Ecosystem-based management objectives for the North Sea: riding the forage fish rollercoaster

Abstract

Dickey-Collas, M., Engelhard, G. H., Rindorf, A., Raab, K., Smout, S., Aarts, G., van Deurs, M., Brunel, T., Hoff, A., Lauerburg R. A. M., Garthe, S., Haste Andersen, K., Scott, F., van Kooten, T., Beare, D., and Peck, M. A. Ecosystem-based management objectives for the North Sea: riding the forage fish rollercoaster. – ICES Journal of Marine Science, 71: . The North Sea provides a useful model for considering forage fish (FF) within ecosystem-based management as it has a complex assemblage of FF species. This paper is designed to encourage further debate and dialogue between stakeholders about management objectives. Changing the management of fisheries on FF will have economic consequences for all fleets in the North Sea. The predators that are vulnerable to the depletion of FF are Sandwich terns, great skua and common guillemots, and to a lesser extent, marine mammals. Comparative evaluations of management strategies are required to consider whether maintaining the reserves of prey biomass or a more integral approach of monitoring mortality rates across the trophic system is more robust under the ecosystem approach. In terms of trophic energy transfer, stability, and resilience of the ecosystem, FF should be considered as both a sized-based pool of biomass and as species components of the system by managers and modellers. Policy developers should not consider the knowledge base robust enough to embark on major projects of ecosystem engineering. Management plans appear able to maintain sustainable exploitation in the short term. Changes in the productivity of FF populations are inevitable so management should remain responsive and adaptive.

European anchovy (Engraulis encrasicolus) age structure and growth rate in two contrasted areas of the Mediterranean Sea: the paradox of faster growth in oligotrophic seas

“…Given the evidence confirmed here of a significant effect of temperature on growth, global warming would be expected to enhance the growth of the youngest age classes but with a reduced effect on the growth in older individuals. This supports the need to integrate effective management of small pelagic fishes with climate-driven variations in productivity, the variety of ecosystem interactions, and the trophic pathways through an ecosystembased approach (Dickey-Collas et al, 2014). Although temperature and primary production show significant effects on anchovy growth, further investigations on the trophic ecology combined with biomass-at-age data are needed in order to evaluate these effects and better understand the mechanisms that control fish production.…”

Prey or predator—expanding the food web role of sandeel Ammodytes marinus

“…This potential may offer an additional explanation for the rollercoaster stock dynamics of many forage fishes (Dickey-Collas et al 2014), which have traditionally been explained by predation mor-tality from higher trophic levels and variation in food availability (Frank et al 2005, Ware & Thomson 2005. Notably, our findings do not disqualify these 2 mechanisms as key drivers of the forage fish rollercoaster but strongly suggest that cannibalism and piscivory deserve a more prominent role in understanding forage fish stock fluctuations, as well as in the bottom-up and top-down paradigms currently dominating analyses of marine trophic cascading and ecosystem shifts (Fauchald 2010, Frank et al 2011.…”

“…This has pronounced ecological and socio-economic consequences and poses a challenge to sustainable fisheries management (Dickey-Collas et al 2014). Several external drivers of these fluctuations have been identified, typically defined in relation to their impact points in the trophodynamic processes of the marine environment as either bottom-up, e.g.…”

“…Internal drivers of the so-called rollercoaster stock dynamics of forage fishes (Dickey-Collas et al 2014) seem to be overlooked in the bottom-up versus topdown paradigm for investigating population dynamics and interactions in the marine ecosystem described above. Cannibalism is widespread among teleosts (Smith & Reay 1991), and theory predicts that cannibalism in general can have profound effects on population structure and dynamics (Kohlmeier & Ebenhöh 1995, Magnússon 1999; cannibalism could thus potentially be a hitherto overlooked co-driver of forage fish population dynamics.…”

Seabird diets as bioindicators of Atlantic herring recruitment and stock size: a new tool for ecosystem-based fisheries management

“…Successful application of this approach, often referred to as ecosystem-based fishery management or EBFM, is widely recognised as essential to the maintenance of healthy marine ecosystems and the communities they support (Christensen et al 1996;Dickey-Collas et al 2013;Skern-Mauritzen et al 2016).…”