Crescimento e mortalidade da pescada-gó Macrodon anacylodon (Bloch & Schneider, 1801) capturada na região norte

Abstract

The pescada-gó, Macrodon ancylodon occurs in shallow continental shelf, stands out as a fishing resource of great importance for coastal fisheries in Brazil. Throvgh the importance of the species in the economic scenario of the region, it is necessary to understand its biology. Thus the objective is to study the growth and mortality of the species in northern Brazil. During the period from 1997 to 2008 were recorded measurements of total length from the fleet of fishing craft and landed in the industrial districts of Bragança, Vigia, Curuçá, São João de Pirabas and Belém. Data were grouped into length class of 0,5 em and then calculated the measures of central tendency and dispersion, besides the caleulation of the percentage of yuong and adults. The mean lengths Wwere compared using the Student t test with significance level of 5%. The asymptotic maximum growith (L ∞) and growth rate (K) were estimated in the program FISAT, which used the methods of Bhattacharya and Gulland and Holt to decompose the cohorts and to estimate L ∞ and K respectively. Natural mortality (M) was estimated by Pauly and Rickter and Efanov the fishing mortality (F) was obtained by the difference between Z (total) and M, Z was obtained by the equation of Beverton and Holt and the exploitation rate (E) by dividing F by Z. The total sample consisted of 61.120 individuals. Measures of central tendency and dispersion presented for the months and years of different fleets and gear pattern with high amplitudes and variances and a low standard deviation and error except for a few months whose variances were low due to the high number of individuals in classes of smaller lengths. The highest concentration of young people occurred in the period from April to October, a period of lower rainfall with concentration in the sharp catch in fishing fixed traps "currais". The average lengths of the specimens captured in artisanal and industrial statistical differences for the mean length over the years, gillnet fishery and fleets. The annual average length has decreased in recent years ago for pescada-gó caught in north coast. O Leo was estimated to be 55,25 em, K equal 0,45 year" parameter and inítial condition (t₀) of - 0,267. O M was calculated at 0,88 ⁻¹ year and 0,97 ⁻¹ year by Pauly and Rickter and Efanov respectively. Z = 2,39 ⁻¹ year and F = 1,42 ⁻¹ year 39; E = 1,00. Thus it is concluded that the fishing fixed traps; currais; and fishing capture more young individuals than the other giilnet fisheries. The pescada-gó has a high growth rate and asymptotic length low and high natural mortality characterizing the species as strategist r. The pescada-gó fishery is overfished, because the rate of exploitation is greater than 0,5 and the average annual length are decrcasing.