Small pelagic fish dynamics: a review of mechanisms in the Gulf of Lions

Type Article
Date 2019-01
Language English
Author(s) Saraux Claire1, Van Beveren Elisabeth1, 2, Brosset Pablo1, 2, Queiros Quentin1, Bourdeix Jean-Herve1, Dutto Gilbert3, Gasset Eric1, Jac Cyrielle1, Bonhommeau SylvainORCID1, 4, Fromentin Jean-Marc1
Affiliation(s) 1 : Univ Montpellier, MARBEC, CNRS, Ifremer,IRD, Sete, France.
2 : Fisheries & Oceans Canada, Maurice Lamontagne Inst, 850 Route Mer, Mont Joli, PQ G5H 3Z4, Canada.
3 : IFREMER, Chemin Maguelone, F-34250 Palavas Les Flots, France.
4 : IFREMER, Delegat Ocean Indien, Rue Jean Bertho,BP60, F-97822 Le Port, France.
Source Deep-sea Research Part Ii-topical Studies In Oceanography (0967-0645) (Pergamon-elsevier Science Ltd), 2019-01 , Vol. 159 , P. 52-61
DOI 10.1016/j.dsr2.2018.02.010
WOS© Times Cited 1
Keyword(s) Population dynamics, Top-down, Disease, Zooplankton, Exploited species, Bottom-up
Abstract

Around 2008, an ecosystem shift occurred in the Gulf of Lions, highlighted by considerable changes in biomass and fish mean weight of its two main small pelagic fish stocks (European anchovy, Engraulis encrasicolus; European sardine, Sardina pilchardus). Surprisingly these changes did not appear to be mediated by a decrease in fish recruitment rates (which remained high) or by a high fishing pressure (exploitation rates being extremely low). Here, we review the current knowledge on the population's dynamics and its potential causes. We used an integrative ecosystem approach exploring alternative hypotheses, ranging from bottom-up to top-down control, not forgetting epizootic diseases. First, the study of multiple population characteristics highlighted a decrease in body condition for both species as well as an important decrease in size resulting both from a slower growth and a progressive disappearance of older sardines. Interestingly, older sardines were more affected by the decrease in condition than younger ones, another sign of an unbalanced population structure. While top-down control by bluefin tuna or dolphins, emigration and disease were mostly discarded as important drivers, bottom-up control mediated by potential changes in the plankton community appeared to play an important role via a decrease in fish energy income and hence growth, condition and size. Isotopic and stomach content analyses indicated a dietary shift pre- and post-2008 and modeled mesozooplankton abundance was directly linked to fish condition. Despite low energy reserves from 2008 onwards, sardines and anchovies maintained if not increased their reproductive investment, likely altering the life-history trade-off between reproduction and survival and resulting in higher natural mortality. The current worrying situation might thus have resulted from changes in plankton availability/diversity, which remains to be thoroughly investigated together with fish phenotypic plasticity.

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Saraux Claire, Van Beveren Elisabeth, Brosset Pablo, Queiros Quentin, Bourdeix Jean-Herve, Dutto Gilbert, Gasset Eric, Jac Cyrielle, Bonhommeau Sylvain, Fromentin Jean-Marc (2019). Small pelagic fish dynamics: a review of mechanisms in the Gulf of Lions. Deep-sea Research Part Ii-topical Studies In Oceanography, 159, 52-61. Publisher's official version : https://doi.org/10.1016/j.dsr2.2018.02.010 , Open Access version : https://archimer.ifremer.fr/doc/00427/53861/