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Marine Salmon Interactions Program

Live Capture of Young-of-the-Year Slope Rockfish

aquarium codend
Figure 1.  Aquarium codend (livebox) ascending the stern ramp of the vessel Medeia.  A trap door in the stern of the aquarium codend allows fish and invertebrates to enter a water-filled chamber free of turbulence.
 

Slope rockfish (Sebastes spp.) are an important part of the ecosystem and a valuable fishery in the North Pacific Ocean. The most abundant and historically most harvested slope rockfish is the Pacific ocean perch (S. alutus). Other important slope rockfish species include shortraker (S. borealis), rougheye (S. aleutianus), and northern rockfish (S. polyspinis).

As young-of-the-year, slope rockfish can be found in the upper water column over abyssal depths. Eventually, they adapt to a demersal life and are associated with the benthos. The relationship between juvenile slope rockfish and benthic habitat is poorly understood due to the depths at which the fish reside, which is usually greater than 150-200 m. Aside from broad-scale habitat associations determined from trawl data and limited observations from submersibles and ROVs (remotely operated vehicles), little data exist that detail habitat use of these deep-dwelling rockfish species.

Because it is difficult and expensive to bring scientists to the natural milieu of slope rockfish, new research is bringing slope rockfish to scientists, with the ultimate objective of identifying habitat utilization amongst various benthic habitat types such as sponge and coral. In September 2007, scientists from Auke Bay Laboratories (ABL) Marine Salmon Interactions (MSI) Program and the Marine Ecology and Stock Assessment Program took part in research activities aimed at capturing live young-of-the-year slope rockfish.

  unidentified rockfish
Figure 2.  Unidentified rockfish (Sebastes spp.) caught with an aquarium codend in surface waters offshore of Southeast Alaska.

Thirty-three surface trawls were performed onboard the Alaska Department of Fish and Game (ADF&G) vessel Medeia. Trawling took place up to 60 nautical miles offshore of Southeast Alaska between Icy Point and Cape Ommaney. The trawl was equipped with an aluminum aquarium codend (livebox) (Fig. 1) that directed fish and invertebrates into a calm water-filled holding chamber. Once on deck, live specimens were transferred from the aquarium codend to holding tanks with running seawater. At the conclusion of the cruise, live rockfish were transferred to ABLís Little Port Walter Marine Station and placed in aquariums in the stationís behavior laboratory. Of the 230 rockfish captured, about 95% survived the trawling process including fish as small as 14 mm (Fig. 2).

An estimated eight or nine different species of rockfish were captured, although genetic analyses will confirm species identifications. The aquarium codend caught other live species as well, including juvenile and adult salmon (Oncorhynchus spp.), Pacific saury (Cololabis saira), larval rex (Glyptocephalus zachirus), Dover sole (Microstomus pacificus), and Pacific herring (Clupea pallasii). Many unidentified small squid were also captured live. The greatest biomass in the catch was attributed to jellyfish, primarily Aequorea sp.

Once the rockfish are acclimated to conditions in the behavior lab, they will be observed in four distinct habitat types (coral, sponge, cobble, and gravel) under both daytime and nighttime conditions and in the presence and absence of a predator. This study will build on previous work that focused on quillback rockfish (S. maliger), a demersal shelf rockfish. These assessments will be helpful in determining the relative productivity of various habitats and will aid in establishing priorities for their protection.

By Pat Malecha


SECM Pink Salmon Forecast on Target for 2007

Since 2004, ABL researchers have used information from the Southeast Alaska Coastal Monitoring (SECM) project to forecast adult pink salmon commercial harvest in Southeast Alaska. The SECM research, which focuses on juvenile salmon and their associated epipelagic species and oceanographic parameters, occurs from May to August as juvenile salmon migrate seaward to the Gulf of Alaska from southeastern Alaska. The parameters used in the forecast model are peak monthly average catch-per-haul of juvenile pink salmon and spring ocean temperatures.

The SECM forecast for 2007 was 40.0 million pink salmon. The ADF&G preliminary harvest estimate for the 2007 season is 44.0 million pink salmon. An accurate forecast has major economic consequences to the industry because it enables processors and fisherman to devote the proper amount of resources to the anticipated harvest, which for pink salmon has an average exvessel value of about $20 million in the Southeast Alaska region.

In 2007, for the first time, ADF&G scientists used SECM juvenile pink salmon catch-per-haul data to improve their forecast, which previously relied exclusively on an exponential smoothing model of past harvest levels. By incorporating the SECM juvenile salmon index data into their model, ADF&G adjusted their original forecast for the 2007 harvest from 58.0 million to 47.0 million, much closer to the realized harvest of 44.0 million fish. The convergence of the two different forecast models towards similar predictions is indicative of the utility of the juvenile salmon index time series.

Catches of juvenile pink salmon during the 2007 SECM cruises were the lowest in the 11-year time series of the project, suggesting that pink salmon returns to Southeast Alaska in 2008 will be poor. The 2007 survey data are currently being finalized, and results and the 2008 SECM forecast will be presented at the Southeast Alaska Purse Seine Task Force meeting in Ketchikan, Alaska, on 28 November 2007. The task force meeting is an annual event sponsored by the ADF&G, the commercial purse seine fishing fleet, fishing industry processor representatives, and other resource stakeholders from Southeast Alaska communities.

By Alex Wertheimer, Joe Orsi, Molly Sturdevant, and Emily Fergusson
 

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