DIVING PATTERNS OF NORTHERN ELEPHANT SEAL BULLS

We used small microprocessor-based, time-depth recorders to document the diving patterns of six adult male northern elephant seals ( Mirounga angustirostris ) from San Miguel Island, California. The recorders stored measurements of hydrostatic pressure every 30 or 60 set while the seals were at sea for 107 to 145 d in spring and early summer; collectively, over 36,000 dives were recorded. Seals dove continually while at sea, most often to depths of 350–450 m although two seals had secondary modes at about 700–800 m; maximum depths for two seals of 1,333 m and 1,529 m are the deepest yet measured for air-breathing vertebrates. Seals were submerged about 86% of the time they were at sea, rarely spending more than 5 min at the surface between dives; 99% of all post-dive surface intervals were shorter than 10 min. Dives averaged 21–24 min, the longest was 77 min. The uninterrupted patterns of long dives punctuated by brief surface periods suggest that most if not all dives were well within these seals'aerobic limits. Dives of bulls were, on average, about 18% longer than those published earlier for cows, evidently because of the substantially greater body mass of bulls and allometric scaling of dive endurance. Dive depths and dive durations varied seasonally; depths were greatest in spring, durations greatest in early summer. During each season dives were deepest during the day and shallowest at night except for the sixth seal whose consistently shallow dives (50–150 m) in spring were independent of time of day. Prey remains recovered by lavage from seals'stomachs were primarily of vertically migrating, epi- and meso-pelagic squid. The die1 patterns in dive depths suggest that five seals dove to and foraged in the offshore mesopelagic zone, pursuing those vertically migrating prey. The sixth seal behaved similarly in early spring and early summer but may have foraged in nearshore epibenthic habitats in spring.     

Diving pattern and performance in the macaroni penguin Eudptes chrysolophus

The pattern and characteristics of diving in two female macaroni penguins Eudyptes chrysolophus was studied, during the brooding period, using continuous-recording time-depth recorders, for a total of I8 days (15 consecutive days) during which the depth, duration and timing of 4876 dives were recorded. Diving in the first 11 days was exclusively diurnal, averaging 244 dives on trips lasting 12 hours. Near the end of the brooding period trips were longer and included diving at night. About half of all trips (except those involving continuous night-time diving) was spent in diving and dive rate averaged 14–25 dives per hour (42 per hour at night). The duration of day time dives varied between trips, and averaged 1.4–1.7 min, with a subsequent surface interval of 0.5–0.9 min. Dive duration was significantly directly related to depth, the latter accounting for 53% of the variation. The average depths of daytime dives were 20–35 m (maximum depth 11 5 m). Dives at night were shorter (average duration 0.9 min) and much shallower (maximum 11 m); depth accounted for only 6% of the variation in duration. Estimates of potential prey capture rates (3–5 krill per dive; one krill every 17–20 s) are made. Daily weight changes in chicks were directly related to number of dives, but not to foraging trip duration nor time spent diving. Of the other species at the same site which live by diving to catch krill, gentoo penguins forage exclusively diurnally, making longer. deeper dives; Antarctic fur seals, which dive to similar depths as macaroni penguins, do so mainly at night.     

Diving patterns of a Ross seal (Ommatophoca rossii ) near the eastern coast of the Antarctic Peninsula

In January 1987 we documented the diving patterns of a female Ross seal (Ommatophoca rossii) in the marginal pack-ice zone near the eastern coast of the Antarctic Peninsula for 2 days using a microprocessor-based time-depth recorder. The seal hauled out during the day and dived continually when in the water at night. Dives averaged 110 m deep and 6.4 min long; the deepest dive was 212 m and the longest 9.8 min. Dives were deepest near twilight and shallowest at night; this pattern suggests that the seal's prey, presumably mid-water squid and fish, may have been making vertical migrations or changing predator-avoidance behavior in response to diel light patterns. The dives of this Ross seal were substantially deeper, on average, than those of crabeater seals (Lobodon carcinophagus), which forage in the same areas on Antarctic krill (Euphausia superba). Received: 15 August 1996 / Accepted: 22 February 1997     

SUMMER DIVING BEHAVIOR OF MALE WALRUSES IN BRISTOL BAY, ALASKA

Pacific walruses ( Odobenus rosmarus divergens ) make trips from ice or land haul-out sites to forage for benthic prey. We describe dive and trip characteristics from time-depth-recorder data collected over a one-month period during summer from four male Pacific walruses in Bristol Bay, Alaska. Dives were classified into four types. Shallow (4 m), short (2.7 min), square-shaped dives accounted for 11% of trip time, and many were probably associated with traveling. Shallow (2 m) and very short (0.5 min) dives composed only 1% of trip time. Deep (41 m), long (7.2 min), square-shaped dives accounted for 46% of trip time and were undoubtedly associated with benthic foraging. V-shaped dives ranged widely in depth, were of moderate duration (4.7 min), and composed 3% of trip time. These dives may have been associated with navigation or exploration of the seafloor for potential prey habitat. Surface intervals between dives were similar among dive types, and generally lasted 1–2 min. Total foraging time was strongly correlated with trip duration and there was no apparent diel pattern of diving in any dive type among animals. We found no correlation between dive duration and postdive surface interval within dive types, suggesting that diving occurred within aerobic dive limits. Trip duration varied considerably within and among walruses (0.3–9.4 d), and there was evidence that some of the very short trips were unrelated to foraging. Overall, walruses were in the water for 76.6% of the time, of which 60.3% was spent diving.     

Diving behaviour of dugongs, Dugong dugon

The diving behaviour of 15 dugongs (Dugong dugon) was documented using time-depth recorders (TDRs), which logged a total of 39,507 dives. The TDRs were deployed on dugongs caught at three study sites in northern Australia: Shark Bay, the Gulf of Carpentaria and Shoalwater Bay. The average time for which the dive data were collected per dugong was 10.4±1.1 (S.E.) days. Overall, these dugongs spent 47% of their daily activities within 1.5 m of the sea surface and 72% less than 3 m from the sea surface. Their mean maximum dive depth was 4.8±0.4 m (S.E.), mean dive duration was 2.7±0.17 min and the number of dives per hour averaged 11.8±1.2. The maximum dive depth recorded was 20.5 m; the maximum dive time in water >1.5 m deep was 12.3 min. The effects of dugong sex, location (study site), time of day and tidal cycle on diving rates (dives per hour), mean maximum dive depths, durations of dives, and time spent ≤1.5 m from the surface were investigated using weighted split-plot analysis of variance. The dugongs exhibited substantial interindividual variation in all dive parameters. The interaction between location and time of day was significant for diving rates, mean maximum dive depths and time spent within 1.5 m of the surface. In all these cases, there was substantial variation among individuals within locations among times of day. Thus, it was the variation among individuals that dominated all other effects. Dives were categorised into five types based on the shape of the time-depth profile. Of these, 67% of dives were interpreted as feeding dives (square and U-shaped), 8% as exploratory dives (V-shaped), 22% as travelling dives (shallow-erratic) and 3% as shallow resting dives. There was systematic variation in the distribution of dive types among the factors examined. Most of this variation was among individuals, but this differed across both time of day and tidal state. Not surprisingly, there was a positive relationship between dive duration and depth and a negative relationship between the number of dives per hour and the time spent within 1.5 m of the surface after a dive.     

Diving pattern and performance in relation to foraging ecology in the gentoo penguin, Pygoscelis papua

We present data on diving pattern and performance (dive depth, duration, frequency and organization during the foraging trip) in gentoo penguins Pygoscelis papua , obtained using time-depth recorders ( n = 9 birds, 99 foraging trips). These data are used to estimate various parameters of foraging activity, e.g. foraging range, prey capture rates, and are compared in relation to breeding chronology. Foraging trip duration was 6 h and 10 h, and trip frequency 1.0/day and 0.96/day, during the brooding and creche periods, respectively. Birds spent on average 52%of each foraging trip diving. Dive depth and duration were highly bimodal: shallow dives (< 21 m) averaged 4 m and 0.23 min, and deep dives (> 30 m) 80 m and 2.5 min, respectively. Birds spent on average 71%and 25%of total diving time in deep and shallow dives, respectively. For deep dives, dive duration exceeded the subsequent surface interval, but shallow dives were followed by surface intervals 2–3 times dive duration. We suggest that most shallow dives are searching/exploratory dives and most deep dives are feeding dives. Deep dives showed clear diel patterns averaging 40 m at dawn and dusk and 80–90 m at midday. Estimated foraging ranges were 2.3 km and 4.1 km during the brood and creche period, respectively. Foraging trip duration increased by 4 h between the brood and creche periods but total time spent in deep dives (i.e. time spent feeding) was the same (3 h). Of 99 foraging trips, 56%consisted of only one dive bout and 44%of 2–4 bouts delimited by extended surface intervals > 10 min. We suggest that this pattern of diving activity reflects variation in spatial distribution of prey rather than the effect of physiological constraints on diving ability.     

Diving patterns and performance in the Antarctic blue-eyed shag Phalacrocorax atriceps

The pattern and characteristics of diving of two male blue-eyed shags Phalacrocorax atriceps were studied, using continuous-recording time-depth recorders, for a total of 15 consecutive days during which the depth, duration, bottom time, ascent and descent rates and surface intervals of 674 dives were recorded. Deep dives (> 35 m, averages80–90 m, max. 116 m) were twice as common (64% versus 34%) as shallow dives (< 21 m and 90% < 10 m). Deep dives were long (averages 2.7-4.1 min, max. 5.2 min) with half the time spent near maximum depth and fast travel speeds (averages 1.0-2.4 m s⁻¹). Shallow dives were short (average 0.5 min, max. 1.3 min), without bottom time and with slow travel speeds (0.1–0.6 m s⁻¹). The time spent at depth and the diet (mainly benthic fish and octopus) is consistent with benthic foraging; the function of shallow dives is uncertain. Male shags forage mainly in the afternoon in3–5 distinct bouts of diving. Within bouts (and shorter homogeneous sequences of diving) surface intervals are consistently2–3 times the preceding dive duration; in other shags the reverse is the case. Blue-eyed shag diving depth, duration and pattern is extreme amongst shags; and the relationship between dives and surface intervals suggests that they may regularly exceed their aerobic dive limit.     

Shallow food for deep divers: Dynamic foraging behavior of male sperm whales in a high latitude habitat

Groups of female and immature sperm whales live at low latitudes and show a stereotypical diving and foraging behavior with dives lasting about 45 min to depths of between 400 and 1200 m. In comparison, physically mature male sperm whales migrate to high latitudes where little is known about their foraging behavior and ecology. Here we use acoustic recording tags to study the diving and acoustic behavior of male sperm whales foraging off northern Norway. Sixty-five hours of tag data provide detailed information about the movements and sound repertoire of four male sperm whales performing 83 dives lasting between 6 and 60 min. Dives ranged in depth between 14 and 1860 m, with a median depth of 175 m, and 92% of the surfacings lasted less than 15 min. The four whales clicked for an average 91% (SD = 10) of the dive duration, where the first usual click was produced at depths ranging between 4 and 218 m and the last usual click at depths ranging between 1 and 1114 m. Echolocation buzzes, which are used as an indication of prey capture attempts, were emitted at depths between 17 and 1860 m, during both the descent and ascent phase of deep dives. The foraging behavior varied markedly with depth, with the timing and duration of prey capture attempts during shallow dives suggesting that the whales target more sparsely distributed prey. In contrast, deep dives involve frequent prey capture attempts and seem to target more dense food layers. The evidence of exploitation of different food layers, including epipelagic prey, is consistent with the hypothesis that male sperm whales may migrate to high latitudes to access a productive, multi-layered foraging habitat.     

SUCCESSFUL USE OF A TRANSLOCATION PROGRAM TO INVESTIGATE DIVING BEHAVIOR IN A MALE AUSTRALIAN FUR SEAL, ARCTOCEPHALUS PUSILLUS DORIFERUS

This study reports some of the first foraging behavior data collected for male fur seals. A nonbreeding male Australian fur seal, Arctocephalus pusillus doriferus , captured at a commercial salmon farm in southern Tasmania, Australia, was relocated 450 km from the site of capture. The animal was equipped with a geolocating time-depth recorder that recorded diving behavior and approximate location for the 14.4 d that it took the seal to travel down the east coast of Tasmania and be recaptured at the salmon farm. During its time at sea, the seal spent most of its time over the relatively shallow shelf waters. It spent 30% of its time ashore on a number of different haul-out sites. The deepest dive was 102 m and the maximum duration was 6.8 min. "Foraging" type dives made up 31.2% of the time at sea and had a median duration of 2.5 min and a median depth of 14 m. The seal performed these dives more commonly during the latter part of its time at sea, while it was on the east coast. Unlike other fur seal species studied to date, there was no evidence of a diurnal foraging pattern; it made dives at all times of the day and night.     

ANALYSIS OF SWIM VELOCITIES DURING DEEP AND SHALLOW DIVES OF TWO NORTHERN FUR SEALS, CALLORHINUS URSINUS

Swim velocities at 15-sec intervals and maximum depth per dive were recorded by microprocessor units on two "mixed diver" adult female northern fur seals during summer foraging trips. These records allowed comparison of swim velocities of deep (>75 m) and shallow (<75 m) dives.
Deep dives averaged 120 m depth and 3 min duration; shallow dives averaged 30 m and 1.2 min. Mean swim velocities on deep dives were 1.8 and 1.5 m/sec for the two animals; mean swim velocities on shallow dives were 1.5 and 1.2 m/sec. The number of minutes per hour spent diving during the deep and shallow dive patterns were 11 and 27 min, respectively.
Swim velocity, and hence, relative metabolic rate, did not account for the differences in dive durations between deep and shallow dives. The long surface durations associated with deep dives, and estimates of metabolic rates for the observed swim velocities, suggest that deep dives involve significant anaerobic metabolism.     

Diving behaviour of a reptile (Crocodylus johnstoni) in the wild: interactions with heart rate and body temperature

The differences in physical properties of air and water pose unique behavioural and physiological demands on semiaquatic animals. The aim of this study was to describe the diving behaviour of the freshwater crocodile Crocodylus johnstoni in the wild and to assess the relationships between diving, body temperature, and heart rate. Time-depth recorders, temperature-sensitive radio transmitters, and heart rate transmitters were deployed on each of six C. johnstoni (4.0-26.5 kg), and data were obtained from five animals. Crocodiles showed the greatest diving activity in the morning (0600-1200 hours) and were least active at night, remaining at the water surface. Surprisingly, activity pattern was asynchronous with thermoregulation, and activity was correlated to light rather than to body temperature. Nonetheless, crocodiles thermoregulated and showed a typical heart rate hysteresis pattern (heart rate during heating greater than heart rate during cooling) in response to heating and cooling. Additionally, dive length decreased with increasing body temperature. Maximum diving length was 119.6 min, but the greatest proportion of diving time was spent on relatively short (<45 min) and shallow (<0.4 m) dives. A bradycardia was observed during diving, although heart rate during submergence was only 12% lower than when animals were at the surface.     

The physiological and behavioural development of diving in Australian fur seal (<Emphasis Type="Italic">Arctocephalus pusillus doriferus</Emphasis>) pups

The physiological and behavioural development of diving was examined in Australian fur seal (Arctocephalus pusillus doriferus) pups to assess whether animals at weaning are capable of exploiting the same resources as adult females. Haematocrit, haemoglobin and myoglobin contents all increased throughout pup development though total body oxygen stores reached only 71% of adult female levels just prior to weaning. Oxygen storage components, however, did not develop at the same pace. Whereas blood oxygen stores had reached adult female levels by 9 months of age, muscle oxygen stores were slower to develop, reaching only 23% of adult levels by this age. Increases in diving behaviour corresponded to the physiological changes observed. Pups spent little time (<8%) in the water prior to moulting (age 1–2 months) whereas following the moult, they spent >27% of time in the water and made mid-water dives (maximum depth 35.7 ± 2.9 m) with durations of 0.35 ± 0.03 min. By 9 months (just prior to weaning), 30.5 ± 9.3% of all dives performed were U-shaped benthic dives (maximum depth 65.0 ± 6.0 m) with mean durations of 0.87 ± 0.25 min, significantly shorter than those of adult females. These results suggest that while Australian fur seal pups approaching the age of weaning are able to reach similar depths as adult females, they do not have the physiological capacity to remain at these depths for sufficient durations to exploit them to the same efficiency.     

Three-dimensional movements and swimming activity of a northern elephant seal

We attached a video system and data recorder to a northern elephant seal to track its three-dimensional movements and observe propulsive strokes of the hind flippers. During 6 h of recording, the seal made 20 dives and spent 90% of the time submerged. Average dive duration, maximum depth and swimming speed were 14.9 min+/-6.1 S.D., 289 m+/-117 S.D. and 1.1 m s(-1)+/-0.12 S.D., respectively. The distance swum during a dive averaged 925 m+/-339 S.D., and the average descent and ascent angles were 41 degrees +/-18 S.D. and 50 degrees +/-21 S.D., respectively. Dive paths were remarkably straight suggesting that the seal was navigating while submerged. We identified three modes of swimming based on the interval between propulsive strokes: continuous stroking; stroke-and-glide swimming; and prolonged gliding. The seal used continuous stroking from the surface to a mean depth of 20 m followed by stroke-and-glide swimming. Prolonged gliding started at a mean depth of 60 m and continued to the bottom of dives. For dives to depths of 300 m or more, 75% of the descent time was spent in prolonged gliding and 10% in stroke-and-glide swimming, amounting to 5.9-9.6 min of passive descent per dive. Average swimming speed varied little with swimming mode and was not a good indicator of propulsive effort. It appears that the seal can use prolonged gliding to reduce the cost of transport and increase dive duration. Energetically efficient locomotion may help explain the long and deep dives that routinely exceed the theoretical aerobic dive limit in this species.     

Diel and lunar variation in diving behavior of rough-toothed dolphins (Steno bredanensis) off Kauaʻi,Hawaiʻi

Observational studies describe rough-toothed dolphins (Steno bredanensis) actively foraging during the day on epipelagic species. Using data from depth-transmitting satellite tags deployed on nine individuals off Kauaʻi, we investigated diving behavior and the effects of lunar phase and solar light levels on vertical movements. Overall, tagged rough-toothed dolphins primarily used near-surface waters, spending between 83.6% and 93.7% of their time in the top 30 m of the water column. When diving, grand mean, median, and maximum dive depths were 76.9 m, 67.5 m, and 399.5 m, although individuals were in water with depths from approximately 700–1,450 m. Dive rates varied by time of day, being lowest during the day and at dawn and highest at dusk and night. Dives were deepest (M = 133.7 m, SD = 52.6 m, median = 106.5 m) and longest (M = 4.0 min, SD = 0.4 min, median = 4.0 min) at dusk, suggesting dolphins were taking advantage of prey rising to the surface in response to reduced light levels. Lunar phase indirectly affected diving, with deeper and longer dives occurring with increasing illumination. The variations in dive behavior across solar and lunar cycles indicate diving patterns shift based on the distribution of prey.     

Deep-diving behaviour of the northern bottlenose whale,Hyperoodon ampullatus (Cetacea: Ziphiidae)

Using suction-cup attached time–depth recorder/VHF radio tags, we have obtained the first diving data on northern bottlenose whales (Hyperoodon ampullatus), the first such data on any species within the family Ziphiidae. Two deployments in 1997 on northern bottlenose whales in a submarine canyon off Nova Scotia demonstrated their exceptional diving ability, with dives approximately every 80 min to over 800 m (maximum 1453 m), and up to 70 min in duration. Sonar traces of non-tagged, diving bottlenose whales in 1996 and 1997 suggest that such deep dives are not unusual. This combined evidence leads us to hypothesize that these whales may make greater use of deep portions of the water column than any other mammal so far studied. Many of the recorded dives of the tagged animals were to, or close to, the sea floor, consistent with benthic or bathypelagic foraging. A lack of correlation between dive times and surface intervals suggests that the dives were predominately aerobic.     

Diving in shallow water: the foraging ecology of darters (Aves: Anhingidae)

Diving birds have to overcome buoyancy, especially when diving in shallow water. Darters and anhingas (Anhingidae) are specialist shallow-water divers, with adaptations for reducing their buoyancy. Compared to closely-related cormorants (Phalacrocoracidae), darters have fully wettable plumage, smaller air sacs and denser bones. A previous study of darter diving behaviour reported no relationship between dive duration and water depth, contrary to optimal dive models. In this study I provide more extensive observations of African darters Anhinga melanogaster rufa diving in water<5 m deep at two sites. Dive duration increases with water depth at both sites, but the relationship is weak. Dives were longer than dives by cormorants in water of similar depth (max 108 s in water 2.5 m deep), with dives of up to 68 s observed in water<0.5 m deep. Initial dives in a bout were shorter than expected, possibly because their plumage was not fully saturated. Dive efficiency (dive:rest ratio) was 5–6, greater than cormorants (2.7±0.4 for 18 species) and other families of diving birds (average 0.2–4.3). Post-dive recovery periods increased with dive duration, but only slowly, resulting in a strong increase in efficiency with dive duration. All dives are likely to fall within the theoretical anaerobic dive limit. Foraging bouts were short (17.8±4.3 min) compared to cormorants, with birds spending 80±5% of time underwater. Darters take advantage of their low buoyancy to forage efficiently in shallow water, and their slow, stealthy dives are qualitatively different from those of other diving birds. However, they are forced to limit the duration of foraging bouts by increased thermoregulatory costs associated with wettable plumage.     

Distribution and diving behaviour of harp seals (<Emphasis Type="Italic">Pagophilus groenlandicus</Emphasis>) from the Greenland Sea stock

The distribution and diving behaviour of 16 adult harp seals (Pagophilus groenlandicus) from the Greenland Sea stock were studied in 1993 and 1999, using satellite-linked dive recorders (SDRs). The seals remained near the pack-ice edge in the Greenland Sea between breeding and moulting (April/May 1993; 6F) and during the first 7 weeks after moulting (June/July, 1999; 4F, 6M), there diving to depths of <100 m. In mid-July 1999, seven out of eight seals with active SDRs migrated into the Barents Sea, there diving to <400 m and sharing feeding grounds with the Barents Sea harp seal stock. Between September and December, six of these seals joined the eighth seal in the Denmark Strait until March 2000, there diving to depths of 100–400 m. Overall, dives were significantly deeper in the day and in winter than at night and in summer, with some regional differences. Harp seals are considered pack-ice-associated seals, but our tagged seals spent a considerable proportion of their time in open water, their distribution largely overlapping with that of capelin (Mallotus villosus).     

A lifetime at depth: vertical distribution of southern elephant seals in the water column

Although numerous studies have addressed the migration and dive behaviour of southern elephant seals (Mirounga leonina), questions remain about their habitat use in the marine environment. We report on the vertical use of the water column in the species and the potential lifetime implications for southern elephant seals from Marion Island. Long-term mark-resight data were used to complement vertical habitat use for 35 known individuals tagged with satellite-relay data loggers, resulting in cumulative depth use extrapolated for each individual over its estimated lifespan. Seals spent on average 77.59% of their lives diving at sea, 7.06% at the sea surface, and 15.35% hauled out on land. Some segregation was observed in maximum dive depths and depth use between male and female animals—males evidently being physiologically more capable of exploiting increased depths. Females and males spent 86.98 and 80.89% of their lives at sea, respectively. While at sea, all animals spent more time between 300 and 400 m depth, than any other depth category. Males and females spent comparable percentages of their lifetimes below 100 m depth (males: 65.54%; females: 68.92%), though males spent 8.98% of their lives at depths in excess of 700 m, compared to females’ 1.84% at such depths. Adult males often performed benthic dives in excess of 2,000 m, including the deepest known recorded dive of any air-breathing vertebrate (>2,133 m). Our results provide a close approximation of vertical habitat use by southern elephant seals, extrapolated over their lifespans, and we discuss some physiological and developmental implications of their variable depth use.     

Long-term monitoring of leatherback turtle diving behaviour during oceanic movements

The diving behaviour of four leatherback turtles (Dermochelys coriacea) was recorded for periods of 0.5-8.1 months during their postnesting movements in the Indian and Atlantic Oceans, when they covered 1569-18,994 km. Dive data were obtained using satellite-linked transmitters which also provided information on the dive depths and profiles of the turtles. Turtles mainly dove to depths < 200 m, with maximum dive durations under 30-40 min and exhibited diel variations in their diving activity for most part of the routes, with dives being usually longer at night. Diurnal dives were in general quite short, but cases of very deep (> 900 m) and prolonged (> 70 min) dives were however recorded only during daytime. The three turtles that were tracked for the longest time showed a marked change in behaviour during the tracking, decreasing their dive durations and ceasing to dive deeply. Moreover, diel variations disappeared, with nocturnal dives becoming short and numerous. This change in turtle diving activity appeared to be related to water temperature, suggesting an influence of seasonal prey availability on their diving behaviour. The turtle diving activity was independent on the shape of their routes, with no changes between linear movements in the core of main currents or looping segments in presence of oceanic eddies.     

Seasonal activity budget of adult baltic ringed seals

Although ringed seals are important components in oceanic and fresh water ecosystems at high latitudes, little is known about how they exploit these harsh environments. Seasonal activity and diving behaviour of 19 adult Baltic ringed seals were studied by satellite telemetry. We elaborated an activity budget for ten months of the year, extending over the period from moult to the breeding season. Seals from three main regions showed explicit site fidelity and the distributions of animals tagged from different areas did not overlap, suggesting separate stocks. Both the mean duration and the mean depth of dives peaked in June and July. Seals spent 70% (females) to 85% (males) of their time diving in June and July which decreased to 50% in late autumn. Less than one percent of dives exceeded 10 min in females, while 10% of male dives lasted longer than 10 min in June to September. Less than one percent of dives lasted for more than 25 min. Both females and males were most active during day time and hauled out predominantly during the night. Activity patterns during the summer are suggested to be correlated to energy accumulation and prey availability. The information on seasonal activity budget is crucial for developing population energetic models where interactions between ringed seals and other trophic levels can be evaluated.