ABSTRACT: Elasmobranchs are being depleted on a global scale, caused mainly by fisheries. Demersal trawling is a component of mortality but is often not assessed. This could pose risk to benthic/demersal elasmobranchs which are often endemic and therefore vulnerable to fisheries when species ranges are within (or mainly within) trawl footprints. Northern New South Wales (NSW) is an area with endemism but also an area with fisheries such as the ocean prawn trawl (OPT) (penaeid sector). The OPT may interact with elasmobranchs, but this has never been comprehensively studied. To identify high assessment-priority species, determine spatiotemporal stratification for designing future monitoring, and to report catch rates of individuals caught during a trip (i.e. form baseline), we implemented an observer programme (2017 to 2019). To test for stratification of assemblages, we used model-based multivariate analysis. On 435 trawl trips, observers identified elasmobranchs from ~54 species, 13 orders and 34 families from variable catches. Only 2 elasmobranchs were protected in NSW, ~7% qualified for conservation listing, and ~33 and ~17% were endemic and lifeboat (listed elsewhere) species, respectively. Models suggested common elasmobranch assemblages were significantly affected by all strata (geographic zone, season and depth). Elasmobranch catch rates were low compared to other taxonomic groups (e.g. teleost fish), with 2 species captured at >10, 5 species at >2, and the remaining species <2 individuals per trip. The occurrence of endemism and spatiotemporal assemblage variation was explained by mesoscale climate transitions and oceanography. This study forms a timely baseline which can be used to assess the impact of the OPT on elasmobranchs in the future.

中文翻译：

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短期纬度监测揭示东澳大利亚底层拖网软骨鱼类兼捕特征

摘要：软骨鱼类在全球范围内正在枯竭，这主要是由渔业造成的。底层拖网捕捞是死亡率的一个组成部分，但通常没有得到评估。这可能会对底栖/底栖软骨鱼造成风险，这些软骨鱼通常是地方性的，因此当物种范围位于（或主要位于）拖网足迹内时，它们很容易受到渔业的影响。新南威尔士州北部 (NSW) 是一个特有物种区域，但也是一个渔业区域，例如大洋虾拖网 (OPT)（对虾部门）。OPT 可能与软骨鱼相互作用，但这从未得到过全面的研究。为了识别高评估优先物种，确定设计未来监测的时空分层，并报告旅行期间捕获的个体的捕获率（即形成基线），我们实施了观察员计划（2017年至2019年）。为了测试组合的分层，我们使用基于模型的多元分析。在 435 次拖网航行中，观察者从不同渔获物中识别出来自约 54 个物种、13 个目和 34 个科的软骨鱼。新南威尔士州只有 2 种软骨鱼受到保护，约 7% 符合保护名录，约 33% 和约 17% 分别是特有物种和救生艇物种（在其他地方列出）。模型表明常见的软骨鱼组合受到所有地层（地理区域、季节和深度）的显着影响。与其他分类类群（例如硬骨鱼）相比，软骨鱼类的捕获率较低，有 2 个物种捕获量 >10 只，5 个物种捕获量 >2 只，其余物种每次捕获<2 只。特有现象和时空组合变异的发生可以通过中尺度气候转变和海洋学来解释。这项研究形成了一个及时的基线，可用于评估未来OPT对软骨鱼的影响。