NMFS Groundfish Trawl Surveys Data Partnerships

NMFS Groundfish Trawl Surveys

The IPHC partners with the National Marine Fisheries Service 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 NMFS Trawl Survey in 2018

Overview

The National Marine Fisheries Service (NMFS) has conducted annual bottom trawl surveys on the eastern Bering Sea (EBS) continental shelf since 1979. In cooperation with NMFS, a field biologist from the International Pacific Halibut Commission (IPHC) has been deployed on the NMFS survey every year since 1998 to collect Pacific halibut (Hippoglossus stenolepis) samples. When participating in the NMFS trawl survey, the IPHC biologist 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 biologist serves as a Pacific halibut specialist, and also assists NMFS biologists in achieving their survey goals.

The IPHC operates a coastwide longline survey as the primary fishery-independent source of data for the Pacific halibut stock assessment (Goen et al. 2017). 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 NMFS 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 setline survey in the Bering Sea region in order to compare information from these stations with data collected on the NMFS trawl survey. After the study in 2006, the IPHC staff concluded that the trawl survey, along with periodic IPHC 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 commercial fishery.

In 2018, there was also a “rapid-response” survey that extended into the northern Bering Sea (NBS). The emergency 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 survey area. The rapid response NBS 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 NMFS 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 survey and black plus signs are stations sampled in the 2010 and 2017 standard NBS surveys.

Sampling During the 2018 Survey

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

Pacific halibut were measured on all standard survey tows aboard both vessels. Pacific halibut from tows aboard the IPHC-staffed vessel 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 NMFS 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 Forsberg et al. (2016).

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 biologist were measured for fork length and randomly divided into two groups: tagging and no sample. Tagging criteria was the same as for the IPHC-staffed vessel. Those fish in the no sample group were released.

Results

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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 NMFS 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 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 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 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 NMFS rapid response NBS survey in 2018 with the standard NBS surveys conducted in 2010 and 2017.

Additional information

  • Interactive survey data maps are available on the NOAA survey maps page.
  • Full summary reports are prepared by NMFS/RACE for each survey, usually within one year of completion of the survey.  
  • Summary reports focused on Pacific halibut for surveys conducted prior to 2018 and where IPHC has participated, are available in Report of Assessment and Research Activity documents that can be accessed on the IPHC documents webpage.
  • NMFS protocols for groundfish bottom trawl surveys (Stauffer 2004).
  • IPHC protocols for sampling and tagging of Pacific halibut aboard the NMFS groundfish bottom trawl surveys in 2018. 

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 halibut abundance from NMFS trawl surveys. Int. Pac. Halibut Comm. Tech. Rep. 37.

Forsberg, J., Sadorus, L., Logan, P., Kelleher, Z., Pedersen, C. 2016. Wire tagging Pacific halibut on NMFS trawl surveys: 2015 pilot study. Int. Pac. Halibut Comm. Report of Assessment and Research Activities 2015: 464-477.

Goen, J., Geernaert, T., Henry, E., Soderlund, E., Ranta, A. M., Kong, T. M., and Forsberg, J. 2017. Fishery-independent setline survey (FISS) design and implementation in 2017, including current and future expansions. Prepared for the AM094: IPHC-2018-AM094-06 Rev 1.

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

Webster, R. A. 2014. Construction of a density index for Area 4CDE. Int. Pac. Halibut Comm. Report of Assessment and Research Activities 2013: 261-288.

Aleutian Islands NMFS Groundfish Trawl Survey in 2018

Overview

In 2018 the International Pacific Halibut Commission (IPHC) participated in the National Marine Fisheries Service (NMFS) 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 NMFS 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 (Goen et al. 2017) 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 NMFS trawl survey, the IPHC biologist 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 biologist serves as a Pacific halibut specialist, and also assists NMFS biologists in achieving their survey goals.

iphc-2018-aiom.jpg

Figure 1. Sampling stations and catch for the 2018 NMFS Aleutian Islands bottom trawl survey.

Sampling During the 2018 Survey

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

Pacific halibut caught by the IPHC-staffed vessel 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 NMFS 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 Forsberg et al. (2016). 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 NMFS 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 NMFS/RACE for each survey, usually within one year of completion of the survey.  The 2016 Aleutian Islands report is available here
  • Summary reports focused on Pacific halibut for surveys conducted prior to 2018 and where IPHC has participated, are available in Report of Assessment and Research Activity documents that can be accessed on the IPHC documents webpage.
  • NMFS protocols for groundfish bottom trawl surveys (Stauffer 2004).
  • IPHC protocols for sampling and tagging of Pacific halibut aboard the NMFS groundfish bottom trawl surveys in 2018. 

References

Forsberg, J., Sadorus, L., Logan, P., Kelleher, Z., Pedersen, C. 2016. Wire tagging Pacific halibut on NMFS trawl surveys: 2015 pilot study. Int. Pac. Halibut Comm. Report of Assessment and Research Activities 2015: 464-477.

Goen, J., Geernaert, T., Henry, E., Soderlund, E., Ranta, A. M., Kong, T. M., and Forsberg, J. 2017. Fishery-independent setline survey (FISS) design and implementation in 2017, including current and future expansions. Prepared for the AM094: IPHC-2018-AM094-06 Rev 1.

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

Document Title PDF Availability
IPHC-2018-Trawl Field Manual for IPHC Personnel Aboard NMFS Trawl Surveys in 2018: Aleutian Islands and Bering Sea PDF icon 04 Dec 2018