Towards the integration of ecophysiology with fisheries stock assessment for conservation policy and evaluating the status of the Mediterranean Sea

Abstract

Recent European Union (EU) regulations have been introduced to discourage the capture of undersized specimens with the aim of reducing the bycatch mortality imposed by commercial fisheries. We argue that we still lack accurate data regarding basic information required to properly implement these regulations for most Mediterranean ecosystems, including the true mortality imposed by fisheries, escape rates from fishing gears and the capability of specimens to survive following discard. We suggest that additional reliance on physiological biomarkers could assist in all aspects of the data collection required to support implementation of the EU discard ban (aka landing obligation), particularly in determining which species should receive special dispensation from this policy. Ideally, this new approach, here termed the ‘Fisheries Environmental and Physiological Stress Analysis’ (FEPSA), would become an important step for any fish stock assessment within the ecosystem approach to fisheries management and the recognition of Good Environmental Status, as established by the EU in the Marine Strategy Framework Directive (2008/56/EC). In particular, the main goal of FEPSA would be applying the study of physiological stressors to exploited stocks to estimate the so-called collateral fishing mortality, which includes the mortality experienced by fish that escape after interacting with fishing gears or that are discarded, with some degree of injury or physiological stress. The approach outlined here, which is described for bottom trawls but adaptable to any other type of fishing gear, is not a trivial undertaking but is a requirement for collecting the data required by recent EU fisheries policies. While we agree that the threats to marine biodiversity posed by fishing and associated discard practices require strong policy interventions, we emphasize that the research programs needed to support such initiatives, including the landing obligation, should be given equal priority. This is particularly true for Mediterranean fisheries, which are at a complex intersection of jurisdictional boundaries, numerous additional ecosystem threats including widespread pollution, thermal variation and hypoxia, and are historically understudied as compared to fisheries and species in more northern climates.

Stress related blood values in Scyliorhinus canicula as live-indicators of physiological status after bottom trawling capture activity

“…The low commercial value of dogfish compared to other demersal species it in the Mediterranean Sea (Ragonese et al, 2013) commonly results in only specimens larger than 36 cm total body length (TL) being retained for human consumption, while all specimens <36 cm TL are discarded back to the sea (Abella and Serena, 2005) because it is estimated that Scyliorhinus caniculas could reach the first maturity after that body size (Bendiab et al, 2012). Many individuals that are discarded or incidentally captured (i.e., bycatch) are either already dead, experience post-release mortality, or suffer detrimental long-term sub-lethal effects as reported by (Falco et al, 2022). Dogfish are commonly captured with bottom trawl fishing gear off the coast of Sicily (Falco et al, 2022;Peristeraki et al, 2020;Ragonese et al, 2013).…”

“…Many individuals that are discarded or incidentally captured (i.e., bycatch) are either already dead, experience post-release mortality, or suffer detrimental long-term sub-lethal effects as reported by (Falco et al, 2022). Dogfish are commonly captured with bottom trawl fishing gear off the coast of Sicily (Falco et al, 2022;Peristeraki et al, 2020;Ragonese et al, 2013). This fishing gear can subject the captured dogfish to cumulative physical trauma and physiological stress through: a) prolonged exposure (e.g., in excess of 60 mins) to compression from all the biomass accumulated in the cod end of the net with additional potential exposure to dangerous items (such as solid litter including metals); b) repeated attempts to escape through the mesh of the cod end of the net; c) marked changes to ambient temperatures, salinity and light intensity as the gear ascends from the deep waters to the surface; d) exposure on the deck of the boat to air and direct sunlight for extended periods of time; e) handling operations by the crew; f) exposure to different ambient conditions following discard back to the sea; and, finally, g) release into a new location that may not be as favorable to the dogfish as the original location of capture.…”

“…The current study quantified how capture by bottom trawl affected the physiological stress levels in dogfish using the Fisheries Environmental and Physiological Stress Analysis (FEPSA) approach (Falco et al, 2022). The FEPSA approach suggests the use of specific physiological biomarkers to estimate the health status of exploited species and infer collateral fishing mortality after specimens are caught and discarded.…”

The role of temperature in vitality and survival assessments of beam-trawled and discarded European plaice (Pleuronectes platessa)

“…Arguably, as previous research had indicated, discarding plaice that have gone through a commercial beam-trawl capture event in summer is likely to be fatal ( Uhlmann et al., 2016 , 2021 , 2023 ). Accordingly, it can be sensible to grant an actionable exemption in those seasons and regions when release survival can be maximized and routinely collect vitality-relevant parameters during at-sea monitoring campaigns ( Falco et al., 2022 ). It is likely that under current climate change scenarios, warming seawater temperatures will only further compromise the reasoning behind the existing high survival exemption for plaice.…”

Capture and discard practises associated with an ornamental fishery affect the metabolic rate and aerobic capacity of three-striped dwarf cichlids Apistogramma trifasciata

“…For commercial fisheries, individuals are commonly discarded if they are non-target species or unable to be retained due to legislation (e.g. they are of a non-legal size or are out of season ( Falco et al, 2022 )). In the case of recreational fishing, ‘catch-and-release’ angling is often performed as a conservation strategy, with the assumption that fish can generally recover and survive after being returned to their natural environment after capture ( Arlinghaus et al, 2007 ; Cooke and Schramm, 2007 ).…”