Extrapolating predation mortalities back in time: an example from North-east Arctic cod cannibalism

Kovalev, Yury; Chetyrkin, A. A.

doi:10.1080/17451000.2017.1396342

Cited by 7 publications

(3 citation statements)

References 15 publications

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“…The Russian quantitative data from the joint database and the qualitative Russian diet data , which are not yet fully digitized, are not publicly available due to the institution policy, but access to these data is granted through contracted collaboration in joint projects with the Polar Branch of VNIRO. Summaries, descriptions and analyses of the Russian data can be found in the following publications: Zenkevich and Brotskaya (1931), Zatsepin and Petrova (1939), Mehl and Yaragina (1992), Dolgov et al (2007), Dolgov (2011), Holt et al (2019), Yaragina et al (2009), and Yaragina and Dolgov (2011).…”

Section: Data Availabilitymentioning

confidence: 99%

Diets of the Barents Sea cod (<i>Gadus morhua</i>) from the 1930s to 2018

Townhill

Holt

Bogstad

et al. 2021

Earth Syst. Sci. Data

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Abstract. 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). The UK and Norwegian data (Townhill et al., 2020) are being released with this paper at https://doi.org/10.21335/NMDC-2139169383.

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Section: Data Availabilitymentioning

confidence: 99%

Diets of the Barents Sea cod (<i>Gadus morhua</i>) from the 1930s to 2018

Townhill

Holt

Bogstad

et al. 2021

Earth Syst. Sci. Data

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“…Both environmental and biological factors have for many years been included in predictions of cod recruitment (ICES, 2020). Cod cannibalism and its inverse relationship with capelin abundance is one important factor affecting cod recruitment (e.g., Yaragina et al, 2009Yaragina et al, , 2018. More generally, considerations of trophic interactions and their impacts on important stocks like cod, haddock, and capelin, and their incorporation into stockassessment and/or strategic models, have been in operation in fisheries decision-making frameworks in the BS since the 1990s (Howell and Bogstad, 2010;Bogstad and Filin, 2011).…”

Section: Discussionmentioning

confidence: 99%

Comparative Modeling of Cod-Capelin Dynamics in the Newfoundland-Labrador Shelves and Barents Sea Ecosystems

2021

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The Atlantic cod (Gadus morhua) stocks in the Newfoundland-Labrador Shelves (NL) and Barents Sea (BS) ecosystems have shown divergent trajectories over the last 40 years. Both stocks experienced either an important decline (BS) or a collapse (NL) in the mid-1980s and early 1990s, respectively. After these population reductions, the BS stock quickly rebounded and it is currently at record high levels, while the NL stock, despite showing some improvement since the mid-2000s, remains at low levels. Fishing and environmental conditions are known to be important drivers of cod dynamics in both ecosystems, especially the availability of high energy prey like capelin (Mallotus villosus), however, the question of how different or similar these two stocks truly are remains. Could, for example, the NL cod stock rebuild if presented to conditions like the ones experienced by BS cod? To explore such questions, we developed a simple biomass dynamic model for cod using a bioenergetic-allometric approach. This model includes fisheries catches and capelin availability as external drivers and was implemented for both ecosystems. Despite the contrasting trends, the model produced very good fits, and showed some remarkably similar estimated parameters in both systems. We explored these similarities by (a) performing the thought experiment of transferring cod stocks between ecosystems by switching estimated key parameters between models and comparing the output, and (b) implementing an integrated model architecture which allowed fitting common parameters for both stocks to evaluate the similarity of key vital rates. Our results indicate that cod trajectories in NL and BS can be reliably described using simple bioenergetic-allometric arguments, fishery catches, and capelin availability. Model parameters that encapsulate intrinsic vital rates were not significantly different between stocks. This indicates that NL and BS cod stocks are biologically similar, and that the differences in their trajectories are driven by the ecosystem context in which these stocks are embedded, and suggests that the NL stock would be expected to rebuild if enough capelin were available. This also indicates that capelin status and trend should be an important consideration for effective management of these cod stocks.

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“…Although many piscivores in the region feed on capelin, cod is by far their primary predator, consuming more than three million t per year (Dolgov 2002). Amplified year-to-year fluctuations in capelin in the 1980s and 1990s also shaped cod biomass rebuilding patterns: for example, cod cannibalism peaked after capelin collapses (Yaragina and Kovalev 2018). The collapses, particularly the first one, propagated further through the rest of the food web (Gjøsaeter and Bogstad 2009).…”

Section: Study Systemmentioning

confidence: 99%

Tradeoffs of managing cod as a sustainable resource in fluctuating environments

Goto

Filin

Howell

et al. 2021

Ecological Applications

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Sustainable human exploitation of living marine resources stems from a delicate balance between yield stability and population persistence to achieve socioeconomic and conservation goals. But our imperfect knowledge of how oceanic oscillations regulate temporal variation in an exploited species can obscure the risk of missing management targets. We illustrate how applying a management policy to suppress fluctuations in fishery yield in variable environments (prey density and regional climate) can present unintended outcomes in harvested predators and the sustainability of harvesting. Using Atlantic cod (Gadus morhua, an apex predatory fish) in the Barents Sea as a case study we simulate age‐structured population and harvest dynamics through time‐varying, density‐dependent and density‐independent processes with a stochastic, process‐based model informed by 27‐year monitoring data. In this model, capelin (Mallotus villosus, a pelagic forage fish), a primary prey of cod, fluctuations modulate the strength of density‐dependent regulation primarily through cannibalistic pressure on juvenile cod survival; sea temperature fluctuations modulate thermal regulation of cod feeding, growth, maturation, and reproduction. We first explore how capelin and temperature fluctuations filtered through cod intrinsic dynamics modify catch stability and then evaluate how management to suppress short‐term variability in catch targets alters overharvest risk. Analyses revealed that suppressing year‐to‐year catch variability impedes management responses to adjust fishing pressure, which becomes progressively out of sync with variations in cod abundance. This asynchrony becomes amplified in fluctuating environments, magnifying the amplitudes of both fishing pressure and cod abundance and then intensifying the density‐dependent regulation of juvenile survival through cannibalism. Although these transient dynamics theoretically give higher average catches, emergent, quasicyclic behaviors of the population would increase long‐term yield variability and elevate overharvest risk. Management strategies that overlook the interplay of extrinsic (fishing and environment) and intrinsic (life history and demography) fluctuations thus can inadvertently destabilize fish stocks, thereby jeopardizing the sustainability of harvesting. These policy implications underscore the value of ecosystem approaches to designing management measures to sustainably harvest ecologically connected resources while achieving socioeconomic security.

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Extrapolating predation mortalities back in time: an example from North-east Arctic cod cannibalism

Cited by 7 publications

References 15 publications

Diets of the Barents Sea cod (<i>Gadus morhua</i>) from the 1930s to 2018

Diets of the Barents Sea cod (<i>Gadus morhua</i>) from the 1930s to 2018

Comparative Modeling of Cod-Capelin Dynamics in the Newfoundland-Labrador Shelves and Barents Sea Ecosystems

Tradeoffs of managing cod as a sustainable resource in fluctuating environments

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Extrapolating predation mortalities back in time: an example from North-east Arctic cod cannibalism

Cited by 7 publications

References 15 publications

Diets of the Barents Sea cod (&lt;i&gt;Gadus morhua&lt;/i&gt;) from the 1930s to 2018

Diets of the Barents Sea cod (&lt;i&gt;Gadus morhua&lt;/i&gt;) from the 1930s to 2018

Comparative Modeling of Cod-Capelin Dynamics in the Newfoundland-Labrador Shelves and Barents Sea Ecosystems

Tradeoffs of managing cod as a sustainable resource in fluctuating environments

Contact Info

Product

Resources

About

Diets of the Barents Sea cod (<i>Gadus morhua</i>) from the 1930s to 2018

Diets of the Barents Sea cod (<i>Gadus morhua</i>) from the 1930s to 2018