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We develop the age-structured fishery model by including endogenous harvesting selectivity and stochastic recruitment, as a growing body of fishery ecological evidence suggests these factors to be critical for fisheries management. Optimal harvesting selectivity aims to direct fishing towards age classes that are preferable to catch given information on fish growth, natural mortality, and recruitment in addition to implications on harvesting cost. We analytically show that maximum sustainable yield (MSY) leads to potentially serious and previously unrecognized deviation from economic optimality, as it neglects the dependence of harvesting costs on gear selectivity. We further show that the steady-state population level may fall below the MSY population even with zero discounting and stock-dependent harvesting costs. We quantify our results using empirical data for Baltic cod. Applying the age-structured model with endogenous harvesting selectivity, we find large differences between maximum sustainable yield and the economic optimum, although the classic biomass model suggests that these differences should be unimportant. Stochastic recruitment implies a threefold increase in young age classes, but the stochastic solution can be accurately approximated by the certainty equivalence principle.

International audience; Climate change is rapidly modifying marine fish assemblages in the Arctic. As fish eggs and larvae have a narrower thermal tolerance than nonreproductive adults, their response to increasing temperatures is likely one of the main drivers of these changes. In this study, we described ichthyoplankton assemblages in West Greenland between 62 and 73 °N, during summers 2017–2019, and investigated the relationship between sea surface temperature in the spring and summer and the survival of Arctic cod (Boreogadus saida (Lepechin, 1774)) early life stages over the hatching season. Warm years were associated with partial recruitment failures resulting from thermal stress to the eggs and larvae hatched late in the season. Using past environmental conditions, we forecasted an imminent decline in Arctic cod recruitment in the regions of Uummannaq and Disko Bay. Observations from fjords suggested that glacial meltwater could create a subsurface thermal refuge allowing Arctic cod larvae to survive despite very high summer sea surface temperature (ca. 10 °C). As the Greenland ice sheet is melting at an unprecedented speed, the mechanism underlying the “glacial meltwater summer refuge hypothesis” could curb some of the negative effects of ocean warming on the survival of young Arctic cod in West Greenland and other Arctic fjord systems.

Place: Hoboken Publisher: Wiley WOS:000531167600001; Many deep-water fish populations, being K-selected species, have little resilience to overexploitation and may be at serious risk of depletion as a consequence. Sea warming represents an additional threat. In this study, the condition, or health, of several populations of common ling (Molva molva), blue ling (Molva dypterygia) and Mediterranean or Spanish ling (Molva macrophthalma) inhabiting different areas in the North Atlantic and the Mediterranean was evaluated, to shed light on the challenges these deep-water species are facing in the context of fishing activity and a warming climate. The data on the condition of Molva populations which are analysed here have been complemented with data on abundance and, for the southernmost species (Mediterranean ling), with two other health indicators (parasitism and hepato-somatic index). Despite some exceptions (e.g., common ling in Icelandic waters), this study shows that the condition of many populations of Molva species in the northeastern Atlantic and the Mediterranean Sea has worsened, a trend which, in recent decades, has usually been found to be accompanied by a decline in their abundance. In addition, the poor health status of most populations of common ling, blue ling and Mediterranean ling considered in this analysis points to a lower sustainability of these populations in the future. Overall, the health status and abundance of Molva populations in the northeastern Atlantic and the Mediterranean suggest that only some populations located in the North Atlantic may be able to rebuild, whereas the populations in southern North Atlantic and the Mediterranean, which are probably most at risk from sea warming, are facing serious difficulties in doing so. In the context of fisheries and global warming, this study's results strongly indicate that management bodies need to consider the health status of many of the populations of Molva species, particularly in southern European waters, before implementing their decisions.

An experiment was conducted to assess the selectivity in a typical Mediterranean bottom trawl, equipped with a square-mesh panel inserted in front of the cod end, for Atlantic horse mackerel (Trachurus trachurus), European hake (Merluccius merluccius), red mullet (Mullus barbatus), poor cod (Trisopterus minutus), broadtail shortfin squid (Illex coindetii), and deep-water rose shrimp (Parapaeneus longirostris). The release efficiency of undersized individuals through the panel was low. The differences in selectivity between the gear with and without the panel were very small. The low release efficiency of the square-mesh panel was caused by the lack of fish contact with the panel as they drifted towards the cod end, since the average contact probability was estimated not to exceed 9% for any of the species investigated. A low probability of contact with the selection device was thus found to be the reason for the low efficiency of the square-mesh panel.

The importance of survival and growth variations early in life for population dynamics depends on the degrees of compensatory density dependence and size dependence in survival at later life stages. Quantifying density- and size-dependent mortality at different juvenile stages is therefore important to understand and potentially predict the recruitment to the population. We applied a statistical state-space modelling approach to analyse time series of abundance and mean body size of larval and juvenile fish. The focus was to identify the importance of abundance and body size for growth and survival through successive larval and juvenile age intervals, and to quantify how the dynamics propagate through the early life to influence recruitment. We thus identified both relevant ages and mechanisms (i.e. density dependence and size dependence in survival and growth) linking recruitment variability to early life dynamics. The analysis was conducted on six economically and ecologically important fish populations from cold temperate and sub-arctic marine ecosystems. Our results underscore the importance of size for survival early in life. The comparative analysis suggests that size-dependent mortality and density-dependent growth frequently occur at a transition from pelagic to demersal habitats, which may be linked to competition for suitable habitat. The generality of this hypothesis warrants testing in future research.

This paper examines variations in gender-specific body growth, morphology and reproduction of the bearded goby (Sufflogobius bibarbatus) across the Namibian shelf, built on previous work on male reproductive modes. The results indicate a spatial variation in the size composition, condition factor and maturation of gobies across the shelf area. Low oxygen (

Catecholamines protect the fish heart during hypoxia. However, the humoral adrenergic stress response may only be invoked in extremis. We investigated the hypothesis that endogenous (e.g., neuronal) myocardial catecholamines may also impact cardiac performance during hypoxia in a hypoxia-tolerant tropical fish, the red-bellied piranha (Pygocentrus nattereri). First, we measured endogenous tissue catecholamines and in vitro catecholamine release from piranha myocardium using ultraperformance liquid chromatography. Ventricle homogenates contained detectable levels of both adrenaline (7.27 ng/g) and noradrenaline (14.48 ng/g), but only noradrenaline was released from ventricular tissue incubated in Ringer’s solution. Noradrenaline released in this assay was not affected by hypoxia but was promoted by the catecholamine releasing agent tyramine. Our second series of experiments explored cardiac contractile performance in vitro using tyramine, exogenous noradrenaline or adrenaline, and propranolol (a β-adrenoceptor antagonist). In ventricular strip preparations, β-adrenergic blockade with propranolol had no effects on twitch force or contraction kinetics in either normoxia or hypoxia, confirming that spontaneous endogenous catecholamine release did not impact cardiac performance. However, in the absence of propranolol, tyramine mimicked the positive inotropic effect of noradrenaline (10 µM) during hypoxia, although adrenaline was capable of generating larger effects. Our results suggest that, although it is not spontaneously released, inducible endogenous noradrenaline release may have a significant β-adrenoceptor-dependent impact on hypoxic performance in the fish heart.

Vertical migration is the most widespread migration in the aquatic world, yet the mechanisms limiting the extent of this behavior are largely unknown. In the Baltic Sea, some Atlantic cod Gadus morhua perform vertical foraging migrations into severely hypoxic demersal zones where aerobic metabolism is insufficient to cover energy requirements. After foraging, the fish return to better oxygenated waters for physiological recovery and digestion. To test the influence of phenotypic variation in aerobic scope (AS; the difference between the maximum and the minimum metabolic rate) on the capacity to migrate into severely hypoxic zones, we incorporated AS into a state-dependent individual-based model simulating vertical foraging migrations of G. morhua. We found little effect of individual variation in AS on the capacity for vertical migration when the zone used for physiological recovery was normoxic. In contrast, when there was moderate hypoxia (30% air saturation, O-2sat) in the zone used for physiological recovery, the high AS phenotype had a clear advantage because it could forage 3-4 times longer in the severely hypoxic (16% O-2sat, i.e. below the threshold for aerobic metabolism of the species) demersal zone compared to the low AS phenotype. Thus, phenotypic variation in AS is only important when there is moderate hypoxia in the zone used for physiological recovery, suggesting that the influence of AS variation on the capacity for vertical migration is context dependent. We propose that elevated AS may be evolutionarily favorable when hypoxia prevails in the water column.

Harvest control rules (HCRs) have been implemented for many fisheries worldwide. However, in most instances, those HCRs are not based on the explicit feedbacks between stock properties and economic considerations. This paper develops a bio-economic model that evaluates the HCR adopted in 2004 by the Joint Norwegian–Russian Fishery Commission to manage the world's largest cod stock, Northeast Arctic cod (NEA). The model considered here is biologically and economically detailed, and is the first to compare the performance of the stock's current HCR with that of alternative HCRs derived with optimality criteria. In particular, HCRs are optimized for economic objectives including fleet profits, economic welfare, and total yield and the emerging properties are analyzed. The performance of these optimal HCRs was compared with the currently used HCR. This paper show that the current HCR does in fact comes very close to maximizing profits. Furthermore, the results reveal that the HCR that maximizes profits is the most precautionary one among the considered HCRs. Finally, the HCR that maximizes yield leads to un-precautionary low levels of biomass. In these ways, the implementation of the HCR for NEA cod can be viewed as a success story that may provide valuable lessons for other fisheries., Highlights ► We examine harvest control rules (HCRs) for Northeast Arctic cod, the world's largest cod stock. ► The bio-economic model is detailed and estimated with long-term data. ► The currently used HCR is compared with alternatives optimizing profit, welfare or yield. ► The currently used HCR comes very close to the one that maximizes profits. ► Maximizing yield leads to un-precautionary low levels of biomass.

Link to publishers version: 10.1371/journal.pone.0160354 It is well established that increasing mesh number in the circumference of a diamond-mesh trawl codend can reduce size selection for round fish, whereas selection for flat fish species is unaffected. This effect has also been documented in Mediterranean trawl fisheries. In contrast, no information is available with regard to the effect of increasing mesh number in the circumference of square-mesh codends on the size selection of round fish and flat fish species. A field study was devised to bridge this gap and formulate proposals aimed at improving trawl fishery management. Size selection data were collected for a round fish species, red mullet (Mullus barbatus), and two flat fish species, Mediterranean scaldfish (Arnoglossus laterna) and solenette (Buglossidium luteum). Fishing trials were conducted in the Adriatic Sea (Central Mediterranean) using three square-mesh codends that differed only in mesh number around the circumference. Results demonstrated that increasing the number of meshes from 107 to 213 reduced the 50% retention length (L50) for red mullet by 2.5 cm but did not affect size selection for the two flat fish species. In some fisheries, regulatory provisions regarding the number of meshes in the circumference should therefore be carefully considered both for diamond- and square-mesh codends.

International audience; Soft sediments in coastal shallow waters constitute nursery habitats for juveniles of several flatfishes. The quality of a nursery is defined by its capacity to optimize the growth and the survival of juvenile fish. The influence of biotic factors, such as food availability, is poorly studied at the scale of a nursery ground. Whether food availability limits juvenile survival is still uncertain. A spatial approach is used to understand the influence of food availability on the distribution of juvenile fish of various benthic and demersal species in the Bay of Vilaine (France), a productive nursery ground. We quantified the spatial overlap between benthic macro-invertebrates and their predators (juvenile fish) to assess if the latter were spatially covering the most productive areas of the Bay. Three scenarios describing the shapes of the predator prey spatial relationship were tested to quantify the strength of the relationship and consequently the importance of food availability in determining fish distribution. Our results underline that both.food availability and fish densities vary greatly over the nursery ground. When considering small organisational levels (e.g., a single fish species), the predator prey spatial relationship was not dear, likely because of additional environmental effects not identified here; but at larger organisational level (the whole juvenile fish community), a strong overlap between the fish predators and their prey was identified. The evidence that fish concentrate in sectors with high food availability suggests that either food is the limiting factor in that nursery or/and fish display behavioural responses by optimising their energetic expenditures associated with foraging. Further investigations are needed to test the two hypotheses and to assess the impact of benthic and demersal juvenile fish in the food web of coastal nurseries. (C) 2015 Elsevier B.V. All rights reserved.

Catch per unit effort (CPUE) is commonly used as an indicator for monitoring developments in stock size. To ensure proportionality between average CPUE and total stock size, two processes that should be accounted for are the degree of targeting behaviour of the fleet and the management-induced responses in fishing behaviour. We studied the effect of restrictive individual quotas and targeting behaviour on average CPUE in the Dutch beam trawl fleet. Fishing opportunities varied in time and across species due to changes in quotas. Using catch and effort data by fishing trip of the total fleet and haul-by-haul data from a reference fleet, targeting behaviour of the beam trawl fleet was quantified for sole and plaice, at various space and time scales. Sole was targeted on all scales examined, whereas plaice was only targeted on a micro-scale of 10 × 10 nautical miles. When sole quota restrictions were relaxed, the fleet increasingly targeted sole instead of plaice. Targeting indices for sole and plaice were negatively correlated. Our findings indicate that catch and effort data by fishing trip are sufficient to characterise targeting behaviour on a macro-scale, whereas haul-by-haul data are needed to quantify the targeting on a micro-scale (30 × 30 nautical miles). The micro-scale targeting index can be used to standardize macro-scale CPUE data for bias due to variations in directed fishing among local fishing grounds.