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Midwater Assessment & Conservation Engineering (MACE) Program

Gulf of Alaska, Integrated Ecosystem Research Program (GOA IERP)

Gulf of Alaska map, see caption
Figure 1.  Map showing the Gulf of Alaska Integrated Ecosystem Research Project (GOA IERP) study area, Middle Trophic Level sites, and other GOA IERP-related station locations including the those for the spring cruise aboard the R/V Thomas G. Thompson.

Scientists from the AFSC's Midwater Assessment & Conservation Engineering (MACE) Program and Resource Ecology and Fisheries Management (REFM) Division participated in two pilot studies for the Middle Trophic Level (MLT) (or forage fish) component of the Gulf of Alaska Integrated Ecosystem Research Project (GOA IERP), funded by NOAA and the North Pacific Research Board.

The first pilot study occurred aboard the chartered fishing vessel Sea View, a 54-foot longliner, during 14-25 July in the eastern Gulf of Alaska (Fig. 1). The second study occurred aboard the chartered fishing vessel Gold Rush, a 99-foot trawler, from 23 October to 2 November in the central GOA.

The work focused mostly on small forage fish such as capelin (Mallotus villosus) and Pacific sand lance (Ammodytes hexapterus) as well as on juvenile stages of walleye pollock (Theragra chalcogramma) and Pacific cod (Gadus macrocephalus).

The aspect of the MTL work presented here focused on the shallow (<40 m) near-shore habitat range of these fishes where use of specialized gear is needed to effectively sample these shallow depths and small fish sizes. In addition to verifying the suitability of proposed sampling sites (Fig. 1) such as accessibility to vessel, the objective of the two pilot studies was to evaluate whether a variety of fishing gears, including a beach seine, a purse seine, a variable-mesh vertical gill net, a midwater trawl, and a beam trawl were appropriate samplers for these species in their nearshore habitat.

In addition, a conventional fine-mesh try net (i.e. a miniature bottom trawl) was modified into a small single-warp midwater net by the Research Fishing Gear Program staff and Research Nets, Inc. (Bothell, Washington) to evaluate during the second pilot study.

Acoustic measurements of fish abundance were made using three calibrated acoustic systems:  1) a Simrad ER60 echosounder and towed fin with 38- and 120-kHz transducers was deployed from the Sea View,  2) the vessel-mounted Simrad ES70 38-kHz system was used aboard the Gold Rush,  and 3) a portable ER60 system with a pole-mounted 120-kHz transducer was deployed from a work skiff. A lowered video camera also was used to assess aquatic vegetation and identify fish species, and a conductivity-temperature-depth instrument was used to take vertical profile measurements to define hydrographic structures such as fronts relevant to the distribution of the near-shore fishes.

These pilot studies provided critical information during the early stages of the GOA IERP project to develop a comprehensive survey plan appropriate for the near-shore areas using a variety of sampling tools and methods. An important result of this field work was that the new midwater try-net could be effectively deployed using a single warp, which is important as future work will be conducted on smaller vessels that likely do not have the capability to fish double warp trawls. Also, large concentrations of young-of-year capelin (~5 cm standard length) were detected and successfully captured with the different sampling devices in the vicinity of the Barren Islands.

Results of these two feasibility studies have provided valuable insight for planning the subsequent GOA IERP near-shore MLT field work is scheduled for April, July, and September in 2011 and 2012.

By Chris Wilson

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