Dive profile

Abstract: SUMMARY Lunge feeding in rorqual whales is a drag-based feeding mechanism that is thought to entail a high energetic cost and consequently limit the maximum dive time of these extraordinarily large predators. Although the kinematics of lunge feeding in fin whales supports this hypothesis, it is unclear whether respiratory compensation occurs as a consequence of lunge-feeding activity. We used high-resolution digital tags on foraging humpback whales ( Megaptera novaengliae ) to determine the number of lunges executed per dive as well as respiratory frequency between dives. Data from two whales are reported, which together performed 58 foraging dives and 451 lunges. During one study, we tracked one tagged whale for approximately 2 h and examined the spatial distribution of prey using a digital echosounder. These data were integrated with the dive profile to reveal that lunges are directed toward the upper boundary of dense krill aggregations. Foraging dives were characterized by a gliding descent, up to 15 lunges at depth, and an ascent powered by steady swimming. Longer dives were required to perform more lunges at depth and these extended apneas were followed by an increase in the number of breaths taken after a dive. Maximum dive durations during foraging were approximately half of those previously reported for singing (i.e. non-feeding) humpback whales. At the highest lunge frequencies (10 to 15 lunges per dive), respiratory rate was at least threefold higher than that of singing humpback whales that underwent a similar degree of apnea. These data suggest that the high energetic cost associated with lunge feeding in blue and fin whales also occurs in intermediate sized rorquals.

Abstract: A new concept based on analysis of dive depth data was developed to help estimate prey consumption in ten free-ranging Magellanic penguins (Spheniscus magellanicus) that were brooding chicks. By simultaneously analysing the undulations in the dive depth profile (measured by time-depth recorders, TDRs) and beak opening (obtained from the recently developed intra-mandibular angle sensors, IMASEN), it was possible to determine the proportions of the undulations in the dive profile that resulted (or not) in prey capture. This methodology allowed the number of prey consumed to be estimated with a mean error of 10±6% using TDR data alone. If the mean mass of prey is known, then the overall mass of prey consumed per unit time can be determined. Additionally, the method allows estimation of the depth at which prey is taken and thus indicates how penguins exploit the water column. Due to its simplicity, the proposed methodology has applications for other Spheniscus penguin species and should be considered for other marine endotherm divers that show undulations in the dive depth profile.

Abstract: 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.

Abstract: There is dispute as to whether paradoxical gas embolism is an important aetiological factor in neurological decompression illness, particularly when the spinal cord is aected. We performed a blind case-controlled study to determine the relationship between manifestations of neurological decompression illness and causes in 100 consecutive divers with neurological decompression illness and 123 unaected historical control divers. The clinical eects of neurological decompression illness (including the sites of lesions and latency of onset) were correlated with the presence of right-to-left shunts, lung disease and a provocative dive profile. The prevalence and size of shunts determined by contrast echocardiography were compared in aected divers and controls. Right-to-left shunts, particularly those which were large and present without a Valsalva manoeuvre, were significantly more common in divers who had neurological decompression illness than in controls (P ! 0.001). Shunts graded as large or medium in size were present in 52% of aected divers and 12.2% of controls (P ! 0.001). Spinal decompression illness occurred in 26 out of 52 divers with large or medium shunts and in 12 out of 48 without (P ! 0.02). The distribution of latencies of symptoms diered markedly in the 52 divers with a large or medium shunt and in the 30 divers who had lung disease or a provocative dive profile. In most cases of neurological decompression illness the cause can be determined by taking a history of the dive profile and latency of onset, and by performing investigations to detect a right-to-left shunt and lung disease. Using this information it is possible to advise divers on the risk of returning to diving and on ways of reducing the risk if diving is resumed. Most cases of spinal decompression illness are associated with a right-to-left shunt.