[1] Natl Inst Water & Atmospher Res, Hamilton, New Zealand
[2] Waikato Univ, Sch Sci, Hamilton, New Zealand
[3] Univ Auckland, Inst Marine Sci, Waipapa Taumata Rau, Auckland, New Zealand
[4] Oregon State Univ, Marine Mammal Inst, Dept Fisheries Wildlife & Conservat Sci, Corvallis, OR USA
[5] Natl Inst Water & Atmospher Res, Wellington, New Zealand
[6] Univ Auckland, Sch Biol Sci, Waipapa Taumata Rau, Auckland, New Zealand