Sushihunter
Active Member
http://peninsulaclarion.com/news/2012-03-18/biology-may-play-biggest-role-in-alaska-halibut-battle
Biology may play biggest role in Alaska halibut battle
Posted: March 18, 2012 - 9:40pm
By Andrew Jensen peninsulaclarion.com March 18, 2012 - 09:40pm
Biology may play biggest role in Alaska halibut battle
Alaska Journal of Commerce
If halibut thrived on hard feelings, there would likely be a trophy fish for everyone by now.
With another round of deep cuts to the halibut harvest for the 2012 season that began March 17, and regulatory actions to manage trawl bycatch and the allocations between commercial and sport fishermen bogged down in controversy, there has been no shortage of finger-pointing among user groups over the last few months.
Commercial halibut fishermen have absorbed seven straight years of harvest cuts, and they now point at charter operators in Southeast for going over their allocations by more than 3.7 million pounds from 2004 to 2010.
Charter operators, in turn, point at the commercial harvest during the same period and the strategy employed by the International Pacific Halibut Commission that resulted in catch quotas subsequently estimated to be millions of pounds in excess of the target rates.
And everyone, it seems, is pointing at the Gulf of Alaska groundfish trawlers who are allowed to take up to 4.4 million pounds of halibut as bycatch every year. Bycatch is the taking of a nontarget species, such as catching halibut while fishing for cod. Halibut is a prohibited species catch for these fishermen and must be discarded rather than retained.
Besides the trawlers, plenty of blame is also being heaped on the North Pacific Fishery Management Council for its decades of inaction when it comes to reducing the amount of trawl halibut bycatch since the current limit was set in 1986.
In the end, though, while fishing pressure and bycatch undoubtedly are having an impact, the biggest problem with the halibut resource may be biological.
The average size of halibut has declined drastically over the last 10 to 20 years, and the “size-at-age” of surveyed halibut is smaller than at any point since measurements began back in the 1920s.
According to the IPHC, the average weight of a 12-year-old halibut has dropped from 25 pounds in net weight in 1993 to less than 15 pounds in 2011. The average net weight of a 20-year-old halibut has declined from more than 100 pounds in 1993 to less than 40 pounds in 2011.
Females reach maturity around age 11 and continue to grow, while males reach maturity around age 8 and the growth rate slows greatly. At the current rates, many males may never grow into the legal size of 32 inches, confounding projections of future abundance and possibly exacerbating the rebuilding efforts as spawning-age females represent a greater proportion of the harvest.
The decline in average size-at-age defies easy explanations when considering the possibility for man-caused effects. Similarly, the lack of information about ocean conditions and species complexes from the early 20th century makes it equally difficult to pinpoint common environmental effects that could be causing the reduced size of halibut.
“If this were simple, I think we would have solved it,” said IPHC Executive Director Bruce Leaman. “If it was as easy as pointing a finger, I’d be glad to do it.”
Theories abound
There was no trawl fishery in the Gulf of Alaska during the 1920s during the last period when such small average sizes of halibut were observed.
There was a heavy bottom trawl effort by foreign fleets off Alaska’s coasts during the 1960s and 1970s when halibut quotas were far smaller than even the current low levels, but the average size-at-age was more than double what it is today.
The targeting of the largest halibut in the commercial and charter sectors has also been considered based on a theory that removing the females predisposed to growing the largest and capable of laying the most eggs is contributing to the decline.
However, the IPHC notes that the largest females represent a small percentage of the total spawners, and that by the time they have reached such a size they have already contributed a decade or more worth of their genetics to future age classes.
The possibility of “fishery induced evolution” — changes in average size caused by removing only halibut of a legal length — has also been generally dismissed as a factor.
The commercial halibut fishery in Alaska is second only to salmon in terms of its history, dating back to the 1880s, and if the stock were impacted by size selectivity of fishermen it is believed such an effect would have been observed long before now.
One of the more common theories is that the decline in average size of halibut is caused by food competition among halibut and arrowtooth flounder.
After the “regime shift” in the late 1970s that significantly altered ocean conditions in the North Pacific, the total biomass of halibut and arrowtooth flounder have expanded in tandem.
Arrowtooth flounder is now the largest fishery resource in the Gulf of Alaska, but it is also one of the cheapest. There was enough arrowtooth flounder in the Gulf to set a harvest of as much as 213,000 metric tons in 2011, yet the harvest quota was set at 43,000 metric tons and about 30,000 metric tons were actually taken.
Besides the low value of the arrowtooth flounder, targeting the fish results in high halibut bycatch rates of 25 percent or more that typically close the fishery before the total arrowtooth flounder quota can be taken.
Human environment
Some trawl representatives have suggested that constraining their fleet because of the current halibut bycatch caps may be contributing to the issue of food competition by leaving so much arrowtooth flounder in the water.
A similar argument is made with respect to the large percentage of juvenile halibut that makes up the majority of trawl bycatch. The argument goes that an abundance of small halibut is causing the reduced average size, and that leaving more in the water will lead to more food competition and many of the fish saved will never reach the legal size anyway.
That sort of thinking rings hollow for the commercial halibut fishermen, whose catch of juveniles on longlines at least have a shot at growing into a legal size after being released alive while those killed after being mashed up in trawl nets have none.
According to IPHC analysis, trawl halibut bycatch is made up of about 75 percent juveniles by number of fish. But by weight, more than 60 percent of the trawl bycatch is made up of fish larger than the legal size of 32 inches.
The high relative abundance of juvenile halibut in the coastwide estimates often referred to by the trawl fleet is not concentrated in the Gulf of Alaska, either, but is in the Bering Sea.
The total biomass of halibut and the overall number of fish is flat or declining in the central Gulf of Alaska — considered the nexus of the Pacific halibut stock — where the derby-style race for groundfish continues and observer coverage is 30 percent or less.
In the Bering Sea — where the head-and-gut trawl catcher-processors (known as the Amendment 80 fleet) were organized into cooperatives in 2008 and now have 100 percent observer coverage — the number of juvenile halibut is up while bycatch has declined over the past four seasons.
Halibut migrate across the North Pacific from northwest to southeast, and the IPHC has provided information to the council stating that each pound of halibut saved in bycatch will increase yield by more than 1.1 pounds. Further, because females grow larger than males, each pound of bycatch saved is estimated to yield an additional 2.2 pounds to the spawning biomass.
Biology may play biggest role in Alaska halibut battle
Posted: March 18, 2012 - 9:40pm
By Andrew Jensen peninsulaclarion.com March 18, 2012 - 09:40pm
Biology may play biggest role in Alaska halibut battle
Alaska Journal of Commerce
If halibut thrived on hard feelings, there would likely be a trophy fish for everyone by now.
With another round of deep cuts to the halibut harvest for the 2012 season that began March 17, and regulatory actions to manage trawl bycatch and the allocations between commercial and sport fishermen bogged down in controversy, there has been no shortage of finger-pointing among user groups over the last few months.
Commercial halibut fishermen have absorbed seven straight years of harvest cuts, and they now point at charter operators in Southeast for going over their allocations by more than 3.7 million pounds from 2004 to 2010.
Charter operators, in turn, point at the commercial harvest during the same period and the strategy employed by the International Pacific Halibut Commission that resulted in catch quotas subsequently estimated to be millions of pounds in excess of the target rates.
And everyone, it seems, is pointing at the Gulf of Alaska groundfish trawlers who are allowed to take up to 4.4 million pounds of halibut as bycatch every year. Bycatch is the taking of a nontarget species, such as catching halibut while fishing for cod. Halibut is a prohibited species catch for these fishermen and must be discarded rather than retained.
Besides the trawlers, plenty of blame is also being heaped on the North Pacific Fishery Management Council for its decades of inaction when it comes to reducing the amount of trawl halibut bycatch since the current limit was set in 1986.
In the end, though, while fishing pressure and bycatch undoubtedly are having an impact, the biggest problem with the halibut resource may be biological.
The average size of halibut has declined drastically over the last 10 to 20 years, and the “size-at-age” of surveyed halibut is smaller than at any point since measurements began back in the 1920s.
According to the IPHC, the average weight of a 12-year-old halibut has dropped from 25 pounds in net weight in 1993 to less than 15 pounds in 2011. The average net weight of a 20-year-old halibut has declined from more than 100 pounds in 1993 to less than 40 pounds in 2011.
Females reach maturity around age 11 and continue to grow, while males reach maturity around age 8 and the growth rate slows greatly. At the current rates, many males may never grow into the legal size of 32 inches, confounding projections of future abundance and possibly exacerbating the rebuilding efforts as spawning-age females represent a greater proportion of the harvest.
The decline in average size-at-age defies easy explanations when considering the possibility for man-caused effects. Similarly, the lack of information about ocean conditions and species complexes from the early 20th century makes it equally difficult to pinpoint common environmental effects that could be causing the reduced size of halibut.
“If this were simple, I think we would have solved it,” said IPHC Executive Director Bruce Leaman. “If it was as easy as pointing a finger, I’d be glad to do it.”
Theories abound
There was no trawl fishery in the Gulf of Alaska during the 1920s during the last period when such small average sizes of halibut were observed.
There was a heavy bottom trawl effort by foreign fleets off Alaska’s coasts during the 1960s and 1970s when halibut quotas were far smaller than even the current low levels, but the average size-at-age was more than double what it is today.
The targeting of the largest halibut in the commercial and charter sectors has also been considered based on a theory that removing the females predisposed to growing the largest and capable of laying the most eggs is contributing to the decline.
However, the IPHC notes that the largest females represent a small percentage of the total spawners, and that by the time they have reached such a size they have already contributed a decade or more worth of their genetics to future age classes.
The possibility of “fishery induced evolution” — changes in average size caused by removing only halibut of a legal length — has also been generally dismissed as a factor.
The commercial halibut fishery in Alaska is second only to salmon in terms of its history, dating back to the 1880s, and if the stock were impacted by size selectivity of fishermen it is believed such an effect would have been observed long before now.
One of the more common theories is that the decline in average size of halibut is caused by food competition among halibut and arrowtooth flounder.
After the “regime shift” in the late 1970s that significantly altered ocean conditions in the North Pacific, the total biomass of halibut and arrowtooth flounder have expanded in tandem.
Arrowtooth flounder is now the largest fishery resource in the Gulf of Alaska, but it is also one of the cheapest. There was enough arrowtooth flounder in the Gulf to set a harvest of as much as 213,000 metric tons in 2011, yet the harvest quota was set at 43,000 metric tons and about 30,000 metric tons were actually taken.
Besides the low value of the arrowtooth flounder, targeting the fish results in high halibut bycatch rates of 25 percent or more that typically close the fishery before the total arrowtooth flounder quota can be taken.
Human environment
Some trawl representatives have suggested that constraining their fleet because of the current halibut bycatch caps may be contributing to the issue of food competition by leaving so much arrowtooth flounder in the water.
A similar argument is made with respect to the large percentage of juvenile halibut that makes up the majority of trawl bycatch. The argument goes that an abundance of small halibut is causing the reduced average size, and that leaving more in the water will lead to more food competition and many of the fish saved will never reach the legal size anyway.
That sort of thinking rings hollow for the commercial halibut fishermen, whose catch of juveniles on longlines at least have a shot at growing into a legal size after being released alive while those killed after being mashed up in trawl nets have none.
According to IPHC analysis, trawl halibut bycatch is made up of about 75 percent juveniles by number of fish. But by weight, more than 60 percent of the trawl bycatch is made up of fish larger than the legal size of 32 inches.
The high relative abundance of juvenile halibut in the coastwide estimates often referred to by the trawl fleet is not concentrated in the Gulf of Alaska, either, but is in the Bering Sea.
The total biomass of halibut and the overall number of fish is flat or declining in the central Gulf of Alaska — considered the nexus of the Pacific halibut stock — where the derby-style race for groundfish continues and observer coverage is 30 percent or less.
In the Bering Sea — where the head-and-gut trawl catcher-processors (known as the Amendment 80 fleet) were organized into cooperatives in 2008 and now have 100 percent observer coverage — the number of juvenile halibut is up while bycatch has declined over the past four seasons.
Halibut migrate across the North Pacific from northwest to southeast, and the IPHC has provided information to the council stating that each pound of halibut saved in bycatch will increase yield by more than 1.1 pounds. Further, because females grow larger than males, each pound of bycatch saved is estimated to yield an additional 2.2 pounds to the spawning biomass.
