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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

1 1 1 1 1
ftAPE BLANCO

1. ,

0% 1

1 1 JACK MACKEREL LARVAE

1 i 1952

** tCAPE MENDOCINO 1

* V^ '

• ■'4 ^

•'> ft^AN FRANCISCO \

° ° V

o V. s

° o7 \

"•^ ° •=■ l^POINT CONrEPTlON ^
^^ ' ^KKK^t^Jjk^^ \SAN DIEGO' y^

Tj^"'". -*.

CUMULATIVE TOTALS "' • , Sk „ " „ " ^^'^ "S^

Niii^i

* ^ 0 „ • \^ -\

.-6 ° '^ $^° ,''\ If

« o o "X

' • o ■ v\

—

o •"^^-i; N^P

mH 61-600 ° ^o ° Nfo

^1 OVER 600

• STATIONS OCCUPIED

• —

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)

1 1 1 1 1 1 1 1 1 1

m
o

.40
DIAMETER {

—

S
S

1 1

1 1 1

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

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

total

Month

Total

number

of larvae

Percentage

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

10.1

August

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

161

241

321

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

1
30-35

1
5

Mm.

5-6

7
7

8
8
7

11
9

Mm.
8
16

9
14

Secondary rays

Pectoral rays

Anal spines

Anal rays

First dorsal spines

Second dorsal spine

Second dorsal rays

Ventral spine

Ventral rays

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

1
0

100

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)

2.0

2.6

2.9

3.4

3.5

3.7

3.8

3.7

3.5

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

No.

1.005

1.646

1,614

842

679

567

445

506

335

124

No.

1,603

4,126

3.690

2.040

1.184

672

685

524

271

No.

791

1.797

3.026

2,803

1.509

869

750

964

436

160

No.

333

805

1,662

1.486

1,225

962

560

601

211

No.

2,173

4,283

4,570

3,610

1,881

1,291

677

808

375

207

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

11.25-12.25

12.25-13.25

13.25-14.25

ro-

ot
(ji

"1 1 — I — I I I 1 1

o
o

NUMBERS OF LARVAE

'o
o

-1 1 — I — I I I I

"1 1 — I — I I III

o
o
o
o
o

H
X

ro-
Ci-

"T 1 1 — r

o ^ -

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.

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).

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

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.

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.

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.

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.

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.

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