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Kodiak Laboratory

Gulf of Alaska Small-mesh Trawl Survey, 2009

figure 8, haul locations map
Figure 8.  Haul locations (triangles) in the central and western Gulf of Alaska showing haul locations from the 2009 small mesh survey.

The annual small mesh trawl survey for shrimp and forage fish was conducted jointly by scientists from the RACE Division and the ADF&G in October 2009. The ADF&G research vessel Resolution conducted 134 tows which focused on the bays around Kodiak Island and also bays along the Alaska Peninsula including Pavlof Bay (Fig. 8).

The October 2009 survey was the most recent example of collaborative shrimp research by the two agencies dating back to 1971. Prior to 1971, the AFSC conducted exploratory shrimp surveys throughout the Gulf of Alaska and eastern Aleutian Islands. As a result of those surveys, a major shrimp fishery developed in the 1970s, and the ADF&G then became actively involved in small mesh surveys as well.

With the subsequent decline of the fishery in the 1980s, survey efforts declined; the RACE Division limited its survey efforts to Pavlof Bay, while the ADF&G continued surveys in Prince William Sound, Kodiak, and the Gulf of Alaska as far west as the Shumagin Islands. Currently, the RACE Division has withdrawn from directly conducting small mesh surveys but supports ADF&G surveys with personnel and financial support.

The length of the small-mesh time series makes it an important source of information on the changes to the marine ecosystem that have occurred in the North Pacific. For example, the time series was instrumental in documenting the transition from a community rich in shrimp and capelin to a community rich in groundfish following the 1976-77 regime shift tied to the Pacific Decadal Oscillation (PDO).

Results showed declining capelin (Mallotus villosus) and pink shrimp (Pandalus borealis) catch per unit effort (CPUE) and increases in arrowtooth flounder (Atheresthes stomias) and Pacific cod (Gadus macrocephalus) CPUE following the regime shift. In most parts of the survey area, results of the 2009 survey found these basic trends continued.

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

This community shift is perhaps best illustrated by the catch time series from Pavlof Bay on the south coast of the Alaska Peninsula (Fig. 9), the most consistently sampled bay in the survey area.

The 2009 survey in Pavlof showed little change in the overall composition of the post-regime shift community where pink shrimp and capelin remain at low levels and flatfish and cod playing a predominant role in the marine community. The long-term response to the 1976-77 regime shift, however, has not been uniform across the surveyed region.

  Aaren Ellsworth, Sherry Barker, and Colin Hakkinson
Figure 10.  Aaren Ellsworth, Sherry Barker, and Colin Hakkinson sort the shrimp catch on board the ADF&G research vessel Resolution.  The white bin contains juvenile walleye pollock.  Photo by Dan Urban.

The CPUE trends from Inner Marmot Bay on the northeast Kodiak archipelago are quite different from those found in Pavlof Bay (Fig. 9). Both bays saw dramatic shifts in community composition following the 1976-77 PDO regime shift, but in Marmot Bay shrimp catch rates stabilized at a much higher level (CPUE in 2009 of 12.5 kg km-1) compared to Pavlof Bay where CPUE has remained at historically low levels (CPUE in 2009 of 3.8 kg km-1). The reason for the differences in community organization between these two bays is poorly understood but may relate to bathymetry differences. Pavlof Bay is generally shallower and warmer than Inner Marmot Bay.

Also of note, the 2009 survey saw an approximately 30% increase in flathead sole and arrowtooth flounder in the bays around Kodiak compared to the 2007 survey which also targeted those bays. At the same time, some hauls contained over 50% pandalid shrimp, something not seen in recent years (Fig. 10). The smooth pink shrimp (P. jordani), a lower-latitude species which had been widespread in the past several small mesh surveys, virtually disappeared from the catch in 2009. The low catch rate may be in response to cooler water temperatures recorded recently.

Future work for the small mesh survey project includes completion of metadata for the 200-plus surveys in the database, the real-time integration of the ADF&G and AFSC databases including survey data from Cook Inlet and the outer Kenai coast not currently part of the dataset, and the inclusion of data recovered through a NOAA grant.

By Dan Urban

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