13 Jan 2023
 | 13 Jan 2023

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

Anna-Marie Winter, Nadezda Vasilyeva, and Artem Vladimirov

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: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1248', Anonymous Referee #1, 21 Feb 2023
    • AC1: 'Reply on RC1', Nadezda Vasilyeva, 10 May 2023
  • RC2: 'Comment on egusphere-2022-1248', Anonymous Referee #2, 31 Mar 2023
    • AC2: 'Reply on RC2', Nadezda Vasilyeva, 10 May 2023
  • EC1: 'Comment on egusphere-2022-1248', Kenneth Rose, 31 Mar 2023
    • AC3: 'Reply on EC1', Nadezda Vasilyeva, 10 May 2023

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.