Muestreo bioestadístico de pescado en el puerto de Mar del Plata. Caballa (Scomber japonicus). Período 1986-1991.

Abstract

This paper deals with the commercial landings of Bonaerensis mackerel (Scomber japonicus) at the Port of Mar del Plata (Buenos Aires province, Argentina) during the years 1986 to 1991 and the relationship between sea temperature and depth with the presence of schools. The mean catch was about 5417.91 t per season. A total of 46 fish samples were taken for total length distributions (n=4516), and 29 sub-samples (n=1972) were analyzed to record individual data (total length and weight, sex, sexual stage, age from otoliths readings). Embryonic stage cannibalism is remarked, because egg occurrence in embryo stomachs confirms mackerel spawning at this time of the year. Ordinary length-weight relationships by fishing season were fitted, and the results were as follows: 1) 1986/87: W=8.5x 10 super(-7)x l super(3.392); 2)1987/88: W=7.6x 10 super(-6)x l super(2.972); 3)1988/89: W=6.5x 10 super(-6)x l super(3.070); 4)1989/90: W=2.3x 10 super(-7)x l super(3.640); 5)1990/91: W=1.6x 10 super(-5)x l super(3.220). The von Bertalanffy growth function in length was fitted using the methods of Walford and Gaschutz et al. The Csirke and Caddy method of estimation of mortality rates was applied to data corresponding to the 1970/71 to 1988/90 periods values of MSY=11,216 t and natural mortality rate (M)=0.51 were obtained. The estimation of M from growth parameters ranged from 0.28 to 0.51. The biomass was estimated (seasons 1986/87-1989/90) by cohort analysis with two natural mortality values (0.33 and 0.40). The yield-per recruit and optimum effort were also estimated. The lineal regression between total length/gas bladder length and potential regression between total length/gas bladder volume were calculated. The total geographical distribution in Argentina (35 degree S-45 degree S) was also analyzed and mackerels from Mar del Plata (38 degree S) area and southern Buenos Aires Province, Argentina, were compared (39 degree S). For this study meristic characters (applied variance analysis) were used. The results suggest the presence of two distinct mackerel groups. Some considerations on school displacements and acoustic blank strength are also made.