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Status of Stocks & Multispecies Assessment Program

Discard Mortality for Octopus

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octopus
Giant Pacific octopus on deck during the AFSC Aleutian Islands trawl survey.  Photo by Christina Conrath,
AFSC, Kodiak.
 

Among the many issues currently being discussed by the North Pacific Fishery Management Council's Plan Teams and AFSC scientists is a proposal to use discard mortality in catch accounting for the new Bering Sea and Gulf of Alaska octopus complexes.

The Council has recently divided the old "other species" complex in both fishery management plans into separate management categories for sculpins, sharks, skates, squid, and octopus. Current federal regulations require that any of these species groups that are retained and sold must have an annual upper catch limit, even if they are not target species.

Monitoring and regulating these groups separately will provide better overall ecosystem management, but some problems have come up due to the lack of data for many of the new groups. Octopus, in particular, is problematic because the AFSC bottom trawl surveys that are used to evaluate abundance of most groundfish do not work well for these animals.

octopus
A small octopus getting its length and weight recorded.  Photo by M. Elizabeth Conners, AFSC, Seattle.
 

In 2011, the Bering Sea Plan Team set catch limits on the new octopus complex under Tier 6 of the Council's assessment structure, using the maximum of incidental catch taken from 1997-2007 as the overfishing limit (OFL) for this group. However, fishermen caught more octopus in the Bering Sea in 2011 than ever before, and reached the OFL in early October. The consequent early closure of the Pacific cod pot fishery has brought a lot of attention to the issues of these new species groups.

Octopus are different from most groundfish in that they do not have a swim bladder, so the sudden pressure changes from being brought to the surface do not cause traumatic injury. Fishermen and scientists observe that most octopus caught in cod pots are alive and very active when brought to the surface.

Because of this, the octopus stock assessment author suggested that Plan Teams consider using a discard mortality factor in catch accounting for octopus. This is an approach in which the condition of a discarded animal is considered, and animals or fish that are expected to survive capture and discard are not counted toward the overall "take" of the fishery.

Since many of the octopus caught are discarded rather than kept for market or bait, this method could reduce the impact of octopus bycatch on the Pacific cod fishery. At present, this approach is used in Alaska only for Pacific halibut. All other groundfish accounting uses the conservative assumption of 100% mortality for all fish caught, whether retained or discarded.

giant Pacific octopus
AFSC Biologist Christina Conrath releases a giant Pacific octopus.  Photo by Tschersich, ADF&G, Kodiak.
 

Data on the condition of discarded octopus was collected from 2006-07 and 2010-11 in an observer special project. Observers recorded the condition of octopus based on color and mobility and the presence of visible wounds. Data from both projects suggest that counting all discarded octopus as dead may be overestimating the impact of fishing on this group.

In this study, less than 5% of the octopus caught with pot gear were dead or visibly injured when examined by observers. Approximately 20% of octopus in longline gear were dead or injured. Octopus caught in pelagic or bottom trawl nets were generally in poorer condition, probably because of the longer time between capture and processing. In trawl gear, 50%-85% of the octopus were dead or seriously injured.

Research needed for this approach is not complete. While the observer project data give us a good idea of what percentage of octopus are discarded in good condition, we still need to estimate how many of those discarded octopus survive to return to the bottom.

AFSC scientists have proposed projects to look at the longer-term effects of capture and handling on octopus by holding caught octopus in running seawater tanks, either on board an actively fishing vessel or in the AFSC Kodiak Laboratory. Once these studies have been completed, the Council and Plan Teams can decide whether the extra complication of including discard mortality in octopus catch accounting is justified to improve the management of octopus and cod fisheries.

By M. Elizabeth Conners
 

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