Table_5_Vulnerability of Demersal Fish Assemblages to Trawling Activities: A Traits-Based Index.docx

Reducing the impact on vulnerable species through changes in fishing practices, such as the spatial or temporal avoidance of certain areas, is key to increase the ecological sustainability of fisheries. However, it is often hampered by the availability of sufficiently detailed data and robust indicators. Existing trawl surveys are a cost-effective data source to assess the vulnerability of fishing areas based on the quantities of vulnerable species caught. We developed a biological traits-based approach to the vulnerability of demersal assemblages using commercial trawl catch data. An expert-based approach identified a set of biological traits that are expected to condition the species’ response to trawling impact and are combined to produce the vulnerability index ranked into four levels (low, moderate, high, and very high vulnerability). The approach was tested in four southern European fishing grounds showing evidence of over-exploitation, through catches being dominated by species of relatively low vulnerability to fishing impacts. The general distribution of species’ biomass amongst vulnerability groups was highly homogenous across case studies, despite local differences in fishing fleet structure, target species and fishing depths. Within all areas the species with moderate vulnerability dominated and, in most instances, species of “very high” vulnerability were not recorded. Nevertheless, differences emerged when comparing the proportions of highly vulnerable species in the catches. Variability in vulnerability level of the catch was also observed at small spatial scales, which was principally explained by differences in habitat type and depth and, secondarily, by fishing effort. In fine mud in the shallower areas there was a higher presence of low vulnerable fauna. Furthermore, vulnerable organisms decreased in their presence in sandier substrates on the continental shelf. The spatial heterogeneity in assemblage vulnerability composition encourages the potential for adoption of this index in the spatial management of fishing grounds aiming at ensuring a sustainable exploitation by mitigating trawl impacts on the most vulnerable components of the demersal assemblages.

通过调整捕捞作业方式（例如在空间或时间上避开特定海域）以降低对脆弱物种的负面影响，是提升渔业生态可持续性的核心举措。然而，这一目标往往因缺乏足够精细的观测数据与可靠的评估指标而难以落地。现有拖网调查（trawl surveys）是基于捕捞所得脆弱物种数量，评估捕捞区域脆弱性的低成本高效数据源。我们开发了一种基于生物学性状的评估方法，可利用商业拖网捕捞数据分析底栖生物群落（demersal assemblages）的脆弱性。该方法通过专家经验法筛选出一系列可决定物种对拖网捕捞响应的关键生物学性状，并将这些性状整合为脆弱性指数（vulnerability index），将物种脆弱性划分为四个等级：低、中、高、极高脆弱性。我们在四个受过度捕捞影响的南欧捕捞海域对该方法进行了验证，结果显示这些海域的渔获物以对捕捞影响相对低脆弱性的物种为主。尽管各研究区域在捕捞船队结构、目标捕捞物种与作业水深上存在局部差异，但各脆弱性等级下的物种生物量整体分布高度一致。所有研究区域均以中等脆弱性物种占主导，且多数区域未记录到“极高”脆弱性物种。不过，渔获物中高脆弱性物种的占比仍存在区域差异。在较小空间尺度上，渔获物的脆弱性等级分布也存在异质性，其主要影响因素为栖息地类型与水深，其次为捕捞努力量（fishing effort）。在浅水区的细泥质生境中，低脆弱性物种的占比更高；而在大陆架的沙质底质生境中，脆弱性物种的占比则有所降低。该方法所揭示的生物群落脆弱性组成的空间异质性，表明其具备应用于捕捞海域空间管理的潜力——通过减轻拖网捕捞对底栖生物群落中最脆弱组分的影响，保障渔业的可持续开发。