Seabird‐induced natural mortality of forage fish varies with fish abundance: Evidence from five ecosystems

Type Article
Date 2021-03
Language English
Author(s) Saraux Claire1, 2, Sydeman William J.3, Piatt John F.4, Anker‐nilssen Tycho5, Hentati‐sundberg Jonas6, Bertrand Sophie7, Cury Philippe M.7, Furness Robert W.8, Mills James A.9, 10, Österblom Henrik11, Passuni Giannina12, Roux Jean-Paul13, 14, Shannon Lynne J.15, Crawford Robert J. M.16
Affiliation(s) 1 : IPHC CNRS Université de Strasbourg Strasbourg, France
2 : MARBEC CNRS IRD IFREMER Université de Montpellier Sète ,France
3 : Farallon Institute for Advanced Ecosystem Research Petaluma CA ,USA
4 : US Geological Survey Alaska Science Center Anchorage AK ,USA
5 : Norwegian Institute for Nature Research Trondheim, Norway
6 : Department of Aquatic Resources Swedish University of Agricultural Sciences Lysekil ,Sweden
7 : IRD UMR MARBEC (Université de Montpellier/CNRS/IRD/IFREMER) Sète, France
8 : University of Glasgow Glasgow, UK
9 : Kaikoura, New Zealand
10 : Corning NY ,USA
11 : Stockholm Resilience centre Stockholm University Stockholm, Sweden
12 : Institute of Hydrobiology and Fisheries Science University of Hamburg Hamburg ,Germany
13 : Namibia Nature Fundation and SEACODE Lüderitz ,Namibia
14 : Ministry of Fisheries and Marine Resources Lüderitz, Namibia
15 : Department of Biological Sciences University of Cape Town Cape Town, South Africa
16 : Department of Environment, Forestry and Fisheries Branch Oceans and Coasts Cape Town, South Africa
Source Fish And Fisheries (1467-2960) (Wiley), 2021-03 , Vol. 22 , N. 2 , P. 262-279
DOI 10.1111/faf.12517
WOS© Times Cited 7
Keyword(s) Benguela, Baltic Sea, Humboldt, predator-prey, prey consumption, Shetland
Abstract

Forage fish populations often undergo large and rapid fluctuations in abundance. However, most of their predators are buffered against such fluctuations owing to their slower pace of life, which allows them to maintain more stable populations, at least during short periods of food scarcity. In this study, we investigated top‐down processes exerted by seabirds on forage fish stocks in five contrasted marine ecosystems, compiling numerous data sets on seabird counts, diets, energetic needs and prey energy content and abundance. Off Norway, South Africa, Peru, Sweden and Scotland, we found that predation pressure—estimated as the proportion of a fish stock consumed by seabirds—was generally low (median = 1%), but increased sharply at low levels of prey abundance. When prey biomass decreased below 15–18% of its maximum recorded value, predation by seabirds became a source of important additional pressure on prey stocks (~20% of prey biomass is consumed by seabirds). An earlier empirical study advocated for keeping forage stocks from falling below a threshold of 33% of long‐term maximum prey biomass in order to safeguard seabird breeding success, but here we further suggest that a threshold of 18% should be considered as a limit not to be exceeded for the sake of the forage fish themselves, and below which extra cautious management of fisheries may be required. Nevertheless, despite exceptionally high rates of predation on some occasions, predation pressure was not correlated with prey dynamics, suggesting an absence of prey entrapment due to seabirds alone in these five ecosystems.

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Saraux Claire, Sydeman William J., Piatt John F., Anker‐nilssen Tycho, Hentati‐sundberg Jonas, Bertrand Sophie, Cury Philippe M., Furness Robert W., Mills James A., Österblom Henrik, Passuni Giannina, Roux Jean-Paul, Shannon Lynne J., Crawford Robert J. M. (2021). Seabird‐induced natural mortality of forage fish varies with fish abundance: Evidence from five ecosystems. Fish And Fisheries, 22(2), 262-279. Publisher's official version : https://doi.org/10.1111/faf.12517 , Open Access version : https://archimer.ifremer.fr/doc/00655/76693/