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.A.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 Bureau has assigned the preparation of synopses on various economically important species to a number of its laboratories. These synopses will be published in the Special Scientific Report--Fisheries series, and will follow the format presented in "Preparation of Synopses on the Biology of Species of Living Aquatic Organisms" 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 initiating 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. IDENTITY 1.1 Nomenclature 1.11 Valid name Trachurus symmetricus (Ayres), Proc. Cal. 1.12 Synonymy Caranx symmetricus Ayres, Proc. Cal. Acad. Trachurus symmetricus (Ayres) Gill, Proc. Caranx picturatus (Bowdich); Jordan and Gil- Trachurus picturatus (Bowdich), Jordan and Trachurus picturatus (Bowdich). Jordan and Decapterus polyaspis Walford 1.2 Taxonomy 1.21 Affinities Phylum Order Chordata Teleostomi Perciformes TRACHURUS Scomber Linnaeus, 1758, Systema naturae, Trachurus Rafinesque, 1810: Caratteri di Alcuni Nuovi Generi e Nuove Specie di Figure 1.--Trachurus symmetricus (Ayres) (Drawing by George Mattson USFWS). The genus Trachurus may be separated from the other genera of the subfamily Caranginae 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); anal II-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. tra churus (L) and T. picturatus (Bowdich), with T. symmetricus in the latter. In 1920 Nichols described the Peruvian form as T. murphyi and included a key to the species of Trachurus. Hildebrand (1946) was unable to separate T. symmetricus and T. murphyi 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 pectoral fin length to separate the two species. Hildebrand found that seven specimens of murphyi 485 to 497 mm. 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. Although not stated by Hildebrand, his pectoralin-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 pectoralin-head given by Walford and Meyers (1944) for five large specimens of symmetricus 380 to 510 mm. ranged from 4.2 to 4.9. Apparently as in other Carangids (Berry, 1959), the pectoral length increases at a relatively greater rate with growth than does body length. species. Roedel and Fitch expressed scale height as a percentage of head length. Data from both as percentage of head length are as follows: T. symmetricus (Calif.) Curved Straight 9.5-14.1 12.2-16.9 10.5-11.9 12.7-14.9 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 appears that the relative lengths of the pectoral fins increase, and the last two rays in the dorsal and anal fins become more finletlike in appearance. 1.32 Cytomorphology No data available. 1.33 Protein specificity No data. 2 Hildebrand used height of highest scale in the Roedel and Fitch (1952)......... T. murphyi (Peru) 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 symmetricus 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 available to us, T. symmetricus appears to be readily distinguishable from all other species 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- The name sanctioned by the state of California 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 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 north as Washington State. In August 1955, eggs and larvae were taken on a special cruise (NORPAC) at stations off the Oregon and Washington coasts to 1500 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 (1956) 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 |