motile.

The apparent relation between numbers of larvae and length for the range 8.75 to 13.75 mm. may be described by log Y = 5.57267 - 0.24594X, at this size range survival is 57 percent for each millimeter of length increase. This rate of survival would reduce the larval population to 1 fish at 22.5 mm. More prob- ably, the larval mortality is decreasing with increasing size and motility of the fish above 8 mm.; the increasing nnotility of the fish also increases its ability to avoid the net, thus causing progressively greater undersampling of fish over 8 mm. There is no indication of a "critical period" in survival, and the only "abrupt" change in the survival curve occurs at the time of fin formation.

3.23 Adolescent phase

Little is known about the juvenile jack mackerel. Food studies show that copepods, euphausiids and pteropods constitute most of the food in stomachs, and that copepods are a more important food among juveniles than among adults (Anonymous, 1953).

3.3 Adult phase

3.31 Longevity

Most of the fish taken in the commercial catch are less than 6 years old; the majority are 2, 3, and 4 years old. On rare occasions very large jack mackerel from 10 to over 25

years old appear in the commercial catch (Anonymous, 1953) and some fish taken in the sport fishery have been reliably aged at over 30 years (Fitch, 1956).

3.32 Hardiness No data.

3.33 Competitors

The Pacific mackerel, which is often caught with the jack mackerel and which has many similar habits, is probably the principal com- petitor.

3.34 Predators

Predation other than by man has not been studied.

3.35 Parasites, diseases, injuries, and abnormalities

No data.

3.4 Nutrition and growth

3.41 Feeding

Feeding takes place at any time of day. One method of catching mackerel at night makes use of chumming under lights, but whether or not they feed in the dark is un- known. Food is taken by selection and pursuit of individual food items.

3.42 Food

One study of food habits revealed that 90 percent by numbers of identifiable items in jack mackerel stomachs consisted of euphausiids, large copepods, and pteropods. Samples from cannery landings showed that at times jack mackerel feed almost exclusively on juvenile squid and anchovies. Large jack mackerel taken in offshore waters at night contained lantern fish. Both the mackerel and lantern fish were probably attracted to a light suspended over the stern of the vessel. Large jack mackerel taken by the sport fishery are usually caught with large adult anchovies as bait (Fitch, 1956).

3,42 Growth rate

Fish 2 years old are about 250 mm. long and 3 years, 350 mm. (Fitch, 1956), No other data have been published on growth of juvenile or adult jack mackerel. The following data on preserved specimens are available for condi- tion factor K = ^^^^^t x 10?

Standard length3).

11

Numbers of fish

Standard length range (mm^

Condition factor

Date

Mean

Range

11-20-59

UI-25-52

VI- 9-60

VII-19-53

VIII-11-56

2 5

10

1

7

14

147-193 211-218 233-260 215 146-186 170-202

146 128 163 172 139 130

135-147 120-135 140-177 172 121-164

Vni-28-52

122-136

3.44 Metabolism No data. 3.5 Behavior

3.51 Migrations and local movements

Practically nothing is known about the nni- grations and movements of the population. Very large specimens, to over 76 cm. and 2 l/4 kg. are taken in the inshore waters of, southern California a month or two each summer by sport fishermen. These fish rennain in the area a relatively short time and numbers caught fluctuate greatly from season to season as is shown in the following table (Fitch, 1956),

Sports catch of jack nnackerel

Year

Number

Best month

1947

4,500

2,400

2.900

600

200

4,400

196,300

19,400

39,600

September

August

Do.

1948

1949

1950

July Do.

1951

1952

May

August

June

1953

1954

1955

May

3.52 Schooling

The jack mackerel is a schooling fish, and tends to school by size. It is taken in com- pany with Pacific mackerel and sardines as well as in pure schools.

3.53 Responses to stimuli

The jack mackerel is attracted to lights at night, or at least by the food attracted to the lights.

4 POPULATION

4.1 Structure

4.1 1 Sex ratio

The sex ratio of the catch appears to be about 1:1.

4.12 Age composition

Most of the jack mackerel in the comnner- cial catch have been less than 6 years old and the majority either 2, 3, or 4 years.

Sexual maturity is attained by 50 percent of the female mackerel at age 2 and 100 percent at age 3,

Very large mackerel, nnore generally taken by the sport fishery, are as old as 30 years or more.

4.13 Size composition

Most of the connmercial catch consists of fish 20 to 38 cm. total length.

Sexual maturity is attained by 50 percent of the female nnackerel at 25 cm. fork length (2 years old) and 100 percent at 35 cm. fork length (3 years old).

Jack mackerel taken erratically in the salt- water sport fishery range from 45 to over 75 cm. total length and to 2.3 kg. These large jack mackerel appear in inshore waters only a month or two during the summer (Fitch, 1956).

From preserved material fork length was found to equal 1.08 times standard length, and total length was 1.19 times standard length.

4.2 Abundance and density (of population) No data available.

4.3 Natality and recruitment No data available.

4.4 Mortality and morbidity No data available.

4.5 Dynamics of population (as a whole) No data available.

4.6 The population in the connnnunity and the ecosystem

No data available.

12

5 EXPLOITATION

5.1 Fishing equipment

5.11 Gears

Jack mackerel have been taken incidentally to the sardine and Pacific mackerel fisheries for many years by the same gear used in these fisheries. When the mackerel fishery developed suddenly in 1947 because of the decline in sardines and to a lesser extent Pacific mack- erel, the purse seines of the sardine and Pa- cific nnackerel fishery continued to be used for the jack mackerel. Scofield (1951) de- scribed in detail purse seines and other round haul nets that have been used in California fisheries. Before the development of the fishery for jack nnackerel they were also taken in small quantities in the ring nets and lampara nets used by the sardine fishery before the purse seine came into general use.

Jack mackerel are also taken by the fisher- men who fish for Pacific mackerel for the fresh fish market and to a lesser extent for canneries. Various methods have been and are used in this fishery, including hand lines, long lines, jigs, gill nets, and scoop nets, often in conjunction with chumming and/or lights (Croker, 1933, 1938).

Improvements in ship gear and fishing methods of the purse seine fleet include in- stallation of ship-to-ship radios, echo-sound- ing gear, and power blocks, and the use of nnotor skiffs, synthetic netting nnaterials, and airplane scouting.

5.12 Boats

The jack mackerel is taken primarily as a substitute or alternate cannery fish by the sardine fishing fleet. The sardine fleet con- sists of large purse seiners (over 60 feet or 18.3 meters in length) and assorted smaller purse seiners and lampara boats that are used in other fisheries when sardines are not avail- able. Since the big increase in jack nnackerel landings in 1947, this fleet attained its largest size during the 1949-50 season when it con- sisted of 372 vessels (including 135 smaller boats). In the 1960-61 season the California sardine fleet consisted of only 28 vessels (11 large purse seiners, 2 small purse seiners, and 15 lampara boats).

5.2 Fishing areas

Most jack mackerel are landed in the Los Angeles area (Roedel, 1953). Because this fishery is so closely allied to the sardine fishery, the area of the jack mackerel fishery closely coincides with that of the sardine (Fig. 6). The purse seiners are primarily

seeking sardines; if sardines are scarce and there is a market for jack mackerel, these fish are taken instead whenever encountered. Actually the jack mackerel is distributed farther offshore than the sardine. In the 1 952- 53 sardine season the sardine catch was only about 3,000 tons, compared to over 120,000 tons the previous year. In the same season the jack mackerel catch was a record 73,000 tons, but 67 percent of this catch was made in the Tanner Bank-Cortez Bank area about 80 nauti- cal miles offshore (Clothier and Greenhood, 1956). When sardines are more abundant the purse seiners do not range so far offshore.

Jack mackerel are also taken in unknown but relatively small amounts by Mexican purse seiners off northern Baja California.

In southern California and to a lesser extent in central California, jack mackerel are taken in small quantities primarily for the fresh fish market.

5.3 Fishing seasons

Clothier and Greenhood (1956) stated: "Jack mackerel are present in the waters off Cali- fornia throughout the entire year, but since the fishery is carried on simultaneously with the sardine and Pacific mackerel fishery, and these species are taken chiefly during the fall and winter months, the jack mackerel landings decline to a minimum in the spring and early summer."

5.4 Fishing operations and results

5.41 Effort and intensity

Effort and intensity are so influenced by the relationship to the sardine and Pacific mackerel fisheries as to be meaningless.

5.42 Selectivity

Selection factors primarily involved are the fishermen's ability to identify the species, size of school, and size of fish before setting their nets.

5.43 Catches

Table II gives the catch of Pacific nnackerel, jack mackerel, and all mackerel for the years 1916-63,

6 PROTECTION AND MANAGEMENT

6.1 Regulatory measures

6.11 Limitation or reduction of total catch

There are no legislative limitations on catch specifically pertaining to the jack mack- erel. Canneries often place limits on the ton- nage of jack mackerel that they will accept.

13

SEASONS 1952-53 1953-54 1954-55

OMC dot EQUALS 90 TONS

Figure 6. — Commercial fishing areas for jack mackerel in California (figures 3 and 4 of Clothier and Greenhood, 1956).

based on facilities available for handling the fish and on economic considerations.

6.12 Protection of portions of popu- lation

California has regulations pertaining to fish- ing gear and craft and also restrictions on commercial fishing in several relatively small areas. These regulations were not passed specifically to control the jack mackerel fishery and probably have little or no effect on it. There are no closed seasons or other restrictions on the jack mackerel fishery. California law prohibits the use of fish for reduction except that the fish offal may be reduced. The law also provides that the Fish and Game Commission may grant permits for the reduction of whole fish, but none have been granted for any species except sardines, and even reduction of sardines has not been allowed since 1948.

6.2 Control or alterations of physical features of the environment

None.

6.3 Control or alteration of chemical fea- tures of the environment

None.

6.4 Control or alteration of the biological features of the environment

None except those that may arise incident- ally from fishing for jack mackerel, its predators, or competitors.

6.5 Artificial stocking None.

7 POND FISH CULTURE Does not apply.

14

Table 2. --California mackerel landings'''

Year

Pacific mackerel Tons

Jack mackerel

Tons

Percent of total landings

Total Tons

1926. 1927. 1928. 1929. 1930. 1931. 1932. 1933. 1934. 1935. 1936. 1937. 1938. 1939. 1940. 1941. 1942. 1943. 1944. 1945. 1946. 1947. 1948. 1949. 1950. 1951. 1952. 1953. 1954. 1955. 1956. 1957. 1958. 1959. 1960. 1961. 1962. 1963.

1,805 2,364 17,626 28,987 8,266 7,127 6,237 34,907 56,924 73,214 50,271 30,468 39,924 40,455 60,252 39,084 26,277 37,607 41,828 26,858 26,938 23,239 19,693 24,881 16,325 16,759 10,302 3,751 12,696 11,656 25,007 31,022 13,824 18,801 18,404 22,055 22,490 18,259

118

231

269

349

184

282

268

505

791

4,992

2,300

3,271

2,067

1,880

716

1,034

2,674

6,349

6,389

4,516

7,547

64,534

36,449

25,625

66,628

44,919

73,261

27,875

8,667

17,877

37,881

41,006

11,033

18,754

37,473

48,803

46,707

48,319

6.1 8.9 1.5 1.2 2.2 3.8 4.1 1.4 1.4 6.4 4.4 9.7 4.9 4.4 1.2 2.6 9.2

.4 .3 .4 .9 .5 .9 .7 .3

14.

13.

14.

21.

73.

64.

50.

80.

72.8

87.7

88.1

40.6

60.5

60.2

56.9

44.4

49.9

67.1

68.9

67.5

72.6

1,923 2,596 17,895 29,336 8,450 7,409 6,505 35,312 57,715 78,206 52,571 33,739 41,991 42,335 60,969 40,118 28,951 43,957 48,217 31,375 34,484 87,763 56,142 50,506 82,953 61,678 83,563 31,626 21,363 29,533 62,888 72,028 24,857 37,555 55,877 70,858 69,197 66,578

Landings of the two species of mackerel were not recorded separately in 1916-25. Combined landings (tons) were: 1916, 557; 1917, 1673; 1918, 2003; 1919, 1327; 1920, 1499; 1921, 1457; 1922, 1233; 1923, 1777; 1924, 1614; 1925, 1753.

15

REFERENCES

AHLSTROM, ELBERT H.

1956. Eggs and larvae of anchovy, jack mackerel, and Pacific mackerel. Calif. Coop. Oceanic Fish. Invest. Progr. Rep., 1955-1956:33-42. 1959. Vertical distribution of pelagic fish eggs and larvae off California and Baja California. U.S. Fish Wildl. Serv., Fish. Bull. 60:107-146. AHLSTROM, ELBERT H., and ORVILLE P. BALL. 1954. Description of eggs and larvae of jack mackerel (Trachurus symmetricus) and distribution and abundance of larvae in 1950 and 1951. U.S. Fish Wildl. Serv., Fish. Bull. 56:209-245. BERRY, FREDERICK H.

1959. Young jack crevalles (Caranx species) off the southeastern Atlantic coast of the United States. U.S. Fish Wildl. Serv., Fish. Bull. 59:417-535. CALIFORNIA COOPERATIVE OCEANIC FISH- ERIES INVESTIGATIONS. 1953. Sardines and "substitute sardines." Its Progr. Rep., 1952-1953:31-44. CLEMENS, H. B., and J. C. NOWELL.

1963. Fishes collected in the eastern Pa- cific during tuna cruises, 1952 through 1959. Calif. Fish Game 49(4):240-246. CLOTHIER, CHARLES R.

1950. A key to some southern California fishes based on vertebral characters. Calif. Div. Fish Game, Fish Bull. 79. 83 p. CLOTHIER, CHARLES R. and EDWARD C. GREENHOOD. 1956. Jack mackerel and sardine yield per area fronn California waters, 1946-47 through 1954-55. Calif. Dep. Fish Game, Fish Bull. 102:7-16. CROKER, RICHARD S.

1933. The California mackerel fishery. Calif. Div. Fish Game. Fish Bull. 40, 149 p.

1938. Historical account of the Los Angeles nnackerel fishery. Calif. Div. Fish Game, Fish Bull., 52,62 p. FARRIS, DAVID A.

1959. A change in the early growth rates of four larval marine fishes. Limnol. Oceanogr. 4(l):29-36.

1960. The effect of three different types of growth curves on estimates of larval fish survival. J. Cons. 25(3):294- 306.

1961. Abundance and distribution of eggs and larvae and survival of larvae of jack mackerel ( Trachurus symmetri- cus). U.S. Fish Wildl. Serv., Fish. Bull. 61:247-279.

FITCH, J. E.

1956. Jack mackerel. Calif. Coop. Oceanic Fish. Invest., Progr. Rep., 1955- 1956: 27-28. HILDEBRAND, SAMUEL F.

1946. A descriptive catalog of the shore fishes of Peru. U.S. Nat. Mus., Bull. 189, 530 p. NICHOLS, J. T.

1920. A key to the species of Trachurus. Amer. Mus. Nat. Hist., Bull. 42(13): 477-481. ROEDEL, P. M.

1953. The jack mackerel, Trachurus sym- metricus: A review of the California fishery and of current biological knowl- edge. Calif, Fish Game 39(l):45-68. ROEDEL, PHIL M. and JOHN E. FITCH.

1952. The status of the carangid fishes Trachurus and Decapterus on the Pa- cific coast of Canada and the United States. Copeia, 1952 {1)4-6. SCOFIELD, W. L.

1951. Purse seines and other roundhaul nets in California. Calif. Dep. Fish Game, Fish. Bull. 81,83 p. WALFORD, LIONEL A. and GEORGE S. MEYERS 1944. A new species of carangid fish fronn the northeastern Pacific. Copeia 1944 (l):44-47.

MS # 1478

16

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