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Experiments were completed to examine the periodicity of otolith increment formation in the sagittal otoliths of juvenile sablefish (age 0, size range 73 mm to 186 mm). Otolith increments are alternating light and dark bands visible under a transmitted light compound microscope at magnifications of 250X to 1,000X. A daily periodicity of otolith increment formation in juvenile sablefish (age 0) has been postulated but never validated. The periodicity of otolith increment formation was tested in this study by chemically marking the otoliths of captive juvenile sablefish with strontium chloride (SrCl2).
Approximately 30 post larval neustonic sablefish were captured along the continental shelf and transported alive to Auke Bay Laboratory on 1 June 2000. The fish were maintained in seawater tanks for up to 104 days. The water temperature was elevated and held at a constant 13°C, and the photo period was lengthened and held at a constant 16 hours of light per day. The otoliths were chemically marked by immersing the live fish in seawater containing 1,000 ppm SrCl2. For chemical marking, the fish were split into three groups of roughly equal size. The first group was marked in June, the second group was marked in July, and the third group was marked in August. Each group was marked twice over a period of between 15 - 17 days, and each group was sacrificed between 14 -17 days after the second marking event. The otoliths of marked fish were processed into thin sections and the resulting strontium bands were detected with electron scanning microscopy by staff at the University of Alaska, Fairbanks. For each otolith, the number of increments between strontium bands were counted and compared to the number of days between SrCl2 immersions. The number of otolith increments detected between strontium bands ranged from 10 to 25, and in general did not agree with the number of days between marking events (15 - 17 days, average percent error in agreement 19.5%). These results suggest that either the otolith increments detected in this study did not form with a daily periodicity or that the methods used in the study to detect otolith increments were not accurate. In either case, the use of a less complicated structure, such as the lapilli otolith, or a more accurate otolith increment detection method, such as scanning electron microscopy, may be required to validate the periodicity otolith increment formation for the size range of juvenile sablefish examined in this study.
Age determinations of juvenile sablefish from lapilli otoliths were completed for fish collected in the Gulf of Alaska from 1999-2001. Up to 30 lapilli were read for daily age by staff under contract at the Hatfield Marine Science Center, Oregon State University. Age determinations will be used to estimate birth date and calculate growth rates for comparisons with year-class strength, estimated from age-structured modeling of adult sablefish.
By Dean Courtney.
Data entry of sablefish tag releases and recoveries and administration of the tag reward program continues. About 600 tags have been received for 2001 so far, down slightly from the last 3 years. Tag releases for adults and juveniles, now total 308,970. There are 24,004 recoveries to date. Over 17% of the fish recovered in 2001 had been at liberty longer than 15 years. The three fish at liberty the longest (28+ years) were all released in upper Chatham Strait in 1973. Two were recovered in Chatham Strait and one off Queen Charlotte Sound in Canada.
The tagged fish otolith collection was brought up to date recently. There are now over 900 sets of otoliths in the collection. The number of tagged fish otoliths being collected has increased dramatically during recent years, due to increased coverage of the fishery by National Marine Fisheries Service (NMFS) observers. Many of the recovered fish were out over 10 years and most were out at least 2 years before recapture, and they should provide good information on growth and ageing when they are processed.
By Nancy Maloney.
All the abundant species of slope rockfish in Alaska are usually assumed to be extremely variable or clustered in their distribution. Little analysis, however, has been done on this subject, especially regarding comparisons of variability among the different species. In this study, ABL scientists first examined data for Pacific ocean perch, shortraker rockfish, and rougheye rockfish from three experimental bottom trawl surveys in the Gulf of Alaska in 1993, 1998, and 1999 to compare the variability of catches for each species. Although these surveys were relatively small in scope, they all used the same survey vessel, the F/V Unimak and the same experienced rockfish commercial captain, together with a net specifically designed for catching rockfish. Thus, they likely provide some of the best survey data available for these three species in Alaska. When catches of each species were analyzed within their optimum habitat, the coefficient of variation for Pacific ocean perch was approximately 2.5 to 3 times greater than that of shortraker and rougheye rockfish, indicating that Pacific ocean perch are much more clustered in their distribution. Shortraker and rougheye rockfish were similar to each other in their variability.
To provide additional comparisons of variability over a broader geographic area, catches of the three species were also examined from seven large-scale trawl surveys conducted by the AFSC Resource Assessment and Conservation Engineering (RACE) Division in the Gulf of Alaska from 1984 to 2001. Again, the analysis only included hauls that were made within the optimum habitat for each species. Results were very similar to the previous results from the experimental surveys: variability of Pacific ocean perch catches was about 2-3 times greater than that for either shortraker or rougheye rockfish. Overall results of this study indicate that a stratified random trawl survey directed at shortraker and rougheye rockfish would be logistically feasible, because the low variability of these two species would require relatively few hauls to be made. However, a similar random survey aimed at a highly variable species such as Pacific ocean perch is probably not feasible because it would require too many stations to be cost effective. New and innovative methodologies for surveying Pacific ocean perch, such as the use of echosounders in combination with trawling, will be necessary to improve assessment of this species. Results of this study were presented at the 2002 Western Groundfish Conference in Ocean Shores, Washington, in February 2002.
By David Clausen.
We examined distribution, habitat, and behavior of rockfish, Sebastes spp., with a remotely operated vehicle (ROV) in coastal waters less than 90 m deep of southeastern Alaska from 1998 to 2000. We identified black, canary, China, copper, dusky, harlequin, Puget Sound, quillback, redstripe, rosethorn, silvergray, tiger, yelloweye, and yellowtail rockfish. Quillback and dusky rockfish were the most widely distributed species, China and harlequin rockfish were the least widely distributed species. Species abundance was greater at sites on or near the outer coast than at sites in more inside, sheltered waters. Most (>75%) observations of rockfish were over complex bottoms of boulder and rock or in vertical bedrock wall habitats. Few rockfish were observed over soft bottoms with no relief. Median depth of observation was less than or equal to 30 m for black, copper, dusky, and yellowtail rockfish and greater than 30 m for all other species. Median temperature of observation ranged from 6.1EC for harlequin rockfish to 9.4EC for black rockfish. Size of fish was positively correlated (p <0.036) with depth for dusky, quillback, and yelloweye rockfish. Species often observed alone were China (67%), copper (46%), quillback (46%), and rosethorn (43%) rockfish. Most (>70%) observations of harlequin, Puget Sound, silvergray, tiger, and yelloweye rockfish were in mixed species assemblages. When first observed, the behavior of most rockfish species was swimming or hovering. Notable exceptions were China, harlequin, rosethorn, and tiger rockfish; 33-57% were resting on bottom or in a hole or crevice. This information will be helpful in defining the habitat requirements of rockfish species in southeast Alaska.
By Scott Johnson.
Passive sampling devices were deployed into Auke Lake, a small oligotrophic lake near Juneau, Alaska, to determine seasonal input of aromatic hydrocarbons. Auke Lake, which provides rearing and/or spawning habitat for seven salmonid species, receives hydrocarbon input both from seasonal recreational use of personal watercraft with two-stroke engines and from year-round urban use such as automobile highway runoff and fuel oil spills. Sampling devices were deployed in the lake for 21-day periods throughout 2001. Like many recreational lakes, Auke Lake had seasonal increases in petroleum hydrocarbon input, primarily into the surface waters. Relative input of polycyclic hydrocarbons increased in the summer with peaks occurring during times of highest recreational personal watercraft use. The characterization of the aromatic hydrocarbon profiles by gas chromatography mass spectrometry (GC/MS) was consistent with the exhaust output of small combustion engines rather than from urban runoff.
By Jeep Rice.
ABL staff serve as mentors for high school students during the local school-sponsored science fair. The Alaska Science Fair, sponsored by the Society for Technical Communications (STC), is an opportunity for local high school students to do hands-on science. Students seek out mentors from the scientific community in a variety of disciplines and compete at local, state, and international levels. ABL staff members Mark Carls, Scott Johnson, K Koski, Adam Moles, and Joe Orsi served as project mentors for secondary school students competing at the local level in Juneau, and six staff members volunteered as judges. Eight projects were conducted in Auke Bay laboratories over the winter. The winning entry at the statewide fair held in Anchorage on 14 March was a project mentored and conducted at ABL on the effects of untreated sewage on mussels. That project qualified to compete at the International Science and Engineering Fair in Tennessee in May of 2002.
By Adam Moles.
The total run of pink salmon, Oncorhynchus gorbuscha, in Prince William Sound (PWS), Alaska, for the years 1990-2001 averaged 31.0 million fish per year. Sea ranching from a system of large hatcheries produced over 80% of the run. The degree to which hatchery production actually may have replaced, rather than enhanced, wild stock production is controversial. To examine if hatchery releases have reduced wild stock productivity, a generalized linear version of the Ricker spawner-recruit model was used to analyze the relationship of wild stock productivity with the number of hatchery juveniles released and an array of other environmental variables. Three time periods of wild stock spawner-recruit data were analyzed; the time periods were defined by the availability of the associated environmental data. For all time periods, indices of conditions in the marine environment best explained the variability in wild stock production in PWS. No significant effect of hatchery releases on productivity was observed for the 1980-98 brood years (with the most comprehensive set of environmental variables) or for the 1960-98 brood years (with the longest time series of spawner/recruit data and measures of environmental change). For the time period of the 1975-98 brood, hatchery releases were identified as affecting wild stock productivity, but did not explain as much of the variability as did an index of density-independent marine survival conditions. Based on these results and a simulation model for the time period in which a detectable hatchery effect was identified, for return years 1990-2000 the annual loss in wild production due to displacement by hatchery fish was estimated to be 0-4.6 million pink salmon, and the commensurate annual net gain in total returns was estimated to be 20.6 million-25.3 million pink salmon. Thus sea ranching of pink salmon in PWS has provided large net benefits to the salmon fisheries of the region.
By Alex Wertheimer.
Research is currently under way at Little Port Walter (LPW) to provide more information on the complex relationship between anadromous steelhead and resident rainbow trout inhabiting the same sections of streams. Currently, little is known about the genetic relationships between the two groups. Recent genetic studies have indicated that in one population in Oregon there appears to be little interchange and the groups are genetically distinct, while another population in British Columbia appears to have significant gene flow. For accurate determination of evolutionarily significant units (ESUs) and their status, this type of information is critical.
A small stream (Sashin Creek) at LPW with a wild steelhead population and a large resident rainbow trout population may provide additional information on gene flow between groups including frequency and quantity. Researchers at LPW are PIT-tagging all adult steelhead entering the creek and taking DNA samples on each fish. A new smolt and kelt trap is now allowing the monitoring of all fish migrating to the sea, and up to 50% of the smolt migration each year is PIT-tagged and sampled for DNA. We currently are reaching enough years of sampling to soon be able to determine the proportion of each years smolt production that was produced by anadromous fish or resident fish. The project is already yielding new important life history information on Southeast Alaska coastal steelhead trout with regard to stream life of males and females, repeat spawning frequency, and mortality rates. The project is part of a long-term inbreeding and outbreeding depression project designed to provide more information for captive breeding programs and hatchery-wild interactions.
By Frank Thrower.
Cooperative research on salmon and trout using the Auke Lake system continued in the first quarter of this year. The system supports endemic populations of pink, chum, sockeye, coho salmon, Dolly Varden char, and cutthroat and steelhead trout. Some of the data sets have been continued since the early 1960s. In 1983 an interagency cooperative agreement relating to Auke Creek weir was established between the NMFS, University of Alaska-Fairbanks (UA), and the Alaska Department of Fish and Game (ADF&G). Many cooperative studies and graduate theses have been conducted under this agreement. An interagency meeting of all participating interagency personnel is held annually. A report of fish counts from daily weir operations and other information related to salmonid research at Auke Creek is prepared by the NMFS project leader. The Auke Creek weir annual report is available on the Auke Bay Laboratory website , http://www.afsc.noaa.gov/abl.
Auke Bay Lab