Bottom trawl catch comparison in the Mediterranean Sea: Flexible Turtle Excluder Device (TED) vs traditional gear

Crowding in the middle of marine food webs: A focus on Raja asterias and other mediterranean batoids

The Mediterranean Sea is among the three biodiversity hotspots of the world where elasmobranchs are severely threatened. Elasmobranchs act as apex or meso-predators within marine food webs and the loss/decline of apex predators determines the mesopredator release, leading in turn to increased predation on smaller prey. However, also several mesopredators (including rays, skates and small sharks) are intensively fished, being of commercial interest, or by-caught, and thus mesopredators increase could not be so evident. We analysed the trophic ecology of an endemic Mediterranean ray, the starry ray Raja asterias, at a seasonal scale from the Adriatic basin, one of the most intensively exploited area of the Mediterranean, by means of stomach contents and stable isotopes analyses. Our results evidenced that starry rays rely on benthic sources including species of local commercial values, such as swimming crabs, small cephalopods, and stomatopods and share the same trophic position with other elasmobranchs (rays, skates, and small sharks) and other mesopredators (e.g., common soles, Norway lobsters and mullets). As all mesopredators are overexploited, as well as their benthic prey are affected by intense trawl-fishing, the whole food webs are disrupted and neither the classical trophic cascade nor the mesopredator release hypothesis could be verified. Conservation measures for these species, such as the release after capture or the application of exclusion grids to the net, should be applied in areas where populations are strongly impacted by trawling.

Analysis of risk factors associated with gas embolism and evaluation of predictors of mortality in 482 loggerhead sea turtles

Sea turtles that are entrapped in static and towed nets may develop gas embolism which can lead to severe organ injury and death. Trawling characteristics, physical and physiologic factors associated with gas-embolism and predictors of mortality were analysed from 482 bycaught loggerheads. We found 204 turtles affected by gas-embolism and significant positive correlations between the presence of gas-embolism and duration, depth, ascent rate of trawl, turtle size and temperature, and between mortality and ascent time, neurological deficits, significant acidosis and involvement of > 12 cardiovascular sites and the left atrium and sinus venosus-right atrium. About 90% turtles with GE alive upon arrival at Sea Turtle Clinic recovered from the disease without any supportive drug therapy. Results of this study may be useful in clinical evaluation, prognostication, and management for turtles affected by gas-embolism, but bycatch reduction must become a priority for major international organizations. According to the results of the present study the measures to be considered to reduce the catches or mortality of sea turtles for trawling are to be found in the modification of fishing nets or fishing operations and in greater awareness and education of fishermen.

Mismatch Between Risk and Response May Amplify Lethal and Non-lethal Effects of Humans on Wild Animal Populations

Human activity has rapidly transformed the planet, leading to declines of animal populations around the world through a range of direct and indirect pathways. Humans have strong numerical effects on wild animal populations, as highly efficient hunters and through unintentional impacts of human activity and development. Human disturbance also induces costly non-lethal effects by changing the behavior of risk-averse animals. Here, we suggest that the unique strength of these lethal and non-lethal effects is amplified by mismatches between the nature of risk associated with anthropogenic stimuli and the corresponding response by wild animals. We discuss the unique characteristics of cues associated with anthropogenic stimuli in the context of animal ecology and evolutionary history to explore why and when animals fail to appropriately (a) detect, (b) assess, and (c) respond to both benign and lethal stimuli. We then explore the costs of over-response to a benign stimulus (Type I error) and under-response to a lethal stimulus (Type II error), which can scale up to affect individual fitness and ultimately drive population dynamics and shape ecological interactions. Finally, we highlight avenues for future research and discuss conservation measures that can better align animal perception and response with risk to mitigate unintended consequences of human disturbance.