Are Your Sardines Seabird Safe? by Don Orth

Seabirds are the most threatened group of birds (IUCN 2018). Major threats relate to fisheries bycatch and competition. Fishing occurs on more than 55% of ocean area and has a spatial extent more than four times that of agriculture (Kroodsma et al. 2018). This fisheries footprint estimate is made possible by the automatic identification system required on marine vessels for tracking.  Long line (45%), purse seines (17%), and trawls (9.4%) are the three most widespread forms of ocean fishing. Impacts of fishing go well beyond the species targeted for harvest. Bycatch effects are obvious, but industrial fisheries are also implicated in starving seabirds (Grémillet et al. 2016). Recent evidence shows that fisheries compete with seabirds by taking the same fishes, a limited resource, and the take has fitness consequences for seabirds. There is no such thing as a free lunch, or a tuna sandwich that does not have seabird consequences.  

 

Global footprint of fishing coverage.  From Kroodsma et al. (2018).

Gremillett et al (2018) reconstructed global fisheries catches since 1970 to compare with seabird diets. Global harvesting reduced abundance of fish eaten by many seabirds and competition was identified in 48% of all areas, notably the Southern Ocean, Asian shelves, Mediterranean Sea, Norwegian Sea, and Californian coast.  The decrease primarily occurred in the Southern Ocean and in the North Atlantic and was most marked in diving petrels (−66%), terns (−48%), and frigatebirds (−47%).

Competition with fisheries significantly constrains a vanishing seabird community. from Grémillett et al. 2018.

Calls for changes in fisheries management goals began over 40 years ago. Larkin wrote this epitaph for the Maximum Sustained Yield concept (MSY) in 1976 and  OSY, or optimum sustained yield, was the logical successor.  OSY is the deliberate melding of social, economic and biological benefits. Among these many benefits, we seek a unique management goal exists for each fishery that balances the many conflicting goals.  One of the benefits relates to seabirds.  And herein lies the challenge. 

M.S.Y.
1930s-1970s

Here lies the concept, MSY.

It advocated yields too high,

And didn’t spell out how to slice the pie.

We bury it with the best of wishes,

Especially on behalf of fishes.

We don’t know yet what will take its place,

But hope it’s as good for the human race.

R.I.P.

M.S.Y. is still alive and kicking.  However, major databases such as the Data Seabird Information Network, launched by the World Seabird Union, and Tracking Ocean Wanderers database, maintained by BirdLife International can assist in detecting decreasing seabird population trends. We need to get beyond observations, such as this Arctic tern (Sterna paradisaea) eating a sandeel and apply ecosystem-based fisheries management models that consider data on abundance of non-target ecosystem components, including pinnipeds, orcas, seagrasses, cownose rays, whales, cephalopods, and more (Pikitch et al. 2014).  In the mid-Atlantic region we might manage Atlantic Menhaden harvests and protect some menhaden for consumption by Striped Bass, Humpback Whales, and Bluefin Tuna. Black Skimmer, which have declined, also eat Atlantic Menhaden (Gordon et al. 2000) - but how much?  However, the trophic models used for these analyses (Pikitch et al. 2014) make assumptions that need to be tested. Evidence that harvesting forage species competes with other top predators in well-studied US fisheries is equivocal (Hilborn et al. 2017).  

Black-footed Penguin (Spheniscus demersus) pair hunting sardines, Cape Town, South Africa. Photo by Peter Verhoog.

Globally, competition with fisheries should be assessed as one of the numerous stressors acting upon the fitness of individual seabirds, and population trajectories (Grémillett et al. 2016; Lescroël et al. 2016).  It won't be easy to do.  To assess seabird-fisheries competition, we can design and implement localized prey depletion experiments and work to improve the trophic models of intermediate complexity (Sydeman et al. 2017).  No one wants to hear that a lot more research will be needed.

Gannet eats a mackerel.  Photo by Rob Ellis. Flickr

For more sustainable food systems, we should eat less livestock and more seafood low on the food chain (Hilborn et al. 2018).  However, not all fisheries operate in a sustainable manner. To convince consumers to eat sustainable seafood, we need reliable means for evaluating and labeling marine products.  You won’t find a 'seabird safe' label at your seafood market. But how does one know?   That’s the subject for another post.

References

Amélineau F. Fort J. Mathewson P.D. Speirs D.C. Courbin N. Perret S. Porter W.P. Wilson R.J. Grémillet D. 2018. Energyscapes and prey fields shape a North Atlantic seabird wintering hotspot under climate change. Royal Society Open Science 5: 171883

Gordon, C.A., D.A. Cristol, and R.A. Beck. 2000.  Low reproductive success of black skimmers associated with low food availability.  Waterbirds: The International Journal of Waterbird Biology 23:468-474.

 Grémillet D. Péron C. Kato A. Amélineau F. Ropert-Coudert Y. Ryan P.G. Pichegru et al. 2016. Starving seabirds: unprofitable foraging and its fitness consequences in Cape gannets competing with fisheries in the Benguela upwelling ecosystem. Marine Biology 163: 35

 Grémillett,D.,  A. Ponchon, M. Paleczny, M-L. D. Palomares, V Karpouzi and D. Pauly. 2018. Persisting worldwide seabird-fishery competition despite seabird community decline. Current Biology 28:1-5. https://doi.org/10.1016/j.cub.2018.10.051.

 Hilborn, R., R.O. Amorosa, E. Bogazzi, O.P. Jensen, A.M. Parma, C. Szuwalski, and C.J. Walters.  2017.  When does fishing forage species affect their predators?  Fisheries Research 191:211-221.

Hilborn, R., J. Bonobi, S.J. Hall, T. Pucylowski, and T.E. Walsworth.   2018. The environmental cost of animal source foods. Frontiers in Ecology and the Environment 16(6):329-335.

IUCN 2018. The IUCN Red List of Threatened Species, Version 2018-2. http://www.iucnredlist.org.

Kroodsma, D.A., et al. 2018. Tracking the global footprint of fisheries. Science 359:904-908.

Larkin, P.A. 1977. An epitaph for the concept of maximum sustained yield. Transactions of the American Fisheries Society 106:1-11.

Lescroël, A., R. Mathevet, C. Peron, M. Authier, P. Provost, A. Takahashi, and D. Grémillet, D. 2016. Seeing the ocean through the eyes of seabirds: A new path for marine conservation? Marine Policy 68:212–220.

Pikitch, E.K., and nineteen coauthors. 2014. The global contribution of forage fish to marine fisheries and ecosystems. Fish and Fisheries 15(1):43-64. doi:10.1111/faf.12004

Sydeman, W.J., S.A. Thompson. T. Anker-Nilssen, M. Arimitsu, A. Bennison, S. Bertrand, P. Boersch-Supan, C. Boyd, N.C. Bransome, R.J. Crawford et al. 2017.  Best practices for assessing forage fish fisheries-seabird resource competition. Fisheries Research 194:209-221