Trophic relationships of the spinner dolphin at Fernando de Noronha Archipelago, SW Atlantic

Iván Sazima,Cristina Sazima,Flávio José De Lima Silva,José Martins Silva-Jr

doi:10.3989/scimar.2007.71n3505

Abstract

We present an overview of predator-prey and other trophic relationships of spinner dolphins ( Stenella longirostris ) around Fernando de Noronha Archipelago, off northeastern Brazil, with use of original data and a brief review of data published elsewhere. Records were made while snorkelling among the dolphins in daytime. Individual fish pursuit and coordinated school herding were the two hunting tactics recorded. Three small prey types (oceanic squids, fishes, and prawns) were recovered from vomits collected in situ and from stomachs of two stranded dolphins. In their turn, spinners were preyed on by the cookiecutter sharks (Dalatiidae) as evidenced by round and crater-like wounds and circular scars. Additionally, the dolphins were preyed on by large sharks (Lamnidae, Carcharhinidae), as evidenced by crescent-shaped wounds and scars. Unidentified fishes bit fin pieces, as evidenced by variably-shaped marks. On the other hand, dolphins’ particulate faeces, vomits and live roundworms were eaten by plankton-feeding fishes. Thus, the trophic role of the spinner dolphins of Fernando de Noronha may be summarised as that of : 1) a predator of small oceanic squids, fishes, and prawns; 2) a prey for the small, piece-eating cookiecutter sharks and other unidentified fishes; 3) a prey for large sharks able to kill a dolphin; and 4) a particulate food supplier for plankton-eating fishes.

Highlights

The spinner dolphin (Stenella longirostris, Delphinidae) is one of the best-studied delphinid species, most of the current knowledge stems from studies on the Pacific populations in Hawaii
SUMMARY: We present an overview of predator-prey and other trophic relationships of spinner dolphins (Stenella longirostris) around Fernando de Noronha Archipelago, off northeastern Brazil, with use of original data and a brief review of data published elsewhere
Three small prey types were recovered from vomits collected in situ and from stomachs of two stranded dolphins

Summary

Introduction

The spinner dolphin (Stenella longirostris, Delphinidae) is one of the best-studied delphinid species, most of the current knowledge stems from studies on the Pacific populations in Hawaii (review in Norris et al, 1994). Studies on the tropical West Atlantic populations are few and deal mostly with behaviours displayed by surfacing dolphins, data on frequency, and permanence at given sites taken from land-based observation points (Lodi and Fiori, 1987; Silva-Jr. et al, 1996). Recent studies on the underwater behaviour of Atlantic spinners are scarce (Sazima et al, 2003; Silva-Jr. et al, 2005). 2000 individuals are recorded throughout the year at the cove known as Dolphins’ Bay (Silva-Jr. et al, 1996, 2005). At this site the dolphins rest, socialise, mate, nurse, and play—situations that are favourable for underwater records at close quarters, due to the clear waters and the large numbers of spinners (Silva-Jr. et al, 2005). Spinner groups congregate in Dolphin’s Bay during the morning and early afternoon, leaving the bay in the afternoon to forage in the open sea (Silva-Jr. et al, 1996)

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