Dive Duration Research Articles

Formal Comment on Schorr GS, Falcone EA, Moretti DJ, Andrews RD (2014) First Long-Term Behavioral Records from Cuvier's Beaked Whales (Ziphius cavirostris) Reveal Record-Breaking Dives. PLoS ONE 9(3): e92633. doi:10.1371/journal.pone.0092633.

Formal Comment on Schorr GS, Falcone EA, Moretti DJ, Andrews RD (2014) First Long-Term Behavioral Records from Cuvier's Beaked Whales (Ziphius cavirostris) Reveal Record-Breaking Dives. PLoS ONE 9(3): e92633. doi:10.1371/journal.pone.0092633.

Gas exchange and dive characteristics of the free-swimming backswimmer Anisops deanei.

Many aquatic insects utilise air bubbles on the surface of their bodies to supply O2 while they dive. The bubbles can simply store O2, as in the case of an 'air store', or they can act as a physical 'gas gill', extracting O2 from the water. Backswimmers of the genus Anisops augment their air store with O2 from haemoglobin cells located in the abdomen. The O2 release from the haemoglobin helps stabilise bubble volume, enabling backswimmers to remain near neutrally buoyant for a period of the dive. It is generally assumed that the backswimmer air store does not act as a gas gill and that gas exchange with the water is negligible. This study combines measurements of dive characteristics under different exotic gases (N2, He, SF6, CO) with mathematical modelling, to show that the air store of the backswimmer Anisops deanei does exchange gases with the water. Our results indicate that approximately 20% of O2 consumed during a dive is obtained directly from the water. Oxygen from the water complements that released from the haemoglobin, extending the period of near-neutral buoyancy and increasing dive duration.

The role of eddies in the diving behaviour of female southern elephant seals

As the Antarctic Circumpolar Current crosses the South-West Indian Ocean Ridge, it creates an extensive eddy field characterised by high sea level anomaly variability. We investigated the diving behaviour of female southern elephant seals from Marion Island during their post-moult migrations in relation to this eddy field in order to determine its role in the animals’ at-sea dispersal. Most seals dived within the region significantly more often than predicted by chance, and these dives were generally shallower and shorter than dives outside the eddy field. Mixed effects models estimated reductions of 44.33 ± 3.00 m (maximum depth) and 6.37 ± 0.10 min (dive duration) as a result of diving within the region, along with low between-seal variability (maximum depth: 5.5 % and dive duration: 8.4 %). U-shaped dives increased in frequency inside the eddy field, whereas W-shaped dives with multiple vertical movements decreased. Results suggest that Marion Island’s adult female elephant seals’ dives are characterised by lowered cost-of-transport when they encounter the eddy field during the start and end of their post-moult migrations. This might result from changes in buoyancy associated with varying body condition upon leaving and returning to the island. Our results do not suggest that the eddy field is a vital foraging ground for Marion Island’s southern elephant seals. However, because seals preferentially travel through this area and likely forage opportunistically while minimising transport costs, we hypothesise that climate-mediated changes in the nature or position of this region may alter the seals’ at-sea dispersal patterns.

Foraging behaviour and energy budgets of sea snakes: insights from implanted data loggers

AbstractInformation on the foraging behaviour of sea snakes has the potential to clarify adaptive pathways involved in the evolutionary invasion of marine habitats by terrestrial vertebrates. However, logistical obstacles have precluded studies in this field. To obtain preliminary data of diving behaviour, we surgically implanted temperature‐depth loggers into two sympatric, amphibious, benthic foraging sea krait species from New Caledonia. Based on logger recovery from three snakes (1 Laticauda laticaudata and 2 L. saintgironsi), we obtained data on a total of 1850 dives carried out over eight foraging trips and 39.6 days at sea. Almost 99% of dives were <30 m deep. Average dive depth was 10.7 ± 7.0 m, but snakes dived as deep as 82.6 m. Maximum dive duration was ≥123.7 min. At sea, snakes dived continuously, with over 90% of surface recovery periods lasting less than 3 min in L. saintgironsi (n = 1). Periods at the surface (between successive dives) were longer at night than by day, plausibly reflecting more intense hunting activity by the snake. Locomotor speed, as measured by the rate of vertical descent or ascent during diving, was low (0.15 m s−1). In combination with other data on these species, we estimate that metabolic expenditure was about 10 times greater while the snakes were at sea than on land; and their overall field metabolic rate (70–145 kJ kg−1 day−1) was an order of magnitude less than has been reported for diving endotherms. Despite low sample sizes, our study shows that implanted data loggers can provide novel insights into sea snake biology. Our data emphasize the behavioural and ecological consequences of ectothermy for secondary marine vertebrates. In particular, they illustrate how ectothermy allows species to thrive on rates of energy intake vastly lower than are required for their endothermic competitors.

Adjustment of diving behaviour with prey encounters and body condition in a deep diving predator: the Southern Elephant Seal

Summary Optimal diving models have been developed to investigate how air‐breathing predators should adjust their diving behaviour to optimize their foraging efficiency. Using time‐depth recorders and 3D accelerometers, we addressed this question on six free‐ranging Southern Elephant Seal (SES) females equipped on Kerguelen Island. We hypothesize that seals would initially increase their foraging time with distance to the foraging patches before reducing it for physiological reasons, regardless of the prey encountered. We expect that SES spends more time at depths where more Prey Catch Attempts (PCA) occur, that is at the bottom. We also hypothesize that bottom time should be related to both the seal body density and the swimming effort dedicated to catching prey, as we expect seals to be more active when catching prey. Finally, because oxygen is acquired at the surface only, we expect that recovery times increase with the duration of the previous dives. A total of 72·6% of PCA detected by accelerometer occurred at the bottom of the dive. At shallow depths (<300 m), seals spent more time at the bottom in dives where PCA occurred compared to non‐PCA dives. At deeper depths, SES had shorter bottom times in PCA dives due to higher swimming effort. When only dives associated with PCA were considered, the time spent at the bottom increased with the number of PCA. In addition, the closer the seal was to neutral buoyancy, the longer was the bottom duration. Body density, that is buoyancy, was found to be a critical factor in controlling variations in the dive duration through the swimming effort to access the prey at the bottom of the dive. Finally, post‐dive surface intervals were related to the duration and swimming effort of the previous dive. This study reveals how a marine top predator adjusts the time spent at the bottom depending on its body density, prey encounter rate and prey accessibility. It also highlights that using the duration of the foraging phase as a proxy of foraging success can be seriously misleading in SES. Finally, the need to use an energetic approach with bio‐logging technology to study behavioural ecology is emphasized.

Muddy waters: the influence of high suspended-sediment concentration on the diving behaviour of a bimodally respiring freshwater turtle from north-eastern Australia

Increased suspended-sediment concentrations (SS) in rivers can affect aquatic respiration in riverine fauna by impairing respiratory function. Bimodally respiring freshwater turtles are likely to be sensitive to changes in SS because increased concentrations may affect their ability to aquatically respire. However, the impact of SS on the diving behaviour of bimodally respiring freshwater turtles has not been formally investigated. To test this, we examined the influence of dissolved oxygen (DO) saturation (25%, 100%) and temperature (17°C, 25°C) on the diving behaviour of Elseya irwini under clear (0mgL–1) and turbid (79mgL–1) conditions. We hypothesised that low temperature and high DO % saturation would increase dive duration and that high SS would negate the effect of DO, decreasing dive duration under highly oxygenated conditions. Our data demonstrated that increased SS significantly reduced mean dive duration by 73% (97.4±10.1min in 0mgL–1 trials v. 26.4±3.2min in 79mgL–1 trials) under conditions of low temperature (17°C) and high DO % saturation (100%) only. Increased SS directly affects the utilisation of DO by this species, so as to extend submergence times (aquatic respiration) under optimal conditions, raising concerns about the effect of SS on the persistence of populations of physiologically specialised freshwater turtles.

Seasonal, Oceanographic and Atmospheric Drivers of Diving Behaviour in a Temperate Seal Species Living in the High Arctic.

The harbour seal (Phoca vitulina) population in Svalbard marks the northernmost limit of the species’ range. This small population experiences environmental extremes in sea and air temperatures, sea ice cover and also in light regime for this normally temperate species. This study deployed Conductivity Temperature Depth Satellite Relay Data Loggers (CTD-SRDLs) on 30 adult and juvenile harbour seals in 2009 and 2010 to study their foraging behaviour across multiple seasons. A total of 189,104 dives and 16,640 CTD casts (mean depth 72 m ± 59) were recorded. Individuals dove to a mean depth of 41 m ± 24 with a maximum dive depth range of 24 – 403 m. Dives lasted on average 204 sec ± 120 with maximum durations ranging between 240 – 2,220 sec. Average daily depth and duration of dives, number of dives, time spent diving and dive time/surface time were influenced by date, while sex, age, sea-ice concentration and their interactions were not particularly influential. Dives were deeper (~150 m), longer (~480 sec), less numerous (~250 dives/day) and more pelagic during the winter/early spring compared to the fall and animals spent proportionally less time at the bottom of their dives during the winter. Influxes of warm saline water, corresponding to Atlantic Water characteristics, were observed intermittently at depths ~100 m during both winters in this study. The seasonal changes in diving behaviour were linked to average weekly wind stresses from the north or north-east, which induced upwelling events onto the shelf through offshore Ekman transport. During these events the shelf became flooded with AW from the West Spitsbergen Current, which presumably brought Atlantic fish species close to shore and within the seals’ foraging depth-range. Predicted increased in the influx of AW in this region are likely going to favour the growth and geographic expansion of this harbour seal population in the future.

Persistence in diving American mink

American mink forage on land and in water, with aquatic prey often constituting a large proportion of their diet. Their long, thin body shape and relatively poor insulation make them vulnerable to heat loss, particularly in water, yet some individuals dive over 100 times a day. At the level of individual dives, previous research found no difference in dive depth or duration, or the total number of dives per day between seasons, but mink did appear to make more dives per active hour in winter than in summer. There was also no difference in the depth or duration of individual dives between the sexes, but there was some evidence that females made more dives per day than males. However, because individual mink dives tend to be extremely short in duration, persistence (quantified as the number of consecutive dives performed) may be a more appropriate metric with which to compare diving behaviour under different scenarios. Mink performed up to 28 consecutive dives, and dived continually for up to 36 min. Periods of more loosely aggregated diving (termed ‘aquatic activity sessions’) comprised up to 80 dives, carried out over up to 162.8 min. Contrary to our predictions, persistence was inversely proportional to body weight, with small animals more persistent than large ones, and (for females, but not for males) increased with decreasing temperature. For both sexes, persistence was greater during the day than during the night. The observed body weight effect may point to inter-sexual niche partitioning, since in mink the smallest animals are females and the largest are males. The results may equally point to individual specialism’s, since persistence was also highly variable among individuals. Given the energetic costs involved, the extreme persistence of some animals observed in winter suggests that the costs of occasional prolonged activity in cold water are outweighed by the energetic gains. Analysing dive persistence can provide information on an animal’s physical capabilities for performing multiple dives and may reveal how such behaviour is affected by different conditions. Further development of monitoring and biologging methodology to allow quantification of hunting success, and thus the rewards obtained under alternative scenarios, would be insightful.

Diel diving behavior of breeding gentoo penguins on King George Island in Antarctica

Many marine birds dive to catch prey in water. The gentoo penguin (Pygoscelis papua), a specialized diving seabird that preys on krill and fish, is distributed from the sub-Antarctic islands to Antarctic regions. Here, we observed the diving behavior of breeding gentoo penguins on King George Island, South Shetland Islands, Antarctica. Using a time–depth recorder, we collected diving depths every second from seven gentoo breeders for 5–21 days during the chick-rearing period and analyzed their diving characteristics. Most dives occurred in shallow water, although the dive efficiency (=bottom duration time/[dive duration + post-dive surface time]) was highest at depths of 30–35 m and decreased as the penguins dove deeper. Gentoo penguins did not dive more frequently during the day than at night, but during nighttime, most dives occurred in shallow water (<20 m) and the dive efficiency was also higher at this time. As penguins repeated their foraging trips, the number of dives, depth of dives, and trip duration did not change significantly. Our results suggest that the diel dive patterns of gentoo penguins might be related to the vertical migration of krill (upward to the surface at night). In addition, we observed that gentoo penguins could perform active diving behavior even at night, possibly aided by civil twilight during the chick-rearing period in Antarctic regions.

Characterization of postdive recovery using sound recordings and its relationship to dive duration, exertion, and foraging effort of southern elephant seals (Mirounga leonina)

AbstractIt is notoriously difficult to measure physiological parameters in cryptic free‐ranging marine mammals. However, it is critical to understand how marine mammals manage their energy expenditure and their diving behavior in environments where the predation risks are low and where survival is mainly linked to capacities to maintain physiological homeostasis and energy budget balance. Elephant seals are top marine predators that dive deeply and continuously when at sea. Using acoustic recorders deployed on two postbreeding southern elephant seals (SES) females, we developed methods to automatically estimate breathing frequency at the surface. Using this method, we found that seals took successive identical breaths at high frequency (0.29 Hz) when recovering at the surface and that breath count was strongly related to postdive surfacing time. In addition, dive depth was the main factor explaining surfacing time through the effects of dive duration and total underwater swimming effort exerted. Finally, we found that recovery does not only occur over one dive timescale, but over a multidive time scale for one individual. The way these predators manage their recovery will determine how they respond to the change in oceanic water column structure in the future.

Options for modulating intra-specific competition in colonial pinnipeds: the case of harbour seals (Phoca vitulina) in the Wadden Sea.

Colonial pinnipeds may be subject to substantial consumptive competition because they are large, slow-moving central place foragers. We examined possible mechanisms for reducing this competition by examining the diving behaviour of harbour seals (Phoca vitulina) after equipping 34 seals (11 females, 23 males) foraging from three locations; Rømø, Denmark and Lorenzenplate and Helgoland, Germany, in the Wadden Sea area with time-depth recorders. Analysis of 319,021 dives revealed little between-colony variation but appreciable inter-sex differences, with males diving deeper than females, but for shorter periods. Males also had higher vertical descent rates. This result suggests that males may have higher overall swim speeds, which would increase higher oxygen consumption, and may explain the shorter dive durations compared to females. Intersex variation in swim speed alone is predicted to lead to fundamental differences in the time use of three-dimensional space, which may help reduce consumptive competition in harbour seals and other colonial pinnipeds.

Winter use of sea ice and ocean water mass habitat by southern elephant seals: The length and breadth of the mystery

Understanding the responses of animals to the environment is crucial for identifying critical foraging habitat. Elephant seals (Mirounga leonina) from the Kerguelen Islands (49°20′S, 70°20′E) have several different foraging strategies. Why some individuals undertake long trips to the Antarctic continent while others utilize the relatively close frontal zones is poorly understood. Here, we investigate how physical properties within the sea ice zone are linked to foraging activities of southern elephant seals (SES). To do this, we first developed a new approach using indices of foraging derived from high temporal resolution dive and accelerometry data to predict foraging behaviour in an extensive, low resolution dataset from CTD-Satellite Relay Data Loggers (CTD-SRDLs). A sample of 37 post-breeding SES females were used to construct a predictive model applied to demersal and pelagic dive strategies relating prey encounter events (PEE) to dive parameters (dive duration, bottom duration, hunting-time, maximum depth, ascent speed, descent speed, sinuosity, and horizontal speed) for each strategy. We applied these models to a second sample of 35 seals, 20 males and 15 females, during the post-moult foraging trip to the Antarctic continental shelf between 2004 and 2013, which did not have fine-scale behavioural data. The females were widely distributed with important foraging activity south of the Southern Boundary Front, while males predominately travelled to the south-eastern part of the East Antarctica region. Combining our predictions of PEE with environmental features (sea ice concentration, water masses at the bottom phase of dives, bathymetry and slope index) we found higher foraging activity for females over shallower seabed depths and at the boundary between the overlying Antarctic Surface Water (AASW) and the underlying Modified Circumpolar Deep Water (MCDW). Increased biological activity associated with the upper boundary of MCDW, may provide overwintering areas for SES prey. Male foraging activity was strongly associated with pelagic dives within the Antarctic Slope Front where upwelling of nutrient rich Circumpolar Deep Water onto surface water may enhance and concentrate resources. A positive association between sea ice and foraging activity was found for both sexes where increased biological activity may sustain an under-ice ecosystem. Variability of the East Antarctic sea ice season duration is likely a crucial element to allow air-breathing predators to benefit from profitable prey patches within the pack ice habitat.

Validating the relationship between 3-dimensional body acceleration and oxygen consumption in trained Steller sea lions.

We tested the ability of overall dynamic body acceleration (ODBA) to predict the rate of oxygen consumption ([Formula: see text]) in freely diving Steller sea lions (Eumetopias jubatus) while resting at the surface and diving. The trained sea lions executed three dive types-single dives, bouts of multiple long dives with 4-6 dives per bout, or bouts of multiple short dives with 10-12 dives per bout-to depths of 40 m, resulting in a range of activity and oxygen consumption levels. Average metabolic rate (AMR) over the dive cycle or dive bout calculated was calculated from [Formula: see text]. We found that ODBA could statistically predict AMR when data from all dive types were combined, but that dive type was a significant model factor. However, there were no significant linear relationships between AMR and ODBA when data for each dive type were analyzed separately. The potential relationships between AMR and ODBA were not improved by including dive duration, food consumed, proportion of dive cycle spent submerged, or number of dives per bout. It is not clear whether the lack of predictive power within dive type was due to low statistical power, or whether it reflected a true absence of a relationship between ODBA and AMR. The average percent error for predicting AMR from ODBA was 7-11 %, and standard error of the estimated AMR was 5-32 %. Overall, the extensive range of dive behaviors and physiological conditions we tested indicated that ODBA was not suitable for estimating AMR in the field due to considerable error and the inconclusive effects of dive type.

Low prey abundance leads to less efficient foraging behavior in Steller sea lions

Breath-hold divers should adjust their dive behaviors to maximize the benefits and minimize the costs of foraging on prey patches of different densities at different depths. However, few studies have quantified how animals respond to changes in prey availability (depth and density), and how this affects their foraging efficiency. We tested the effects of changes in prey availability on the foraging behavior and efficiency of Steller sea lions (Eumetopias jubatus) by measuring diving metabolic rate, dive durations, and food intake of 4 trained sea lions diving in the open ocean on controlled prey patches of different densities at different depths. Sea lions completed bouts of 5 consecutive dives on high- or low-density prey patches at two depths (10m and 40m). We found that the rate of energy expenditure did not change under any of the imposed foraging conditions (mean±SD: 0.22±0.02kJmin−1kg−1), but that the proportion of time spent consuming prey increased with prey patch density due to changes in diving patterns. At both depths, sea lions spent a greater proportion of the dive bout foraging on prey patches with high prey density, which led to high rates of energy gain (4.3±0.96kJmin−1kg−1) and high foraging efficiency (cost:benefit was 1:20). In contrast, the sea lions spent a smaller proportion of their dive bout actively feeding on prey patches with low prey density, and consequently had a lower energetic gain (0.91±0.29kJmin−1kg−1) and foraging efficiency (1:4). The 5-fold differences in foraging efficiency between the two types of prey patches were greater than the 3-fold differences that we expected based on differences in food availability. Our results suggest that sea lions faced with reduced prey availability forage less efficiently and therefore would have greater difficulty obtaining their daily energy requirements.

Structure and dynamics of minke whale surfacing patterns in the Gulf of St. Lawrence, Canada.

Animal behavioral patterns can help us understand physiological and ecological constraints on animals and its influence on fitness. The surfacing patterns of aquatic air-breathing mammals constitute a behavioral pattern that has evolved as a trade-off between the need to replenish oxygen stores at the surface and the need to conduct other activities underwater. This study aims to better understand the surfacing pattern of a marine top predator, the minke whale (Balaenoptera acutorostrata), by investigating how their dive duration and surfacing pattern changes across their activity range. Activities were classified into resting, traveling, surface feeding and foraging at depth. For each activity, we classified dives into short and long dives and then estimated the temporal dependence between dive types. We found that minke whales modified their surfacing pattern in an activity-specific manner, both by changing the expression of their dives (i.e. density distribution) and the temporal dependence (transition probability) between dive types. As the depth of the prey layer increased between activities, the surfacing pattern of foraging whales became increasingly structured, going from a pattern dominated by long dives, when feeding at the surface, to a pattern where isolated long dives were followed by an increasing number of breaths (i.e. short dives), when the whale was foraging at depth. A similar shift in surfacing pattern occurred when prey handling time (inferred from surface corralling maneuvers) increased for surface feeding whales. The surfacing pattern also differed between feeding and non-feeding whales. Resting whales did not structure their surfacing pattern, while traveling whales did, possibly as a way to minimize cost of transport. Our results also suggest that minke whales might balance their oxygen level over multiple, rather than single, dive cycles.

Summer migration to temperate foraging habitats and active winter diving of juvenile loggerhead turtles Caretta caretta in the western North Pacific

Endangered loggerhead turtles (Caretta caretta) are highly migratory marine reptiles that spend extended maturation periods at sea. Although an understanding of the biology and ecology of juveniles is essential for effective conservation of this species, such information is still limited, especially for the North Pacific population. The first quantitative bycatch survey in northern Japan revealed that the Sanriku coastal area served as an important summer foraging habitat for large juvenile loggerhead turtles in the western North Pacific. To examine their year-round distribution and diving behaviour, we deployed satellite-relayed data loggers on six turtles (mean SCLn–t ± SD = 69.2 ± 9.2 cm, range = 58.3–82.5 cm). While turtles predominantly utilize the Sanriku coastal area and surrounding oceanic waters during summer, all turtles spent most of their time travelling in oceanic waters (>200 m) several kilometres east of Japan and sometimes in association with the Kuroshio Extension Current during winter. Although water temperature experienced by turtles significantly decreased during winter, they predominantly stayed in water >15 °C. There was no strong seasonal pattern in diving behaviour, and daily average dive duration was 20.9 ± 11.6 min regardless of summer or winter. In addition, turtles sporadically performed deep dives, including the deepest dive (>340 m) ever recorded for this species, during winter. These results suggest that juveniles remained active and possibly foraging in oceanic habitats throughout the winter rather than adopting the quiescent overwintering strategy (i.e. undertaking prolonged dives lasting >300 min) previously reported in adult females.

Diving behaviour of benthic feeding Black Guillemots

Capsule Dive behaviour in Black Guillemots Cepphus grylle was close to that predicted for a benthic forager by allometry based on body mass.Aims To report the diving behaviour of Black Guillemots in Northern Ireland.Methods A time-depth-recorders and GPS logger were deployed on four chick-rearing breeding Black Guillemots.Results Dive shape implied most dives were benthic with a small number at the start of each bout associated with searching. Diving only occurred during daylight hours, but dive depth was unrelated to light availability outside of the twilight periods. Dive durations (max = 90 s; mean = 54 s) were shorter and dive depths (max = 15 m; mean = 9 m) were shallower than recorded for guillemots elsewhere. The birds dived a maximum of 1.8 km from the colony.Conclusions Black Guillemots' dive duration was similar to the value predicted from allometry, and is therefore likely representative of this species. Bathymetry likely influences the dive behaviour of this benthic-feeding species because most dives were U-shaped and dive depths were shallow, which is typical for the relatively shallow water where the birds were observed foraging.

Longest recorded underwater dive by a polar bear

The maximum dive duration for a wild polar bear (Ursus maritimus) of any age is unknown, and opportunities to document long dives by undisturbed bears are rare. We describe the longest dive reported to date, by a wild undisturbed adult male polar bear. This dive was made during an aquatic stalk of three bearded seals (Erignathus barbatus) lying several meters from each other at the edge of an annual ice floe. The bear dove for a total duration of 3 min 10 s and swam 45–50 m without surfacing to breathe or to reorient itself to the locations of the seals. The duration of this dive may be approaching its maximum capability. Polar bears diverged from brown bears (Ursus arctos) about 4–500,000 years ago, which is recent in evolutionary terms. Thus, it is possible that the ability to hold its breath for so long may indicate the initial development of a significant adaptation for living and hunting in its marine environment. However, increased diving ability cannot evolve rapidly enough to compensate for the increasing difficulty of hunting seals because of the rapidly declining availability of sea ice during the open-water period resulting from climate warming.

Comparative seabird diving physiology: first measures of haematological parameters and oxygen stores in three New Zealand Procellariiformes

Within breath-hold diving endotherms, procellariiform seabirds present an intriguing anomaly as they regularly dive to depths not predicted by allometric models. How this is achieved is not known as even basic measures of physiological diving capacity have not been undertaken in this group. To remedy this we combined time depth recorder (TDR) measurements of dive behaviour with haematology and oxygen store estimates for 3 procellariiform species (common diving petrels Pelecanoides urinatrix urinatrix; grey-faced petrels Pterodroma macro ptera gouldi; and sooty shearwaters Puffinus griseus) during their incubation phase. Among species, we found distinct differences in dive depth (average and maximal), dive duration and dives h �1 , with sooty shearwaters diving deeper and for longer than grey-faced petrels and common diving petrels. Conversely, common diving petrels dove much more frequently, albeit to shallow depths, whereas grey-faced petrels rarely dived whatsoever. Such differences in dive behaviour were reflected in haematological parameters, with sooty shearwaters having higher red blood cell counts and haematocrit (Hct) values compared to common diving and grey-faced petrels; whereas common diving petrels had significantly lower Hct but possessed higher haemoglobin concentrations per cell and greater respiratory oxygen stores than both sooty shearwaters and grey-faced petrels. Such results provide the first insights into the physiological traits underpinning procellariiform dive behaviour, and confirm the trend for deep-diving seabirds to have proportionally lower blood and respiratory oxygen stores than shallow divers.

Fine-scale foraging ecology of leatherback turtles

Remote tracking of migratory species and statistical modeling of behaviors have enabled identification of areas that are of high ecological value to these widely distributed taxa. However, direct observations at fine spatio-temporal scales are often needed to correctly interpret behaviors. In this study, we combined GPS-derived locations and archival dive records (1 sec sampling rate) with animal-borne video footage from foraging leatherback turtles (Dermochelys coriacea) in Nova Scotia, Canada (Northwest Atlantic Ocean) to generate the most highly detailed description of natural leatherback behavior presented to date. Turtles traveled shorter distances at slower rates and increased diving rates in areas of high prey abundance, which resulted in higher prey capture rates. Increased foraging effort (e.g., dive rate, dive duration, prey handling time, number of bites) was not associated with increased time at the surface breathing to replenish oxygen stores. Instead, leatherbacks generally performed short, shallow dives in the photic zone to or above the thermocline, where they disproportionately captured prey at bottoms of dives and during ascents. This foraging strategy supports visual prey detection, allows leatherbacks to exploit physically structured prey at relatively shallow depths (typically <30m), and increases time turtles spend in warmer water temperatures, thus optimizing net energy acquisition. Our results demonstrate that leatherbacks appear to be continuously foraging during daylight hours while in continental shelf waters of Nova Scotia, and that leatherback foraging behavior is driven by prey availability, not by whether or not a turtle is in a resource patch characterized by a particular size or prey density. Our study demonstrates the fundamental importance of obtaining field-based, direct observations of true behaviors at fine spatial and temporal scales to enhance our efforts to both study and manage migratory species.