Abstract:
This dataset consists of biomass data and diet composition of mackerel icefish (Champsocephalus gunnari) from the South Georgia groundfish survey, collected during scientific trawl surveys from 1986 to 2023. These data were primarily collected to produce estimates of mackerel icefish biomass to inform management of the icefish fishery, and to further our understanding of icefish ecology, distribution, and diet. Data were primarily collected by Martin A. Collins, Mark Belchier, Inigo Everson, Jude Brown, Phil Hollyman, Simeon Hill, Tom Marlow, Caradoc Jones, Rebecca Mitchell & Sue Gregory.
Since 1990, the South Georgia groundfish surveys were funded by the Government of South Georgia and the South Sandwich Islands. Earlier surveys were funded by the US and Polish governments.
Keywords:
demersal fish, diet composition, fish biomass, trawl survey
Collins, M., Belchier, M., Gregory, S., Hollyman, P., Everson, I., & Jones, T. (2026). Mackerel icefish (Champsocephalus gunnari) catches, biomass and diet composition from the South Georgia (southwest Atlantic) groundfish survey, 1986-2023 (Version 1.0) [Data set]. NERC EDS UK Polar Data Centre. https://doi.org/10.5285/93a1239d-e0b6-4ed4-889f-63126d0ffb80
| Access Constraints: | None |
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| Use Constraints: | This data is governed by the NERC data policy (http://www.nerc.ac.uk/research/sites/data/policy/) and supplied under Open Government Licence v.3 (http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/). |
| Creation Date: | 2026-01-15 |
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| Dataset Progress: | Planned |
| Dataset Language: | English |
| ISO Topic Categories: |
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| Parameters: |
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| Personnel: | |
| Name | UK Polar Data Centre |
| Role(s) | Metadata Author |
| Organisation | British Antarctic Survey |
| Name | Martin A Collins |
| Role(s) | Investigator, Technical Contact |
| Organisation | British Antarctic Survey |
| Name | Mark Belchier |
| Role(s) | Investigator |
| Organisation | Government of South Georgia & the South Sandwich Islands |
| Name | Sue Gregory |
| Role(s) | Investigator |
| Organisation | Government of South Georgia & the South Sandwich Islands |
| Name | Philip R Hollyman |
| Role(s) | Investigator |
| Organisation | Bangor University |
| Name | Inigo Everson |
| Role(s) | Investigator |
| Organisation | University of East Anglia |
| Name | Timothy Jones |
| Role(s) | Investigator |
| Organisation | British Antarctic Survey |
| Parent Dataset: | N/A |
| Reference: | Hollyman, P.R., Hill, S.L., Laptikhovsky, V.V., Belchier, M., Gregory, S., Clement, A. and Collins, M.A., 2021. A long road to recovery: dynamics and ecology of the marbled rockcod (Notothenia rossii, family: Nototheniidae) at South Georgia, 50 years after overexploitation. ICES Journal of Marine Science, 78(8), pp.2745-2756. https://doi.org/10.1093/icesjms/fsab150 Gregory, S., Collins, M.A. and Belchier, M., 2017. Demersal fish communities of the shelf and slope of South Georgia and Shag Rocks (Southern Ocean). Polar Biology, 40(1), pp.107-121. https://doi.org/10.1007/s00300-016-1929-7 Jones, T., Warwick-Evans, V., Hill, S.H. and Collins, M.A., 2026. Informing krill fishery management through modelling spatial distribution and diet of a major krill predator, mackerel icefish (Champsocephalus gunnari), at South Georgia. ICES Journal of Marine Science, XX(X), pp.XXXX-XXXX. |
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| Quality: | Raw trawl data were cleaned to remove trawls hauled early due to unsuitable ground, and those that were deemed unrepresentative due to gear failure. | |
| Lineage/Methodology: | Trawl surveys Data on the abundance and distribution of Champsocephalus gunnari were collected during 28 demersal trawl surveys conducted primarily during the austral summer (Nov-Feb) at South Georgia and Shag Rocks, between 1987 and 2023. The survey design has remained constant throughout the time series despite changes in survey vessel. From the 1991 survey onwards, gear was standardized (commercial sized otter trawl FP-120, wingspread 18-20 m, headline height 3-6 m, cod end mesh 40 mm). Before this, broadly similar gear was used on each of the early surveys (Belchier et al., 2015). The area was surveyed using a random-stratified design, subdividing into five sectors: Shag Rocks plus the four quadrants of the South Georgia shelf; northwest, northeast, southwest, and southeast. Trawls were conducted for 30 minutes at a speed of 3-4 knots, and at two depth zones: 100-200 m and 201-350 m. The trawl dataset also contains data from winter surveys, performed using the standard survey design but in April/May (2008 and 2021) or September (1997 and 2007), and dedicated deepwater surveys (350-1000 m) During each survey, the total catch of C. gunnari in each trawl was recorded along with information on trawl location, time, depth, and trawl characteristics (trawl duration, distance trawled, horizontal and vertical net opening). Diet data Since 2004, stomach contents of mackerel icefish have been collected on a routine basis using a standard methodology developed by Main et al. (2009). Samples of C. gunnari (typically less than or equal to 30 per trawl) were collected from all trawls in which the species was caught. Sampled fish were measured and weighed, stomachs were removed and immediately frozen at -20 degrees centigrade, for later processing and macroscopic identification of stomach contents. Stomach contents were thawed and sorted in the laboratory at King Edward Point, South Georgia. Once the stomach contents were sorted, individual prey items were counted and weighed to the nearest 0.01g. Diet composition per fish sampled were aggregated at two levels. Gross survey averages of diet composition were produced by first assigning prey items into one of 11 broad taxonomic groups (Euphausia superba, Other Euphausia spp., Thysanoessa sp., Themisto gaudichaudii, Antarctomysis sp., Other/unknown crustacean, Nototheniidae, Channichthyidae, Myctophidae, Other/unknown fish, Other/unknown), then finding the summed mass for each group across all fish sampled from the Shag Rocks and South Georgia shelves per survey. These are then presented as proportional composition by dividing by the net total across groups per survey and shelf area. The proportion of krill in stomach contents per trawl was calculated by taking the summed mass of krill and dividing by the summed mass across all prey taxa, where the sums are performed across fish stomach contents from each trawl with diet information. |
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| Temporal Coverage: | |
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| Start Date | 1986-11-29 |
| End Date | 2023-02-10 |
| Start Date | 2004-01-07 |
| End Date | 2023-02-10 |
| Spatial Coverage: | |
| Latitude | |
| Southernmost | -55.499 |
| Northernmost | -53.277 |
| Longitude | |
| Westernmost | -42.982 |
| Easternmost | -34.275 |
| Altitude | |
| Min Altitude | N/A |
| Max Altitude | N/A |
| Depth | |
| Min Depth | 75 |
| Max Depth | 917 |
| Location: | |
| Location | South Atlantic Ocean |
| Detailed Location | South Georgia, Scotia Sea |
| Location | South Atlantic Ocean |
| Detailed Location | Shag Rocks, South Georgia, Scotia Sea |
| Data Collection: | All data processing and cleaning were performed in R version 4.3.3 (R Core Team 2024). |
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| Data Storage: | 4x.csv files as follows: SG_Mackerel_icefish_catch_data This CSV file contains information on catch by trawl for mackerel icefish (Champsocephalus gunnari) from the South Georgia groundfish survey collected from 1986 to 2023. The SG groundfish survey is performed approximately biennially (annually in earlier years) since 1987. For more information on the format and design of the groundfish survey see Hollyman et al. (2021). Data are structured by trawl and contain information on total catch mass (kg) of C. gunnari along with information on trawl date, location and average trawl depth. SG_Mackerel_icefish_diet_gross_survey_average Information on diet composition of mackerel icefish (Champsocephalus gunnari) from the South Georgia groundfish survey, collected from 2004 to 2023, aggregated to survey level. Data represent the survey-average proportion by mass of alternate prey items across different taxonomic groups for fish collected on the South Georgia and Shag Rocks shelves. SG_Mackerel_icefish_diet_trawl_krill_proportions Information on diet composition of mackerel icefish (Champsocephalus gunnari) from the South Georgia groundfish survey, collected from 2004 to 2023. Data represent the trawl-average proportion by mass of krill found in mackerel icefish stomach samples for each trawl where stomach contents sampling of mackerel icefish was performed. SG_Mackerel_icefish_trawl_summary Summary of demersal trawl surveys contained in the associated catch dataset. |
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