OCCURRENCE AND ENCOUNTER RATES OF MARINE MAMMALS IN THE WATERS AROUND THE MALPELO ISLAND AND TO THE CONTINENT

Abstract

This work compiles a decade (2001-2010) of marine mammal sightings in the Malpelo Fauna and Flora Sanctuary (FFS) and the area between the island and mainland coast. Four separate sources of data were consulted, which used visual searching during cruising efforts while Malpelo’s surrounding waters were surveyed from a vantage point. Seven species were identified in the FFS: October and November were the months with higher species richness. Tursiops truncatus had the highest encounter rates (17.78 groups/100 h), followed by Megaptera novaeangliae (1.62) and Stenella attenuata (0.88). These species were usually within 6 km from the island. Other species seen around the island include Stenella coeruleoalba, Delphinus delphis, Stenella longirostris and Zalophus wollebaeki. On the other hand, thirteen species were identified during cruises, and March and April were the months with the highest species richness. Megaptera novaeangliae had the highest encounter rate (5.94), followed by T. truncatus (3.30), S. attenuata (3.08), D. delphis (3.08) and S. coeruleoalba, Globicephala macrorhynchus and Orcinus orca, each one with 0.66. Other species seen during the cruises include Steno bredanensis, Pseudorca crassidens, Grampus griseus, Peponocephala electra, Physeter macrocephalus and Ziphius cavirostris. Megaptera novaeangliae were associated to the continental shelf, T. trunctaus and D. delphis to oceanic waters, and S. attenuata to both the continental shelf and oceanic waters. Delphinus delphis was more abundant in intermediate waters, during the first trimester (January-March), while T. truncatus was the most abundant species around the Sanctuary during all seasons, suggesting that is the same population. The latter was also the only species found all year round in both zones (around the island and in oceanic waters), and encounter rates did not change across years. Megaptera novaeangliae had a seasonal presence (mostly June to November) with a higher abundance during the third trimester (July-September), both around Malpelo and the transect. The presence of humpback whales calves suggests that Malpelo is used for reproductive purposes. This new information about the marine mammals found in Malpelo FFS and the area between the island and the continent contributes to the understanding of these species in Colombian waters.