The study in Canada's British Columbia waters compared so-called individual transferable quotas with a previously used system of trip limits where vessels are only allowed to land a certain quantity of each species every two months.
The findings come at a time when individual transferable quotas are being considered for the west coast of the United States.
"Economic models have assumed all along that individual transferable quotas increase discards," says Trevor Branch, who earned his doctorate in aquatic and fishery sciences at the University of Washington and is lead author of an article published online this week by the journal Marine Policy.
But discards did not increase - they declined for most species, report Trevor and co-authors Kate Rutherford, biologist with Fisheries and Oceans Canada in British Columbia, and Ray Hilborn, UW professor of aquatic and fishery sciences.
The study, "Replacing Trip Limits with Individual Transferable Quotas: Implications for Discarding," is the first to look at 35 species instead of only a handful, or even just a single species, before and after quotas were implemented.
With individual transferable quotas, the total allowable catch is divided among a limited number of boats with each quota holder receiving a specific proportion of the total catch. Quota holders then decide how and when to fish, and whether to buy additional quotas or lease or sell their quotas.
Such a system was implemented in British Columbia waters in 1997, after a one-year transition from individual trip limits and overall caps on the fleet. After a period of adjustment, rates have remained generally similar or even less than the 15 percent of fish discarded in 1996.
Discarding occurs when, for example, unmarketable fish are caught or where trip limits are imposed and once the maximum of a certain fish is caught, all the rest of that type of fish that is caught must be discarded.
Trip limits are used in U.S. waters to protect overfished stocks and they have proved effective, Branch says. "It's just that perhaps the mortality could have been reduced just as much under individual transferable quotas and without discarding large amounts of marketable fish, an economic loss for fishers that is hard to estimate," he says.
Under British Columbia's individual transferable quota system, for instance, skippers have had more flexibility to choose when, where and how to fish so fewer small, unmarketable fish were caught. Then too, skippers with more than their quota of a certain kind of fish could try to arrange to lease or buy another's quota to cover the overage.
Other differences between the two systems include full mortality accounting in the British Columbia fishery - meaning any marketable fish that was discarded at sea was deducted from the amount the vessel was allowed to bring to shore - and the presence of observers on every boat. In the U.S. West Coast fishery, there is no deduction when marketable fish are discarded and in recent seasons monitors were on board 13 to 16 percent of the vessels.
In comparing the two fisheries, the researchers found British Columbia discard rates of 14 percent and 19 percent in two recent fishing seasons, compared with 43 percent and 31 percent for those same seasons in U.S. West Coast waters - the drop to 31 percent partly because new Groundfish Conservation Areas put some fishing grounds off limits, the scientists note. Which animals live once returned to the sea depends on the organism; for instance, species of rockfish all tend to die while lingcod and sablefish are among the fish with better survival rates.
"This research is interesting because it dramatically illustrates how discarding practices are influences by the regulation system," Branch says. "In the British Columbia fishery, individual transferable quotas combined with 100 percent observer coverage reduce discard rates of marketable fish to negligible amounts, whereas trip limits imposed on U.S. West Coast fishers force them to discard fish over their limits resulting in high discard rates."
Even if the United States started using a system similar to that in British Columbia, the challenge of dealing with overfished species may mean U.S. fisheries may never have discard rates as low as those of British Columbia, the authors say.
Such a change also would involve the cost of 100 percent observer coverage, although the authors write the costs may be outweighed by the benefits. "In many ITQ [individual transferable quotas] fisheries, increased profitability enables on-board observers to be funded from cost-recovery programs, increased retention of marketable fish would usually increase the profits of fishers and there may be considerable economic value attached to more accurate and reliable stock assessments."
Branch, who earned his doctorate from the UW with funding from the South African National Research Foundation and the U.S. National Marine Fisheries Service, is currently conducting marine assessment and management research at the University of Cape Town, South Africa.