Resource Assessment and Conservation Engineering quarterly research reports for Jul-Sept 1998 for the Alaska Fisheries Science Center

GROUNDFISH ASSESSMENT

1998 West Coast Triennial Bottom Trawl Survey Completed

The Resource Assessment and Conservation Engineering (RACE) Division’s Groundfish Assessment Program completed the eighth in a series of triennial bottom trawl surveys of the groundfish resources off California, Oregon, Washington, and British Columbia. This year the survey began 1 June in Seattle. Fishing operations started 8 June near Pt. Conception, California, and continued through 7 August, ending off the central coast of Vancouver Island, British Columbia. During the regular survey activities, the chartered fishing vessels Dominator and Vesteraalen successfully completed trawl hauls at 528 predetermined stations. Diligent work, good weather, and more seaworthy vessels allowed us to nearly complete sampling of all planned regular survey stations, despite a shorter charter period than in the 1995 triennial west coast survey and allocating 8 days to a research project looking at the interaction between our survey trawls and the fish they encounter (see accompanying article). In addition to RACE groundfish staff, cooperating scientists participated from the AFSC’s Resource Ecology and Fisheries Management (REFM) Division, the Northwest Fisheries Science Center’s Fishery Resource Analysis and Monitoring Division, the Southwest Fisheries Science Center’s (SWFSC) La Jolla Laboratory, the Oregon Department of Fish and Wildlife, Orange County College, Oregon State University, University of Washington, and the International Pacific Halibut Commission.

The west coast triennial survey dates back to 1977, when it was conducted to provide a benchmark of the distribution and abundance of groundfish stocks off the coast. The emphasis of the earlier surveys (1977 through 1986) was to provide estimates of rockfish abundance to help managers regulate the harvests of those resources. Our experience during those surveys showed that rockfish abundance estimates derived from area-swept trawl surveys were not precise enough to meet management needs. In designing subsequent surveys, the emphasis of the triennial surveys was shifted to monitor the distribution, abundance, and population biology of a broader spectrum of commercially important west coast groundfish. In particular, the survey has provided good assessments of Pacific hake (Pacific whiting), Merluccius productus, and juvenile sablefish, Anoplopoma fimbria. The survey design was altered in 1989 to include the objective of improving the biomass estimates of these two species and promoting the multispecies objectives of the survey.

This year’s survey replicated the survey completed in 1995. The current survey covers depths ranging from 30 to 275 fm (55-500 m); surveys prior to 1995 covered 30-200 fm (55-366 m). The survey data has been edited and added to the RACE database. Preliminary analysis of the average catch per unit of effort (CPUE) for the major species over the entire area and depth range of the survey shows some interesting trends when compared to results of the 1995 survey. The overall CPUE estimates for Pacific hake, arrowtooth flounder, and widow rockfish were virtually unchanged. CPUE estimates of Pacific sanddab and several rockfish species (stripetail, darkblotched, splitnose, greenstriped, chilipepper, and sharpchin, as well as shortspine thornyhead) fell to lower levels. We saw increases in the overall average CPUE estimates of lingcod, sablefish, Pacific ocean perch, and several flatfish (Dover, rex, petrale, and English soles and Pacific halibut). Notably larger overall average CPUE estimates were seen for yellowtail rockfish, Pacific herring, American shad, and spiny dogfish.

Data from the survey will be analyzed fully this fall and results will be provided to stock assessment scientists as well as comprehensively reported in a Data Report. RACE biologists and researchers from other agencies and institutions will also be conducting a number of biological studies using specimens and data collected during this survey.

By Mark Wilkins.

Trawl Efficiency Work

In addition to conducting the 1998 triennial bottom trawl survey of west coast groundfish resources, RACE groundfish staff conducted a footrope efficiency study designed to compare two methods for determining rates of fish escapement. The first method utilizes an auxiliary bag (trawl) placed behind the standard survey trawl’s footrope to collect fish escaping under the footrope of the survey trawl. Efficiency is defined as the number of captures in the survey trawl divided by the total encounters or the sum of the number captured in the primary trawl and those collected in the auxiliary bag. Because of the auxiliary bag’s vulnerability to rough bottom conditions, this technique is limited to areas of soft, smooth terrain, areas which represent a fraction of the total area sampled during RACE groundfish assessment surveys.

The second method for estimating footrope efficiency is based upon direct observations of escaping fish. This method uses one or more underwater video camera systems tethered to the survey trawl and aimed at the footrope. An advantage of the video method is that it can be used in areas with rougher bottom conditions than can be sampled with the auxiliary bag. Because of questions about the validity of the video technique as a method for estimating footrope efficiency, the study was designed with the following objectives:

A paired-tow experimental design was implemented, incorporating standard RACE survey towing practices using the west coast triennial survey bottom trawl—a high-rise poly-Nor’eastern roller gear and fished with 5ЂД 7Ђ V-doors. Each tow of every pair was made in the same direction, at the same depth, for the same length of time, and separated by approximately 0.2 km. All tows used the auxiliary bag, and all tows had two camera systems tethered to the trawl. One tow of each pair was made with the lights on and the other tow with the lights off.   A total of 60 tows were made in the 8 days allotted for the experiment yielding 21 pairs for analysis.

By Ken Weinberg

Comparing Groundfish Densities in Trawlable and Untrawlable Areas

This summer RACE staff completed the first stages of a National Undersea Research Program- sponsored project in a small study area off the northwest Washington coast. This project is a cooperative effort between the Washington Department of Fish and Wildlife and RACE Division’s Groundfish Assessment Program. The main goal of the project is to determine if some commercially important groundfish species, such as canary rockfish (Sebastes pinniger) and lingcod (Ophiodon elongatus), are more abundant in rocky areas which are untrawlable, and therefore not assessed by the NMFS triennial bottom trawl survey.

After reviewing the history of NMFS bottom trawl surveys, we selected a study site that contains approximately equal areas of flat, soft ground, which has historically been sampled by the NMFS survey and rough, rocky ground generally not successfully sampled by the survey trawls. This 3 by 16 nmi area is off Cape Flattery, between Juan de Fuca Canyon and Nitinat Canyon, and is approximately 100-150 m in depth.

In late April and early May, a detailed sidescan sonar mosaic and bathymetric map of the study site was made. We divided the mosaic into 800-m2 sampling units, and by overlaying the NMFS trawling history, we labeled each square as either trawlable or untrawlable. In early July dives were made in the minisubmersible Delta on eight randomly selected trawlable and eight randomly selected untrawlable sampling units. Each dive consisted of three, 800-m long parallel transects across a sampling unit and took approximately 2 hours to complete. Forward and side facing, externally-mounted video recorders documented the fish and terrain along each transect, while an observer onboard made verbal comments about fish and features out of the camera range, which were also recorded on the tapes.

Data analysis is just beginning, and a thorough review of the tapes will be completed in several months. During the dives, however, it was apparent that several assumptions would be validated. We were correct in our division of sampling units into trawlable and untrawlable areas by use of the sidescan mosaic and trawling history. The untrawlable areas consisted largely of boulder fields, as we had expected. These untrawlable areas had numerous schools of small, possibly juvenile rockfish, along with numerous larger, solitary rockfish such as greenstriped (S. elongatus) and rosethorn (S. helvomaculatus), and some lingcod. The trawlable areas were generally flat, muddy or sandy, and covered with brittlestars. There were fewer total fish in the trawlable areas, and very few rockfish and lingcod, although the complete analysis may show there were more flatfish. Additionally, we noticed some trawl door scouring in the trawlable area but did not find any derelict fishing gear. Semipelagic species such as yellowtail rockfish (S. flavidus), also a significant commercial species, could not be assessed with the submersible because they were above viewing level.

By Mark Zimmermann.

Eastern Bering Sea Crab/Groundfish Survey

The annual crab-groundfish demersal trawl survey of the eastern Bering Sea shelf was completed from 5 June to 5 August 1998. The 500,000-km2 area from inner Bristol Bay to the shelf edge and from Unimak Pass to lat. 62oN near St. Matthew Island was sampled at 376 stations including 355 stations in the standard area used for annual abundance estimates. The chartered vessels Arcturus and Aldebaran were used for the sixth consecutive year.

Preliminary biomass estimates indicate that most commercial species were down in abundance from 1997, but only Atheresthes spp. (arrowtooth and Kamchatka flounders), rock sole, Alaska plaice, and walleye pollock were down significantly. The Pacific cod stock continued its recent decline, but the 1996 year class appeared in significantly higher numbers than expected and provides optimism for this valuable species in the near future.

Bottom temperatures were considerably higher than normal on the shelf with an average of 3.26oC versus a long-term mean since 1982 of 2.49 oC. The ‘cold pool’ of water with temperatures less than 2oC usually extends through the middle domain (50-100 m) of the Bering Sea shelf from the northern boundary of the standard survey area to the south and east into outer Bristol Bay. This water is residual from the receding spring ice pack in an area of low current flow. In 1998, the pool did not even reach an area near the Pribilof Islands. On average, 111 stations in the standard survey area would have temperatures below 2 oC , and 28 stations would have negative temperatures. In 1998, only 55 stations were below 2oC, and none had negative values.

For several years the RACE Division has considered reducing tow duration from 30 minutes to 15 minutes in order to decrease the number of catches that must be split (large scale subsampling). In most years, 50%-75 % of the catches are split. Pamela Goddard of the RACE Division showed in her master’s thesis (1997) that this reduction in tow duration was acceptable statistically for almost all the major fish species, but did not have sufficient data to examine crabs. In 1998 a major effort was planned by the AFSC’s Kodiak Laboratory and carried out during and after the survey. Sixty pairs of 15/30 minute comparisons were made by the two vessels on the red king crab grounds of Bristol Bay utilizing the standard survey tows, as well as additional pairs on the mid-lines between stations. The two vessels also completed 18 pairs of comparisons for Tanner crabs (Chionoecetes bairdi) and snow crabs (C. opilio) during the survey. After the survey, the Aldebaran completed another 16 pairs of comparison tows for   Tanner, snow, and king crabs near the Pribilof Islands. The Arturus also carried out work begun in 1997 looking at escapement of crabs under the footrope of the trawl using a specially constructed net with an auxiliary bag behind and under the main bag. It was also used in tandem with a 3-m beam trawl to examine the escapement of very small crabs under both nets. All these data are being analyzed and will be used to make a final determination on the feasibility of reducing tow duration during the survey.

By Gary Walters.

Life History Aspects of Noncommercial Species in the Eastern Bering Sea

Noncommercial species are a significant portion of the fish fauna occurring in the Bering Sea, but due to their small biomass or lack of marketability, are rarely harvested. However, these fishes may be valuable indicators of changes occurring to the Bering Sea ecosystem due to natural or man-made influences. Relative changes in population estimates from 1982 to 1997 were determined for 12 noncommercial fish species common in the Eastern Bering Sea shelf region.

Studies have shown that environmental temperatures and fish populations fluctuate in cyclical patterns. Noncommercial fishes from the Bering Sea show similar cyclical fluctuations in population levels that may be linked to environmental changes such as temperature. However, specific mechanisms of how environmental changes influence fish populations over long periods of time is often difficult to discern. For example, do environmental changes alter the fishes’ habitat (substrate or structure) or does it act directly on some aspect of the fishes’ biology (spawning time, egg viability, food availability)? Important aspects of the biology of each species (in this case for threaded sculpin) such as length at age and length frequencies provide important information on fish longevity, growth rates, and recruitment. By comparing the ecology and biology between species, common life history aspects can help determine vulnerabilities to changing environmental conditions.

By Gerald R. Hoff.

Participation in Alaska Department of Fish and Game Gulf of Alaska Seasonality Study

The AFSC continued cooperative participation in the second phase of a Alaska Department of Fish and Game (ADF&G) seasonal bottom trawl study of Marmot Bay off Kodiak and Afognak Islands in the Gulf of Alaska (GOA) 24-30 August aboard the ADF&G research vessel Resolution. The primary purpose of the study, which includes additional sampling periods scheduled for October 1998 and January, March, and June 1999, is to document seasonal trends in depth and inshore/offshore distribution of crab and groundfish resources including Tanner crab, Pacific cod, walleye pollock, arrowtooth flounder, flathead sole, rock sole, yellowfin sole, and skates. Additionally, the seasonal nature of the sampling design will provide quantitative measures of changes in co-occurrence of the demersal groundfish and crab complex, document the changes in distribution of Pacific cod relative to Federal and state waters, and document intra-annual changes in the distribution of Tanner crab associated with maturation. Along with these objectives, the ADF&G invited AFSC scientists to conduct ancillary studies including specimen collections, food habit studies, research in seasonal gonad development and size-at-maturity for selected species.

Thirty-one bottom trawl samples were completed during the August sampling period with the ADF&G standard 400-mesh Eastern survey trawl at depths ranging from 35 to 250 m. All catches were sampled and processed to obtain species composition by weight for all components of the catch. Length frequencies were obtained electronically for all commercial groundfish species. Additionally, Geoff Lang of the AFSC’s Resource Ecology and Ecosystem Modeling Program expanded the stomach and otolith collections begun in June to include additional commercial species such as flathead sole and arrowtooth flounder. A reproductive study of Pacific cod and flathead sole is scheduled to begin during the October phase of the seasonality study.

By Eric Brown.

Midwater Assessment & Conservation Engineering (MACE) Research Cruise

Scientists from the MACE program conducted the eighth triennial echo integration-trawl (EIT) survey of Pacific whiting off theWest Coast from Monterey, California, (lat. 36EN) to the Queen Charlotte Islands, Canada, during 6 July to 27 August 1998 aboard the NOAA research vessel Miller Freeman.   The survey covered about 3,600 nmi of acoustic trackline and conducted 108 midwater and bottom trawls to determine the distribution, biomass, and biological composition of Pacific whiting. A centerboard-mounted 38- and 120-kHz scientific acoustic system and the MACE free-drifting acoustic buoy were calibrated using standard sphere techniques. Underway system noise levels were routinely measured along offshore cross-transects over deep water throughout the survey. Pacific whiting target strength data were collected using both the centerboard and drop-transducer systems and may be used to scale the echo integration data to estimates of absolute abundance.   Data from the acoustic buoy will be used to determine whether Pacific whiting exhibit a behavioral response to the vessel and trawl noise. A total of 18 Methot trawl hauls were conducted throughout the survey area to examine the distributional patterns and biological characteristics of common macro-zooplankton species (e.g., euphausiids). An intership calibration between the Miller Freeman and the Canadian research vessel W.E. Ricker was completed as part of the collaborative Pacific whiting survey effort conducted by the United States and Canada. Vessel-mounted acoustic Doppler current profiler data and surface temperature and salinity measurements were collected continuously throughout the survey. Vertical profiles of temperature and salinity were also collected at selected sites. Other AFSC ancillary projects included volumetrically-derived catch estimates for comparison with load cell measurements of catch size and Pacific whiting stomach collections to assess Pacific whiting food habits. The Miller Freeman was also outfitted by SWFSC scientists with a submerged pumping system which allowed this group to collect near-surface samples to identify and map the horizontal distribution of epipelagic fish eggs.

Fisheries-Oceanography Coordinated Investigations (FOCI)

Fisheries Oceanography Coordinated Investigations (FOCI) continued the southeast Bering Sea fall juvenile studies initiated in 1994 with a cruise aboard the chartered Russian research vessel Professor Kaganovsky during 6-18 September. Center participants included Ric Brodeur, Matt Wilson, Frank Morado, Annette Brown, Chris Baier, and Elaina Jorgensen who were joined by scientists from the Pacific Marine Environmental Laboratory (PMEL), Pacific Marine Center, University of Washington, and Pacific Fisheries Research Centre in Vladivostok, Russia. Four transects were occupied around the Pribilof Islands. For each transect, observations were made on physical and biological conditions, including acoustic measurements, plankton sampling, and midwater trawling for juvenile pollock and their predators. During the last 4 days of the cruise, CTD (conductivity-temperature-depth) casts and bongo and CalVet net tows were made across the middle shelf transect line as part of our long-term monitoring efforts. This sampling provided us with highly contrasting conditions within and outside a bloom of coccolithophores.

By Ric Brodeur.

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