Spatial Heterogeneity in Fishing Creates de facto Refugia for Endangered Celtic Sea Elasmobranchs

Abstract

The life history characteristics of some elasmobranchs make them particularly vulnerable to fishing mortality; about a third of all species are listed by the IUCN as Threatened or Near Threatened. Marine Protected Areas (MPAs) have been suggested as a tool for conservation of elasmobranchs, but they are likely to be effective only if such populations respond to fishing impacts at spatial-scales corresponding to MPA size. Using the example of the Celtic Sea, we modelled elasmobranch biomass (kg h−1) in fisheries-independent survey hauls as a function of environmental variables and ‘local’ (within 20 km radius) fishing effort (h y−1) recorded from Vessel Monitoring Systems data. Model selection using AIC suggested strongest support for linear mixed effects models in which the variables (i) fishing effort, (ii) geographic location and (iii) demersal fish assemblage had approximately equal importance in explaining elasmobranch biomass. In the eastern Celtic Sea, sampling sites that occurred in the lowest 10% of the observed fishing effort range recorded 10 species of elasmobranch including the critically endangered Dipturus spp. The most intensely fished 10% of sites had only three elasmobranch species, with two IUCN listed as Least Concern. Our results suggest that stable spatial heterogeneity in fishing effort creates de facto refugia for elasmobranchs in the Celtic Sea. However, changes in the present fisheries management regime could impair the refuge effect by changing fisher's behaviour and displacing effort into these areas.

Patterns of extirpation. I. Changes in habitat use by thornback rays Raja clavata in the German Bight for 1902-1908, 1930-1932, and 1991-2009

“…1), appears likely to enable recovery. In line with modeling studies (Wiegand et al 2011), a fishing ban had a significant positive effect for thornback rays in a 500 km 2 protected area in the English Channel (Blyth-Skyrme et al 2006), and even locally reduced fishing effort may provide effective refuges for elasmobranchs (Shephard et al 2012).…”

Are guitarfishes the next sawfishes? Extinction risk and an urgent call for conservation action

“…An example is remnant populations of the skate species complex Dipturus spp. around the western British Isles, which appear to be afforded protection by seabed that is difficult to trawl (Shephard et al 2012, Neat et al 2015.…”

Advanced Spatial Modeling to Inform Management of Data-Poor Juvenile and Adult Female Rays

“…While fishing mortality is often considered to be the key driver of population change in demersal stocks [36,37], ray fishery LPUE had little influence on surveyed ray CPUE (Figure 1), suggesting environmental and teleost variables are more important drivers of their current spatial distribution. However, the LPUE dataset only overlaps 28% of the ray trawl survey data, with juvenile rays only present in 9% of those overlap-area trawls, mature females in 7%.…”

“…Alternately, commercial fishing pressure may be shared across the range of the scientific sampling data, driven by the movements of these fish. Distinctions in species diversity and individual body size have proven the existence of refugia in the Irish and Celtic Seas [36], but the fisheries-independent survey may fail to capture this for the same reasons the commercial fishery fails to capture rays in those areas: the depth is too low and/or the substrate too rocky to reliably trawl there.…”