Pike (Esox lucius) constitute an important target species in recreational fisheries across their distributional range and belong to the top three target species of anglers in Germany. Anglers and fishers impact on the abundance of target species, usually reducing biomass and leading to size and age truncation through mortality. Additionally, in angling with artificial lures hook avoidance learning and selection may lead to angling-induced timidity effects, where the reactivity of surviving pike to future capture is reduced. In the present study, catch per unit effort as a measure of abundance as revealed by different gear types were compared between three marine protected areas (MPA) and nearby open access areas (OA) in lagoons of the southern Baltic Sea in Germany. Additionally, pike behavior towards lures was examined using the MPA vs. OA contrast as a natural experiment in differential exposure to past fishing pressure. It was hypothesized that fisheries mortality leads to higher abundances and larger sizes of pike inside MPAs and that timidity is present in exploited parts of the population and manifests in differential angling vulnerability of individuals between MPA and OA sites. In support of the first and second hypothesis, it was found that inside MPAs pike were more abundant and the share of large fish was higher relative to OA sites in two areas. Supporting the third hypothesis, pike inside MPAs exhibited increased levels of aggression towards artificial lures. Moreover, it was found that the fish vulnerable to angling in OA sites encompassed the faster growing phenotypes, suggesting the potential for selection. Comparison of relative abundances between MPAs and OAs assessed by angling and non-angling gears could not quantify the absolute effect of timidity on catch rates, either due to a small effect size or because sampling gear biases prevented an unpolluted measure of true relative abundance differences among sites. In light of the collective evidence in this thesis, it is concluded that differences in pike angling catch rates among MPA and OA sites were mainly driven by the abundance-increasing impact of pike protection in MPAs, with angling-induced timidity having second-order effect. The presented evidence shows that pike in the coastal areas of the German Baltic coast exhibit angling-induced timidity and that pike removals reduce abundance and catch rates. The possible angling-selection on faster-growing pike may reduce the growth potential of the evolving stock in the future. Controls on total fisheries mortality, commercial and recreational, is needed to protect pike abundances and high catch rates. Rotating spatial closures may be one underutilized option that might protect both pike and pike catch rates to anglers, but in order to reap the benefits access to temporarily opened sites must also be allowed to anglers and not just fishers.
Examining Evidence for Angling-Induced Timidity in Northern Pike (Esox lucius L.): A Case Study from Lagoons in the Southern Baltic Sea
Projekt Boddenhecht , Master
Roser, P. 2023. Examining Evidence for Angling-Induced Timidity in Northern Pike (Esox lucius L.): A Case Study from Lagoons in the Southern Baltic Sea. Master-Thesis, Humboldt-Universität zu Berlin, Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB) Berlin.
Erschienen in : Master-Thesis, Humboldt-Universität zu Berlin, Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB) Berlin