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Integrating multiple technologies to understand the foraging behaviour of Hawaiian monk seals

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ABSTRACT

The objective of this research was to investigate and describe the foraging behaviour of monk seals in the main Hawaiian Islands. Specifically, our goal was to identify a metric to classify foraging behaviour from telemetry instruments. We deployed accelerometers, seal-mounted cameras and GPS tags on six monk seals during 2012–2014 on the islands of Molokai, Kauai and Oahu. We used pitch, calculated from the accelerometer, to identify search events and thus classify foraging dives. A search event and consequent ‘foraging dive’ occurred when the pitch was greater than or equal to 70° at a depth less than or equal to −3 m. By integrating data from the accelerometers with video and GPS, we were able to ground-truth this classification method and identify environmental variables associated with each foraging dive. We used Bayesian logistic regression to identify the variables that influenced search events. Dive depth, body motion (mean overall dynamic body acceleration during the dive) and proximity to the sea floor were the best predictors of search events for these seals. Search events typically occurred on long, deep dives, with more time spent at the bottom (more than 50% bottom time). We can now identify where monk seals are foraging in the main Hawaiian Islands (MHI) and what covariates influence foraging behaviour in this region. This increased understanding will inform management strategies and supplement outreach and recovery efforts.

No MeSH data available.


Capture locations of Hawaiian Monk Seals in the main Hawaiian Islands. Three seals were instrumented on Oahu, nine on Molokai and four on Kauai.
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RSOS160703F1: Capture locations of Hawaiian Monk Seals in the main Hawaiian Islands. Three seals were instrumented on Oahu, nine on Molokai and four on Kauai.

Mentions: We captured sub-adult and adult seals on Oahu (n = 3), Molokai (n = 9) and Kauai (n = 4) (figure 1) following the methods of Baker & Johanos [29]. Due to capture guidelines that restrict the capture of pregnant or potentially pregnant females [29], we only instrumented one female during the first year of fieldwork. For the remainder of the study, therefore, we targeted sub-adult and adult males. Seals were captured on the beach with a hoop net and sedated with Diazepam (5 mg ml−1 at 0.1–0.25 mg kg−1 IV). The instrument package included a National Geographic Crittercam, Loggerhead Instruments Open Tag (3-axis accelerometer, magnetometer, gyroscope and pressure sensor), a Sea Mammal Research Unit GSM phone tag and a VHF transmitter (table 1). We glued the package to the pelage of the animal, along the dorsal midline between the shoulder blades using 10 min epoxy (Devcon, Danvers, MA, USA) (figure 2). GPS tags were programmed to record a position estimate every 20 min unless the seal was underwater or hauled out on land [25]; the Open Tags recorded continuously on all sensors at 100 Hz until the battery was exhausted (approximately 4–6 days). We programmed Crittercams to record for 30 min of every 2 h cycle between the hours of 8.00 and 17.00 (Hawaii Standard Time), when the camera was wet. Four to 6 days after deployment, we used the GPS and VHF tags to find and recapture the seals to recover the Crittercam and Open Tag; the GPS tag was left on the animal to collect long-term movement and summary dive data for an additional 3–6 months.Figure 1.


Integrating multiple technologies to understand the foraging behaviour of Hawaiian monk seals
Capture locations of Hawaiian Monk Seals in the main Hawaiian Islands. Three seals were instrumented on Oahu, nine on Molokai and four on Kauai.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383815&req=5

RSOS160703F1: Capture locations of Hawaiian Monk Seals in the main Hawaiian Islands. Three seals were instrumented on Oahu, nine on Molokai and four on Kauai.
Mentions: We captured sub-adult and adult seals on Oahu (n = 3), Molokai (n = 9) and Kauai (n = 4) (figure 1) following the methods of Baker & Johanos [29]. Due to capture guidelines that restrict the capture of pregnant or potentially pregnant females [29], we only instrumented one female during the first year of fieldwork. For the remainder of the study, therefore, we targeted sub-adult and adult males. Seals were captured on the beach with a hoop net and sedated with Diazepam (5 mg ml−1 at 0.1–0.25 mg kg−1 IV). The instrument package included a National Geographic Crittercam, Loggerhead Instruments Open Tag (3-axis accelerometer, magnetometer, gyroscope and pressure sensor), a Sea Mammal Research Unit GSM phone tag and a VHF transmitter (table 1). We glued the package to the pelage of the animal, along the dorsal midline between the shoulder blades using 10 min epoxy (Devcon, Danvers, MA, USA) (figure 2). GPS tags were programmed to record a position estimate every 20 min unless the seal was underwater or hauled out on land [25]; the Open Tags recorded continuously on all sensors at 100 Hz until the battery was exhausted (approximately 4–6 days). We programmed Crittercams to record for 30 min of every 2 h cycle between the hours of 8.00 and 17.00 (Hawaii Standard Time), when the camera was wet. Four to 6 days after deployment, we used the GPS and VHF tags to find and recapture the seals to recover the Crittercam and Open Tag; the GPS tag was left on the animal to collect long-term movement and summary dive data for an additional 3–6 months.Figure 1.

View Article: PubMed Central - PubMed

ABSTRACT

The objective of this research was to investigate and describe the foraging behaviour of monk seals in the main Hawaiian Islands. Specifically, our goal was to identify a metric to classify foraging behaviour from telemetry instruments. We deployed accelerometers, seal-mounted cameras and GPS tags on six monk seals during 2012–2014 on the islands of Molokai, Kauai and Oahu. We used pitch, calculated from the accelerometer, to identify search events and thus classify foraging dives. A search event and consequent ‘foraging dive’ occurred when the pitch was greater than or equal to 70° at a depth less than or equal to −3 m. By integrating data from the accelerometers with video and GPS, we were able to ground-truth this classification method and identify environmental variables associated with each foraging dive. We used Bayesian logistic regression to identify the variables that influenced search events. Dive depth, body motion (mean overall dynamic body acceleration during the dive) and proximity to the sea floor were the best predictors of search events for these seals. Search events typically occurred on long, deep dives, with more time spent at the bottom (more than 50% bottom time). We can now identify where monk seals are foraging in the main Hawaiian Islands (MHI) and what covariates influence foraging behaviour in this region. This increased understanding will inform management strategies and supplement outreach and recovery efforts.

No MeSH data available.