Overview (adapted from the proposal)
Some long-term studies of marine predators, mainly seabirds and seals, have revealed relationships between prey density or abundance and indices of predator performance. In other cases no relationship can be detected. We collated information from several marine ecosystems of the world to search for functional relationships and model their form. Where functional relationships were observed, they generally exhibited non-linearity, often with thresholds. This is caused in part by the behavioural plasticity of predators that allows them to harvest sufficient food above some threshold of prey density. Below the threshold, predators have difficulty obtaining sufficient food as is reflected by rapid changes in demographic or foraging parameters. In our analyses, thresholds were identified using standard models and T-GAM (Threshold Generalized Additive Models). In cases where functional relationships were not observed, the predators involved generally had a high capacity for buffering against fluctuations in food abundance. In other cases, data were insufficient to model responses, for example, when there was not enough contrast in prey density. We believe that thresholds are a fundamental feature of predator-prey relationships that can be used to quantify the minimum prey biomass needed to sustain marine predators. They are needed to determine precautionary reference points above which prey abundance should be maintained by fisheries managers, as mandated in an Ecosystem Approach to Fisheries (EAF) currently adopted by many fisheries organizations.
The general objective of this Foresight Workshop is to assemble relevant world long-term data series on top-predators versus the abundance of their prey in the marine environment. Using data, we will explore the drastic changes in food abundance affecting land-breeding marine predator populations (birds, mammals) and their direct/indirect effect on marine ecosystems (many predators suffer from lack of food in the marine environment). At present, there are a number of indicators at the European level (cf. The European Marine Strategy Framework Directive) that are not substantiated by real observations and/or reference points. This is particularly the case for marine top predators so that the amount of prey that is needed to sustain their populations is unknown or calculated theoretically. This FWS will deliver a strategy to evaluate (from the observations) the threshold values for prey species. It is expected that this FWS will stimulate research on the challenging topic of trophic interactions in marine ecosystems by combining modelling and empirical approaches. It will also build a group that will address the inclusion in ecosystem models of land-based, marine top predators and will propose a methodology for defining how much food should be left in the sea for those predators.
Organizing scientists and institutions
- Philippe Cury, IRD, France
- Lynne Shannon, UCT, South Africa
- A vision and a roadmap of how this group will structure its activities within EUR-OCEANS in the future to respond to the challenge of understanding and implementing (in ecosystem models and in ecosystem-based indicators) interactions between land-breeding marine predators and forage resources (an important and unsolved issue). An executive summary will be written during the FWS to synthesize the vision and the roadmap.
- A reference paper published in a high profile journal that will be the first approach to exploring thresholds of prey necessary for land-breeding marine predators at the world level and that should consider all available long-term data sets.
To keep the group efficient, its size will be limited, selecting only the international experts that can deliver the expertise and the long-term data on this issue. Additional EUR-OCEANS participants will be considered as long as they contribute significantly to the present dynamics. Foreseen participants include: •Philippe Cury, IRD, France •Elisa Goya, IMARPE, Peru •John F. Piatt, Marrowstone Marine Station, USGS, Alaska •Robert Furness, Institute of Biomedical and Life Sciences, Shetland •Jean-Paul Roux, Ministry of Fisheries and Marine Resources, Namibia •Ian L. Boyd , University of St Andrews, UK •Robert J.M. Crawford, Department of Environmental Affairs, South Africa •Lynne J. Shannon UCT, South Africa •Yunne Jai Shin, IRD, France/South Africa •Eugene Murphy, BAS, UK •Tycho Anker-Nilssen, Norwegian Institute for Nature Research, Norway •James A. Mills, New Zealand •Bill Sydeman, Farallon Institute, Petaluma, California •Sylvain Bonhommeau, Ifremer, France
The foresight workshop led to the publication of an article in Science. The article is co-authored by Philippe M. Cury, Ian L. Boyd, Sylvain Bonhommeau, Tycho Anker-Nilssen, Robert J. M. Crawford, Robert W. Furness, James A. Mills, Eugene J. Murphy, Henrik Österblom, Michelle Paleczny, John F. Piatt, Jean-Paul Roux, Lynne Shannon and William J. Sydeman.
- P. M. Cury et al., Global Seabird Response to Forage Fish Depletion—One-Third for the Birds, Science 334, 6063 (2011) - http://www.sciencemag.org/content/334/6063/1703.abstract
The New York Times derived a paper (22 Dec. 2011) from this scientific article (http://www.nytimes.com/2011/12/22/science/scientists-urge-protection-of-forage-fish-for-seabirds-sake.html?_r=2&src=twrhp).
For a brief comment of these publications, please refer to the following news on this website: http://www.eur-oceans.eu/?q=node/28872