Abstract

The number of cormorants has rapidly increased in the northernmost Baltic Sea. In 2018, 50 km × 50 km ICES catch rectangle 55H1 had 3140 breeding pairs. To estimate the predation effect of cormorants on perch populations, we Passive Integrated Tags tagged 1977 perch and 9.9% of tags were found. The median instantaneous cormorant-induced mortality during the breeding time, with consumption by non-breeding individuals, was estimated at 0.23 and at 0.35 during the whole residing period. We estimated with a yeild-per-recruit model that the long-term maximum loss of perch yield of tagged sub-population would be at 80% probability interval 32–67%, and when extended to the entire 55H1, 10–33%, respectively. The cormorants’ share of the >2-year-old perch biomass and production would be 8%, while that of other natural mortality would be 63% and that of fishing 29% in 55H1. The yield-per-recruit-results should be interpreted as an estimate of maximum cormorant effect because the dependence of predation rate on prey density was not accounted for, and density-dependence of growth, mortality, and reproduction of perch could partly compensate the loss. The results indicate that high density of cormorants can reduce the perch stocks and catches locally.

中文翻译：

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在沿海鲈鱼（Perca fluviatilis）种群上的（Ph）捕食：基于PIT标签标记捕获实验的估计效果

摘要

在最北端的波罗的海，of的数量迅速增加。2018年，50 km×50 km ICES捕捉矩形55H1拥有3140个繁殖对。为了评估of对鲈鱼种群的捕食效果，我们对1977鲈鱼进行了标签的被动集成标签，发现了9.9％的标签。在繁殖期间，由非繁殖个体消耗的瞬时cor诱导的平均死亡率估计为0.23，而整个居留期间为0.35。我们使用每招募率模型估计，标记亚种群的鲈鱼产量的长期最大损失将以80％的概率区间32–67％传播，而当扩展到整个55H1时，则为10–33％，分别。2-在2岁以上的鲈鱼生物量和产量中所占的份额为8％，而在55H1中，其他自然死亡率的比率为63％，而渔业为29％。每招募产量应解释为对最大cor效应的估计，因为没有考虑捕食率对猎物密度的依赖性，而密度对生长，死亡率和鲈鱼繁殖的依赖性可以部分弥补损失。结果表明，高密度的can可以减少鲈鱼种群和局部捕获。