Does the closed fishing season influence the ichthyofauna consumed by Larus dominicanus?

Abstract Fish that are incidentally caught by shrimp trawling represent a predictable and abundant resource for feeding several bird species, especially for the gull Larus dominicanus. This fishing activity is subject to disruptions throughout the year during closed fishing seasons, when other fishing modalities are exercised, which can alter the composition, abundance and size of the fish bycatch. This study evaluated the influence of the restriction of fishing period of shrimp (closed season) on the diet of L. dominicanus, on the Paraná State coast. From December 2013 to August 2014, 10 pellets were collected per month in two distinct areas that have shrimp trawl fishery as the main economic activity: one continental and another in an estuarine island. In total, 920 fish were identified, divided into four families and 15 species, especially the family Sciaenidae with 11 species. There were differences in abundance and biomass of species between areas and between seasons of pre-closure, closure and post-closure. Differences for the mean total length of the species were only detected between the pre-closed and closed seasons in one area. This study evidenced the strong relationship between L. dominicanus and the shrimp trawl fishery, the species composition identified in the pellets and their respective morphometric measurements follow the same pattern of the literature for fish discarded in trawling activities.

摘要 虾拖网作业兼捕所得的鱼类，是多种鸟类（尤其是南美鸥（Larus dominicanus））可稳定获取的充足食物资源。该拖网作业在全年禁渔期会受到作业干扰，此时会开展其他类型的捕捞活动，这可能改变兼捕渔获物的组成、丰度与体型大小。本研究于巴西巴拉那州沿岸海域，评估了虾类捕捞禁渔期对南美鸥食性的影响。2013年12月至2014年8月期间，研究人员在两个以虾拖网捕捞为核心经济产业的区域每月收集10份鸥类食团：一处为大陆沿岸区域，另一处为河口岛屿区域。本次研究共鉴定出920尾鱼类，隶属于4科15种，其中石首鱼科（Sciaenidae）包含11种。不同区域以及禁渔前、禁渔期、禁渔后三个时段的鱼类丰度与生物量均存在显著差异。仅在其中一个区域的禁渔前与禁渔期时段，鱼类的平均总长度存在显著差异。本研究证实了南美鸥与虾拖网捕捞之间存在紧密的生态关联；食团中鉴定出的鱼类组成及其对应的形态测量数据，与拖网作业中被丢弃的兼捕鱼群的文献记录模式一致。