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.

Analysis of occurrence patterns and biological factors of cetaceans based on long‐term and fine‐scale data from platforms of opportunity: Madeira Island as a case study

“…The present study supports previous literature (e.g. Arcangeli et al, ; Hupman et al, ) by demonstrating that despite their limitations, platforms of opportunity, and specifically whale‐watching vessels, constitute highly cost‐effective tools and valuable vehicles that can provide robust data sets. The similarity of the values presented in this study to those from dedicated surveys for the proportion of calves, group sizes, and inter‐specific relationships in Globicephala macrorhynchus and Tursiops truncatus in Madeira (Alves, ; Dinis, Alves, et al, ) supports the reliability of the results obtained from platforms of opportunity.…”

“…In order to minimize such bias, studies from this type of platform commonly use the number of sightings per total surveys conducted (e.g. Hupman et al, ) or per surveyed day (e.g. Pérez‐Vallazza et al, ).…”

“…Inter-specific relationships were considered as when two or more species were observed in close association and exhibiting similar behaviour during the entire duration of the encounter. were detected, the group with the largest size was retained, as it is probably the most accurate representation (Hupman et al, 2015). In addition, to minimize bias, this analysis considered only the sightings collected by the most experienced observers (all authors of the present study, who have extensive experience in marine mammal identification), and the ones collected at a close distance to the animals.…”

“…Prieto, Tobeña, & Silva, 2017;Silva et al, 2014;Tobeña et al, 2016) and whalewatching boats with targeted observational efforts (e.g. Hauser, VanBlaricom, Holmes, & Osborne, 2006;Hupman, Visser, Martinez, & Stockin, 2015;Stockin, Binedell, Wiseman, Brunron, & Orams, 2009). Generally, all types are suboptimal and have inherent procedural limitations (Moura et al, 2012), but can provide large data sets of fine-scale data covering long-term periods that would otherwise be unavailable.…”

“…Generally, all types are suboptimal and have inherent procedural limitations (Moura et al, 2012), but can provide large data sets of fine-scale data covering long-term periods that would otherwise be unavailable. Moreover, the collection of sighting information from platforms of opportunity may be the first step in providing a broader overview of cetacean diversity and occurrence, and therefore in reporting an area of interest that could be further investigated using a more refined survey methodology (Evans & Hammond, 2004;Hupman et al, 2015;Pérez-Vallazza, Álvarez-Vázquez, Cardona, Pintado, & Hernández-Brito, 2008).…”