Fisheries discards have become a surprisingly hot topic of late. Thanks to campaigns such as Hugh’s fish fight it is now relatively commonly known that around 8% of all captured fish are thrown overboard again, where they mostly then die. This amounts to perhaps 7 million tonnes of fish worldwide per year, a massive and unsustainable amount. It was recently agreed that discarding edible fish stocks will be banned from January 2014, with discarding ‘white fish’ banned from January 2016. Sadly progress in politics takes time.
Perhaps less known is that fisheries discards have actually become a regularly used food source for seabirds. As fisheries have become more intensive the amount of food available to seabirds has increased, reducing their numbers worldwide. This has been a double edged-sword however, as fishing boats subsequently provide a source of food via the discarding of bycatch, which is comparatively easily found due to the conspicuousness of a boat compared to small (underwater) fish.
Fisheries discards may have helped to limit the decline of seabird numbers, perhaps even artificially elevating that of some scavenging species, like gulls and skuas, which may actually have higher populations as a consequence of discards than would have been the case in the absence of fishing.
So what are the likely consequences for seabirds of banning the practise of discards? This is the subject of a new paper, in Journal of Applied Ecology, focusing particularly on seabirds that spend at least part of their lives in the waters of the EU.
For birds that feed entirely on fish, but do not specialise on particular fish species (for example gannets and some shearwaters) the impact will be unclear. The birds may be able to simply change their foraging strategy to catch live fish again; the issue is whether there will be sufficient fish left to sustain the current seabird populations. It seems reasonable to expect that they will suffer some sort of decline, as they simply will simply suffer a reduction in the availability of food.
Perhaps more complex are the generalist seabirds who do not simply rely on discards, or even rely purely on going to sea to obtain food; the generalists and scavengers. A bird of particular interest is the skua-as well as feeding on discarded fish, they also steal food from other birds, and even eat smaller birds. In fact, skuas have been found to consume over 47,000 seabirds around the isle of St Kilda (Scotland) alone. One worry is that as fishing becomes more difficult, skuas will start predating on small seabirds more. These smaller birds will already likely be suffering because of a reduction in their food supply, if this is coupled with an increase in predation their numbers could be hard-hit, as they are damaged from both sides.
Perhaps the only saving grace for seabirds is that when boats stop throwing dead and dying fish overboard, it is likely that birds will stop seeing them as a source of food, and so will be less likely to associate with them, reducing the numbers drowning in nets. It is currently too early to speculate if the reduction in premature death by drowning will mitigate the loss of food, however.
Please note though, dear reader, this is not a blog defending discards. Throwing away such a high proportion of captured fish, simply for them to die anyways is illogical and damned unsustainable. Global fish stocks are declining on the whole, and we need to learn to better use what we catch. Over 1 billion people currently rely on fish as their main source of protein, so this is a resource that we must manage with care.
This is however a regular theme in ecology-changes in humanity’s policies affect the natural world in numerous ways, many of which are difficult to foresee. There is very little that we do that is without consequence: whether the initial large-scale reduction in fish stocks, or our tweaking of our actions subsequently. It is the place of ecologists to attempt to study these impacts, so that we may better predict the impacts of our actions in the future. It is hoped that other fisheries will enact anti-discards policy in the future, hopefully studies predicting the consequences, and later measuring them, will help any future conservation efforts, and maybe help humanity manage the world that little bit better.