Following the population increase in continental cormorants throughout the Europe, numbers of wintering birds in Slovenia also increase. This increase has caused concern among both commercial ...fishermen and anglers. In this paper we provide general data about cormorants in Slovenia with special emphasis on fishponds Race and the Drava river. In general numbers of cormorants during winter in Slovenia in period 1994-1999 increase (r = 0.86, P 0.05, n 0.05, n = 6) and on the rivers Sava and Krka (rs = 0.46, P 0.05, n = 6). Moreover, on fishponds Race number of cormorants between 1983-1999 increased but not significantly (rs = 0.43, P 0.05, n = 17). For fishponds Race we also calculate how many fishes were eaten by cormorants for particular year and months. Using the bird numbers of each year and month and an individual daily food ration of 560g/day (taken into account also fishes which were injured by Cormorants), the total fish consumption was estimated. The results are presented in Tables 1 and 2. During last six years on the Drava river in average about 1125 cormorants are present during the winter, which means about 7.8 cormorants/km. However we must take into account that cormorants from the Drava river are present also on tributaries. Taking into account all suitable waters along the Drava river (more then 2350ha) this mean less then one cormorants/2ha. According to ringing recoveries cormorants wintering in Slovenia mainly come from Baltic region (e.g. Denmark, Poland and Sweden).
Waterfowl are vectors of nutrients, metals, and other pollutants (i.e. PCBs and microorganisms) on wetlands and other water bodies, especially when bird population density is high, e.g., in nesting, ...roosting or breeding periods. This work reports the effects caused by the increase in breeding pairs of herons and cormorants between 2010 and 2014 on sediments in an eutrophic Mediterranean wetland belonging to La Mancha Húmeda Biosphere Reserve. Nutrients, metals, metalloids, and isotopic composition (δ15N and δ13C) were analysed in sediments and faeces at several points in the Tablas de Daimiel National Park (TDNP), as well as in the nearby Navaseca wetland, which receives inputs from a wastewater treatment plant (WWTP). Sediments from Navaseca and from one site that is affected by heron colonies (Garcera) in the TDNP showed higher concentrations of organic matter, total organic carbon, total nitrogen, total phosphorus, Al, Co, Cu, Cr, Fe, Ni and Zn than the rest of the sampling sites. Significant correlations between these variables were found, probably suggesting that they have a common organic source. The highest δ15N values in sediments of the TDNP were registered in Guadiana, a site where there is no impact from colonies; these values might therefore be due to anthropogenic activities. Metal and metalloid content in sediments was lower than the regional reference values in soils, except for Se in the TDNP, and Zn and Cu in Navaseca. High Se level in TDNP sediment may be caused by seleniferous soils located upstream. Results showed a low impact of bird droppings compared to other sources of nutrients in the annual input in the TDNP.
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•Heronry and WWTP pond sediments showed the highest levels of N, P and organic C.•Heronry sediment showed the highest levels of Al, Co, Cu, Cr, Fe, Ni and Zn in TDNP.•The highest δ15N was found in a non-bird-affected site, but by human inputs.•Se levels in heronry sediment exceeded baseline soil concentration for the region.•N and P inputs from faeces were negligible compared to river and runoff inputs.
Double‐crested cormorant Phalacrocorox auritus Lesson (cormorant) populations have increased throughout the Great Lakes region of North America causing concern related to the impact of cormorant ...predation on fish communities. A recent decline in yellow perch Perca flavescens (Mitchill) abundance within the Lake Winnebago System, Wisconsin, USA, prompted an assessment of cormorant diets to evaluate potential effects of cormorant predation on the sportfish community. Diets were collected from 883 cormorants (417 from Lake Winnebago and 466 from Lake Butte des Morts) between 2015 and 2017. Cormorant diets on both waterbodies consisted mostly of freshwater drum Aplodinotus grunniens Rafinesque and gizzard shad Dorosoma cepedianum (Lesueur). Yellow perch and walleye Sander vitreus (Mitchill) observations were infrequent and represented < 5% of cormorant diets by weight each year. Under current conditions, cormorant predation likely has minimal impact on the Lake Winnebago sportfish community, but more research is needed to assess potential impacts on Lake Butte des Morts.
Concentrations of perfluorooctane sulfonate (PFOS) in San Francisco Bay (SF Bay) wildlife have historically been among the highest reported globally. To track continuing exposures to PFASs and assess ...the impact of the 2002 phase-out of production of PFOS and related chemicals in the US, nine perfluoroalkyl carboxylic acids (PFCAs; C4-C12), three perfluoroalkyl sulfonic acids (PFSAs; C4, C6, C8) and perfluorooctane sulfonamide (PFOSA, a PFOS precursor) were measured in SF Bay cormorant eggs in 2012 and harbor seal serum sampled between 2009 and 2014. PFOS remained the dominant perfluoroalkyl acid (PFAA) in both cormorant eggs (36.1–466 ng/g) and seals (12.6–796 ng/g) from 2012 and 2014, respectively. Concentrations in seal and bird eggs from the South Bay have declined approximately 70% in both matrices. To elucidate potential pathways of exposure, prey fish, sediments and wastewater effluent were analyzed for PFASs, and in the case of sediment and effluent, a suite of PFAA precursors. PFOS was the dominant PFAA in prey fish and sediment. In effluent, different mixtures of PFAAs were measured, with PFOS, PFHxA, and PFOA detected in the highest concentrations. Polyfluoroalkyl phosphate diesters (PFCA-precursors) were observed at concentrations over an order of magnitude higher than PFCAs in sediment, highlighting their importance as a potential, on-going source of PFCAs to SF Bay wildlife. These findings suggest that the PFOS phase-out has resulted in reduced burdens to wildlife in SF Bay, but that exposure to diverse and incompletely characterized PFASs continues.
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•Concentrations of PFOS in San Francisco Bay cormorant and seals are some of the highest concentrations observed worldwide.•PFOS remains the dominant PFAS detected in biota.•PFOS concentrations have declined in birds and seals in the most recent sampling event.•Some of the precursors detected in sediment and effluent were higher than PFOS.•The source of these chemicals to the foodweb remains to be elucidated.
Cormorant fishing is a traditional Japanese fishing method using captive Japanese cormorants (Phalacrocorax capillatus). Between June and July 2017, an avian pox outbreak was reported in captive ...cormorant populations throughout several distant cities in Japan. We examined the lesions obtained from two such affected cormorants, which were raised in distant cities. The affected cormorants were grossly characterized by the development of cutaneous nodules around the base of the beak. Histopathologically, these nodules consisted of marked epidermal hyperplasia with ballooning degeneration of spinous cells and eosinophilic intracytoplasmic inclusions (Bollinger bodies). The lesions displayed 4b core protein (P4b) of Avipoxvirus (APV) and DNA polymerase genes, which were detected by PCR. Moreover, the nucleotide sequences detected from both cormorants were found to be identical. No identical sequence was found in any international database. These findings suggest that both examined cormorants were infected with an identical APV, which has never been previously reported. According to the phylogenetic analysis, the detected sequences were observed to cluster in subclade A3, which consists mainly of the sequences detected from several marine birds, including other cormorant species. This observation suggests that the viruses might be maintained in Japanese cormorants in nature.
Fish stock assessment may be constrained by incomplete knowledge on all mortality sources. Seal and cormorant raiding fishing gear to access the catch has been asserted by fishers to be a ...considerable problem in the small-scale European eel fishery along the Swedish Baltic Sea coast. We analysed logbook data and found predator losses in fisheries at 13.6 ± 12.6% among catches landed in 16 Swedish harbours in subdivisions 25, 27 and 29 of the Baltic Sea in 2019–2021. These numbers were used to assess the total predator damage along this coast at 12 ± 10 tonnes of caught eel at a landings value (about 10% of the retail value) of 105,000 ± 97,000 euros in 2020. This may constrain prospects of the declining commercial small-scale coastal eel fishery. Moreover, this quantitative estimate may be useful in future assessments of the local stock component, with potentially important implications for ecological, economic and social sustainability.
•European eel is fished along the Swedish Baltic Sea coast.•This fishery is affected by depredation.•Predators damaged 12 ± 10 tonnes of eel in 2020.•The landings value of this damage was 105,000 ± 97,000 euros.•The retail value of the damage was approximately 10 times as high.
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.
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