Save Shipwrecks to Save Fish (and Fishing)
A few years ago in the Black Sea, off the Turkish coast, a marine archaeology expedition discovered a 2,400-year-old wooden shipwreck. It was still in good condition because of low-oxygen levels at its resting depth, and a video revealed human bones and vase-like clay storage vessels, called amphora, still intact. But when the crew returned to investigate the following year, fishing nets dragged across the bottom had reduced the entire wreck to scattered rubble. It was, said one archaeologist, like somebody drove a bulldozer through a museum.
The same thing has happened to roughly 45 percent of the estimated 3 million shipwrecks in the world’s lakes and oceans because of the industrial-scale trawling that has also decimated fish stocks worldwide.
But in a new study being published in the journal Marine Policy, an archaeologist and an ecologist propose a solution they say will protect these underwater cultural artifacts and at the same time boost fish populations and improve commercial fisheries.
The key insight came one day when Jason S. Krumholz, an ecologist with the National Marine Fisheries Service, was sitting with his five-year-old son watching videos taken by a remotely operated vehicle visiting shipwrecks in the Mediterranean. “We started to notice that some of these wrecks have a ton of fish, and some have almost none,” Krumholz recalled.
That led him and Michael Brennan, a University of Rhode Island oceanographer who had participated in that expedition off the Turkish coast, to ask what makes the difference. For their new study, they looked at videos from 18 ancient shipwrecks and found that “shipwrecks in areas historically excluded from fishing are in better condition and support larger and more diverse fish communities than wrecks which have been damaged by trawling.”
Moreover, they argue that those shipwrecks, protected by steep terrain, underwater cables, rocky waters, or other circumstances, become breeding grounds for commercially valuable fish, and that these populations “spill over” to increase the haul for commercial fishing outside the protected area. And that suggested a strategy to benefit archaeologists and fishermen alike by siting Marine Protected Areas, where fishing is outlawed, around sites that are already rich with shipwrecks.
The idea of Marine Protected Areas is, of course, not new. But they have become increasingly popular with conservationists and the fishing industry alike because experience has shown that they work. In one recent study, properly planned and managed MPAs had five times the tonnage of large fish and 14 times the shark biomass compared with fished areas. Siting new MPAs around areas with extensive shipwrecks is simply a way to make them more effective, according to Krumholz and Brennan.
Krumholz explained how these MPAs work by analogy with lobster fishing in Maine. Regulations there strictly limit the take to lobsters with a carapace length from 3.25 to 5 inches. That protects “all lobsters until they’ve had a chance to breed at least once” and also the lucky few that manage to elude the fishery long enough to outgrow it. Big, old lobsters make many more eggs than younger ones—up to 100,000 per year, versus 5,000 or 10,000 for the youngsters. They can also keep restocking the lobster fishery for a life span up to 100 years.
The higher reproductive output by older individuals is true for most fish species, said Krumholz. But while the commercial fishers can protect younger and smaller fish by adjusting the size of the mesh on nets, they can’t avoid killing the big ones: Any fish that gets caught in a trawl net is a dead one. Instead, MPAs around shipwrecks could be a logical counterpart to the upper limit on the lobster catch: They’d provide a refuge where big, old breeders could continue pumping out eggs in peace.
MPAs are becoming a practical tool because most fishing boats now use global positioning software that can clearly indicate the borders of an off-limits area. “Very few fishermen cheat,” said Krumholz. “They know the MPAs are there for their own benefit, and they’re pretty good at participating in the process to site MPAs and then observing those rules.”
A few MPAs sited on shipwrecks already exist, notably Thunder Bay National Marine Sanctuary in Michigan’s Lake Huron and the Monitor National Marine Sanctuary off the coast of Virginia. It’s also a common strategy to support fisheries, said Krumholz, by “spending a lot of money sinking ships and dumping airplanes to build up artificial reefs.”
The new study asks, in effect, why not take better advantage of the shipwrecks that are already there?