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

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.

摘要 粗鳞竹荚鱼（rough scad，Trachurus lathami Nichols, 1920）是分布于西大西洋沿岸的小型中上层鱼类。其种群丰度在巴西南部海域（28°30’-34°S）及巴西东南部海盆（Southeastern Brazilian Bight, SEBB, 22°-28°30’S）最高。该鱼种的捕捞作业以围网（purse seines）为主，围网的核心捕捞目标为巴西沙丁鱼（Sardinella brasiliensis (Steindachner, 1879)）。年龄与生长特征是解析物种生命周期、开展渔业管理及构建生态系统模型的核心基础。本研究旨在评估拉氏真鲹的年龄与生长特征，明确其在巴西东南部海盆的年龄结构，并探究导致竹荚鱼属（Trachurus）物种间体型与生长参数存在显著差异的成因。本研究所用的拉氏真鲹样本数据采集于2008至2010年间巴西东南部海盆的渔业调查。研究共分析了278枚完整耳石（otoliths），对应样本的总长度范围为27 mm至208 mm，并将分析结果与1975年的唯一现存耳石数据集进行对比。本研究采用传统鱼类年龄与生长研究方法开展了3次盲法读数，并进行一致性评估。结果显示，耳石上存在0至8个年轮，每个年轮对应该物种个体1年的生命周期。本研究拟合得到的冯·贝塔朗菲（von Bertalanffy）生长模型参数为：渐近体长L∞=211.90 mm，生长系数K=0.319 年⁻¹。分析结果显示，1975年与2008-2010年的样本数据具有相似性，表明拉氏真鲹的耳石发育、生长模式及年龄结构未发生显著变化。拉氏真鲹是竹荚鱼属中体型最小的物种，同时也是该属中生长速率最快的物种。这一特征可能与幼体/稚体及成体所处的生长水温差异、未承受高强度捕捞压力以及种群的年代际变异性相关。