The role of fisheries and the environment in driving the decline of elasmobranchs in the northern Adriatic Sea

Abstract

Elasmobranch populations are declining worldwide, calling for urgent assessment of fishery exploitation and application of effective conservation strategies. Here, we applied a novel approach, integrating long-term time-series of landings (1945–2012) and extensive surveys at the fish market of Chioggia, Italy, home of the major fishing fleet of the northern Adriatic Sea, to evaluate the status of elasmobranch populations and fisheries in the one of the most fished Mediterranean basins. The time-series highlight a dramatic decline in elasmobranch landings, particularly for skates and catsharks (Scyliorhinus spp.), whose current catch rates are 2.4 and 10.6% of the average 1940s levels, respectively. These data likely reflect similar large reductions in abundance, as indicated by the analysis of catch-per unit-effort time-series. The biomass of landed skates and catsharks showed regular fluctuations that disappeared after the collapse of the landings. Elasmobranch market composition, assessed through the sampling of 11 900 specimens from 2006 to 2013, included 14 species, but was dominated by just two: Mustelus mustelus and M. punctulatus, which represented more than 60% of the catch. The proportion of sexually immature individuals was generally very high, up to 83% of landed females and 71% of landed males, depending on the species. Although some correlations were detected between landings and local hydrography or climatic indices, the analyses of landings and surveys at the fish market identified fishery exploitation as the main driver of the striking, long-term elasmobranch decline in the northern Adriatic Sea, calling for urgent management actions to improve the conservation status of these fish.

Community–environment interactions explain octopus-catshark spatial overlap

“…These patterns in the community indicators agree with the high fishing pressure observed nearby the Ebro river mouth (Coll et al, 2012;Navarro et al, 2015Navarro et al, , 2016. Due to the long-living strategy, elasmobranchs are very sensitive to long-term disturbances such as fishing pressure since populations present low resilience and recovery Barausse et al, 2014;Navarro et al, 2015Navarro et al, , 2016Quetglas et al, 2016). In accordance with previous research Navarro et al, 2015Navarro et al, , 2016, these results point the high fishing pressure of this area as responsible for the decline of elasmobranch Figure 3.…”

Higher temperatures increase developmental rate & reduce body size at hatching in the small‐eyed skate Raja microocellata: implications for exploitation of an elasmobranch in warming seas

“…Although over‐exploitation is well recognized as being the most likely cause of population reduction of elasmobranchs globally (Dulvy et al, ; Stevens et al, ; Worm et al, ), additive or synergistic factors such as increasing sea temperatures may also influence abundance of these long‐lived, slow‐to‐reproduce fishes (Barausse et al, ). Large‐scale movements of elasmobranch populations throughout their life‐cycle are often correlated with temperature ( i.e ., thermotaxis; Di Santo & Bennett, ; Economakis & Lobel, ; Hight & Lowe, ; Hunter et al, ; Matern et al, ; Vaudo & Lowe, ; Wallman & Bennett, ), which is not unsurprising given the influence of temperature on many biological processes in fishes (Magnuson et al, ; Magnuson & Destasio, ).…”

Large marine protected areas (LMPAs) in the Mediterranean Sea: The opportunity of the Adriatic Sea

“…Along the western (Italian) Adriatic coasts, fishing effort has historically been greater whereas along the eastern (Croatian) side, fisheries have developed more slowly and in a less industrialized fashion. As an effect of this historical fishing pressure, in the last 60 years catch rates and landings of elasmobranchs have declined by 494% and 80-89% respectively in the central and northern Adriatic Sea [23,108]. However, these declines were not homogeneous throughout the basin.…”