Marine Research Findings of the VECTORS Project

This website provides access to the research results of the VECTORS project, which can be used to support marine management decisions, policies and governance as well as future research and investment. VECTORS was a large scale project that brought together more than 200 expert researchers from 16 different countries. It examined the significant changes taking place in European seas, their causes, and the impacts they will have on society.

Food-web induced variations of natural mortality of exploited stocks under sustainable management strategy

One of the objectives linked to sustainable fisheries is for European fish stocks to reach sustainable levels by 2015. Classically, the reference sustainable levels are assessed analytically by single-species approach estimating the Maximum Sustainable Yield (MSY), usually with constant natural mortality term. However, while moving towards ecosystem-based fisheries management (EBFM), it is necessary to consider predator-prey relationships when assessing the dynamics of fish stocks. Recently, in the Baltic Sea, the variability of the natural mortality due to predator-prey relationship has been integrated to the assessment of stocks. Here, using an ecosystem model we aim at evaluating the variability of mortality sources under various fishing pressures for several exploited stocks of the eastern English Channel.

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Ecosystem model based on opportunistic predation (OSMOSE) shows that predation mortality undergoes by target stocks varies unpredictably under changing fishing mortality

For a first set of species, when increasing the fishing mortality, the predation mortality decreases but slightly, resulting in increasing total mortality. This illustrates the existence of competition between fisheries and predators, which can switch their diet for more prey.

For a second set of species, increasing fishing mortality leads predation mortality and total mortality both increasing. This pattern has to be linked to the importance of the species in trophic functioning, as the amount of food eaten is not reducing, even under strong fishing pressure.

Lastly, for some species, there is no linear response between changes in fishing mortality and predation mortality. For those species, still to be investigated, an increase in fishing mortality can lead to a switch of ecosystem functioning and thus a different trophic position for the species of interest.

These results are of importance when aiming in short term to reach sustainable levels for all exploited stocks, as they will interact and single-species MSY may not be the reference target to reach if predators and/or competitors are to vary consequently.

Relevance for Policy:
  • Common Fisheries Policy

Lead Author:

Morgane Travers-Trolet
(Morganenospam.Travers@ifremer.fr)
Agrocampus Ouest (AGRO)
Date of research: July 2014

Related articles:

Population dynamics of sprat in the Baltic Sea 

Changes in the upper trophic level: impact on fish

Changes on stocks and management in saithe fishery 

Early life stage survival of Baltic cod

Fish distributions and spatial management measures 

Impact of jellyfish on fisheries and tourism 

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This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 266445
© Vectors 2015. Coordinated by Plymouth Marine Laboratory.