For many Homer residents, last weekend’s inaugural Halibut Festival provided an opportunity to be immersed in the marine world. 

From a fun run to a fish fry to a halibut cabaret, most of the weekend was a celebration of Homer’s iconic resource. But much of the discussion at Saturday’s “State of Our Halibut” lecture series at the Alaska Islands and Ocean Visitor Center was serious and centered around a major issue: the total mass of Pacific halibut is shrinking and no one is entirely sure why or what to do about it.

That’s not entirely new information. Nearly ever year of the past decade, the International Pacific Halibut Commission’s annual survey reported decreases in both Pacific halibut population and biomass (the combined weight of all living halibut in the area). Data from the 2014 survey indicates that population numbers seem to be leveling out, but the fish are still getting smaller.

That conclusion is based on size-at-age comparisons, which contrast the size of fish at a given age over time. In 1975, IPHC ecologist Claude L. Dykstra explained on Saturday, the coastwide mean weight for a 14-year-old female halibut was 55 pounds. In 2014, it was 25 pounds. Males saw a similar decrease.

The biomass loss has been tough on fishermen, who’ve seen an extreme drop in allowable halibut harvest. In 2010, the total halibut harvest in Alaska was 41.8 million pounds; in 2014, it was 16.6 million, said Alaska Seafood Marketing Institute project manager Kate Consenstein.

As Dykstra explained to the audience of mostly fishermen, the weight loss has marine biologists scratching their heads. It’s not that they don’t have theories about what’s causing it — they do. But no one thing seems to explain the phenomenon. 

“It could be a combination of three or four factors,” said Dykstra. Or, it could be normal fluctuation, he explained. Halibut biomass was low in the 1970s before reaching a historic high in 1990s, according to Bruce Leaman, executive director of the IPHC. Even further back, the numbers were low during the 1920s, and high in the 1940s.

“We could also be asking, why did we see so many before?” said Dykstra.

A probable explanation seems to involve both human and environmental influences. Ecologists say the decrease in halibut biomass may be related to competition with arrowtooth flounder, whose populations have greatly increased but whose low value makes them less appealing to fishermen, so they remain in the water to reproduce. Or perhaps size-selective fishing has something to do with it, although the IPHC points out that most of the largest fish being caught are females who have already reproduced enough to pass on their genes to the next generation.

Maybe the biomass reduction is a result of ocean acidification, an indicator of climate change in marine ecosystems, ventured one audience member.

Researchers haven’t been able to successfully monitor the eating habits of halibut. The fish regurgitate the contents of their stomachs when caught, and other methods of studying feeding behavior are limited because of the depths the fish frequent. So a change in diet could be one possible factor, as another audience member pointed out.

Another factor at the forefront of the discussion is bycatch. Bycatch is the “oops” of fishing: anything caught that is outside a fisherman’s quota or not covered by his permit. Legally, all bycatch must be thrown back, but the fish often die before fishermen can return them to the sea, or are harmed to the extent that they can’t reproduce. Bycatch mortality steadily increased from 2011 to 2014, according to IPHC data. The 2015 numbers are not yet available, but ecologists expect to see a continuation of the trend.

As many local fishermen see it, the issue is that as halibut biomass has declined, legal bycatch levels have remained relatively static. That “oops” adds up. According to the Alaska Journal of Commerce, “IPHC biologists estimate that 93 percent of all 2015 halibut removals in the Bering Sea would be from bycatch, not the directed fishery.” That’s millions of pounds of halibut wasted each year, decreasing the amount of fish that fishermen can harvest and sell.

Additionally, the relatively small size of halibut caught by fishermen looking for other species could be a contributor to the problem — the inverse of the one presented by catching only large fish: “The average size of a bycatch halibut in the Bering Sea last year was just over 4 pounds. This tells us that the majority of halibut being harvested as bycatch are juvenile halibut, fish that need to stay in the water in order to migrate out to the many other areas of the North Pacific, for which the Bering Sea serves as a major nursery ground,” explained Hannah Heimbuch, the Alaska Marine Conservation Council’s community organizer, in an email following the Halibut Festival.

Bycatch isn’t an easy problem to address. The North Pacific Fishery Management Council’s June regulatory reduction of halibut bycatch by 25 percent was a compromise between fishermen desperate for a steep reduction and large companies who didn’t want to see an economic impact on their trawl fleets. It left both sides unsatisfied.

The biomass decrease also comes around the same time as the discovery of a parasite that’s spread stealthily through the Pacific halibut population. According to IPHC’s research, 45.1 percent of commercial sized (at least 32 inch-long) halibut coastwide are infected with Ichthyophonus sp., a single-celled parasite of fish, with characteristics somewhere between fungus and amoeba; that’s the highest prevalence among any species they studied. 

Dykstra was quick to point out that correlation doesn’t equal causation. Although the parasite causes herring die-off and decreases the quality of salmon and pollock, ecologists have found no reason to believe it’s connected to the decreasing biomass in halibut. And it has no effect on humans or other warm-blooded predators of fish.

Whether it’s a result of some combination of these factors or of something else entirely, the biomass decrease is causing a lot of halibut-flavored headaches for Alaska fishermen: a need to fish for several species to make a profit, tension between commercial and charter companies, and a migraine worth of bycatch-related conflict with trawler companies.

Whatever is causing the biomass to drop, Heimbuch says she’s glad people are paying attention. She called the weekend’s festival a great success.

“We had a huge amount of community support — from volunteers to our amazing sponsors. … Great ideas for collaboration and expansion in the future have already come up,” she wrote to the Homer News.

She says she hopes people stay involved in the discussion.

“It’s important that people in Homer know that halibut represent a vital source of culture and economy for our community, from sport anglers to the charter fleet to our commercial fishing families, captains and crew,” she wrote. “These animals are part of a dynamic and changing system, and it’s up to all of us as coastal residents to be aware of how the choices we make as voters, fishermen and citizens impact that system.”

Annie Rosenthal can be reached at annie.rosenthal@homernews.com.