Local communities, of course, aren’t the only ones who eat fish, or even most of it. Much of the world is increasingly getting its fish from giant ships that roam the oceans and harvest in the process. Another paper in science This week, comparing the fate of seabirds in the northern and southern hemisphere, suggests that intensive commercial fishing could make life on a warming planet much more difficult for birds.
When an international team of scientists analyzed the average number of young birds that emerged from carefully monitored nests of 66 species of seabirds between 1966 and 2018, an international team of scientists discovered remarkable differences between the hemispheres. The average number of young animals per nest that were successfully reared by birds whose diet consists at least partially of fish decreased significantly more in the northern hemisphere, which can ultimately lead to a decline in population numbers.
“The northern hemisphere is warming faster and more affected by human pressures such as fishing and pollution,” said William Sydeman, ecologist of the Farallon Institute in California, who led the study. “This makes it difficult to use this data to distinguish between the relative importance of the two.” However, the greater impact on birds known to depend on fish suggests that they are at the heart of the problem. “Most plankton-eating birds raise as many chicks as they used to.”
There are several ways that climate change and other human pressures could make it difficult for seabirds to find the fish they need to feed their young, says Sydeman. As the oceans get warmer and fish move to cooler areas, birds may have to travel greater distances between foraging areas and breeding colonies, or dive deeper to find food, while fish move to the cooler depths. “Some species, like kittiwakes, just can’t,” he says.
Because of their fast metabolism, seabirds have to catch around half their body weight in fish every day to survive and even more to feed their young, says Sydeman. “This makes them vulnerable to changes in the accessibility of their prey.”
Don’t eat all of the birdseed
Indeed, if the effects of climate change on seabirding success are mainly due to difficulties in finding fish, we must do something else to help them survive climate change, the researchers argue in the paper: Limit fishing in Space and time.
“In the northern hemisphere in particular, we need more restrictive measures to support the recovery of bird populations,” says Sydeman. “And in the southern hemisphere, where fisheries are increasing, we should avoid making the same mistakes.”
In the southern hemisphere, there are growing concerns about fishing, which is focused on smaller species like anchovies or even the krill that many birds feed their young. “For the birds, it’s really about the food,” says Sydeman. “Anything we can do to preserve their prey, especially closing fisheries in the colonies during the breeding season when they really need food, would be very welcome.”
There are promising examples of this: for example, areas in the North Sea where commercial fishing has been banned to help kittiwakes raise more young. Even the critically endangered African penguin, a fish eater from the southern hemisphere, appears to have benefited from a local ban on purse seine fishing for sardines and anchovies – their favorite fish – around their breeding colonies.
“A modest improvement in breeding success can have positive effects over a longer period of time,” says Sydeman. “But more needs to be done in this case because these penguins are in big trouble.”
Aside from local restrictions on breeding colonies, which are often temporary, Sydeman and colleagues argue in the paper that large marine reserves, where marine animals can find safe sanctuaries and abundant food year-round, are also important to seabird survival to support.
The same is certainly true of coral reefs, says Knowlton, and there are benefits to humans as well. âMarine protected areas also benefit fisheries. They offer an opportunity for a more sustainable harvest. “
Plus, she says, they can buy species time while we get our climate house in order. âOur climate efforts are really important, but it will take a few decades for them to be effective in the best possible scenario. These things, which we can already do on site, will also be very important. “