A recent study from the Biological Conservation journal brings shocking news: every year across the globe, an estimated 400,000 seabirds are killed by gillnets.
Gillnets, a common term for any net used to entangle and catch fish, are used all over the world, and at any depth. These nets, whether used in subsistence or commercial fishing, trap anything that swims through them. When unintended marine wildlife, or “bycatch,” is caught in these nets, the results can be significant.
“Fishermen do not try to catch seabirds or other unwanted species, but they usually set their nets in productive marine areas with abundant fish resources, which are also home of other marine fauna,” co-author Ramunas Zydelis told mongabay.com in an interview. “In such places seabird habitats overlap with fishing grounds and subsequently some diving birds accidentally entangle in fishing nets and drawn as they cannot return to the water surface.”
The study synthesized previously collected data from around the world. Overall, it identified 148 different seabird species at risk for becoming gillnet victims, of which 81 have been officially reported as bycatch.
“Bird bycatch in gillnets is net type-specific and species-specific. Not all the nets are equally dangerous. Nets set in deep waters are less likely to catch birds than nets in shallow places or drifting at the surface,” Zydelis says. “Whether a bird species is likely to be caught in fishing nets also depends highly on species foraging behavior and diving habits.”
The birds most likely to be affected by gillnets are those that hunt underwater, such as penguins, loons and cormorants. In particular, the study found that auk species have the highest chances of becoming entangled.
“The highest numbers of seabirds get caught in gillnets set in cold sub-arctic and temperate seas of the northern hemisphere, where very large numbers of diving birds live and rich marine resources attract intensive fisheries.” Zydelis told mongabay.com. “High bycatch occurs in the Russian offshore waters of the northwestern Pacific; possibly a lot of birds get caught around Iceland; the Baltic Sea is another area with high bycatch.”
“But sometimes even low numbers of birds dying in fishing nets could be considered as a significant bycatch when affected bird population are small,” Zydelis added. “Examples could be bycatch of Humboldt penguins in Peru and Chile and bycatch of Magellanic penguins off the southeastern coast of Brazil.”
Humboldt penguins are listed as Vulnerable,” and Magellanic as Near Threatened by the International Union for the Conservation of Nature’s Red List.
Zydelis and other scientists find hope in the restrictions passed by the state of California in the 1980s, a decade after the introduction of monofilament gillnets. In the halibut fishery alone, these nets caught more than 13,000 common guillemots – a seabird native to the Pacific coast. By 2000, central California began enforcing a closure to gillnets greater than 60 fathoms deep. Since then, only one guillemot death has been reported in the same fishery, according to the study.
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