Sperm whales off Peru during IMARPE surveys (1995-2002)

Instituto del Mar del Perú (IMARPE)

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.

To show the general pattern of distribution of sperm whales off Peru, a previously important whaling ground.

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Attributes in dataset

Attribute (table column)	Description
date	Date of observation
long	Longitude of observation
lat	Latitude of observation
obs_count	Number of animals observed
species	Species observed
tsn	Species ITIS TSN
surveycode
vessel	R/V Humboldt & R/V Olaya
oid	Unique ID number (generated by SEAMAP)