A1 Journal article (refereed)
Invasive catfish in northern Italy and their impacts on waterbirds (2022)

Milardi, M., Green, A. J., Mancini, M., Trotti, P., Kiljunen, M., Torniainen, J., & Castaldelli, G. (2022). Invasive catfish in northern Italy and their impacts on waterbirds. NeoBiota, 72, 109-128. https://doi.org/10.3897/neobiota.72.80500

JYU authors or editors

Publication details

All authors or editors: Milardi, Marco; Green, Andy J.; Mancini, Marco; Trotti, Paolo; Kiljunen, Mikko; Torniainen, Jyrki; Castaldelli, Giuseppe

Journal or series: NeoBiota

eISSN: 1314-2488

Publication year: 2022

Publication date: 25/03/2022

Volume: 72

Pages range: 109-128

Publisher: Pensoft Publishers

Publication country: Bulgaria

Publication language: English

DOI: https://doi.org/10.3897/neobiota.72.80500

Publication open access: Openly available

Publication channel open access: Open Access channel

Publication is parallel published (JYX): https://jyx.jyu.fi/handle/123456789/80528

Abstract

Predatory fish have occasionally been observed preying on birds, sometimes repeatedly, but few studies were able to unravel the overall significance of avian prey in fish diet and the predation impacts on bird populations. We used a control/impact study setup, using a Nature Reserve in northern Italy and a nearby control area, to determine: 1) the contribution of waterbirds to wels catfish diet in the Reserve, 2) the population density of wels catfish in the Reserve and control area and 3) the potential impacts of waterbird depredation by wels catfish on waterbird population trends. Our stable isotope Bayesian mixing model indicated that birds contributed 12.2% (5–27.9%, 50% confidence interval) of the diet of large wels catfish (> 98 cm in total length). Large individuals constituted the majority of the population in the shoreline areas of the reserve in 2013–2019, where the population was stable despite control efforts. Numbers were below detectable levels in the control area. Large wels catfish consumed an average of 224, 148 and 187 kg of birds during the 2019 chick growing period, as estimated through three different bioenergetic models. Compared to the control area, mallard reproductive success was diminished in the Reserve, likely due to higher rates of fish predation, although effects were variable in different years. Overall, our data suggest that high densities of invasive wels catfish might impact waterbird reproductive success through predation on bird chicks, but further studies would be needed to reduce uncertainties related to the intrinsic variability of field ecology data. Our study constitutes a preliminary attempt to assess the potential of introduced wels catfish to affect the conservation value of waterbird protection areas, and should be repeated at broader spatial and temporal scales.

Keywords: birds; water birds; protected areas; nature reserves; fishes; predatory fishes; Silurus glanis; catfishes; diets; nutrition; predation; biological effects; bird populations; populations

Free keywords: predation; pulsed resources; Silurus glanis; stable isotopes; waterbirds; wels catfish

Contributing organizations

Ministry reporting: Yes

Reporting Year: 2022

JUFO rating: 1