PETERSBURG – Earlier this month the buzz around a monster halibut caught by local commercial fishermen in Thomas Bay went crazy after news of the catch spread through social media sites.
Many of the comments expressed amazement for the monster catch, but some talked about sadness because another “breeder” was taken out of the reproduction equation. Multiple people talked about the cruelty of killing such a remarkable fish or simply said, “Should have put it back.”
No matter what your stance is, there are two undeniable truths. First, the fishermen were doing their job. Second, putting the fish back would have been illegal, according to Ian Stewart, head stock assessment scientist for the International Pacific Halibut Commission (IPHC).
“There is currently a regulation in the fishery that they are required to retain any legal halibut that they capture,” he says. “So in this particular case it would not have been legal for those fishermen to release that fish.”
The IPHC often fields questions regarding the impact of large fish being caught, and the organization has even kicked around the idea of mandatory release when dealing with them. On paper, the idea of mandatory release to sustain a large-bodied breeder should work, but results would rely heavily on survival rate. The IPHC has conducted studies by tagging and releasing fish in various stages of condition from injured to healthy, Stewart says.
“The problem is that its very difficult to pin down what the absolute rate of discard mortality is for the fish that are in the best condition,” he says. “It turns out to be, scientifically, a very difficult question to test.”
Based off the IPHCs efforts, Stewart assumes around 60 percent of halibut released do not survive. The other unknown in the scenario for the IPHC revolves around reproduction of large fish versus its much smaller counterparts.
“Certainly a 400-pound fish will produce a lot more eggs than a 40-pound fish, because its ten times heavier,” Stewart says. “But it wont necessarily produce more eggs than ten 40-pound fish.”
Almost all big halibut, anything over 100 pounds, are female because males simply fail to reach that size. Halibut are broadcast spawners, and researchers assume the quantity of eggs the species produce is a function of the body weight. However, when it comes to contributing to spawning stock, the 396-pound halibut caught by the F/V Day Spring is certainly in the minority.
“The vast majority of the spawners in the halibut stock are much smaller than that particular fish,” Stewart says. “The potential contribution relative to the tens of thousands of fish that are in the 20 to 40 pound range is very small on a population level.”
Stewart says another misconception made about large halibut is the thought their size indicates old age. Many comments on Facebook referred to the fish caught by Mattson and Corl near Petersburg as “ancient.” The age will never be known, because Corl wanted to save the otolith bone for a souvenir and the aging process would have destroyed the keepsake. But it turns out, extremely large fish are usually middle aged fish typically somewhere between 15 and 35 years old, according to Stewart.
“These tend to be middle aged fish that have a really fast growth trajectory,” he says. “So just like people some halibut dont ever get very big and some halibut get really big.”
The reasons for the accelerated growth could be genetics or conditions the fish experienced, but scientists cannot say for sure. Stewart readily admits there are a lot of unknowns when it comes to studying halibut and other species making their home below water.
“I certainly dont want to understate our uncertainty,” he says. “Fish are hard to study. Theyre not like going to the forest and looking at trees where you can count them and put a tag on each one and you can go back and look at them a few years later.”
For instance, halibut spawn in the winter time and the eggs and larvae spend a couple months floating in the Gulf of Alaska where observing the event is extremely challenging. Then the juveniles settle out in shallow, sandy areas, and spend one to two years “basically unobserved” in inaccessible locations. After that period they begin making an appearance in troll surveys and fisheries as three- and five- year olds. To combat this and other information gaps, scientists at the IPHC have extensive data going back to the turn of the last century, Stewart says.
“As a scientist part of my job is to explain to people what we do know, but a lot of the fascination is in exploring some of the things we dont know about the stock,” he says. “The more data we collect, the more we start to understand what we dont know.”
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