Cormorant (Phalacrocorax carbo) predation on a coastal perch (Perca fluviatilis) population: estimated effects based on PIT tag mark-recapture experiment

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.

Species Traits Drive Long-Term Population Trends of Common Breeding Birds in Northern Italy

“…Among the species resulting on increase, the Great Cormorant exhibited a remarkable positive trend (+12,060 %) in the last fourteen years. This finding suggest the need of further and specific investigations in order to assess in detail the absolute dimension of the population, considering the impact that the species may have on herons [ 124 ], fish species [ 125 ] and economic activities as fisheries [ 126 ]. All tits (included the Long-tail Tit), resulted significantly on increase, except the Coal Tit ( Periparus ater ) that showed a positive but non-significant trend.…”

Effects of passive integrated transponder tags on short‐term feeding patterns in European perch (Perca fluviatilis)

“…At the same time, P. fluviatilis is a highly valued target species in several European recreational and commercial fisheries ( e.g ., Haakana & Huuskonen, 2008; Skov et al ., 2017) and is commercially farmed ( e.g ., Toner, 2015). Due to its important ecological and economical role, P. fluviatilis has been studied extensively and often in combination with the use of PIT telemetry; various aspects such as growth, condition, physiology (Baras et al ., 2000; Zakęś et al ., 2017) and predation rates from aquatic birds (Skov et al ., 2014; Veneranta et al ., 2020) have been explored.…”

Habitat segregation of plate phenotypes in a rapidly expanding population of three‐spined stickleback

“…Inshore, local decreases in perch and pike populations may have increased recruitment and juvenile survival of stickleback in some areas ( € Ostman et al 2014, Bergstr€ om et al 2015, Hansson et al 2018. The local decreases in pike and perch are caused by loss or degradation of reproduction habitats due to wetland drainage, coastal constructions, and boating (Nilsson et al 2014, Sundblad and Bergstrom 2014, Hansen et al 2019) and, potentially, increased predation from seals and cormorants ( € Ostman et al 2014, Hansson et al 2018, Veneranta et al 2020. Today, there is a strong inverse relationship between local abundances of stickleback on the one hand and perch and pike on the other (Bergstr€ om et al 2015), and we have indications that in large abundances the stickleback themselves limit the perch population by consuming their eggs and larvae (Bystr€ om et al 2015, Ekl€ of et al 2020.…”