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Posted on September 15, 2015 by

Crab Survey Suggests Declines in Snow Crab, Red King Crab Biomass in Alaska

By: John Sackton,  SeafoodNews.com

The Crab Plan Team is meeting in Seattle this week, and yesterday they were given the results of the 2015 crab trawl survey.  Overall, the survey showed a decline in the mature male biomass for both Red King crab and Opilio, and a mixed picture for Bairdi or Tanner Crab.

The lower biomass suggests that it is likely that final harvest quotas for both snow crab and red king crab will decrease for this coming year.  The ADF&G normally announces the quotas at the end of September or in the first week of October, and the season opens on Oct 15th.

The models used in the survey measure both males and females, and calculate the mature male biomass, which is not just the legal minimum size, but the preferred size which the fleet retains. The mature males of legal and/or preferred size are the most important numbers used in calculating harvest levels.

One of the issues this year is the change to the model used in converting the trawl data to predicted legal male biomass, and subsequently the levels of harvest.

For snow crab, the model that is recommended would eliminate estimates of catch mortality, i.e. smaller crabs that are thrown back, as these estimates have been shown to introduce bias in the data.

Because of these changes, it is premature to assume a direct corelation between the volumes of biomass and the actual changes to harvest levels, however the trend toward lower legal male biomass will definitely have an impact on harvest levels.

The biomass surveys for all three crab species are giving fairly clear signals.

The 2015 Legal Male abundance of Red King Crab was 8.7 million crabs. This is 30% lower than 2014’s 12.4 million crabs. In 2014 the harvest level was set at 9.986 million pounds. The current abundance in 2015 is similar to the long term average in Bristol Bay. It is higher than in 2011 and 2012, but slightly lower than the 9.4 million crabs abundance measured in 2013. That year the harvest level was set at 8.6 million pounds. So one likely extrapolation may be a reduction in harvests in the 15% to 25% range.

For snow crab, there is a more significant change in the survey. Total Mature Male with greater than 95 mm carapace fell from 105,441 tons estimated in 2014 to 46,410 tons estimated in 2015. This is below the 20 year long term average, and a change in biomass of 56%. In 2013 the mature male biomass was 58,389 tons, and the harvest level was 53,983 tons. In 2014 the mature male biomass was 105,441 tons, and the harvest was increased to 67,950 tons. The drop in the mature male biomass to 46,410 tons suggests a significant reduction in Opilio harvests, likely in excess of 20%.

However, there was strong recruitment noted for snow crab, which appears to show that future year abundance may increase again and this may impact ADF&G’s analysis.

The crab species that showed some increase in biomass for legal sized males was Bairdi or Tanner Crab. The 2015 Estimate for the Eastern Bering Sea was for 22,853 tons, substantially above the 20 year average of 12,590 tons, but down from the 30,404 tons estimatedin 2014. However the Eastern Bering Sea legal male biomass is the 2nd largest since 1994.

In 2013 when this fishery reopened, the Eastern Bering Sea quota was set at 1.463 million pounds. In 2014 that increased to 8.48 million pounds. For 2015, the mature male biomass has dropped 26%, but the increase in retention of smaller size Bairdi has also occured. In 2014 the Board of fish changed the legal carapace size to below 5 inches from 5.5 inches in both the Eastern and Western Districts. However, industry practice is to aim for retention of a 4.9 inch carapace size. The current survey appears to support a continued robust fishery for Eastern Bering Sea Bairdi crab.

For the Western Area west of 166 degrees, the legal male biomass over 110 mm increased from 24,859 tons to 27,067 tons. This is the highest estimate in the time series since 1991. In 2014, the harvest level was set at 6.625 million pounds. The survey appears to support continuation or increase of this harvest level.

The crab plan team does not make actual harvest level recommendations to the ADF&G, but instead vets the survey and model data and raises questions which they feel the ADF&G should consider in the interpretation of these results.

However, the overall trend of the survey data shows the liklihood of a reduction in harvest levels for red king crab and Opilio, and likely Bairdi/Tanner crab as well. To sum up it appears from our review of prior years, that king crab harvests could be set 15% to 25% lower, Opilio harvests are likely to be cut by 20% or more, and Bairdi Harvests may be slightly adjusted with overall totals perhaps less than a 20% change.

The key point is that these are not excessive drops, but consistent with the variability seen in these crab populations over the past five years, and at least with Opilio there is good future recruitment. The survey data suggests that harvest levels, which spiked in 2014, will come back down closer to their recent five year averages.

Reprinted with permission of SeafoodNews.com