Atlantic Cod Gadus Morhua Research Articles

Absence of predator control increases cod extirpation risk in a Northwest Atlantic ecosystem: inference from multispecies modelling

Atlantic cod Gadus morhua in the southern Gulf of St. Lawrence (sGSL) declined to low abundance in the early 1990s and have since failed to recover due to high natural mortality, which has been linked to predation by grey seals Halichoerus grypus. Increased grey seal harvests have been suggested to improve cod survival; however, predicting the response of cod to changes in seal abundance in the sGSL is complicated by a hypothesized triangular food web involving seals, cod, and small pelagic fishes, wherein the pelagic fishes are prey for cod and grey seals, but may also prey on young cod. Grey seals may therefore have an indirect positive effect on pre-recruit cod survival via predation on pelagic fish. Using a multispecies model of intermediate complexity fitted to various scientific and fisheries data, we found that seal predation accounted for the majority of recent cod mortality and that cod will likely be extirpated without a strong and rapid reduction in grey seal abundance. We did not find evidence that reducing grey seal abundance will impair cod recovery by causing large increases in pelagic biomass so long as pelagic fishing mortality continues at historical levels.

Sex-specific vertical movements of spawning atlantic cod in coastal habitats inferred from acoustic telemetry.

Fish spawning location and behaviour can be challenging to detect, especially in deep water. Here we utilise two large acoustic telemetry datasets from western and mid Norway to study the vertical movement dimension of individual Atlantic cod Gadus morhua spawning behaviour in their natural habitats. The datasets comprise ~ 6million depth detections from 644 sexed, mature cod, collected at seven different Norwegian coastal cod spawning grounds during 2017-2021. During the spawning period, females were typically found at shallower depths compared to males, while this pattern was much less pronounced or absent outside this period. Furthermore, we identify a hitherto undescribed sex-dependent vertical movement behaviour: periodic descents, where females made deep dives, putatively associated with egg release and spawning, approximately every third day. Females not showing this behaviour tended to occupy deeper positions in the water column than the "periodic descent" females and hence may approach and retreat from spawning males more horizontally. These observed sex-specific behaviours correspond well to the lek-like description of the cod mating system and with cod reproductive physiology, where females are known to mature and release batches of eggs at intervals of several days as part of a bet-hedging strategy.

Impact of mercury released from permafrost on food safety in Switzerland

ABSTRACT (ENGLISH) Climate change has caused the permafrost to thaw, releasing the previously sequestered mercury into the environment. Mercury has the ability to convert to methylmercury, a bioaccumulative neurotoxin. Exposure occurs in humans through the ingestion of contaminated food and it is associated with adverse health effects. In the context of global warming, this report aims to provide a basis for discussion on the impact of mercury released from permafrost on Switzerland's food safety. Data available in the scientific literature and in databases were reviewed in order to identify the relevant fish indicating the mercury exposure of the Swiss population and the potential evolution of the situation in the coming years. To assess the current relevance for Switzerland of undertaking mercury monitoring in indicator fish, gaps in the literature were identified. In addition, several experts were contacted regarding the topics described above in order to complement and refine the results of the literature review. The main results suggest that the current situation does not yet pose a threat to the Swiss population. However, mercury is certainly being released from the permafrost and its future impact remains uncertain at present. Two species provide some indication of the amount of mercury released by thawing permafrost: Atlantic cod Gadus morhua, one of the fish most imported into Switzerland from FAO zones 18, 21, 27 and 67, and Arctic cod Boreogadus saida because of its position in the Arctic food chain. To conclude, although fish is not a major component of the Swiss diet, it would be worthwhile to monitor the contamination of mercury in the two species mentioned above due to the uncertainty of the situation. It is not necessary for Switzerland to conduct its own chemical analyses of mercury in fish but it is important to regularly consult databases such as, the Arctic database(s) Seafood Data and to identify any possible increasing trend.

Exploring mechanisms of spatial segregation between body size groups within fish populations under environmental change

Ample evidence has indicated shifts in distribution of fish populations in response to environmental stress. However, most studies focused at the whole population scale. This neglects the spatial dynamics between groups of different body size (body size groups), that fundamentally shapes the spatial structure of a population. Here, we explored the mechanisms that modulate spatial dynamics of body size groups, and applied our analyses to three North Sea fish populations which experienced severe declines in biomass from 1977 to 2019: Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangius. All three populations exhibited strong declines in the overlapped area between body size groups in winter over 43 years, yet their mechanisms differed. These declines were either due to 1) different magnitudes of contraction of the distribution area of body size groups; and/or 2) different speeds and directions of spatial shift among various body size groups, both increasing spatial segregation within populations. These patterns were either associated with ocean warming, and/or declining population biomass, and such associations often varied according to distinct body size groups. Increasing spatial segregation between size groups of a population likely hampers life‐cycle connectivity and stability to local perturbations. Our analytical approach provides a powerful tool for identifying vulnerable populations under environmental stress and can be generalized to study a variety of size/age structured populations at various ecosystem types.

Non-trophic interactions amplify kelp harvest-induced biomass oscillations and biomass changes in a kelp forest ecological network model

Kelp forests are important marine ecosystems providing habitat for numerous species. Despite over 50 yr of mechanical harvesting in the Northeast Atlantic, the indirect impacts of kelp harvesting and associated habitat loss on faunal species within kelp forests remain poorly understood. We investigated the consequences of kelp harvesting by developing an allometric trophic network model for a subtidal Northeast Atlantic kelp forest (dominated by Laminaria hyperborea). Additionally, we designed a novel mechanistic model to explore the non-trophic interactions between kelp and age-class 0 Atlantic cod Gadus morhua and between kelp and European lobster Homarus gammarus, specifically focusing on the increased survival benefits provided by the kelp habitat. Simulations were conducted over a 50 yr period, incorporating harvesting cycles of 2, 5, and 9 yr, as well as low and high harvesting intensities. Our findings reveal the complex dynamics resulting from kelp harvesting. The recovery of kelp biomass was observed with 5 and 9 yr harvesting cycles, whereas a decline was observed with a 2 yr cycle. Furthermore, the non-trophic interactions facilitated a higher pre-harvest biomass for both European lobster and Atlantic cod compared to scenarios without this interaction. These results highlight the multitrophic effects of kelp harvesting and emphasize that the recovery of kelp-associated species may not necessarily align with kelp recovery, depending on harvesting intensity and recovery periods. Importantly, our study contributes to a better understanding of the ecological consequences of kelp harvesting and underscores the need for sustainable management practices to mitigate habitat loss in kelp ecosystems.

Movement diversity and partial sympatry of coastal and Northeast Arctic cod ecotypes at high latitudes.

Movement diversity within species represent an important but often neglected, component of biodiversity that affects ecological and genetic interactions, as well as the productivity of exploited systems. By combining individual tracking data from acoustic telemetry with novel genetic analyses, we describe the movement diversity of two Atlantic cod Gadus morhua ecotypes in two high-latitude fjord systems: the highly migratory Northeast Arctic cod (NEA cod) that supports the largest cod fishery in the world, and the more sedentary Norwegian coastal cod, which is currently in a depleted state. As predicted, coastal cod displayed a higher level of fjord residency than NEA cod. Of the cod tagged during the spawning season, NEA cod left the fjords permanently to a greater extent and earlier compared to coastal cod, which to a greater extent remained resident and left the fjords temporarily. Despite this overall pattern, horizontal movements atypical for the ecotypes were common with some NEA cod remaining within the fjords year-round and some coastal cod displaying a low fjord fidelity. Fjord residency and exit timing also differed with spawning status and body size, with spawning cod and large individuals tagged during the feeding season more prone to leave the fjords and earlier than non-spawning and smaller individuals. While our results confirm a lower fjord dependency for NEA cod, they highlight a movement diversity within each ecotype and sympatric residency between ecotypes, previously undetected by population-level monitoring. This new knowledge is relevant for the management, which should base their fisheries advice for these interacting ecotypes on their habitat use and seasonal movements.

Environmental abundances of the non-native round goby Neogobius melanostomus influence feeding of native fish predators.

The authors assessed the importance of the round goby Neogobius melanostomus as prey for three native predatory fish species, Atlantic cod Gadus morhua, European perch Perca fluviatilis and northern pike Esox lucius, in a northern and southern area of the Baltic Proper, using a combination of visual analysis and DNA metabarcoding of predator stomach contents. To explore the influence of environmental abundances of N. melanostomus on predation, they related the occurrence of N. melanostomus in predator diets to its abundance in survey fishing. Gadus morhua and E. lucius in the southern area showed the highest tendency to feed on N. melanostomus when it was abundant, as N. melanostomus occurred in up to 100% of stomachs and constituted up to 88% of the total diet volume proportion. The diet contribution of N. melanostomus was associated with N. melanostomus abundances for G. morhua and E. lucius, and when N. melanostomus was abundant, these predators exhibited lower prey richness and a higher degree of piscivory. G. morhua and P. fluviatilis also fed less on crustacean prey when N. melanostomus was abundant. The high importance of N. melanostomus in diets of native fish predators may modify indirect interactions between N. melanostomus and native prey species in invaded coastal communities.

ANALYSIS OF THE COMPOSITION OF OSMOTICALLY ACTIVE PROTEIN FRACTION IN BLOOD SERUM FROM ATLANTIC COD <i>GADUS MORHUA</i>

A search and identification of osmotically active proteins (OAP) in the composition of blood serum anodic fraction from Atlantic cod Gadus morhua were undertaken using polyacrylamide gel electrophoresis and MALDI mass-spectrometry. 17 OAP have been identified. According to the annotations of Gene Ontology for candidates, 13 OAP were classified as extracellular and 4 OAP- as intracellular proteins. The relative content of OAP in cod serum was ~50% of the total protein. Extracellular proteins apolipoproteins (in the composition of high-density lipoproteins) and hemopexin were dominated in OAP pool. Moreover, the relative content of ApoA-I was ~25% of the total serum protein. Of the intracellular proteins on the serum proteomic map, low molecular weight fragments of the myosin heavy chain were dominated. The results obtained are consistent with the provisions of the “albumin-free” hypothesis of capillary exchange, which considers multiple extracellular and intracellular proteins from different functional classes as osmotically active plasma proteins of “albumin-free” teleost fish.

Serum Osmotically Active Proteins in the Atlantic Cod Gadus morhua

Serum Osmotically Active Proteins in the Atlantic Cod Gadus morhua

A new in-situ method to estimate fish target strength reveals high variability in broadband measurements

Fish Target Strength (TS) is a requirement for estimating abundance from surveys of pelagic fish using echosounders. This paper describes a novel in-situ method to estimate TS as a function of fish body length (L), according to the standard equation TS = 20 log (L) +b20, where b20 is the species-specific factor to be estimated. We made measurements of TS with a broadband scientific echosounder, which is becoming the new tool of choice in fisheries acoustics due to its enhanced signal-to-noise ratio, and higher range resolution and the ability to measure the frequency response. A split-beam 38 kHz broadband transducer was pole-mounted on a small boat in the fjords of Nuuk, Greenland. With the boat stationary, individual Atlantic cod Gadus morhua were detected as echotraces, caught with a fishing line, measured in length and then released. Video footage, from a camera attached to the line, was inspected to verify a single individual was attracted to the lure and caught. Fish echotrace tracking techniques were applied to estimate the tilt of the fish from each acoustic sample and the measured TS was adjusted accordingly with the use of a Kirchhoff-Approximation scattering model. The b20 parameter was estimated by linear regression. This method combines the benefits of associating TS from single fish of known length, which is typical of ex-situ methods, with the in-situ advantages of measuring TS of an undisturbed fish in its natural environment. Results yielded a b20 of − 65.6 dB ( ± 0.83 dB C.I.), which is within the range of previously published values for Atlantic cod measured with narrowband systems. Large variability of TS was observed within fish tracks (average s.d. of 5.55 dB). This is the first description of TS for Atlantic cod with broadband equipment. The high variability could not be attributed to variation in fish length nor tilt angle. Other physiological and behavioural aspects were also discarded. It is possible that this may be an intrinsic property of broadband acoustics, which indicates a need for re-evaluating TS to length relationships as fisheries science moves towards the wider application of broadband acoustics.

Effects of weathered polyethylene microplastic ingestion on sexual maturation, fecundity and egg quality in maturing broodstock Atlantic cod Gadus morhua

Microplastics (MPs) have become a global issue as they are omnipresent in the ocean. Fish ingesting MPs through feed could be affected in their physiological function, e.g., disrupted enzyme production and function, reduction of feeding and reproductive failure. This study assessed the effects of feed containing naturally weathered MPs from the Oslofjord (Norway) on the reproductive physiology of Atlantic cod (Gadus morhua). Farmed cod broodstock were fed either control (C-diet) or feeds containing 1% microplastic (MP-diet) starting nine months prior to spawning, from June until May. No major differences were found between diet groups in overall biometrics or gonad histology. Sex steroid levels (testosterone, 11-ketotestosterone and 17β-estradiol) resulted in expected profiles increasing over time without any significant differences between treatments. Gene expression levels of the steroidogenic enzyme 20β-hydroxysteroid dehydrogenase (20β-hsd) and vitellogenin1 (vtg1) showed significant differences between dietary treatments with lower expression in the control group. This can be a direct effect of MPs, but endocrine disrupting effects of potentially leachable plastic additives cannot be completely ruled out. Thus, these enzymes could be indicators of exposure to contaminants that disrupt sexual maturation by affecting the production of primarily maturation-inducing steroid. Although the concentration of MPs employed in this study may not be high enough to elicit any observable short-term biological effects, the observed gene expression suggests that long-term consequences should be considered caused by an expected increase of MPs in marine environments.

Effect of sea cage aquaculture on the length, weight, and condition of wild Atlantic cod Gadus morhua

Wild fish have been shown to associate with sea cage aquaculture and consume waste feed; however, little is known about the effects of waste feed consumption on wild fish. We used Atlantic cod Gadus morhua collected in the direct vicinity of sea cages and reference Northwest Atlantic Fisheries Organization divisions, either outside the direct vicinity (‘local division’) or completely removed from aquaculture (‘outside divisions’), to compare length, weight, and condition for cod ages 2 to 4. Concentrations of vegetable oil-based fatty acids (linoleic acid and α-linolenic acid) were then used as biomarkers for waste feed consumption to determine their role in explaining differences in length, weight, and Fulton’s condition index among cage-associated cod. Age 2 cage-associated cod were in lower condition than age 2 cod from the local division and lighter than age 2 cod from all outside divisions. Age 3 cage-associated cod were comparable to age 3 cod from the local division but in lower condition than age 3 cod from all outside divisions. However, age 4 cage-associated cod were longer and heavier than age 4 cod from the local division, but in lower condition than age 4 cod from 2 of 3 outside divisions. Additionally, there were positive relationships between fatty acid concentrations and length and weight for age 2 cage-associated cod, but no significant relationships for age 3 or 4 cage-associated cod. Results suggest the effects of waste feed consumption are contradictory but not consistent enough to disrupt established growth and condition patterns among divisions.

Condition, size, and winter duration affect winter survival probability of juvenile Atlantic cod Gadus morhua in a coastal subarctic ecosystem

Juvenile Atlantic cod Gadus morhua in coastal Newfoundland, Canada, settle in nearshore habitats in 3-6 pulsed events each year, from mid-summer to early winter, creating a broad size range of age-0 fish within each year-class, with potentially different survival trajectories entering their first winter. We hypothesized that early-arriving pulses, high autumn body condition, and low winter severity would contribute to high first-winter survival of age-0 cod. To test these hypotheses, we examined juvenile cod catch data, archived samples, and winter temperature records to determine the impact of winter duration, body condition, and settlement time on winter survival from 2001 to 2019. Settlement pulse, pre-winter condition, and winter duration had an interactive effect on survival. Fish condition did not vary across pulses within a given year-class, but we observed improved winter survival during long winters when body condition was high, with highest survival among the larger, early-arriving pulses of fish. Late-arriving pulses of fish were small-sized before winter onset, but these pulses unexpectedly survived better than pulses settling earlier in the season during short winters when body condition was high. However, all settlement pulses had a survival advantage when settlement occurred earlier on average (associated with warmer autumns), suggesting that increased growth and size within a pulse can also contribute to overwintering success. Our findings challenge some assumptions of overwintering ecology (e.g. ‘bigger is better’, low temperature stress) but illustrate the importance of cohort effects for overwintering survival in a sub-arctic marine ecosystem in a changing climate.

High-frequency depth changes in Atlantic cod studied with implanted data storage tags

The main aim of this study was to investigate high-frequency depth changes in wild adult Atlantic cod Gadus morhua. The analysis was based on depth measurements collected with implanted data storage tags. The study was part of a ranching project carried out in an Icelandic fjord. In the project, net bags with frozen fish were regularly provided during the daytime at 4 stations where some cod formed distinct ‘herds’ (‘herd cod’) that did not mingle much with the rest of the unconditioned cod in the fjord (‘wild cod’). After tagging, some of the cod resumed life in the herds, whereas other cod left the herds immediately. On 20 subsequent Mondays, the electronic tags were programmed to measure at the highest frequency (every 30 s), and these results were used to study high-frequency depth changes in 4 wild cod and 4 herd cod, the latter as a control group. Several times, rapid cyclical depth changes were observed in both groups. This behaviour, which sometimes lasted for hours, was highest during dawn and dusk in wild cod but peaked during daytime in herd cod after deployment of the feed bags. The occurrence and properties of these vertical undulations varied greatly between fish, dates, and time of day. Most commonly, the periods of the cycles varied between 1 and 4 min and the heights between 2 and 4 m, but there were examples of much larger undulations. The results indicate that wild adult cod swim along vertically undulating paths when searching for prey, most likely to optimize foraging.

Increase in bycatch rates of plunge- and surface-feeding seabirds observed while setting and hauling bottom set gillnets equipped with LED lights

Seabird bycatch in gillnets is a worldwide problem with few if any available mitigation tools. LED lights attached to the gillnets have been suggested as a potential solution, and a study in Peru showed promising results where bycatch of diving seabirds was reduced by adding LED lights to bottom set gillnets. In this study the potential bycatch reduction of LED lights was tested in a set gillnet fishery that targets Atlantic cod Gadus morhua in Iceland. A variety of seabirds such as common guillemots, cormorants, eiders, northern gannets, northern fulmars, and gulls have been observed as bycatch in that fishery. In a paired trial, nets with and without LEDs were fished off a commercial gillnetter in western Iceland. The LED-equipped net sets caught significantly more seabirds while a slight but statistically insignificant reduction in fish catches was also observed. The seabirds caught in the LED-equipped nets were mainly northern gannets and northern fulmars, plunge- and surface-feeding birds, which seemed to be attracted to the lights while hauling and setting the nets. Caution should be taken when implementing the use of LED lights on gillnets or trawls as while they might reduce bycatch of some taxa of diving seabirds or sea turtles, it is possible that some bird species or groups of bird species are attracted to the lights, in particular during hauling and setting of the nets.

Jan Mayen—a new spawning and fishing area for Atlantic cod Gadus morhua

In 2018, commercially exploitable concentrations of Atlantic cod Gadus morhua were found on the shelf around the Arctic island Jan Mayen (7 1°N, 8–9 °W) and in 2019–2021 an exploratory cod fishery with longline was carried out in the area. The total catch in the period 2018–2021 was 1737 tonnes. The first records of cod fishery in the Jan Mayen area are from the early 1930s but catches before 2018 were minimal. In 2019–2020 cod spawning was documented in this area for the first time. Catches in 2019 and 2020 were dominated by cod between 70 and 100 cm, while in 2021 the main part of the catches was cod between 60 and 100 cm. Catch rates were highest in autumn. We summarize the history of cod observations and the experience from the recent exploratory fishery in this shelf area where there has been no regular monitoring of demersal fish abundance. Further, we consider possible links with cod stocks in other Arctic and sub-Arctic areas and discuss the occurrence of cod in the Jan Mayen area in relation to the biology and recent development of other cod stocks.

ПОИСК И ИДЕНТИФИКАЦИЯ ОСМОТИЧЕСКИ АКТИВНЫХ БЕЛКОВ В СЫВОРОТКЕ КРОВИ АТЛАНТИЧЕСКОЙ ТРЕСКИ GADUSMORHUA

A search for osmotically active proteins (OAPs) in the blood serum of the Atlantic cod Gadus morhua was undertaken using polyacrylamide gel electrophoresis methods. OAPs were identified using MALDI mass spectrometry. The results showed the presence of multiple OAPs in the anodic fraction of cod serum, among which hemopexins, inhibitors of serine proteinases and apolipoproteins in the composition of high density lipoproteins dominate. Minor OAPs were represented mainly by intracellular proteins. The osmot-ically active protein albumin, characteristic of mammals, was not found in cod's blood serum. The results of the work confirm the provisions of the “albumin-free” hypothesis of capillary exchange (Andreeva, 2020), which considers multiple proteins of different functional classes as osmotically active protein factors in the plasma of “albumin-free” teleost fish.

Population Status, Breeding Biology and Diet of Norwegian Great Cormorants

Two subspecies of the Great Cormorant breed in Norway, the continental Phalacrocorax carbo sinensis in the south, along the Skagerrak coast, and the marine P. c. carbo from central Norway and northwards. Here we review the information existing until 2017 on population status and trends, breeding performance and diet of these two subspecies in Norway. The most recent national population estimates are approximately 2500 (in 2012) and 19,000 (in 2012–2014) breeding pairs of sinensis and carbo, respectively. The sinensis population established itself in 1996 in Rogaland at the south-western tip of Norway, and in 1997 in Østfold close to the Swedish border; in both areas it increased for about ten years. Since then, the numbers have stabilised. For carbo, the population increased from 21,000 pairs in the early 1980s to 27,000 in 1995, and then decreased to the current number of 19,000 pairs. Significant annual variations in clutch size and reproductive output have been observed, but the drivers of these changes have not been identified. Unidentified gadoids and Atlantic Cod Gadus morhua were the most common prey of carbo, whereas inshore species such as Corkwing Wrasse Symphodus melops, Rockcook Centrolabrus exoletus, Goldsinny Wrasse Ctenolabrus rupestris and Black Goby Gobius niger were the most common prey in the eastern Skagerrak caught by sinensis. Carbo took very large numbers of 1–3-year-old gadoids during the year, and we cannot exclude the possibility this can have local effects on fish mortality rates.

Comment on “Five centuries of cod catches in eastern Canada,” by Schijns et al

Abstract Schijns et al. use a historical time series to inform a stock assessment model for the northern Atlantic cod (Gadus morhua) fishery from 1508 to 2019. They find that catches from the sixteenth century to the 1950s did not exceed 200000 t per annum and could have been sustained today “if fishing effort and mortality had been stabilized in the 1980s”. Had Schijns et al. used a more complete and representative time series (as identified below), they would have found that catches were substantially higher during much of the time period, possibly affecting their conclusions regarding the timing and onset of unsustainable exploitation. In an earlier paper, based on original archival documentation, we have argued that total landings in the Newfoundland fishery averaged 400000 t in the eighteenth century and peaked at 600000 t in 1788. We contend that pre-industrial technology was sufficient to have a significant impact on marine life.

Fish Skin Grafts with Omega-3 for Treatment of Chronic Wounds: Exploring the Role of Omega-3 Fatty Acids in Wound Healing and A Review of Clinical Healing Outcomes.

Chronic, non-healing wounds, such as diabetic foot ulcers and venous leg ulcers, have a significant economic impact on healthcare and are associated with elevated patient morbidity. Among the toolset of treatment options available to clinicians, skin grafts from other species (xenografts) are often used to promote wound closure. While porcine xenografts have been the most used skin xenograft over the years, acellular fish skin grafts from Atlantic cod (Gadus morhua) have steadily gained traction in usage. Unlike other skin grafts, acellular fish skin grafts have a substantial lipid profile primarily composed of omega-3 fatty acids, notably eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Fish oil supplementation has been shown to result in faster rates of wound epithelialization, and omega 3 fatty acids provide barrier protection against bacteria and alter the inflammatory profile of wounds. EPA and DHA have been shown to have modulatory effects on the progression of wound healing. These characteristic omega-3 fatty acids and their metabolites alter skin physiology at a cellular and molecular level. Clinically, fish skin grafts continually demonstrate increased efficacy in treatment of wounds. When applied to non-responsive diabetic foot ulcers, acellular fish skin grafts have resulted in accelerated healing rates and significantly more fully healed wounds when compared to standard options. Here, we explore the role of omega-3 fatty acids in wound regeneration and repair, with particular focus on EPA and DHA. Then, we review clinical research outcomes to address notable clinical research studies and highlight the therapeutic potential of fish skin grafts with omega-3 as a treatment for chronic, non-healing wounds.