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

Optimizing the prediction of discard survival of bottom-trawled plaice based on vitality indicators

Predicting the discard survival of aquatic animals after fisheries capture using vitality indicators (i.e. individual scores or indices of physical condition) is a resource-efficient approach compared to estimating discard survival from captive observation. But such indicators do not always lead to accurate and robust predictions. Individual scores of reflex impairments and injuries are typically given the same weight when being aggregated into an index, while some reflexes or injuries may contribute to mortality more than others. This study established an analytical methodology and created an index based on differential contributions of individual reflexes and injuries to optimize the prediction of discard survival of bottom-trawled European plaice (Pleuronectes platessa). The optimization procedures were applied to a dataset from vitality assessment of 1122 undersized plaice caught during 16 commercial fishing trips and 58 gear deployments in Belgium and Denmark. As welfare indicators, we considered and evaluated against post-capture survival of plaice: original vs. optimized reflex impairment and injury (R&I) index, number of absent reflexes, number of present injuries, number of absent reflexes and present injuries, categorical vitality score and individual reflex and injury scores. These were used in eight candidate generalized linear models (one without any vitality indicator) as explanatory variables to predict survival, with or without biological, environmental, technical and operational covariates, either at the individual fish or trip level. Bruising to the head and body were the most relevant predictors. The optimized R&I index did not perform better than any other vitality indicator, and all the indicators performed poorly in predicting survival probability both at the fish and trip levels without information on air exposure and seawater temperature. This means that they cannot be considered to be independent measures. The categorical vitality score provided a viable alternative to the more labour-intensive, scoring method of reflex responsiveness. Use of reflexes as proxies may not be accurate when they are not independent of environmental, biological or technical variables.

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

Thermal stress can influence the recovery of fish released after capture. Vitality assessments using reflex and behavioural responses require that responses can be observed reliably, independent of temperature. Here, we tested whether reflex and behavioural impairment and survival of beam-trawled and discarded European plaice (Pleuronectes platessa) are independent from seasonal air and water temperature deviations. In total, 324 beam-trawled plaice (n = 196 in summer and n = 128 in winter) were exposed to two air temperature treatments and two water treatments (i.e. modified and ambient temperatures for both). The modified treatments (i.e. cooled in summer, warmed in winter) represent the thermal shock a fish may experience when being returned to the water. All reflexes and tested behaviours were affected by ambient temperature, with high impairment noted in summer. None of the reflexes were affected by temperature shocks alone, only body flex was. Body flex was highly impaired under every exposure combination. Fish size and duration of air exposure further influenced impairment of reflexes such as head complex and tail grab. More generally, post-release survival was assessed as 21% [95% CI: 16-28%] in summer and 99% [97-100%] in winter. Beam trawling in summer is likely to induce high reflex impairment and mortality in discarded plaice, and therefore spatial-temporal mitigation approaches should be prioritized over control of on-board temperatures.

Using vitality indicators to predict survival of aquatic animals released from fisheries

Estimating the survival probability of animals released from fisheries can improve the overall understanding of animal biology with implications for fisheries management, conservation and animal welfare. Vitality indicators are simple visual measures of animal condition that change in response to stressors (like fisheries capture) and can be assessed to predict post-release survival. These indicators typically include immediate reflex responses which are typically combined into a score. Vitality indicators are straight-forward and non-invasive metrics that allow users to quantify how close (or far) an animal is from a normal, 'healthy' or baseline state, which in turn can be correlated with outcomes such as survival probability, given appropriate calibration. The literature on using vitality indicators to predict post-release survival of animals has grown rapidly over the past decade. We identified 136 papers that used vitality indicators in a fisheries context. These studies were primarily focused on marine and freshwater fishes, with a few examples using herptiles and crustaceans. The types of vitality indicators are diverse and sometimes taxa-specific (e.g. pinching leg of turtles, spraying water at nictitating membrane of sharks) with the most commonly used indicators being those that assess escape response or righting response given the vulnerability of animals when those reflexes are impaired. By presenting Pacific salmon fisheries as a case study, we propose a framework for using vitality indicators to predict survival across taxa and fisheries.

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

Fishing causes direct removal of individuals from wild populations but can also cause a physiological disturbance in fish that are released or discarded after capture. While sublethal physiological effects of fish capture have been well studied in commercial and recreational fisheries, this issue has been overlooked for the ornamental fish trade, where it is common to capture fish from the wild and discard non-target species. We examined metabolic responses to capture and discard procedures in the three-striped dwarf cichlid Apistogramma trifasciata, a popular Amazonian aquarium species that nonetheless may be discarded when not a target species. Individuals (n = 34) were tagged and exposed to each of four treatments designed to simulate procedures during the capture and discard process: 1) a non-handling control; 2) netting; 3) netting +30 seconds of air exposure; and 4) netting +60 seconds of air exposure. Metabolic rates were estimated using intermittent-flow respirometry, immediately following each treatment then throughout recovery overnight. Increasing amounts of netting and air exposure caused an acute increase in oxygen uptake and decrease in available aerobic scope. In general, recovery occurred quickly, with rapid decreases in oxygen uptake within the first 30 minutes post-handling. Notably, however, male fish exposed to netting +60 seconds of air exposure showed a delayed response whereby available aerobic scope was constrained <75% of maximum until ~4-6 hours post-stress. Larger fish showed a greater initial increase in oxygen uptake post-stress and slower rates of recovery. The results suggest that in the period following discard, this species may experience a reduced aerobic capacity for additional behavioural/physiological responses including feeding, territory defence and predator avoidance. These results are among the first to examine impacts of discard practises in the ornamental fishery and suggest ecophysiological research can provide valuable insight towards increasing sustainable practises in this global trade.

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

The quantification of capture-related physiological stress is an important factor when assessing the potential for post-release survival in sharks that are incidentally captured. In the absence of these biological data and when the post-release fate is unknown, effective management plans cannot be formulated and may lead to highly susceptible shark populations being overfished. Here, we measured the levels of lactate, glucose, alanine amino transferase (ALT), aspartate amino transferase (AST), Ca2+, Na+ K+,Cl - Mg 2+ and Pi in the plasma of mature and immature lesser spotted dogfish (Scyliorhinus canicula, herein dogfish) which were incidentally captured at two depths (shallow: 50-200 m, and deep: 201-500 m) by bottom trawl off the coast of southern Sicily. These values were used as biomarkers and physiological indicators of the secondary stress response associated with capture. This study found that dogfish captured in deeper waters (below 200 m) had elevated levels of glucose, Na+, Ca2+ and K+ compared to those inhabiting depths less than <200 m. We hypothesize that the elevated levels of physiological stress in dogfish captured at greater depths may be related to the prolonged duration of the interactions with the fishing gear in the area off southern Sicily. Our findings provide new data on the capture-related stress in dogfish and increase the understanding of the potential for post-release survival in sharks captured at two depths by bottom trawl, information that is important for improving the general management plans for the fishery. However, our PC Analysis results revealed that Maturity have a positive contribution from the sample weight, sample length, ALT, AST and a negative contribution from Pi.

Investigating the effects of microplastic ingestion in Scyliorhinus canicula from the South of Sicily

Plastic pollution is increasing dramatically worldwide, causing adverse effects on a wide variety of marine organisms at all trophic levels. As predators, sharks play a key role in marine ecosystems and they could especially be threatened by the ingestion of microplastics. This study contributes to expand the existing data on the MPs ingestion by a Mediterranean elasmobranch species, Scyliorhinus canicula, adding new information on the potential impact that this class of contaminants can have on the metabolism of this ecologically relevant species. The present research is aimed: i) to assess if the ingestion of MPs in S. canicula is related to sex, size and depth of catch; ii) to evaluate the effect of MPs on fish body condition; iii) to evaluate if the ingested MPs influence the amino acid and fatty acid composition of eye and liver. A total of 61 specimens of S. canicula were analysed. Forty-nine individuals (80.3 %) had ingested plastic items. Totally, 147 plastic elements were found, mainly belonging to small MPs (49 %), and large MPs (46 %), mostly represented by fibers (84 %). The predominant colour was black. No differences were found between sex and size. A difference in the number of items/specimens related to the deep, highest between 50 and 100 m (4.4), while the lowest between 101 and 500 m (2.1) was found. The condition factor (Kn) value was equal to 1.00 highlighting the wellness of the fish. Arginine (20.1 %), Glutamate (17.4), Phenylalanine (15.7 %), Proline (15.6 %) and were the most abundant amino acids in the eyes of S. canicula. The relative fatty acid composition of the livers was dominated by fatty acids SA (30.2 %) (SFA), CA (29.9 %) (SFA) and OA (22.4 %) (MUFA). This paper reports a study on the relationship between amino acids and fatty acids composition and ingested MPs, highlighting that no significant effects were found.