13 Jan 2023
13 Jan 2023
Status: this preprint is open for discussion.

Spawner weight and ocean temperature drive Allee effect dynamics in Atlantic cod, Gadus Morhua: inherent and emergent density regulation

Anna-Marie Winter1,a, Nadezda Vasilyeva2, and Artem Vladimirov2,3 Anna-Marie Winter et al.
  • 1Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, 0316 Oslo, Norway
  • 2Interdisciplinary Laboratory for Mathematical Modeling of Soil Systems, V.V. Dokuchaev Soil Science Institute, Pyzhevsky per. 7/2, 119017 Moscow, Russian Federation
  • 3Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna Russian Federation
  • acurrently at: Wageningen Marine Research, Wageningen University and Research, Ijmuiden, Netherlands

Abstract. Stocks of Atlantic cod, Gadus Morhua, show diverse recovery responses when fishing pressure is relieved. The expected outcome of reduced fishing pressure is that the population regains its size. However, there are also cod stocks that seem to be locked in a state of low abundance from which population growth does not, or only slowly, occur. A plausible explanation for this phenomenon can be provided by the Allee effect, which takes place when recruitment per capita is positively related to population density or abundance. However, because of methodological limitations and data constraints, such a phenomenon is often perceived as being rare or non-existent in marine fish.

In this study, we used time-series of 17 Atlantic cod stocks to fit a family of population equations that consider the abundance of spawners, their body weight as well as sea water temperature as independent components of recruitment. The developed stock-recruitment function disentangles the effects of spawner abundance, spawner weight and temperature on recruitment dynamics and captures the diversity of density dependencies (compensation, Allee effect) of the recruitment production in Atlantic cod.

The results show for 13 cod stocks an inherent, spawner abundance related Allee effect. Allee effect strength, i.e. the relative change between maximum and minimum recruitment per capita at low abundance, was increased when recruitment production was suppressed by unfavorable changes in water temperature and/or in spawner weight. The latter can be a concomitant of heavy fishing or a result of temperature related altered body growth. Allee effect strength was decreased when spawner weight and/or temperature elevated recruitment production. We show how anthropogenic stress can increase the risk of Allee effects in stocks where ocean temperature and/or spawner weight had been beneficial in the past, but are likely to “unmask” and strengthen an inherent Allee effect under future conditions.

Anna-Marie Winter et al.

Status: open (until 24 Feb 2023)

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Anna-Marie Winter et al.

Anna-Marie Winter et al.


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Short summary
There is an increasing number of fish in poor state, and many do not recover, even when fishing pressure is ceased. An Allee effect can hinder population recovery, because it suppresses the fish's productivity at low abundance. With a model fitted to 17 Atlantic cod stocks, we find that ocean warming and fishing can cause an Allee effect. If present, the Allee effect hinders fish recovery. This shows that Allee effects are dynamic, not uncommon and calls for precautionary management measures.