Submesoscale distribution of Antarctic krill and its avian and pinniped predators before and after a near gale

We conducted two ship-based surveys of the nearshore ecosystem north of Livingston Island, Antarctica during 2–10 February 2005. Between the two surveys, a low-pressure system (963 mbar) passed through the area providing the opportunity to measure ecosystem parameters before and after a near gale. A ship-based multiple-frequency acoustic-backscatter survey was used to assess the distribution and relative abundance of Antarctic krill (Euphausia superba). Net tows, hydrographic profiles, and meteorological data were collected to measure biological and physical processes that might affect the krill population. During the survey, the distribution and behavior of several krill predators [chinstrap penguins (Pygoscelis antarctica), cape petrels (Daption capense), and Antarctic fur seals (Arctocephalus gazella)] were measured from the vessel by visual observations. The survey encompassed an area of roughly 2,500 km², containing two submarine canyons with one to the west and one to the east of Cape Shirreff, which had different abundances of krill and predators. Several aspects of the nearshore ecosystem changed after the near gale including: hydrography of the upper 100 m of the water column, phytoplankton biomass, the abundance and distribution of krill, and the distribution of some krill predators. Differences in these parameters were also measured between the two canyons. These changes in the physical and biological environment during the survey period are quantified and show that the ecosystem exhibited significant changes over relatively short spatial (tens of kilometers) and time (tens of hours) scales.     

Dynamic intra-seasonal habitat use by Antarctic fur seals suggests migratory hotspots near the Antarctic Peninsula

Antarctic fur seals (Arctocephalus gazella) are major secondary consumers in the Southern Ocean, placing them in potential competition with commercial fisheries and requiring research to understand their seasonal habitat use. Using the data obtained during 14 shipboard surveys sampled on a fixed grid (150 K km²) during mid- to late summer, I quantified the spatial distribution and intra-seasonal variability of fur seal sightings relative to distance to land and hydrographic boundaries. I test the hypothesis that fur seals display an increase in their at-sea abundance during mid- to late summer near the Antarctic Peninsula as they prepare to take up wintering grounds. I also test whether abundances of their potential prey, krill and myctophids, exhibit intra-seasonal variability. During midsummer, high-abundance areas are located near major breeding colonies; however, during late summer, there is an order-of-magnitude increase in fur seal abundance, coinciding with an increase in the number of high-abundance areas located in Bransfield Strait. Coincidently, abundance of Euphausia superba decreased and the myctophid Electrona antarctica increased between mid- and late-summer surveys. High-abundance areas of fur seals are not associated with the southern Antarctic Circumpolar Current front but are concentrated within 100 km from land, potentially indicating the location of haul out and important coastal habitat use areas. The dynamic increase in the number and location of high-abundance areas during late summer represents a considerable amount of mammalian predators entering the Antarctic Peninsula marine ecosystem. This information is important for understanding the seasonal impact of fur seals on regional marine food webs and their potential interaction with the autumn–winter krill fishery.     

Linking predator and prey behaviour: contrasts between Antarctic fur seals and macaroni penguins at South Georgia

Antarctic fur seals Arctocephalus gazella and macaroni penguins Eudyptes chrysolophus are the two main land-based krill Euphausia superba consumers in the northern Scotia Sea. Using a combination of concurrent at-sea (predator observations, net hauls and multi-frequency acoustics), and land-based (animal tracking and diet analysis) techniques, we examined variability in the foraging ecology of these sympatric top predators during the austral summer and autumn of 2004. Krill availability derived from acoustic surveys was low during summer, increasing in autumn. During the breeding season, krill occurred in 80% of fur seal diet samples, with fish remains in 37% of samples. Penguin diets contained the highest proportion of fish in over 20 years of routine monitoring (46% by mass; particularly the myctophid Electrona antarctica), with krill (33%) and amphipods (Themisto gaudichaudii; 21%) also occurring. When constrained by the need to return and feed their offspring both predator species foraged to the northwest of South Georgia, consistent with an area of high macrozooplankton biomass, but fur seals were apparently more successful at exploiting krill. When unconstrained by chick-rearing (during March) penguins foraged close to the Shag Rocks shelf-break, probably exploiting the high daytime biomass of fish in this area. Penguins and seals are able to respond differently to periods of reduced krill abundance (in terms of variability in diet and foraging behaviour), without detriment to the breeding success of either species. This highlights the importance of myctophid fish as an alternative trophic pathway for land-based predators in the Scotia Sea ecosystem.     

Winter distribution and haul-out behaviour of female Antarctic fur seals from South Georgia

Telemetry-based techniques have revealed the foraging patterns of many land breeding marine predators, especially during the summer breeding season. However, during the winter, when freed from the constraints of provisioning their young, such animals are more difficult to track. Using geolocation (Global Location Sensing, GLS) loggers and satellite tags (Platform Terminal Transmitters, PTTs) we successfully tracked 16 female Antarctic fur seals from South Georgia during the austral winter. The majority of females concentrated their winter foraging in the waters around the breeding beaches (90% of locations were within 510 km). However, as the winter progressed, two of the seals spent a number of months to the south, in and around the seasonal ice edge, and five seals migrated north and northwest from South Georgia. Four of these seals clearly crossed the Polar Front and two reached the Patagonian Shelf, apparently exploiting the continental shelf edge and the Subantarctic Front. Activity (saltwater immersion) data suggested that seals spent the majority of the winter months at sea but there were rare occasions when seals hauled out, either on land or on ice floes. We obtained data from two individuals that enabled us to compare the performance of PTT and GLS devices. For these seals the mean distance between GLS and PTT locations was 122 and 132 km. Although the recovery rates were low in this study, given improvements in attachment techniques, we have demonstrated that these micro-geolocation loggers provide an ideal tool with which to study the long-term dispersal of diving marine predators at larger scales. This is the first study to show that female fur seals from South Georgia remain at sea for almost the entirety of the non-breeding winter period. Using land-based observations it has been assumed that the fur seal population at South Georgia has little temporal overlap with the krill fishery that operates mostly during the winter months in this region. We have shown that a large proportion of the female fur seals that breed on South Georgia potentially remain in the vicinity of the island and are thus in direct competition with the region’s fisheries activities.     

Modelling predation by transient leopard seals for an ecosystem-based management of Southern Ocean fisheries

Correctly quantifying the impacts of rare apex marine predators is essential to ecosystem-based approaches to fisheries management, where harvesting must be sustainable for targeted species and their dependent predators. This requires modelling the uncertainty in such processes as predator life history, seasonal abundance and movement, size-based predation, energetic requirements, and prey vulnerability. We combined these uncertainties to evaluate the predatory impact of transient leopard seals on a community of mesopredators (seals and penguins) and their prey at South Georgia, and assess the implications for an ecosystem-based management. The mesopredators are highly dependent on Antarctic krill and icefish, which are targeted by regional fisheries. We used a state-space formulation to combine (1) a mark-recapture open-population model and individual identification data to assess seasonally variable leopard seal arrival and departure dates, numbers, and residency times; (2) a size-based bioenergetic model; and (3) a size-based prey choice model from a diet analysis. Our models indicated that prey choice and consumption reflected seasonal changes in leopard seal population size and structure, size-selective predation and prey vulnerability. A population of 104 (90–125) leopard seals, of which 64% were juveniles, consumed less than 2% of the Antarctic fur seal pup production of the area (50% of total ingested energy, IE), but ca. 12–16% of the local gentoo penguin population (20% IE). Antarctic krill (28% IE) were the only observed food of leopard seal pups and supplemented the diet of older individuals. Direct impacts on krill and fish were negligible, but the “escapement” due to leopard seal predation on fur seal pups and penguins could be significant for the mackerel icefish fishery at South Georgia. These results suggest that: (1) rare apex predators like leopard seals may control, and may depend on, populations of mesopredators dependent on prey species targeted by fisheries; and (2) predatory impacts and community control may vary throughout the predator's geographic range, and differ across ecosystems and management areas, depending on the seasonal abundance of the prey and the predator's dispersal movements. This understanding is important to integrate the predator needs as natural mortality of its prey in models to set prey catch limits for fisheries. Reliable estimates of the variability of these needs are essential for a precautionary interpretation in the context of an ecosystem-based management.     

Are penguins and seals in competition for Antarctic krill at South Georgia?

The Antarctic fur seal (Arctocephalus gazella) and macaroni penguin (Eudyptes chrysolophus) are sympatric top predators that occur in the Southern Ocean around South Georgia where they are, respectively, the main mammal and bird consumers of Antarctic krill (Euphausia superba). In recent years the population of fur seals has increased, whereas that of macaroni penguins has declined. Both species feed on krill of similar size ranges, dive to similar depths and are restricted in their foraging range at least while provisioning their offspring. In this study we test the hypothesis that the increased fur seal population at South Georgia may have resulted in greater competition for the prey of macaroni penguins, leading to the decline in their population. We used: (1) satellite-tracking data to investigate the spatial separation of the Bird Island populations of these two species whilst at sea during the breeding seasons of 1999 and 2000 and (2) diet data to assess potential changes in their trophic niches between 1989 and 2000. Foraging ranges of the two species showed considerable overlap in both years, but the concentrations of foraging activity were significantly segregated spatially. The size of krill taken by both species was very similar, but over the last 12 years the prevalence of krill in their diets has diverged, with nowadays less krill in the diet of macaroni penguins than in that of Antarctic fur seals. Despite a significant degree of segregation in spatial resource use by the study populations, it is likely that the South Georgia populations of Antarctic fur seal and macaroni penguin exploit the same krill population during their breeding season. For explaining the opposing population trends of the two species, the relative contributions of independent differential response to interannual variation in krill availability and of interspecies competition cannot be resolved with available evidence. The likely competitive advantage of Antarctic fur seals will be enhanced as their population continues to increase, particularly in years of krill scarcity.     

Coastal hazard due to submarine canyons in active insular volcanoes: examples from Lipari Island (southern Tyrrhenian Sea)

The recent high-resolution multibeam bathymetry surveys around Lipari Island allowed to evidence several submarine canyons, whose head often cut back up to very shallow water and at a few tens of meters far from the coast. These canyons are mainly located in the eastern and southern side of the island and are characterized by an ongoing retrogressive (landward) erosion, that also controlled the shape and the evolution of the coastline. The canyon heads are formed by minor slide scars. By coupling slide scar morphometry and simple numerical model we have been able to roughly estimate the potential tsunami wave amplitudes generated by related slope failures. Moreover, the retrogressive erosion of canyon heads can be claimed as a cause of the enhanced subsidence reported in the last few thousand years in the eastern part of Lipari, where the main villages are located. Based on these evidence, we propose a first assessment of the coastal hazard due to marine retrogressive activity in the largest and most densely populated island of the Aeolian Archipelago.     

A Bayesian hierarchical model of Antarctic fur seal foraging and pup growth related to sea ice and prey abundance

We created a Bayesian hierarchical model (BHM) to investigate ecosystem relationships between the physical ecosystem (sea ice extent), a prey measure (krill density), predator behaviors (diving and foraging effort of female Antarctic fur seals, Arctocephalus gazella, with pups) and predator characteristics (mass of maternal fur seals and pups). We collected data on Antarctic fur seals from 1987/1988 to 1994/1995 at Seal Island, Antarctica. The BHM allowed us to link together predators and prey into a model that uses all the data efficiently and accounts for major sources of uncertainty. Based on the literature, we made hypotheses about the relationships in the model, which we compared with the model outcome after fitting the BHM. For each BHM parameter, we calculated the mean of the posterior density and the 95% credible interval. Our model confirmed others' findings that increased sea ice was related to increased krill density. Higher krill density led to reduced dive intensity of maternal fur seals, as measured by dive depth and duration, and to less time spent foraging by maternal fur seals. Heavier maternal fur seals and lower maternal foraging effort resulted in heavier pups at 22 d. No relationship was found between krill density and maternal mass, or between maternal mass and foraging effort on pup growth rates between 22 and 85 days of age. Maternal mass may have reflected environmental conditions prior to the pup provisioning season, rather than summer prey densities. Maternal mass and foraging effort were not related to pup growth rates between 22 and 85 d, possibly indicating that food was not limiting, food sources other than krill were being used, or differences occurred before pups reached age 22 d.     

Marine Protected Area Design and the Spatial and Temporal Distribution of Cetaceans in a Submarine Canyon

Abstract: The Gully, the largest submarine canyon off the coast of eastern Canada, is currently under consideration as a marine conservation area, primarily because of the increasing interest in oil and gas production on the Scotian Shelf. Cetaceans, as a guild of abundant, large organisms that are relatively sensitive to such threats, provide a reliable means to determine the boundaries for a conservation area in this region. We compared the abundance of cetaceans between the Gully and other parts of the Scotian Shelf and Slope and found that abundance was higher in the Gully. We also assessed cetacean distribution and relative abundance within the Gully relative to search effort for several spatial and temporal parameters: depth, slope, sea surface temperature, and month. Distribution within the Gully was most strongly correlated with depth, but was also significantly correlated with sea surface temperature and month. Five of the 11 cetacean species commonly found in the Gully, and all those for which the Gully formed significant habitat on the Scotian Shelf, were concentrated in the deep (200–2000 m) mouth of the canyon. We suggest that a year-round marine protected area is necessary for the Gully. A core protection zone should be defined in the Gully based on depth and bounded by the 200-m isobath. A buffer zone around the core zone should be defined to provide protection from activities with further-reaching effects, such as noise, dredging, and chemical pollution.     

Predicting changes in the Antarctic krill, Euphausia superba, population at South Georgia

Variability in the Southern Ocean is frequently reflected in changes in the abundance of Antarctic krill Euphausia superba and subsequent effects on dependent predators. However, the nature and consequences of changes in krill population dynamics that accompany fluctuations in its abundance are essentially unknown. A conceptual model, developed from quantitative measures of krill length in the diet of predators at South Georgia from 1991 to 1997, allowed predictions to be made about the abundance and population structure of krill in 1998 and the consequences for predators. Consistent with model predictions, in 1998 there was a serial change in krill population structure, low krill biomass and low reproductive performance of predators. The change in the modal size of krill, from 56 mm in December to 42 mm in March, was apparently a result of the transport of krill into the region. This is the first occasion when the future status and structure of the krill population at South Georgia has been successfully predicted. By representing local krill population dynamics, which may also reflect large-scale physical and biological processes, predators have a potential key role as indicators of environmental variation in the Southern Ocean at a range of spatial scales. Received: 6 March 1999 / Accepted: 3 September 1999     

The influence of subsurface thermal structure on the diving behavior of northern fur seals (<Emphasis Type="Italic">Callorhinus ursinus</Emphasis>) during the breeding season

In the heterogeneous marine environment, predators can increase foraging success by targeting physical oceanographic features, which often aggregate prey. For northern fur seals (Callorhinus ursinus), two prevalent oceanographic features characterize foraging areas during summer in the Bering Sea: a stable thermocline and a subsurface “cold pool”. The objective of this study was to examine the influence of these features on foraging behavior by equipping fur seals from St. Paul Island (Alaska, USA) with time-depth recorders that also measured water temperature. Foraging bout variables (e.g., mean dive depth and percent time diving in a bout) were compared with respect to subsurface thermal characteristics (thermocline presence and strength and cold pool presence). Over 74% of bouts occurred in association with strong thermoclines (temperature change > 5°C). Few differences were found for dive behavior in relation to the presence of a thermocline and the cold pool, but for epipelagic bouts, a strong thermocline resulted in increased bottom times, number of dive wiggles, and percent time diving when compared to moderate thermoclines. There was also a positive relationship between mean dive depth and thermocline depth. The combination of increasing foraging effort in areas with strong thermoclines and diving to depths closely related to the thermocline indicates this feature is important foraging habitat for northern fur seals and may act to concentrate prey and increase foraging success. By recognizing the environmental features northern fur seals use to find prey, managers will be better equipped to identify and protect foraging habitat that is important to northern fur seals, and possibly other marine predators in the Bering Sea.     

Can marine mammals be used to monitor oceanographic conditions?

The breeding performance of higher predators has often been used to monitor fluctuations in the abundance of important prey stocks in marine ecosystems. The development of electronic data-loggers in recent years has also provided the opportunity of using wide-ranging marine animals to measure physical oceanographic conditions. In this study, time–depth recorders (TDRs) programmed to record temperature were deployed on female Antarctic fur seals (Arctocephalus gazella) at Bird Island, South Georgia (54°00′S; 38°02′W) during the breeding seasons 1994 to 1998. Temperature sensors had relatively slow response times, and thermal radiation errors occurred during the day when seals spent a large proportion of their time at the surface. Nevertheless, measurements provided temperature–depth profiles which were typical of the vertical stratification of the ocean. During the early stages of a foraging trip temperature increased, suggesting that fur seals travelled northwards from South Georgia towards the warmer waters of the Polar Front. In addition, higher temperatures were recorded by females that remained at sea for longer, implying that these individuals also travelled further. Mean sea-surface temperature (SST) increased from ∼1 to 4 °C from December to March and agreed with SSTs from ship, buoy and satellite. Future studies on marine mammals which combine satellite tracking with oceanographic measurements are likely to provide valuable information on biophysical aspects of the ocean. Received: 16 June 1998 / Accepted: 13 February 1999     

The Scotia Sea krill fishery and its possible impacts on dependent predators: modeling localized depletion of prey

The nature and impact of fishing on predators that share a fished resource is an important consideration in ecosystem-based fisheries management. Krill (Euphausia superba) is a keystone species in the Antarctic, serving as a fundamental forage source for predators and simultaneously being subject to fishing. We developed a spatial multispecies operating model (SMOM) of krill-predator fishery dynamics to help advise on allocation of the total krill catch among 15 small-scale management units (SSMUs) in the Scotia Sea, with a goal to reduce the potential impact of fishing on krill predators. The operating model describes the underlying population dynamics and is used in simulations to compare different management options for adjusting fishing activities (e.g., a different spatial distribution of catches). The numerous uncertainties regarding the choice of parameter values pose a major impediment to constructing reliable ecosystem models. The pragmatic solution proposed here involves the use of operating models that are composed of alternative combinations of parameters that essentially try to bound the uncertainty in, for example, the choice of survival rate estimates as well as the functional relationships between predators and prey. Despite the large uncertainties, it is possible to discriminate the ecosystem impacts of different spatial fishing allocations. The spatial structure of the model is fundamental to addressing concerns of localized depletion of prey in the vicinity of land-based predator breeding colonies. Results of the model have been considered in recent management deliberations for spatial allocations of krill catches in the Scotia Sea and their associated impacts on dependent predator species.     

Geographical variation in the behaviour of a central place forager: Antarctic fur seals foraging in contrasting environments

Foragers show adaptive responses to changes within their environment, and such behavioural plasticity can be a significant driving force in speciation. We investigated how lactating Antarctic fur seals, Arctocephalus gazella, adapt their foraging within two contrasting ecosystems. Location and diving data were collected concurrently, between December 2003 and February 2004, from 43 seals at Bird Island, where krill, Euphausia superba, are the main prey, and 39 at Heard Island, where mostly fish are consumed. Seals at Heard Island were shorter and lighter than those at Bird Island and they spent longer at sea, dived more frequently and spent more time in the bottom phase of dives. Generalized additive mixed effects models showed that diving behaviours differed between the islands. Both populations exploited diel vertically migrating prey species but, on average, Heard Island seals dived deeper and exceeded their estimated aerobic dive limits. We propose that the recovery of the Heard Island population may be limited by the relative inaccessibility and scarcity of food, whereas at Bird Island, the presence of abundant krill resources helps sustain extremely high numbers of seals, even with increased intra- and inter-specific competition. Both populations of fur seals appear to be constrained by their physiological limits, in terms of their optimal diving behaviour. However, there does appear to be some flexibility in strategy at the level of trip with animals adjusting their time at sea and foraging effort, in order to maximize the rate of delivery of energy to their pups.     

Growth of Antarctic krill Euphausia superba at South Georgia

 Antarctic krill Euphausia superba has a central role in the ecosystem of the Southern Ocean and knowledge of its growth rate is central to determining the factors influencing population dynamics. The length of Antarctic krill in the diet of Antarctic fur seals Arctocephalus gazella at South Georgia revealed a consistent increase in size between ca. 42 and ca. 54 mm over the period October–March, indicating growth rates much higher than predicted by existing models. Geographical variation in growth rate may result in 2-year-old krill at South Georgia attaining the same size as 3-year-old krill in the Antarctic Peninsula region. The effect of geographical variation in growth rate on the population structure of krill has important implications for comparing the fate of individual cohorts over large scales and in the interpretation of krill life-cycles. Received: 20 May 2000 / Accepted: 11 August 2000     

Spatio-temporal variations of biomass and abundance in bathyal non-crustacean megafauna in the Catalan Sea (North-western Mediterranean)

The spatio-temporal variations in diversity, biomass and abundance of bathyal invertebrates (excluding decapod crustaceans, which have been analysed elsewhere) from the North-western Mediterranean margin are described. The upper canyon (∼450 m), middle slope (∼650 m) and lower slope (∼1,200 m) habitats were investigated throughout the year. The first two sites are visited daily by a specialised commercial fisheries’ fleet, while the deeper site has not been impacted by fishing activities. A total of 140 species from 12 phyla were collected from the 3 study areas. Of these, the Mollusca, Echinodermata, Polychaeta and Cnidaria were the most speciose groups. The patterns of species diversity (H′) and evenness (E) were similar in time and space. The upper canyon and middle-slope sites were dominated by echinoderms and molluscs, while the lower-slope site was dominated by cnidarians and sponges. Multifactorial ANOVA showed significant spatio-temporal differences in the biomass and/or abundance only in echinoderms, molluscs, cnidarians and polychaetes. The faunal differences observed were explained by habitat type, but not by season. The role of submarine canyons and commercial fishing on shaping the diversity and biomass of bathyal Mediterranean invertebrates is discussed. Luis Dantart: Deceased March 2005     

Where the wild things are: predicting hotspots of seabird aggregations in the California Current System

Marine protected areas (MPAs) provide an important tool for conservation of marine ecosystems. To be most effective, these areas should be strategically located in a manner that supports ecosystem function. To inform marine spatial planning and support strategic establishment of MPAs within the California Current System, we identified areas predicted to support multispecies aggregations of seabirds ("hotspots"). We developed habitat-association models for 16 species using information from at-sea observations collected over an 11-year period (1997-2008), bathymetric data, and remotely sensed oceanographic data for an area from north of Vancouver Island, Canada, to the USA/Mexico border and seaward 600 km from the coast. This approach enabled us to predict distribution and abundance of seabirds even in areas of few or no surveys. We developed single-species predictive models using a machine-learning algorithm: bagged decision trees. Single-species predictions were then combined to identify potential hotspots of seabird aggregation, using three criteria: (1) overall abundance among species, (2) importance of specific areas ("core areas") to individual species, and (3) predicted persistence of hotspots across years. Model predictions were applied to the entire California Current for four seasons (represented by February, May, July, and October) in each of 11 years. Overall, bathymetric variables were often important predictive variables, whereas oceanographic variables derived from remotely sensed data were generally less important. Predicted hotspots often aligned with currently protected areas (e.g., National Marine Sanctuaries), but we also identified potential hotspots in Northern California/Southern Oregon (from Cape Mendocino to Heceta Bank), Southern California (adjacent to the Channel Islands), and adjacent to Vancouver Island, British Columbia, that are not currently included in protected areas. Prioritization and identification of multispecies hotspots will depend on which group of species is of highest management priority. Modeling hotspots at a broad spatial scale can contribute to MPA site selection, particularly if complemented by fine-scale information for focal areas.     

Temporal variation in Adélie penguin diet at Béchervaise Island,east Antarctica and its relationship to reproductive performance

Diet, and in particular, food quality and quantity can influence the reproductive performance of marine predators. Also, the diet of specialist predators is often monitored in programmes that model and manage ecosystems. We examined the diet of Adélie penguins (Pygoscelis adeliae), an important consumer of Southern Ocean living resources, at Béchervaise Island, east Antarctica, during the chick-rearing periods for 11 years between 1991–1992 and 2002–2003. We also investigated the relationship between diet and annual reproductive performance. Substantial inter- and intra-annual variation in both meal mass and composition was evident: adults generally returned with larger food loads during the crèche compared with the guard stages, and diet composition was dominated by two prey types, krill and fish, which combined contributed to >90% of the diet by mass in 7 out of 11 years. Females generally brought back meals dominated by krill; males generally consumed fish-dominated meals. However, both sexes returned with a high proportion of krill when annual mean meal mass was also high, suggesting that more food was available in high krill years. There was also evidence that years of high reproductive performance were positively correlated with years of both high meal and krill mass. We believe that our results indicate that there is significant long-term inter- and intra-annual variability in the amount of food available to Adélie penguins and that this was reflected in their diet and measures of reproductive performance. Coupled with the observation that penguins did not switch prey, this indicates that Adélie penguins from Béchervaise Island are dependent predators of krill. This contrasts with populations in other locations but supports the notion that Adélie penguins are an informative species to monitor the management of Southern Ocean marine living resources in this region.     

Use of pelagic prey subsidies by demersal predators in rocky reefs: insight from movement patterns of lingcod

Allochthonous subsidies of energy and nutrients can affect community structure in patchy marine habitats, including rocky reefs, and their ecological consequences may depend on the mechanism of energy transfer. Lingcod (Ophiodon elongatus) are demersal predators that trophically link nearshore rocky reefs with offshore pelagic habitats through consumption of pelagic fishes. We quantified lingcod habitat use and movement patterns to make inferences about the temporal and spatial conditions under which lingcod may acquire pelagic prey. Lingcod maintained small home ranges (21,272 ± 13,630 m²) within a rocky reef in the San Juan Archipelago, Washington; eight of nine individuals used rocky habitat exclusively. Depths occupied by lingcod (0–50 m) coincided with pelagic fish distribution on the rocky reef; however, diel patterns in lingcod activity varied inversely with occurrence of pelagic fishes on the reef. Our findings suggest that the pelagic subsidy to lingcod is not strongly mediated through directed off-reef foraging by lingcod.     

Fine-scale habitat modeling of a top marine predator: do prey data improve predictive capacity?

Predators and prey assort themselves relative to each other, the availability of resources and refuges, and the temporal and spatial scale of their interaction. Predictive models of predator distributions often rely on these relationships by incorporating data on environmental variability and prey availability to determine predator habitat selection patterns. This approach to predictive modeling holds true in marine systems where observations of predators are logistically difficult, emphasizing the need for accurate models. In this paper, we ask whether including prey distribution data in fine-scale predictive models of bottlenose dolphin (Tursiops truncatus) habitat selection in Florida Bay, Florida, U.S.A., improves predictive capacity. Environmental characteristics are often used as predictor variables in habitat models of top marine predators with the assumption that they act as proxies of prey distribution. We examine the validity of this assumption by comparing the response of dolphin distribution and fish catch rates to the same environmental variables. Next, the predictive capacities of four models, with and without prey distribution data, are tested to determine whether dolphin habitat selection can be predicted without recourse to describing the distribution of their prey. The final analysis determines the accuracy of predictive maps of dolphin distribution produced by modeling areas of high fish catch based on significant environmental characteristics. We use spatial analysis and independent data sets to train and test the models. Our results indicate that, due to high habitat heterogeneity and the spatial variability of prey patches, fine-scale models of dolphin habitat selection in coastal habitats will be more successful if environmental variables are used as predictor variables of predator distributions rather than relying on prey data as explanatory variables. However, predictive modeling of prey distribution as the response variable based on environmental variability did produce high predictive performance of dolphin habitat selection, particularly foraging habitat.