New Zealand sea lion movement and dive data - Campbell Island/Motu Ihupuku

Brief description

We hypothesised that New Zealand sea lions from Campbell Island/Motu Ihupuku of various sex and age classes would utilise the water column differently due to differing physiological constraints and therefore have different accessibility to prey resources. We tested whether sea lion diving behaviour varied in relation to (i) age and sex class, (ii) time of day and (iii) water depth. We also hypothesized that the proportion of benthic/pelagic diving, and consequently risk of fisheries interaction, would vary in relation to age and sex. Satellite telemetry tags were deployed on 25 NZSL from a range of age/sex classes recording dive depth, duration and location. Adult females and juveniles used inshore, benthic habitats, while sub-adult males also utilised benthic habitats, they predominantly used pelagic habitat at greater distances from the island. Adult females and juveniles exhibited shorter dives than the same age/sex classes at the Auckland Islands, suggesting a lower dive effort for these age/sex classes at Campbell Island.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: The study was conducted over three years (2012-2014) at Campbell Island/Motu/Ihupuku (52°32′S 169°8′E), 644 km south of New Zealand. The most recent estimate (2009/10) of Campbell Island pup production was 681 pups, approximately 27% of the total species pup production (Maloney et al., 2009, Maloney et al., 2012). In 2012 and 2013, juveniles and lactating adult female sea lions were captured manually at four different haul-out sites in Perseverance Harbour (Table 1) using a specialised hoop net (Research Nets Inc., Kirkland, USA and Fuhrman Diversified Inc., Seabrook, USA) and then sedated using 2-4% isoflurane in 4L of oxygen. Isoflurane was administered by facemask using a closed circuit portable anaesthetic gas machine (Stinger, Advanced Anaesthesia Specialists, North Ryde, Australia) (Gales and Mattlin, 1998). In 2014, lactating adult females and sub-adult males were captured by remote injection using a Telinject rifle using 3mL darts (Telinject Veterinarmedizinische Spezialgerate Gmbh, Romberberg, Germany). Sea lions were darted with Zoletil® 100 (Virbac (Australia) Pty. Ltd, Milperra, Australia) at dose of 1.4-2.0mg/kg (average of 1.8mg/kg based on estimated body weight) (Geschke and Chilvers, 2009) and supplemented with isoflurane in oxygen as above. The sea lions were equipped with satellite-linked SPLASH tags (Wildlife Computers, Redmond, United States), 138 x 38 x 20 mm, weight 145 g, which estimated locations using Argos satellites, and transmitted dive depth (± 0.5 m) and duration (s). The tags were attached onto the fur on the dorsal midline of the sea lion, posterior to the scapulae, with a fine layer of epoxy. Dive depth and duration information were recorded each second during dives. Each individual dive was binned into 14 user-defined data ranges over 6h summary periods prior to transmission, producing four summary histograms daily. The histogram periods ranged from, 1:00 to 6:59:59, 7:00 to 12:59:59, 13:00 to 18:59:59, 19:00 to 0:59:59 GMT. As the age of the individual NZSL was unknown, each sea lion was allocated to an age and sex class based on their standard length: females with standard lengths greater than or equal to 1.7 m were classified as adult, males greater than or equal to 1.7 m were classified as sub-adult (as no adult males were captured) (Childerhouse et al., 2010). All animals less than 1.7 m were classified as juveniles. Data were extracted using the WC-DAP program (Wildlife Computers Data Analysis Programs, V:3.0.326.0 09). Dives <10 m were not recorded for the 2014 cohort, and so these shallow dives were also excluded from the 2012 and 2013 datasets. Dives with durations <20 seconds were also discarded, as dives within these ranges were transiting or reflecting other surface behaviours. We used a Kalman filter (Crawl package in R, (Johnson, 2016, Johnson et al., 2008)) to obtain the best, estimated movement path of each sea lion, using two-hour time steps. One location every two hours corresponded to the overall mean daily rate of location estimates (12 per day) provided by Argos. Mean dive depth (m) and dive duration (s) and the proportion of dives within each depth/duration bin were estimated for each six-hourly period following (Lea et al., 2010). The filtered tracks provided three estimated locations for each six-hourly period, and for each of these the distance from Campbell Island/Motu Ihupuku was calculated, as was the bathymetry for each location. Bathymetry data were extracted from the National Oceanic and Atmospheric Administration (http://www.ngdc.noaa.gov/mgg/bathymetry/multibeam.html). Each six-hourly period was then categorised as inshore when maximum bathymetry was ≤200 m and offshore when maximum bathymetry >200 m. Please see https://doi.org/10.1002/ece3.10601 for references.

Notes

Credit
We acknowledge the major supporting institutions; Institute for Marine and Antarctic Studies (University of Tasmania), New Zealand Department of Conservation and the National Institute of Water and Atmospheric Research (grant number TMMA103 to Marine Wildlife Research). We also gratefully acknowledge the following people for their contributions, Simon Wotherspoon, Ben Arthur (analysis assistance), Jim Roberts, Dave Boyle, Penny Pascoe, Marcus Salton, and Henk Haazen (RV Tiama and crew). Animal Ethics permits were obtained from the National Institute of Water and Atmospheric Research to manipulate New Zealand sea lions at Campbell Island, with the proviso that all work would be undertaken with approval from the Department of Conservation and the NZ Department of Conservation permit (SO-32768-MAR) issued under the Marine Mammal Protection Act (1978).