Using platforms of opportunity to determine the occurrence and group characteristics of orca (Orcinus orca) in the Hauraki Gulf, New Zealand

Abstract

We present the first fine-scale data relating to the occurrence and group characteristics for killer whales (Orcinus orca) in the Hauraki Gulf, New Zealand, as observed from a platform of opportunity (PoP). Group size and composition were examined in relation to water depth and sea surface temperature (SST). From 2000 to 2010, 119 orca encounters were recorded, involving 1 to 18 animals. The encounter rate varied seasonally, being highest in austral spring and lowest in summer. Water depth in which whales were observed was significantly affected by group composition. Sixty-seven percent of groups contained immature animals. Group size was highly skewed towards smaller groups comprising two animals. While this study illustrates that PoPs can be used to indicate the occurrence and group characteristics of highly mobile social species, biases clearly exist. Through identifying such inaccuracies, we present recommendations on how future data should be collected to minimise error and improve datasets for scientific use.