Numéro du document:
WG-EMM-2022/18
Soumis par:
Martin Collins (Royaume-Uni)
Approuvé par:
Chris Darby
Point(s) de l'ordre du jour
Résumé
- This paper provides an overview of CCAMLR-related ecosystem monitoring and scientific activities undertaken by the British Antarctic Survey (BAS) during the period April 2021 to March 2022.
- BAS research is focussed on the Scotia Sea region (Area 48) and the 2021/22 season saw reduced sea ice extent in the Scotia Sea with above average sea surface temperatures in early summer and slightly warmer temperatures during the winter.
- Evidence from the Western Core Box mooring, plankton trawls in the Bay of Isles and Cumberland Bay, and Antarctic fur seal (Arctocephalus gazella) scats and condition indicated that Antarctic krill (Euphausia superba) was scarce at South Georgia (Subarea 48.3) for an extended period from late austral summer (early 2021) to October 2021. This coincided with the fishery failing to find exploitable aggregations of krill at South Georgia during the austral winter of 2021. However, there was evidence from multiple sources of an influx of small krill in October 2021.
- There was no Western Core Box krill acoustic survey in the 2021/22 austral summer (due to ship time constraints), which followed a limited survey in 2020/21 (due to covid-19). Data collected using a mooring located in the Western Core Box region indicated low levels of water column acoustic backscatter on-shelf at South Georgia from April 2021 to October 2021, indicative of a lack of zooplankton and specifically few krill-swarm-like targets. Higher levels of total water column acoustic backscatter were observed between November 2021 and January 2022 consistent with the return of krill to the higher predator diets.
- The size of krill caught in coastal plankton nets at South Georgia (October 2021 to January 2022) was small (20 -35 mm TL), which was reflected in summer predator diets from South Georgia (mean < 45 mm TL) and Signy Island (mean < 40 mm TL).
- The numbers of fur seals and gentoo (Pygoscelis papua) and macaroni (Eudyptes chrysolophus) penguins attempting to breed at South Georgia CEMP sites (Bird Island and Maiviken) was low, but breeding success was moderate. The reduced number of breeders was likely a consequence of the scarcity of krill during the winter and early spring.
- At Signy Island (Subarea 48.2), fledging weights of Adélie (Pygoscelis adeliae) and chinstrap penguin (P. antarcticus) chicks were around average, however fledging success of chinstrap penguins was around half of the average level. Smaller than usual krill were found in the diets suggesting adult penguins struggled to provision their chicks. Due to the timing of ship calls at Signy Island (base operational 01/01/2022 to 19/03/2022) several key monitoring parameters were missed such that it is not possible to provide a full analysis of the 2021/22 season.
- Port Lockroy base on Goudier Island (Subarea 48.1) was operational 19/01/22 to 22/03/22, with a reduced level of monitoring possible.
- The South Georgia Groundfish survey (May 2021) indicated low biomass of mackerel icefish (Champsocephalus gunnari) on the South Georgia and Shag Rocks shelves and a low level of krill in the icefish diet which is consistent with other indicators of low krill biomass during the 2021 winter. There was evidence of a strong year class (40 -50 cm TL) of juvenile Patagonian toothfish (Dissostichus eleginoides).
- The number of items of beached debris recorded was above average at Signy Island and Bird Island, with slightly above average levels of debris associated with seabird colonies. However, the number of fur seal entanglements were below average levels. There was one foul-hooked wandering albatross (Diomedea exulans) and no records of hydrocarbon soiling reported.