The consumption of food by the four species of breeding penguins at the Prince Edward Islands is assessed on an annual and seasonal basis. Total annual food consumption was estimated at 880 000 t, of which king penguins accounted for 74%, macaroni penguins 21%, rockhopper penguins 5% and gentoo penguins
There is no abstract available for this document.
There is no abstract available for this document.
Abstract:
Predator-prey interactions play an important role in determining the dynamics of pelagic ecosystems. Human intervention in such interactions can have effects that cascade throughout these ecosystems. Recently, concerns have arisen due to the commercial harvesting of Euphausia superba, the Antarctic krill, a keystone prey species in the Southern Ocean food web. It has been difficult to evaluate these concerns because of problems associated with determining the availability of krill to their natural predators. Here, we report a novel method for assessing prey availability to an important krill predator, Pygoscelis antarctica, the chinstrap penguin. Acoustic techniques were used to analyze the three-dimensional distribution of krill within a 1852 X 1852 X 100 m volume of ocean. Our study revealed the presence of at least six, distinct krill aggregations and substantial vertical and horizontal patchiness at scales of 10s to 100s of metres. Monte Carlo simulations revealed significant spatial concordance between the surface distribution of penguins and krill distributed in the 30 - 40 m depth layer; no spatial concordance was detected in shallower layers. We conclude that fine-scale, depth-dependent patterns of kill patchiness must be incorporated into analyses of krill availability to predator populations if we hope to predict predator responses to a changing food environment.
Abstract:
Since penguins rely on the main planktonic resources of the Southern Ocean, knowledge of their diet may be used for monitoring these resources. During winter and spring of 1987 and 1989, we investigated the composition of the diet of gentoo penguins, Pygoscelis papua, in relation to changes in the availability of two prey species, Euphausia vallentini and Themisto gaudichaudii, sampled during plankton surveys in the Kerguelen Islands. The comparison between plankton surveys and diet analysis was performed on samples taken 2–4 km from the studied colonies. Data on the abundance of zooplankton derived from penguins' diet matched closely those from net hauls during a year of high plankton availability (1987). On the other hand, a weaker correspondence was found during a year of restricted availability (1989). The mean sizes of amphipods caught by penguins and net hauls were very similar but the size distribution showed comparatively fewer small and large individuals in net-hauls than in penguin stomachs. Detailed studies on the feeding range and foraging effort of penguins are therefore needed in the near future to validate the potential of penguin diet as a measure of plankton abundance.
Abstract:
Dynamics of distribution, growth, life span and feeding were studied in the endemic Antarctic euphausiid Euphausia crystallorophias in the central part of the Indian sector of the Southern Ocean during the austral summer, from 1977 to 1990, and in the Lazarev Sea during the summer 1990/91. Both larvae and adult E.crystallorophias were found in abundance in shelf waters of 100-500 m depth. Maximum abundances of larvae (up to 7688 ind.∙m-2) and adults (up to 1267 ind. ∙m-2) were found in the Prydz Bay region. Size frequency analysis indicated that the generation time was ~ 3 years in the Indian sector of the Southern Ocean. Total life span of E.crystallorophias may exceed 5 years in the Prydz Bay region and 4 years in the Cosmonaut Sea. Analysis of size distribution by sex showed that male E.crystallorophias had a shorter life span than females, although their growth rates were similar. Assuming growth for only 180 days per year, mean growth rates ranged from 0.070-0.075 to 0.019-0.022 mm per day during the first and the fourth year, respectively. Von Bertalanffy growth curves calculated for different areas were similar to those obtained by Siege1 (1987) in the Antarctic Peninsula region. In the Prydz Bay and the Cosmonaut Sea, spawning of E.crystallorophias appears to peak from the end of November to early December and may extend to the beginning of January. Most larvae were in the stage of metanauplius/calyptopis I at the beginning of January and calyptopis III/furcilia I during February. The year-l cohort was identified in January-February and exhibited a mean length in the range 10.8-16.8 mm. In situ feeding rates were estimated in the Lazarev Sea using the gut fluorescence method. Ingestion rates during austral summer l990/91 ranged from 52 to 471 ng (pigm)∙ind-1∙h-1 in adults and from 2.5 to 25.2 ng (pigm)∙ind-1∙h-1 in calyptopis III larvae. Total population impact on the phytoplankton stock varied between 160-2860 and 215-652 μg (C)∙m-2∙d-l for adults and larvae, respectively. This is equivalent to 0.06-1.12% and 0.02-0.07% of total daily production. In areas with dense E.crystallorophias swarms, however, daily consumption rates may attain levels as high as 13.6-96.5% of daily primary production. The longterm monitoring of different populations of E.crystallorophias allowed the identification of covariance patterns between its abundance, spawning success and the formation of coastal polynyas, especially in the Prydz Bay region.
Abstract:
The distribution and abundance of Antarctic krill (Euphausia superba) were estimated from four acoustic surveys conducted in the vicinity of Elephant Island, Antarctica, from mid-January to mid-March, 1994. The first and last surveys covered approximately 15,000 n.mile2 around Elephant Island and the eastern end of King George Island; the second and third surveys covered approximately 2100 n.mile2 immediately north of Elephant Island. During the first survey, the highest densities of krill were mapped north of King George Island and over a broad band northwest of Elephant Island. For a portion of the survey area centered on Elephant Island (aproximate1y 12,000 n. mile2), biomass was estimated to be 401 X 106 t. Five weeks later highest densities of krill were mapped north of Elephant Island and biomass in the same survey portion was estimated to be 359 X 106 t. During the second and third surveys high densities of krill were mapped in the shoal waters to the north of Elephant Island; biomasses were estimated to be 87 X l06 t and 97 x 106 t, respectively. Average bill densities were the lowest observed during the last five years of AMLR surveys in the Elephant Island study area and one-fifth of the 1990-1992 average density. In spite of the low krill densities, the reproductive success of land-breeding predators did not appear to be adversely affected.
Abstract:
The CCAMLR Secretariat has been requested to provide annual calculations of the catch of krill within the critical period-distance of land-based predators in Subareas 48.1 and 48.2 (100km from colonies, December - March). This index of the overlap of predators and the fishery is unsuitable for a number of reasons. An alternative method of calculating an index of fishery-predator interaction is developed, which is based on a detailed model of the supposed functional interaction between these two utilisers of the krill resource.
Abstract:
Being prepared by a collective of authors, this paper demonstrates some approaches to mathematical modelling of Antarctic krill population in the Cooperation Sea. The choice of investigation area is not casual since there are data on YugNIRO long-term observations over kri11 biological state here, its stocks, other pelagic system components, inhabitancy conditions, landing by FVs for the period from 1978 to 1984 and 1988.
The objective of the researches was to reveal causes of sharp fluctuations in krill abundance in the Cooperation Sea basing on mathematical modelling. The main task was to assess variations in parameters of the ecosystem and its staunchness against their impact.
A possibility is shown to apply logical-information modelling for future creation of a prognostic model of functioning of Antarctic krill population.