NOAA Groundfish Trawl Surveys Data Partnerships

NOAA Fisheries Groundfish Trawl Surveys

The IPHC partners with the National Oceanic and Atmospheric Administration to collect Pacific halibut data during their groundfish bottom trawl surveys conducted in the summer months. The Bering Sea is surveyed annually and both the Gulf of Alaska and Aleutian Islands are surveyed biennially. Summaries of Pacific halibut data collection and results on the trawl surveys are provided here, and within each summary are links to additional information and data.

Bering Sea NOAA-Fisheries Bottom Trawl Survey in 2018

Posted January 2019. This report was prepared in cooperation with NOAA Fisheries/Alaska Fisheries Science Center

Overview

The National Oceanic and Atmospheric Administration (NOAA) - Fisheries has conducted annual bottom trawl surveys on the eastern Bering Sea (EBS) continental shelf since 1979. In cooperation with NOAA-Fisheries, the International Pacific Halibut Commission (IPHC) has deployed a staff member (sea sampler) on the NOAA-Fisheries survey every year since 1998 to collect Pacific halibut (Hippoglossus stenolepis) samples. When participating in the NOAA trawl survey, the IPHC sea sampler becomes part of a team of scientists that are tasked with carrying out sampling objectives related to stock assessment and year-class strength estimation for numerous groundfish and crab species. The IPHC sea sampler serves as a Pacific halibut specialist, and also assists NOAA biologists in achieving their survey goals.

The IPHC operates a coastwide fishery-independent setline survey as the primary source of data for the Pacific halibut stock assessment (IPHC 2019). However, Pacific halibut occupy a vast area of the Bering Sea shelf for which the IPHC lacks the financial resources to sample in its entirety on a regular basis. Therefore, in most years, the NOAA trawl survey is the only measure of abundance for much of this area.

Survey trawl gear has different size selectivity than setline gear, making it necessary to apply a selectivity curve to include these data directly in the Pacific halibut stock assessment that is generated by the IPHC. Pacific halibut are vulnerable to the trawl from about 20-100 cm fork length (FL) (Clark et al. 1997), but a substantial portion of the commercial-sized population (O32 or > 81.3 cm FL) exceeds 100 cm. In 2006, and again in 2015, the IPHC added shelf stations to its fishery-independent setline survey in the Bering Sea region in order to compare information from these stations with data collected on the NOAA trawl survey. After the study in 2006, the IPHC concluded that the trawl survey, along with periodic IPHC fishery-independent setline survey calibrations, provided an adequate accounting of Pacific halibut biomass on the EBS shelf (Clark and Hare 2007) and is a useful tool for constructing a population-density index for the IPHC stock assessment (Webster 2014). The 2015 calibration confirmed this earlier finding. In addition to its use as a stock assessment tool, trawl survey information is useful as a forecasting tool for cohorts approaching recruitment into the directed commercial fishery.

In 2018, there was also a “rapid-response” trawl survey that extended into the northern Bering Sea (NBS). The emergency trawl survey was prompted by unusually warm bottom temperatures on the EBS shelf and concerns that many fish populations had shifted north outside of the regular trawl survey area. The rapid response NBS trawl survey covered a similar but smaller area (158,286 km2) than the earlier standard NBS surveys in 2010 and 2017 (200,207 km2), and it utilized a 30x30 nautical mile grid, rather than a 20x20 nautical mile sampling grid. This resulted in only 49 stations sampled compared to the standard 144 stations (Fig. 1).

iphc-2018-nmfsbs1.jpg

Figure 1. Sampling station design for the 2018 NOAA Bering Sea bottom trawl survey. Note that the grid north of the yellow area denotes the northern Bering Sea (NBS) extension. Black dots are stations sampled in the 2018 “rapid-response” NBS trawl survey and black plus signs are stations sampled in the 2010 and 2017 standard NBS trawl surveys.

Sampling During the 2018 Trawl Survey

For the first three of four trips, the IPHC sea sampler was aboard the F/V Vesteraalen, one of two vessels chartered by NOAA to complete the EBS trawl survey. During the final trip which included the northern extension, the IPHC sea sampler was aboard the F/V Alaska Knight.

Pacific halibut were measured on all standard trawl survey tows aboard both vessels. Pacific halibut from tows aboard the vessel with an IPHC sea sampler onboard were assigned randomly into one of two groups: one for biological sampling, and one for wire tagging; with the goal of assigning 50% of the fish to each group. Fish in the tagging sample that were > 81 cm fork length, were released as soon as possible without a tag. Fish < 82 cm fork length were kept briefly in a live tank while sorting was taking place, and then assessed for condition using NOAA observer criteria and assigned to one of three condition categories (Excellent, Poor, Dead). Those fish with an assessment of Excellent and Poor were considered to have a high to moderate chance of survival and were outfitted with a wire tag through the operculum and released. Those fish assessed in the Dead category were measured and discarded. A fin clip was collected from each tagged fish for genetic analysis. For a full description of the tagging project, see the IPHC webpages on tagging.

Fish in the biological sample group were assessed for sex, maturity, and prior hooking injuries (PHI), and the otolith was removed for aging. An additional subsample was selected for the extraction of muscle samples as part of a study investigating growth patterns and for fin clips which will be used for a genetics study. Northern extension stations were treated the same as standard stations for sampling. Pacific halibut caught in tows at corner crab stations, and during duplicate tows, were excluded from the regular sample.

Pacific halibut from the vessel not staffed with an IPHC sea sampler were measured for fork length and randomly divided into two groups: tagging and no sample. Tagging criteria was the same as for the vessel with an IPHC sea sampler. Those fish in the no sample group were released.

Results

iphc-2018-beringsresults.png

Abundance and Biomass Estimates

In 2018, total Pacific halibut abundance in the EBS as estimated using catch data collected during the trawl survey was 50.5 million fish, a small decrease from the 53 million fish estimated in 2017, and a continuation of the decreasing trend started in 2006.  Total biomass was estimated at just under 278 million pounds, which was only a slight decrease from the 279 million pounds estimated in 2017 (Fig. 2).

iphc-2018-ebsph.png

Figure 2. Pacific halibut abundance (millions of fish) and biomass (millions of pounds) in the eastern Bering Sea as estimated using data collected during the NOAA Bering Sea groundfish trawl survey for the years 1982-2018. 

In order to make the abundance and biomass estimates comparable between the 2018 rapid response northern Bering Sea (NBS) survey and the 2010 and 2017 standard NBS trawl surveys, estimates for 2010 and 2017 excluded nearshore stations where no sampling was conducted in 2018. Comparing three years of survey data for the sampling area of the NBS, total Pacific halibut abundance and biomass estimates indicated a modest increase over the 2017 trawl survey (Fig. 3). The average fork length in the north was 65.6 cm, substantially larger than the 54.1 cm average fork length observed during the standard EBS trawl survey. Both the 2010 and 2017 northern extensions displayed similar size variations.

iphc-2018-ebsomb.jpg

Figure 3. Pacific halibut abundance (millions of fish) and biomass (millions of pounds) in the northern Bering Sea (NBS) as estimated comparing the same areas sampled during the NOAA rapid response NBS trawl survey in 2018 with the standard NBS trawl surveys conducted in 2010 and 2017.

Additional information

  • Interactive trawl survey data maps are available on the NOAA survey maps page.
  • Full summary reports are prepared by NOAA/RACE for each trawl survey, usually within one year of completion of the trawl survey.  
  • NMFS protocols for groundfish bottom trawl surveys (Stauffer 2004).

References

Clark W G and Hare S H. 2007. Assessment of the Pacific halibut stock at the end of 2006.  IPHC Report of Assessment and Research Activities 2006: 97-128.

Clark W G, St-Pierre G, and Brown E S. 1997. Estimates of [Pacific] halibut abundance from NMFS trawl surveys. Int. Pac. Halibut Comm. Tech. Rep. 37.

IPHC (Erikson L., Soderlund E., and Geernaert T.). 2018. Fishery-independent setline survey (FISS) design and implementation in 2018, including current and future expansions. IPHC-2019-AM095-06.

Stauffer G. (compiler). 2004. NOAA Protocols for groundfish bottom trawl surveys of the nation’s fishery resources. NOAA technical memorandum NMFS-F/SP0-65.

Aleutian Islands NOAA-Fisheries Groundfish Trawl Survey in 2018

Posted January 2019. This report was prepared in cooperation with NOAA Fisheries/Alaska Fisheries Science Center

Overview

In 2018 the International Pacific Halibut Commission (IPHC) participated in the National Oceanic and Atmospheric Administration (NOAA) - Fisheries  Aleutian Islands groundfish bottom trawl survey for the fourth time since 2000 (other years include 2012, 2014, and 2016). This survey has taken place every two years since 2000 (except in 2008) and every three years prior to that, dating back to 1980. The IPHC uses the NOAA-Fisheries trawl survey to collect information on Pacific halibut (Hippoglossus stenolepis) that are not yet vulnerable to the gear used for the IPHC fishery-independent setline survey (FISS) (IPHC 2019) or commercial fishery (note that trawl survey gear can catch fish as small as 20 cm fork length), and as an additional data source and verification tool for stock analysis. 

 When participating in the NOAA-Fisheries trawl survey, the IPHC Secretariat’s field staff member (sea sampler)  becomes part of a team of scientists that are tasked with carrying out sampling objectives related to stock assessment and year-class strength estimation for numerous groundfish and invertebrate species. The IPHC sea sampler serves as a Pacific halibut specialist, and also assists NOAA biologists in achieving their survey goals.

iphc-2018-aiom.jpg

Figure 1. Sampling stations and catch for the 2018 NOAA-Fisheries Aleutian Islands bottom trawl survey. 

Sampling During the 2018 Survey

The NOAA-Fisheries survey was divided into three trips, and for all three trips, the IPHC sea sampler was aboard the F/V Ocean Explorer, one of two vessels chartered by NOAA to complete the Aleutian Islands survey. Pacific halibut were measured on all standard survey tows aboard both vessels.

Pacific halibut caught were assigned randomly into one of two groups: one for biological sampling, and one for wire tagging; with the goal of assigning 50% of the fish to each group. Fish in the tagging sample that were > 81 cm fork length, were released as soon as possible without a tag. Fish < 82 cm fork length were kept briefly in a live tank while sorting was taking place, and then assessed for condition using NOAA observer criteria and assigned to one of three condition categories (Excellent, Poor, Dead). Those fish with an assessment of Excellent or Poor were considered to have a high to moderate chance of survival and were outfitted with a wire tag through the operculum and released. Those fish assessed in the Dead category were measured and discarded. A fin clip was collected from each tagged fish for genetic analysis. For a full description of the tagging project, see the IPHC’s ‘tagging’ webpages. Fish in the biological sample group were assessed for sex, maturity, and prior hooking injuries (PHI), and the otolith was removed for aging.

Results

iphc-2018-airesults.png

Abundance and Biomass Estimates

In 2018, total Pacific halibut abundance in the Aleutian Islands as estimated using catch data collected during the trawl survey was 6.7 million fish, a decrease from the 7.0 million fish estimated in 2016. Abundance has decreased slightly in most surveyed years since about 2006, but the overall decrease has been relatively minor. Total biomass was estimated at 63 million pounds in 2018, which was essentially unchanged from 2016 (Fig. 2). iphc-2018-aiabundance.png

Figure 2. Pacific halibut abundance (millions of fish) and biomass (millions of pounds) in the Aleutian Islands as estimated using data collected during the NOAA-Fisheries Aleutian Islands groundfish trawl survey for the years 1980-2018. 

Additional information

  • Interactive survey data maps are available on the NOAA survey maps page.
  • Full summary reports are prepared by NOAA-Fisheries (NMFS)/RACE for each survey, usually within one year of completion of the survey. The 2016 Aleutian Islands report is available here
  • NMFS protocols for groundfish bottom trawl surveys (Stauffer 2004).

References

IPHC (Erikson, L., Soderlund, E. and Geernaert, T.). 2018.  Fishery-independent setline survey (FISS) design and implementation in 2018, including current and future expansions. IPHC-2019-AM095-06.

Stauffer, G. (compiler). 2004. NOAA Protocols for groundfish bottom trawl surveys of the nation’s fishery resources. NOAA technical memorandum NMFS-F/SP0-65.