DOI: 10.5061/dryad.rr4xgxd79
title: Summer circumpolar acoustic occurrence and call rates of Ross (Ommatophoca rossii) and leopard (Hydrurga leptonyx) seals in the Southern Ocean

description: Two of the Antarctic pack ice seals, Ross, Ommatophoca rossii, and
 leopard, Hydrurga leptonyx, seals, are extremely dificult to study via
 traditional visual survey techniques, yet are ideal for an acoustic survey
 as they are highly vociferous and produce an array of underwater sounds
 during the austral summer. To determine their acoustic occurrence in the
 Antarctic pack ice, we use their calls, detected within 680 acoustic
 recordings made between 1999 and 2009 as part of two multinational
 programmes. Siren calls of Ross seals were detected mainly in January, and
 9.88 calls per minute from low siren calls was the highest call rate for
 this species. High numbers of Ross seal calls were detected close to the
 ice edge in areas between 0° and 20° E and 60° and 130° E, suggesting
 these are important summer habitats. Leopard seal calls were detected
 mainly in December and January, and December had the highest percentage of
 calls. Call rate of 11.93 calls per minute from low double trills was the
 highest call rate for leopard seals. Leopard seal calls were detected
 throughout the Southern Ocean with more calls detected throughout the pack
 ice. There was little spatio-temporal overlap in call occurrence of Ross
 and leopard seals, but both species were more vocally active during the
 day. Longitude and latitude were the most important predictors of Ross
 seal occurrence, and month of the year highly predicted leopard seal
 occurrence. This is the irst study to examine the circumpolar acoustic
 occurrence of Ross and leopard seals in the Southern Ocean pack ice.
description: The acoustic dataset from the SCAR-APIS Programme consisted of
 112 underwater passive acoustic recordings made remotely at fixed points
 using sonobuoys [Sparton Electronics AN/SSQ-57A, mean sensitivity: −
 155.20 (range: − 158.50 to − 151.00) dB re 1 V μPa−1)] in the Southern
 Ocean from 4 December 1999 to 12 January 2000 within the pack ice between
 64° 31′ S; 62° 42′ E and 67° 17′ S; 149° 31′ E (Rogers et al. 2013; Fig.
 1). Sonobuoys sampled over 10 to 22,000 Hz and had omni-directional
 hydrophone that had been deployed to a depth of 18 m below the water’s
 surface. Signals were received on the survey platform, the mast of the RSV
 Aurora Australis, using two, 9-element custom-built stainless steel Yaggi
 antennas (YH09, RF Industries Pty Ltd) with a series of AR2001 receivers
 (AOR Ltd, AR 2001). Antennas were secured at a height of 30 m above the
 sea level. The ship was on survey mode during sonobuoy deployment and kept
 steaming through the sea ice conducting visual search for seals until the
 radio signal was lost (Rogers et al. 2013). No anti-aliasing ilters were
 used during data collection. The acoustic signal was recorded using a Sony
 Digital Audio Tape recorder (DAT TCD-D8) with a frequency bandwidth of 10
 and 22,000 Hz ± 3 dB. Recordings were randomly made throughout the day and
 were from at least 30-min to 2 h in duration depending on the amount of
 time the ship remained within range of detecting the signal from
 sonobuoys. For analyses of acoustic data for calls of
 Ross and leopard seals performed on SCAR-APIS data, the number of calls
 within at least 30-min recording period was counted by a manual observer
 using Signal 3.1 (Engineering Design, Belmont, USA) and SpectraPRO 3.32
 (Sound Technology Inc., USA). The first 10-15 min of the SCAR-APIS
 recordings was ignored, as ship noise (propeller cavitation) masked the
 signal.
description: Shabangu FW, Rogers TL (2021) Summer circumpolar
 acoustic occurrence and call rates of Ross, <i>Ommatophoca
 rossii</i>, and leopard, <i>Hydrurga leptonyx</i>, seals
 in the Southern Ocean. Polar Biology https://doi.org/10.1007/s0030
 0-020-02795-z Rogers TL, Ciaglia MB,
 Klinck H, Southwell C (2013) Density can be misleading for low-density
 species: Beneits of passive acoustic monitoring. PLoS ONE 8(1):e52542.
 https://doi.org/10.1371/journ al.pone.0052542