BAILEY; DESCRIPTION AND SURFACE DISTRIBUTION OF JACK MACKEREL 



lateral line and the accessory lateral line was not 

 visible. In fish smaller than 25 mm FL the lateral 

 line was not fully developed, but the specimens had 

 the typical shape, pigmentation pattern, and pro- 

 cumbent dorsal spine of Trachurus juveniles (Haigh 

 1972). Jack mackerel collected on Coriolis were too 

 digested to measure accurately, but from general 

 body size they were similar to the Townsend Crom- 

 well samples. 



SURFACE DISTRIBUTION 



Trachurus murphyi is a schooling, pelagic species 

 found along the west coast of South America from 

 northern Peru and the Galapagos Islands to south- 

 ern Chile (Gutierrez 1986). Eggs and larvae have 

 been found over 1,000 km from this coastline (San- 

 tander and de Castillo 1971; Gutierrez 1986), and 

 recently two larvae and a juvenile were caught in 

 the Subtropical Convergence Zone at lat. 39°42'S, 

 long. 125°46'W and 40°46'S, long. 139°28'W re- 

 spectively (Evseenko 1987). In addition, adults have 

 recently been discovered off the east coast of New 

 Zealand, particularly over the Chatham Rise (Kawa- 

 hara et al. 1988). The surface distribution of juvenile 

 Trachurus murphyi shown in Figure 1 was drawn 

 from the positions where they were netted or found 

 in albacore stomachs. The limits of the distribution 

 are from lat. 34°35'S to 42°02'S and long. 127°00' 

 W to 165°00'W. These limits reflect the cruise 

 tracks and fishing effort of Toumsend Cromwell and 

 Coriolis. 



Albacore from the Toumsend Cromwell and Corio- 

 lis survey areas had similar diets. Trachurus mur- 

 phyi occurred in 93% of the 174 stomachs examined 

 that contained food (66 stomachs from TC-86-01, 72 

 from TC-87-01, and 36 from Prosgermon87) and 

 comprised 90% of the diet by volume. That albacore 

 fed so heavily on a single prey species in the two 

 areas suggests that T. murphyi are relatively abun- 

 dant and probably present in the unsurveyed area 

 between 140°W and 147°W. Albacore caught to the 

 west of 165° W during the same periods (9 fish from 

 TC-86-01 and 126 from RV Kaharoa^ cruises K03/86 

 and K04/87) had not fed on T. murphyi or other 

 jack mackerel. Unfortunately the number of alba- 

 core caught between the easternmost edge of the 

 Chatham Rise (about 175° W) and 165°W was very 

 low and the presence or absence of jack mackerel 

 can not be inferred. 



The present study indicates that jack mackerel oc- 



cur in the area of the Subtropical Convergence Zone 

 encountered by Townsend Cromwell (Laurs et al.'^'^ 

 and in Subtropical Surface Waters to the north. The 

 Subtropical Convergence Zone is characterized by 

 summer surface temperatures of 15° to 18°C 

 (Roberts 1980; Heath 1985); during this study jack 

 mackerel occurred in temperatures of 16.4° to 

 21.3°C. During cruise TC-87-01 jack mackerel were 

 found in water 0.5° to 3.0°C warmer than in 1986. 

 This may be due to the greater amount of fishing 

 effort in more northern waters in 1987. 



DISCUSSION 



Body features most often used to separate and 

 identify Trachurus species include the number of 

 scales and scutes along the lateral line, the height 

 (or depth) of the largest of these scales and scutes, 

 the endpoint of the accessory lateral line, and the 

 number of gill rakers and dorsal and anal softrays 

 (Berry and Cohen 1974; Shaboneyev and Kotlyar 

 1979; Stephenson and Robertson 1977). Three spe- 

 cies of Trachurus are recognized from the South 

 Pacific: T. declivis and T. novaezelandiae from tem- 

 perate waters of New Zealand and Australia 

 (Stephenson and Robertson 1977), and T. murphyi. 

 The latter can be separated from the former two 

 species by having on average 18 more scales and 

 scutes along the lateral line. 



The juvenile Trachurus murphyi examined here 

 are identical in most respects with published descrip- 

 tions of the species (Table 3) and closely resemble 

 the large jack mackerel from New Zealand waters 

 identified as T. murphyi by Kawahara et al. (1988). 

 Unfortunately, Evseenko (1987) did not provide a 

 description of his juvenile T. muryhyi from the cen- 

 tral South Pacific. 



A noticeable difference with the present speci- 

 mens is the significantly fewer gill rakers as com- 

 pared with the descriptions of Shaboneyev and 

 Kotlyar (1979) (Z test, P < 0.05) and Berry and 

 Cohen (1974) (Student's t test, P < 0.05, df = 48). 

 This difference is probably related to the size of fish 

 examined as Ahlstrom and Ball (1954) found a 

 similar difference in gill raker number between 

 juveniles and adults of the closely related T. sym- 

 metricus. Other diagnostic features appear com- 



^Ministry of Agriculture and Fisheries, Fisheries Research 

 Centre, P.O. Box 297, Wellington, New Zealand. 



•Laurs, R. M., K. A. Bliss, andJ. A. Wetherall. 1986. Prelim- 

 inary results from IW Tmimsend Cromwell South Pacific albacore 

 research survey. Southwest Fish. Cent. La Jolla Lab., Natl. Mar. 

 Fish. Serv., NOAA, Admin. Rep LJ-86-13. 80 p. 



'Laurs, R. M.. K. Bliss, J. Wetherall, and B. Nishimoto. 1987. 

 South Pacific albacore fishery exploration conducted by U.S. jig 

 boats during early 1987. Southwest Fish. Cent. La Jolla Lab., 

 Natl. Mar. Fish. Serv., NOAA. Admin. Rep LJ-87-22, 31 p. 



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