Taking 'big mamas' doesn't hurt resource, say scientists
Hang out with halibut fishermen of any kind, and inevitably the question comes up: Is it OK to take the big, 200-pound plus halibut, almost always older breeding females?
It's not OK, some say. Targeting those "big mamas" takes the prime breeders out of the population.
Yes, it is OK, others say. While large females produce more eggs, they are such a small part of the total female spawning population that catching them doesn't have a major effect.
Scientists say it's all right to take large females. The official answer from the International Pacific Halibut Commission on its "frequently asked questions" page of its website says, "IPHC biologists see no benefit to preserving the largest females from a conservation standpoint."
As Steven Hare, a quantitative scientist with the IPHC, Seattle, said about taking big females, "If it were negative, we would have acted by now."
Here's what's known about spawning females in general:
- Female halibut start spawning at age 8.
- Females ages 12 to 16 are the biggest contributors to the spawning biomass.
- According to IPHC estimates for 2011, the female spawning biomass - the total weight of all mature females - is 350 million pounds for the Pacific halibut population.
- Fifty-four percent of those females by pound are ages 12 to 16.
- Five percent of those females by pound are 20 years and older.
- Of 14.7 million spawning females by number, about 500,000 are age 20 and older.
- The largest group, those age 10, are about 3 million spawning females.
- The average size of halibut in general by age has decreased over the last 20 years.
- In 1990, the average weight of a 15-year-old female was 100 pounds.
- Today, the average weight of a 15-year-old female is 35 pounds.
With the size of halibut getting smaller, that means not many females will reach trophy size.
"The actual contribution in terms of the number of females over 25-years-old to the spawning biomass is minimal," Hare said. "They do not contribute a lot numerically by weight or number to the spawning biomass."
Sugpiaq Alutiiq fishermen don't target big fish. The Alaska Natives who have traditionally fished for halibut in lower Cook Inlet follow the wisdom of their ancestors, said Nick Tanape Sr. of Nanwalek, who has fished for 65 years.
"The big halibut - we would never take it in," Tanape said. "We knew it was producers of halibut. Our parents and others told us."
Tanape said Sugpiaq Alutiiq will release anything more than 80 pounds as long as the hook isn't set in the head and the fish could survive.
Alaska Natives can take halibut for subsistence purposes using skates - hooks set on longlines - hang jigs, or rod and reel. Tanape said he usually sets a skate of 15 hooks off the beach and takes about four or five halibut.
"I just prefer to get what I need," he said.
Commercial fishermen tend to respect the best science and agree targeting big females isn't a major concern - yet.
"While I think most commercial fishermen would like to say it's of no consequence, in the back of their minds they're thinking it may be a consequence," said Don Lane, a longline fishermen of almost 30 years.
In the past when exploitable halibut stocks had been in abundance, the effect of taking big females hadn't been a major concern. Now that stocks are declining, "most commercial fishermen think we need to look at this more closely," Lane said.
Another consideration is genetic selection. One theory is that by removing big females, females with genes that produce larger fish get removed. Scientists don't think that's the case, Hare said. Since the 1920s when the IPHC began and started studying Pacific halibut, research shows the age-weight average has gone from low weights to high weights and back to low weights. If taking big fish affected the genetic makeup, then there wouldn't have been larger fish later, Hare said.
That raises a question: Why have fish on average by age gotten smaller? The total biomass has grown, as has the number of fish, but the average weight has gone down and the biomass of larger fish has decreased.
The current theory is that competition with other species, like arrow-tooth flounder, has increased, particularly among juveniles - the density or crowding effect. Hare compared the North Pacific Ocean to an aquarium tank. The more fish you put in, the less food they can get.
Sugpiaq Alutiiq also have a reason why they don't take big halibut: they don't taste as good.
"The taste on them isn't as good as the smaller ones," Tanape said. "A lot of people think it dries up pretty quickly."
That's not a concern among fish buyers, Lane said. Some commercial fishermen like big halibut because it can be a more efficient way to make money. Pull in a 150-pound halibut and that could be a $900 fish. Lane said buyers sometimes pay more for big fish, with a price difference of 30 cents and more a pound.
For himself, Lane doesn't like to catch big fish.
"They're a lot of work," he said, and can be a two- to three-person job. "There's a point where they're almost dangerous to handle."
Longline gear can be set up so that big fish don't get caught, as with using smaller hooks.
Some say large females have better quality eggs - another reason not to target them. Research for other fish species like rockfish does show large females produce better surviving eggs with more fat. That's not the case for halibut, Hare said.
"They go for quantity, not quality," he said.
Lane points out another reason not to target large halibut: the accumulation of mercury in big fish. The larger and older the fish, the more mercury that can build up.
In a 2007 Epidemiology Bulletin, the Alaska Department of Health and Social Services says it's OK for older boys and men to eat as much halibut as they want. Pregnant women, nursing mothers and children under 12 can eat as much halibut under 20 pounds as they want, but should restrict eating large halibut - less than four meals a month of halibut weighing more than 90 pounds.
Michael Armstrong can be reached at firstname.lastname@example.org. McKibben Jackinsky also contributed to this story.