Understanding crab movement throughout different seasons is critical information in the management of Bering Sea crab fisheries. For instance, it tells us what habitats are important for crab and which habitats they use at different times of the year. For many years, researchers have studied where crab move using tags attached to crabs captured at sea. Researchers affix tags to captured crabs, release them and then wait for the crabs to be recaptured. Their location is documented when they are caught again and then researchers know where they travelled since tagging. This method only tells us two positions: where the crab was when it was tagged, and where it was when it was recovered. Recovery times and locations are also limited to when/where there is a fishery. These methods are typically limited by small sample sizes from very few tag recoveries.

To gather more information about other locations where crabs go between tagging and recovery, BSFRF scientists are collaborating with NMFS research partners Dr. Bob Foy and Dr. Leah Zacher to use new technology this summer.  The new technology uses VEMCO acoustic tags that communicate with unmanned drones that sail on the surface of the water. These Saildrones look like small sail boats. As they sail on the sea surface near tagged crabs, the Saildrones receive a ‘ping’ from the tags on the crabs. The Saildrones can then collect location data on these crabs without needing to recapture them. This method of releasing tags that “talk back” to a receiver has the ability to greatly improve sample sizes where multiple positions could be received from a single tagged crab once they are located by the Saildrone. In addition, the Saildrone can be sent out in different seasons in any location, so data are not restricted to when and where there is a fishery.

In June, BSFRF captured Bristol Bay red king crab during summer surveying (see article below) using pots. A total of 148 captured crabs were tagged and released and two “marker tags” were set out as reference points, attached to weights and dropped to the seabed. For each of the 148 red king crabs, tags were attached with a harness looped through a muscle in the back of the carapace, so the tags will be retained through crab molting. Each tagged crab had its tag “switched on” so that it began pinging, and the pings were tested for reception as each crab was released. In October, two Saildrones will be deployed from Dutch Harbor to sail out to the study grounds to relocate crabs that were tagged in June. The study is designed to determine crab movement from June to immediately prior to the commercial fishery which typically opens October 15. In March-April, 2020, the Saildrones will again be deployed to relocate tagged crabs and continue monitoring crab movement.

All vessels are asked to avoid the Saildrones to ensure they remain undamaged. Any commercial fishermen that captures a tagged red king crab should note the capture coordinates and tag number and quickly release it unharmed back into the water in the same location in was captured. If it is possible to measure the length and get a shell condition (soft, new, old shell), that information will also be helpful, but only if it can be done quickly without harm to the crab. Only if the crab is dead or heavily damaged should the tag be removed and returned to the researchers. The contact info of researchers to report Saildrone sightings or tagged crab encounters are; Dr. Leah Zacher (project lead for NOAA) reachable at [email protected], (907) 481-1730 work. Scott Goodman of BSFRF can also be reached at [email protected], (206) 285-3480 work, and (425) 232-5986 mobile.

Please stay tuned as BSFRF and NOAA will be conducting outreach related to this research in July 2019 through April 2020 to alert harvesters about the research project. Other research partners, including Alaska Department of Fish and Game and the Alaska Bering Sea Crabbers will assist in getting the word out to the fleet.

BSFRF is continuing its research into the growth rate of Tanner and snow crab in order to better inform the crab stock assessment models used in harvest management decisions. This project is a continuing effort, building on prior years’ sampling and growth monitoring. Our research team, which was led by Madison Shipley, BSFRF/NRC and included Erin Fedewa of NOAA (Kodiak), and Charles Heller, BSFRF/NRC, returned in April from a ten-day sampling trip to capture pre-molt Tanner and snow crab around the Pribilof Islands. The study is looking at how much crab grow between molts and to improve upon the limited samples of growth per molt that are available from Bering Sea crabs.

We were operating onboard the F/V Half Moon Bay under charter to complete the growth sample collections. We used a specialized Nephrops trawl which can capture very small-sized crabs while maintaining optimum contact with the sea bottom. We completed 34 trawl tows, capturing several thousand crabs, and retained 464 crab samples within targeted size classes between 15 mm and 105 mm. After capture, crabs were sorted to retain only “pre-molt” crabs which were held in small-mesh bags in tanks on deck during the charter. After return to port, crab were transported to the Kodiak NOAA shellfish laboratory and placed individually into stacked plastic containers. Crabs were then monitored daily for molting. Once a molt occurs, the old carapace and the newly formed carapace widths are measured and the growth increment is recorded.

The growth per molt of both Bering Sea snow crab, Chionoecetes opilio , and southern Tanner crab, Chionoecetes bairdi , has proven to be a critical poplulation parameter that informs the annual status estimates of these crab stocks. Improving the understanding of growth for the snow and Tanner crab is expected to improve the stock assessments, management, and sustainability of these commercially important stocks over time. This research is another example of how BSFRF works with our research partners to improve the science of crab management in the Bering Sea.

BSFRF has recently completed our primary summer survey activity. The approach for this year’s field work was to maximize the time on the water to accomplish as many research objectives as possible which included collections for a number of other collaborating projects. The main objectives included using the BSFRF Nephrops trawl to target juvenile Tanner crab areas and to then switch gears and use standard crab pots for the capture of red king crab for our first efforts with new tagging technology. Both main project objectives were achieved during sampling. The F/V Royal American was chartered for a 22-day period in June out of Dutch Harbor and served as an excellent research platform as it is a capable and active catcher vessel, with current gear and capacity for both trawling and crab pot fishing.

From June 8-25 BSFRF completed crab-specific trawl surveying in outer Bristol Bay for juvenile Bering Sea Tanner crab. A total of 115 trawl tows were completed over 29 NMFS survey blocks within the standard NMFS survey area. The BSFRF Nephrops trawl was used during these 115 tows for sampling juvenile Tanner crab at 4 randomly selected locations within each NMFS block. The blocks covered this year were identified during BSFRF’s prior years of sampling for juvenile Tanner crab (2016-2018). The results from this June’s work are expected to be added to prior years’ work to help further inform NMFS trawl efficiency, independent estimates of juvenile Tanner crab year classes, and potential estimates of natural mortality.

For the red king crab capture and tagging work the capture, tagging and release of the full planned sample was a success. The Royal American was in communication with both NMFS survey vessels (the F/V Vesteraalen and F/V Alaska Knight) to obtain the locations of red king crab catches during NMFS surveys. Contingent plans for the BSFRF pot surveying importantly included coordinating with 4 other specially-permitted industry crabbers that were on standby, each ready to also deploy 10 pots. The contingent planning was designed to allow for a total of 50 pots soaking to help find crabs for tagging in the event that catch rates were low. During June 13-15, a total of 10 commercial red king crab pots from the Royal American were baited, soaked for 48 hours and hauled to catch the targeted mature red king crab males. Catch rates were high enough that by the fourth pot pull, all of the target sample of 150 mature males had been captured, tagged and released. The remaining six pots were pulled and all crabs were released unharmed. The contingent vessels were notified that no further help from them was required. During the soaking period, the Royal American was able to switch back to continued trawl surveying.

One of the important aspects of BSFRF field work is to allow a spot for our major cooperative research partners to participate first-hand with our research. For our summer field work, this typically means that we hold a spot for both NOAA and ADFG to have their scientists come out with us on our surveys. The science party onboard the Royal American in June was again a combination of our cooperating research partners. Madison Shipley, BSFRF/NRC led the research as the field party chief. Dr. Leah Zacher, NOAA/Kodiak, Julia Dissen, ADFG/Kodiak, and Charles Heller, BSFRF/NRC made up the science party onboard, working well together for the successful completion of this work.