Publication links gillnets and seabird mortality
While the 1992 cod moratorium was certainly a game changer for the cultural and economic landscapes of this province, it also provided a unique opportunity for biologists to watch how such a drastic move would affect other species. And cod isn’t the only species of interest.
A paper recently co-published by MUN biologist Bill Montevecchi takes advantage of the sudden change in our oceans that occurred once the moratorium was implemented by looking at how the disappearance of gillnets affected seabirds known to get caught in the fishing gear.
Gillnets are basically sheets of netting used to catch fish. Unfortunately, the target species of a fisherman isn’t the only thing they haul in. Montevecchi says it’s been known for years that gillnets catch a lot of seabirds, specifically seabirds that dive for their food rather than feed on the surface. Knowing the nets were a problem for seabirds wasn’t enough to fully understand how much of a problem gillnets really were for the diving birds.
“It was not possible, essentially, to pin those high numbers to population consequences,” says Montevecchi.
The moratorium offered a unique experiment.
“When the moratorium kicked in in 1992, there were essentially two major gillnet fisheries shut down.”
One was cod and the other was the gillnetting of salmon, which closed about the same time. In 1992, tens of thousands of nets came out of the water and didn’t go back in.
“This is a big impact. It’s an ocean-based experiment. All of a sudden the gear is gone,” says Montevecchi. “Everybody knows and everybody says there’s lots of mortality and now all the gear is out and it’s out for 20 years.”
So the authors of the paper went to the areas where they knew a lot about the breeding populations of seabird species — the ecological reserves such as Witless bay, the Funk Islands and the Gannet Islands off Labrador. Those places have been areas of long-term study allowing biologists to look at how the populations changed post moratorium and post gillnet.
“So here’s a chance by restricting our analysis to the breeding population in summer to see (what happened). If there was a lot of mortality, we should see positive population increases as a consequence of those closures,” says Montevecchi.
What they found was what has been predicted for years. Birds vulnerable to being trapped and killed in gillnets — the diving seabirds — have seen a positive effect on their breeding population numbers since gillnets were removed from the water.
They found one of the most vulnerable species to gillnets was the common murre.
“We actually showed a year-to-year analysis that a change was directly related to the fishing effort within its foraging range,” says Montevecchi.
Basically, wherever there was more fishing, there was also more mortality of common murres.
“It is the first time, in fact, that you can link (fishing) to population effects. So it got a lot of attention internationally.”
Compared to the gillnet heyday of the pre-moratorium 1980s, little gillnet fishing is done now. Still, Montevecchi says vigilance is imperative, especially considering the most productive places for birds and other animals detrimentally affected by gillnets will be the places fishermen search out, too.
“The hot spots tend to be where the caplin go and that’s where the cod go. The whales follow and the seabirds follow,” Montevecchi says. “So there’s always going to be that kind of interaction and that’s what we really need to look at carefully.”
Montevecchi is also quick to point out fishermen aren’t seeking out the bycatch intentionally and have worked with biologists to reduce such negative effects.
Another interesting aspect of the paper looks not at the diving seabirds but at the surface feeders, such as gulls and kittiwakes. During the large-scale commercial fisheries, Montevecchi says tonnes of fish offal was available to those seabird species but that food source has been largely eliminated since the moratorium.
“So we predicted, if anything, those birds would have negative consequences,” he says.
That is, in fact, what they found. With the buffet gone, breeding numbers decreased.
In addition to Montevecchi, Paul Regular, April Hedd, Gregory Robertson and Sabina Wilhelm were also authors of the paper. It was published in the journal, Biology Letters.