Bernie J. McConnell

Foraging ecology of southern elephant seals in relation to the bathymetry and productivity of the Southern Ocean

Southern elephant seals ( Mirounga leonina ) are among the most proficient of mammalian divers and are a major component of the Antarctic food web. Yet little is known of their movements or interaction with their oceanic environment. Specially designed satellite-link data loggers allowed us to visualize the 3-D movements of elephant seals as they swam rapidly from South Georgia to distant (up to 2650 km) areas of Antarctic continental shelf. One seal dived continuously to the sea bed in one small area for a month, implying consumption of benthic prey. Dives here were shorter even though average swimming velocity was lower. It is suggested that the physiological requirements of feeding and digestion reduced the aerobic dive limit. Long distance travel to relocatable hydrographic or topographical features, such as shelf breaks, may allow large predators to locate prey more consistently than from mid-ocean searches.

SEASONAL AND SEX-RELATED VARIATION IN THE ACTIVITY PATTERNS OF COMMON SEALS (PHOCA VITULINA)

SUMMARY (1) Radio-telemetry was used to study common seal activity patterns around Orkney, and to assess the degree of individual, seasonal and sex-related variation in haul-out behaviour in 1984-86. (2) During the summer, both males and females hauled-out regularly, in a marked diurnal pattern, but there were differences in other aspects of their haul-out behaviour. (3) Males showed a marked change in their haul-out behaviour at the beginning of moult. At this time, they hauled-out every day and, consequently, male behaviour became more synchronous. The change in behaviour of the male followed in 1985 was closely related to changes in abundance at the haul-out site that he used over this period. (4) In contrast, females showed no sign of a similar change in behaviour at the beginning of moult, but appeared to spend more of their time at sea after lactation. (5) During the winter, seals appeared to spend more time in offshore waters, although they regularly returned to the inshore study area to haul-out. At this time of year there was no marked diurnal haul-out pattern. (6) There was a high degree of individual variation in the effect of the tidal cycle on activity patterns, which appeared to be related to tide-related changes in food and habitat availability. Overall, however, the tidal cycle had less effect on haul-out behaviour in summer, when strong circadian patterns were more important. (7) The variations in activity patterns found in this study are discussed in relation to seasonal changes in feeding activity and the demands of breeding and moult.

Overcoming the Constraints of Long Range Radio Telemetry from Animals: Getting More Useful Data from Smaller Packages

Abstract Many species carry out their most interesting activities where they cannot readily be observed or monitored. Marine mammals are extreme among this group, accomplishing their most astounding activities both distant from land and deep in the sea. Collection, storage and transmission of data about these activities are constrained by the energy requirements and size of the recording loggers and transmitters. The more bits of information collected, stored and transmitted, the more battery is required and the larger the tag must be. We therefore need to be selective about the information we collect, while maintaining detail and fidelity. To accomplish this in the study of marine mammals, we have designed “intelligent” data logger/transmitters that provide context-driven data compression, data relay, and automated data base storage. We later combine these data with remotely sensed environmental information and other oceanographic data sets to recreate the environmental context for the animals activity, and we display the combined data using computer animation techniques. In this way, the system can provide near real time “observation” of animal behavior and physiology from the remotest parts of the globe.

A general discrete-time modeling framework for animal movement using multistate random walks

Recent developments in animal tracking technology have permitted the collection of detailed data on the movement paths of individuals from many species. However, analysis methods for these data have not developed at a similar pace, largely due to a lack of suitable candidate models, coupled with the technical difficulties of fitting such models to data. To facilitate a general modeling framework, we propose that complex movement paths can be conceived as a series of movement strategies among which animals transition as they are affected by changes in their internal and external environment. We synthesize previously existing and novel methodologies to develop a general suite of mechanistic models based on biased and correlated random walks that allow different behavioral states for directed (e.g., migration), exploratory (e.g., dispersal), area-restricted (e.g., foraging), and other types of movement. Using this “toolbox” of nested model components, multistate movement models may be custom-built for a wide variety of species and applications. As a unified state-space modeling framework, it allows the simultaneous investigation of numerous hypotheses about animal movement from imperfectly observed data, including time allocations to different movement behavior states, transitions between states, the use of memory or navigation, and strengths of attraction (or repulsion) to specific locations. The inclusion of covariate information permits further investigation of specific hypotheses related to factors driving different types of movement behavior. Using reversible-jump Markov chain Monte Carlo methods to facilitate Bayesian model selection and multi-model inference, we apply the proposed methodology to real data by adapting it to the natural history of the grey seal (Halichoerus grypus) in the North Sea. Although previous grey seal studies tended to focus on correlated movements, we found overwhelming evidence that bias toward haul-out or foraging locations better explained seal movement than did simple or correlated random walks. Posterior model probabilities also provided evidence that seals transition among directed, area-restricted, and exploratory movements associated with haul-out, foraging, and other behaviors. With this intuitive framework for modeling and interpreting animal movement, we believe that the development and application of custom-made movement models will become more accessible to ecologists and non-statisticians.

Comparative distribution, movements and diet of harbour and grey seals from the Moray Firth, N.E. Scotland

The distribution, movements and foraging activity of harbour and grey seals from the inner Moray Firth, N.E. Scotland, were compared using a combination of observations at haul-out sites, VHF and satellite-link telemetry, and analyses of diet composition. Terrestrial abundance of both grey and harbour seals was highest during the summer but there were marked differences in the extent to which the two species moved between different haul-out sites. Harbour seals showed local seasonal changes in distribution, but all 21 radio-tagged seals moved only to alternative haul-out sites within a range of 75 km. In contrast, four of the five grey seals tracked from the Moray Firth moved to haul-out sites 125-365km away, and provided evidence of interchange between the Moray Firth and other grey seal breeding areas in Orkney, the Firth of Forth and the Farne Islands. All harbour seals foraged within 60 km of their haul-out sites, but showed seasonal variation in their foraging areas which was related to changes in their terrestrial distribution. In contrast, those grey seals which foraged within the Moray Firth travelled up to 145 km from haul-out sites. Nevertheless, there was some overlap in the foraging areas used by harbour seals and grey seals in more inshore areas. Sandeels, gadoids, flatfish and cephalopods formed over 95% of the diet of both species. However, dietary data, particularly for grey seals, may be biased toward those individuals which fed in more inshore areas. These results suggest that Moray Firth harbour seals can be considered as a relatively discrete population, with clear links between breeding, feeding and resting areas, and little exchange of adults between this and adjacent breeding areas in Orkney and the Tay Estuary. In contrast, grey seals from several different breeding sites appear to move into the Moray Firth in summer and use the area primarily for foraging and non-breeding haul-out.

Salinity and temperature structure of a freezing Arctic fjord: monitored by white whales (Delphinapterus leucas)

Received 10 May 2002; accepted 29 August 2002; published 11 December 2002. [1] In this study we report results from satellite-linked conductivity-temperature-depth (CTD) loggers that were deployed on wild, free-ranging white whales to study the oceanographic structure of an Arctic fjord, Storfjorden, Svalbard. The whales dove to the bottom of the fjord routinely during the study and occupied areas with up to 90% ice-cover, where performance of conventional ship-based CTD-castswouldhavebeendifficult.Duringtheinitialperiod of freezing in the fjord, over a period of approximately 2 weeks, 540 CTD profiles were successfully transmitted. The dataindicatethatStorfjordenhasasubstantialinflowofwarm NorthAtlanticWater;thisiscontrarytoconventionalwisdom thathassuggestedthatitcontainsonlycoldArcticwater.This study confirms that marine-mammal-based CTDs have enormous potential for cost-effective, future oceanographic studies; many different marine mammal species target oceanographic discontinuities for foraging and thus may be good ‘adaptive samplers’ that naturally seek areas of high oceanographic interest. INDEX TERMS: 4294 Oceanography: General:Instrumentsandtechniques;4536Oceanography:Physical: Hydrography; 4219 Oceanography: General: Continental shelf processes; 1635 Global Change: Oceans (4203); KEYWORDS: CTD-measurements, Arctic oceanography, marine mammals, satellite telemetry. Citation: Lydersen, C., O. A. Nost, P. Lovell, B. J. McConnell, T. Gammelsrod, C. Hunter, M. A. Fedak, and K. M. Kovacs, Salinity and temperature structure of a freezing Arctic fjord—monitored by white whales (Delphinapterus leucas), Geophys. Res. Lett. , 29(23), 2119, doi:10.1029/2002GL015462, 2002.

Using GPS data to evaluate the accuracy of state–space methods for correction of Argos satellite telemetry error

Recent studies have applied state-space models to satellite telemetry data in order to remove noise from raw location estimates and infer the true tracks of animals. However, while the resulting tracks may appear plausible, it is difficult to determine the accuracy of the estimated positions, especially for position estimates interpolated to times between satellite locations. In this study, we use data from two gray seals (Halichoerus grypus) carrying tags that transmitted Fastloc GPS positions via Argos satellites. This combination of Service Argos data and highly accurate GPS data allowed examination of the accuracy of state-space position estimates and their uncertainty derived from satellite telemetry data. After applying a speed filter to remove aberrant satellite telemetry locations, we fit a continuous-time Kalman filter to estimate the parameters of a random walk, used Kalman smoothing to infer positions at the times of the GPS measurements, and then compared the filtered telemetry estimates with the actual GPS measurements. We investigated the effect of varying maximum speed thresholds in the speed-filtering algorithm on the root mean-square error (RMSE) estimates and used minimum RMSE as a criterion to guide the final choice of speed threshold. The optimal speed thresholds differed between the two animals (1.1 m/s and 2.5 m/s) and retained 50% and 65% of the data for each seal. However, using a speed filter of 1.1 m/s resulted in very similar RMSE for both animals. For the two seals, the RMSE of the Kalman-filtered estimates of location were 5.9 and 12.76 km, respectively, and 75% of the modeled positions had errors less than 6.25 km and 11.7 km for each seal. Confidence interval coverage was close to correct at typical levels (80-95%), although it tended to be overly generous at smaller sizes. The reliability of uncertainty estimates was also affected by the chosen speed threshold. The combination of speed and Kalman filtering allows for effective calculation of location and also indicates the limits of accuracy when correcting service Argos locations and linking satellite telemetry data to spatial covariate and habitat data.

Individual-Based Model Framework to Assess Population Consequences of Polychlorinated Biphenyl Exposure in Bottlenose Dolphins

Marine mammals are susceptible to the effects of anthropogenic contaminants. Here we examine the effect of different polychlorinated biphenyl (PCB) accumulation scenarios on potential population growth rates using, as an example, data obtained for the population of bottlenose dolphins from Sarasota Bay, Florida. To achieve this goal, we developed an individual-based model framework that simulates the accumulation of PCBs in the population and modifies first-year calf survival based on maternal blubber PCB levels. In our example the current estimated annual PCB accumulation rate for the Sarasota Bay dolphin population might be depressing the potential population growth rate. However, our predictions are limited both by model naivety and parameter uncertainty. We emphasize the need for more data collection on the relationship between maternal blubber PCB levels and calf survivorship, the annual accumulation of PCBs in the blubber of females, and the transfer of PCBs to the calf through the placenta and during lactation. Such data require continued efforts directed toward long-term studies of known individuals in wild and semi-wild populations.

Post-Breeding Distribution and Diving Behavior of Adult Male Southern Elephant Seals from Patagonia

Seven post-breeding adult male southern elephant seals, Mirounga leonina, were tracked using satellite-relay data loggers (SRDL) in 1994-1996. Two animals also were instrumented with a time depth recorder(TDR). Animals were monitored for 31-112 days at the end of the breeding season as they left Peninsula Valdes, Argentina. Males traveled ≤1,300 km from the breeding rookery but remained in temperate waters of the SW Atlantic Ocean, between 42°S and 55°S. The maximum travel distance recorded for the entire trip for any one seal was >4,500 km. Five males swam across the continental shelf in 3-11 days and stayed along the shelf margin or break where travel rates decreased markedly and remained low, suggesting that they may have reached foraging grounds. The other two males remained on the continental shelf during the entire time that they were tracked at sea. One of them was tracked for 66 days and concentrated his activity only 6-10 km off the coast of Patagonia in two areas located 700-800 km S of Peninsula Valdes. He never dived deeper than 94 m. The diving behavior sampled by one working TDR and several SRDL were similar. Dives over the continental shelf were mostly down to the seabed. Some dives over the shelf break were to the seabed (down to 1,500 m) but most were mid-water (300-600 m) and were deeper during the day. Previously studied post-breeding and post-molt adult females from the same colony spent virtually all their time over deep water off the shelf in the latitudinal range of 36-50°S. Their movements were less localized than those of males and dives did not take them to near the ocean bottom.

Marine mammals trace anthropogenic structures at sea

On land, species from all trophic levels have adapted to fill vacant niches in environments heavily modified by humans (e.g. [1]). In the marine environment, ocean infrastructure has led to artificial reefs, resulting in localized increases in fish and crustacean density [2]. Whether marine apex predators exhibit behavioural adaptations to utilise such a scattered potential resource is unknown. Using high resolution GPS data we show how infrastructure, including wind turbines and pipelines, shapes the movements of individuals from two seal species (Phoca vitulina and Halichoerus grypus). Using state-space models, we infer that these animals are using structures to forage. We highlight the ecological consequences of such behaviour, at a time of unprecedented developments in marine infrastructure.