Dive Patterns Research Articles

Foraging behavior of Adélie penguins during incubation period in Lützow-Holm Bay

The diving behavior of Adelie penguins Pygoscelis adeliae was investigated using time–depth recorders during the incubation period in the fast sea-ice area of Lutzow-Holm Bay, Antarctica. Dive profiles and activity/time allocation suggested that penguins were obligated to walk on the fast-ice for 90–100 km until a polynya, which they used as an access to the pack-ice zone. Dive depth did not differ between males and females, though males’ dive duration was longer than that of females. Dive depth was slightly shallower and dive duration was shorter during the incubation than during the chick-rearing phase. Birds dove throughout the day, although less frequently around midnight, and there was no clear diel change in dive depth. This daily dive pattern during incubation period was similar to that previously observed during the chick-rearing period in a fast sea-ice area, but differed from that observed in sea-ice-free area. Variations in diving behavior resulted from different environmental conditions, such as foraging area with different sea-ice condition, as well as from different life history strategies.

Effect of animal-borne camera and flash on the diving behaviour of the female Antarctic fur seal ( Arctocephalus gazella)

Studies have documented effects of drag created by data-logging units attached to seals, but the effect of visual stimuli from such units has not been investigated. We evaluated potential effects of camera attachment including near-infrared flash operation by comparing the diving behaviour of 15 female Antarctic fur seals ( Arctocephalus gazella) with cameras and 10 seals without cameras. Irrespective of the presence of the camera or flash, all seals exhibited an expected diel dive pattern with shallower, shorter dives, less time at the bottom of a dive, and slower ascent and descent rates at night following krill vertical migration. We also observed a previously unreported foraging trip dive pattern with faster ascents and descents near the end of trips. With cameras present, dive duration and bottom time increased and ascents were slower. During flash operation, dive duration increased and bottom time remained constant throughout the day contrary to the expected diel trend. Also during flash operation, bottom time was shorter at the beginning of a foraging trip and dives were deeper, with longer duration and bottom time later in the trip. We were unable to conclude whether the flash emission spectrum overlapped with the visual sensitivity of seals and Antarctic krill ( Euphausia superba) since visual sensitivity data for seals and krill at longer wavelengths were not available. It is possible that the flash was bright enough for the seals or krill to detect; however, although there was a change in diving behaviour observed during flash operation this behaviour was within the range of values normally observed for these seals and should not cause ethical concern.

Diving behavior of the Hawaiian green turtle ( Chelonia mydas) during oceanic migrations

The diving behavior of an adult female and two adult male green turtles was recorded during their roundtrip breeding migration from Laniakea, Oahu, to French Frigate Shoals in the Northwestern Hawaiian Islands. These data represent the first detailed records of diving behavior of green turtles as they migrate to their breeding grounds. All three turtles exhibited a biphasic diving behavior. During the daylight hours, diving depth was shallow (1–4 m) and duration was short (1–18 min). It was assumed that the turtles were moving deliberately toward their destination during this time. Between 1900 and 1930 h daily, the turtles began a diving pattern consisting of deep dives with a mean maximum dive depth of 35–55 m and a mean duration of 35 to 44 min. The shallow diurnal diving began between 0600 and 0700 h, after the nocturnal deep-diving pattern ended. The adult female made two dives in excess of 135 m and one male made several dives in excess of 100 m. These are the deepest dives ever recorded for a naturally diving green turtle. It took an average of 36 days for the turtles to make the trip to French Frigate Shoals and an average of 30 days to make the return trip. The deep nocturnal diving was unexpected and this behavior is in need of further investigation.

Dive and beak movement patterns in leatherback turtles Dermochelys coriacea during internesting intervals in French Guiana

1. Investigating the foraging patterns of free-ranging species is essential to estimate energy/time budgets for assessing their real reproductive strategy. Leatherback turtles Dermochelys coriacea (Vandelli 1761), commonly considered as capital breeders, have been reported recently to prospect actively during the breeding season in French Guiana, Atlantic Ocean. In this study we investigate the possibility of this active behaviour being associated with foraging, by studying concurrently diving and beak movement patterns in gravid females equipped with IMASEN (Inter-MAndibular Angle SENsor). 2. Four turtles provided data for periods varying from 7.3 to 56.1 h while exhibiting continuous short and shallow benthic dives. Beak movement ('b-m') events occurred in 34% of the dives, on average 1.8 +/- 1.4 times per dive. These b-m events lasted between 1.5 and 20 s and occurred as isolated or grouped (two to five consecutive beak movements) events in 96.0 +/- 4.0% of the recorded cases, and to a lesser extent in series (> five consecutive beak movements). 3. Most b-m events occurred during wiggles at the bottom of U- and W-shaped dives and at the beginning and end of the bottom phase of the dives. W-shaped dives were associated most frequently with beak movements (65% of such dives) and in particular with grouped beak movements. 4. Previous studies proposed wiggles to be indicator of predatory activity, U- and W-shaped dives being putative foraging dives. Beak movements recorded in leatherbacks during the first hours of their internesting interval in French Guiana may be related to feeding attempts. 5. In French Guiana, leatherbacks show different mouth-opening patterns for different dive patterns, suggesting that they forage opportunistically on occasional prey, with up to 17% of the dives appearing to be successful feeding dives. 6. This study highlights the contrasted strategies adopted by gravid leatherbacks nesting on the Pacific coasts of Costa Rica, in the deep-water Caribbean Sea and in the French Guianan shallow continental shelf, and may be related to different local prey accessibility among sites. Our results may help to explain recently reported site-specific individual body size and population dynamics.

Fine-scale habitat selection of crabeater seals as determined by diving behavior

Abstract Previous studies within the Marguerite Bay region of the Antarctic Peninsula (∼67°S, ∼67°W) demonstrated that during winter, crabeater seals (Lobodon carcinophagus) were not randomly distributed across available habitat, but instead were more likely to be located in nearshore waters where bathymetric gradients and ice concentrations were high. Here, we investigate how the diving patterns of crabeater seals vary in response to these habitat characteristics, and interpret seal behaviors in light of information on the distribution of their primary prey, krill (Euphausia superba or Euphausia crystallorophias). Diving and movement patterns were obtained from 34 seals (16 male, 18 female) fitted with satellite-relayed data loggers (SRDLs) during the 2001 and 2002 Southern Ocean GLOBEC cruises. Tags transmitted position and dive information for 4–174 days, during which time we received an average of 21 positions/day, and information on a total of 124,681 dives. A series of generalized linear mixed-effect models (GLMM) were used to evaluate the relationship between diving behavior and temporal and physical features of the habitat, and models contrasted using AICc and BIC weights. Overall, we found that the most parsimonious models included year, month, and period (day, dusk, night). In general, seals dived deeper (158 vs. 73 m) and longer (432 vs. 360 s) during the day than at night. In addition, daytime dives included slightly more time at the foraging depths (142 vs. 102 s), and were slightly more efficient (24% vs. 21% of the dive cycle spent at the bottom). When dive patterns were examined with respect to bathymetry, models indicated that seals were foraging in shallower waters (366 vs. 410 m) and closer to the bottom (dives were 50.3% vs. 26.3% of bathymetric depth) during the day than at night. In combination, these findings suggest that crabeater seals foraging during the day exploited zooplankton schools compressed along the bottom. At night, when zooplankton were dispersed and light levels low, foraging activity was less frequent and seals concentrated their diving closer to the surface over a broader range of habitat depths. As individual seals moved an average of only 4.1±1.4 km between daytime and nighttime positions, these results suggest that crabeater seals diving along the Western Antarctic Peninsula select areas of high bathymetric gradients so that they can maximize foraging success over a 24-h cycle without the need to travel long distances. However, annual differences in behavior and the generally low amount of deviation explained by models also suggests that seals vary their diving behavior in response to finer-scale biological, temporal, and/or physical features that were not monitored as part of this study.

The marine temperature and depth preferences of Arctic charr (Salvelinus alpinus) and sea trout (Salmo trutta), as recorded by data storage tags

AbstractEleven Arctic charr (Salvelinus alpinus) (370–512 mm) and eight sea trout (Salmo trutta) (370–585 mm in length) were tagged externally or internally with depth‐ and temperature‐measuring data‐storage tags (DST) before they were released into the sea in the Alta Fjord in north Norway in June 2002. All sea trout were recaptured after they spent 1–40 days at sea, while all Arctic charr were recaptured after 0.5–33 days at sea. On average, trout preferred water about 0.6 m deeper and 1.3°C warmer than Arctic charr. Arctic charr spent >50% of their time between 0 and 1 m depth, while trout spent >50% of their time between 1 and 2 m depth. Both species spent >90% of their time in water no deeper than 3 m from the water surface. However, sea trout dove more frequently and to greater depths (max. 28 m) than Arctic charr (max. 16 m), and these deep dives were most frequently performed at the end of the sea migration. Arctic charr demonstrated a diel diving pattern, staying on average about 0.5 m deeper between 08:00 hours and about 15:00 hours than during the rest of the 24 h, even though there was continuous daylight during the experiments. When comparing data obtained from the DSTs with temperature measurements within the fjord system, the two species were observed to select different feeding areas during their sea migration, the sea trout choosing the inner and warmer parts of the fjord, in contrast to the Arctic charr that preferred the outer, colder parts of the fjord. The observed differences in migration behaviour between the two species are discussed in relation to species preferences for prey and habitat selection, and their optimal temperatures for growth.

Dimensions of diet segregation in grey seals Halichoerus grypus revealed through stable isotopes of carbon (δ13C) and nitrogen (δ15N)

Although many studies have documented diets for terrestrial mammals, much less is known about prey selection in marine mammals. Variation in body size of terrestrial carnivores is cor- related with mass of prey consumed, and predator size often determines dietary overlap. Grey seals Halichoerus grypus are a size-dimorphic phocid seal inhabiting the Northwest Atlantic, with males 1.5× larger than females. Stable isotopes of carbon (δ 13 C) and nitrogen (δ 15 N) provide useful tools for estimating trophic positions and carbon flow to consumers in food webs. δ 13 C and δ 15 N were analyzed for individual adult grey seals from Sable Island, Canada, between 1996 and 2001. Samples of skin were taken in May or September and the same animals were re-sampled when they returned to the breeding colony in January. In addition, samples were taken from juveniles (n = 29) in January 2004. δ 13 C and δ 15 N were also analyzed for 12 fish and 3 invertebrate species from the Scotian Shelf. Adult male (n = 36) and female (n = 36) grey seals exhibited significantly different δ 13 C and δ 15 N values (F1, 70 = 22.40; p < 0.001). On average, males were more enriched in both δ 13 C and δ 15 N than females. While there were no differences between sex in juveniles, signatures were significantly different from adults (F2,101 = 28.05; p < 0.001). Comparison of isotope values from potential prey suggests that adult males feed more heavily on benthic prey, whereas adult females appear to feed more on pelagic prey. Juveniles also appear to feed more on pelagic prey. These results are consistent with known dif- ferences in dive patterns and foraging behaviour in this population. In addition, there was a positive effect of body size on both δ 13 C (t = 2.54, p = 0.014) and δ 15 N (t = 2.48, p = 0.016) and a positive rela- tionship between δ 15 N and the rate of fat accumulation (kg d -1 ). These results suggest an underlying energetic basis to diet variation in grey seals. Finally, examination of the variance in stable isotope ratios suggested that while individual grey seals appear to be relative specialists in their diet, niche breadth was 1.5× greater in males than in females. On average, adult grey seals had a 2 × higher niche breadth than juveniles.

Dispersal and dive patterns in gravid leatherback turtles during the nesting season in French Guiana

We present the first combined analysis of diving behaviour and dispersal data collected from gravid leatherback turtles during 3 consecutive nesting seasons in French Guiana. In total, 23 turtles were fitted with Argos satellite transmitters and 16 individuals (including 6 that were concur- rently satellite-tracked) were equipped with an electronic time-depth recorder for single inter- nesting intervals, i.e. between 2 consecutive ovi-positions. The leatherbacks dispersed over the con- tinental shelf—from the coastal zone to the shelf break—and moved over 546.2 ± 154.1 km (mean ± SD) in waters of French Guiana and neighbouring Suriname. They mostly performed shallow (9.4 ± 9.2 m) and short (4.4 ± 3.4 min) dives with a slight diurnal pattern. They dived deeper as they moved away from the coast, suggesting that they were predominantly following the seabed. Inter-nesting intervals could be divided into 2 phases: the first comprised 75% of the time turtles spent at sea, dur- ing which they dived on average 47 min h -1 , while the second was characterised by lower and more variable diving effort as the turtles returned to shore. The extended movements of leatherbacks and the fine analysis of dive shapes suggest that, in French Guiana, leatherbacks may feed during the inter-nesting interval, probably to compensate for the energy costs associated with reproduction. Consequently, this critically endangered species is exposed to a high risk of interaction with local fisheries over the continental shelf.

Offshore Bottlenose Dolphins (Tursiops truncatus): Movement and Dive Behavior Near the Bermuda Pedestal

The behavior of offshore bottlenose dolphins (Tursiops truncatus) in deep water and near oceanic islands is not well known. Using satellite-linked, time-depth recorders, we investigated the movements and dive behavior of offshore bottlenose dolphins in the deep waters surrounding the Bermuda Pedestal. Three dolphins were tracked from 5 to 45 days and traveled a mean distance of 28.3 km/day where mean water depth was −1,402.0 m ± 1,120.7 SD. Regular dives during the night (2100–0259 h local time) to depths greater than 450 m (8.9% of total dives), 46.4% of night dives lasting longer than 5 min, and high hematocrit values reveal the deep-diving capabilities of offshore bottlenose dolphins. During the day (0900–1459 h local time), dives tended to be shallow, with 96% of dives within 50 m of the surface, and of short durations, with 52.7% lasting less than 1 min. At dusk (1500–2059 h local time), the number of dives increased (X̄ = 72.4 ± 19.6), indicating a diel dive cycle. The dive patterns of bottlenose dolphins in Bermuda waters correlate with the reported nightly vertical migrations of mesopelagic prey along the steep-sided Bermuda Pedestal.

Characteristics of the deep scattering layer in the Gulf of Mexico as they relate to sperm whale diving and foraging behavior

In June 2005 we used a 38-kHz ADCP and two Simrad fishery echosounders to collect backscatter data and passive acoustic array recordings of sperm whale sounds, as part of the Sperm Whale Seismic Study (SWSS). Dive profiles and presumed foraging depths of the whales were derived using a 3-D tracking technique [see abstract by Thode and Norris (this conference)]. Relationships are examined between dive profiles and acoustic backscatter intensity measurements from the main deep scattering layer (DSL) at a daytime depth of 400–600 m. Passive detections of creaks, believed to be associated with prey acquisition, are merged with dive profiles to provide insight between mid-water backscatter returns and foraging effort. Results to date indicate whales diving in three depth ranges: deeper than 800 m, between 500 and 800 m, and less than 500 m. Dive patterns indicate some whales dive through the main DSL into deeper secondary layers seen by the 38-kHz ADCP. There seems to be no difference in dive patterns between night and day. Calibration analysis of ADCP backscatter versus 70-kHz Simrad backscatter shows a positive functional relationship, with 4 units of relative acoustic backscatter intensity equal to 1 dB of Sv.

Underwater behaviour of green turtles monitored with video-time-depth recorders: what’s missing from dive profiles?

We used a turtle-mounted video and data-logging system (Crittercam; National Geo- graphic Society, USA) to study underwater behaviour and dive patterns of green turtles, Chelonia mydas, at a coastal foraging area in the Gulf of California, Mexico. Between August 1997 and June 2002, units were deployed 36 times on 34 green turtles ranging from 64.1 to 96.7 cm in straight cara- pace length and 38.6 to 120.5 kg in weight. A total of 89.5 h of video was recorded with correspond- ing dive data (1065 total dives). Foraging was observed during 8 deployments (28 events) at depths of 3.0 to 32.0 m and occurred while turtles were swimming in the midwater column and stationary on the seafloor; 4 marine algae and 5 invertebrate prey species were identified. Resting behaviour was seen during 9 deployments (33 dives) as turtles set on the seafloor at depths of 7.0 to 26.5 m. Overall, 6 dive types were observed and labeled Type 1 to Type 6 dives. Green turtles foraged during Type 1, Type 3, and Type 5 dives, whereas they rested only during Type 1 dives. In addition to elucidating the importance of specific habitats and resources in neritic foraging areas, our results confirm that a vari- ety of underwater behaviours can be reflected by 1 specific dive profile. These data indicate caution should be exercised when ascertaining in-water activity solely based on the appearance of dive profiles.

Diving behaviour of an immature Kemp's ridley turtle (Lepidochelys kempii) from Gullivan Bay, Ten Thousand Islands, south-west Florida

We report on the first successfully deployed time-depth recorder on an immature Kemp's ridley turtle in a coastal foraging habitat in south-west Florida. The turtle exhibited three distinct dive patterns interpreted as: post release stress (26 h) post release transition (8 h) and normal (&gt;34 h). The normal pattern consists of short periods on the surface followed by longer periods on the bottom in 2–3 m of water which we speculate is foraging behaviour. Overall, the turtle spent 94% of the time submerged during the normal period. The turtle spent significantly more time submerged at night than during the day, suggesting the turtle was resting. Night dives were consistently longer than dawn, day or dusk dives.

Swim speeds and stroke patterns in wing-propelled divers: a comparison among alcids and a penguin

In diving birds, the volume and resulting buoyancy of air spaces changes with dive depth, and hydrodynamic drag varies with swim speed. These factors are important in the dive patterns and locomotion of alcids that use their wings both for aerial flight and underwater swimming and of penguins that use their wings only for swimming. Using small data-loggers on free-ranging birds diving to 20-30 m depth, we measured depth at 1 Hz and surge and heave accelerations at 32-64 Hz of four species of alcids (0.6-1.0 kg mass) and the smallest penguin species (1.2 kg). Low- and high-frequency components of the fluctuation of acceleration yielded estimates of body angles and stroke frequencies, respectively. Swim speed was estimated from body angle and rate of depth change. Brünnich's (Uria lomvia) and common (Uria aalge) guillemots descended almost vertically, whereas descent of razorbills (Alca torda), rhinoceros auklets (Cerorhinca monocerata) and little penguins (Eudyptula minor) was more oblique. For all species, swim speed during descent was within a relatively narrow range. Above depths of 20-30 m, where they were all positively buoyant, all species ascended without wing stroking. During descent, little penguins made forward accelerations on both the upstroke and downstroke regardless of dive depth. By contrast, descending alcids produced forward accelerations on both upstroke and downstroke at depths of <10 m but mainly on the downstroke at greater depths; this change seemed to correspond to the decrease of buoyancy with increasing depth. The magnitude of surge (forward) acceleration during downstrokes was smaller, and that during upstrokes greater, in little penguins than in alcids. This pattern presumably reflected the proportionally greater mass of upstroke muscles in penguins compared with alcids and may allow little penguins to swim at less variable instantaneous speeds.

Home range and habitat use of juvenile Atlantic green turtles (Chelonia mydas L.) on shallow reef habitats in Palm Beach, Florida, USA

Many animals, including sea turtles, alter their movements and home range in relation to the particular type and quality of the habitat occupied. When sufficient resources are available, individuals may develop affini- ties to specific areas for activities, such as foraging and (or) resting. In the case of green sea turtles (Chelonia mydas L.), after a number of years in the open ocean, juveniles recruit to shallow-water developmental habi- tats where they occupy distinct home ranges as they feed and grow to maturity. Our goal was to study the habitat use and home range movements of juvenile green turtles along a shallow, worm-rock reef tract in Palm Beach, Florida. Six turtles, measuring from 27.9 to 48.1 cm in straight carapace length and from 7.2 to 12.6 kg in mass, were tracked via ultrasonic telemetry from August to November 2003. Upon capture, each turtle's esophagus was flushed via lavage to determine recently ingested foods. In addition, four turtles were recaptured and fit- ted with a time-depth recorder to study dive patterns. Home range areas measured with 100% minimum con- vex polygon and 95% fixed kernel estimators varied from 0.69 to 5.05 km 2 (mean=2.38±1.78 km 2 ) and 0.73 to 4.89 km 2 (mean=2.09±1.80 km 2 ), respectively. Home ranges and core areas of turtles were largely restricted to the reef tract itself, and showed consider- able overlap between food and shelter sites. The mean number of dives during daylight hours (0600- 1800 hours) was 84±5.0 dives, while the mean during night hours (1800-0600 hours) was 39±3.0 dives. Dives during the day were shallower (mean=3.20±1.26 m) than dives at night (mean=5.59±0.09 m). All six turtles were found to have a mixed diet of similar macroalgae and sponge fragments. Our results reveal that juvenile green turtles occupy stable home ranges along the nearshore worm-rock reefs of Southeast Florida, during the summer and fall. Determining which habitats are used by green turtles will assist conservation managers in their global effort to protect this endangered species.

Bioenergetics and diving activity of internesting leatherback turtlesDermochelys coriaceaat Parque Nacional Marino Las Baulas, Costa Rica

Physiology, environment and life history demands interact to influence marine turtle bioenergetics and activity. However, metabolism and diving behavior of free-swimming marine turtles have not been measured simultaneously. Using doubly labeled water, we obtained the first field metabolic rates (FMRs; 0.20-0.74 W kg(-1)) and water fluxes (16-30% TBW day(-1), where TBW=total body water) for free-ranging marine turtles and combined these data with dive information from electronic archival tags to investigate the bioenergetics and diving activity of reproductive adult female leatherback turtles Dermochelys coriacea. Mean dive durations (7.8+/-2.4 min (+/-1 s.d.), bottom times (2.7+/-0.8 min), and percentage of time spent in water temperatures (Tw) < or =24 degrees C (9.5+/-5.7%) increased with increasing mean maximum dive depths (22.6+/-7.1 m; all P< or =0.001). The FMRs increased with longer mean dive durations, bottom times and surface intervals and increased time spent in Tw< or =24 degrees C (all r2> or =0.99). This suggests that low FMRs and activity levels, combined with shuttling between different water temperatures, could allow leatherbacks to avoid overheating while in warm tropical waters. Additionally, internesting leatherback dive durations were consistently shorter than aerobic dive limits calculated from our FMRs (11.7-44.3 min). Our results indicate that internesting female leatherbacks maintained low FMRs and activity levels, thereby spending relatively little energy while active at sea. Future studies should incorporate data on metabolic rate, dive patterns, water temperatures, and body temperatures to develop further the relationship between physiological and life history demands and marine turtle bioenergetics and activity.

Migratory and reproductive movements of male leatherback turtles (Dermochelys coriacea)

The biology of the endangered leatherback turtle (Dermochelys coriacea) at sea is poorly understood. As research has been almost exclusively limited to studies of nesting females, the movements of male turtles and the timing and location of mating activity have remained unknown. We report on the first deployments of satellite tags on male leatherbacks. Male migration to and residency in waters adjacent low-latitude nesting beaches in the western Atlantic suggest that this is where mating occurs, and return migration to these areas reveals male fidelity for breeding sites. Rate of travel decreased markedly after arriving in coastal breeding areas, where males remained for up to 96 days before assuming northward migrations. The initiation of these northward migrations coincided with peak nesting activity in adjacent nesting colonies. Data from satellite-linked time-depth recorders attached to two males revealed diel dive patterns in breeding areas and marked differences in diving behaviour between migratory and breeding periods in one turtle. When male turtles were in waters adjacent nesting colonies, their movements differed from those reported for nesting females, with females ranging farther from shore. Our results suggest that male leatherbacks may be vulnerable to entanglement in coastal fishing gear in waters adjacent nesting beaches.

Diving behaviour of two Ross seals off east Antarctica

The Ross seal (Ommatophoca rossii) is the least frequently sighted and least known of the Antarctic pinnipeds. Current knowledge of foraging and diving behaviour is based on observations of a single seal over &lt;2 days. The current study provides some additional data on the diving behaviour of two Ross seals off east Antarctica over periods of 31 and 12 days during December–January 1999–2000 using satellite-linked dive recorders. Both seals remained over the continental shelf for these times, the female remaining some distance from the coast and the male moving close to the coast approximately half-way through his transmission period. Most dives by the female reached depths &gt;150 m (maximum depth 372 m) and the modal duration was 10–11 min. The male’s dives were slightly shallower (most &gt;100 m) and shorter (mode 6–7 min) when distant from the continental coast, and were truncated to a depth of 180 m when close to the coast, presumably by the sea floor. These dive patterns suggest that their prey species, thought to comprise mostly fish and squid, were relatively unavailable at depths &lt;100 m.

Forage and migration habitat of loggerhead (Caretta caretta) and olive ridley (Lepidochelys olivacea) sea turtles in the central North Pacific Ocean

AbstractSatellite telemetry from 26 loggerhead (Caretta caretta) and 10 olive ridley (Lepidochelys olivacea) sea turtles captured and released from pelagic longline fishing gear provided information on the turtles’ position and movement in the central North Pacific. These data together with environmental data from satellite remote sensing are used to describe the oceanic habitat used by these turtles. The results indicate that loggerheads travel westward, move seasonally north and south primarily through the region 28–40°N, and occupy sea surface temperatures (SST) of 15–25°C. Their dive depth distribution indicated that they spend 40% of their time at the surface and 90% of their time at depths &lt;40 m. Loggerheads are found in association with fronts, eddies, and geostrophic currents. Specifically, the Transition Zone Chlorophyll Front (TZCF) and the southern edge of the Kuroshio Extension Current (KEC) appear to be important forage and migration habitats for loggerheads. In contrast, olive ridleys were found primarily south of loggerhead habitat in the region 8–31°N latitude, occupying warmer water with SSTs of 23–28°C. They have a deeper dive pattern than loggerheads, spending only 20% of their time at the surface and 60% shallower than 40 m. However, the three olive ridleys identified from genetics to be of western Pacific origin spent some time associated with major ocean currents, specifically the southern edge of the KEC, the North Equatorial Current (NEC), and the Equatorial Counter Current (ECC). These habitats were not used by any olive ridleys of eastern Pacific origin suggesting that olive ridleys from different populations may occupy different oceanic habitats.

ENERGETICS OF A BENTHIC DIVER: SEASONAL FORAGING ECOLOGY OF THE AUSTRALIAN SEA LION, NEOPHOCA CINEREA

This research examines the foraging energetics and diving behavior of the Australian sea lion, Neophoca cinerea. We examine whether the foraging ecology of the Australian sea lion is typical for an animal that has evolved to exploit benthic habitats. Such a strategy is in marked contrast to those utilized by some seabirds and other pinnipeds that feed in the midwater, where travel and search components of the time at sea become more important. Onshore and at-sea field metabolic rates (FMR) were measured using doubly labeled water in lactating sea lions at Kangaroo Island, South Australia, during the winter of 1988 (early lactation, breeding season 1) and the summer of 1990 (early lactation, breeding season 2). Dive behavior was also measured with dataloggers during these seasons, as well as in the summer of 1991 (late lactation, breeding season 2). The foraging behavior of Neophoca cinerea indicated that it works hard to exploit benthic habitats in the waters around its breeding site. Sea lions maximized time spent at or near the benthos, with 61% of each dive and 35% of their time at sea being spent at the deepest 20% of the dives. The dive pattern was characterized by almost continuous diving when at sea, with 57.9% of their time at sea spent at depths ≥6 m, and dive rates of 10.7 dives/h. Mean surface intervals (1.0–1.9 min) accounted for only 42% of mean dive durations (2.2–4.1 min). Mean dive depths ranged from 41.5 m to 83.1 m, with maximum dives ranging from 60 m to 105 m. The energetic costs of this strategy are high when compared with those of other otariids: the mean at-sea FMR was 7.05 ± 0.99 W/kg. We report seasonal variability in foraging energetics and dive behavior that is likely to be sensitive to regional oceanography, the maintenance costs of female sea lions and their offspring, and the distribution and behavior of their prey. Further, we note that Australian sea lions are functionally adapted to benefit from benthic foraging strategies because their larger size and insulating blubber convey an advantage over the generally smaller sympatric fur seals that would have a decrease in air/fur insulation with compression at deeper depths and would experience greater water infiltration of the fur with longer dives. Corresponding Editor: C. Martínez del Rio.

An application of optimal diving models to diving behaviour of Brünnich's guillemots

Although theoretical models predict that the quality of foraging patches has little effect on optimal dive time with increasing depth, many empirical studies show that dive time at a given depth may vary. We developed a model that incorporated patch quality as a parameter of energy intake as a nonlinear function of time, and applied it to the diving behaviour of Brünnich's guillemots, Uria lomvia. The model indicated that optimal dive time can vary widely depending on the parameter. It also explained the convergence of observed dive times with travel time. Assuming the birds dived optimally, this parameter can be estimated from travel time and dive time for each dive. Foraging patches with larger estimated parameter values were favoured by the birds, suggesting that the parameter indicated patch quality. We used this parameter to test an optimal patch use model in divers. The results indicate that Brünnich's guillemots adjust their diving behaviour adaptively depending on patch quality, and that the optimal diving model is valid for prediction of observed dive patterns if patch quality is incorporated appropriately. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.