ABSTRACT

Understanding the environmental influence on the demographic structure of a shark population within a specific ecosystem has direct implications for developing effective management and conservation measures. We studied the physical environment influence on the inter-annual demographic variation of the narrownose smooth-hound shark (Mustelus schmitti) in a key coastal ecosystem. The analyses were based on the size assemblage concept of co-occurring length classes that share common traits. We used bottom-trawl datasets (n = 334) collected over 8 spring periods (1994-2012). The analyses indicated that the population was structured in eight size assemblages that represented its main ontogenetic levels. Those corresponding to sub-adult females, young adult males, and juveniles contributed to most of the population similarity. The population structure presented high (>57.7%) inter-annual dissimilarities and showed three main similarity levels with significant differences associated with a higher abundance and similarity contribution of the main assemblages. All size assemblages were more abundant in shallow (<34.5 m), warmer (>14.9 °C), and fresher (<33.24) waters. Although the temperature variations better explained the spatial distribution of abundance, the inter-annual variation in the population similarity matched the spatial coverage of low salinities (<33.5). Overall, the environmental variation explained the variability in the abundance of size assemblages in consecutive years.

摘要

了解环境对特定生态系统中鲨鱼种群结构的影响，对制定有效的管理和保护措施具有直接的意义。我们研究了物理环境对关键沿海生态系统中窄鼻smooth鲨（Mustelus schmitti）的年际人口变化的影响。这些分析基于具有共同特征的同现长度类的大小组合概念。我们使用了底拖网数据集（n= 334）在8个春季（1994-2012）期间收集。分析表明，种群由八个大小的组合组成，代表了其主要的个体发育水平。与亚成年女性，成年男性和青少年相对应的人群为大多数人口相似性做出了贡献。种群结构表现出较高的年际差异（> 57.7％），并显示出三个主要相似度水平，其中显着差异与主要群体的较高丰度和相似度贡献相关。在浅水（<34.5 m），较温暖的水（> 14.9°C）和较新鲜的水（<33.24）中，所有大小的组合都更为丰富。尽管温度变化可以更好地解释丰度的空间分布，种群相似度的年际变化与低盐度的空间覆盖率相匹配（<33.5）。总体而言，环境变化说明了连续几年中大量尺寸组合的变化。