Showing papers on "Gadus published in 2015"
TL;DR: It is found that cod stocks declined continuously during intense warming in the North Atlantic, and managing fisheries in a warming world is going to be increasingly problematic.
Abstract: Several studies have documented fish populations changing in response to long-term warming. Over the past decade, sea surface temperatures in the Gulf of Maine increased faster than 99% of the global ocean. The warming, which was related to a northward shift in the Gulf Stream and to changes in the Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation, led to reduced recruitment and increased mortality in the region’s Atlantic cod (Gadus morhua) stock. Failure to recognize the impact of warming on cod contributed to overfishing. Recovery of this fishery depends on sound management, but the size of the stock depends on future temperature conditions. The experience in the Gulf of Maine highlights the need to incorporate environmental factors into resource management.
638 citations
TL;DR: The data suggest that adaptive responses to the environmental conditions in the Baltic Sea may contribute to a strong and effective reproductive barrier, and that Baltic cod can be viewed as an example of ongoing speciation.
Abstract: How genomic selection enables species to adapt to divergent environments is a fundamental question in ecology and evolution. We investigated the genomic signatures of local adaptation in Atlantic cod (Gadus morhua L.) along a natural salinity gradient, ranging from 35% in the North Sea to 7% within the Baltic Sea. By utilizing a 12 K SNPchip, we simultaneously assessed neutral and adaptive genetic divergence across the Atlantic cod genome. Combining outlier analyses with a landscape genomic approach, we identified a set of directionally selected loci that are strongly correlated with habitat differences in salinity, oxygen, and temperature. Our results show that discrete regions within the Atlantic cod genome are subject to directional selection and associated with adaptation to the local environmental conditions in the Baltic- and the North Sea, indicating divergence hitchhiking and the presence of genomic islands of divergence. We report a suite of outlier single nucleotide polymorphisms within or closely located to genes associated with osmoregulation, as well as genes known to play important roles in the hydration and development of oocytes. These genes are likely to have key functions within a general osmoregulatory framework and are important for the survival of eggs and larvae, contributing to the buildup of reproductive isolation between the low-salinity adapted Baltic cod and the adjacent cod populations. Hence, our data suggest that adaptive responses to the environmental conditions in the Baltic Sea may contribute to a strong and effective reproductive barrier, and that Baltic cod can be viewed as an example of ongoing speciation.
186 citations
TL;DR: In this paper, the authors summarize the knowledge of recent changes in cod biology and ecosystem conditions, describe the subsequent challenges for stock assessment, and highlight the key questions where answers are urgently needed to understand the present stock status and provide scientifically solid support for cod management in the Baltic Sea.
Abstract: The eastern Baltic (EB) cod (Gadus morhua) stock was depleted and overexploited for decades until the mid-2000s, when fishing mortality rapidly declined and biomass started to increase, as shown by stock assessments. These positive developments were partly assigned to effective management measures, and the EB cod was considered one of the most successful stock recoveries in recent times. In contrast to this optimistic view, the analytical stock assessment failed in 2014, leaving the present stock status unclear. Deteriorated quality of some basic input data for stock assessment in combination with changes in environmental and ecological conditions has led to an unusual situation for cod in the Baltic Sea, which poses new challenges for stock assessment and management advice. A number of adverse developments such as low nutritional condition and disappearance of larger individuals indicate that the stock is in distress. In this study, we (i) summarize the knowledge of recent changes in cod biology and ecosystem conditions, (ii) describe the subsequent challenges for stock assessment, and (iii) highlight the key questions where answers are urgently needed to understand the present stock status and provide scientifically solid support for cod management in the Baltic Sea.
139 citations
TL;DR: This study suggests that strong selection in the host structures the cod larval microbiota and changes in community structure observed with increasing age can be explained by altered selection pressure due to development of the intestinal system.
Abstract: Marine fish larvae are immature upon hatching, and share their environment with high numbers of bacteria. The microbial communities associated with developing fish larvae might be structured by other factors than those important in developing terrestrial animals. Here, we analysed the beta (β)-diversity of the microbiota associated with developing cod larvae and compared it with the bacterial communities in water and live feed by applying pyrosequencing of bar coded v4 16S rDNA amplicons. A total of 15 phyla were observed in the cod larval microbiota. Proteobacteria was the most abundant, followed by Firmicutes, Bacteroidetes and Actinobacteria. The composition and diversity of the cod larval microbiota changed considerably with age. The temporal and spatial patterns of β-diversity could not be explained by stochastic processes, and did not coincide with changes in the rearing conditions. Furthermore, the larval microbiota was highly distinct from the water and the live feed microbiota, particularly at early developmental stages. However, the similarity between larval and water microbiota increased with age. This study suggests that strong selection in the host structures the cod larval microbiota. The changes in community structure observed with increasing age can be explained by altered selection pressure due to development of the intestinal system.
86 citations
TL;DR: The great northern cod (Gadus morhua) stock is making a major comeback after nearly two decades of depletion and non-recovery of marine fishes as discussed by the authors, and the stock is one of the largest fishes in the world.
Abstract: The great “northern” cod (Gadus morhua) stock, formerly among the world’s largest and the icon for depletion and supposed nonrecovery of marine fishes, is making a major comeback after nearly two d...
85 citations
TL;DR: Larvae fed rotifers/Artemia had a higher whole body lipid content than larvae fed copepods at the end of the experiment after the fish had been fed the same formulated diet for approximately 2 weeks.
Abstract: The current commercial production protocols for Atlantic cod depend on enriched rotifers and Artemia during first-feeding, but development and growth remain inferior to fish fed natural zooplankton. Two experiments were conducted in order to identify the underlying factors for this phenomenon. In the first experiment (Exp-1), groups of cod larvae were fed either (a) natural zooplankton, mainly copepods, increasing the size of prey as the larvae grew or (b) enriched rotifers followed by Artemia (the intensive group). In the second experiment (Exp-2), two groups of larvae were fed as in Exp-1, while a third group was fed copepod nauplii (approximately the size of rotifers) throughout the larval stage. In both experiments, growth was not significantly different between the groups during the first three weeks after hatching, but from the last part of the rotifer feeding period and onwards, the growth of the larvae fed copepods was higher than that of the intensive group. In Exp-2, the growth was similar between the two copepod groups during the expeimental period, indicating that nutrient composition, not prey size caused the better growth on copepods. Analyses of the prey showed that total fatty acid composition and the ratio of phospholipids to total lipids was slightly different in the prey organisms, and that protein, taurine, astaxanthin and zinc were lower on a dry weight basis in rotifers than in copepods. Other measured nutrients as DHA, all analysed vitamins, manganese, copper and selenium were similar or higher in the rotifers. When compared to the present knowledge on nutrient requirements, protein and taurine appeared to be the most likely limiting nutrients for growth in cod larvae fed rotifers and Artemia. Larvae fed rotifers/Artemia had a higher whole body lipid content than larvae fed copepods at the end of the experiment (stage 5) after the fish had been fed the same formulated diet for approximately 2 weeks.
76 citations
TL;DR: The findings suggest that future and ongoing rises in sea surface temperature may increasingly deprive cod in this region from shallow feeding areas during summer, which may be detrimental for local populations of the species.
Abstract: Understanding responses of marine species to temperature variability is essential to predict impacts of future climate change in the oceans. Most ectotherms are expected to adjust their behavior to avoid extreme temperatures and minimize acute changes in body temperature. However, measuring such behavioral plasticity in the wild is challenging. Combining 4 years of telemetry-derived behavioral data on juvenile and adult (30-80 cm) Atlantic cod (Gadus morhua), and in situ ocean temperature measurements, we found a significant effect of sea temperature on cod depth use and activity level in coastal Skagerrak. During summer, cod were found in deeper waters when sea surface temperature increased. Further, this effect of temperature was stronger on larger cod. Diel vertical migration, which consists in a nighttime rise to shallow feeding habitats, was stronger among smaller cod. As surface temperature increased beyond ∼15°C, their vertical migration was limited to deeper waters. In addition to larger diel vertical migrations, smaller cod were more active and travelled larger distances compared to larger specimens. Cold temperatures during winter tended, however, to reduce the magnitude of diel vertical migrations, as well as the activity level and distance moved by those smaller individuals. Our findings suggest that future and ongoing rises in sea surface temperature may increasingly deprive cod in this region from shallow feeding areas during summer, which may be detrimental for local populations of the species.
60 citations
TL;DR: It is demonstrated that at low harvest levels, evolution has minimal effect on r for all three species, however, at the harvest rates experienced by many fish stocks, evolution increases r and reduces the risk of collapse for cod and whitefish.
Abstract: By removing individuals with certain heritable characteristics such as large body size, harvesting may induce rapid evolutionary change in fish life history. There is controversy, however, as to the prevalence of fisheries-induced evolution (FIE) and to what extent it should be considered as part of sustainable resource management. Recent research has shown that FIE can be difficult to detect and its economic effects might not always be significant. Here, we show how population growth rate (r), a critical factor affecting sustainability and recovery, is affected by FIE through the analysis of a simulation model that demonstrates the link between individual-level genetic processes and stock dynamics. We examine how different levels of evolvability, fishing intensity, and density-dependence interact to influence r in three commercially harvested species: Atlantic cod (Gadus morhua), lake whitefish (Coregonus clupeaformis), and yellow perch (Perca flavescens). We demonstrate that at low harvest levels, evolution has minimal effect on r for all three species. However, at the harvest rates experienced by many fish stocks, evolution increases r and reduces the risk of collapse for cod and whitefish. During the initial stages of a harvest moratorium, a switch occurs, and r becomes reduced as a consequence of evolution. These results explain how evolution increases stock resilience, but also impedes recovery after periods of intense harvesting.
60 citations
TL;DR: The results demonstrate that the timing of acoustic disturbances can impact survival-related measures during development, and the role of noise regularity and its importance for noise management and mitigation measures should be considered.
Abstract: Anthropogenic noise impacts behaviour and physiology in many species, but responses could change with repeat exposures. As repeat exposures can vary in regularity, identifying regimes with less impact is important for regulation. We use a 16-day split-brood experiment to compare effects of regular and random acoustic noise (playbacks of recordings of ships), relative to ambient-noise controls, on behaviour, growth and development of larval Atlantic cod (Gadus morhua). Short-term noise caused startle responses in newly hatched fish, irrespective of rearing noise. Two days of both regular and random noise regimes reduced growth, while regular noise led to faster yolk sac use. After 16 days, growth in all three sound treatments converged, although fish exposed to regular noise had lower body width-length ratios. Larvae with lower body width-length ratios were easier to catch in a predator-avoidance experiment. Our results demonstrate that the timing of acoustic disturbances can impact survival-related measures during development. Much current work focuses on sound levels, but future studies should consider the role of noise regularity and its importance for noise management and mitigation measures.
56 citations
TL;DR: In this article, Herrmann et al. studied the effects of panel area, panel position, and stimulation of escape response on the release efficiency of Atlantic cod from trawls with a square mesh panel.
Abstract: Understanding the release efficiency of Atlantic cod (Gadus morhua) from trawls with a square mesh panel: effects of panel area, panel position, and stimulation of escape response Bent Herrmann1*, Harald Wienbeck2, Junita Diana Karlsen3, Daniel Stepputtis4, Erdmann Dahm2, and Waldemar Moderhak5 SINTEF Fisheries and Aquaculture, North Sea Science Park, Hirtshals DK-9850, Denmark Thunen-Institute of Baltic Sea Fisheries, Palmaille 9, Hamburg 22767, Germany National Institute of Aquatic Resources, Technical University of Denmark, North Sea Science Park, PO Box 101, Hirtshals DK-9850, Denmark Thunen-Institute of Baltic Sea Fisheries, Alter Hafen Sud 2, Rostock 18069, Germany Morski Instytut Rybacki w Gdyni, Sea Fisheries Institute in Gdynia, ul. Kollataja 1, 81332 Gdynia, Poland *Corresponding author: tel: +45 29617964; fax: +45 9894 2226; e-mail: bent.herrmann@sintef.no
56 citations
TL;DR: In this article, the influence of environmental exposure of juvenile Atlantic cod (Gadus morhua) to inform interpretations of natal origins and movement patterns using otolith geochemistry was evaluated.
Abstract: We evaluated the influence of environmental exposure of juvenile Atlantic cod (Gadus morhua) to inform interpretations of natal origins and movement patterns using otolith geochemistry. Laboratory rearing experiments were conducted with a variety of temperature (∼5, 8.5, and 12°C) and salinity (∼25, 28.5, and 32 PSU) combinations. We measured magnesium (Mg), manganese (Mn), strontium (Sr), and barium (Ba), expressed as a ratio to calcium (Ca), using laser ablation inductively coupled plasma mass spectrometry (ICP-MS), and stable carbon (δ13C) and oxygen (δ18O) isotopes using isotope ratio monitoring mass spectrometry. Temperature and salinity significantly affected all elements and isotopes measured, except salinity on Mg:Ca. We detected significant interactions among temperature and salinity for Mn:Ca and Ba:Ca partition coefficients (ratio of otolith chemistry to water chemistry), with significant temperature effects only detected in the 32 and 28.5 PSU salinity treatments. Similarly, we detected a significant interaction between temperature and salinity in incorporation of δ13C, with a significant temperature effect except at intermediate salinity. These results support the contention that environmental mediation of otolith composition varies among species, thus limiting the ability of generalized models to infer life history patterns from chemistry. Our results provide essential baseline information detailing environmental influence on juvenile Atlantic cod otolith composition, punctuating the importance of laboratory validations to translate species-specific otolith composition when inferring in situ life histories and movements.
TL;DR: Investigation of the impact of anthropogenic noise on Atlantic cod stress response using cortisol as a biomarker as well as on broodstock spawning performance showed that artificial noise can induce a transient and mild cortisol elevation with a clear noise intensity dose response.
TL;DR: Irrespective of BM cold water temperatures resulted in a reduction (30-35%) of MS whereas the reduction of MS at warm temperatures was only evident for larger fish (200 and 450g), caused by plateauing of MMR at 10°C and above.
Abstract: Changes in ambient temperature affect the physiology and metabolism and thus the distribution of fish. In this study we used intermittent flow respirometry to determine the effect of temperature (2, 5, 10, 15 and 20°C) and wet body mass (BM) (~30-460g) on standard metabolic rate (SMR, mgO2h(-1)), maximum metabolic rate (MMR, mgO2h(-1)) and metabolic scope (MS, mgO2h(-1)) of juvenile Atlantic cod. SMR increased with BM irrespectively of temperature, resulting in an average scaling exponent of 0.87 (0.82-0.92). Q10 values were 1.8-2.1 at temperatures between 5 and 15°C but higher (2.6-4.3) between 2 and 5°C and lower (1.6-1.4) between 15 and 20°C in 200 and 450g cod. MMR increased with temperature in the smallest cod (50g) but in the larger cod MMR plateaued between 10, 15 and 20°C. This resulted in a negative correlation between the optimal temperature for MS (Topt) and BM, Topt being respectively 14.5, 11.8 and 10.9°C in a 50, 200 and 450g cod. Irrespective of BM cold water temperatures resulted in a reduction (30-35%) of MS whereas the reduction of MS at warm temperatures was only evident for larger fish (200 and 450g), caused by plateauing of MMR at 10°C and above. Warm temperatures thus seem favourable for smaller (50g) juvenile cod, but not for larger conspecifics (200 and 450g).
TL;DR: This work tracks 80 years of Atlantic cod population dynamics in West Greenland using DNA from archived otoliths in combination with fish population and niche based modeling to document how the interacting effects of climate change and high fishing pressure lead to dramatic spatiotemporal changes.
Abstract: Fishing and climate change impact the demography of marine fishes, but it is generally ignored that many species are made up of genetically distinct locally adapted populations that may show idiosyncratic responses to environmental and anthropogenic pressures. Here, we track 80 years of Atlantic cod (Gadus morhua) population dynamics in West Greenland using DNA from archived otoliths in combination with fish population and niche based modeling. We document how the interacting effects of climate change and high fishing pressure lead to dramatic spatiotemporal changes in the proportions and abundance of different genetic populations, and eventually drove the cod fishery to a collapse in the early 1970s. Our results highlight the relevance of fisheries management at the level of genetic populations under future scenarios of climate change.
TL;DR: In a follow-up study, 97.8% of similarly selected cod managed to dive following immediate release, whereas 2.2% were floaters as discussed by the authors, likely due to cumulative stress from ongoing barotrauma and exposure to warm surface water.
Abstract: Atlantic cod (Gadus morhua) caught in recreational fisheries are commonly released, often with barotrauma after rapid decompression. Mouth-hooked, non-bleeding cod kept in a floating net pen showed mortalities =40% when angled from >50 m depth, likely because of cumulative stress from ongoing barotrauma and exposure to warm surface water. In a natural setting, however, cod have the opportunity to descend after release and are not restricted to the surface. In a follow-up study, 97.8% of similarly selected cod managed to dive following immediate release, whereas 2.2% were floaters. No mortality was observed for divers kept in cages, which were lowered to capture depth for 72 h. While the floaters would likely have died in a natural setting, no mortality was observed when they were recompressed and kept at capture depth for 72 h. The occurrence of swim bladder ruptures, swollen coelomic cavities, venous gas embolisms, and gas release around the anus was significantly influenced by capture depth (range 090 m). A supplementary radiology study showed inflated swim bladders in 87% of the cod after 72 h, and most barotrauma signs had disappeared after 1 month. This study encourages investigation of survival potential for physoclistous species when high mortalities are assumed but undocumented. Matching natural post-release and containment environment is essential in the experimental setup, as failure to do so may bias survival estimates, particularly when a thermocline is present. Assuming minimal predation, short-term mortality of cod experiencing barotrauma is negligible if cod submerge quickly by themselves and are otherwise not substantially injured. Survival of floaters may be increased by forced recompression to capture depth. Sublethal and long-term impacts of barotrauma remain to be studied. To ensure that cod have sufficient energy to submerge, anglers are encouraged to avoid fighting the fish to exhaustion and to minimize handling before release.
TL;DR: The results indicate that probiotic treatment aiming for colonization with new strains in the cod larvae is difficult, and challenges the probiotic concept for the larval stage unless continuous or repeated addition to the fish larvae is used.
TL;DR: In this article, the authors compared the catch efficiency of two different setups where the sweep length with bottom contact was different and estimated that the setup with the lifted sweeps captured on average 33% fewer cod than the setup that kept the sweeps at the seabed.
TL;DR: Increased temperature was observed to modulate the antibacterial responses of all IRF transcripts, and the antiviral responses of Irf4b and Irf10-v2, which supports earlier studies which reported that elevated temperature modulates the expression of many immune genes in Atlantic cod.
TL;DR: The results indicate that seal presence drives the distribution in the southern parts of the Baltic and that low salinity, or some other variable which correlates with salination, limits the distribution of sealworm in the northern part.
Abstract: The anisakid nematode Pseudoterranova decipiens, known as the sealworm or cod worm, can infect the flesh of several fish species. The parasite causes cosmetic problems for the fish industry and can cause abdominal discomfort if consumed by humans. There are only scattered studies on the abundance or distribution of the sealworm in fish and seals in the Baltic Sea. To remedy this situation, the extent of sealworm infection was investigated in cod (Gadus morhua) and shorthorn sculpin (Myoxocephalus scorpius) collected along the Swedish coast. A relative presence of the sealworm was also investigated in samples from grey seal (Halichoerus grypus) stomachs. Up to 100 % of the fish were infected in some of the areas. Sculpin were generally worse infected than cod, both in abundance and prevalence of parasites. General linear models showed a significant correlation between the number of seals in an area and the prevalence of sealworms in cod. There was a sharp decrease of infected fish in areas with salinity lower than 7 ‰. Even though the northern Baltic proper and the southern Bothnian Sea have a high number of grey seals, only one sealworm was found in a sculpin in that region, and none in cod. In grey seal stomachs the sealworm was only found in samples from the central Baltic proper; further north, all anisakid nematodes identified in seals were Contracaecum osculatum. The results indicate that seal presence drives the distribution in the southern parts of the Baltic and that low salinity, or some other variable which correlates with salinity, limits the distribution in the northern part.
TL;DR: Results indicate an ontogenetic shift in the diet of Atlantic cod Gadus morhua, one of the most important high-level predators of small fish in the North Atlantic, caught during one research vessel cruise from West and East Greenlandic waters.
Abstract: Parasites, being an integral part of every ecosystem and trophically transmitted along the food webs, can provide detailed insights into the structure of food webs and can close the information gap between short-term stomach content anal- yses and long-term fish otolith analyses. They are useful for tracking ontogenetic shifts in the host's diet, the occurrence of specific organisms or migratory behaviour of their hosts, even in inaccessible environments. In the present study, stomach content analyses and parasitological examinations were per- formed on 70 Atlantic cod Gadus morhua, one of the most important high-level predators of small fish in the North Atlantic, caught during one research vessel cruise from West and East Greenlandic waters. Analyses revealed significant differences in fish size with higher values for East Greenland (average total length (TL) of 50.5 cm) compared to West Greenland (average TL of 33.3 cm). Clear differences were also present in prey and parasite composition. Crustacea was the main food source for all fish (IRI=10082.70), while the importance of teleosts increased with fish size. With a preva- lence of 85 % in West Greenland and 100 % in East Greenland, Nematoda were the most abundant parasite group. The results indicate an ontogenetic shift in the diet, which are discussed in the context of the common distribution theory, stock dynamics and migratory behaviour.
TL;DR: Of the samples examined, the lowest level of selenium was found in farmed Atlantic salmon (0.17 mg Se kg(−1) dm), and the totalSelenium extraction efficiency by phosphate buffer was 2.5 times higher in sea plankton and shellfish samples than in fish samples.
TL;DR: In this article, the authors evaluated the effectiveness of a spawning closure for Atlantic cod (Gadus morhua) in the Firth of Clyde off the Scottish West Coast (ICES Area VIa) and found no evidence of local recovery in terms of abundance, biomass or reduced mortality in the Clyde more than a decade after establishing the closure.
Abstract: Fish that aggregate at predictable locations and times to spawn are often vulnerable to over-exploitation. Seasonal closures have often been implemented
in an attempt to alleviate such impacts but the effectiveness of these measures is rarely tested. This study evaluates the effectiveness of a
spawning closure for Atlantic cod (Gadus morhua) in the Firth of Clyde off the Scottish West Coast (ICES Area VIa). This closurewas introduced in
March 2001 as an emergency measure to allowas many cod as possible to spawn and avoid the build-up of displaced effort from another spawning
closure. Genetic, tagging, and otolith microchemistry investigations indicate that cod inhabiting the Clyde are reproductively isolated from other
resident groups in the central and northern part of the Scottish WestCoast stock. This study used a beyond-Before-After, Control-Impact approach
to compare population trends of the Clyde spawning aggregation before and after the introduced area closure, using two other sub-population
spawning grounds as control areas. There was no evidence of local recovery in terms of abundance, biomass, or reduced mortality in the Clyde more
than a decade after establishing the closure. Mortality mayhave remained high because young cod are still caught as bycatch in the Nephrops fishery
in the area and the predation rate may have increased due to an expanding whiting population. Considering the state of the already severely
depleted Clyde sub-population when the closure was implemented the measure appears to have been too little and too late. The tendency to
implement such spawning closures on nearly collapsed stocks may be why these measures often appear to have been ineffective.
TL;DR: Comparisons with a large-scale bottom trawl survey data suggested highly dynamic and species-specific interactions between fish movements, changing environmental conditions and the physical presence of an offshore platform, and there is a need to identify biological mechanisms behind such dynamic interactions.
TL;DR: In this paper, the influence of partial protection on the demography of Atlantic cod Gadus morhua along the Norwegian Skagerrak coast was investigated, and the authors showed that partial protection can increase the survival rate of cod.
Abstract: Summary
In recent years, marine protected areas (MPAs) excluding all or some fishing activities have become widely applied as a tool to rebuild marine ecosystems and fisheries, but still, our knowledge of the effects of MPAs on the demography of harvested populations remains scarce, especially in cases where partly protected areas are still supporting some fishing activities.
Here, we investigated the influence of partial protection – excluding fixed gears such as gillnets and traps but still allowing a hook and line fishery – on the demography of Atlantic cod Gadus morhua along the Norwegian Skagerrak coast. To do so, we applied novel multi-event models to a 9-year data set containing both live recaptures and dead recoveries of marked fish of different sizes collected before and after the implementation of an MPA, also including several unprotected sites.
At the MPA site, the annual proportion of deaths due to fishing decreased from 0·59 before MPA implementation to 0·32 after MPA implementation. As a result, annual survival increased by 167% (from 0·09 to 0·24) for small (16–44 cm) and 83% (from 0·23 to 0·42) for big (45–97 cm) cod, respectively.
Average survival was lower in unprotected areas, and annual fishing mortality was higher, representing almost 100% of the total mortality of large-sized cod in some years.
Annual emigration rates (i.e. spillover from the MPA) increased in the last years of the study, but no differences in body growth were detected between sites.
Closure of the fishery within the MPA would further increase the annual survival of smaller individuals by 100% (from 0·24 ± 0·07 to 0·48 ± 0·11) and that of larger individuals by 44% (from 0·42 ± 0·05 to 0·60 ± 0·09).
Synthesis and applications. Our study reveals how current marine protected areas (MPAs) function and provides important insights for guiding a future adaptive management process. Given that harvested populations will not be able to sustain annual survival rates consistently below 30%, as found here; our results underscore the urgency of effective management measures such as no-take zones in areas where local populations are particularly reduced or in dire need of demographic rescue.
TL;DR: In this article, the authors evaluated the efficacy of EM for cod (Gadus morhua) catches on vessels in a mixed bottom-trawl fishery and tested the hypothesis that cod catches are difficult to detect with video monitoring, specifically in catches with large volumes of bycatch.
Abstract: In the context of the landing obligation under the European Common Fisheries Policy, electronic monitoring (EM) is often presented as one of the solutions to fully document catches. EM includes video monitoring to record the catch handling process on board the vessels. This study evaluated the efficacy of EM for cod (Gadus morhua) catches on vessels in a mixed bottom-trawl fishery and tested the hypothesis that cod catches are difficult to detect with video monitoring, specifically in catches with large volumes of bycatch. In 2011, a catch quota pilot study started for cod in the Dutch bottom-trawl fishery in which EM was used as an audit system to review the consistency of reported cod catches. Eleven vessels joined the pilot study on a voluntary basis. Participants received a 30% increase in individual quota for cod and were compensated with extra effort in days at sea. In return, all cod catches were counted against their cod quota. This mixed bottom-trawl fishery differs from fisheries where EM was proven to be a successful method, e.g. hook and line or single-species fisheries with low bycatch volumes. We conclude that distinguishing small numbers of cod in catches of mixed bottom-trawl fisheries is difficult because there is a low correlation between logbook and video data (Pearson r = 0.17). We expect similar difficulty in other mixed demersal trawl fisheries with large bycatch volumes, when similar-looking species are targeted. Meanwhile, implementing a landing obligation will pose large challenges for fisheries with large volumes of bycatch. Limitations in the applicability of EM to control one of the most common types of fisheries in Europe will be a burden on the implementation of the European landing obligation. Improved protocols and technical adaptations may reduce some of the limitations encountered in this study.
TL;DR: It is argued that fishing mortality, either through demographic or evolutionary change, has served as an effective driver for changing spawning locations in cod, and that additional explanatory factors related to climate add no significant information.
Abstract: Harvesting may be a potent driver of demographic change and contemporary evolution, which both may have great impacts on animal populations. Research has focused on changes in phenotypic traits that are easily quantifiable and for which time series exist, such as size, age, sex, or gonad size, whereas potential changes in behavioural traits have been under-studied. Here, we analyse potential drivers of long-term changes in a behavioural trait for the Northeast Arctic stock of Atlantic cod Gadus morhua, namely choice of spawning location. For 104 years (1866–1969), commercial catches were recorded annually and reported by county along the Norwegian coast. During this time period, spawning ground distribution has fluctuated with a trend towards more northerly spawning. Spawning location is analysed against a suite of explanatory factors including climate, fishing pressure, density dependence, and demography. We find that demography (age or age at maturation) had the highest explanatory power for variation in spawning location, while climate had a limited effect below statistical significance. As to potential mechanisms, some effects of climate may act through demography, and explanatory variables for demography may also have absorbed direct evolutionary change in migration distance for which proxies were unavailable. Despite these caveats, we argue that fishing mortality, either through demographic or evolutionary change, has served as an effective driver for changing spawning locations in cod, and that additional explanatory factors related to climate add no significant information.
TL;DR: This study demonstrates for the first time genetic differentiation by the use of a large number of SNPs between eastern and western Baltic populations existing in differentiated salinity conditions.
TL;DR: The results indicate that these fish are able to assess and respond to spatial variation in predation risk at very large spatial scales, and suggest that non-consumptive 'risk' effects may be an important component of the declines in productivity of seal prey in this ecosystem, and of the indirect effects at lower trophic levels.
Abstract: 1. Numerous studies have shown that, at spatial scales of metres to several kilometres, animals balance the trade-off between foraging success and predation mortality by increasing their use of safer but less profitable habitats as predation risk increases. However, it is less clear whether prey respond similarly at the larger spatiotemporal scales of many ecosystems. 2. We determine whether this behaviour is evident in a large marine ecosystem, the southern Gulf of St. Lawrence (sGSL, 75 000 km(2) ) over a 42-year period. This ecosystem is characterized by a recent increase in the abundance of a large marine predator, the grey seal (Halichoerus grypus Fabricius), by more than an order of magnitude. 3. We compared changes in spatial distribution over the 1971-2012 period between important prey of grey seals (Atlantic cod, Gadus morhua L.; white hake, Urophycis tenuis Mitchill; and thorny skate, Amblyraja radiata Donovan) and non-prey fishes. 4. Distribution was modelled using generalized additive models incorporating spatially variable effects of predation risk, density dependence and water temperature. Distributions of cod, hake and skate were strongly related to risk of predation by seals, with distribution shifting into lower risk areas as predation risk increased. Non-prey species did not show similar changes in habitat use. Spatial variation in fish condition suggests that these low-risk areas are also less profitable for cod and skate in terms of food availability. The effects of density dependence and water temperature were also important in models, but did not account for the changes in habitat use as the risk of predation increased. 5. These results indicate that these fish are able to assess and respond to spatial variation in predation risk at very large spatial scales. They also suggest that non-consumptive 'risk' effects may be an important component of the declines in productivity of seal prey in this ecosystem, and of the indirect effects at lower trophic levels.
TL;DR: To investigate the effects of C&R on Atlantic cod in their natural environment, 80 cod were caught in fyke nets, fitted with acoustic transmitters, and released and it was shown that three individuals underwent short-term alterations.
Abstract: Studying the sublethal effects of catch-and-release (C&R) is challenging, as there are several potential sources of bias. For example, if behavioural alterations immediately after the release event...
TL;DR: It is found that alpha and beta diversity increased with decreases in cod occurrence; fish communities were less homogeneous and more variable in systems where cod no longer dominated, and these effects were most pronounced in the colder north-eastern parts of the Scotian Shelf.
Abstract: Summary 1. Exploitation of living marine resources has resulted in major changes to populations of targeted species and functional groups of large-bodied species in the ocean. However, the effects of overfishing and collapse of large top predators on the broad-scale biodiversity of oceanic ecosystems remain largely unexplored. 2. Populations of the Atlantic cod (Gadus morhua) were overfished and several collapsed in the early 1990s across Atlantic Canada, providing a unique opportunity to study potential ecosystem-level effects of the reduction of a dominant predator on fish biodiversity, and to identify how such effects might interact with other environmental factors, such as changes in climate, over time. 3. We combined causal modelling with model selection and multimodel inference to analyse 41 years of fishery-independent survey data (1970–2010) and quantify ecosystem-level effects of overfishing and climate variation on the biodiversity of fishes across a broad area (172 000 km 2 ) of the Scotian Shelf. 4. We found that alpha and beta diversity increased with decreases in cod occurrence; fish communities were less homogeneous and more variable in systems where cod no longer dominated. These effects were most pronounced in the colder north-eastern parts of the Scotian Shelf. 5. Our results provide strong evidence that intensive harvesting (and collapse) of marine apex predators can have large impacts on biodiversity, with far-reaching consequences for ecological stability across an entire ecosystem.