Ethical Debate: Bycatch and the Great Skua

Most marine conservationists and environmentally conscious citizens believe that fisheries bycatch is a major problem that needs to be solved soon. In most cases, they are correct, but an

interesting paper from Nature shows that bycatch can sometimes be good for certain species. Consider the case of the Great Skua.

Image from

The Great Skua is a large predatory seabird that lives in northern Europe. In the past, it has been known to feed on many smaller local seabird species, including the Leach’s Storm Petrel, the Northern Fulmar, the Northern Gannet, the Lesser Black-Backed Gull, and the Herring Gull. In the last few decades, Great Skua populations have increased tremendously.

Ordinarily, when the population of a predator increases, the populations of its prey decrease. This doesn’t seem to be the case among populations of the seabird species in northern Europe. How can this be?

The answer to this apparent ecological enigma has to do with fisheries bycatch. The oceans around northern Europe support many large-scale fisheries, such as the sandeel fishery. Like most large-scale fisheries, the sandeel fishery has a significant amount of bycatch (fish that were caught merely because they were swimming near the sandeel) associated with it. Since the fishermen only have a permit to sell sandeel, the bycatch species  are dumped overboard…where they are devoured by Great Skua.

In other words, Great Skua have found a new steady source of food. Great Skua populations have increased without a decrease in the populations smaller seabirds that they ate in the past.

Modern sentiments, however, have turned against bycatch. Efforts to reduce bycatch in commercial fisheries are underway in many countries worldwide. What will this mean for the seabird communities of northern Europe?

Well, it’s possible (and for the purposes of this discussion, we’ll assume it will definitely happen) that without their new source of food (bycatch dumped over the side of fishing  vessels), Great Skua will return to eating their previous prey- the smaller seabirds of northern Europe. Since there are many more Great Skua than there used to be, this would be very bad news for the smaller seabirds in the area, and could easily make several seabird species endangered.

The question for this week’s ethical debate is simple: Do you think that we should continue with efforts to reduce bycatch in Northern Europe even if it means that local seabird species will become endangered?

I should note that the authors of this paper stated that “it would not be appropriate to maintain current rates of discarding for the sake of seabirds”.

Votier SC, Furness RW, Bearhop S, Crane JE, Caldow RW, Catry P, Ensor K, Hamer KC, Hudson AV, Kalmbach E, Klomp NI, Pfeiffer S, Phillips RA, Prieto I, & Thompson DR (2004). Changes in fisheries discard rates and seabird communities. Nature, 427 (6976), 727-30 PMID: 14973483


April 16, 2010 • 11:05 am