For the first time, ecologists have been able to quantify how important fish stock is shared among humans, seals and birds and their findings are raising difficult questions about how to manage food resources alongside growing wildlife populations.
‘We found that the impact of wildlife on fish stocks is real,’ says Sture Hannson, ecologist at Stockholm University who carried out the study with researchers from the Swedish University of Agricultural Sciences. Hannson estimates that humans consume 700,000 tonnes of fish, seals 100,000 tonnes and birds 100,000 tonnes. In other words, birds and seals are eating about one-fifth of the catch between them.
‘When it comes to coastal fish species such as whitefish, perch and pike, we can see a clear impact on these populations from seal and cormorant predation,’ says Hannson. 100 years ago there were 100,000 grey seals in the Baltic sea but industrial-scale hunting meant that by the 1940s this had dropped to 20,000 individuals and by the 1970s, a mere 4,000 individuals remained.
Since protections were introduced, their numbers have been able to grow to 50,000 and continue to increase by around eight per cent every year. Similarly, fish-eating birds such as cormorants have been allowed to flourish now that they are no longer persecuted. The flip side to this growth is that now both predator populations are stronger, they are coming into conflict with the fishing industry.