DESCRIPTION AND SURFACE DISTRIBUTION OF JUVENILE 



PERUVIAN JACK MACKEREL, TRACHURUS MURPHYI, NICHOLS 



FROM THE SUBTROPICAL CONVERGENCE ZONE OF 



THE CENTRAL SOUTH PACIFIC 



Kevin Bailey' 



ABSTRACT 



Juvenile Peruvian jack mackerel, Trachunts murphyi. were collected with a dip net and from albacore 

 stomachs during research cruises to the Subtropical Convergence Zone of the central South Pacific 

 between January and March of 1986 and 1987. The morphometries and meristics of 40 specimens measur- 

 ing 46 to 83 mm SL are presented. The predominance of T. murphyi in the diet of albacore suggests 

 that the jack mackerel are abundant between latitudes 34°S and 41°S, longitudes 127°W and 165°W 

 during the austral summer. Evidence of the transpacific distribution of T. murphyi along the Subtropical 

 Convergence Zone is presented. 



Between January and March of 1986 and 1987, 

 research vessels of the New Zealand, United States, 

 and French Governments surveyed the Subtropical 

 Convergence Zone east of New Zealand to deter- 

 mine the extent of the albacore, Thunnus alalunga, 

 resource and its potential for exploitation by sur- 

 face trolling. Stomachs of troll caught albacore were 

 collected to investigate their feeding habits. 



A preliminary analysis of stomachs collected dur- 

 ing 1986 showed that albacore from the central 

 South Pacific fed almost exclusively on juvenile jack 

 mackerel of the genus Trachui~us. Although partial- 

 ly digested, the jack mackerel were identifiable as 

 T. murphyi Nichols from the descriptions of Berry 

 and Cohen (1974), Kotlyar (1976), and Shaboneyev 

 (1980). This identification was supported by Smith- 

 Vaniz^ and confirmed wdth live specimens caught in 

 1987. 



This paper summarizes the morphometries and 

 meristics of juvenile jack mackerel from the Sub- 

 tropical Convergence Zone of the central South 

 Pacific, and describes their surface distribution with 

 respect to predation by albacore. 



MATERIAL AND METHODS 



Jack mackerel were collected from the stomachs 



and regurgitum of albacore caught during daytime 

 surface trolling by RV Toumsend Cromwell^ (cruises 

 TC-86-01 and TC-87-01) and RV Coriolis* (cruise 

 Prosgermon87), and by dipnetting from schools of 

 jack mackerel attracted to the Toumsend CromwelFs 

 lights during the night. Stomach contents were pre- 

 served in buffered 10% formalin on Townsend Crom- 

 well and frozen on Coriolis. In the laboratory the 

 contents were sorted and counted, and their dis- 

 placement volumes measured. The least digested 

 mackerel were measured to the nearest lower mm 

 of fork length. Where possible the number of scales 

 and scutes along the lateral line and the end point 

 of the accessory lateral line were determined to 

 verify that only one species of Trachurus was pres- 

 ent (Berry and Cohen 1974). 



Live Trachurus murphyi were caught with a dip 

 net on two occasions during cruise TC-87-01. These 

 specimens were photographed and preserved in 70% 

 ethanol. On three other occasions, dipnetting was 

 unsuccessful. 



Forty jack mackerel (46-83 mm SL) were exam- 

 ined in detail, 1 collected in 1986 and 39 in 1987 

 (Table 1). Five specimens are catalogued in the Na- 

 tional Museum of New Zealand, Wellington (NMNZ 

 21410) and four in the Academy of Natural Sciences, 

 Philadelphia (ANSP 158517). 



'Ministry of Agriculture and Fisheries. Fisheries Research 

 Centre. P.O. Box 297. Wellington, New Zealand; present address: 

 South Pacific Commission. Tuna and Billfish Assessment Pro- 

 gramme, B.P. D5, Noumea Cedex, New Caledonia. 



^W. Smith-Vaniz, Academy of Natural Sciences, Philadelphia, 

 PA 19103, pers. commun. August 1986. 



Manuscript accepted January 1989. 

 Fishery Bulletin. U.S. 87;273-278. 



'U.S. Department of Commerce, National Oceanic and Atmos- 

 pheric Administration, National Ocean Service, Pacific Marine 

 Center, 1801 Fairview Avenue East, Seattle, WA 98102-3767, 

 U.S.A. 



^Groupement pour La Gestion de Navires Oceanologiques, B.P. 

 310, 29273 Brest, CEDEX, France. 



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