Environmental Variables Affecting the Residence of Spinner Dolphins (<I>Stenella longirostris</I>) in a Bay of Tahiti (French Polynesia)

Abstract

The spinner dolphin (Stenella longirostris) is the most common among 16 species in the Society Islands (French Polynesia). They are observed yearround during daytime in sheltered bays or within lagoons. From 1995 to 2002, we studied spinner dolphins from a shore site in Baie des Pêcheurs, a bay on the west coast of Tahiti, performing 1,033 sighting sessions with binoculars. Presence, position, and school size were noted, as well as various behavioral and environmental variables. Human presence also was recorded. Dolphins were present on average 73.3% of the days, with a higher presence rate from May to November (81.0%) than from December to April (66.7%). Dolphins stayed within the bay from early morning until 1200 to 1500 h and had school sizes ranging from as small as 15 to 30 to as large as 100 to 140 individuals. Dolphins began to move slowly offshore after 1100 h. On average, they stayed 400 m from shore, although they approached as close as 100 to 150 m. Dolphin presence and residence time seemed to be negatively affected by surface water turbidity (river flow) and lagoon current strength. Recreational dolphin watching was low from Monday to Thursday (0.20 to 0.35 boat per sighting session) and high on Sunday, with an average of 1.67 boats per session. There was a lower dolphin presence rate from Monday to Thursday (69%) than from Friday to Sunday (78%). Presence patterns were similar to those found in Hawaii, accounting for differences in environmental characteristics.

Structure of a toothed cetacean community around a tropical island (Mayotte, Mozambique Channel)

“…Habitat features of spinner dolphin around Mayotte are slightly different from those in other areas. In French Polynesia, Hawaii, and the Maldivian atolls, these dolphins enter atolls, sheltered bays and lagoons through reef channels in the morning and leave in the afternoon to feed overnight (Würsig et al 1994, Anderson 2005, Gannier and Petiau 2006. Around Mayotte, the spinner dolphins under study generally inhabited the outer-reef slope, within a greater depth range than has been previously reported (Würsig et al 1994, Gannier andPetiau 2006).…”

Passive acoustic monitoring of coastally associated Hawaiian spinner dolphins, Stenella longirostris, ground-truthed through visual surveys

“…In the waters around Hawai'i, USA, island-associated spinner dolphins spend their nights foraging intensively offshore for approximately eleven hours each night and return to shallow areas during the day, particularly from late morning to early afternoon (Norris and Dohl, 1980;Benoit-Bird and Au, 2003;Benoit-Bird, 2004;Tyne et al, 2015). This daily behavioral pattern has also been observed in Fiji (Cribb et al, 2012), French Polynesia (Gannier and Petiau, 2006;Oremus et al, 2007), Egypt (Notarbartolo-di-Sciara et al, 2009), Mauritius (Webster et al, 2015), Brazil (Silva-Jr et al, 2005), and both the northwestern (Karczmarski et al, 2005;Andrews et al, 2010) and main Hawaiian Islands (Norris and Dohl, 1980;Wursig et al, 1994;Tyne et al, 2015) This rigid daily behavioral schedule of spinner dolphins is a driver of an industry focused on human-dolphin interactions in Hawai'i (Heenehan et al, 2014). The rapid increase of human-dolphin interactions and the demands of intensive cooperative night-time foraging have led to concern about the effects of these interactions, particularly the consistent disruption of dolphin rest (NMFS and NOAA, 2006;Courbis and Timmel, 2009;Tyne et al, 2015).…”

Habitat selection of two island-associated dolphin species from the south-west Indian Ocean

“…Recent habitat modelling studies conducted in Hawaii, also demonstrated that spinner dolphins favor flat sandy seabeds, close to the 100m isobath (Thorne et al, 2012, Tyne et al, 2015. Although few specific substrate data analyses have been undertaken, other studies in Hawaii (Norris et al, 1994), in Hawaii's Midway Atoll (Karczmarski et al, 2005), in Tahiti (Gannier and Petiau, 2006) and in Mauritius (Webster, 2011), also reported the occurrence of spinner dolphin sightings in white-sand environments. This marked preference is consistent with the hypothesis first proposed by Norris et al (1994) that the species favors white sandy bays to improve visual detection of predators, especially during resting periods.…”

“…This preference for flat areas at the outer part of the shelf, close to open waters, might be related to the species' ecological needs. Spinner dolphins generally use sheltered coastal or reef-associated habitat during the morning for resting and socializing and travels to deeper waters later in the afternoon where it forages at night (De Lima Silva and Da Silva, 2009;Gannier and Petiau, 2006;Kiszka et al, 2011;Lammers, 2004;Norris et al, 1994;Notarbartolo-Di-Sciara et al, 2008;Thorne et al, 2012;Tyne et al, 2015). It has been hypothesis that selecting resting habitat at close proximity to deep waters could be a strategy to reduce travelling time and energy costs during transit between oceanic and coastal habitats (Norris et al, 1994;Thorne et al, 2012;Tyne et al, 2015).…”

“…depth, slope and distance from shore, temperature, salinity, etc. ), mainly because they are fixed parameters that can be accurately and systematically measured (Cribb et al, 2008;Embling et al, 2010;Gannier and Petiau, 2006;Mannocci et al 2015, Praca andGannier, 2008;Praca et al, 2009;Roberts et al, 2016). Based on remote sensing data, biotic factors such as chlorophyll-a concentration are sometimes used as a proxy of productivity and prey abundance at a large spatial scale (Mannocci et al, 2015;Panigada et al, 2008, Praca et al, 2009Roberts et al, 2016).…”