Evaluation of Antarctic krill biomass and distribution off the South Orkney Islands 2011-2015

GSTDTAP > 气候变化

	Evaluation of Antarctic krill biomass and distribution off the South Orkney Islands 2011-2015
	Skaret, Georg; Krafft, Bjørn Arne; Calise, Lucio; Watkins, J; Pedersen, Ronald; Godø, Olav Rune
	2015-06-22
出版年	2015
语种	英语
国家	挪威
出版者	CCAMLR
领域	气候变化
英文摘要	Annual acoustic trawl surveys for krill monitoring have been carried out by the Institute of Marine research, Norway near the South Orkney Islands since 2011. The survey has been conducted early in the fishing season (January/February), using two different krill fishing vessels as platforms. The vessels were equipped with similar Simrad echo sounder systems suitable for quantitative assessments, but the frequencies operated varied between vessels and years. In addition, the survey coverage has varied between years in particular due to ice. In order to allow for comparison of distribution and abundance of krill near the South Orkneys among years, we here attempt to generate a coherent series of krill density estimates from the 5 years of surveys. We follow the CCAMLR protocol for biomass estimation as far as practically possible, given that we work with unconventional sets of frequencies for target strength estimation and target identification. In order to avoid variability due to differences in coverage, we also define a stratum within the survey area on the north side of the islands with full coverage in all years except 2013. The results show that except from the year 2015, krill densities were high, in the range 100-300 g/m2 based on the 120 kHz recordings, and a total estimated biomass of ca. 8 million tons of krill within the stratum in the peak year 2014. There were also consistently higher values of acoustic backscatter on the north side of the islands where the fisheries occur, than on the south side. Values were particularly high in the north-west shelf area associated with underwater canyons. In 2012, and particularly in 2015, low proportions of the acoustic backscatter were allocated to krill. The low proportions are probably caused by shortcomings in the krill identification techniques when other pairs of frequencies than combinations of 38, 120 and 200 kHz are used
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来源平台	Center for International Climate and Environmental Research-Oslo (CICERO)
文献类型	科技报告
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/2052
专题	气候变化
推荐引用方式 GB/T 7714	Skaret, Georg,Krafft, Bjørn Arne,Calise, Lucio,et al. Evaluation of Antarctic krill biomass and distribution off the South Orkney Islands 2011-2015:CCAMLR,2015.