SPATIAL ECOLOGY AND FISHERIES INTERACTIONS OF RAJIDAE IN THE UK

Abstract

The spatial occurrence of a species is a fundamental part of its ecology, playing a role in shaping the evolution of its life history, driving population level processes and species interactions. Within this spatial occurrence, species may show a tendency to occupy areas with particular abiotic or biotic factors, known as a habitat association. In addition some species have the capacity to select preferred habitat at a particular time and, when species are sympatric, resource partitioning can allow their coexistence and reduce competition among them.
The Rajidae (skate) are cryptic benthic mesopredators, which bury in the sediment for extended periods of time with some species inhabiting turbid coastal waters in higher latitudes. Consequently, identifying skate fine-scale spatial ecology is challenging and has lacked detailed study, despite them being commercially important species in the UK, as well as being at risk of population decline due to overfishing. This research aimed to examine the fine-scale spatial occurrence, habitat selection and resource partitioning among the four skates across a coastal area off Plymouth, UK, in the western English Channel. In addition, I investigated the interaction of Rajidae with commercial fisheries to determine if interactions between species were different and whether existing management measures are effective. First using a combination of research surveys, conventional and electronic tagging I investigate the fine-scale spatial ecology of four sympatric skates. Second I use stable isotope analysis of Rajidae eye lenses to provide an insight into juvenile feeding and spatial ecology. Finally this research used commercial landings data and conventional tagging to investigate fisheries interactions and current management efficacy.
Results show that Rajidae were not randomly distributed at fine-scales within the coastal zone but instead associated with particular locations and depths. In addition, only one of the four species inhabited both marine and brackish habitats. I present evidence demonstrating inter- and intra-species groups partitioned by both habitat and diet along with evidence for active habitat selection. Habitat partitioning between these four species influenced their interaction with commercial fisheries and the degree of protection offered by existing Marine Protected Areas (MPAs). I also demonstrate that legislation specifically designed to protect skates may not be effectively enforced and indicate where further investigation will be required to ensure that the conservation of skates is realised.

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ORCID for David Sims: orcid.org/0000-0002-0916-7363

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