Identifying critical areas and habitat preferences of bottlenose dolphins Tursiops truncatus

Abstract

We present the findings of a 2-yr study of habitat use by bottlenose dolphins in the outer Shannon estuary on the west coast of Ireland. Data were collected during repeated, standardised, boat-based surveys of dolphins in a predefined 150 km 2 area of the outer estuary. Areas found to exceed a uniform-use pattern were termed 'critical areas' and delimited using the 50% contour derived from harmonic mean transformation of sighting locations. Dolphins exhibited preferential use of areas of the estuary with the greatest benthic slope and depth, highlighting the influence of environmental heterogeneity on habitat use by this species. Additionally, photo-identification was used to catalogue sightings of uniquely marked dolphins which provided distribution data at an individual level. Although the ranges of frequently sighted dolphins overlapped, a degree of partitioning was found in the use of up-river parts of the study area. The methods presented here could be applied at a range of spatial scales and we suggest that the identification of critical areas within a population's range is a priority when planning any conservation management strategy for marine mammals. KEY WORDS: Bottlenose dolphins · Habitat use · Critical areas · ConservationResale or republication not permitted without written consent of the publisher

Behavior Patterns of Bottlenose Dolphins in San Luis Pass, Texas

“…Perhaps the use of SLP /CB solely by resident dolphins indicates resource partitioning, a behavior also noted in other dolphins that seasonally inhabit bays (Ingram and Rogan, 2002). Therefore, the foraging behavior observed in each area could be merely an artifact of the bottom characteristics of the area, and these in turn may differ between resident and Gulf dolphins because of their exclusive use of each area.…”

“…Environmental factors such as sea temperature, tidal activity, depth, seafloor slope, and sediment type can also affect cetacean behavior (Wiirsig and Wursig, 1979;Ingram and Rogan, 2002;Hastie et al, 2004). Several studies have demonstrated an increase in the foraging activity of bottlenose dolphins in deep channel areas with steep slopes (Wilson et al, 1997;Ingram and Rogan, 2002), This increase in foraging may indicate a higher concentration of prey as they bottleneck in narrow channels, or perhaps the steep slopes aid dolphins in herding and catching fish.…”

“…Several studies have demonstrated an increase in the foraging activity of bottlenose dolphins in deep channel areas with steep slopes (Wilson et al, 1997;Ingram and Rogan, 2002), This increase in foraging may indicate a higher concentration of prey as they bottleneck in narrow channels, or perhaps the steep slopes aid dolphins in herding and catching fish. In addition, there are often seasonal shifts in behavior, including increased migration, seasonal use of bays or inlets, and variation in duration and modes of behavior (Wilson et a!., 1997;Weller, 1998;Barco et a!., 1999).…”

Seasonal variations in spatial usage by the estuarine dolphin, Sotalia guianensis (van Bénéden, 1864) (Cetacea; Delphinidae) at its southern limit of distribution

“…For this reason, the core areas may be regarded as critical habitats for conservation (e.g. Ingram and Rogan, 2002;Karczmarski et al, 2000).…”

Ranging patterns of bottlenose dolphins living in oceanic waters: implications for population structure

“…1987: Wilson et aJ. 1999: Ingram and Rogan 2002. However, th e size of the stud y site alone cannot acco unt for th e large num ber of transient dolphins recogni zed during th e sur veys.…”