Decline of large ocean fish debated

From Ocean Navigator #132
September/October 2003
The health of fish stock around the world is under constant scrutiny.

This 350-lb Indo-Pacific blue marlin was caught near Breaksea Spit, north of Fraser Island on the southernmost edge of the Great Barrier Reef in Australia. The fish was snagged with a stainless-steel billfish snare designed to secure the animal safely for dehooking and revival by towing behind the boat to pass fresh seawater over the gills. It was tagged and released.
   Image Credit: Scott Bannerot

There can be no doubt that humans have significantly impacted fish populations, but to what degree? The pro-ocean lobby Oceana ( recently reported that “90 percent of the world’s large ocean species (including cod, halibut, tuna and swordfish) have disappeared from the world’s oceans in recent decades.”

We turned to Contributing Editor Scott Bannerot, a marine biologist based in the South Pacific aboard his voyaging boat Élan, which he lives aboard with his wife Wendy and son Ryan, to learn what he has witnessed – from the perspective of fisherman, sailor and scientist – regarding the population of large fish. (The Bannerots are also the authors of The Cruiser’s Handbook of Fishing.)

“I am aware of several organizations making similar statements. The species listed as €˜large oceanic fish’ appears to be very broad, lumping demersal species (those dwelling at or near the bottom), like cod and halibut, with pelagic species (those dwelling at or near the surface), like tuna and swordfish. And when they say “tuna,” for example, which species do they mean? I worked with the NMFS (National Marine Fisheries Service) analysis group that did the annual analysis of bluefin tuna stocks in the Atlantic in the early ’80s, and primarily the Japanese had indeed hammered that population to a small fraction of its pre-fished level. Yellowfin tuna, on the other hand, appear to be so prolific that even the heavy pressure of purse seiners from Taiwan, Korea and the U.S.A. do not yet appear to have made a similar dent in their population. Cod and other demersal species probably have suffered 90 percent drops, particularly offshore of New England, where they were fished to near total collapse before the federal fishery management councils could finally rise above professional fishing lobby groups and enact strict conservation measures (way too late).

“Swordfish have certainly been fished hard, with longliners doing most of the damage, although swordfish are so widespread that they are relatively more difficult to fish to biologically critical levels (economic extinction occurs first). Nevertheless, U.S. longliners have been severely restricted, and we are already seeing results – gamefishing for swordfish off of southeastern Florida, for example, is getting really good again. Billfish belonging to the family Istiophoridae (marlin, sailfish, spearfish) mainly get in trouble by getting in the way of gear targeting other species. Tuna purse seiners capture about four to five blue marlin per set in the tropics over broad areas. White marlin (an Atlantic species) are believed to be in severe danger due to decimation by longliners targeting tuna and swordfish. Striped marlin (Indo-Pacific) seem to be in pretty good shape, as do black and blue marlin in the Indo-Pacific. Spearfish (longbill, an Atlantic species; and shortbill, found in the Indo-Pacific and Mediterranean) are relatively rare, ephemeral and poorly understood. (So who knows about them?)

“Sailfish in the western Atlantic appear to be in excellent shape, as they do on the Pacific side of Central America. Sharks are easy to overfish because of slow reproductive rates, but here again strict management in the U.S. and worldwide seems to have caught this in time; big species like tiger sharks, dusky, sandbar, lemon, great white and mako sharks, for example, all seem to be doing fine and, if anything, are definitely on the increase.

“Some of the most destructive fishing methods, like drift nets offshore and cyanide poisoning and bleach fishing on coral reefs, has been widely condemned and regulated against. Some of it still goes on, but hopefully enforcement will defeat exploitation on these fronts.

“In summary, a heck of a lot of well-documented destruction has indeed occurred. Russia and Japan led the way early on; Spain and Portugal are well-known for unscrupulous disregard for conservation; and the U.S. and other countries have done their part, too. Fishery management has traditionally lagged behind exploitation, unable to act proactively because of the timeworn lack-of-information arguments always made by professional fishing lobbyists. Repeated wanton destruction has changed this somewhat. Governments are beginning to say, €˜Sure, we don’t have all of the data for an airtight case, but we’re going to take the conservative path this time on the basis of what information we do have. If you don’t like it, too bad.’

“Regarding my own opinions: We tend to spend time in many remote areas least available to heavy commercial fishing. Thus, we encounter at least as many big yellowfin tuna, blue marlin, black marlin, striped marlin and other species as ever. We have noted serious depletion of reef and inshore fishes, even in relatively small island groups, anytime there’s a significant number of people around.”

By Ocean Navigator