1. This study evaluated the circle hook use as a tool for shark management in the pelagic longline fishery in the Gulf of Gabès.
2. The usual J‐hook No. 2 with 10° offset, which has been traditionally used by the fishery, was compared to the 18/0 non‐offset circle hook in an alternating fashion along the main line. In total, 22 experimental longline sets were deployed through the shark fishing seasons of 2016 and 2017 to examine the effects of hook types on the catch composition, the catch rates, the hooking location, and the status at haulback.
3. The catch composition differed significantly among hook types. Moreover, an overall increase in catch rates for the main species, the sandbar shark Carcharhinus plumbeus , and the shortfin mako shark Isurus oxyrinchus , was observed when using circle hooks.
4. There was no size‐selective effect of circle hooks for the common species. The circle hooks were not effective at reducing at‐haulback mortality of sandbar shark. Conversely, shortfin mako and smooth‐hound shark Mustelus mustelus showed significantly lower relative mortality at haulback with circle hooks than with J‐hooks. Furthermore, circle hooks were more frequently hooked externally than the J‐hooks for the three shark species.
5. Results demonstrated that the use of 18/0 non‐offset circle hooks in the pelagic shark longline fishery can reduce mortality at haulback for some species without any benefit for the dominant species, the sandbar shark.
6. Overall, it is difficult to promote the adoption of the use of circle hooks as a management measure in this specialized fishery. Management measures focusing on fishing effort controls, fishing closures in critical habitats, and size limits could have significant benefits for the conservation of shark species and may help to improve the sustainability of the shark fishery in the Gulf of Gabès.

中文翻译：

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圆钩在加贝斯湾中上层鲨鱼延绳钓渔业中是否有效的管理措施？

1. 这项研究评估了圆形钩在加贝斯湾中上层延绳钓渔业中作为鲨鱼管理工具的用途。
2. 渔业传统上使用的通常具有10°偏移量的J型弯钩2号，沿着主线以交替的方式与18/0非偏置圆钩相比较。在2016年和2017年的鲨鱼捕捞季节中，总共部署了22个实验性延绳钓套装，以研究钩子类型对渔获物组成，渔获率，钩住位置和回捕状况的影响。
3. 钩子类型的鱼钩组成差异很大。此外，使用圆钩时，观察到主要物种沙洲鲨Carcharhinus plumbeus和短鳍fin鲨Isurus oxyrinchus的捕捞率总体增加。
4. 对于普通种类，没有圆钩的尺寸选择作用。圆钩在降低沙洲鲨的回生死亡率方面无效。相反，与J钩相比，带圈钩的短鳍鲨和顺滑鲨鼬Mustelus mustelus的相对死亡率要低得多。此外，与三种鲨鱼的J钩相比，圆形钩在外部钩的频率更高。
5. 结果表明，在远洋鲨鱼延绳钓渔业中使用18/0非偏心圆钩可以降低某些物种回捕时的死亡率，而对优势物种沙洲鲨没有任何好处。
6. 总体而言，在这种专门渔业中，很难促进采用圆钩作为管理手段。侧重于捕捞努力控制，关键栖息地的捕捞封闭和规模限制的管理措施可能对鲨鱼物种的保护具有重大益处，并可能有助于提高加贝斯湾鲨鱼渔业的可持续性。