(Quarterly Report for Jan-Feb-March 1999)
ASSESSMENT: Continued Participation in ADF&G Seasonality Study of Marmot Bay
Members of the RACE Division participated in the third phase of an 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) 7-17 January 1999 aboard the ADF&G research vessel Resolution. The primary purpose of the study, which includes sampling already completed in June, August and October 1998 and additional sampling periods scheduled for March and June 1999, is to document seasonal trends in depth and inshore/offshore distribution of crab and groundfish resources including Tanner crab (Chionoecetes bairdi), 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 cooccurrence 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 January 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, 960 stomachs, 863 ovaries, and 986 otoliths were taken from the major groundfish species occurring in the study area.
By Eric Brown.
Fishing Gear-Seafloor Impacts Workshop
A 2-day workshop on AFSC seafloor research in Alaska was held on 27-28 January 1999 in Seattle at the AFSC. Participants included fisheries scientists from the ABL and the RACE and REFM Divisions. The objectives of the workshop were to 1) review current and planned trawling impact research in the Aleutian Islands region (AI), eastern Bering Sea (EBS) and the Gulf of Alaska (GOA); 2) review current and planned acoustic seabed classification research in the EBS and GOA; 3) discuss the utility and performance of underwater video and trawls for research data collection; and 4) discuss future program directions.
The specific objectives of the
AFSCs bottom trawl impact studies were to document long-term and short-term effects
on both physical (e.g., grain size distribution, organic carbon concentration) and
biological (population and community) parameters, as well as to review historical fishing
effort. Study areas consisted of soft and hard bottom habitat in the Aleutian
Islands (Seguam Pass), the EBS (Bristol Bay), and the GOA (Dixon Entrance and Kodiak and
Kruzof Islands). Methodologies included the study of short-term effects of
experimental fishing and more chronic effects of commercial activity by comparing heavily
fished and unfished areas. Sampling gear included benthic grab samplers, modified
research trawls, and both towed and submersible-mounted underwater video systems.
Evidence for trawling-related effects identified by individual studies included physical disturbances such as displacement of boulders, persistent scour marks, reduction of mean grain size, and elevated organic carbon levels. Observed effects on biological populations were mixed although there was an overall result demonstrating that megafauna populations in shallow, naturally-disturbed areas are sensitive to trawling. Certain emergent epifauna (e.g., some sponges, anthozoans, bryozoans) and biogenic substrate (snail shells), were reduced in abundance or damaged, affecting available structural habitat. Motile epifauna, on the other hand, was generally unaffected with a few exceptions. Asterias, displaying opportunistic tendencies, increased in abundance, while snails and snail eggs were reduced. Community-level effects were reduced biological diversity and increased patchiness of sedentary taxa. Overall, the ecological interpretation of these findings is hindered by the lack of basic information about affected taxa.
Three new gear types have been evaluated for use in AFSC gear impact studies. One of these, a depth-regulating video sled for high relief areas (TACOS or towed automatically compensating observation system) proved functional in extreme current areas. However, its capability to collect quantitative data is uncertain. Another project involved the evaluation of three USBL (ultra-short baseline) acoustic systems for trawl positioning. Two of these (Nautronix ATS II and ORE Trackpoint II Plus) proved sufficiently accurate for real-time trawl positioning. Finally, underwater laser line scan systems (LLSS) appear capable of providing useful biological assessment data in areas too turbid for conventional video systems, albeit at a relatively high cost. In addition, data quality of LLSS is limited by sea state, depth of field, and target motion.
Research on acoustic seabed
classification addresses the new Sustainable Fisheries Act mandates to characterize
essential fish habitat (EFH). Another motivation for this type of research is to
improve the precision of fish abundance estimates with habitat-based stratification of
research trawl surveys.
The overall objective for the studies presented at this workshop was to evaluate Quester Tangent Corporation (QTC) technology for background data collection during routine AFSC survey operations (e.g., acoustic and trawl surveys). Individual studies are being conducted to identify an optimum classification scheme (i.e., determine optima for frequency, number of bottom type classes, algorithms to extract shape parameters, and calibration sites), produce seafloor maps, determine operational limits, and establish survey designs. Work conducted between 1997 and 1998 in the EBS simultaneously collected digitized echo returns with a QTC ISAH-S system at two different frequencies (38 and 120 kHz) along a 14,000-km track. A bottom type map generated from the 120 kHz data will be used for preliminary EFH analyses. The 38kHz data were of poor quality, due to unidentified interference. A new dual frequency data set will be collected during the 1999 field season, with shipboard quality assurance/quality control and redundant hardware systems.
Research on the operational limits of the QTC View with a hull-mounted transducer was conducted in the GOA in 1997. Speeds between 3 and 12 knots did not significantly affect the QTC View classification performance, and no depth effect was observed for depths less than at least 230 m. Classification performance was, however, negatively impacted by bottom slopes greater than 5 to 8 degrees. A quantitative relationship was also established between survey effort (to estimate quantity of fish habitat) and seafloor heterogeneity. It clearly indicated that compromises between effort and classification precision are necessary.
The performance of a prototype rawl-mounted acoustic-video system will be evaluated during the 1999 GOA groundfish survey. The impetus for seabed classification under this configuration are:
To overcome the limitations of slope and depth as identified by the research conducted in 1997.
Directly relate fish abundance and bottom type.
Obtain improved spatial resolution
of seafloor types.
The video portion of the workshop focused on the role of video in fishing gear impact studies and the potential for automated image processing. Some generalizations from the discussions of video cameras and trawls as sampling devices were:
Choice of video or trawls as the primary sampling gear in these studies likely reflects the past experience of the principal investigators.
Both gears have been successfully used to collect relative abundance data for invertebrates.
Video has inherently greater spatial resolution than trawls.
Trawls effectively sample multiple taxa, while it is advisable to limit video data collection to a single taxon during each viewing of the tape.
Video is useful for calibrating trawl sampling efficiency.
Processing of video images to extract data is time-consuming and costly.
Relatively slow tow speeds are required to count and identify targets with video, effectively reducing data collection efficiency.
Poor image quality at slow playback speeds with analog video systems is improved somewhat with digital systems.
Video systems cannot directly collect biomass data.
Hardware and software incompatibilities currently limit automated video processing options.
Fish burial, avoidance of artificial light and variable water clarity can introduce bias/error in video data, while gear avoidance, herding and escapement under the footrope are similarly problematic for trawls.
It is frequently difficult to
specify taxonomy, ages and size of targets in video images.
A discussion of the long-term direction of AFSC gear impact studies called for:
The development of a prioritized research plan, to include fixed gear studies, potential gear design issues and recovery processes.
Consideration of second generation studies to evaluate ecological implications of effects attributed to bottom trawls, including basic studies of affected invertebrate species.
A concerted effort to investigate automated video processing options used in other disciplines (e.g., medicine and the military) via a personal services contract.
By Bob McConnaughey.
MIDWATER ASSESSMENT: Echo Integration-trawl Survey of Walleye Pollock in the Southeastern Aleutian Basin near Bogoslof Island, February-March 1999
The Hokkaido National Fisheries Research Institute (HNF) and the National Research Institute of Fisheries Engineering (NRIFE) of Japan conducted an echo integration-trawl survey of walleye pollock in the southeastern Bering Sea aboard the Japanese research vessel Kaiyo maru. The Midwater Assessment and Conservation Engineering (MACE) program at the AFSC has conducted this survey annually since 1988; in 1999 MACE collaborated with the HNF and NRIFE aboard their vessel because the NOAA ship Miller Freeman was in dry dock for repairs. Leg 1 (1-12 February) began in Dutch Harbor, and leg 2 (21 February- 4 March) began in Kodiak, Alaska. The primary cruise objective was to determine the distribution and abundance of pollock that spawn in early March in the Bogoslof Island area. The survey design consisted of north-south parallel transects at 10 nautical miles (nmi) spacing on leg 1, and 10 or 5 nmi spacing on leg 2 depending on fish distribution. During leg 1, pollock were encountered along the southern ends of transects, near the Aleutian Islands, especially in the Samalga Pass area northeast of the Islands of Four Mountains. During leg 2, distribution was similar, but pollock aggregations appeared to be larger and more concentrated than during leg 1. Abundance appeared similar to that in winter 1998. Pollock caught in the six midwater trawls made during leg 1 had lengths ranging from 42 to 65 cm; those caught in the eight hauls made during leg 2 had lengths ranging from 39 to 67 cm. Hauls made on the easternmost transects north of Akutan Island caught smaller pollock (length modes between 42-45 cm) than those in the central and western part of the survey area (length modes 53-57 cm for males, and 55-59 cm for females). Average gonadosomatic index (GSI) for mature female pollock increased from 12.6 during leg 1 to 16.1 during leg 2.
By Chris Wilson.