Behavior of free-ranging common dolphins (Delphinussp.) in the Hauraki Gulf, New Zealand

Abstract

Here we present the first data describing the behavior of common dolphins (Delphinus sp.) in the Hauraki Gulf, New Zealand. Activity budgets are used to assess the effects of diel, season, depth, sea surface temperature, group size, and composition on dolphin behavior. Additionally, the presence/absence of Bryde's whale (Balaenoptera brydei) and Australasian gannet (Morus serrator) is examined in relation to dolphin behavior. Behavioral data were collected from 686 independent dolphin groups during boat-based surveys conducted between February 2002 and January 2005. Foraging (46.7%) and social (7.2%) were the most and least frequently observed 283 284 MARINE MAMMAL SCIENCE, VOL. 25, NO. 2, 2009 behaviors, respectively. Travel (28.9%), mill (9.5%), and rest (7.7%) accounted for the remainder of the activity budget. Behavior varied seasonally, with the highest proportion of foraging and resting groups observed during the spring and autumn, respectively. Behavior also varied with water depth, with foraging animals observed in the deepest and resting groups recorded in the shallowest regions of the Hauraki Gulf. A correlation between group size and behavior was evident, although behavior did not vary with the composition of dolphin groups. Resting, milling, and socializing animals were more frequently observed in smaller group sizes. Foraging behavior was prevalent in both small and large group sizes, suggesting foraging plasticity exists within this population. Behavior differed between single-and multispecies groups, with foraging more frequent in multispecies groups. Resting, milling, or socializing was rarely observed in the presence of any associated species, indicating the primary mechanism for association is likely prey related.

Distribution and Population Demographics of Common Dolphins (<I>Delphinus delphis</I>) in the Gulf St. Vincent, South Australia

“…Observations of seabirds were used in addition to surface activity of dolphins (i.e., jumping and splashing) to detect dolphin schools (Stockin et al, 2008b). Observers could view approximately 250 m to either side of the boat, resulting in the survey track width of approximately 0.5 km.…”

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

“…Likewise, the use of opportunistic platforms for data collection has been increasingly recognised as providing an alternative means for scientific data collection on cetaceans (e.g. Williams et al 2006;Ingram et al 2007;Macleod et al 2009;Stockin et al 2009;de Boer 2010;Wiseman et al 2011;Eyre & Frizell 2012;Isojunno et al 2012;Palacios et al 2012;Davidson et al 2014). Such platforms can include large shipping vessels (Williams et al 2006), ferries (Kiszka et al 2007;Macleod et al 2009;Arcangeli et al 2013), cruise ships (Compton et al 2007;Palacios et al 2012) and commercial tour vessels (Hauser et al 2006;Perez-Vallazza et al 2008;Azzellino et al 2008;Stockin et al 2009;Visser et al 2010;Wiseman et al 2011;Davidson et al 2014).…”

Using non-systematic surveys to investigate effects of regional climate variability on Australasian gannets in the Hauraki Gulf, New Zealand

“…1); and in water depths N10 m. Data presented here represent all months of each year with the exception of August-September 2002 and January-May 2007, when the vessel was on dry dock. While surveys were non-systematic, survey routes selected were based on prevailing weather and sea conditions, with an attempt made to cover regions not previously surveyed within that month in on order to facilitate on-board research focusing on common dolphin (Delphinus sp., Stockin et al, 2008bStockin et al, , 2009) and Bryde's whales (Balaenoptera edeni, Wiseman et al, 2011).…”