Investigations on by-catch of fishes captured during krill fishing by F/V Chiyo Maru No. 3 were made from 3 February to 6 March, 1996 to the north of the South Shetland Islands. Among 147 hauls examined, a total of 99 specimens belonging to 5 families and 14 species were captured as by-catch in 41 hauls. Notothenioid juveniles were found in 30 hauls carried out in waters with a depth of 87-853m (average 186m). On the contrary, bathypelagic fishes (myctophids and paralepidids) were recognized in 11 hauls operated at some distance from the shelf, in the offshore waters with a depth of 275-1780m (average 1006m). Notothenioid juveniles never caught with bathypelagic fish species in all hauls examined. Among by-catch fishes, juvenile Lepidonotothen larseni was the most abundant. This species was found in 15 hauls, and its estimated value of an arithmetic mean was 4±19 ind./t (0 to 140 ind./t) of catch and 51±217 ind./h (0 to 3927 ind./h) trawling respectively. Bathypelagic fish species, Electrona carlsbergi, which was found in samples from 6 hauls, was the next in abundance. Its arithmetic mean was 3±21 ind./t (0 to 220 ind./t) of catch and 32±178 ind./h (0 to 1509 ind./h) trawling. Although the krill CPUE of hauls without by-catch of fish ranged widely, the large incidental catch of fish usually occurred in hauls with lower krill CPUE.
Abstract:
Monthly CPUEs during winter operation of Japanese krill trawlers around South Georgia were calculated. The range of CPUE values in 1991 season (poor year of krill) was comparable to the range of summer operation around Elephant Island and Livingston Island. Vertical distribution presumed from net towing depth. Net tow depth data implied that overall krill distribution in the the winter season might be deeper than the summer season. Interannual variability of vertical distribution was also suggeted. Length frequency distribution implied the evidence of strong krill influx from the Antarctic Peninsula region and Weddell Sea.
Abstract:
CPUE and Recruitment indices during 1980 to 1995 were calculated based on the log book data from commercial krill trawlers. Long-term variation of monthly CPUE was shown but this trend might be the result of the alternation of operational strategy in relation to the product quality. Recruitment indices in this paper agreed with Sigel and Loeb (1995) in genaral trend, however, some disagreements were also adressed.
Abstract:
At Seal Island breeding predators which incorporated an overnight period into their foraging trip such as Antarctic fur seals (Arctocephalus gazella) and overnight foraging chinstrap penguins (Pygoscelis antarctica) went beyond the inshore region and foraged in the slope/offshore region, even though the slope/offshore region was less abundant with krill and more remote from their breeding sites than the inshore region. Only diurnal chinstrap penguins foraged in the inshore region. The following advantages are considered for visual predators to feed in the slope/offshore region at night:(l) krill showed more uniformal distribution in the slope/offshore region in contrast to its very patchy distribution in the inshore region so that krill may be easily found in the slope/offshore region; (2) krill tend to be larger in body size and more matured in the slope/offshore region than those in the inshore region; larger gravid female krill, which may be easily found and captured by predators, were available in the slope/offshore region; (3) Myctophid fish occurred near surface at night in the slope/offshore region; their ventral light organs may become easier target for predators at night. Thus, aggregation pattern of krill, body size/maturity stage of krill and availability of myctophid fish may make the slope/offshore region favorable foraging areas in spite of its lower krill density.
Abstract:
The methods and preliminary data on evaluation of krill transfer factors results in subarea 48.2 in the period of 19.02-07.03.96 are presented. The polygon of 80 x 240 miles was situated in interaction zone of the two circulating systems of the climatic scale: Antarctic Circumpolar Current and Weddell Sea waters. The experiment was carried out in two stages: evaluation of krill transport through the polygon boundaries; hydroacoustic evaluation of krill biomass and distribution in the polygon and researches of krill transport peculiarities through the polygon depending on water dinamics.
Krill transport through the polygon boundaries was calculated as product of the two values, inteagrated for the layer of 0-200 m: krill density (t/cubic mile) and water output (cubic mile/hour) through 1 mile of the polygon boundary per hour. The value (t/hour) characterizes transport intensity of krill biomass through 1 mile of polygon boundary. The results of krill density evaluation, geostrophical velocities and water outputs on the polygon boundaries are presented. Average krill transport intensity (absolute values) were: mean=7.2 t/hour, s.d.=15.5 t/hour. There is sufficient variability of krill transport through polygon boundaries by value of biomass transported and by transport direction as well. The total balance of krill input-output through all the polygon boundaries was positive (2088 ±831 t/hour).
The obtained values of krill transport are compared with those of for the polygon 30 x 30 miles, situated on the western periphery of the Doubling Anticyclonic Current, doubling South Orkneys (R/V "Dmitry Stephanov", April 19.
Abstract:
In the period from 24 February to 7 March 1996 in the cruise of RV "Atlantida" acoustic assessment of krill biomass and distribution was carried out in study area restricted with 59° 10' S - 60°30' S and 42 °00' W - 50°00 'w within Subarea 48.2. The study area of 19.200 sq.mi1es was located in the zone of two circulation systems of climatic scale interaction: Antarctic Circumpolar Current and Weddell Sea water circulation. Researches in the study area included a broad spectrum of hydrobiological and oceanographic observations and studies.Onboard hydroacoustic complex was represented by the measuring system EK-5001BI 500. Calibration of echo sounder EK-500 was performed by specialists of Simrad company in Horten, Norway. Echosurvey was carried out using uniform square grid of tacks with between-tacks distance of 20 miles. The echosurvey was carried out diurnally. Krill target strength was estimated by means of TS/length relationship, recommended by WG-krill (SC-CAMLR, 1991). Recorded range of MSBS values variations was (-77÷-43) dB. Kri11 biomass estimation in the study area amounted to 1.12 mln. t at 95% confidence limit CL=93.1 thous.t. Variation coefficients of krill density and biomass within strata speciefied exceeded no 8%. Previous data obtained by AtlantNIRO showed that biomass estimated was below that expected. One of the reasons is diurnal regime of echo survey execution. According to Demer and Hewitt (1995) exclusion of kri11 vertical diurnal migrations from consideration results in underestimated acoustic biomass by 1.9 dB at s.d. = 0.6 dB. Besides, the study area selected included no the southern part (southwards of 60 ° 30'S) of Subarea 48.2 where southwards off Coronation Island considerable kri11 fishing grounds occure. According to AtlantNIRO data krill biomass southwards of 60 ° 30'S amounts about (883±264.9) thous. t.
Therefore, total krill biomass in Subarea 48.2 may be assessed as 2.6 mln.t at 95(% confidence limit CL=298.2 thous.t
Abstract:
There are presented some results of atmospheric circulation features evaluation over Antarctic Sector of Atlantic, thermochaline conditions and surface geostrophic transfers.
There are obtained daily indeses of atmospheric circulation for the period February-March 1996, calculated average values for ten-days periods and for month.
There are calculated cyclogenesis intensity characteristics for the period, which along with atmospheric circulation data allow to determine atmospheric circulation features over ASA area at the summer period.
There are obtained data on thermochaline conditions on the polygon near South Orkneys. There are calculated and presented maximum temperature distribution on the polygon, allowing to provide the most clear marking of the main water masses and Secondary Frontal Zone position and geostrophical current velocities distribution in the limits of the polygon investigated.
There are observed exceeding of the atmospheric circulation in the period of investigation (February-March of 1996) over the average for many years one and predominance of the meridional transfer over the zonal one.
There are stated the negative anomalies of the thermochaline characteristics in the subarea 48.02.
The presence of Doubling Anticyclonic Current is revealed near the South Orkneys.
Abstract:
In the paper the attempt was made to compare selective features of several midwater krill trawls within the frame of krill density precise estimates provision problem in echo-surveys. The results of fishing one krill aggregation with two types of trawls (PT 72/308 commercial trawl and Isaacs-Kidd research trawl IKTM) are presented. Selectivity differences of those trawls resulted in significant variability of krill size composition in catches. Average krill length differed more than in 6 mm which caused deviations of TS values, estimated with TS/length relationship (SC-CAMLR, 1991) in ΔTS=2.1 dB. Associated variation in density estimates for the same MSBS value amounted to 1.65 .
Theoretical study of trawl selectivity features was carried out using statistical model. It was shown that selectivity of midwater trawl depended both on its design, trawling velocity, and catch value. Trawl selectivity features will especially affect the estimates of composition, abundance and biomass by krill size groups, and primarily in young krill assessment.
Analysis of abundance biomass estimates on the basis of various echo-surveys data requires to take into consideration selective features of trawl used.