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Status of Stocks & Multispecies Assessment Program

Nearshore Research In Bristol Bay

figure 2, see caption
Figure 2.  (Note: not to scale.)  Top, a Crangonid shrimp captured in Nushagak Bay, Alaska; middle, juvenile rainbow smelt (Osmerus mordax); bottom, captured helmet crabs (Telmessus cheiragonus) awaiting their return to the water after being measured.  Photos by Olav Ormseth.

This summer, Dr. Olav Ormseth of the Status of Stocks and Multispecies Assessment (SSMA) Program conducted a nearshore fish and invertebrate survey in northern Bristol Bay, Alaska. The purpose of the project was to investigate the distribution and habitat of forage fishes and juvenile flatfishes and gadids in an area that has received little research attention.

Most of the AFSC's survey efforts are focused on offshore areas in water greater than 20 m depth. Ormseth's survey was an attempt to "fill the gap" by sampling from the 20-m depth contour in to the shoreline.

Two areas of the bay were sampled: one week was spent in Nushagak Bay, and a second week was spent to the west of the Nushagak Peninsula sampling in Kulukak and Togiak Bays and points in between.

Bad weather was constant on this trip, and wind direction and tidal state determined sampling locations in Nushagak Bay. (In other words, most of the sampling could only be conducted at low tide and on a lee shore).

A chartered Bristol Bay salmon gillnetter, F/V Willow, was the ideal vessel for this work. Limited to 32 ft in length by law (an attempt to limit effort) and designed to operate in shallow water, the vessel was able to accommodate several different gear types.

A beach seine was used to sample the shoreline and was deployed using a large skiff that was towed behind the boat when not in use. A small-mesh bottom trawl employing a heavyweight aluminum beam to provide horizontal spread was deployed off the net reel. These were the two main sampling types.

Ormseth also experimented with a Kodiak trawl, a large surface net that is towed by two vessels (the skiff served as the second vessel). While this gear proved effective (especially at catching young-of-the-year herring), it was cumbersome to deploy with all the other gear on board. One of the disadvantages of a small boat is the limited deck and storage space, as well as the number of scientific personnel (two) that can be accommodated.

Salinity and temperature are important habitat variables and were sampled using conductivity-temperature-depth recorders (CTDs). The CTDs used in this project were originally designed for groundwater monitoring and were small, lightweight, and relatively inexpensive units. Since they contained a memory chip, they could be deployed on moorings to look at changes in temperature and salinity over time. This was especially useful in Nushagak Bay, which has a huge tidal range.

Four CTDs deployed on simple moorings at different points in the bay revealed dramatic fluctuations in salinity over the course of a tidal cycle. Because fish species differ in their ability to handle varying salinity, such daily changes might be significant for fish distribution.

Catches in both areas were dominated by shrimp and smelts (Fig. 2). The vast majority of the shrimps were members of the family Crangonidae and were small (less than 6 cm). The smelts were mainly juvenile rainbow smelt, Osmerus mordax, as well as some adults of this species. These two groups were found in almost every haul in both areas.

In the Togiak area, small yellowfin sole (Limanda aspera) were abundant. Other fishes in the catches included a variety of sculpins, poachers, and Stichaeids. In general, catches were small and almost all of the captured fishes were small as well.

Perhaps the most unexpected result of the survey was the consistent species composition. Ormseth had hypothesized that the Togiak/Kulukak area would have a much different species composition due to the differences in topography and oceanography. However, the species composition appeared to change only gradually as the vessel headed west.

Shrimp became less common and juvenile flatfishes and helmet crabs (Telmessus cheiragonus) (Fig. 2) more common. These results are preliminary and data will be analyzed further in the coming year.

The survey was a success, and Ormseth hopes to do more sampling in this area. One important addition will be to sample in several different seasons. Researchers at the University of Alaska Fairbanks' Bristol Bay campus are conducting similar work in the upper parts of Nushagak Bay, and Ormseth hopes to coordinate his activities with them in the future.

By Olav Ormseth

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