Adult Male Dungeness Crab (Metacarcinus magister) Movements near Reedsport, Oregon; A Collaborative Mark-Reacpture Study

Defense Date

3-25-2016

Document Type

Capstone

Degree Name

M.S. Coastal Zone Management

First Advisor

Bernhard Riegl

Second Advisor

Sam Purkis

Abstract

Oregon’s commercial fishing industry is concerned about potential effects from proposed wave energy projects being planned in Oregon’s Territorial Sea (OTS). These concerns range from where devices will be put in relation to important fishing areas, from concerns about marine species such as Dungeness crab. Specific concerns about Dungeness crab are about potential impediments to their movement, behavior, and harvest. Though crabbing has been an important species economically for decades, there is little scientific information available on the movements of adult Dungeness crab, and no recent studies conducted in Oregon.

To help address this critical information gap, The Oregon Wave Energy Trust (OWET), the Oregon Dungeness Crab Commission (ODCC), granted funds to Oregon Sea Grant (OSG) to design and implement a collaborative research study on the movement of adult male Dungeness crab. Legal Sized male crabs (6 1/4” carapace width) were tagged at three locations near Reedsport, Oregon in October and November of 2009. A total of 2788 tags were deployed and crabs were recaptured in the commercial crab fishery, which stated on December 1st, 2009. Tags were returned to Oregon Sea Grant with recapture locations and a $20 reward per tag was given to the fishermen or vessel who returned the tag. Outreach materials were sent out to commercial Dungeness crab permit holders, seafood processors, ports, and were also at locations that commercial fishermen frequent (gear yards, marine supply stores, etc.).

Out of 2788 tagged crabs released, 952 crabs were recaptured and the tags returned to Oregon Sea Grant. A total of 626 tags were returned with location data of sufficient detail for analysis. The overall return rate of 34.15% is notably high for a mark-recapture study; however, this is not unreasonable because adult male crabs are what commercial crabbers are allowed to retain, thus a high percentage of adult male crabs are harvested each season. Additionally this study was specifically designed to have a high mark-recapture rate. A historic Oregon crab tagging study had a similar return rate. Crabs traveled distances ranging from 0.27 km to 90.68 km. 65% of crabs traveled less than 20 km, 77.7% of crabs traveled less than 30 km, and 95.5% of crabs traveled less than 50km. Crabs moved primarily in the alongshore direction, with minimal across shelf movement.

While the primary goal of this study was to study movements of adult male Dungeness crabs in Oregon, the secondary goal was to have a collaborative research project with commercial fishermen. To evaluate our secondary goal, we mailed surveys to fishermen who had returned at least one tag. We asked 10 questions, relating to their motivation for participating in the study, the value they thought they added to the study, perceived risks of participation, and ease of participation. 85 surveys were mailed and 42 surveys were returned, giving a survey return rate of 49.41%. 88% percent of respondents were commercial fishermen, 12% were recreational fishermen, 7% were seafood processors or unloaders, and 5% were charter fishermen.

60% percent of participants reported they participated in the study because they were concerned about wave energy. 57% participated because they wanted the reward and 48% reported their interest in research as a motivating factor. Respondents were allowed to select multiple reasons for participation, thus percentages do not add up to 100%. Most respondents did not think there was a drawback to participating in the study and 95% said they would participate in again in the future. Respondents were also asked open ended questions relating to any suggestions they have for future studies. These answers typically fell into four categories 1) concerns about potential environmental effects from wave energy 2) concerns about the priority of fishermen’s interests in wave energy and territorial sea planning activities 3) comments on clerical issues and 4) suggestions for future tagging studies.

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