AUTHOR=Fariñas-Bermejo Andrea , Berrow Simon , Gras Michaël , O’Donnell Ciaran , Valavanis Vasilis , Wall Dave , Pierce Graham J. 

TITLE=Response of cetaceans to fluctuations of pelagic fish stocks and environmental conditions within the Celtic Sea ecosystem

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 10 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1033758

DOI=10.3389/fmars.2023.1033758

ISSN=2296-7745

ABSTRACT=Inshore waters off the south coast of Ireland are an important foraging area for a range of cetacean species. Herring and sprat are economically valuable species as well as being the main prey for baleen whales and part of the diet of common dolphins in this area. The Celtic Sea herring stock suffered a marked decline in 2013. The present study aimed to address concerns raised about ecosystem changes associated to the decline and its potential impacts on predators. Here we analyzed sightings information of common dolphins, fin, minke, humpback and unidentified whale species, acoustic data of herring and sprat, and a range of environmental variables mainly derived from satellites. Firstly, we characterized spatio-temporal patterns in the relative abundance of predator and prey species, and environmental variables, and compared periods before and since the herring decline. Secondly, we modelled the effects of prey density and environmental conditions on the relative abundance and distribution of cetaceans, as well as the effects of environmental conditions on prey density, between 2005-2018 by applying Hurdle Generalized Additive Models. Since the 2013 herring decline, (i) the herring stock has mainly concentrated in south-eastern coastal waters and southern offshore Irish waters, (ii) sprat density has increased, (iii) chlorophyll concentration has decreased, (iv) sea surface temperature has risen, and (v) the euphotic layer has extended deeper. The models for herring and sprat support the idea that these species have different environmental relationships. The presence and relative abundance of common dolphins were affected by both environmental conditions and herring density. Whale species presence and relative abundance were found to be correlated with sea surface temperature and prey density. The model results suggest differences in prey choice among whale species. Understanding the dynamic relationships between predators, prey and the environment is important to inform an ecosystem-based approach to fisheries management.