Maximum Dive Depth Research Articles

Pedalling downhill and freewheeling up; a penguin perspective on foraging

Depth-dependent buoyancy resulting from the compression of body-associated air is a major force modulating energy expenditure in diving seabirds, yet quantification of its effects in free- living animals is problematic. Between November 2006 and December 2008, we used multiple chan- nel loggers (daily diaries (DDs)); recording triaxial acceleration, depth and speed, during foraging of 34 Magellanic penguins Spheniscus magellanicus from 3 colonies in Argentina to derive a new proxy for energy expenditure, overall dynamic body acceleration (ODBA). Assuming ODBA to be linearly related to power, energy expenditure was highest during dive descent, nearer the surface and in those dives terminating at greater depths due to steeper descent angles. Swim speed during descent was invariant of maximum dive depth. Calculated energy expenditure during the bottom phase of the dive was invariant of depth, but energy expenditure of birds returning to the surface was lowest at any given depth for birds that had engaged in deeper dives due to the effects of buoyancy. Four birds, equipped with beak angle-measuring sensors as part of the DDs, captured 89% of their prey (nor- mally pelagic school fish) during fast passive ascents using buoyancy to aid in capture. Details from one of these birds showed that this passive ascent occurred at a mean velocity of 1.94 m s -1 for a mean of 2.02 s; ascent angles during such rushes were steeper when the bird was deeper, which was pre- sumed to reflect a response to the diminished buoyant force at greater pressures. Passive ascents during prey capture appear to be an important mechanism for Magellanic penguins to capture fast- moving prey with minimal energy expenditure.

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.

Comparison of trip duration, activity pattern and diving behaviour by Red-tailed Tropicbirds (Phaethon rubricauda) during incubation and chick-rearing

In the tropical marine environment food resources are scarce and often patchily distributed. Consequently, nesting tropical seabirds must balance travelling to productive areas and sharing incubation or providing food to the chick. Changes in foraging behaviour occur when adults switch from feeding only for themselves during incubation to feeding a chick and fulfilling their own energy requirements. Externally attached data-devices were used to compare the duration of foraging trips, flight activity and depth of dives of incubating and chick-rearing Red-tailed Tropicbirds (Phaethon rubricauda) on Christmas Island, Indian Ocean. Adults with chicks had a bimodal pattern of foraging, with alternating short and long foraging trips (mean duration±s.d. of short trips = 3.0 ± 4.1 h, of long trips = 57.4 ± 41.1 h), whereas incubating adults undertook only longer trips (mean duration ± s.d. = 152.9 ± 47.2 h). This strategy is stimulated by partner behaviour, rather than body mass as reported for many other seabirds, and may enable the optimisation of simultaneous food delivery to chicks and self-feeding when local resources are poor. The proportion of time spent in flight (flight activity) by adults with chicks averaged 90.1% during short trips whereas incubating birds spent only 62.4% of their trips flying. Overall mean depth of foraging dives by adults with chicks averaged 0.6 ± 0.3 m during short trips; mean maximum depth of dives by incubating adults were recorded using maximum-depth recorders and were significantly deeper at 10.7 ± 8.7 m, reaching a maximum depth of 25.6 m.

Changes in the foraging dive behaviour and energetics of king penguins through summer and autumn: a month by month analysis

King penguins Aptenodytes patagonicus are known to change their diving behaviour in response to changes in both prey location and their breeding status through the early stages of the breeding cycle (austral summer and autumn). However, little information exists on whether and how these changes affect the energy expenditure of such behaviour. By deploying heart rate and hydro- static pressure data loggers, we investigated detailed changes in the dive time budgeting of king penguins during foraging dives across the breeding season, in the same individuals, and the associ- ated changes in estimated oxygen consumption during those dives. Maximum dive depth, duration, bottom duration, feeding events (indicated by wiggles) per dive and post-dive duration increased through the study period. While a foraging dive later in the breeding season was energetically more costly than a dive earlier in the season, the overall rate of energy expenditure did not change, nor did energy cost per unit prey capture. These findings indicate an ability of king penguins to adjust their foraging dive behaviours through the summer and autumn without affecting the energetic costs of diving to capture prey. Such plasticity may be necessary to compensate for changes both in prey loca- tion and abundance, and in the energy requirements of the chick over time.

Diving behaviour in two distinct populations of gravid Flatback turtlesNatator depressus

This paper presents the first data on the diving behaviour of Flatback turtles, Natator depressus, between nesting events. Dive profiles were recorded in turtles from breeding populations at Curtis Island in Queensland and at Bare Sand Island in the Northern Territory, using Time-Depth Recorders (TDRs). Both populations displayed dive types typical of those described in other internesting sea turtles. Dives spent on the seabed were most prevalent, accounting for 57% of the time at depth. While on the sea bed, the turtles apparently remained inactive, cyclical changes in depth reflecting the tidal cycle. These inactive dives were long compared to those typical of other large sea turtles such as C. mydas and C. caretta, up to 98 min (mean 80±12 min), and with a mean and median of 50 and 52 min, respectively. In both populations, these dives occurred more commonly by day, by an average of 14%, and were most prevalent in the middle third of the internesting interval in most turtles, while the eggs were maturing. The turtles spent only 10% of their time at or near the surface and surface intervals rarely exceeded a few minutes, insufficient to be attributed to a need for either rest or thermoregulation. The Bare Sand Island population showed longer dive durations and proportionally more dives with a gradual ascent phase, a phase presumed to be a method of compensating for buoyancy loss and a way for turtles to conserve energy in mid-water while still moving around. Maximum dive depths of 29 m and 44 m were recorded at Curtis Island and Bare Sand Island respectively, probably reflecting differences in bathymetry.

Changes in flipper beat frequency, body angle and swimming speed of female green turtles Chelonia mydas

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 386:275-286 (2009) - DOI: https://doi.org/10.3354/meps08084 Changes in flipper beat frequency, body angle and swimming speed of female green turtles Chelonia mydas Tohya Yasuda1,2,*, Nobuaki Arai1 1Department of Social Informatics, Graduate school of Informatics, Kyoto University, Yoshidahonmachi, Sakyo-ku, Kyoto 606-8501, Japan 2Present address: School of Agriculture, Kinki University, Nakamachi 3327-204, Nara 631-8505, Japan *Email: tohya.yasuda@gmail.com ABSTRACT: Data loggers were utilized to record depth, temperature, biaxial motion and swimming speed for female green turtles Chelonia mydas between nesting events in Thailand. The present study demonstrated clear alternations in swimming effort with depth. Both resident and maximum dive depths significantly affected flipper beat frequency, suggesting that turtles change flipper beat frequency with current buoyancy in ways similar to other diving mammals and birds. Body angles became steepest during the initial phases of descent and ascent, but were <60°. Swimming speeds were related to flipper beat frequency and current buoyancy. Swimming speeds based on the dominant stroke frequency during the inter-nesting period (0.18 to 0.21 Hz) were estimated at 0.52 to 0.60 curved carapace lengths s–1. These values are similar to the modal speeds of the leatherback turtles Dermochelys coriacea and the mean speeds during the initial descent of the loggerhead turtles Caretta caretta. We calculated the dynamic body acceleration (DBA) as the index of activity during the descent and ascent phases and found a relationship between maximum dive depth and DBA. Although active stroking during deeper dives may result in a shorter dive duration, daytime dives (ca. 16 to 26 m) were deeper than those observed during the night (ca. 9 to 13 m). This result suggests a beneficial reproductive strategy for females that involves changes in vertical space, for example, to obtain refuge from energy-consuming encounters with males or predators. KEY WORDS: Diving behaviour · Chelonia mydas · Sea turtles · Flipper beat frequency · Swimming speed · Body angle Full text in pdf format PreviousNextCite this article as: Yasuda T, Arai N (2009) Changes in flipper beat frequency, body angle and swimming speed of female green turtles Chelonia mydas. Mar Ecol Prog Ser 386:275-286. https://doi.org/10.3354/meps08084 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 386. Online publication date: July 02, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Ecological studies of marine mammals using a seabed-mounted echosounder

Abstract Doksæter, L., Godø, O. R., Olsen, E., Nøttestad, L., and Patel, R. 2009. Ecological studies of marine mammals using a seabed-mounted echosounder. – ICES Journal of Marine Science, 66: 1029–1036. A seabed-mounted, upward-looking, 38 kHz echosounder (Simrad EK60) was used to monitor cetaceans for 128 d between July 2004 and June 2005. The echosounder was placed at 52°N 30°W at a depth of 910 m, in a frontal area with continuous upwelling creating a hotspot of marine life at all trophic levels. Echo tracks were observed, apparently resulting from one or more animals in close temporal and spatial proximity. The 69 “acoustic detections” were examined with a principal component analysis (PCA) considering mean target strength (TS), group size, and maximum dive depth and duration. The PCA conservatively classified 45 of the acoustic detections as “cetaceans”. Their mean TS values varied between −5 and −36 dB, in agreement with earlier TS measurements of whales and dolphins. Several of the supposed cetaceans were apparently feeding in the “deep-scattering layer” when this ascended at night. This study demonstrates that cetacean behaviour, including swimming, feeding, and vocalizing, can be observed and monitored with stationary active-acoustic instrumentation.

Plunging Behaviour in Chick-rearing Brown Boobies

ABSTRACT Brown Boobies (Sula leucogaster) obtain prey by plunge dives. In order to investigate the foraging behaviour of Brown Boobies underwater, we attached acceleration data loggers to chick-rearing Brown Boobies at Nakanokamishima Island in Japan. We documented, for the first time, Brown Boobies performing many rapid and shallow V-shaped dives and some W-shaped dives during the daylight period. The average and maximum dive depth and duration were 1.03 m and 3.81 m and 1.83 s and 21 s, respectively. Furthermore, Brown Boobies used buoyancy to ascend to the water surface. Our data suggest that Brown Boobies mainly depend on shallow-plunging, contrary to the pursuit divers such as gannets, due to their ecological and/or physiological constraints.

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.

Dysbaric Osteonecrosis Screening in Turkish Navy Divers

Dysbaric osteonecrosis (DON) is regarded as an occupational disease for caisson workers, commercial, and military divers. Magnetic resonance imaging (MRI) was suggested for the surveillance of military divers for DON. This study aimed to determine the prevalence of DON in Turkish Navy divers. The shoulder, hip, and knee joints of 106 male divers were screened for DON with MRI. A questionnaire was used to obtain information about subjects' medical history and diving experience. The mean age of divers was 34.3 +/- 5.8 yr. The divers had spent an average of 12.1 +/- 6.1 yr at their occupation. The average of total hours of diving was 834 +/- 458 h. The maximum diving depth was 53.0 +/- 18.4 m (175 +/- 61 ft) and the average diving depth was 13.3 +/- 8.4 m (44 +/- 28 ft). MRI examinations of divers did not reveal bone lesions consistent with osteonecrosis. We concluded that the risk of DON is very low for military divers who strictly obey the decompression rules and who undergo periodic medical examination. The use of MRI for routine screening of military divers is not justified.

Maximum dive depths of eight New Zealand Procellariiformes, including Pterodroma species

Lightweight capillary tube depth gauges were attached to eight petrel species breeding at New Zealand colonies during the period 1998-2008. This paper presents the first information on the diving ability of Pterodroma petrels.Grey-faced Petrels, Pterodroma macroptera gouldi, recorded maximum dives down to 23 m. Males (6.3 ± 6.3 m SD) dived deeper on average than females (3.6 2.5 m) during the incubation period but not significantly so (P=0.06). Breeding birds dived significantly deeper on average than non-breeders, and breeding males dived significantly deeper on average than non-breeding males. The two small Pterodroma species sampled, Pterodroma pycrofti and Pterodroma nigripennis, only exhibited shallow dives down to 2 m but sample sizes were small. Sooty Shearwaters, Puffinus griseus, had mean maximum dive depths of 42.7 ± 23.7 m, with males (53.0 ± 17.3 m) diving significantly deeper on average than females (20.1 ± 20.4 m) during the incubation period. One male Sooty Shearwater dived to nearly 93 m, the deepest dive so far recorded in the order Procellariiformes. Flesh-footed Shearwaters, Puffinus carneipes, dived to 28 m, with a mean maximum dive depth of 13.6 ± 7.9 m. Hutton's Shearwaters, Puffinus huttoni, had a mean maximum dive depth of 23.0 ± 8.5 m (range 11.1-36.6 m). A single Fluttering Shearwater, Puffinus gavia, recovered with a dive gauge had dived to 29 m. Mean maximum dives made by Common Diving-Petrels, Pelecanoides urinatrix, of 10.9 ± 6.1 m (range 6.9-22.2 m) were shallower than results reported from other sites but may have been biased by gauge failures. Capillary gauges provide the best means we have at present to understand the diving capability ofsmall seabirds. While studies elsewhere have shown these gauges may overestimate diving performance by about 10-15%, other factors identified in this study indicate that sometimes diving performance will be underestimated using this simple technique.

Foraging while breeding: alternative mating strategies by male Weddell seals?

1. In terrestrially breeding phocid seals males are significantly larger than females with their large size conferring advantage in male–male competition, and increasing their ability to fast during the breeding season, prolonging tenure and hence mating opportunities. 2. For aquatically breeding seals, the opportunity to feed during the breeding season may offset the need for large size and the ability to fast. 3. Individual differences in male breeding success, behaviour and mass changes for Weddell seals (Leptonychotes weddellii) at Turtle Rock, McMurdo Sound (77.727S, 166.85E) during 1997, 1998 and 1999 were recorded. 4. Males were tracked under the ice through each breeding season using an acoustic array (n=15). Mass changes were measured for 30 males, all of which were successfully genotyped and were aged between 6 and 20 years (mean 13.7). 5. Territory use was dynamic, with some males spending most of the time either at or near the surface, others diving deep and others switching from regular diving to near surface behaviour. 6. Rate of mass loss varied more than three-fold (mean 2.1 ± 0.53 kg day−1, range 0.0 to 4.1) as did mass-specific loss (mean 0.53 ± 0.23). 7. Maximum dive depth for the individuals also varied dramatically (10 to 518 m) and was inversely related to the rate of mass-specific loss, suggesting that the deep diving males may offset the costs of breeding by foraging. 8. Males that stayed near the surface successfully sired pups as did males that continued to dive. Both strategies therefore seemed to be equally successful. 9. Foraging during the breeding season may be a male strategy that may potentially prolong tenure, but appears to be facultative rather than obligative. Copyright © 2008 John Wiley & Sons, Ltd.

Role of the bowhead whale as a predator in West Greenland

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 346:285-297 (2007) - DOI: https://doi.org/10.3354/meps06995 Role of the bowhead whale as a predator in West Greenland Kristin L. Laidre1,3,* Mads Peter Heide-Jørgensen1, Torkel Gissel Nielsen2 1Greenland Institute of Natural Resources, Box 570, 3900 Nuuk, Greenland 2National Environmental Research Institute, Department of Marine Ecology, Frederiksborgvej 399, PO Box 358, 4000 Roskilde, Denmark 3Present address: Polar Science Center, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Seattle, Washington 98105, USA *Email: klaidre@apl.washington.edu ABSTRACT: We examined the spatial and temporal linkage between primary production, zooplankton distribution and density, and bowhead whale Balaena mysticetus foraging behavior in Disko Bay, West Greenland using concurrent ship-based oceanographic and net sampling together with instrumentation of whales with satellite-linked transmitters and dive recorders. Estimates of bowhead whale abundance were used in a bioenergetic model to calculate the potential consumption of zooplankton during their 4 mo stay in Disko Bay. Between 2001 and 2006, 30 whales were fitted with satellite transmitters that provided information on daily movements, and 14 whales were tracked with archival time–depth or time–depth–fluorescence recorders that provided detailed dive data. Simultaneous data were collected on water column structure, phytoplankton and zooplankton density, taxa and biomass at 25 stations south of Disko Island in 2003, 2005 and 2006. After the retreat of annual winter sea ice, bowhead whales explored a limited area along the south coast of Disko Island and had high interannual site fidelity. Mean dive depths varied between 53 (SD = 35) and 109 (SD = 41) m but maximum dive depths were >400 m. Most dives targeted the bottom and dive durations >40 min were observed for several whales. Available prey for bowhead whales was dominated by calanoid copepods, with Calanus finmarchicus, C. glacialis and C. hyperboreus occurring at 90 to 100% of all stations between 0 and 50 m and contributing 78 ± 25% of the total biomass. Bottom sampling for epizooplankton in 2006 resulted in unprecedented densities of C. finmarchicus, several orders of magnitude higher than at any other depth. Bioenergetic modeling indicated the population consumes ~220 US t of zooplankton per day or >21000 t during the 4 mo stay in Disko Bay. Although the total biomass of zooplankton in the upper 50 m of the water column theoretically could support this predation level, benthic zooplankton densities and behavioral data suggest whales target preascension stage epibenthic copepods in high density patches. KEY WORDS: Bowhead whale · Foraging · Zooplankton · Calanus · Greenland Full text in pdf format PreviousNextCite this article as: Laidre KL, Peter Heide-Jørgensen M, Gissel Nielsen T (2007) Role of the bowhead whale as a predator in West Greenland. Mar Ecol Prog Ser 346:285-297. https://doi.org/10.3354/meps06995 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 346. Online publication date: September 27, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Linking foraging behaviour of the northern elephant seal with oceanography and bathymetry at mesoscales

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 346:265-275 (2007) - DOI: https://doi.org/10.3354/meps07014 Linking foraging behaviour of the northern elephant seal with oceanography and bathymetry at mesoscales Samantha E. Simmons1,*, Daniel E. Crocker2, Raphael M. Kudela3, Daniel P. Costa1 1Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Center for Ocean Health, 100 Shaffer Road, Santa Cruz, California 95060-5730, USA 2Department of Biology, Sonoma State University, Rohnert Park, California 94928, USA 3Department of Ocean Sciences, University of California, Santa Cruz, California 95064, USA *Email: simmons@biology.ucsc.edu ABSTRACT: We examined the foraging behaviour of 12 adult female northern elephant seals in relation to mesoscale oceanographic features between 1995 and 1997. Females were divided into 3 groups based on the geographic region to which they migrated (‘coastal’, ‘coastal-oceanic’ and ‘oceanic’). We defined focal foraging areas (FFAs) using satellite telemetry and average daily transit rates of ≤0.4 m s–1, and examined characteristics of FFAs with respect to sea surface temperature (SST), sea surface temperature gradient (SSTg), sea level anomaly (SLA) and bathymetry using logistic regression models. Shallow bathymetry was significant for the coastal grouping of females and we examined the prevalence of benthic dives using a dive index ratio (DI), calculated by dividing mean maximum dive depth (m) by ocean depth (m) at each location for all 12 females. An additional 6 adult males were included in this analysis to quantify and elucidate differences in benthic foraging mode between the sexes. DI comparisons revealed significantly greater prevalence of benthic diving in FFAs in males than females (χ2 = 10.588, p < 0.01). However, one coastal female did show a higher occurrence of benthic dives in FFAs than other females, and had significantly greater rates of mass gain. The importance of each oceanographic variable differed between the 3 groups of females. Overall, model results showed SST to be the most influential factor related to FFAs. Additionally, 6 females had FFAs that were characterised by greater SSTg and higher SLA. These characteristics are consistent with anti-cyclonic eddies that occur throughout the range of elephant seals. Semi-permanent eddies, such as the Haida and Sitka eddies of the Alaska gyre, may be particularly important in determining FFAs for some female northern elephant seals. KEY WORDS: Mirounga angustirostris · Temperature · Benthic · Mesoscale · Eddies · Sex Full text in pdf format PreviousNextCite this article as: Simmons SE, Crocker DE, Kudela RM, Costa DP (2007) Linking foraging behaviour of the northern elephant seal with oceanography and bathymetry at mesoscales. Mar Ecol Prog Ser 346:265-275. https://doi.org/10.3354/meps07014 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 346. Online publication date: September 27, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Mechanics of airway and alveolar collapse in human breath-hold diving

A computational model of the human respiratory tract was developed to study airway and alveolar compression and re-expansion during deep breath-hold dives. The model incorporates the chest wall, supraglottic airway, trachea, branched airway tree, and elastic alveoli assigned time-dependent surfactant properties. Total lung collapse with degassing of all alveoli is predicted to occur around 235 m, much deeper than estimates for aquatic mammals. Hysteresis of the pressure-volume loop increases with maximum diving depth due to progressive alveolar collapse. Reopening of alveoli occurs stochastically as airway pressure overcomes adhesive and compressive forces on ascent. Surface area for gas exchange vanishes at collapse depth, implying that the risk of decompression sickness should reach a plateau beyond this depth. Pulmonary capillary transmural stresses cannot increase after local alveolar collapse. Consolidation of lung parenchyma might provide protection from capillary injury or leakage caused by vascular engorgement due to outward chest wall recoil at extreme depths.

Locomotion in diving elephant seals: physical and physiological constraints

To better understand how elephant seals (Mirounga angustirostris) use negative buoyancy to reduce energy metabolism and prolong dive duration, we modelled the energetic cost of transit and deep foraging dives in an elephant seal. A numerical integration technique was used to model the effects of swim speed, descent and ascent angles, and modes of locomotion (i.e. stroking and gliding) on diving metabolic rate, aerobic dive limit, vertical displacement (maximum dive depth) and horizontal displacement (maximum horizontal distance along a straight line between the beginning and end locations of the dive) for aerobic transit and foraging dives. Realistic values of the various parameters were taken from previous experimental data. Our results indicate that there is little energetic advantage to transit dives with gliding descent compared with horizontal swimming beneath the surface. Other factors such as feeding and predator avoidance may favour diving to depth during migration. Gliding descent showed variable energy savings for foraging dives. Deep mid-water foraging dives showed the greatest energy savings (approx. 18%) as a result of gliding during descent. In contrast, flat-bottom foraging dives with horizontal swimming at a depth of 400m showed less of an energetic advantage with gliding descent, primarily because more of the dive involved stroking. Additional data are needed before the advantages of gliding descent can be fully understood for male and female elephant seals of different age and body composition. This type of data will require animal-borne instruments that can record the behaviour, three-dimensional movements and locomotory performance of free-ranging animals at depth.

Hematocrit Change in Tropical Scuba Divers

Direct evidence that dehydration results from scuba diving is scanty. Increased hematocrit (Ht) is a commonly used proxy measure for dehydration. This study sought evidence that an increase in Ht occurs over the course of a scuba dive in tropical conditions. As a secondary outcome, evidence was sought that the degree of Ht increase is correlated to pressure exposure. Twenty male and 21 female scuba divers were recruited at a remote tropical dive site. Water temperature was 30 degrees C (+/- 1 degrees C). Each diver gave venous blood relating to 1 dive only. Mean maximum dive depth was 13.6 m (+/- 3.7 m [SD]) and mean duration 39.5 minutes (+/- 4.5 minutes [SD]) using air as the breathing gas. Blood was taken at a mean of 12.4 minutes (+/- 3.5 minutes [SD]) before diving and a mean of 16.2 minutes (+/- 3.7 minutes [SD]) after diving. After centrifugation of microcapillaries, Ht was estimated on a visual plate reader. A paired Wilcoxon test showed evidence (P < .001) for a change in Ht. The mean difference between predive and postdive measurements was 0.0073 (95% confidence interval: 0.0104-0.0042), equating to a mean relative Ht increase of 1.78%. Similar results were found for the sexes individually. A correlation between maximum depth of dive and Ht increase was statistically significant, although the correlation itself was weak (P = .049, Spearman's r = .326). There is evidence of a statistically significant increase in Ht over the course of a single warm-water scuba dive. This increase is small and is within the range of error associated with the techniques of Ht estimation employed in this study. Depth exposure was found to correlate with Ht increase. In view of the small magnitude of change in the Ht, there is no reason to amend protocols for fluid resuscitation of recreational scuba divers suspected to have experienced decompression injury in tropical locations.

Southern elephant seals from Kerguelen Islands confronted by Antarctic Sea ice. Changes in movements and in diving behaviour

The behaviour of southern elephant seals from Kerguelen Island (49ring operator50′S, 70ring operator30′E) was investigated in relation to the oceanographic regions of the Southern Ocean. The oceanographic and the seal behaviour data, including location and diving activity, were collected using a new generation of satellite-relayed devices measuring and transmitting pressure, temperature, and salinity along with locations. Dive duration, maximum diving depth, time spent at the bottom of the dives, and shape of dive profiles were compared between male and female seals, and were related to the oceanographic characteristics of areas prospected by the seals. Most animals travelled to the Antarctic shelf. However, during winter, adult females travelled away from the continent, remained and foraged within the marginal sea-ice zone, while juvenile males remained within the pack ice to forage mainly on the Antarctic shelf. Therefore, as the ice expanded females appeared to shift from benthic to pelagic foraging farther north, while males continued to forage almost exclusively benthically on the continental shelf. This difference is likely related to the different energetic requirements between the two sexes, but also may be related to pregnant females having to return to Kerguelen in early spring in order to give birth and successfully raise their pups, while males can remain in the ice. Our results show an important link between elephant seals and Antarctic sea ice and suggest that changes in sea-ice conditions could strongly affect the behaviour of this species.

Satellite tracking reveals unusual diving characteristics for a marine reptile, the olive ridley turtle Lepidochelys olivacea

The movements, diving behaviour and thermal environment occupied by 4 adult female olive ridley turtles Lepidochelys olivacea in northern Australia were determined through satellite telemetry. Patterns of behaviour recorded were rather unusual compared to other sea turtles in that dives were mainly deep, largely benthic and exceptionally long (>2 h) in some cases, characteristics typical of over-wintering turtles in colder environments. One individual occupied shallow coastal for- aging zones, while the others foraged far from land (probably on the seabed) in relatively deep water (>100 m). Individuals performed long dives (frequently >100 min), but from the short post-dive inter- vals we suggest that these dives were mainly aerobic. Maximum dive depth recorded was 200 ± 20 m (mean maximum depths ranged from 20.1 to 46.7 m across individuals; n = 17 328 dives in total; depths ≥3 m were considered 'dives') and the maximum duration was 200 ± 20 min (mean durations ranged from 24.5 to 48.0 min across individuals). Temperature profiles indicate that turtles experi- enced temperatures ranging from 23 to 29°C at the surface, with the lowest temperature recorded (18.7°C) at a depth of 98 m. Only 6.9% of the dives were in water <20°C. From time-allocation at depth (TAD) scores, we demonstrated that many dives reaching the known or inferred sea bottom were U-shaped, but there was no apparent diel signal in dive depth. This suggests that many benthic dives were not associated exclusively with resting behaviour and likely had a foraging component as well. The ability to perform long benthic dives allows this species to exploit deeper benthic environ- ments in addition to the shallow coastal areas more generally occupied by adult hard-shelled sea tur- tles (e.g. green and hawksbill turtles). Deep benthic dives also occur in certain marine mammals (e.g. narwhals) and sea birds (e.g. rockhopper penguins) and therefore seem to be a general foraging strategy exploited by animals that can perform long dives.

Does Scuba Diving Cause Hearing Loss?

The aim of this prospective study was to investigate the hearing levels and transient evoked otoacoustic emissions (TEOAEs) of scuba divers. The study group consisted of 15 scuba divers (9 males, 6 females) and 30 ears. The control group consisted of 15 healthy nondiver patients (9 males, 6 females) and 30 ears. For the study group, total diving duration (TDD), total diving score (TDS), duration after the last dive (DALD), and maximum diving depth (MDD) were obtained by questionnaire. All subjects were evaluated by an otolaryngologic examination, pure-tone and high-frequency audiometry, and transient evoked otoacoustic emissions (TEOAEs). There was no significant difference between the hearing thresholds and TEOAEs of the study and control groups. For divers, age, higher TDDs and TDSs, and a higher MDD caused an increase in hearing thresholds and a decrease in TEOAEs. When the DALD increased, cochlear functions again achieved nearly normal levels. We recommend that divers' hearing levels and cochlear functions be evaluated before diving. Noninfected status and differences in the volume of the mastoid cell system may explain the results of our study.