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Shellfish Assessment Program

Gulf of Alaska Small-Mesh Trawl Survey

figure 7, see caption
Figure 7.  Haul locations (triangles) in the central and western Gulf of the 2010 small-mesh trawl survey.

The annual small-mesh trawl survey for shrimp and forage fish was conducted jointly by scientists from the RACE Division and the Alaska Department of Fish and Game (ADF&G) in October 2010. The ADF&G research vessel Resolution conducted 160 tows around Kodiak Island, Shelikof Strait, and along the Alaska Peninsula (Fig. 7). This recent survey was the latest effort in a collaboration that dates back to 1972.

The length of the small-mesh time series makes it one of the premier datasets in the North Pacific. It was instrumental, for example, in documenting the major Gulf of Alaska marine regime shift of 1976-77. Recently it has been combined with datasets from around the world for retrospective fishery analyses on a global scale including articles in the journals Science, "Rebuilding Global Fisheries" by Boris Worm et al. and Nature, "The Trophic Fingerprint of Marine Fishes" by Trevor Branch et al.

  figure 8, see caption
Figure 8.  Catch trends (3-year running average) of arrowtooth flounder, Pacific cod, and northern shrimp from Inner Marmot (A) and Pavlof Bays (B) from the 2010 small-mesh survey.

The Gulf of Alaska marine ecosystem changes documented in the 1976/77 regime shift are perhaps best illustrated by survey catches in Pavlof Bay, on the south side of the Alaska Peninsula. This bay has been the most consistently sampled in the survey area and still exhibits effects of the reorganization which resulted in the decline of shrimp and capelin (Mallotus villosus) and the rise of flatfish and Pacific cod (Gadus macrocephalus) (Fig. 8).

The 2010 survey saw little change in species composition from previous years although shrimp catches have recently increased modestly to around 3 kg/km. The long-term response across the Gulf of Alaska to the 1976/77 shift, however, has not been uniform. Marmot Bay on the northeast corner of Kodiak Island also saw community reorganization during the regime shift but shrimp populations, after a period of decline, stabilized at relatively high levels of approximately 25 kg/km (Fig. 8).

An interesting finding from the 2010 survey was the collapse of northern shrimp (Pandalus eous) in Wide Bay. Catch rates declined from 50 kg/km in 2009 to only 1.5 kg/km in 2010. The cause of this decline is not known, but the 2009 catch of 125 plain sculpin (Myoxocephalus jaok) per kilometer suggests that predation may have played a role in the decline.

Examination of plain sculpin stomachs during the 2010 survey revealed numerous northern shrimp, even at the current low shrimp densities. Also of interest is the near record level of eulachon Thaleichthys pacificus catches with the highest catches of 160 kg/km found in Stepovak Bay. Other areas with high densities of eulachon were Marmot Bay and Shelikof Strait.

Efforts continue to refine and integrate the databases that make up the time series of small-mesh surveys in the Gulf of Alaska from RACE Division and multiple ADF&G offices. Metadata has been developed, data proofing and editing methods have been implemented, and a method for versioning has been identified so that this dataset can continue to be updated while being made available to the public. Future efforts will continue to incorporate historical archived datasets into the database and to ultimately provide a tool for researchers to access the metadata and existing publications associated with this time series.

By Dan Urban
 

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