APPARENT GROWTH OF YELLOWFIN TUNA FROM THE 



EASTERN ATLANTIC OCEAN 



J. C. Le Guen'-^ and Gary T. Sakagawa'-' 



ABSTRACT 



Apparent growth of yellowfin tuna from the eastern Atlantic Ocean was estimated from 

 modal progression of length-frequency distributions by two methods. One was to use 

 fish of unknown age, which gave estimates of parameters of the von Bertalanffy growth 

 function of L „ ^ 194.8 cm and A' ^ 0.035, on a monthly basis. The other was 

 to u.se fish of apparent known age, which resulted in L^ = 175.2 cm and K = 0.044. 

 Although the parameter estimates were different, estimates of length at ages 1.5-4.5 

 years were quite similar with both approaches. 



A comparison of growth estimates of yellowfin tuna was made. Estimates from anal- 

 ysis of length-frequency distributions appeared to be superior to those from analysis 

 of scales because they were based on a larger range of fish sizes. However, observed 

 lengths at ages 1.5-5 years were similar for both types of analysis and for yellowfin tuna 

 from both the Atlantic and Pacific Oceans. 



It is recommended that observed sizes at age rather than the estimated sizes at age 

 from the von Bertalanff"y function be used in estimating yield per recruitment of yellowfin 

 tuna. 



There have been several studies (e.g., Le Guen, 

 Baudin-Laurencin, and Champagnat, 1969; 

 Yang, Nose, and Hiyama, 1969) on growth of 

 Atlantic yellowfin tuna (Thunmis albacares) but 

 little agreement among them. The disagreement 

 can be traced to at least three sources: first, 

 the kinds of data, e.g., length-frequency distri- 

 butions and scale readings have been different; 

 second, the method of fitting the von Bertalanffy 

 growth function has varied; and third, the range 

 of fish sizes employed has been different. Be- 

 cause an accurate estimate of growth is impor- 

 tant for estimating yield per recruitment by the 

 Beverton and Holt approach (Schaefer and 

 Beverton, 1963), one method that can provide 

 information for rational management of the re- 

 source, a study was initiated to estimate growth 

 from the best series of data available and, hope- 

 fully, to resolve the disagreement. In this report 



^ Alphabetical authorship since the paper is based on 

 independent studies of both authors. 



- Office de la Recherche Scientifique et Technique 

 Outre-Mer, Centre de Pointe-Noire, P.O. Box 1286, 

 Pointe-Noire, Republic of Congo. 



^ Southwest Fisheries Center, National Marine Fish- 

 eries Service, NOAA, La JoUa, CA 92037. 



Manuscript accepted May 1972. 



FISHERY BULLETIN: VOL. 71, NO. 1, 1973. 



the results of that study on apparent growth of 

 yellowfin tuna from modal progression of length- 

 frequency distributions are presented and com- 

 pared to growth estimates derived from pub- 

 lished data and computed by standardized pro- 

 cedures. 



PLAN OF ANALYSIS 



Length frequency samples from commercial 

 landings were employed in our study (Table 1). 

 The fish were caught off Africa by baitboats and 

 purse seiners and were sampled by French and 

 Inter-American Tropical Tuna Commission 

 (lATTC) scientists. (Scientists of the lATTC 

 sampled the Atlantic tuna catch of U.S. vessels 

 under a contract from the National Marine Fish- 

 eries Service.) The French scientists sampled 

 the French catches, which were from three gen- 

 eral regions — Abidjan, Ivory Coast; Dakar, 

 Senegal; and Pointe-Noire, Congo — and the 

 lATTC scientists sampled the American catches, 

 which were from primarily the Gulf of Guinea. 

 The lATTC samples were caught in both the 

 Abidjan and Pointe-Noire regions, but because 



175 



