Overlooking a potential hotspot at Great Barrier Island for the nationally endangered bottlenose dolphin of New Zealand

Abstract

Conservation initiatives are typically constrained by economic circumstances, a factor certainly true for marine mammal conservation in New Zealand. Most research in this field has been conducted following concerns over anthropogenic impacts on populations and has therefore been funded and/or driven by stakeholder interest. Bottlenose dolphins Tursiops truncatus are classified as 'Nationally Endangered' in New Zealand waters. Here, we present the first study on occurrence, site fidelity and abundance of this species off Great Barrier Island (GBI), a previously overlooked region within the home range of the North Island population. Dedicated boat-based photo-identification surveys were conducted monthly from 2011−2013, resulting in 1412 sighting records of 154 individuals. Dolphins were recorded during all months of the year, with a higher probability of encounter in deeper waters during summer and shallower waters during winter and spring. Group sizes (median = 35, mean = 36) were higher than previously reported for this population in other regions. Individual re-sighting patterns were variable; however, overall site fidelity was high (mean monthly sighting rate = 0.33). A Robust Design approach resulted in seasonal fluctuations in abundance and temporary emigration. Based on a super-population estimate, 171 dolphins (CI = 162−180) visited the area during 2011−2013. Our data suggest that GBI is a potential hotspot for bottlenose dolphins of the North Island population rather than a corridor to reach other destinations. We highlight the need for researchers, managers and funding agencies to consider the entire range of a population when conducting or funding research.

Occurrence, site fidelity, and associations of oceanic common bottlenose dolphins (Tursiops truncatus) off northeastern New Zealand

“…Our results further show that the home ranges of the oceanic and coastal ecotypes overlap, with over a third of the encounters described in this study observed within 5 km from shore and in areas that are routinely used by the coastal ecotype, e.g., BOI (Constantine, 2002;Tezanos-Pinto et al, 2013) and HG (Berghan et al, 2008;Dwyer et al, 2014). Our findings reveal that, at least in those areas, some interactions between the two ecotypes occur.…”

“…Overall, the total number of photo-identified individuals and the results on discovery rates suggest that the oceanic bottlenose dolphin population is likely significantly larger than what is documented herein. This contrasts with the coastal bottlenose dolphins, for which large numbers of previously unidentified individuals are not typically found after up to 20 years of observations (e.g., Constantine, 2002;Dwyer et al, 2014;Tezanos-Pinto et al, 2013) and corresponds with a much smaller estimated population size of~250 mature individuals for the northeastern North Island area (Baker et al, 2019).…”

High calf mortality in bottlenose dolphins in the Bay of Islands, New Zealand–a local unit in decline

“…) and studies showing new areas with high dolphin encounter rates that were previously under‐reported (Berghan et al . ; Dwyer et al ., ). We also recommend improved documentation of stranded and beachcast dolphins and retrieving of carcasses to determine causes of mortality.…”

“…The decline in abundance (Tezanos-Pinto et al 2013) and high calf mortality are of concern and highlight the need for continued monitoring of this population. Further, other areas along the range of the northeastern North Island bottlenose dolphin population should be monitored given the shift in home ranges observed in the Bay of Islands (Tezanos-Pinto 2009, Hartel et al 2014) and studies showing new areas with high dolphin encounter rates that were previously under-reported (Berghan et al 2008;Dwyer et al, 2014b). We also recommend improved documentation of stranded and beachcast dolphins and retrieving of carcasses to determine causes of mortality.…”

The influence of cooperative foraging with fishermen on the dynamics of a bottlenose dolphin population

“…), which may reveal changes in environmental conditions or seasonal behavioral patterns (Dwyer et al . ), reducing the bias in the estimated survival parameters (Peñaloza et al . ).…”