Search

Understanding how animals use the space in which they are distributed is important for guiding management decisions in conservation, especially where human disturbance can be spatially managed. Here we applied distribution modelling to examine common dolphin (Delphinus sp.) habitat use in the Hauraki Gulf (36°S, 175°E), New Zealand. Given the known importance of the area for foraging and nursing, we assessed which variables affect Delphinus occurrence based on generalised additive models (GAMs), and modelled probability of encounter. Behavioural information was included to assess habitat use by feeding and nursing groups and determine whether persistent hotspots for such activities could be identified and meaningfully used as a spatial management tool. Using data collected from dedicated boat surveys during 2010–2012, depth and sea surface temperature (SST) were frequently identified as important variables. Overall, seasonal predictive occurrence maps for the larger population resembled predictive maps of feeding groups more than nursery groups, suggesting prey availability has important implications for the distribution of Delphinus in this region. In this case, static spatial exclusions would not be the best management option as the core areas of use identified for these activities were large and shifted temporally. It appears that at the scale examined, most of the Hauraki Gulf is important for feeding and nursing rather than specific smaller regions being used for these functions. In cases where static management is not the optimal tool, as suggested here for a highly mobile species, a dynamic approach requires more than a boundary line on a map. [ABSTRACT FROM AUTHOR]

Knowledge about the maturity status of specimens included in evolutionary, taxonomic or life history investigations is fundamentally important. This study investigated the use of the degree of cranial suture fusion, the developmental status of cranial bones, and the degree of tooth wear as indicators for cranial maturity status in Delphinus sp. from New Zealand waters. In total, 15 sutures, one joint and three nonmetric characters were assessed on 66 skulls obtained from stranded and bycaught individuals sampled between 1932 and 2011. A suture index (SI) was computed based on 10 sutures, in which degree of fusion was correlated with age and the three misclassification indices (MI), calculated for a given suture, were <50%. In addition to these, five premaxilla-maxilla fusion and seven tooth wear categories were assessed. Results suggest that New Zealand Delphinus sp. skulls should be regarded as cranially mature if at least two of the following criteria are met: (1) individuals assessed as sexually mature, (2) aged ⩾ 11 yr, (3) SI ⩾ 8, and (4) premaxillamaxilla fusion ⩾ 75% of the length of the dorsal side of the rostrum. Presence of any number of rostral teeth worn to the gum line provided further evidence for cranial maturity. [ABSTRACT FROM AUTHOR]

New Zealand is the southernmost limit of the common dolphin's (genus Delphinus) distribution in the Pacific Ocean. In this area, common dolphins occur in both coastal and oceanic habitats, exhibit seasonal and resident occurrence, and present high morphological variability. Here we investigated the population structure and the taxonomic identity of common dolphins ( Delphinus sp.) within New Zealand waters using 14 microsatellite loci, 577 bp of the mt DNA control region, and 1,120 bp of the mt DNA cytochrome b gene across 90 individuals. We found high genetic variability and evidence of population expansion. Phylogenetic analyses conducted to clarify the taxonomic status of New Zealand common dolphins did not show any clustering reflecting geographic origin or morphotypes. The microsatellite analysis showed genetic differentiation between Coastal and Oceanic putative populations, while mt DNA revealed significant genetic differentiation only between the Hauraki Gulf and other putative groups. Our results suggest that differences in habitat choice and possible female site fidelity may play a role in shaping population structure of New Zealand common dolphins. [ABSTRACT FROM AUTHOR]

While coastal cetaceans can become habituated to watercraft, that may not prevent their injury or mortality as a consequence of vessel strike. Here we report a case of a likely collision between a Common Dolphin Delphinus sp. and a recreational vessel in the Hauraki Gulf, New Zealand. Injuries sustained by the immature male dolphin were fatal. Recovery and subsequent post-mortem of the carcass revealed a transection of the spinal cord, with the vertebral column sustaining fractures between L17 and Cd7 and between Cd3 and Cd8 of the neural and transverse processes, respectively. Cd4 likely received the brunt of the impact given the vertebral body and epiphyses were also fractured. Paralysis of the lower truck and associated extensive internal injuries resulted in a live stranding and subsequent mortality. Injuries sustained were consistent of those of blunt force trauma, a consequence of an impact caused by a collision with a small watercraft, most likely a jet-ski. This incident reinforces the need for continued public education concerning safe water practices around marine mammals, which are protected under the New Zealand Marine Mammals Protection Act 1978 and Marine Mammals Protection Regulations 1992. [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]