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Resource Assessment &
Conservation Engineering

(Quarterly Report for Oct-Nov-Dec 1997)
  

Groundfish Assessment: NMFS/ADF&G Trawl Comparison Study

On 24 October 1997, scientists from the AFSC’s 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 Nor’eastern 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 Nor’eastern 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 Nor’eastern 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. 3450’N) 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 AFSC’s Fisheries Oceanography Coordinated Investigations (FOCI) observed anomalous atmospheric and oceanographic features over the Bering Sea shelf this past summer during cruises as part of NOAA’s 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 NASA’s 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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