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Research article2024Peer reviewedOpen access

Occurrence and Strength of Instantaneous and Intracohort Density-Dependence in Northeast Atlantic Fish Stocks

Cardinale, Massimiliano; Bartolino, Valerio; Winker, Henning; Orio, Alessandro; Griffiths, Christopher A.; Kell, Laurie

Abstract

Biological reference points (BRPs) used in fisheries management do not include density-dependent (DD) growth, with DD processes only considered in the stock recruitment relationship. Not accounting for DD on somatic growth has led to criticism that such BRPs underestimate the compensatory effects of DD at low stock size, and therefore risk foregone catch opportunities. Here, we analyse 81 stocks from the Northeast Atlantic for evidence of DD growth, defined as the process in which stock size affects somatic weight. We evaluate the following questions: (1) How many stocks have experienced instantaneous DD growth and do stocks of the same species display similar trends? (2) Is there a common instantaneous DD growth relationship shared by all stocks? (3) For stocks exhibiting significant instantaneous DD growth, can we quantify the strength of the relationship? (4) Is DD growth operating as an intra-cohort process as opposed to an instantaneous effect? Results reveal that only the weight of recruits exhibits a common instantaneous DD growth while the other responses analysed show a positive, noncompensatory effect, suggesting that other processes are at work. All responses examined showed significant temporal autocorrelation, which, when not accounted for, suggest apparent instantaneous DD growth in several stocks. Comparison of instantaneous against intracohort DD growth showed an increase in the number of stocks with significant DD growth, although, as for instantaneous DD growth, this declined greatly when temporal autocorrelation was accounted for. Our results counteract the a priori assumption that DD growth compensation is related only to stock biomass or density, suggesting that DD growth should be dealt case-by-case. Consequently, management practices that aim to fish down stock biomass with the anticipation of triggering DD growth will be associated with greater asymmetric risks than keeping biomass at levels where replacement yield does not rely on it.Around 80% of the tested key productivity parameters exhibit a positive global effect in somatic growth expressed as weight at age as opposed to the classic negative density-dependent relationship when instantaneous growth is analysed. The frequency and strength of density-dependence in weight at age is low and weak at the stock level when instantaneous growth is analysed. Significant temporal autocorrelation exists, which when not accounted for, reveals apparent density-dependence in several stocks when instantaneous growth is analysed. The frequency of detection of density-dependent weight at age increases when intracohort growth is analysed. However, even when considering intracohort growth, spurious density-dependence in several stocks is detected when temporal autocorrelation is not accounted for, with at best 15% of the stocks exhibiting significant classic negative density-dependence. Consequently, management practices that aim to fish down stock biomass with the anticipation of triggering density-dependent growth, will be associated with greater asymmetric risks than keeping biomass at levels where replacement yield does not rely on it.image

Keywords

density-dependence; intracohort analysis; reference points; spawning potential ratio; weight-at-age

Published in

Ecology and Evolution
2024, volume: 14, number: 10, article number: e70375

SLU Authors

Global goals (SDG)

SDG14 Life below water

UKÄ Subject classification

Fish and Aquacultural Science

Publication identifier

  • DOI: https://doi.org/10.1002/ece3.70375

Permanent link to this page (URI)

https://res.slu.se/id/publ/132879