Distribution Of Krill Research Articles

Submarine canyons represent an essential habitat network for krill hotspots in a Large Marine Ecosystem

Submarine canyon systems are ubiquitous features of marine ecosystems, known to support high levels of biodiversity. Canyons may be important to benthic-pelagic ecosystem coupling, but their role in concentrating plankton and structuring pelagic communities is not well known. We hypothesize that at the scale of a large marine ecosystem, canyons provide a critical habitat network, which maintain energy flow and trophic interactions. We evaluate canyon characteristics relative to the distribution and abundance of krill, critically important prey in the California Current Ecosystem. Using a geological database, we conducted a census of canyon locations, evaluated their dimensions, and quantified functional relationships with krill hotspots (i.e., sites of persistently elevated abundance) derived from hydro-acoustic surveys. We found that 76% of krill hotspots occurred within and adjacent to canyons. Most krill hotspots were associated with large shelf-incising canyons. Krill hotspots and canyon dimensions displayed similar coherence as a function of latitude and indicate a potential regional habitat network. The latitudinal migration of many fish, seabirds and mammals may be enhanced by using this canyon-krill network to maintain foraging opportunities. Biogeographic assessments and predictions of krill and krill-predator distributions under climate change may be improved by accounting for canyons in habitat models.

A biologically relevant method for considering patterns of oceanic retention in the Southern Ocean

Many marine species have planktonic forms – either during a larval stage or throughout their lifecycle – that move passively or are strongly influenced by ocean currents. Understanding these patterns of movement is important for informing marine ecosystem management and for understanding ecological processes generally. Retention of biological particles in a particular area due to ocean currents has received less attention than transport pathways, particularly for the Southern Ocean. We present a method for modelling retention time, based on the half-life for particles in a particular region, that is relevant for biological processes. This method uses geostrophic velocities at the ocean surface, derived from 23years of satellite altimetry data (1993–2016), to simulate the advection of passive particles during the Southern Hemisphere summer season (from December to March). We assess spatial patterns in the retention time of passive particles and evaluate the processes affecting these patterns for the Indian sector of the Southern Ocean. Our results indicate that the distribution of retention time is related to bathymetric features and the resulting ocean dynamics. Our analysis also reveals a moderate level of consistency between spatial patterns of retention time and observations of Antarctic krill (Euphausia superba) distribution.

Progress in Southern Ocean Biologyfrom the Indian Sector: Half-Decadal (2009-13) overview

This manuscript reviews the scientific insight gained from biological studies performed during Indian Southern Ocean Expeditions (ISOE) in the last 5 years. India’s research activities in the Southern Ocean (SO) region emphasize the importance of enhanced understanding of the SO processes, biogeochemical cycles, marine productivity and global climate change scenario. Under the aegis of Ministry of Earth Sciences, Government of India, concerted efforts are put in place by NCAOR to carryout research in Indian sector of the SO since 2004, with a primary focus to comprehend the role (response) of the SO in regional and global climate variability. The findings discussed here are based on of a wide array of biological data collected during different expeditions (4th to 7th expedition conducted during 2009-13) which highlights: causal mechanisms of variability in phytoplankton community structure and productivity among frontal regions (i.e.,Subtropical Front (STF), Subantarctic Front (SAF) and Polar Front (PF)), patterns of phytoplankton biomass distribution within and among the fronts, role of diatoms in deciphering environmental change, food-web dynamics, bio-optical characterisation of water column, response of bacteria and phytoplankton to micronutrient amendments, biochemical profiling of squids, distribution of Antarctic krill, and occurrence of different marine mammals/birds in the above frontal regions. Here, we attempt to succinctly capture the findings of published literature engendered from ISOE to put forward our present perception of this lesser-understood region in the SO. This document is expected to contribute to an increased understanding of the Indian sector of SO, besides providing the much needed visibility to our ongoing scientific endeavours among the international community.

Distributions of larval and juvenile/adult stages of the Antarctic myctophid fish, Electrona antarctica, off Wilkes Land in East Antarctica

Myctophid fish are an important component of the Southern Ocean food web because of their very high biomass. This study investigated the spatial distributions of larval and juvenile/adult stages of the Antarctic myctophid Electrona antarctica. Fish were sampled in January 2011 and 2012 on a transect along 140°E and in January 2013 along 110°E using two different opening/closing net systems. In total, 1075 specimens of E. antarctica were collected: 948 larvae, 127 juveniles/adults, and 2 in the transformation stage. Most larvae were collected at 5–200 m depth, with diel vertical migration (DVM) not apparent. Larvae were mainly distributed in the Modified Circumpolar Deep Water (−1.5 °C–2.0 °C). By contrast, an analysis of the echogram at 38 kHz and discrete depth samples implied that juveniles/adults undertook DVM except in the continental slope area (65.5°S). As the distribution of krill is limited to the cold water mass (<–1.5 °C) along the continental slope, E. antarctica and krill populations are spatially separated off Wilkes Land during summer. According to the previously estimated larval period of 30–47 days, E. antarctica may spawn in late November to December in the marginal ice zone or near the sea ice edge. This study suggests that the environment related to sea ice provides a nursery ground for early stage larvae of E. antarctica.

Spatial point patterns of Antarctic krill fishery in the northern Antarctic Peninsula

As a key species in the Antarctic ecosystem, the spatial distribution of Antarctic krill (thereafter krill) often tends to present aggregation characteristics, which therefore reflects the spatial patterns of krill fishing operation. Based on the fishing data collected from Chinese krill fishing vessels, of which vessel A was professional krill fishing vessel and Vessel B was a fishing vessel which shifted between Chilean jack mackerel (Trachurus murphyi) fishing ground and krill fishing ground. In order to explore the characteristics of spatial distribution pattern and their ecological effects of two obvious different fishing fleets under a high and low nominal catch per unit effort (CPUE), from the viewpoint of spatial point pattern, the present study analyzed the spatial distribution characteristics of krill fishery in the northern Antarctic Peninsula from three aspects: (1) the two vessels' point pattern characteristics of higher CPUEs and lower CPUEs at different scales; (2) correlation of the bivariate point patterns between these points of higher CPUE and lower CPUE; and (3) correlation patterns of CPUE. Under the analysis derived from the Ripley's L function and mark correlation function, the results showed that the point patterns of the higher/lo-wer catch available were similar, both showing an aggregation distribution in this study windows at all scale levels. The aggregation intensity of krill fishing was nearly maximum at 15 km spatial scale, and kept stably higher values at the scale of 15-50 km. The aggregation intensity of krill fishery point patterns could be described in order as higher CPUE of vessel A > lower CPUE of vessel B >higher CPUE of vessel B > higher CPUE of vessel B. The relationship of the higher and lo-wer CPUEs of vessel A showed positive correlation at the spatial scale of 0-75 km, and presented stochastic relationship after 75 km scale, whereas vessel B showed positive correlation at all spatial scales. The point events of higher and lower CPUEs were synchronized, showing significant correlations at most of spatial scales because of the dynamics nature and complex of krill aggregation patterns. The distribution of vessel A's CPUEs was positively correlated at scales of 0-44 km, but negatively correlated at the scales of 44-80 km. The distribution of vessel B's CPUEs was negatively correlated at the scales of 50-70 km, but no significant correlations were found at other scales. The CPUE mark point patterns showed a negative correlation, which indicated that intraspecific competition for space and prey was significant. There were significant differences in spatial point pattern distribution between vessel A with higher fishing capacity and vessel B with lower fishing capacity. The results showed that the professional krill fishing vessel is suitable to conduct the analysis of spatial point pattern and scientific fishery survey.

Krill distribution in relation to environmental parameters in mesoscale structures in the Ross Sea

Krill, a key pelagic resource of the Antarctic food web, provides an important link between primary and secondary plankton production and top predators. Since krill abundance is a crucial factor in Antarctic ecosystem functioning, its monitoring supplies vital data. Acoustic surveys are an effective approach to estimating krill abundance. An acoustic survey was conducted in the western Ross Sea in January 2014–10years after a similar survey by our team - to estimate krill abundance and biomass and monitor oceanographic conditions. Antarctic krill (Euphausia superba) was detected in the northern part of the western Ross Sea and dense swarms of ice krill (Euphausia crystallorophias) were found in its central coastal area. Data analysis revealed an inverse correlation between E. superba density and salinity in the water column, whereas a positive correlation was found between E. crystallorophias abundance and fluorescence; the latter relationship was confirmed in thematic maps of E. crystallorophias spatial distribution and fluorescence. Comparison of 2004 and 2014 biomass data showed a much greater abundance of both species in the more recent survey.

Abundance and distribution of early life stages of krill around Iceland during spring

ABSTRACTAbundance, distribution and development of early life stages of krill (eggs, nauplii, calyptopes and furciliae) around Iceland were studied during the latter half of May 2013. Multivariate analyses were used to examine the relationships between water mass characteristics and phytoplankton spring bloom dynamics and distribution of krill. The results show that krill eggs, nauplii and calyptopes were most abundant over the shelf edges off the southwest and east coasts, while furciliae were most abundant on the shelf off the southwest coast. Meganyctiphanes norvegica and Thysanoessa longicaudata larvae were found mainly in the southwest, while T. inermis larvae were found in highest numbers on the east coast. Redundancy analysis showed that phytoplankton biomass, temperature and bottom depth explained 41% of the distribution pattern of early ontogenetic krill stages. In areas where krill eggs and larvae were most abundant (off the southwest coast), the phytoplankton spring bloom was in an advanced state, and the phytoplankton biomass and temperature were particularly high.

At-Sea Distribution and Prey Selection of Antarctic Petrels and Commercial Krill Fisheries.

Commercial fisheries may impact marine ecosystems and affect populations of predators like seabirds. In the Southern Ocean, there is an extensive fishery for Antarctic krill Euphausia superba that is projected to increase further. Comparing distribution and prey selection of fishing operations versus predators is needed to predict fishery-related impacts on krill-dependent predators. In this context, it is important to consider not only predators breeding near the fishing grounds but also the ones breeding far away and that disperse during the non-breeding season where they may interact with fisheries. In this study, we first quantified the overlap between the distribution of the Antarctic krill fisheries and the distribution of a krill dependent seabird, the Antarctic petrel Thalassoica antarctica, during both the breeding and non-breeding season. We tracked birds from the world biggest Antarctic petrel colony (Svarthamaren, Dronning Maud Land), located >1000 km from the main fishing areas, during three consecutive seasons. The overall spatial overlap between krill fisheries and Antarctic petrels was limited but varied greatly among and within years, and was high in some periods during the non-breeding season. In a second step, we described the length frequency distribution of Antarctic krill consumed by Antarctic petrels, and compared this with results from fisheries, as well as from diet studies in other krill predators. Krill taken by Antarctic petrels did not differ in size from that taken by trawls or from krill taken by most Antarctic krill predators. Selectivity for specific Antarctic krill stages seems generally low in Antarctic predators. Overall, our results show that competition between Antarctic petrels and krill fisheries is currently likely negligible. However, if krill fisheries are to increase in the future, competition with the Antarctic petrel may occur, even with birds breeding thousands of kilometers away.

Winter distribution and size structure of Antarctic krill Euphausia superba populations in-shore along the West Antarctic Peninsula

Antarctic krill Euphausia superba are a key component of food webs in the maritime West Antarctic Peninsula, and their life history is tied to the seasonal cycles of sea ice and primary production in the region. Previous work has shown a general in-shore migration of krill in winter in this region; however, the very near-shore has not often been sampled as part of these surveys. We investigated distribution, abundance, and size structure of krill in 3 fjordic bays along the peninsula, and in the adjacent Gerlache Strait area using vertically stratified MOCNESS net tows and ADCP acoustic biomass estimates. Krill abundance was high within bays, with net estimated densities exceeding 60 krill m-3, while acoustic estimates were an order of magnitude higher. Krill within bays were larger than krill in the Gerlache Strait. Within bays, krill aggregations were observed near the seafloor during the day with aggregations extending to the sediment interface, and exhibited diel vertical migration higher into the water column at night. We suggest these high winter krill abundances within fjords are indicative of an active seasonal migration by krill in the peninsula region. Potential drivers for such a migration include reduced advective losses and costs, and availability of sediment food resources within fjords. Seasonally near-shore krill may also affect stock and recruitment assessments and may have implications for managing the krill fishery in this area.

Environmental correlates of Antarctic krill distribution in the Scotia Sea and southern Drake Passage

Abstract Antarctic krill is a key prey species for many vertebrate and invertebrate predators in the Southern Ocean; it is also an abundant fishery resource in the Scotia Sea and southern Drake Passage. Here, we identify environmental correlates of krill distribution utilizing acoustic data collected during an extensive international survey in January 2000. Separate models (at scales of 10–80 nautical miles) were derived for the full study area and for each of four subregions: northern and southern shelf waters, the seasonally ice-covered open ocean, and the generally ice-free open ocean. Krill distribution was strongly correlated with bathymetry; densities were higher over island shelves and shelf breaks and decreased with increasing distance offshore. Low krill densities occurred in areas of low chlorophyll concentration and high geostrophic velocity. Krill distribution was also related to sea level anomaly but relationships were not consistent between subregions. The models explained a maximum of 44% of the observed deviance in krill density, but did not reliably identify areas of high krill density in the open ocean, and explained a small proportion of the deviance (16%) in offshore areas covered seasonally by sea ice, probably because of the strong, residual influence of retreated ice. The commercial krill fishery is currently concentrated in shelf areas, where high densities of krill are most predictable. As krill are not predictable in the open ocean, the fishery is likely to remain principally a near-shore operation, and should be managed accordingly.

On state of understanding for bioresources of Antarctic, their status and commercial using

Modern state of biological resources in Antarctic is considered using comprehensive systemic analysis of historical and present data of Russian and international fisheries researches, catch data, scientific observations made by Russia and other CCAMLR countries, and materials from CCAMLR database. Distribution and abundance of krill and toothfish is presented for the main fishing grounds in 2013-2014. Legal treatment is given for current and projected state of the bioresources accessible for Russian fishery. Scientific recommendations for rational exploitation of the resources by Russian fishing fleet are presented for the season of 2014/15 and further.

Horizontal niche partitioning of humpback and fin whales around the West Antarctic Peninsula: evidence from a concurrent whale and krill survey

A dedicated aerial cetacean survey was conducted concurrently to a standardised net trawl survey for krill in order to investigate distribution patterns of large whales and different krill species and to investigate relationships of these. Distance sampling data were used to produce density surface models for humpback (Megaptera novaeangliae) and fin whales (Balaenoptera physalus) around the West Antarctic Peninsula (WAP). Abundance for both species was estimated over two strata in the Bransfield Strait and Drake Passage. Distinct distribution patterns suggest horizontal niche partitioning of the two whale species around the WAP, with fin whales aggregating at the shelf edge of the South Shetland Islands in the Drake Passage and humpback whales in the Bransfield Strait. Krill biomass estimated from the concurrent krill survey was used along with CTD data from the same expedition, bathymetric parameters and satellite data on chlorophyll-a and ice concentration to model krill distribution. Comparisons of the predicted distributions of both whale species with the predicted distributions of Euphausia superba, Euphausia crystallorophias and Thysanoessa macrura suggest a complex relationship rather than a straightforward correlation between krill and whales. However, results indicate that fin whales were feeding in an area dominated by T. macrura, while humpback whales were found in areas of higher E. superba biomass. Our results provide abundance estimates for humpback whales and, for the first time, fin whales in the WAP and contribute important information on feeding ecology and habitat use of these two species in the Southern Ocean.

Size and stage composition of age class 0 Antarctic krill (Euphausia superba) in the ice–water interface layer during winter/early spring

The condition and survival of Antarctic krill (Euphausia superba) strongly depends on sea ice conditions during winter. How krill utilize sea ice depends on several factors such as region and developmental stage. A comprehensive understanding of sea ice habitat use by krill, however, remains largely unknown. The aim of this study was to improve the understanding of the krill’s interaction with the sea ice habitat during winter/early spring by conducting large-scale sampling of the ice–water interface (0–2 m) and comparing the size and developmental stage composition of krill with the pelagic population (0–500 m). Results show that the population in the northern Weddell Sea consisted mainly of krill that were <1 year old (age class 0; AC0), and that it was comprised of multiple cohorts. Size per developmental stage differed spatially, indicating that the krill likely were advected from various origins. The size distribution of krill differed between the two depth strata sampled. Larval stages with a relatively small size (mean 7–8 mm) dominated the upper two metre layer of the water column, while larger larvae and AC0 juveniles (mean 14–15 mm) were proportionally more abundant in the 0- to 500-m stratum. Our results show that, as krill mature, their vertical distribution and utilization of the sea ice appear to change gradually. This could be the result of changes in physiology and/or behaviour, as, e.g., the krill’s energy demand and swimming capacity increase with size and age. The degree of sea ice association will have an effect on large-scale spatial distribution patterns of AC0 krill and on predictions of the consequences of sea ice decline on their survival over winter.

Spatial Distribution and Temporal Patterns of Cassin's Auklet Foraging and Their Euphausiid Prey in a Variable Ocean Environment.

Krill (Euphausiids) play a vital ecosystem role in many of the world’s most productive marine regions, providing an important trophic linkage. We introduce a robust modeling approach to link Cassin’s auklet (Ptychoramphus aleuticus) abundance and distribution to large-scale and local oceanic and atmospheric conditions and relate these patterns to similarly modeled distributions of an important prey resource, krill. We carried out at-sea strip transect bird surveys and hydroacoustic assessments of euphausiids (2004–2013). Data informed separate, spatially-explicit predictive models of Cassin’s auklet abundance (zero-inflated negative binomial regression) and krill biomass (two-part model) based on these surveys. We established the type of prey responsible for acoustic backscatter by conducting net tows of the upper 50 m during surveys. We determined the types of prey fed to Cassin’s auklet chicks by collecting diet samples from provisioning adults. Using time-depth-recorders, we found Cassin’s auklets utilized consistent areas in the upper water column, less than 30 m, where krill could be found (99.5% of dives were less than 30 m). Birds primarily preyed upon two species of euphausiids, Euphausia pacifica and Thysanoessa spinifera, which were available in the upper water column. Cassin’s auklet abundance was best predicted by both large scale and localized oceanic processes (upwelling) while krill biomass was best predicted by local factors (temperature, salinity, and fluorescence) and both large scale and localized oceanic processes (upwelling). Models predicted varying krill and bird distribution by month and year. Our work informs the use of Cassin’s auklet as a valuable indicator or krill abundance and distribution and strengthens our understanding of the link between Cassin’s auklet and its primary prey. We expect future increases in frequency and magnitude of anomalous ocean conditions will result in decreased availability of krill leading to declines in the Farallon Islands population of Cassin’s auklets.

Distribution, density and relative abundance of Antarctic krill estimated by maximum likelihood geostatistics on acoustic data collected during commercial fishing operations

There is a substantial harvest for Antarctic krill in the Southern Ocean, but little regular scientific monitoring of the resource. Recently, however, the Commission for the Conservation of Marine Living Resources (CCAMLR) has initialised a process to make use of acoustic data from commercial fisheries to increase the amount of relevant information available for making management decisions. We here provide an example where 34 days of acoustic data, collected during commercial krill fishing operations on the vessel ‘Saga Sea’ were processed to produce probability of presence, conditional density and relative abundance estimates on monthly, weekly and daily basis. Data were analyzed using a maximum likelihood time-series and geostatistical approaches, selected to account for the lack of sampling design, and likely correlation in space and time. The applied method showed low sensitivity of monthly estimates to different repeated measure criteria and location sub-settings. Most weekly estimates, but the last one, were also consistent with the full data (monthly) estimate. Highly variable and lower estimates were obtained, however, from daily data sets. Although our results suggest the method had provided an adequate treatment for time and space correlation, we were not able to evaluate potential bias due to preferential sampling of high density krill aggregations and/or limited area coverage within short time periods. The results suggest that this method, combined with some additional design based coverage by the fishing vessels, can be useful to obtain quantitative evaluations of krill density and distribution for management purposes.

The use of fishing vessels to provide acoustic data on the distribution and abundance of Antarctic krill and other pelagic species

A fishery for Antarctic krill (Euphausia superba) has existed for over 3 decades and the Commission for Conservation of Antarctic Marine Living Resources (CCAMLR) manages this fishery using precautionary catch limits, fishery data collection and a scientific observer programme operating on the fishing vessels. A recent increase in the number of vessels fishing and the rising costs of undertaking scientific research cruises have focussed attention on being able to use fishing vessels to collect more extensive scientific data sets. In 2011, CCAMLR’s Subgroup on Acoustic Survey and Analysis Methods (SG-ASAM) was tasked with assessing the use of acoustic data collected from fishing vessels to provide qualitative and quantitative information on the distribution and relative abundance of Antarctic krill and other pelagic species. SG-ASAM conceived a proof of concept programme and implemented the first stage in 2013 to determine the current setup of acoustic equipment on participating fishing vessels and to establish whether these vessels could collect geo- and time-referenced acoustic data. To date data have been received from 7 krill fishing vessels and SG-ASAM has now focussed on the development of data collection protocols to enable fishing vessels to collect quantitative acoustic data along prescribed transects. While this development work continues, the willingness of fishing industry to participate in such studies has already been demonstrated by several fishing companies, and Norwegian- and Chinese-flagged fishing vessels are undertaking krill biomass surveys in two key fishery Areas in the South Atlantic sector of the Southern Ocean.

Prey-field use by a Southern Ocean top predator: enhanced understanding using integrated datasets

An important challenge for understanding and managing marine ecosystems is determining the relationship between the distributions of prey species and the foraging of top predators. We examined the diet and foraging dynamics of breeding macaroni penguins Eudyptes chrysolophus from sub-Antarctic Heard Island and related these to prey distributions derived from active-acoustics and net-derived data in the foraging zone of the penguins. Consistent with previous findings, we found that penguin diets changed between the guard and creche stages of the breeding cycle and that this change in diet corresponded with a switch from short foraging trips in the guard stage to significantly longer, offshore foraging trips in the creche stage. We related these differences in diet and foraging to characteristics of the prey field—specifically, a relatively uniform distribution of krill over the shelf and in deeper, offshore waters, compared with an increasing abundance of fish further from shore. We developed a simple dynamic energy budget for macaroni penguins to explore whether targeting fish during the creche stage was an energetically favourable strategy. Finally, we extrapolated our energy budget to estimate prey consumption at the colony scale as previous work has suggested that depletion near breeding colonies could contribute to prey switching. We found that prey switching during the creche stage was energetically favourable and was most likely related to a reduction in foraging constraints, rather than prey depletion. This study shows the value of integrating data sets to address questions surrounding variation in diet and the use of alternative prey by marine predators.

Mesoscale variability in the habitat of the Humboldt Current krill, spring 2007

AbstractMesoscale eddies are prominent structures in the world's oceans generating a high degree of spatial and temporal heterogeneity that influences zooplankton distribution. Euphausiids (krill) are a key zooplankton group mainly inhabiting coastal upwelling areas where high productivity, advection, and eddy kinetic energy (EKE) play pivotal roles in the distribution and structure of zooplankton. We analyzed the spatial distribution of the Humboldt Current krill, Euphausia mucronata, in relation to environmental variability and mesoscale circulation during the 2007 austral spring. Using net‐based zooplankton samples, remotely sensed environmental conditions, multivariate analysis, and generalized additive models, we described and tested the effect of oceanographic variability and mesoscale eddies on E. mucronata abundance and biomass. E. mucronata was significantly more abundant in coastal (97%) than oceanic habitats, and more abundant in cyclonic cores (mean: 76 indiv. m−2) than in surrounding waters (mean: 13–29 indiv. m−2). Abundance correlated to current and EKE fields at &gt;10–20 cm s−1 and &gt;50–200 cm2 s−2, respectively, and biomass correlated negatively to sea level anomaly and positively to alongshore winds. Krill abundance and biomass were also strongly coupled to both eddy dynamics and the coastal upwelling regime in spring 2007. Mesoscale eddies may doubly influence the E. mucronata population dynamic by retaining krill within them and, by advection from coastal to oligotrophic regions.

Spatial and temporal variations in the abundance, distribution, and aggregation of krill (Thysanoessa raschii and Meganyctiphanes norvegica) in the lower estuary and Gulf of St. Lawrence

The opportunistic collection of hydroacoustic data during multipurpose, large-scale surveys since 2000 has led to the detection of several, newly-documented krill concentrations throughout the Gulf of St. Lawrence. Based on both historical and these recent results, a series of regional-scale acoustic surveys was initiated in the northwestern Gulf and estuary to quantify the spatial and temporal variations in the regional abundance, distribution and aggregation of northern and Arctic krill. By using a recently-developed multi-frequency method to classify these two krill species, our study re-evaluated the species-specific krill distribution and abundance, previously monitored by plankton-net sampling alone. We show that Thysanoessa raschii is the more coastal species, with its center-of-mass in the shelf and slope habitats. Meganyctiphanes norvegica forms generally less dense aggregations in the slope and channel habitats. Biomass in the northwestern Gulf and estuary was split 60:40 between T. raschii and M. norvegica, and totaled 1.0 million tonnes in August 2009; substantially more than has been reported previously. This re-evaluation should have considerable impact on ecosystem models which have assumed much lower values for these important forage populations. The pattern of krill aggregations identified from large- and regional-scale surveys will have important implications for the interpretation of critical habitat for endangered marine mammals which depend on krill.

Studying the Impacts of Local Oceanographic Processes on Adélie Penguin Foraging Ecology

AbstractWe are conducting a multi-platform field study to investigate the impact of local physical processes on Adélie penguin foraging ecology in the vicinity of Palmer Deep off Anvers Island, Western Antarctic Peninsula (WAP). Guided by real-time remotely sensed surface current measurements of convergence derived from a network of high-frequency radars (HFRs), we adaptively sample the distribution and biomass of phytoplankton and Antarctic krill, which influence Adélie penguin foraging ecology, to understand how local oceanographic processes structure the ecosystem. The recent application of ocean observing and animal telemetry technology over Palmer Deep has led to new understanding and many new questions related to polar ecosystem processes. The HFR coastal surface current mapping network is uniquely equipped to resolve local circulation patterns over Palmer Deep. The surface current measurements enable identification of regions of convergence and divergence in real time. Guided by these maps, our field study adaptively samples the measured convergence and divergence zones within the context of semi-diurnal and diurnal mixed tidal regimes. The in situ sampling includes (a) a mooring deployment, (b) multiple underwater glider deployments, (c) small boat acoustic surveys of Antarctic krill, and (d) penguin ARGOS-linked satellite telemetry and temperature-depth recorders (TDRs). The combination of real-time surface convergence maps with adaptive in situ sampling introduces HFR to the Antarctic in a way that allows us to rigorously and efficiently test the influence of local tidal processes on top predator foraging ecology.