Interannual variations in the liver condition index of cod as an indicator of temperature and feeding conditions in the Barents Sea

Background: Northeast Arctic cod, inhabiting the edge of the species area, experience variable environmental conditions and feeding resources, one of the main of them is capelin. Lipids are an important biochemical link between capelin and cod. Lipids constitute approximately 10-15% of the total wet weight of capelin at the peak of their seasonal cycle in lipid accumulation (Jangaard 1974). In contrast, approximately 1% of the wet weight of the muscle tissue of cod is composed of lipids (Lie et al. 1988). The liver is the primary site of stored lipid reserves in cod. These reserves are utilized during periods of food limitation and the annual cycle of gonad maturation. Starved cod can replenish liver reserves rapidly in response to increased food (Karlsen et al. 1995). Lliver weight is likely to be a dynamic index of the physiological condition of cod

Systematic bias in estimates of reproductive potential of cod stocks: implications for stock/recruit theory and management

Stock/recruit relationships, describing the relationship between the parental population and the number of offspring produced, are a central tool in population ecology. For fish populations the stock/recruit relationship uses spawning stock biomass (SSB) to represent reproductive potential of the parental population. This assumes that the proportion of SSB comprised of females and the relative fecundity (number of eggs produced per unit mass) are both constant over time. To test these two constancy assumptions female-only spawner biomass (FSB) and total egg production (TEP) were estimated for the Northeast Arctic cod stock over a 56-year time period (1946-2001). During that time period the proportion of females (FSB/SSB) varied between 24 and 68% and the variation was systematic with length such that SSB became more female-biased as the mean length of spawners increased and more male-biased as mean length decreased. Over the same time period, relative fecundity of the stock (TEP/SSB) varied between 115 and 355 eggs g-1 and, like FSB/SSB, was significantly, positively correlated mean length of spawners. Because both FSB/SSB and TEP/SSB covaried with length composition, SSB is systematically biased estimate of reproductive potential. FSB and TEP were evaluated as possible replacements for SSB in stock/recruit relationship. Both indices gave a different interpretation of the recruitment response to reductions in stock size (over-compensatory) compared to that obtained using SSB (either compensatory or depensatory). The threshold level of stock size below which recruitment becomes impaired was estimated for each of the different stock/recruit relationships using piecewise linear regression. There was no difference between SSB and FSB in the assessment of stock status, however, in recent years (1980-2001) TEP fell below the threshold level more frequently than SSB fell below. This suggests that using SSB as a measure of stock reproductive potential may lead to overly optimistic assessments of stock status

Egg mortality of Northeast Arctic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus)

This is a pre-copyedited, author-produced PDF of an article accepted for publication in ICES Journal of Marine Science following peer review. The definitive publisher-authenticated version ICES J. Mar. Sci. (2013) is available online at: http://dx.doi.org/10.1093/icesjms/fst00

Combined effects of fishing and oil spills on marine fish: Role of stock demographic structure for offspring overlap with oil

It has been proposed that the multiple pressures of fishing and petroleum activities impact fish stocks in synergy, as fishing-induced demographic changes in a stock may lead to increased sensitivity to detrimental effects of acute oil spills. High fishing pressure may erode the demographic structure of fish stocks, lead to less diverse spawning strategies, and more concentrated distributions of offspring in space and time. Hence an oil spill may potentially hit a larger fraction of a year-class of offspring. Such a link between demographic structure and egg distribution was recently demonstrated for the Northeast Arctic stock of Atlantic cod for years 1959–1993. We here estimate that this variation translates into a two-fold variation in the maximal proportion of cod eggs potentially exposed to a large oil spill. With this information it is possible to quantitatively account for demographic structure in prospective studies of population effects of possible oil spills.acceptedVersio

Diets of the Barents Sea cod (Gadus morhua) from the 1930s to 2018

A new dataset on the diet of Atlantic cod in the Barents Sea from the 1930s to the present day has been compiled to produce one of the largest fish diet datasets available globally. Atlantic cod is one of the most ecologically and commercially important fish species in the North Atlantic. The stock in the Barents Sea is by far the largest, as a result of both successful management and favourable environmental conditions since the early 2000s. As a top predator, cod plays a key role in the Barents Sea ecosystem. The species has a broad diet consisting mainly of crustaceans and teleost fish, and both the amount and type of prey vary in space and time. The data – from Russia, Norway and the United Kingdom – represent quantitative stomach content records from more than 400 000 fish and qualitative data from 2.5 million fish. Many of the data are from joint collaborative surveys between Norway and Russia. The sampling was conducted throughout each year, allowing for seasonal, annual and decadal comparisons to be made. Visual analysis shows cod diets have changed considerably from the start of the dataset in the 1930s to the present day. There was a large proportion of herring in the diets in the 1930s, whereas in more recent decades capelin, invertebrates and other fish dominate. There are also significant interannual asynchronous fluctuations in prey, particularly capelin and euphausiids. Combining these datasets can help us understand how the environment and ecosystems are responding to climatic changes, and what influences the diet and prey switching of cod. Trends in temperature and variability indices can be tested against the occurrence of different prey items, and the effects of fishing pressure on cod and prey stocks on diet composition could be investigated. The dataset will also enable us to improve parametrization of food web models and to forecast how Barents Sea fisheries may respond in the future to management and to climate change. The Russian data are available through joint projects with the Polar Branch of the Russian Federal Research Institute of Fisheries and Oceanography (VNIRO).publishedVersio

Advice on fishing opportunities for Northeast Arctic cod in 2023 in ICES subareas 1 and 2

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Report of the Joint Russian-Norwegian Working Group on Arctic Fisheries (JRN-AFWG) 2022

On 30 th March 2022 all Russian participation in ICES was temporally suspended. Although the announcement of the suspension stressed the role of ICES as a “multilateral science organization”, this suspension applied not only to research activities, but also to the ICES work providing fisheries advice for the sustainable management of fish stocks and ecosystems. As a result of the suspension, the ICES AFWG provided advice only for saithe, coastal cod north, coastal cod south, and golden redfish ( Sebastes norvegicus ). Northeast Arctic (NEA) cod, haddock and beaked redfish ( Sebastes mentella ) assessments have been conducted outside of ICES in a newly constituted Joint Russian-Norwegian Working Group on Arctic Fisheries (JRN-AFWG). Although this work has been conducted independently of ICES, the methodologies agreed at ICES benchmarks and agreed HCRs (Harvest Control Rules) have been followed in providing this advice.publishedVersio

Advice on fishing opportunities for beaked redfish in 2023 and 2024 in ICES subareas 1 and 2

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