Acoustic and ecological investigations into predator-prey interactions between Antarctic krill (Euphausia superba) and seal and bird predators (original) (raw)
Fisheries Research, 2000
Acoustic sampling has been used to investigate the ecology of Antarctic krill (Euphausia superba) and to provide information on dispersion and abundance necessary to manage their harvest. Population estimates based on multi-ship acoustic surveys have been used to set catch limits. More localized acoustic surveys have been conducted to study the response of landbreeding krill predators to local variations in their food supply. These and future surveys may result in additional controls on the ®shery. In this context, the use of acoustics to survey euphausiids is reviewed and major sources of uncertainty are discussed. These issues are organized as they pertain to the two broad steps of acoustic surveys: (1) estimating the volumetric density of krill (measurement uncertainty) and (2) mapping krill distribution and estimating abundance (sampling uncertainty). Published by Elsevier Science B.V.
Target strengths of Antarctic krill (Euphausia superba) at 38 and 120 kHz
The Journal of the Acoustical Society of America, 1990
Encaged aggregations of live krill in good to pristine condition have been ensonified at 38 and 120 kHz. Concurrent underwater television observations of behavior resemble those made by underwater divers in naturally occurring swarms, with comparably high densities of the order of 104 animals/m 3. Mean, single-animal target strengths have been inferred from measurements of echo energy. For aggregations with mean lengths in the range [ 30,39 ] mm, the mean single-krill target strengths are in the range [-88,-83 ] dB at 38 kHz and [-81,-74] dB at 120 kHz. Collateral measurements on some of the same encaged specimens determined a density contrast of 1.0357 q-0.0067 and sound-speed contrast of 1.0279-+-0.0024, relative to seawater. These numbers have been used with the fluid-sphere model as stated by Greenlaw [Limnol. Oceanogr. 24, 226-242 (1979) ]. Computed backscattering cross sections have been averaged over the length distributions of each measured aggregation, resulting in target strength predictions in the range [-86,-80] dB at 38 kHz and [-79,-76] dB at 120 kHz.
Acoustic characterization of the three-dimensional prey field of foraging chinstrap penguins
Marine Ecology-progress Series, 1996
Few studies of diving predators have explicitly addressed the 3-dimensional nature of interactions between predators and prey at the spatial and temporal scales relevant to an individual predator's search behavior Here, we present a new method for examining such interactions using the results from an acoustic survey of krill availability to foraging penguins Analyses of fine-scale krill distributions within a 1852 X 1852 X 50 m volume of ocean revealed substantial prey patchiness in all dimensions. Our survey detected the presence of at least 6 krill aggregations in the survey area. The surface distribution of penguins was associated with the edges of these aggregations and was nonrandomly associated with kl-ill dellsitirs above 0.1 krill m-' in the 30 to 40 m depth layer. The latter association was masked when krill abundance was integrated over the entire water column. Given that lilean daytlme dlve depths for chinstrap penguins fall betwccn 30 and 40 m, our data suggest penguins may fail to detect or choose to pass by shallow, denser prey aggregations and successfully forage on deeper, more homogeneously distributed krill offering higher encounter probabilities per unit volume searched. Thrse findings reveal biologically important features of prey patchiness that cannot be addressed within the limitations of a primarily 2-dimensional analysls of predator-prey distributions. We emphasize that if we hope to gain a predictive understanding of the foraging behavior of dlving predators, then we must consider fine-scale, 3-dimensional patterns of prey patchiness when assessing the availability of prey to diving predators.
Marine Ecology Progress Series, 2013
Interspecific competition is an important structuring element in marine ecosystems, especially in the Southern Ocean which offers few prey choices to comparatively large predator populations. We present the first simultaneous observations of at-sea behaviour and attendance patterns of 3 synchronously breeding, central place, krill foragers at Bouvetøya-a small, isolated, sub-Antarctic island in the South Atlantic. Time depth recorders and satellite transmitters were deployed during the austral summer of 2007/2008 on 47 lactating Antarctic fur seals Arctocephalus gazella (AFS) rearing pups and on 20 macaroni Eudyptes chrysolophus (MAC) and 30 chinstrap Pygoscelis antarctica penguins (CHIN) rearing chicks. All 3 species showed a strong preference for the west side of the island, and their foraging ranges overlapped markedly. Solar elevation influenced the timing of departures from, and arrivals to, the island with markedly different patterns between the seals and the penguins. Diving patterns also showed significant differences among the 3 species, with the frequency of diving being higher at night for the AFS, while both penguin species dove more frequently during the day. But a common, vertical diel pattern occurred in all 3 species, with shallow diving occurring at night and deep diving during the day, consistent with the vertical migration of krill. MACs targeted 2 depth layers for feeding, including a deep prey layer at ~70 m, which was not exploited by AFSs and CHINs. The results suggest that there is potential for competitive overlap among these 3 krill predators at Bouvetøya, but that it is reduced via both spatial (horizontal and vertical) and temporal partitioning of foraging areas.
2019
The primary objective for this krill research activity was twofold 1) to conduct a survey that provides updated estimates of the biomass and distribution of krill which are used in models to estimate sustainable yield in CCAMLR Area 48 and 2) to develop knowledge on the marine environment essential for the implementation of a FeedBack Management (FBM) system. The survey follows a similar design as a survey initiated by CCAMLR in year 2000 for comparative purposes, but in addition focuses on high krill-density areas, contains state-of-the art methods and employs modern technology for the research topics currently in focus. In terms of FBM, Marine Protected Area (MPA) development in CCAMLR Planning Domain 1 encompasses the major krill fishing grounds. Thus, data supporting FBM are critical if the fishery is to be managed by an empirical understanding of krill density, distribution, availability and predator needs as opposed to purely conservation-based measures. A future developed FBM system, requires acoustic data to be collected, processed and reported continuously during the fishing season as a measure of the available prey field. This information can be integrated with finer-scale knowledge of krill predator feeding strategies and updated through specific scientific studies at regular (multiyear) intervals. The survey and coupled FBM process studies took place during the Austral summer 2018-2019. The work was coordinated by Norway and involved collaborative international efforts as well as vessels from Norway, Association of Responsible Krill fishing companies (ARK) and the Norwegian fishing company Aker BioMarine AS, China, Korea, Ukraine and United Kingdom. This report presents preliminary results from the survey performed with the Norwegian RV Kronprins Haakon during 08th January-24th February 2019 and the land-based predator research carried out between 21st November 2018 and 20th February 2019. Content 1 Background 2 Krill Acoustics 3 Plankton, nutrients and environment 4 FlowCam studies 5 Fish and Cephalopods 6 Marine mammals and birds 7 Thermosalinograph and ADCP data 8 CTD data 9 Chemical indicators to monitor Ocean Acidification 10 Dissolved Oxygen 11 Sailbuoy with acoustics 12 LADCP measurements 13 Krill sound speed and density contrast 14 Acoustic backscatter of krill measured with lowered transducer 15 Echosounder moorings 16 Environmental toxicology 17 Metabolism balance in krill 18 Microbial communities 19 Trophic interactions 20 Land based predator research in support of adaptive management of the krill fishery 21 Acknowledgements 22 References 23 Appendix 1. Harstad-trawl rigging and procedures 24 Appendix 2. Scientific personell 25 Appendix 3. Crewlist KPH
Polar Science, 2011
From January to February 2008 the training research vessel TRV Umitaka Maru conducted a comprehensive oceanographic survey of the waters around the 140 E meridian off Adélie Land as part of the Collaborative East Antarctic Marine Census (CEAMARC) project. The acoustic component of this survey was conducted using a scientific echosounder operating at 38 and 70 kHz to estimate the distribution and density of Antarctic krill (Euphausia superba) and ice krill (E. crystallorophias). In addition, the relationship between the vertical distribution of Antarctic krill and the water temperature structure along the 140 E meridian was investigated. Antarctic krill were distributed in the waters of the continental slope at 65e66 S and the maximum value of the mean areal density r in 1 nautical mile (nmi) intervals was 4344 inds. m À2. Ice krill were distributed in the neritic waters of the continental shelf to the south of the 66 S and the maximum r in 1 nmi intervals was 23,669 inds. m À2. Along the 140 E meridian, Antarctic krill were mainly distributed at the water temperatures below 0.5 C. Although they were mostly distributed shallower than approximately 100 m, dense aggregations at approximately 180e200 m were also observed, which coincided with a depression of the water temperature structure.
Fisheries Oceanography, 2009
We investigate the influence of krill (principally Euphausia superba) patchiness on the foraging distributions of seabirds to understand how variation in krill influences patch dynamics between krill and birds. At sea-surveys were conducted near Elephant Island, Antarctica, for 3 yr (2004-2006) during the annual U.S. Antarctic Marine Living Resources (AMLR) program. Standardized strip-transect surveys were used to map seabirds, and a combination of acoustic and net surveys was used to map krill. We measured patch size of krill and seabirds and elucidated how krill patch dynamics influence foraging seabirds. The spatial association between krill and predators was influenced by the size and arrangement of krill patches. We found a negative relationship between abundance and patchiness of krill and predators, indicating that when krill is less abundant, its predators are less abundant and concentrated. We conclude that annual patch dynamics of krill strongly influences the local abundance and distribution of seabirds. Such information should be used to interpret potential interactions between seabirds and krill fisheries operating near Elephant Island.
Acoustic ecology of Antarctic pinnipeds
Marine Ecology Progress Series, 2010
In aquatic-mating pinnipeds, acoustic communication plays an important role in male competition and mate attraction. Vocal repertoire size and composition during the breeding season varies between species and is presumed to be a product of interspecific differences in sexual selection. In this study, we examine seasonal and diel patterns in acoustic repertoire size, composition and call activity of 4 Antarctic pinniped species: Weddell seal Leptonychotes weddellii, leopard seal Hydrurga leptonyx, Ross seal Ommatophoca rossii and crabeater seal Lobodon carcinophaga. An 11 mo (Jan 2006-Jan 2007, no recordings Jul and Nov 2006) near-continuous dataset was collected from the Perennial Acoustic Observatory in the Antarctic Ocean (PALAOA) located on the Ekström Iceshelf. The Weddell seal vocal repertoire consisted of 14 call types. Calls were present throughout the year except in February (11 mo), while repertoire composition varied considerably between months. The leopard seal vocal repertoire consisted of 7 call types. Calls were present between October and January (4 mo). All call types were used in a uniform manner throughout the entire call period. The Ross seal vocal repertoire consisted of 5 call types. Ross seal vocalizations were present from December until February (3 mo). Repertoire composition varied little between months. Crabeater seals produced one vocalization type, present from August to December (5 mo). Vocalizations in these species are likely produced in a breeding context. Inter-specific differences in behavioral ecology and interactions with abiotic and biotic environmental factors shape vocal behavior resulting in each species filling its own acoustic ecological niche.
Marine Ecology Progress Series, 1989
We investigated the joint distributions of seabirds and krill (primarily Euphausia superba) in Bransfield Strait and southern Drake Passage, Southern Ocean. We estimated seabird and krill densities, simultaneously and continuously uslng visual and acoustic techniques while traversing a transect grid standardized for the Second International BIOMASS Experiment (SIBEX) program. This is one of only 3 studies to find a correlation between the densities of seabirds and their prey. We defined 2 statistically independent components of distributional correlation: 'spatial concordance', the tendency for predators and prey to CO-occur in the same sampling unit, and 'numerical concordance', the tendency for densities of spatially concordant predators and prey to covary. Within nautical-mile transect intervals, we found cape petrels Daption capensis and antarctic fulmars Fulmarus glacialoides spatially concordant, and cape petrels, and adelie penguins Pygoscelis adeliae numerically concordant with krill. A few large concentrations of seabirds and krill accounted for the majority of seabird and krill biomass. Such large concentrations were rarely found within the same mile intervals, but were found within a few miles of each other more often than expected by chance. Seabird-krill correlations increased with spatial scale, and attained their maxima over large areas defined by their seabird species composition or krill depth profiles. In general, species specializing on krill as a food resource showed the highest degree of distributional correlation with krill, and species using less than 50 % krill in their diets showed little evidence of distributional correlation with krill. Although significant, correlations at small spatial scales were weak, which we suggest, that although exacerbated by sampling biases, was primarily due to d~fficulties seabirds have in locating and tracking krill swarms Further, we suggest that these difficulties result in (1) most krill swarms being unexploited at any given time, (2) a few very large swarms being disproportionately important to seabirds, and (3) krill densities being a poorer predictor of seabird densities than vice versa.
Marine Biology, 1993
The distributional features and physical characteristics of 4830 krill (Euphausia superba Dana) aggregations detected acoustically in the Southwest Atlantic between 26 January and 21 February 1981 are described. Results are compared with aggregations detected in the Indian Ocean. Aggregations in the Atlantic were larger, closer to the surface and to each other than in the Indian Ocean. Similar patterns in the distribution of aggregation spacing along survey transects were found in the two areas, although the pattern of spacings in the Atlantic indicates differences in the scale of aggregation. Serial interdependence of aggregation variables was minimal in the Atlantic, with aggregation thickness, length and spacing showing weak interrelationships. Weak functional association between water depth and aggregation thickness was evident. Investigation of variability in aggregation structure in relation to prevailing environmental conditions gave equivocal results and no clear association between any aggregation variable and prevailing hydrography was observed. The implications of these results for future studies on krill aggregation are discussed in relation to a conceptual framework which was developed from the present results and aimed at linking krill aggregation characteristics to environmental features.
Acoustic Estimates of Krill Biomass in the Elephant Island Area: 1981 - 1993
1993
des releves precedents ajustes en fonction de la definition recemment proposee de la reponse acoustique d u krill (Greene et al., 1991). Les estimations de la biomasse oscillent entre 267 X 103 tonnes (mars/avril 1985) et 4 880 X 103 tonnes (janvier 1993) et la densite de la biomasse entre 2,5 g/m2 et 134,5 g/m2. La biomasse et la densite moyennes sur la periode de 13 ans 6taient de 1 703 X 103 tonnes et de 53,2 g/m2. n p e~c~a s n e~b~ aKycTaqecKHe oqeHKH ~H O M~C C~I Kpmx B p a i o~e o-sa 3 n e a a~~ B
Behavioral and Physiological Characteristics of the Antarctic Krill, Euphausia superba
Integrative and Comparative Biology, 1991
SYNOPSIS. The antarctic krill, Euphausia superba, is considered a success in the intensely seasonal environment of the Southern Ocean because of its abundance and central role as an important food item for many of the larger carnivores in the ecosystem. The behavioral and physiological characteristics that foster this success are: (1) the ability to find concentrations of food in several types of habitat and efficiently exploit whatever food is available; (2) the close correspondence of the life cycle with seasonal cycles of food availability; and (3) a combination of physiological mechanisms that enable krill to survive the long winter period of low food availability. We evaluated the relative importance of the following four major winter-over mechanisms that have been proposed for adult krill west of the Antarctic Peninsula. The three-fold reduction in metabolic rate is the most important winter-over mechanism for these adults, although lipid utilization and shrinkage also help satisfy energy requirements in the winter. Alternate food sources did not appear to contribute significantly as a winter energy source. However, the extent, predictability and complexity of the ice cover in a region during winter may have a great influence on the relative importance of these winter-over mechanisms for different populations. Ice cover in the waters west of the Antarctic Peninsula is unpredictable and smooth surfaced when it occurs, providing the krill with little refuge from predation. In multi-year pack ice of the Weddell Sea, however, ice cover is predictable and extensive, and there is a complex undersurface that provides hiding places. In this multi-year ice, adult krill have been observed under the ice feeding, whereas west of the Antarctic Peninsula most adult krill are in the water column in the winter and are not feeding. The balance between acquiring energy and avoiding predation may be different in these two regions in the winter because of differences in predictability and complexity of the ice cover.
Marine Ecology Progress Series, 1999
Knowledge of relationships between prey availability and predator performance is the key to using predators as indicators of the state of marine systems and to assessing potential consequences of competition between natural predators and man for common resources. Fluctuations in the abundance of Antarctic knll are beiieved to have a substantial influence on the reproductive performance of krill-dependent top predator species in the Southern Ocean; few quantifications of such interactions exist. At South Georgia, for 2 years in which acoustic surveys revealed a major difference in knll abundance, we compared diet, prov~sioning of offspring and breeding success in 4 main predator species ( 2 penguins, 2 albatrosses, with supporting data from Antarctic fur seal) whose dependence on k r d typically ranges from 20 to 90%. The 4-fold difference in krill biomass between 1986 (ca 30 g m-2) and 1994 (ca 7 g m-2) was accompanied by (1) an 88 to 90% reduction in the mass of krill in predator dlets (and some increase in the fish component), (2) greater prey diversity for most species, (3) reduced diet overlap between species and (4) a switch from krill to amphipods in macaroni penguin but no major dietary change in other species. Rates of provisioning of offspring decreased by 90% in gentoo penguin and 40 to 50% in the other 3 species; this was due to reduced meal size in penguins (by 90% in gentoo and 50% in macaroni) and to doubling of foraging trip duration in albatrosses. Breeding success was reduced by 50% in grey-headed albatross (the species least dependent on krill), by 90% in black-browed albatross and gentoo penguin (only 3 to 4 % of eggs producing fledged chicks) but by only 10% in macaroni penguin, presumably reflecting its a b 5 t y to switch to small prey unprofitable for the other species. However, all species (except for black-browed albatross), particularly macaroni penguin, produced fledglings significantly lighter than usual, probably affecting their subsequent survival. Some effects on adult survival could also be inferred. Our results show a coherent, though complex, pattern of within and between species similarities and differences. These mainly reflect the degree of dependence on krill, the feasibility of taking alternative prey and constraints on trip duration andlor meal size imposed by foraging adaptations (especially relating to travel speeds and diving abilities, whereby flightless divers and pelagic foragers differ markedly). The generality of these principles are explored through comparison with other studies, particularly of Shetland seabirds.
Bioacoustics-the International Journal of Animal Sound and Its Recording, 2020
Crabeater seals (Lobodon carcinophaga) are an important component of the Southern Ocean as they are the most abundant pinniped species in this krill-based ecosystem; however, their acoustic repertoire and ecology remain to be fully described. Seasonal occurrence and diel-calling pattern of crabeater seal off the Maud Rise, eastern Weddell Sea, are described using passive acoustic monitoring data collected over 8 months (mid-January to mid-September) in 2014. We describe a new call type of crabeater seals, the short moan call (mean 90% duration: 2.2 ± 0.3 (SD) s, peak frequency: 596.5 ± 109.4 Hz, and frequency range: 122-1024 Hz), which was the only detected call type and 1871 calls were enumerated. Those crabeater seal calls were detected from April until mid-September (with peak in calling around September), which coincided with the appearance of sea ice. Short moan call rates were highest at night in August (i.e., 6.4 calls per minute) and September, and showed no diel variations for April through July. Distance to the sea ice edge and month of the year were the most important predictors of call occurrence and call rates of crabeater seals. This study highlights the Maud Rise as a useful habitat for this species.
ICES Journal of Marine Science, 2006
Everson, I., Tarling, G. A., and Bergström, B. 2007. Improving acoustic estimates of krill: experience from repeat sampling of northern krill (Meganyctiphanes norvegica) in Gullmarsfjord, Sweden – ICES Journal of Marine Research, 64, 39–48. A series of eight replicated acoustic surveys, four by day and four by night, was undertaken in Gullmarsfjord on the Swedish west coast during two 24-h periods on 8 and 10 September 2003, using a calibrated echosounder operating at 120 and 38 kHz. The difference in signal strength (ΔSv) was used to distinguish northern krill (Meganyctiphanes norvegica) from other acoustic scatterers. The approach is concluded to be very effective, but it can be improved greatly by applying the following series of simple extensions to current protocols: first, set a very low threshold on both frequencies to minimize sampling bias; second, undertake tests to confirm that the data extracted from each acoustic frequency apply to the same scatterers; third, ensure tha...
Lateral target strength of Antarctic krill
ICES Journal of Marine Science …, 1996
An area of high krill (Euphausia superba Dana) density was continuously monitored with down-looking and side-looking sonars over a period of 24 h. Measurements of volume backscattering strength were used to describe the density of krill with depth and the vertical movement of krill over time. In situ measurements were made of dorsal aspect target strength (TS) and, as krill moved into the near-surface layer (0-15 m), in situ measurements were made of lateral-aspect TS. The probability density function (PDF) of TS measurements made with the down-looking transducer had a mode at approximately 73 dB. The PDF of TS measurements made with the side-looking transducer was broader with a mode at approximately 67 dB. Sampled krill had a bi-modal length distribution with a major mode at 44 mm and a minor mode at approximately 30 mm.