School of Natural and Environmental Sciences

Projects

Multispecies models in fisheries

Fish production in UK seas relies on complex interactions among species. Food-webs, essentially maps of what sustains each species, help us understand these and naturally-occurring stable isotopes offer valuable insights because they indicate individuals' food sources and trophic level. This project is exploring how fish species' reliance on benthic (seabed) and pelagic (water column) food-webs vary in space and time and whether this influences the resilience of their stocks to exploitation.

Food web models help describe energy fluxes and relationships between species in marine ecosystems. Such models can assess effects of fishing on ecosystems, capturing direct effects of removing target species and indirect effects on predator-prey relationships that may lead to trophic cascades. The models however rely on assumptions about prey sizes and species favoured by predators, and shifts between benthic and pelagic pathways. The environment and species composition likely affect the structure and stability of communities and fisheries yield; thus fishes  feeding across both benthic and pelagic pathways may be more resilient to perturbation.

Stable isotopes can be used to estimate carbon sources (δ13C) and trophic position (δ15N) of species, therefore quantifying the level of benthic-pelagic coupling for a range of species  and complementing diet analysis. Here combined stable isotope and diet analyses will allow: (1) hierarchical modelling to link coupling to environmental variables such as temperature, depth, mixed layer depth, seasonality and primary production; (2) assessment of coupling dynamics with body size of predators and prey using novel Bayesian mixing models which enable improved estimates of dietary proportions to be made; and (3) new applications of community and food web models to predict whether changes in coupling identified lead to systematic changes in community structure and its response to exploitation in different environments.

Email: nick.polunin@ncl.ac.uk