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Electronic Tagging of Juvenile Sablefish in Southeast Alaska

During September and October of 2003, 13 electronic tags were surgically implanted into juvenile sablefish (age 0+; 160-275 mm fork length) captured in St. John Baptist Bay, a rearing location in coastal southeastern Alaska near Sitka. The tags were programmed to acoustically transmit a record of temperature and depth experienced by the fish. Mobile acoustic receivers located onboard the NOAA ship John N. Cobb were used to monitor juvenile tagged sablefish behavior and habitat utilization in this rearing location. Fixed acoustic receivers located at the head of the bay near the rearing location and the open ocean are used to monitor the timing of juvenile sablefish emigration from nearshore rearing habitat to the more open waters of the Gulf of Alaska. Short-term objectives are to use electronic, acoustically transmitting sonic tags to provide information on 1) juvenile sablefish behavior and habitat use in nearshore rearing areas and 2) the timing and duration of the emigration from nearshore rearing habitat. Behavior of juvenile sablefish as they move to offshore waters is also being monitored by archival tags (76 inserted) and external Floy tags (750 applied).

By Tom Rutecki.

ABL Scientists Present Results at Deep-Sea Coral Symposium

Robert Stone and Patrick Malecha from the ABL attended the 2nd International Symposium on Deep-Sea Corals held in Erlangen, Germany, in September 2003. Stone gave a presentation titled “Deep-Sea Coral Habitat in the Aleutian Islands of Alaska” and Malecha gave a poster presentation titled “Sea Whip (Order Pennatulacea) Resiliency to Simulated Trawl Disturbance.” Stone also chaired a session on biodiversity and community structure, and displayed video footage of the 2002 and 2003 Aleutian studies during a special evening seminar. The conference was attended by more than 140 scientists from 18 countries.

By Bob Stone.

GLOBEC Research in the Gulf of Alaska

Scientists from the ABL and Pacific Marine Environmental Laboratory conduct annual surveys of juvenile salmon and associated marine species in coastal waters of the Gulf of Alaska, as part of the Global Ocean Ecosystem Dynamics (GLOBEC) research program. The surveys investigate physical and biological oceanographic processes affecting the distribution of juvenile salmon in the coastal Gulf of Alaska. Measurements focus on oceanographic properties and the distribution of zooplankton and salmon along 10 transects covering the continental shelf and slope.

The July-August 2003 GLOBEC survey began at Kodiak Island, Alaska, along the Cape Chiniak transect and ended near Yakutat, Alaska, on the Ocean Cape transect. Transects sampled during the survey also included Cape Kaguyak (offshore of the southwestern end of Kodiak Island), Cape Kekurnoi, and Cape Nukshak (located within Shelikof Strait), Gore Point and the Seward Line (located west of Prince William Sound), and Cape Cleare, Cape St. Elias, and Cape Yakataga (located between Yakutat and the Seward Line).

During the survey, 86 trawl stations were sampled and 15,442 salmon were captured. The largest component of the catch was juvenile salmon including pink Oncorhynchus gorbuscha; 52.7% of total catch), chum (O. keta; 16.5%), sockeye (O. nerka; 8.9%), coho (O. kisutch; 8.8%), and chinook (O. tshawytscha; <0.1%). Immature salmon in the catch included chum (4.0%), sockeye (1.2%), and chinook (0.3%); mature salmon in the catch included pink (5.7%), chum (1.1%), sockeye (1.2%), coho (0.4%), and chinook (<0.1%).

Salmon distribution varied by life history stage. Juvenile salmon were distributed mainly along the continental shelf with the highest catch per unit effort (CPUE = number of salmon caught during a 30-minute trawl) of juvenile pink and chum salmon occurring west of Prince William Sound (PWS). The highest CPUE of juvenile coho salmon occurred east of PWS, and the highest CPUE for juvenile sockeye occurred west of PWS and within Shelikof Strait. The highest CPUE for juvenile chinook salmon occurred along the Cape Cleare transect. Immature chum salmon were found along all transects sampled with the largest CPUE generally occurring at offshore locations beyond the 200-m contour. Immature sockeye salmon most commonly were distributed along transects on the Gulf of Alaska side of Kodiak Island. Immature chinook salmon were distributed mainly west of PWS; however, the station with the highest CPUE was located along the Cape Cleare transect. Mature pink and chum salmon were found along all transects sampled.

An additional study was done to determine the relationship between salinity and juvenile salmon distribution and refuted the hypothesis that juvenile salmon would be caught in less-saline Alaska Coastal Current water and not in saltier water located seaward.

By Ed Farley.

Sea Lice Infection of Juvenile Salmon in the Northern Region of Southeastern Alaska

Sea lice (Lepeophtheirus salmonis and Caligus spp.) are parasitic copepods which infect salmonids in both the Pacific and Atlantic Oceans and can cause reduced growth and mortality at high rates of infestation. Sea lice infection in wild Atlantic salmon (Salmo salar), Arctic char (Salvelinus alpinus), and sea trout (Salmo trutta) is a subject of increasing concern because infection rates may be increasing along regular migratory routes where salmon farming is practiced. Recently high rates of sea lice infection were observed for juvenile Pacific salmon in areas adjacent to commercial salmon farms in British Columbia. These observations and concerns about transmission from salmon farms to wild fish have underscored the need for better information on background levels of infection.

In 2003, ABL scientists initiated an assessment of the incidence of sea lice on juvenile Pacific salmon during their first months at sea in nearshore waters of southeastern Alaska, a region in which salmon farming is not practiced. Juvenile chum salmon cultured in seawater net-pens at three sites by a private nonprofit aquaculture corporation, Douglas Island Pink and Chum, Inc. (DIPAC), were sampled at the time of release from the net-pens. Juvenile salmon (pink, chum, sockeye, and coho) were sampled at sea in neritic waters from strait and coastal habitats by trawling from the John N. Cobb. Immature and adult salmon captured concurrently in the trawls were also examined for sea lice.

Differences in infection by sea lice were observed between species of juvenile salmon, between habitats and temporally. For juvenile salmon, prevalence (the percentage of fish with lice) and intensity (the number of sea lice per infected fish) were lowest for pink salmon, and highest for coho salmon over all sampling periods and habitats. Both juvenile pink and chum salmon had low prevalence of sea lice, 2.9% and 4.2%, respectively. For sockeye salmon juveniles, prevalence was 8.4%, and for coho salmon juveniles, prevalence was 53.2%. Prevalence and intensity of infection on adult fish were consistently higher than on juveniles of the same species; prevalence ranged from 33% on adult chum salmon to 100% on adult coho salmon examined.

No evidence of infection was seen on juvenile chum salmon sampled from net-pens in littoral areas after as many as 93 days rearing prior to release in May and early June. In late June, when juvenile salmon were first encountered in neritic waters, no evidence of infection was observed on juvenile pink and chum salmon, and infection of juvenile sockeye and coho salmon was 1.9% and 11.1%, respectively. Prevalence increased for juveniles of all four of these species from June to July, then declined from July to August, except for coho salmon. Prevalence of infection for juvenile salmon in July was higher in the inside strait habitat than in the coastal habitat in the Gulf of Alaska. Juvenile coho salmon were much more susceptible to infection in neritic waters than juveniles from other species.

The timing of infection of juvenile pink and chum salmon and the wide disparity between the prevalence of sea lice on juveniles and adults of these species are consistent with the hypothesis that sea lice infection of salmon also occurs in oceanic waters.

By Alex Wertheimer.


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