OND99 Quarterly Rpt. sidebar
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(Quarterly Report for Oct-Nov-Dec 1997)
Groundfish Assessment: NMFS/ADF&G Trawl Comparison
Study
On 24 October 1997, scientists from
the AFSCs RACE Division in cooperation with the Alaska Department of Fish and Game
(ADF&G) completed a 12-day fishing gear calibration study in waters off the east side
of Kodiak Island, Alaska. The purpose of the study was to detect and measure fishing
power differences between the net and vessel configuration used by the National Marine
Fisheries Service (NMFS) during their Gulf of Alaska (GOA) triennial groundfish surveys
and the net and vessel configuration used by the ADF&G during its annual GOA
crab/groundfish survey. The results will allow both NMFS and the ADF&G to
augment each of their surveys by allowing direct comparisons of their respective databases
for the dominant species encountered during the experiment.
Three vessels, the state of Alaska
research vessels Resolution and Pandalus, along with the NMFS chartered
fishing vessel Peggy Jo, participated in the experiment. The Pandalus,
a 20.1-m (66-ft) research vessel rigged for bottom trawling, is based out of Homer,
Alaska, while the 27.2-m (90-ft) Resolution and 30.1-m (99-ft) commercial trawler
Peggy
Jo are both based out of Kodiak. Participation in the study by the
Pandalus
was terminated prior to the end of the study due to mechanical problems.
Each vessel employed trawling
methods standard to their respective surveys. The Peggy Jo conducted 15
minute tows at 3 nautical mile (nmi)/hour while the ADF&G vessels conducted tows of 1
nmi at a towing speed of 2 nmi/hour. Catches were sorted, weighed, and enumerated by
species using methods common to each survey. Length-frequency measurements were
collected for selected species aboard all three vessels.
Aboard the Peggy Jo, bottom
trawling was conducted with four seam, high-opening polyethylene Noreastern trawls.
Equipped with 14-in rubber bobbin roller gear, this gear is capable of sampling
moderately rough and irregular bottom types typically encountered throughout much of the
GOA. This standard survey trawl has a 27.2-m headrope and 36.7-m footrope consisting
of a 24.9-m center section with adjacent 5.9-m flying wing extensions.
Accessory gear for the Noreastern trawl includes 54.9-m triple dandylines and
1.8 X 2.7-m steel V-doors weighing approximately 850 kg each. The mean path width of
the Noreastern trawl is approximately 14-17 m.
Aboard the Resolution and Pandalus,
the standard survey gear is the 400-mesh eastern otter trawl. This net has a 21-m
headrope and 29-m footrope which lacked roller gear making it well suited for sampling
relatively smooth and soft bottom types. The dandylines are 45.7 m long, consisting
of one 18.3-m section and a double 27.4-m section, one attached to the top and the other
to the bottom of each net wing. The 1.5 X 2.1 steel V-doors weigh approximately 340
kg each. This net was designed to sweep a path of approximately 12 m.
By Eric Brown and Harold Zenger.
Bottom
Trawl Survey of West Coast: Upper Continental Slope Groundfish Resources
The RACE North Pacific Groundfish
Team conducted a bottom trawl survey of the groundfish resources of the West Coast upper
continental slope (WCUCS) between the U.S.-Canada border and Point Arguello (lat.
34°50N) in waters 183-1,280 m deep from 20 October to 25 November aboard the
NOAA ship Miller Freeman. This was the tenth survey in an ongoing series to
monitor long-term trends in the distribution and abundance of WCUCS groundfish
populations. Resource information for management purposes is needed for several
WCUCS species including sablefish (Anoplopoma fimbria), shortspine thornyhead (Sebastolobus
alascanus), longspine thornyhead (S. altivelis), and Dover sole (Microstomus
pacificus). The survey area was expanded this year to cover a much broader
section of the West Coast compared to prior years when only different contiguous sections
were trawled each year. In order to complete the survey in the given amount of time,
we reduced the sampling density by one-third. It was also the third consecutive year
that the WCUCS groundfish trawl survey used slight modifications in trawl gear and towing
protocol. Instituted in 1995, these changes better standardized sampling techniques
and help to stabilize gear performance.
By Bob Lauth.
Seabed
Composition as It Relates to Survey Design
The North Pacific Groundfish Team of
the RACE Groundfish Program has been conducting a retrospective analysis of NMFS triennial
bottom trawl surveys conducted along the West Coast from 1977 to 1995. It is
expected that the combined results of this study will lead to a better understanding of
how our survey samples groundfish populations off the west coast of the United States.
The first objective of the study is
to identify areas where we have been unable to successfully use the standard research
bottom trawl nets. This involves plotting the locations of poor performance hauls
(trawl gear ripped or hung-up on bottom) and stations which were skipped because the
bottom was too rough. Preliminary results show clustering of bad tows in some areas.
For example, in the shallow stratum off northern Washington (U.S.-Vancouver area,
55-183 m), approximately 42% of planned stations were not sampled successfully (1986-95).
We are working with Washington Department of Fish and Wildlife scientists to explore
whether the abundance of some important commercial groundfish species are different in the
untrawlable vs. trawlable areas. Species of particular interest in this study
include lingcod (Ophiodon elongatus) and canary rockfish (Sebastes pinniger).
Along with delineating untrawlable
areas, we plan to create a map of surficial sediments throughout the West Coast survey
area. This will be the first such map created using original data sources with
sediments divided into constituent components (%gravel, %sand, %silt, and %clay).
Previous maps have used data coded by a ternary diagram or only visually classified
samples. To date we have accumulated about 2,000 data points, with good coverage of
the northern half of the survey area and weaker coverage of the southern half. We
are working with the Geological Survey of Canada and the U.S. Geological Survey towards
completing this goal. All data will be imported into a geographic information
systems package so that we can use spatial statistics to interpolate the data and produce
a map which can be easily updated.
We also plan to conduct an
assemblage analysis on the groundfish species, showing which species tend to occur
together. Depth, bottom-water temperature, and sediment texture will be used to
further define these assemblages. Age and length data from our catches, not normally
included in assemblage analysis studies, may help us further refine these assemblages.
Once completed, we plan to use the information to identify stations with similar
catches, group the stations into strata, and then compare these strata to our current
stratification system which is based on depth and latitude. By minimizing differences in
species composition between strata, more accurate estimates of species abundance with
lower variance should be produced.
By Mark Zimmermann.
Fisheries
Oceanography Coordinated Investigations (FOCI)
Members of the AFSCs Fisheries
Oceanography Coordinated Investigations (FOCI) observed anomalous atmospheric and
oceanographic features over the Bering Sea shelf this past summer during cruises as part
of NOAAs Coastal Ocean Program Southeast Bering Sea Carrying Capacity (SEBSCC).
The most visible of these features was sustained discoloration of shelf waters by a
bloom of coccolithophorids (small phytoplankton covered with calcium carbonate plates).
The aquamarine colored waters were first noticed at sea in July and persisted
through September when they were photographed by NASAs new ocean color satellite
(SeaWIFS). The bloom occurred concurrently with massive mortalities of marine birds
(short-tailed shearwaters) and an anomalously low return of salmon to Bristol Bay.
Members of the SEBSCC will report
their findings at the Ocean Sciences Meeting in San Diego, California in January 1998.
By Ric Brodeur.
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