Response of cetaceans to fluctuations of pelagic fish stocks and environmental conditions within the Celtic sea ecosystem

Inshore waters of Ireland are an important foraging area for cetaceans. Some of their main preys are herring and sprat, two valuable fish species. The herring stock suffered a decline in 2013. This study investigates potential changes in the ecosystem associated to the herring decline and to determine the potential impacts on predators. Sightings information of cetaceans, acoustic data of herring and sprat, and environmental variables were analyzed. We characterized spatio-temporal patterns in the relative abundance of predator and prey species, and environmental variables, and compared periods before and after the herring decline. Since 2013, (i) the herring stock has concentrated in SE coastal waters and S offshore Irish waters, (ii) sprat density has increased, (iii) chlorophyll concentration has decreased, (iv) SST has risen, and (v) the euphotic layer has extended deeper. We modelled the effects of prey density and environment on the relative abundance and distribution of cetaceans, as well as the effects of environmental conditions on prey density. The models suggest these species have different environmental relationships. Herring tended to be found in shallower waters than sprat. The presence and relative abundance of common dolphins were significantly affected by both environmental conditions and herring density, whereas whale species presence and relative abundance were found to be correlated with SST and prey density. The results suggest differences in prey choice among whale species.

FARINAS-BERMEJO Andrea;  BERROW Simon;  GRAS Michael;  O'DONNELL Ciaran;  VALAVANIS Vasilis;  WALL Dave;  PIERCE Graham; 

2023-06-19

FRONTIERS MEDIA SA

JRC128715

2296-7745 (online),   

https://www.frontiersin.org/articles/10.3389/fmars.2023.1033758,    https://publications.jrc.ec.europa.eu/repository/handle/JRC128715,   

10.3389/fmars.2023.1033758 (online),