Ecological characteristics contribute to sponge distribution and tool use in bottlenose dolphins Tursiops sp.

Abstract

In Shark Bay, Western Australia, bottlenose dolphins Tursiops sp. carry conical sponges Echinodictyum mesenterinum on their rostra in the only documented cetacean foraging behaviour using a tool ('sponging'). In this study, we examined the influence of various ecological factors on live sponge distribution and the occurrence of sponging in parts of the western gulf of Shark Bay. We assessed sponge distribution and seagrass cover along 12 transects of approximately 11 km length, by recording sponges and seagrass in a total of 1380 quadrats (1 × 1 m), of which 56 quadrats contained conical sponges. The occurrence of sponging dolphins ('spongers') was documented along 10 of these 12 transects. The distribution of conical sponges was negatively correlated with the distribution of seagrass: no conical sponges were observed in water depths of <10 m and no seagrasses were found at depths of >12 m. A digital elevation model, created from the sample depth data, identified channels in the region. Binary logistic and Poisson loglinear generalised linear models showed that water depth and bathymetric features including channel, substrate and slope were significant in predicting the occurrence and the mean number of conical sponges, as well as that of seagrass. Conical sponge distribution was positively correlated with the distribution of sponging, indicating that ecological factors influence where sponging occurs. The greater number of spongers found in this region may be explained by the larger area of habitat suitable for conical sponges in the western than the eastern gulf of Shark Bay.

Cultural transmission of tool use combined with habitat specializations leads to fine-scale genetic structure in bottlenose dolphins

“…The most prominent foraging strategies observed only in shallow water include beach hunting, bottom grubbing and kerplunking [18,19]. Foraging strategies observed in deep water include 'sponging' [20][21][22][23]. The question of whether sponging is a socially transmitted behaviour has been studied extensively in Shark Bay in the past [3,20,21,[24][25][26][27][28].…”

Abundance, survival and temporary emigration of bottlenose dolphins (Tursiops sp.) off Useless Loop in the western gulf of Shark Bay, Western Australia

“…Ten loosely parallel transect lines, each ~11 km in length and 2 km apart, covering an area of 226 km 2 , were designated across depth contours. The study area covers shallow seagrass habitat, as well as five channels of <16-m water depth, disrupted by shallower sand flats (Tyne et al 2012). Previous research in the western gulf study area has concentrated on assessing the factors that drive tool use in bottlenose dolphins (Bacher et al 2010;Tyne et al 2012).…”

“…The study area covers shallow seagrass habitat, as well as five channels of <16-m water depth, disrupted by shallower sand flats (Tyne et al 2012). Previous research in the western gulf study area has concentrated on assessing the factors that drive tool use in bottlenose dolphins (Bacher et al 2010;Tyne et al 2012). A survey was conducted on each individual or group encountered within 300 m of the transect line, thus allowing for a 600-m 'survey zone' (Sargeant et al 2007).…”

Cultural transmission of tool use by Indo-Pacific bottlenose dolphins (Tursiopssp.) provides access to a novel foraging niche

“…WSB samples, however, were sampled randomly at different times (September 2008, April-July 2009) and in two different habitats, allowing us to investigate the effect of habitat on time of sampling FA profiles. For WSB, sampling depth was used as a proxy for habitat [27,43], categorizing samples into the depth classes shallow (less than 5 m), moderate (5-10 m) and deep (more than or equal to 10 m). This classification approximates the underwater topography of WSB, where sea grass coverage decreases to approximately 10% at a depth of 5 m due to limited light penetration, and sponge growth is only evident deeper than 10 m [27].…”

“…For WSB, sampling depth was used as a proxy for habitat [27,43], categorizing samples into the depth classes shallow (less than 5 m), moderate (5-10 m) and deep (more than or equal to 10 m). This classification approximates the underwater topography of WSB, where sea grass coverage decreases to approximately 10% at a depth of 5 m due to limited light penetration, and sponge growth is only evident deeper than 10 m [27]. To minimize any potential edge effects, only samples obtained in shallow and deep areas were compared.…”