IMIS - Marine Onderzoeksgroepen

Thirty-eight sightings of sperm whales (Physeter macrocephalus) were recorded off Peru (3 degrees S - 18 degrees S) during 21 surveys conducted aboard platforms of opportunity between 1995 and 2002, with a search effort of 33,406.6 nautical miles of observation. Two main areas of concentration were detected: northern Peru (19 sightings) and southern Peru (16 sightings), but seasonality could not be confirmed. Almost 58% of sightings occurred during the same or consecutive days. Group size ranged from 1 to 18 individuals, with a mean of 3.5 individuals (SD = 3.9). The modal group size was one, with single whales accounting for 36.8% of sightings. Groups of three or more individuals accounted for 39.5%. An important increase of sightings occurred between 2001 and 2002, accounting 68% of the records, suggesting migratory movements towards Peruvian waters from other regions of the eastern Pacific Ocean. Positive correlations between indices of relative abundance and the anomaly of sea surface temperature were found, although warm events as El Niño appear to increase the uncertainty in sighting rates, reducing correlation values. Positive relationship between indices of relative abundance and fishery's CPUE of Dosidicus gigas suggest some grade of interaction, although the question about the role of D. gigas in the diet of sperm whales in the area must be solved for further conclusions. It is priority to perform specific surveys for population estimation, as well as non-lethal research about feeding and the effect of the fishery competition over sperm whales.