Surfacers change their dive tactics depending on the aim of the dive: evidence from simultaneous measurements of breaths and energy expenditure

Okuyama, Junichi; Tabata, Runa; Nakajima, Kana; Arai, Nobuaki; Kobayashi, Masato; Kagawa, Shiro

doi:10.1098/rspb.2014.0040

Cited by 17 publications

(33 citation statements)

References 47 publications

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“…Rather, leatherbacks are apparently able to maintain high levels of apneic diving and prey handling activity with short surface intervals and fewer breaths to exploit areas of high prey availability. Our results also corroborate recent findings that green turtles (Chelonia mydas) modulate surface durations and number of breaths per surface interval during several consecutive foraging dive cycles to maintain aerobic activity (Okuyama et al, 2014). This pattern of shallow, frequent dives provides further empirical support for the notion that leatherback prey distributions in shelf waters off Nova Scotia appear to be physically structured by local water mass conditions-i.e., at or above the main thermocline (Hamelin et al, 2014)-and that prey are not primarily concentrated at the surface (only 4% of prey captures; Table 3, Figure 10), unlike what has been reported in some other leatherback foraging areas (Houghton et al, 2006).…”

Section: Discussionsupporting

confidence: 80%

Fine-scale foraging ecology of leatherback turtles

Wallace

Zolkewitz²,

James

2015

Front. Ecol. Evol.

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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 s sampling rate) with animal-borne video footage from foraging leatherback turtles (Dermochelys coriacea) off 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 <30 m), 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 off 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 particular 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.

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Section: Discussionsupporting

confidence: 80%

Fine-scale foraging ecology of leatherback turtles

Wallace

Zolkewitz²,

James

2015

Front. Ecol. Evol.

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“…The duration of a turtle's dive is dependent on both the size of a breath taken at the surface and the energy expenditure during a dive. The size of the breath can also influence turtle dive depth as it impacts the depth of neutral buoyancy (Hays et al 2004); turtles modulate the size of their breath based on the intent of the dive (Okuyama et al 2014). Accordingly, we modeled the effect of dive depth and activity level (i.e.…”

Section: Discussionmentioning

confidence: 99%

“…These loggers measure multi-dimensional acceleration, providing precise information on an animal's movements and body orientation, as well as depth and temperature. When combined, these complementary data can reveal behaviors, activity level, and energy expenditure , Okuyama et al 2014. Accelerometers have been proven effective in studies on sea turtle feeding (Okuyama et al 2010), respiratory behavior (Okuyama et al 2014), and for quantifying diving behavior (Fossette et al 2010), swimming speeds, and rates of energy expenditure (Yasuda & Arai 2009, Halsey et al 2011, Okuyama et al 2012, 2014.…”

Section: Introductionmentioning

confidence: 99%

Trading shallow safety for deep sleep: juvenile green turtles select deeper resting sites as they grow

Hart¹,

White²,

Iverson³

et al. 2016

Endang. Species. Res.

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To better protect endangered green sea turtles Chelonia mydas, a more thorough understanding of the behaviors of each life stage is needed. Although dive profile analyses obtained using time-depth loggers have provided some insights into habitat use, recent work has shown that more fine-scale monitoring of body movements is needed to elucidate physical activity patterns. We monitored 11 juvenile green sea turtles with tri-axial acceleration data loggers in their foraging grounds in Dry Tortugas National Park, Florida, USA, for periods ranging from 43 to 118 h (mean ± SD: 72.8 ± 27.3 h). Approximately half of the individuals (n = 5) remained in shallow (overall mean depth < 2 m) water throughout the experiment, whereas the remaining individuals (n = 6) made excursions to deeper (4 to 27 m) waters, often at night. Despite these differences in depth use, acceleration data revealed a consistent pattern of diurnal activity and nocturnal resting in most individuals. Nocturnal depth differences thus do not appear to represent differences in behavior, but rather different strategies to achieve the same behavior: rest. We calculated overall dynamic body acceleration (ODBA) to assess the relative energetic cost of each behavioral strategy in an attempt to explain the differences between them. Animals in deeper water experienced longer resting dives, more time resting per hour, and lower mean hourly ODBA. These results suggest that resting in deeper water provides energetic benefits that outweigh the costs of transiting to deep water and a potential increased risk of predation.

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“…Hence, these transmitters provided data for much longer periods than conventional sensor transmitters would have done. Datastorage tags (also termed archival tags), which store data in a memory, are widely used to understand behaviour and movement of aquatic animals, for example sea turtles [32] and penguins [33]. However, the tag must normally be recovered for data retrieval, which often may be difficult for free-swimming fish [34], especially at sea and in other large water bodies.…”

Section: Discussionmentioning

confidence: 99%

In situ measurement of salinity during seaward migration of Atlantic salmon post-smolts using acoustic transmitters with data-storage capabilities and conventional acoustic transmitters

et al. 2017

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Background: Development of miniature acoustic transmitters and data-storage tags has provided new insights into ecology of free-ranging aquatic animals. In this study, we used a data-storage-type and a conventional acoustic transmitter, both equipped with a salinity sensor, to measure the in situ salinity experienced by Atlantic salmon postsmolts during the first phase of their marine migration in a Norwegian fjord. The data-storage transmitter conveyed stored salinity data accumulated over a period of up to 27 h prior to moving within the range of a receiver, while the conventional transmitter conveyed only real-time salinity data. Five post-smolts tagged with a conventional transmitter were manually tracked from a boat, and 15 post-smolts tagged with the data-storage transmitter were monitored by six transects consisting of 29 stationary receivers deployed from the river and throughout the fjord.Results: All tagged post-smolts primarily showed rapid seaward movements. They occasionally stayed in water with salinity below 20.0 psu in the inner part of the fjord, most likely because they were swimming close to the surface, where the salinity was low due to freshwater supply from the river. In the outer fjord, where full-salinity sea water (26.0-32.0 psu) was recorded in the entire water column, half (3 of 6) of the recorded fish still experienced low salinities (<20.0 psu) for periods between 2.25 and 54 h. Conclusion:Both types of salinity transmitters provided data on ambient salinity of the post-smolts during the seaward movement. In the outer fjord, the post-smolts likely visited one or several river mouths. It is not known whether this behaviour is normal for Atlantic salmon post-smolts during migration, but it might be advantageous in terms of reducing infestation risk from salmon lice, which have low survival in low salinities. The data-storage transmitters provided data on the ambient salinity history of the tagged fish, even when the fish were outside the detection range of receivers. By using this type of transmitters, we were able to collect salinity data during a four times longer period than with conventional transmitters.

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Surfacers change their dive tactics depending on the aim of the dive: evidence from simultaneous measurements of breaths and energy expenditure

Cited by 17 publications

References 47 publications

Fine-scale foraging ecology of leatherback turtles

Fine-scale foraging ecology of leatherback turtles

Trading shallow safety for deep sleep: juvenile green turtles select deeper resting sites as they grow

In situ measurement of salinity during seaward migration of Atlantic salmon post-smolts using acoustic transmitters with data-storage capabilities and conventional acoustic transmitters

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