Evaluating the effectiveness of management measures on skates in a changing world

Abstract

Evaluating the effectiveness of management measures on skates in a changing world ABSTRACT Global declines in elasmobranchs have been observed. Conservation measures such as area closures and fisheries prohibitions have been put in place to support the recovery of vulnerable species. However, the effectiveness of such measures is rarely evaluated in the context of other factors that may affect population abundance. This study investigates the effectiveness of management measures using 1) General additive mixed model derivative changes, taking into account environmental factors that may affect population stochasticity and 2) an age-structured density dependent population dynamic model. The Raja undulata (undulate ray) 2009 targeted fisheries prohibition was used as a case study.Potential beneficial responses on sympatric species Raja clavata (thornback ray) were modelled.A significant increase in abundance was observed in both IUCN red list species during the ban. Surface seawater temperature had a marginal effect on the abundance of both species. The prohibition was in place for an insufficient length of time for long lasting effects to be detected on skate length. The population dynamic model indicated that the increase in abundance was only possible when combining the fisheries ban with increased juvenile discard survival. Our results indicate that species conservation measures may not only have positive effects on the species in question, but also on species with a niche overlap. Nonetheless, due to ongoing fishing for other species, the full potential of fisheries prohibitions may not be realised. For real benefits to be assessed, evaluation of bans should take place once a steady state is observed.

Strongly structured populations and reproductive habitat fragmentation increase the vulnerability of the Mediterranean starry rayRaja asterias(Elasmobranchii, Rajidae)

“…The overall decline of elasmobranch species at the global level has led to the growing and necessary consideration of the degree of fragmentation of populations in relation to their vulnerability to human activities (e.g. climate change effects, overfishing, bycatch and their relative downstream threats; Ferretti et al, 2005; Elliott et al, 2020). To date, mitigation measures, such as the designation of marine protected areas or shark sanctuaries and fishing effort changes, have been adopted at different geographical scales to help allow the recovery and/or protection of local populations of vulnerable species (Baum et al, 2003; Shephard et al, 2012; Ward‐Paige et al, 2012).…”

Modelling the distribution of rare and data-poor diadromous fish at sea for protected area management

“…Gear type detectability Even though little bycatch was observed, given a number of the diadromous fish studied here are threatened, even a small amount of bycatch may impact their populations (Dulvy et al, 2003). Furthermore, misreporting and illegal fishing is likely to remain (Elliott et al, 2020a;ICES, 2005;Stratoudakis et al, 2020;Worm et al, 2013). Bycatch detectability results from our models could help provide management advice so that gear types and areas with higher bycatch rate be avoided.…”

Spatio‐temporal dynamics of the common skate species complex: Evidence of increasing abundance

“…Landing prohibitions have been utilized elsewhere and appear effective in promoting the revival of skate populations. For example, a 2009 fisheries ban for undulate ray led to increases in the target species (Elliott et al, 2020). Moreover, the barndoor skate ( Dipturus laevis ), a large species closely related to the blue skate (Bache‐Jeffreys et al, 2021) occurring in the Northwest Atlantic, underwent large declines between the early 1960s and mid‐1970s due to high levels of fishing mortality (Gedamke et al, 2008; Kulka et al, 2020).…”

“…The action was implemented as a conservation measure to prevent further depletion and fragmentation of populations. Elsewhere, landing prohibitions have proven successful; off the coast of France, the undulate ray ( Raja undulata ) benefited with an increase in abundance when a fishery ban was introduced in 2009 (Elliott et al, 2020). Landings of “skates and rays” in the Celtic Seas ecoregion (around Ireland and the UK) have also been declining since the early 2000s, partly due to a Total Allowable Catch (TAC) being established in 2009, which has ranged between 8032 and 15,748 t since its introduction (ICES, 2021).…”