Consider your suspicions validated—a new study confirms that fisheries are to blame for starving seabirds.
While the theory makes intuitive sense, it proved tricky to test. But scientists from the Centre d’Ecologie Fonctionnelle et Evolutive (CNRS), Montpellier came up with a way: Using Cape Gannets on Malgas Island, South Africa, a small island north of Cape Town, the researchers measured how much daily energy a gannet was using trying to find food, and compared it to how much prey each bird consumed (assessed via measuring the birds’ stomach temperature). The results showed that these seabirds were spending more energy trying to locate food than they gained when they eventually located it and ate. The researchers took measurements of the growth rates of the gannets and their chicks during the 2011-2014 breeding seasons, and found, unsurprisingly, that the adults' body condition and chick growth rates declined during the study period, thanks to this imbalance of energy exerted versus energy consumed.
Overfishing is the primary problem here, said David Grémillet, the study’s lead author and research director at CNRS, Montpellier. “When the fish population declines, the bird population declines too,” he said, adding that the overall gannet population declined during the study period. What makes an area a valuable spot for a fishery—that is, easy access to lots of fish—is also what makes it such a prime feeding spot for seabirds (like the Laysan Albatross and the Pink-footed Shearwater). The seabirds used in the study consume small pelagic fish—sardines, anchovies, and other small coastal fish—but when fishermen capture too many, the birds are left hungry.
A fishery “punches a hole” in the ecosystem if overfishing is prominent, says Daniel Pauly, principal investigator at Sea Around Us and a professor at the University of British Columbia Fisheries Centre. “If you fish modestly, and expand your (fishery) to a larger area, you can coexist with birds. People must agree to also care about the seabirds because that’s how you lose one species to another.”
The problem likely expands beyond the Malgas Islands, both Pauly and Grémillet said. To combat the issue, Grémillet suggests a change in fishery management. “Fisheries should be managed not just to preserve seabirds, but also to preserve the whole marine ecosystem,” he said. It’s also an industry problem, he added, noting that fisheries would be more successful if they strived to benefit local businesses rather than international corporations.
Losing a species has repercussions on any ecosystem, and this scenario is no different. Grémillet wants fisheries to be more mindful of the ecosystem in place before expanding—he thinks it just might save a species from going extinct.
“The seabirds are a big indication of ocean health,” he said. “They show that something needs to be done about how we exploit marine resources.”