Muestreo a bordo de barcos mexicanos para estimar la estructura poblacional del atún aleta amarilla (Thunnus albacaares) del Pacífico Oriental

Abstract

A stratified three-stage sampling design is proposed to obtain furcal length (FL) of yellowfin tuna (Thunnus albacares) on board of Mexican purse-seine vessels in the eastern Pacific Ocean. The strata correspond to the administration regions proposed by the Interamerican Tropical Tuna Commission (IATTC) and are combined with three different sets: dolphin sets (DS), school sets (SS) and log sets (LS). In the first stage, it is obtained a random sample of the trips, over annual period. The second units (fishery sets, in each trip) are through a systematic sampling. Finally, a random sample of yellow fin tunas (third stage) is obtained in each set. This samplig design (SD) allows to estimate the average weight, total number of fishes and total number of fish by length class in the catch. The SD and their estimators were applied to the FL sample in 1997 at sea. It was observed that the average weight of the fishes in DS and SS was significantly larger than in LS (P<0.05), whereas the number of fishes by ton was higher in this last. Moreover, the size structure of fishes in DS and SS tends to values close to 100 cm, whereas in the LS the central values were about 50 cm. These are similar to those obtained by others SD in ports (Tomlinson et al., 1992). However, this SD has the advantage of including information from the bycatch and it of covering a grater zone also.