The current study examined the effect of environmental, operational, temporal and catch-related variables on the discard quantities of four species subject to the EU landing obligation (, European hake, HKE; , deep-water rose shrimp, DPS; , red mullet, MUT; , horse mackerel, HOM) caught in Italian and Greek bottom trawl fisheries. Generalized Additive Models were applied to discards per unit of effort of each species in seven study areas distributed over different sub-divisions of the Mediterranean Sea (Western Mediterranean: (i) Ligurian Sea and Northern Tyrrhenian Sea, (ii) Southern and Central Tyrrhenian Sea; Central Mediterranean: (iii) Southern Adriatic Sea, (iv) Western Ionian Sea; Eastern Mediterranean: (v) Eastern Ionian Sea, (vi) Central and South Aegean Sea, (vii) Crete) and were able to explain 21–96% of the deviance. Geographic coordinates and depth were included as significant covariates in the majority of the final models, showing that discards are affected by bathymetric preferences of the species and sizes, local patterns in productivity and/or possible existence of nursery grounds. Discard rates were higher at the shelf break for HKE and DPS, slightly shallower for HOM, while MUT discards occurred mainly in waters <100 m depth. Positive relationships between discards and volume of catches and negative ones between discards and the mean length (especially for HKE) highlighted the effect of the catch characteristics as well as fishers’ discarding behaviour. Interannual effects seemed to be related to trends in species abundance and recruitment success, while seasonal patterns were usually linked to the recruitment period and/or seasonal fishing intensity. The length of the vessel, vessel age and haul duration were significant in few cases, but there were no common patterns across all regions/species. Overall, the results showed that discarding in Mediterranean bottom trawl fisheries is affected by a large number of variables that should be taken into account for a more effective mitigation of unwanted catches.

中文翻译：

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影响地中海底拖网渔业丢弃物变异性的因素

目前的研究考察了环境、操作、时间和捕捞相关变量对受欧盟登陆义务约束的四种物种丢弃量的影响（欧洲无须鳕，HKE；深水玫瑰虾，DPS；红鲻鱼， MUT；竹荚鱼，HOM）在意大利和希腊底拖网渔业中捕获。广义加性模型应用于分布在地中海不同分区的七个研究区域中每个物种每单位努力的丢弃量（西地中海：（i）利古里亚海和北第勒尼安海，（ii）南第勒尼安海和中第勒尼安海; 中地中海：(iii) 南亚得里亚海，(iv) 西爱奥尼亚海；(v) 东爱奥尼亚海，(vii) 中爱琴海，(vii) 克里特岛）并能够解释 21-96偏差的百分比。地理坐标和深度被作为大多数最终模型中的重要协变量，表明丢弃物受到物种和大小的测深偏好、当地生产力模式和/或可能存在的苗圃地的影响。 HKE 和 DPS 在陆架断裂处的丢弃率较高，HOM 的丢弃率稍浅，而 MUT 的丢弃主要发生在深度 <100 m 的水域。丢弃物与渔获量之间的正相关关系以及丢弃物与平均长度之间的负相关关系（尤其是 HKE）突出了渔获量特征以及渔民丢弃行为的影响。年际效应似乎与物种丰富度和补充成功的趋势有关，而季节性模式通常与补充期和/或季节性捕捞强度有关。在少数情况下，船舶长度、船龄和运输持续时间很重要，但所有地区/物种之间没有共同的模式。总体而言，结果表明地中海底拖网渔业的丢弃行为受到大量变量的影响，为了更有效地减少不需要的渔获量，应考虑这些变量。