Circadian and seasonal rhythms in the behavior of spinner dolphins (Stenella longirostris)

Abstract

The present study investigated both circadian and seasonal fluctuations in the daytime activities of the spinner dolphin, Stenella longirostris, from the Fernando de Noronha Archipelago in Brazil. The number of dolphins, and aerial, and reproductive activities were documented. The observations were carried out from January 1997 to December 2001. Temporal series and rhythmic characteristics (mesor, rhythmic percentage, and acrophase) were obtained by COSINOR analysis and later compared. The dolphins entered the bay in the morning, displayed aerial and reproductive activities during daytime, and left the bay in late afternoon to the open ocean. This study indicated that the rainy season affected the three behaviors investigated decreasing the rhythms parameter and advancing the beginning of these activities. The number of individuals was higher during the dry season and the animals stayed longer inside the bay. During the dry season, there was a bimodal expression of aerial activity, expressing a longer use of the temporal niche than in the rainy season. The phases with high frequencies of aerial activity seemed associated with those showing high reproductive activity, both with peak frequencies at about 0800. The results represent an important contribution to the advancement of chronobiological studies, and to the biology of cetaceans, considering that the existence of circadian and seasonal rhythms was proven in the behavior of spinner dolphins in an area of the SW Atlantic. Moreover, it allows restricting periods of the day for the activities of tourism as a form of minimizing the impacts of the boats on the dolphins.

Marine Mammal Monitoring on Guam

“…These records of observations, documented sightings, and combined anecdotal information provide supporting evidence for a circadian and seasonal pattern in the life of spinner dolphins on Guam as noted in other studies done in Hawaii by Silva (2009). Specifically, these data confirm the same known habitats of S. longirostris as reported for the Hawaiian spinner dolphin populations.…”

Low mtDNA diversity in a highly differentiated population of spinner dolphins (Stenella longirostris) from the Fernando de Noronha Archipelago, Brazil

“…Small population sizes were estimated for islands by photo-identification studies for some Hawaiian Islands, Kure (ffi120 individuals) and Midway (ffi 260 individuals), and were consistent with the scarcity of resting habitat and foraging habitat in this region [76]. This pattern seems not to be applicable to Noronha spinner dolphins (N = 162), which encompasses large numbers of individuals estimated daily by photo-identification studies (ffi 600 individuals) [18]. Instead, an alternative explanation would be low levels of immigration driven by social or demographic forces, as it has been seen in the Tahiti spinner dolphin [2]; or recent demographic bottleneck as demonstrated by significant microsatellite results.…”

“…The temperature of these waters range from 24˚C to 28˚C, seeming to be displaced when the warm Brazil Current meets the cold Malvinas Current [15][16][17]. The Fernando de Noronha Archipelago, north-eastern Brazil, is considered a natural refuge of the species, where large groups of 600 individuals on average are observed daily [18].…”

“…Gray's ecotype from the Fernando de Noronha Archipelago (hereafter referred to as Noronha spinner dolphins) gather in these islands to use their calm waters during the day to rest, play, care for their young and, take refuge from sharks; at night, they move out into deep sea waters to feed [17,19]. While in the Pacific Ocean there are several rest areas along the coast of the Islands and even within atolls [20], in the Atlantic Ocean the Fernando the Noronha Archipelago encompasses the only area in the South West Atlantic Ocean available with resources and resting areas to support the large number of spinner dolphins [18].…”

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

“…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).…”