Dataset: red crab tag_returns

Return Data for Red Crab Tagged

Project Leader:
Richard A. Wahle, Bigelow Laboratory for Ocean Sciences
Additional Participants:
Jon Williams, Benthic Fishing Corp.
Yong Chen, University of Maine

Companion objects:
red crab sampling data
red crab tag data
redcrab camera data
redcrab temp data
red crab trawl log data
redcrab trawl data.

"The objectives of the main project were to: (1) Employ camera-based and net-trawl sampling methodology established by an earlier NMFS red crab surveys (Wigley et al. 1975) to determine wheter abundance, size structure, and sex composition of the population has changed significantly at the same sites sampled in 1974, (2) Conduct sea sampling to better characterize the commercail catch, (3) Conduct tagging to obtain much needed information on red crab growth rates and movement, and (4) Develop three stock assessment modeling approaches of different complexities (size-structured yield-per-recruit model, production model, and size-structuredied simulation model) to evaluate the dynamics of the red crab stock, estimate current status of the fishery, and evaluate alternative management strategies. The supplemental project compared the efficacy of otter-trawl to net trawl in this application.

The benthic sled system for camera surveys combined with net trawl collection generated the first population density estimates and demographic data of red crab in 30 years. The comparison of the two net trawl methods confirmed that otter trawls were the most efficient approach in these surveys. Results of the main project indicated that the abundance of the largest crabs targeted early in the history of the fishery (males>114 mm, 4.5 inches) is down by approximately 42% since 1974. Based on sea sampling data the fishery now harvests smaller male crabs, and the standing biomass of crabs currently harvested is on a par with 1974 levels. The abundance of smaller males and females is substantially higher than in 1974. Some 9600 crabs were tagged over the course of the study, and of about 300 returns there was little evidence of growth, which is consistent with prior evidence of slow growth for this species. However, the limited growth data curtailed application of the stock assessment models. The full parameterization of these models awaits addtional growth data. Models are implemented as Excel spread sheets that and are available from the PI, and will be easy for the user to update as data become available. These results were a key component of the NMFS red crab stock assessment conducted in 2006. "(extracted from: Final Report Submitted to the NORTHEAST CONSORTIUM, December 11, 2006)

Questions regarding this data set should be directed to:
Richard A. Wahle
Bigelow Laboratory for Ocean Sciences
P.O. Box 475
West Boothbay Harbor, ME
04575

Phone: 207 633-9659
E-mail: rwahle@bigelow.org