ABSTRACT

To discriminate potential stock units of the Atlantic horse mackerel Trachurus trachurus within the putative Moroccan–Saharan stock, we investigated the morphological variation of this species from three fishing areas (from the north to the south: Larache, Safi and Dakhla) in the Moroccan Atlantic coastal waters. We used a geometric morphometric approach based on 30 truss measures derived from 14 landmarks in 165 fish specimens. We compared fish from three areas using a multivariate analysis including discriminant analysis and Procrustes technique. We found indications of at least two subunits: a differentiated subgroup in the north off Larache, probably a self-recruiting population or a locally adapted morphotype, and two overlapped subunits, respectively in the mid and southern Moroccan Atlantic coast off Safi and Dakhla. Examination of the contribution of each morphometric variable to canonical functions indicated that differences among samples seemed to be associated with morphological changes in the anterior and posterior parts of body, which may indicate adaptations to local environmental conditions and habitat use. Further investigations using other methods are needed to confirm the identified stock units. The present study and the obtained results on such a vulnerable declining small pelagic species are of great importance for fish stock assessment management and practice, but also have ecological and evolutionary implications related to local adaptations in fish populations that are under intense fishing pressure as an induced evolutionary selective force, which affects several adaptive traits.

摘要

区分大西洋竹荚鱼Trachurus trachurus 的潜在种群单位在推定的摩洛哥-撒哈拉种群中，我们调查了该物种在摩洛哥大西洋沿海水域的三个捕鱼区（从北到南：Larache、Safi 和 Dakhla）的形态变异。我们使用了基于 30 个桁架测量的几何形态测量方法，这些测量源自 165 条鱼标本中的 14 个地标。我们使用多变量分析（包括判别分析和 Procrustes 技术）比较了来自三个区域的鱼。我们发现了至少两个亚基的迹象：拉腊什北部的一个分化亚组，可能是自我招募的种群或局部适应的形态型，以及两个重叠的亚基，分别位于萨菲和达赫拉附近的摩洛哥大西洋沿岸中部和南部。检查每个形态测量变量对规范函数的贡献表明，样本之间的差异似乎与身体前部和后部的形态变化有关，这可能表明对当地环境条件和栖息地使用的适应。需要使用其他方法进行进一步调查以确认库存批次单位。目前的研究和获得的关于这种脆弱的正在下降的小型中上层物种的结果对于鱼类种群评估管理和实践具有重要意义，但也具有与处于强烈捕捞压力下的鱼类种群的局部适应相关的生态和进化影响作为诱导进化选择力，它影响几个适应性特征。