Report for Jan-Feb-Mar 2000)
Workshop on Fishing Gear Impacts
A workshop on fishing
gear impacts and seafloor mapping was hosted
by the Auke Bay Laboratory (ABL) and the NMFS Alaska
Regional Office on 25-27 January 2000. The
focus of the workshop was to improve communications
within NMFS on this subject and coordinate AFSC
studies with the U.S Geological Survey (USGS), the
National Undersea Research Program (NURP), and the
National Ocean Service (NOS), participants in the
NOAA/USGS joint initiative on effects of fishing and
habitat mapping. A major outcome of the
workshop was the development of plans for future
research. Short-term plans focus on
identifying the effects of the various gear types
(i.e., trawls, longlines, pots, and dredges) on fish
habitat for a range of habitat types, mapping
habitat, examining the associations between habitat
features and fish utilization, and defining the
geological processes that will allow comparison of
natural versus gear effects processes. Long-term
plans call for studies that establish the
connections between habitat, fish production, and
population dynamics and the mitigation of effects
through gear design.
By Jon Heifetz.
Groundfish Stock Assessment and Related Activities
The northern rockfish, Sebastes polyspinis, is the second most abundant rockfish in Alaska but little is known about its biology or commercial exploitation. To provide a summary of basic information on northern rockfish in the Gulf of Alaska and Aleutian Islands area, ABL scientists examined data for northern rockfish from commercial fishery observations in 1990-98 and from NMFS trawl surveys in 1980-99. Most of the commercial catch was taken from a number of relatively small and discrete fishing grounds at depths of 75 to 150 m. These grounds, especially in the Gulf of Alaska, are on shallow rises or banks located on the outer continental shelf and often are surrounded by deeper water. One fishing ground, the “Snakehead” south of Kodiak Island, accounted for 46% of the total northern rockfish catch in the Gulf of Alaska. Most of the catch in the Aleutian Islands region was taken as bycatch in the Atka mackerel fishery, whereas in the Gulf of Alaska most of the catch came from direct targeting on northern rockfish.
The survey data revealed generally similar patterns of distribution and size as those seen in the fishery, although some of the fishing grounds did not stand out as areas of particularly high abundance in the surveys. A comparison of age samples in each region showed that Aleutian Islands fish grew significantly slower and reached a smaller maximum size than those in the Gulf of Alaska. In most years the ratio of males to females was nearly 1:1. The surveys showed that juvenile northern rockfish are similar to many other rockfish in that they live in more inshore, shallower areas than adults. Age data indicates recruitment of strong year classes is an infrequent event.
By Dave Clausen.
Collection of commercial fishery data that is used to estimate status of stocks was expanded in 1999. Logbooks for longline vessels over 60 ft were modified to collect detailed information useful for the assessment. The Pacific States Marine Fisheries Commission was contracted to provide log data entry and to develop a database for these data, which is nearly complete. Survey planning for the 2000 longline survey began this quarter. A precruise meeting was held in February with NMFS and Western Administrative Support staff and the managing partner and captain of the contracted survey vessel, Alaskan Leader.
Age determination of juvenile sablefish from their sagitta otoliths has been completed for fish collected in the Gulf of Alaska from 1995 to 1999. Young-of-the-year (YOY) juveniles (captured before their first winter) were collected with gillnets fished opportunistically during adult sablefish longline surveys conducted each year in the Gulf of Alaska. Otoliths for 151 fish, approximately 30 fish per year, were selected. The otoliths contain visible increments that are thought to form daily, much like the yearly rings visible in an adult sablefish otoliths. Daily otolith increment counts revealed that Gulf of Alaska sablefish grew more than one millimeter a day during their first year of life. These growth rates were similar to those reported for sablefish stocks off Oregon and Washington. Analyses also indicated that the first visible otolith increment, possibly the hatching or first-feeding mark, formed sometime during April and May of each year (mean date of approximately May 1). If the first increment corresponds with hatching, then the estimated hatch dates for Alaska sablefish would be almost 1 month later than estimates for sablefish found off Oregon and Washington.
The validity of daily increment formation is being tested by chemically marking the otoliths of YOY sablefish held in captivity at the Auke Bay Laboratory. In 1998 several fish were immersed twice in baths of sea water containing the chemical strontium. The otoliths of marked fish were then processed, and the strontium markers were detected with electron scanning microscopy. The number of increments between chemical markers on each otolith was compared to the number of days between marking events. The results were inconclusive. Apparently, the fish grew very little between marking events and many of the daily increments were indistinguishable. The experimental procedure was reevaluated, and the experiment is being repeated with sablefish collected from the Gulf of Alaska in 1999. Other validation methods are also being explored, including the use of chemically-marked juvenile otoliths obtained from ongoing NMFS studies of sablefish growth off Oregon. The repeatability of daily increment detection is being verified by conducting within and between reader comparisons. Preliminary results from the YOY sablefish age and growth studies will be presented at the 11th Western Groundfish Conference held in April 2000.
By Mike Sigler and Dean Courtney.
Sablefish Tag Program
Processing of 1999 tag recoveries and administration of the tag reward program continued during the quarter. Approximately 200 U.S. tags recovered by Canadian fishermen were forwarded from the Pacific Biological Station in Nanaimo, Canada. Also, 150 tags (many with otoliths) from the NMFS Observer Program were received in March. About 350 Canadian tags recovered in U.S. waters by fishermen or observers during 1999 will be forwarded to Nanaimo after recovery dates and locations are summarized.
Summaries of tag release and recovery data for the years 1988 to present were prepared and sent to Dave Carlile of the Alaska Department of Fish and Game (ADF&G). A separate summary of the NMFS/ADF&G cooperative tag study begun in 1989 is also being prepared. These data will be used by ADF&G in estimating sablefish abundance of Chatham Strait in support of Alaska’s management of this intensive fishery.
By Nancy Maloney.
Is Myxobolus arcticus Stable Over Time?
Parasites enable fishery managers to separate groups of salmon in mixed stock fisheries because parasites acquired in fresh water reflect differences in the rearing environment. Because of its distinct geographic distribution, the myxosporean brain parasite Myxobolus arcticus (formerly identified as M. neurobius) has proven useful in separating salmon stocks. Stability among years is an important criterion for any parasite being used as a biological “tag.” Studies by the Canadian Department of Fisheries and Oceans (CDFO) have demonstrated how quickly Myxobolus can establish itself in a previously uninfected lake, raising concerns that the baseline for parasites in Alaska might have changed. In a cooperative study with the Alaska Department of Fish and Game (ADF&G), the ABL investigated the interannual variability of Myxobolus prevalence in spawning sockeye salmon from 22 lake systems in southeastern Alaska during 1986-87 and again during 1997-99. The Taku River was also sampled by ADF&G annually during 1986–1996 at 12 locations to evaluate intra- and interannual variations in parasite prevalence within a complex riverine system.
Fish from 14 lake systems were more than 80% parasitized, 1 system was 42% parasitized, and the remaining 7 systems were either less than 21% parasitized or unparasitized. There was no significant shift (P = 0.534 - Mann Whitney U-test) in parasite prevalence in the 22 lake systems between reported values from the 1980s and the resampling a decade later. In the Taku River, prevalence of Myxobolus in 1987 at 12 discrete locations ranged from 11% to 82% and prevalence was more stable within a given location in the river. For two locations sampled several times over the decade, there was a 7% range at the lightly parasitized site and a 25% variation at the more heavily parasitized site. In conclusion, coastal lake systems in southeastern Alaska do not have to be resampled frequently for Myxobolus, given the few differences in parasite prevalence over a decade. Several of these lakes had been sampled for Myxobolus by the CDFO in 1983, suggesting prevalence of Myxobolus in coastal lake systems of southeastern Alaska remained similar for 15 years, although the mechanism for this apparent stability is still a matter of speculation. In contrast, prevalence in riverine habitat or in systems with few Myxobolus need to be resampled more frequently.
By Adam Moles.
Life-History Consequences of Oil Pollution in Fish Natal Habitat
Coating by oil from oil spills or from chronic discharges results in the possibility of long-term exposures to eggs incubating in these sediments. Recent research conducted at the ABL, mostly motivated by the Exxon Valdez oil spill, has found that 1) polycyclic aromatic hydrocarbons (PAH) are released from substrate-associated oil films and droplets and at progressively slower rates with increasing molecular weight, leading to greater persistence of larger PAH; 2) eggs from demersally spawning fish accumulate dissolved PAH from oiled substrates, even when the oil is heavily weathered; and 3) PAH accumulated from aqueous concentrations of less than one part per billion can lead to adverse effects appearing during the remainder of an exposed individual’s lifespan. These adverse effects result from genetic damage during early embryogenesis and are caused by superoxide production in response to PAH accumulation. At embryonic exposure, oil poisoning is slow-acting and insidious because 1) adverse consequences may not become manifest until much later in the life of exposed individuals, 2) the frequency of any one symptom is usually low, and 3) the cumulative effects of all symptoms integrated over the life history of an exposed cohort may be considerably higher. These considerations have important policy implications regarding the application of dispersants to spilled oil, the value of oiled-shoreline cleanup efforts, and the placement of urban runoff outfalls.
By Jeep Rice.