Cetacean sighting records during a seismic survey in the New Caledonia Basin, Tasman Sea, 2015-6

Study Extent

New Caledonia Basin, Tasman Sea

Sampling

Cetacean surveys were completed in the southern sector of the New Caledonia Basin in the Tasman Sea to the west of New Zealand’s North Island. A total survey area coverage of 205,000 km2 was achieved, from ~200 km from New Zealand’s west coast (171.430609 E, 37.650542 S), extending 1,200 km onto the New Zealand extended continental shelf (163.322699 E, 32.446492 S). Water depth in the basin ranges from 2,000–3,500 m. The geophysical seismic survey vessel Hai Yang Shi You 718 was deployed to conduct a two-dimensional (2D) marine seismic survey between 18 December 2015 and 28 March 2016. As required under the 2013 New Zealand Code of Conduct for Minimising Acoustic Disturbance to Marine Mammals from Seismic Survey Operations, qualified and80trained marine mammal observers and passive acoustic monitoring (PAM) operators maintained a 24-hour monitoring program for cetaceans, this way serving as an opportunistic observational platform.

Method steps

1. Visual observations were completed by two MMOs in rotating shifts (one MMO on duty at any time) during daylight hours (dawn to dusk) from the bridge, bridge deck and wings of the seismic vessel, providing 360° visibility of the area at a height of 16.5 m above sea level. Observers predominantly scanned the area for cetaceans with the naked eye but used binoculars (7 x 50 magnification) to search the horizon and to determine species and estimate group size. When cetaceans were sighted, observers estimated the radial sighting distance to the animal(s) using the binoculars’ reticules following (Lerczak and Hobbs 1998). Time of day, GPS position, water depth and species were further recorded. Species determination included an indication of observer confidence ranging between ‘certain’ (100%), ‘probable’ (75%) and ‘possible’ (50%).
2. In addition to the visual observations, passive acoustic monitoring (PAM) was conducted continuously by two experienced PAM operators during the entire survey (one PAM operator on duty at any time). There were three complete Seiche PAM systems onboard. Each system comprised one hydrophone array, one tow cable, one deck cable plus all electronics such as computers and audio interfaces. The towed hydrophone array consisted of four hydrophones (two low-frequency and two high-frequency) towed using a 240 m long cable at a depth of 27 m, 20 m forward of the air guns. The AD/DA audio interfaces were RME Fireface 800 - sampling rates up to 192,000 Hz (Hertz) and NI USB-6251 - sampling rates up to 500,000 Hz. At the PAM workstation, an Intel i5-3570 CPU (central processing unit), 3.40 GHz (Gigahertz) with 8 GB (Gigabyte) RAM (random access memory) was running PAMGuard version 1.14.00 Beta. This was connected to the vessel’s global positioning system (GPS) via the National Marine Electronics Association (NMEA) serial port at a baud rate of 9,600. All three hydrophone arrays were tap tested and calibrated for depth while in transit to the survey area. The final PAMGuard configuration was set to detect endemic and vagrant cetaceans using high and low frequency click detectors with respective ranges of 0–24 kHz (kilohertz) and 10 Hz–250 kHz.

Cetaceans (whales and dolphins)

1. Cetartiodactyla
   rank: order

Tasman Sea