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Status of Stocks & Multispecies Assessment

Field Trials of Octopus Tagging: Pot Gear a Success

figure 1, small giant Pacific octopus
Figure 1.  A small giant Pacific octopus captured in habitat pot gear is prepared for measurement.  Photo by Elizabeth Conners.

figure 2, Don Dumm
Figure 2.  Crewman Don Dumm prepares to launch an octopus habitat pot.  Photo by Elizabeth Conners.

Research conducted by the AFSC and the University of Alaska, Fairbanks (UAF), with funding from the North Pacific Research Board (NPRB), is meeting with success in developing field methods for studying the giant Pacific octopus, Enteroctopus dofleini, in Alaskan waters (Fig. 1).

The three-pronged study, begun in 2009, is aimed at collecting basic life history information on this enigmatic species and developing field methods for further scientific study and management. Tagging efforts near Dutch Harbor in fall 2009 and spring 2010 resulted in over 400 tagged octopus, with 42 recaptures. A spring 2010 gear trial of longlined habitat pot gear (Fig. 2) off of Kodiak Island captured 91 live octopus, ranging in size from 2.5 kg (5.5 lbs) to 22 kg (48.5 lbs).

Changes to the fisheries management plan for the Bering Sea that will be enacted in 2011 call for separation of the "other species" category into separate management groups such as sculpins, sharks, squids, and octopuses. This means that the AFSC and the NPFMC will have to monitor and regulate catch for each of these groups separately in federal fisheries. Similar changes are expected for the Gulf of Alaska fisheries management plan within a few years. In preparation for this regulatory change, AFSC scientists have been compiling preliminary stock assessments for these "nontarget" groups. For most of these groups, information on such characteristics as life history, population biomass, growth patterns, and natural mortality is lacking.

Octopus has turned out to be a particularly difficult case. While some groups, like sculpins, can be assessed based on data from the groundfish bottom trawl surveys, a bottom trawl does not effectively sample octopus populations. Studies or surveys of octopus requires a specialized gear directed at octopus. This winter, AFSC and the Alaska Department of Fish and Game collaborated in designing and building "habitat pot" gear specifically for octopus. Small unbaited pots act as temporary lairs for the octopus, which stay inside when the pots are pulled to the surface. Four longline strings consisting of 40-45 pots of varying designs captured 91 octopus in May and June 2010; further testing of this gear is planned for fall 2010.

Tagging studies conducted by UAF scientist Reid Brewer near Dutch Harbor, Alaska, have confirmed the feasibility of a type of tag called a visible implant elastomer (VIE) tag for octopus. Dots of brightly-colored plastic are injected just under the octopus's skin on the back of the mantle, in an area with relatively little natural pigment. By using several different colors, many unique codes of three or four spots are possible. Octopus recaptured after several months still had readily visible tags.

Based on results of the preliminary study, NPRB has funded follow-up octopus tagging work for 2010-12. Researchers hope that tagging studies will document seasonal movement patterns in E. dofleini, which may be important in managing octopus as a state and federal resource. Tagging data may also be fitted to quantitative models that yield estimates of such parameters as natural mortality, growth, and local biomass. These parameters could prove very important for future stock assessment of this group.

In order to find out more about octopus life history, AFSC biologist Christina Conrath is examining gonad development in octopus specimens donated by commercial fishermen and caught during gear trials and trawl surveys. Community involvement from local scuba divers in Kodiak and Dutch Harbor is also being sought to locate octopus dens and incubating egg clusters. Research diving in both locations is planned to document the seasonality of egg laying and incubation in Alaskan waters. The project will continue through winter and spring 2011.

By Elizabeth Conners

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