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 BritishEcologicalSociety.org
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
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Twitter: YellowOctopus
Interesting idea. However, what effect does the increased prey seabird population have on the populations of fish that those birds prey on?
It’s an interesting thought, and more information is needed to form a real idea of what should or shouldn’t happen, depending on the population dynamics.
Also, if seabird species are managed intelligently and efficiently, it’s conceivable that the populations would (maybe) go through a period of being endangered and recover if bycatch is reduced globally. I don’t see any reason to assume that any return to preying on seabirds by great skua would make a single species of seabird go extinct based on the information presented here. Endangered, maybe, but extinct? No.
If bycatch were suddenly and drastically reduced (both are unlikely) I would expect to see an initial decline in great skua, followed by a decline in seabird populations. No reason to assume that they wouldn’t level each other out.
In any case, any reduction in bycatch (anywhere on the globe, really) would likely be more gradual that the effects on the great skua populations might be buffered a little.
But it’s really hard to say without knowing the ecosystem and dynamics of the populations.
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I agree with Sam that more information about the population dynamics needs to be known before an intelligent answer can be formed. But from the way it sounds I think we do not need to implement any policies that will drastically reduce bycatch. Obviously its not going to waste if it is sustaining the Great Skua. However it is regretful that we as humans (who are taking too many fish that is health for the environment as it is) would waste marine life anymore then we have too.
Maybe the best policy would be to reduce the bycatch by some but not drastically. It does seem plausible that the newly amped up Great Skua population, without the bycatch to supplement there diet, could excessively reduce the seabird prey. It appears that the author’s comment (“…for the sake of seabirds”) is contradictory. If he would rather decrease the rate of bycatch for the sake of extra fish, why would he not care about the birds?
Again, more information about the population dynamics needs to be collected before a definite answer can be concluded, however my opinion is that a policy of moderation seems best. And hopefully in the near future (with more info) the degree of that moderation can be ascertained.
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My opinion lies sort of along the lines of what Jeremy said. After reading this post, I can definitely see how bycatch, like many things, can provide positive and negative results. Because my entire academic life has focused around the idea that bycatch is bad, I do feel that some type of policy should be made to decrease the likelihood of this happening. I do, however, like Jeremy, feel that if it is serving as a positive result in another area, that it should not be decreased to the point that it would risk the extinction of the seabird species. With this in mind, I do also realize that many of the effects of bycatch have contributed to “bigger” problems, than that which they seem to be solving right now; so my opinion must stand that while bycatch is, in this case, serving as a positive, I do feel that it must be reduced or at least attempts must be made to reduce it in a way where both, harmful bycatch can be reduced, but perhaps this new positive result can stick around.
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Twitter: kiltdrum
according to the article the bycatch is going to be reduced but no indication as to by what %ages…. the management of the situation will be determined by that. If the reduction is radical and quick then this will severely impact the smaller bird populations as opposed to a more controlled and monitored reduction.
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I believe that the bycatch would be good to reduce is some terms. In the case of Great Skua the bycatch should not be reduce. I don’t know what fish that the fishermen are catching that are bycatch but as long as the bycatch fish are not going into endangerment I believe it is fine to let the fisherman do that. I know it would be hard to enforce this but it would be helpful to the fish, to the birds and to humans.
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I do not believe that Great Skua can account for the use of all bycatch. The reduction of bycatch may be highly advantageous in countries outside of Northern Europe. If bycatch cannot be avoidable, then it should be released back into the water (if the fish are still in a survivable condition) or used resourcefully, like selling it for use in food (if edible) or other products. In order to prevent the extinction of smaller sea birds, scientist should try to slowly reduce the amount of bycatch in Northern Europe and record the changes after a small reduction before reducing the amount of bycathc any further. After continuing to repeat this reduction and recording, maybe one can find a point at which both bycatch can be reduced and the smaller sea birds avoid extinction via the Great Skua.
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