Age structure and growth of the rough scad, Trachurus lathami (Teleostei: Carangidae), in the Southeastern Brazilian Bight

Lygia C Ruas,André M Vaz-Dos-Santos

doi:10.3897/zoologia.34.e20475

Abstract

ABSTRACT The rough scad, Trachurus lathami Nichols, 1920, is a small pelagic species distributed along the West Atlantic coast. It is most abundant in the Southern Brazil (28°30’-34°S) and in the Southeastern Brazilian Bight (SEBB, 22°-28°30’S). The rough scad is fished by purse seines, which main target is the Brazilian sardine, Sardinella brasiliensis (Steindachner, 1879). Age and growth are vital to understand the life cycle of a species, to fishery management and ecosystem modeling. This study aimed to assess the age and growth of T. lathami, to identify its age structure in the SEBB, and to evaluate what causes the wide differences among Trachurus species in terms of body size and growth parameters. Data available on T. lathami was attained between 2008 and 2010 from surveys at SEBB. A total of 278 whole otoliths of T. lathami, total length between 27 mm and 208 mm, were analyzed and compared with the only other source of otolith data, from 1975. Three blind readings were performed and assessed using traditional methods to study fish age and growth. Zero up to eight rings were found, each ring corresponding to one year in the life of an individual of this species. The von Bertalanffy growth model parameters were L∞ = 211.90 mm and K = 0.319 year-1. The results of the analyses have shown similarities between 1975 and 2008-2010, indicating that the otolith development, the growth pattern and the age structure remained stable. T. lathami is the smallest species of Trachurus and it has the highest growth rates among them. This is probably related to the different temperatures where larvae/juvenile and adult grow, to the absence of a strong fishing pressure and to decadal population variability.

Highlights

In the Atlantic Ocean, the rough scad, Trachurus lathami Nichols, 1920, is a pelagic species distributed between the United States and North of Argentina, mainly on the continental shelf
In the SEBB, rough scad landings varied a lot until the end of the 1990’s (Valentini and Pezzutto 2006), a period when this fish was caught in association with the Brazilian sardine (S. brasiliensis) (Fig. 1)
They originate from the only biological data available for this species in the Southwestern Atlantic (Cergole and Dias Neto 2011), and represent the population and the sampling adequately, due to the total length range analyzed

Summary

Introduction

In the Atlantic Ocean, the rough scad, Trachurus lathami Nichols, 1920, is a pelagic species distributed between the United States and North of Argentina, mainly on the continental shelf. In Brazil, their largest concentrations have been recorded both in the Southeastern Brazilian Bight (SEBB, between 22° and 28°30’S) and in the Southern region (between 28°30’ and 34°S) (Saccardo and Haimovici 2007) In these areas, the rough scad is an important fishery resource in purse seines, along with other important pelagic species such as the Sardinella brasiliensis (Steindachner, 1879) and Opisthonema oglinum (Lesueur, 1818) (Saccardo and Haimovici 2007, UNIVALI 2011). Between 2005 and 2008, rough scad landings were around 700 t/year, with a later reduction to an average of 88 t (2009–2010)

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