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Fishery Bulletin 91(4), 1993 



estimates of von Bertalanffy (VB) growth parameters, 

 are important because they are necessary elements 

 in the population dynamic models used in stock 

 assessment. 



We used three independent data sets to estimate 

 albacore growth rates: length-frequencies, vertebral- 

 ring-counts, and tag release-recapture statistics. Esti- 

 mates of VB growth parameters were derived from the 

 length-frequency and vertebral-ring-count data. In both 

 cases, we assumed that the length-frequency modes 

 represent year classes and the vertebral-rings repre- 

 sent annual features. This assumption was tested 

 by using the length increment data from the tag 

 returns. 



Materials and methods 



Collection of length-frequencies 



Length-frequency data were collected by observers from 

 seasonal surface fishery catches between December 

 1986 and May 1991. All albacore measured were caught 

 by troll vessels on the principal fishing grounds for 

 juvenile albacore, namely the Tasman Sea, along the 

 central east coast of New Zealand, and near the Sub- 

 tropical Convergence Zone (STCZ), mainly within the 

 area bounded by 35-42°S and 130-170°W (Fig. 1). 

 Throughout each fishing season (typically extending 

 from December to April), observers sampled as many 

 albacore as possible from the daily catches. Albacore 



were selected at random (i.e., unsystematically), placed 

 on a graduated board, and measured from the tip of 

 the snout (with the mouth closed) to the end of the 

 median caudal ray. These fork-length measurements 

 were rounded down to the nearest centimeter and re- 

 corded with the sampling date and fishing location. 

 Tagged albacore were measured in an identical fash- 

 ion and were combined with the length-frequency 

 samples when it was appropriate. 



Most of the length-frequency sampling occurred dur- 

 ing 1988-1991 in the STCZ, where catch rates and 

 fishing activity were greatest (Labelle, 1993a). In this 

 region, over 100,000 albacore were measured; suffi- 

 cient numbers were obtained to stratify samples by 

 month for December-April each season. The number 

 of measurements per month ranged from 351 to 18,908. 

 These data were compiled into length-frequency histo- 

 grams (Fig. 2), from which VB growth parameters were 

 estimated by using the MULTIFAN computer program 

 (Fournieretal., 1990). 



Vertebra collection and processing 



Caudal vertebrae were collected during the austral 

 summers of 1986 and 1987 from albacore caught by 

 research vessels trolling in the STCZ, the Tasman Sea, 

 and over the Chatham Rise east of New Zealand 

 (Fig. 1). Vertebrae were also collected during the aus- 

 tral winters of 1987, 1988, and 1989 from albacore 

 caught by Japanese longline vessels fishing off the 

 north east coast of New Zealand near East Cape 



140E 



1 50E 



1 60E 



170E 



180W 



1 70W 



60W 



50W 



1 40W 



1 30W 



1 20W 



New Caledonia 



TASMAN 

 SEA 



140E 



150E 



1 60E 



170E 



180W 



1 70W 



1 60W 



1 50W 



40W 



1 30W 



1 20W 



Figure 1 



Sampling locations for the collection of length-frequency measurements and vertebrae. Region A covers the main troll fishing grounds 

 centered over the STCZ. Region B delineates the longline fishing area adjacent to East Cape. Region C delineates the Chatham Ridge 

 area where troll fishing occurs. 



