Report for Jan-Feb-Mar 2001)
Population Response to Decline in Predation
Intensity After Exxon Valdez Oil Spill
Auke Bay Laboratory (ABL) personnel assessed the relative importance of direct effects of the Exxon Valdez oil spill in Prince William Sound, Alaska, and indirect effects of the spill (resulting from a reduction in predation pressure) on mussel, Mytilus trossulus, populations. They compared the mussel population structure 7-8 years after the spill on Knight Island, where the shore was heavily oiled and where sea otter numbers were greatly reduced, with mussel population structure along the northwestern shore of Montague Island (unoiled), where sea otters were unaffected by the spill. Mussel populations were sampled on 1,076 transects in May, June, and July 1996 and 1997 at the two islands.
The density of all mussels ($5 mm in shell length) at Knight Island exceeded that at Montague Island in both years of our study, but the majority of mussels at Knight Island were small, having recruited to the population in the previous 1-2 yrs. The length-frequency and biomass (ash-free dry mass (AFDW)) distributions of the mussels at the oiled location were strongly skewed to the right in both years. The mean density and biomass of mussels greater than or equal to 20 mm in shell length did not differ significantly between study areas in 1996 but was higher at the unoiled beaches than at the oiled beaches in 1997. The density of mussels less than or equal to 40 mm (the size range preferentially consumed by sea otters) was very low at both study areas. The density did not differ between study areas in 1996, but in 1997 was greater at the unoiled locations than at oiled beaches. The mean biomass density of mussels greater than or equal to 40 mm at Knight Island slightly exceeded that at Montague Island in 1996, but it was less than 1/6 that at Montague Island in 1997.
The results indicate that a decrease in sea otter predation on Knight Island after the Exxon Valdez oil spill did not result in an increase in the abundance of large mussels there 7-8 yrs after the spill as would be predicted if sea otters controlled the size-structure of mussels in Prince William Sound. There is no evidence that the direct effects of oil on the mussel population on the oiled beaches of Knight Island extended beyond 1995. The mean density of Nucella lima on oiled beaches exceeded that on unoiled beaches by 2.4 times in 1996 and by 6.6 times in 1997, and the mean density of N. lamellosa on oiled beaches exceeded that on unoiled beaches by 80 times in 1996 and by over 350 times in 1997. Estimates from laboratory feeding rate studies on N. lima and N. lamellosa of the total consumption of Mytilus by Nucella in our study areas were less than or equal to 0.3% and about 4% of the total mussel population in the study areas at Montague Island and Knight Island, respectively. The level of predation of Nucella on Mytilus at Knight Island may have contributed to the creation of a bottleneck in the supply of large mussels in the population despite the release of the large mussels from sea otter predation at Knight Island in the 7-8 yrs after the oil spill.
By Charles O’Clair
Evaluation of Oil in the Intertidal Zone of Prince William Sound From the Exxon Valdez Oil Spill
Members of the ABL Exxon Valdez Oil Spill group have initiated a program to provide a quantitative estimate of the amount of shoreline (length, area, sediment, and volume) that remains contaminated following the March 1989 Exxon Valdez oil spill. Oil from the spill has been surprisingly persistent on some beaches. At the end of the 1992 cleanup season, natural processes were expected to disperse most of the oil remaining on shorelines. However, relatively unweathered oil remains at several locations that were heavily oiled initially and protected from dispersion by storm-generated waves. The extent of the remaining oil is unknown. This uncertainty has caused public and scientific concerns about the potential effects the oil may have on humans and on fauna exposed to the oil directly or indirectly.
A stratified random sample of shoreline will be intensively sampled in summer 2001 for surface and subsurface oil to estimate length of oiled shoreline, area and volume of oiled sediment, and volume of oil. Approximately 8 km will be sampled by digging more than 8,000 pits to discover and quantify subsurface oil. This estimate will provide information for any assessment of the significance of the amount of oil remaining and will be the basis for further management.
By Mandy Lindeberg.
Effects of Hydraulic Pumping on Shock Resistance of Pink Salmon Eggs
Good estimates of the survival of salmon eggs in gravel require accurate discrimination between live and dead eggs. Dead eggs must not be confused with eggs mechanically damaged (shocked) by pumping. To determine the effect of hydraulic pumping on the shock resistance of eggs over time, pink salmon (Oncorhynchus gorbuscha) eggs were pumped from the gravel of the intertidal section of Lovers Cove Creek, southeastern Alaska, six times between 27 September and 15 November 2000. Resistance to shock increased from less than 5% to greater than 95% over the sampling period. We simulated egg pumping in a stream by pumping known-age pink salmon eggs from a barrel of stream gravel. Resistance to shock for the hatchery eggs increased similarly to that of the eggs in the stream, decreasing from 0% to 92.5% from 1 day to 28 days after fertilization.
Misclassification of live eggs as dead was rare in the field because eggs pumped from the stream were removed from water within 5 minutes of pumping, a procedure that arrested the color change from pink to white in shocked eggs. When describing the condition of eggs in a stream, we recommend that the condition be described before the effect of hydraulic pumping on the eggs occurs; thus, shocked eggs and live eggs should be combined into a single “live” category, and dead eggs should only include those that were dead before sampling began. This philosophy differs from that of some other researchers, who combined shocked eggs and dead eggs into a single “dead” category and reported greater egg death in streams sampled when eggs are immature than when sampled after the eyed stage is reached. Our modified method can alleviate discrimination of egg condition problems posed by differing egg maturity within and between streams and over time.
By John Thedinga.
Summary of 2000-2001 Winter Conditions at Auke Bay
Although there was a brief cold snap in mid-March, the Auke Bay 2000-2001 winter was milder than average. Air temperatures were 1.5EC to 2.8EC above average. Sea surface temperatures were generally 1EC to 2EC above average through January and February and slightly below average in March. Precipitation total for January through March was 32.66 cm, a bit higher than the average of 30.96 cm. Snowfall was far below average, with a January-March total of only 58.8 cm compared to the average of 145.0 cm. Auke Lake froze over about 14 December 2000, about 10-14 days later than average. The lake was open from 23 January 2001 through 15 February 2001. Heavy wet snow in mid-February led to the lake refreezing until it opened again on 6 April, 10-14 days earlier than average.
By Bruce Wing.
Unusual Invertebrates Added to ABL Reference Collection
Seventy-one specimens of corals and coral-like animals were received from the ADF&G Mandatory Observer Program in February. The specimens were collected during the golden king crab winter fisheries in the Aleutian Islands region. The collection includes one species of sponge, one species of bryozoan, 11 species of hydrocorals, and 16 species of octocorals. Three hydrocoral specimens, two Errinopora sp. and a Stylaster sp., are of undescribed species seen in earlier collections. Another Errinopora sp. and a Stylaster sp. may also be an undescribed species. Also in the collection is a Stenohela sp., a genus of hydrocoral not previously reported from the North Pacific Ocean. Among the octocorals were specimens of three gorgonian genera which have not been previously recorded in Alaska.
A small collection of Pleistocene mollusks, bryozoans, and crustaceans was received from Dr. Anne Pasch, Department of Geology, University of Alaska Anchorage. It was collected from deposits uncovered by the Bering Glacier outwash. The deposits have been dated using C-14 data at 10,000 years before present. With the exception of one species of snail, all species are known to be presently living in near-shore waters of the Gulf of Alaska and Prince William Sound. One exceptional specimen is a single Leucosyrnix kincaidi Dall, 1919. This is the second specimen ever collected of this species, the first of which was taken from deep water in Shelikof Strait by Dall. Although the specimen is badly eroded, it fits Dall’s description and illustration.
By Bruce Wing.
Development of Bering-Aleutian Salmon International Survey
Staff from the ABL Ocean Carrying Capacity program in conjunction with Kate Myers of the University of Washington, developed an international cooperative research initiative, the Bering-Aleutian Salmon International Survey (BASIS). The initiative was presented 20 March 2001 to the Research Planning and Coordination Meeting of the North Pacific Anadromous Fish Commission (NPAFC) and was well received by national participants.
The scientific concepts behind the BASIS plan are simple, but the results should greatly enhance our understanding of salmon in the Bering Sea. The plan calls for four synoptic 1-month seasonal (spring, summer, fall, winter) surveys per year. The survey area consists of 95 sampling stations spaced at regular intervals across the Bering Sea: from the Aleutian Islands north to 64°N, and from the Alaskan to Russian coasts. Sampling would consist of surface trawls to capture salmon of all ages, CTD (conductivity- temperature-depth) casts, plankton tows, and continuous sampling of ocean conditions (e.g., salinity, temperature). Ongoing, long-term research by Japan in the Bering Sea would also be an integral part of the sampling effort. Coordination of sampling from Russian vessels within the Russian Exclusive Economic Zone (EEZ), U.S. vessels within the U.S. EEZ, Japanese vessels, and other countries’ vessels within international waters would be through the NPAFC.
The plan also calls for in-depth biological and stock identification analyses to determine growth and life-history characteristics of regional stock groups. The stock identification analyses would be based on genetic, parasite, scale, otolith, and tag data, and would require review and enhancement of existing baselines. The BASIS plan is designed to complement long-term climate, ocean, and ecosystem monitoring and research activities by other international organizations such as the North Pacific Marine Science Organization and GLOBEC and will yield the first ever synoptic seasonal information on distribution, abundance, and stock origins of all species, age, and maturity groups of salmon in the Bering Sea - information vital to the fishing industry, fishery managers, conservation organizations, policy makers, and others faced with declines in key salmon populations.
By Steve Ignell.
NPAFC Bulletin Published
The second NPAFC Bulletin entitled “Recent Changes in Ocean Production of Pacific Salmon” was published in March 2001. The bulletin comprises 39 papers given at the NPAFC symposium held in Juneau, Alaska, on 1-2 November 1999. Symposium topics were 1) physical and biological factors affecting ocean production of Pacific salmon; 2) detection of trends, patterns, and changes in historical salmon and environmental data; 3) forecasts and models of Pacific salmon dynamics; and 4) new research methods and techniques in ocean salmon research. ABL scientists contributing to the papers were Jack Helle, Don Mortensen, Dick Carlson, Bruce Wing, Noele Weemes, Michele Masuda, Chuck Guthrie, Dean Courtney, Ellen Martinson, Ed Farley, Jim Murphy, Joe Orsi, Mary Auburn-Cook, and Steve Ignell.
The bulletin is dedicated to Dick Carlson of ABL’s Ocean Carrying Capacity (OCC) program who passed away in July 1999.
Seasonality of Prey Availability in Regions of Contrasting Steller Sea Lion Abundance Trends
The ABL began research in March 2001 to test the hypothesis that sea lion prey diversity and seasonality are related to Steller sea lion population trends. One hypothesis is that the decline in the western population of Steller sea lions may be due to decreased prey availability. This decrease may be exacerbated by fishery removals of prey in sea lion habitat. Area-specific diet diversity and population change of Steller sea lions also appear to be related, with faster declines in areas of lower diet diversity (Merrick et al. 1997). Steller sea lions also may switch diet seasonally, as different prey become more available. The purpose of this set of studies is to test the hypothesis that sea lion prey diversity and seasonality are related to Steller sea lion population trends. Our approach is to measure Steller sea lion prey, prey quality (free fatty acid analysis), and predator abundance and fishery removals near selected rookeries and haulouts, emphasizing seasonal measurements conducted during critical life stages of Steller sea lions. Two regional trend areas, southeastern Alaska and the Kodiak Island area, are being compared. Study haulouts and rookeries were selected based on year-round accessibility. Simultaneous sampling of sea lion abundance, distribution, and diet (scats) is being done in cooperation with other researchers. In southeastern Alaska, ABL is cooperating with the ADF&G, the University of Alaska, and the North Pacific Universities Marine Mammal Research Consortium. This study also is being coordinated with existing University of Alaska studies on Kodiak Island.
By Mike Sigler
Rockfish Age-structured Modeling Workshop
A rockfish (Sebastes spp.) modeling workshop was held at the ABL 20-22 February 2001. The workshop was attended by stock assessment scientists from the Center’s REFM Division and from the ABL. The goal of the workshop was to implement a common model framework for a number of different rockfish populations managed by NMFS. A simple age-structured model (with allowance for size composition data) was agreed upon as a base model and constructed with AD Model Builder Software. The base model was applied to the following Gulf of Alaska stocks: Pacific ocean perch (POP), northern rockfish, dusky rockfish, and rougheye rockfish. Additionally, the model was applied to the Aleutian Islands and eastern Bering Sea POP stock and may be applied to the POP stock off the coast of Washington and Oregon. Because each stock has particular differences in fishery, survey, and biology, features were added to the base model to account for additional data types and special fishery characteristics. The base models will be tuned by individual stock assessment scientists to particular stocks, and the patterns of information will be compared among the stocks for the specific common model. The base model will also be evaluated for sensitivity to assumptions for the different stocks. Results will be summarized in a NOAA technical publication.
By Dean Courtney and Jim Ianelli.
2001 Sablefish Longline Survey
The precruise meeting for the 2001 sablefish longline survey was held 23 March. The meeting covered topics including vessel operations and safety; specific sampling protocols, gear, and special requests, staffing, and survey schedule. The survey will begin sampling in the Bering Sea on 2 June and complete the last station in the Gulf of Alaska 3 September. Eighty-nine regular stations and three seamounts will be fished, and a 2-day hooking experiment will be conducted during the survey. Approximately 130 sablefish will be tagged and released with internal electronic tags.
Young-of-the-Year Sablefish Age and Growth in the Gulf of Alaska
Experiments were conducted to validate the daily periodicity of otolith increment deposition in young-of-the-year (YOY) sablefish. The validity of daily increment formation was tested by chemically marking the otoliths of YOY sablefish held in captivity at the ABL. Approximately 30 YOY sablefish were captured along the continental shelf by NMFS staff from the Oregon Hatfield Marine Science Center and returned alive to the ABL on 1 June 2000. The fish were maintained in seawater tanks at the ABL for up to 104 days. The water temperature was elevated and held at a constant 13EC, and the photo period was lengthened and held at a constant 16 hrs of light per day. The fish were split into three groups of roughly equal size. The otoliths of the fish in each group were marked twice by immersing the live fish in seawater with elevated levels of strontium chloride (SrCl2). For each group, the strontium immersions were separated by a period of approximately 15 days. The first group was marked twice in June, the second was marked twice in July, and the third was marked twice in August. The fish from each group were sacrificed approximately 15 days after the second strontium immersion. The otoliths of marked fish are being processed into thin sections, and the strontium markers will be detected with electron scanning microscopy by staff at the University of Alaska Fairbanks. For each processed otolith, the number of micro-increments (alternating light and dark bands visible under a transmitted-light compound microscope) between detected strontium bands will be counted and compared to the number of days between SrCl2 immersions.
By Dean Courtney.
Young-of-the-Year Sablefish Abundance, Growth, and Diet in the Gulf of Alaska
ABL scientists synthesized basic life history information on YOY sablefish abundance, growth, and diet to determine whether forecasting year class abundance based on YOY surveys was practical. Surface gillnet surveys were conducted annually during the sablefish longline survey from 1995 to 1999 along the seaward edge of the continental shelf of Alaska. Sablefish made up about one-third of the catch and were caught mostly in the central and eastern Gulf of Alaska. Growth averaged 1.2 mm per day. The mean date the first otolith increment formed, 30 April, implied an average spawning date of 30 March. Diet was mainly euphausiids. Growth rate tended to be higher in years when gillnet catches were higher, but no relationship was apparent between diet and gillnet catches. Data for the synthesis was drawn from work conducted in recent years by AFSC staff. Much of this work was presented at the Western Groundfish Conference, held 24-28 April 2000 in Sitka, Alaska. The results are detailed in a manuscript accepted for publication by the Alaska Fishery Research Bulletin.
By Dean Courtney.
Otolith Marking and Pink and Chum Salmon Workshops
Two workshops were held at the University of Washington on 21-23 March. The first, held on March 21, was the North Pacific Anadromous Fish Commission’s (NPAFC) Workshop on Salmonid Otolith Marking. The workshop was well attended by scientists from Russia, Japan, Canada and the United States with several outstanding talks on the relatively new technology of mass marking juvenile hatchery salmon otoliths. Otolith marking of hatchery salmonids is providing a powerful research tool that is bringing Pacific Rim salmon scientists together into a cooperative spirit of joint participation and mutual involvement.
Peter Hagen, Alaska Department of Fish and Game (ADF&G), and Hiko Urawa, National Salmon Research Institute of Japan, were principal co-chair coordinators of the workshop. Eric Volk, Washington Department of Fish and Wildlife, who is considered by many as the chief innovator for otolith marking of Pacific salmon, gave a keynote overview and history of this technology. Joe Orsi and Jack Helle from the Auke Bay Laboratory (ABL) presented papers at the workshop. Orsi’s paper, coauthored with Don Mortensen of ABL and Dian Tersteeg and Ric Focht of Douglas Island Pink and Chum, Inc., a local nonprofit hatchery based in Juneau, was titled “Early Marine Growth and Habitat Utilization of Two Major Alaska Chum Salmon Stocks, Based on Otolith Marks”. Helle’s talk was “Variations in Proportions of Thermally Marked Hatchery Pink and Chum Salmon Juveniles in the Gulf of Alaska, 1996-1998", coauthored with Ed Farley of ABL and Peter Hagen.
The second workshop was the 20th Biennial Northeast Pacific Pink and Chum Salmon Workshop held 21-23 March, also at the University of Washington. At this workshop, Bill Heard from ABL gave the keynote address “Then, Now, and What Next?” about pink and chum salmon resources, past, present, and future research on these fishes, and the workshops that have focused on them. Alex Wertheimer of ABL gave a paper, coauthored with Bill Smoker, Tim Joyce, and Bill Heard on “Hatchery Pink Salmon in Prince William Sound: Enhancement or Displacement?” Poster presentations from ABL were submitted by Joe Orsi, Don Mortensen, Mark Carls, John Thedinga, Molly Sturdevant, and Mike Sigler. Auke Bay contractors from the ABL Ocean Carrying Capacity Program also made oral and poster presentations at the workshop. Jack Helle gave the wrap-up talk at the workshop on “Highlights and Observations of Forty Years of Workshops.” Holding the two workshops at the same time allowed major participation by Japanese and Russian scientists in both workshops.
By Bill Heard.
University of Washington Oceanographic Seaglider
At a January meeting of the Global Ocean Ecosystem Dynamics (GLOBEC), Northeast Pacific Coastal Gulf of Alaska Program, University of Washington oceanographers gave a preview of the new Seaglider sampling device they are developing. The Seaglider is a self propelled, non-tethered vessel for physical, chemical, and some biological oceanographic sampling. It is a low watt, low cost vessel that can sample a large number of parameters while cruising at depths up to 300 m for weeks at a time. The vessel, roughly
1.5 m in length can be programmed to sample at multiple depths, and its position is determined by a sliding battery pack that tips the glider in an up or down position. Negative or positive buoyancy is shifted by slight changes in the location of oil in a fore-aft reservoir-bladder system. When the glider is programmed to return to the surface, a satellite or cell phone transmitting antenna and GPS receiver is activated for uploading data or for retrieval by a surface vessel.
By Bill Heard.