Bigger Picture
Humans’ massive global fish harvest is depriving marine birds of their food. Our voracious appetites mean keystone seabird populations are disappearing
Humans’ massive global fish harvest is depriving marine birds of their food. Our voracious appetites mean keystone seabird populations are disappearing
ALL AROUND US ARE SIGNS OF HOW EXQUISITELY the planet’s creatures have evolved to work together. Take a simplified example from the North American prairies, where I grew up. Microbes in the soil help grasses and sedges grow, harbouring insects. Grasses, in turn, feed deer, pronghorn and other hoofed animals, while insects nourish prairie songbirds. And then meat-eaters big and small enter the picture, stealthily chasing down the herbivores and birds. When death comes to any of them, the microbes take over again, turning the remnants of their bodies into the elements that start the whole process over.
It’s the circle of life, as Elton John sang in The Lion King. It is resilient and inventive and, by definition, highly adaptive. As some players fall out of the circle, others step in so the whole can keep going, even if it takes millions of years for the circle to mend itself. This system has gone on endlessly for 3.5 billion years. It has even weathered five or six spectacular crashes along the way, including the one that took out the non-avian dinosaurs 65 million years ago.
But every now and again, a new study shows us exactly how intertwined the dancers in this circle of life are. A case in point: a paper by University of British Columbia marine biologist Daniel Pauly and others that came out in December 2018 in the academic journal Current Biology.
Pauly, principal investigator of the Sea Around Us project, which has long been funded by the Philadelphia-based Pew Charitable Trusts, is famous for reminding us that when we count how far and how fast fish populations have fallen, we have to keep in mind how big those populations were historically rather than just a few decades ago. He calls it the problem of the “shifting baseline.” Replacing the historical baseline with a more modern one can seriously underestimate the trouble a species is in — and therefore the marine world — by low-balling the depth of the decline.
Now, along with a team of international ecologists including David Grémillet of the University of Montpellier in France, he has taken analytic methods used in the Sea Around Us and applied them to another facet of the health of the sea. When humans take so many fish and other marine species out of the sea for their own use, what happens to the seabirds that rely for food on those same creatures? And not just in a few parts of the world, but globally. The results are shocking. From 1970 to 1989, commercial fisheries that targeted species beloved of seabirds caught an average of 59 million tonnes a year, Pauly calculated. By the period 1990 to 2010, it had risen to 65 million tonnes.
Over those same two periods, the seabirds’ share fell from 70 million tonnes to 57 million tonnes. Just as the human take rose, so — in lockstep — did the seabirds’ drop. In essence, the study found, birds and humans are competing for the same fish.
The seabirds most affected lived in the Southern Ocean (also known as the Antarctic Ocean) and the North Atlantic. Diving petrels, those chunky, greyish stalwarts of the southern waters that feast on krill, squid and small fish, were hardest hit, with a drop of two-thirds in their catch. Food for frigatebirds, the broad-winged, inky swoopers that snatch up fish and squid on the fly, fell by nearly half.
While it’s fiendishly tough to count seabirds (or get historical numbers), another of Pauly’s studies found that from 1950 to 2010, the populations of seabirds that can be counted dropped by 70 per cent. The biggest declines are among birds that fly the longest distances, needing to get their food across big swaths of ocean. The International Union for Conservation of Nature ranks seabirds as the most endangered bird group of all, with nearly four in 10 species globally threatened or near-threatened.
Remove this many fish from the sea, and seabirds starve. It’s not as if they can switch over to prairie insects. We are fiddling with our global biosphere in ways we are only beginning to catalogue.
Since reading Pauly’s paper, I can no longer look at the wild fish displayed on my fishmonger’s mound of crushed ice without also seeing the bird that might have eaten it instead of me. Only by cataloguing the knock-on effects of our actions can we knowledgably decide whether we want to continue doing what we’ve been doing all these decades.1
WHEN HUMANS TAKE SEA FOR OUR OWN USE, THOSE SAME SPECIES
SO MANY FISH AND OTHER SPECIES OUT OF THE WHAT HAPPENS TO THE SEABIRDS THAT RELY ON FOR FOOD? THEY STARVE