Fine scale distribution for a population of New Zealand's only endemic dolphin (Cephalorhynchus hectori) shows long‐term stability of coastal hotspots

Abstract

Marine mammal populations often have “hotspots” of distribution. Understanding what drives these is important for understanding relationships with habitat and evaluating exposure to threats. Few studies investigate the stability of hotspots, yet this information is vital in assessing their importance. In this study, over 9,000 sightings made during systematic surveys over 29 yr are used to establish the existence, locations, and temporal dynamics of hotspots for Hector's dolphins at Banks Peninsula, New Zealand. Sightings were divided into four seasons and three time periods to assess temporal trends in habitat use. Kernel density analysis was performed on sightings, weighted by survey effort. Density values at hotspots and reference areas were modeled according to season and time period using linear mixed models. Fifty percent of weighted sightings (n = 4,513) occurred within 21% of the study area. Hotspots had significantly higher densities during summer and these high‐density areas have remained consistent over time. Such consistency implies importance of these areas to the dolphins' ecology. This information adds to our knowledge of how this endangered species uses its habitat, suggests candidate areas for protection from threats, and provides a baseline for assessing habitat related impacts on Hector's dolphins at Banks Peninsula.© 2018 Society for Marine Mammalogy

Long-Term Demographic and Spatio-Temporal Trends of Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) Bycatch in Bather Protection Nets off KwaZulu-Natal, South Africa

“…The cross-correlation coefficients between neighboring beaches clustered into groups of 3-4 beaches (Figure 3) and may correspond to the "preferred areas" noted by Ross et al (1987Ross et al ( , 1989 and Cockcroft et al (1990Cockcroft et al ( , 1991, each extending over about 30-40 km of coastline. Ross et al (1987) speculated that these are home ranges of local/resident populations and recent research has shown that these areas may persist over long temporal scales (Brough et al, 2019). Cockcroft et al (1992) found that sightings of T. aduncus during aerial surveys along the KZN NC were not random, but corresponded to those identified during previous surveys conducted at the same time of year (May; Ross et al, 1987Ross et al, , 1989 and coincided with peaks of sightings made during boat surveys (Cockcroft et al, 1990).…”

Long‐term stability in core habitat of an endangered population of bottlenose dolphins (Tursiops truncatus): Implications for spatial management

“…These data were partitioned to investigate dolphin habitat use seasonally and over time (e.g. Brough, Rayment, Slooten, & Dawson, 2019). Seasons were defined as summer (December–February), autumn (March–May), winter (June–August), and spring (September–November).…”

“…Henderson, 2013). Fixed KDEs were generated in arcmap 10.6.1 (Environmental Systems Research Institute (ESRI), Redlands, CA) using the ‘Home Range With Barriers’ tool (MacLeod, 2013) to avoid interpolating location points across land features (Brough et al, 2019). KDEs produce a density raster, and 95 and 50% volume contours (PVCs).…”

“…The 95PVC was used to approximate the total range of the population, and the 50PVC was used to approximate the core habitat of the dolphins, hereafter referred to as core habitat (e.g. Brough et al, 2019; Gill et al, 2011; Rayment et al, 2009).…”

Using a recreational grade echosounder to quantify the potential prey field of coastal predators

“…Water depth at the survey regions ranged from 8 to 35m. Three regions were known hotspots for Hector’s dolphin, with the other three being randomly selected ‘reference areas’(see [47] for details). Surveys followed a ‘zig-zag’ pattern in an alongshore direction (Fig 1), at survey speeds between 5 and 6 knots.…”