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Shellfish Assessment Program - Kodiak Laboratory

The Kodiak Laboratory Dive Program

Figure 6, click to enlarge
Figure 6.  Click image to enlarge.



Figure 7, click to enlarge
Figure 7.  Click image to enlarge.



Figure 8, click to enlarge
Figure 8.  Click image to enlarge.



Figure 9, click to enlarge
Figure 9.  Click image to enlarge.



Figure 10, click to enlarge
Figure 10.  Click image to enlarge.
 
 

Soon after the creation of NOAA in the early 1970s, the AFSC Kodiak Laboratory (KL) was established in Kodiak, Alaska, to conduct assessments and research on commercial shellfish resources in Alaska. The scientific divers formally affiliated with the Bureau of Commercial Fisheries became a part of the newly established NOAA Dive Program, which was created to organize the dive efforts of the various branches of NOAA. As the NOAA Dive Program evolved to lead scientific diving development and policies, the KL Dive Program evolved from an intermittent effort by a few minimally trained and marginally equipped divers, to a highly trained and well equipped team of divers conducting year-round field research.

In the early 1980s the red king crab (Paralithodes camtschaticus) fishery off Kodiak collapsed after sustaining average harvests of 20.0 million lb between 1950 and 1984 and a peak harvest of 94.4 million lb in 1965. This prompted scientists in the KL Dive Program to focus efforts on red king crab recruitment processes. In particular, scientists studied red king crab biology and life history in Womens Bay, a red king crab nursery area where dense aggregations (pods) were observed (Fig. 6). Divers located and studied two crab pods intensely for several months with both night and daytime dives. They found a diel pattern where the pods disperse and forage nocturnally and reform during the day. The most frequently observed prey items were sea star, primarily Evasterias troschelii, and the macrophytes Laminaria sp. and Ulva sp.

Also in response to declined crab stocks, scientists in the KL Dive Program identified and studied important nursery habitat on the north end of Kodiak Island. Some of this research was intended as feasibility studies for potential enhancement efforts. Womens Bay was determined to be preferred red king crab habitat compared to nearby Anton Larson Bay and Trident Basin. A study funded by the U.S. Army Corps of Engineers found that artificially-placed wood-piling structures were populated by settling crab larvae similar to that found on other dock pilings in Womens Bay and other areas. While red king crab enhancement never materialized, Womens Bay has continued to sustain a red king crab population, although abundance remains depressed throughout their natural range.

To better understand red king crab spatial distributions and movement patterns within preferred habitat, KL Dive Program scientists have experimented with the use of acoustic tags on individual crabs in Womens Bay. While the focus has been on pods of juveniles, tagged crab have facilitated the long-term monitoring of crab reproductive behavior, growth, cohort mixing, and molting seasons and frequency across all age classes. One juvenile pod was tagged and tracked (Fig. 7) for over 4 years and produced more than 900 individual tag locations to document the podís long-term movement pattern. One hundred and seven dive observations were made, and 66 crab collections were conducted and provided a continuous record of growth for a single cohort. Mass-molting events were observed on several occasions with an entire pod of several thousand crabs molting over a 2-3 week period; juvenile crab growth in one event during the winter was also characterized (Fig. 8).

In addition to red king crab, other species such as Tanner crab (Chionoecetes bairdi) and green sea urchins (Strongylocentrotus droebachiensis) have been studied by scientists in the KL Dive Program. Tanner crab research has focused on the timing of the mating and molting season, maturity, and growth (Fig. 9). The timing and duration of Tanner crab mating seasons was found to vary considerably between pubescent (first time) and multiparous (second time or more) females. Pubescent mating occurs over a wide, 8-month range which peaks in February, whereas multiparous mating takes place over a relatively narrow period that peaks in late April-early May. Multiparous females do not molt at mating and are further constrained by the need to hatch a clutch of eggs prior to subsequent mating. Like Tanner crab research, green sea urchins research has focused on reproduction and growth. A developing urchin fishery off Kodiak needed information on the factors affecting gonad recovery and quality, as well as an estimate of size at age. It was found that maximum roe recovery rates could be obtained by restricting harvest to urchins 50 mm and larger, and the majority of a year class should reach this size by age 3.5 years.

More recent efforts of scientists in the KL Dive Program are focused on understanding the importance of pre- and post-settlement processes that affect early recruitment in red king crab, integrating field and laboratory studies of larval supply, settlement, and predation processes in the earliest benthic stages (Fig. 10). As part of this study scientists will use scuba methods to characterize initial settlement habitat and its utilization.

The KL Dive Program continues to provide an important tool for scientists to better understand the marine benthic community from a unique perspective. The geographic location of the KL in the rich marine waters of the Gulf of Alaska provides the opportunity for year-round and long-term dive and field operations that, when combined with the KL seawater facility, offers researchers a unique capability to conduct research to better understand the marine environment.

By Pete Cummiskey, Eric Munk, and Robert Foy
 

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