SEAFOOD.COM NEWS [Seafoodnews.com] — December 6, 2013 –Last month NMFS released some preliminary data on Gulf of Alaska halibut discards based on the first year of observers on the small boat halibut fleet. The numbers shocked many people, with discards extrapolated across the fleet to be as high as 20 million lbs.
The International Pacific Halibut Commission also estimates halibut discards and its estimates were far lower than those of NMFS. For the past five years, IPHC estimated that total halibut discard mortality was around 1.874 million pounds per year.
The high numbers reported by NMFS to the council raised the question as to whether the fleet had been underreporting discards before the observer program began.
However, recent analysis by the IPHC shows that there were a number of flawed assumptions in the NMFS observer data report, and that in fact estimates of total discard mortality are not that different than those of the IPHC when these problems are corrected.
First, NMFS reported total discards, not mortality, and specifically said that they were not reporting mortality. The conversion used for halibut mortality of discards is 0.16 for hook and line gear. This correction means the mortality reported by NMFS would be about 3.2 million pounds – still far above the IPHC number.
However, the IPHC uses a dressed weight calculation, not live weight, so apply this calculation to NMFS figures, the mortality is reduced to 2.4 million pounds. There is a 75% conversion factor for halibut from round weight to dressed weight.
NMFS also made a gross error in estimating the weight of discards. The overwhelming majority of halibut discards are because they are too small – under 32 inches, which is the minimum legal size. The average weight of these small discards is 8 to 10 lbs. Yet NMFS used the average weight of all halibut, which is 20-25 pounds. Correcting NMFS figures for the correct weight would result in a further substantial reduction.
Taken together these corrections will likely yield an NMFS discard mortality volume of 1.5 to 1.8 million pounds, which is fully consistent with the average discard mortality that has been calculated by the IPHC for the past five years.
There is no ‘smoking gun’ showing that the halibut fleet has excessive discards. There discards and mortality is well within the expected range. However, it may be a long time before this impression is corrected.
This story originally appeared on Seafood.com, a subscription site. It is reprinted with permission.