JFM 2000 Quarterly Rpt. sidebar
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(Quarterly
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
Slope Rockfish
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.
Sablefish
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.
Habitat Investigations
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.
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