The indiscriminate slaughter of vast numbers of turtles, sharks, albatrosses and other endangered marine animals that get unintentionally caught by fishermen as “by-catch” could be prevented by a radical proposal of mobile marine reserves, scientists said yesterday.
Protected areas of the ocean where commercial fishing is banned would work far better if they were not static conservation areas, as they are at present, but moveable reserves that take into account the mobile nature of sea life, they said.
The idea for migrating reserves has come about as a result of a revolution in satellite and tagging technology that has allowed scientists to routinely monitor the seasonal movements of marine creatures, which would have been impossible a decade ago.
Scientists said that existing marine protection areas (MPAs), where fishing is controlled to enable wildlife to recover, frequently fail to do their job because the endangered animals simply migrate to unprotected regions where they get caught accidentally by nets and fishing lines.
This is believed to be the main reason why populations of loggerhead and leatherback turtles, which are both critically endangered, have slumped dramatically in recent years as commercial fishing with nets and extremely long fishing lines has become more intense.
Leatherback turtles, a species as old as the dinosaurs, have suffered particularly badly in the Pacific Ocean where populations have fallen by more than 90 per cent in just 20 years. Sharks and albatrosses have also declined significantly as a result of being caught accidentally by fishermen.
Creating mobile protection areas monitored by satellite and other high-tech systems would enable some of the world’s most endangered species to recover, as well as allowing fishermen to ply their trade in other parts of the ocean where by-catch is less likely, said Larry Crowder, professor of marine biology at Stanford University in California.
“I thought 12 years ago that we would not be able to do this, but I would say in the last 5 years the science has grown so quickly, at least in areas where we have rich data, we are on the cusp of doing this,” Professor Crowder said.
“Small, stationary reserves do little to protect highly mobile animals, like most fish, like the turtles and sharks and seabirds. You might say that the only way to achieve conservation of these kinds of organisms is to protect them everywhere in the ocean, and that was the early approach,” he said.
“But we don’t need to close the entire ocean, we only need to close the place where they are concentrated, where by-catch is particularly likely to be found, and leave the rest of the ocean open,” he told the American Association for the Advancement of Science in Vancouver.
Satellite tagging and other ways of monitoring the movements of marine creatures has shown that sea life tends to congregate near oceanographic features such as “upwellings”, where rising currents bring minerals to the sea surface, and “convergence zones”, where ocean currents collide.
“Those are the buffet lines where everything in the ocean goes to feed, and the fishermen understand that, and the things that they are fishing for understand that,” Professor Crowder said.
These features tend to move, taking sea life with them. One of the best examples is North Pacific convergence zone which moves more than 1,000 miles during the year, he said.
“Satellite technology, tagging and acoustic technology allows to look into the opaque ocean and figure out who is going where,” Professor Crowder said.
“The time is ripe for the idea of mobile marine protection areas and a good candidate to consider is the North Pacific convergence zone. We know it moves seasonally. In the summer it’s about 1,000 miles north of Hawaii and in the winter, it is further south,” he said.
“Fishermen travel 1,000 miles to fish in this feature and for loggerhead turtles migrating back to Japan from Baja California, this is the interstate highway for them,” he added.
“The science is in place, both in terms of the tagging technology for the organisms you are concerned about and the underlying oceanography, so you don’t say that albatrosses are likely to be at 42 degrees north, but that albatrosses are likely to found with this particular moving feature,” he said.
Caught in the net: Threatened species
The number of leatherback turtles in the Pacific have declined by 90 per cent in 20 years with by-catch a main cause. The loggerhead turtle has been hit particularly hard by shrimp trawling.
They can become caught on fishing lines and drown. The northern royal albatross is an endangered species.
An estimated 50 million sharks are caught unintentionally every year. The angel shark, vulnerable to by-catch, is now one of the five most endangered shark species.