Current status of cetaceans in Aragua, Venezuela

Jaime Bolaños-Jiménez

As part of an effort to assess the actual status of the Venezuelan cetaceans, Profauna (the Venezuela Fish and Wildlife Service) is conducting a two-year field research project on the State of Aragua, central coast of Venezuela. It is the first step to get baseline information to devise an action plan for the conservation and research of marine mammals. So far, one flight and 24 boat surveys have been made between October 1996 and June, 1997. During this period, 30 sightings were recorded over the continental shelf. Relative frequencies were as follows: 50% Atlantic spotted dolphins (Stenella frontalis), 17% bottlenose dolphins (Tursiops truncatus), 10% mixed aggregations of these two species, 17% unidentified dolphins and 6% unidentified (Balaenopterid) whales. Group size for Tursiops truncatus ranged from 1-15 individuals and from three to more than 300 for S. frontalis. Spotted dolphins showed a sociable behavior by bowriding, escorting and 'playing' around the boat from only a few minutes to more than one hour. Bottlenose dolphins, on the other hand, very seldom showed this behavior, being rather shy most of the time. While watching a school of more that 300 spotted dolphins underwater, 25 animals bowrode and escorted the boat; as the boat reduced speed while circling the area they dived to 45-60 feet, looping back to the stern of the boat and then bowrode again. This behavior was displayed several times and was always made by the same subgroup. In one of the rare occasions when 10 Tursiops were bowriding, another school of S. frontalis joined them and started bowriding too. Preliminary results suggest the presence of coastal populations of dolphins along the study area during most of the year and, possibly, daily easterly or westerly movements (parallel to the coastline). Stenella frontalis is the most abundant species both in absolute numbers and sighting frequency. Further research will provide information about seasonality of whales presence, as claimed by fishermen. These are preliminary results of Project DLAM 009, funded by Fundacite Aragua.

This study was made with the purpose of generating baseline information of the cetaceans inhabiting the central coast of Venezuela.

When Stenella frontalis and Tursiops truncatus were sighted together, they were contained in one record as 'sf+tt' and their group size included both species. In OBIS-SEAMAP, these records were classified as Delphinidae (TSN: 180415). All Delphinidae records are for 'st+tt' sightings.



In the original data, the group size can be a range (e.g., 30-40). In OBIS-SEAMAP, a mid-value is taken for those having range values. Currently, research on cetaceans is being conducted by the primary dataset contact and the non-governmental organization Sea Vida team.

Overview

Attributes described below represent those in the original dataset provided by the provider.
Only minimum required attributes are visible and downloadable online. Other attributes may be obtained upon provider's permission.

Attributes in dataset

Attribute (table column)	Description
row_id	sighting index
obs_date	date of observation
obs_time	time of observation
latitude	latitude at time of observation in decimal degrees
longitude	longitude at time of observation in decimal degrees
species	species codes assigned by data provider
sp_tsn	ITIS taxonomic serial number
group_size	Group size in text format. Can be a range.
obs_count	Integer group size derived from group_size. Mid value taken for those having range values.
effort	Effort in hours
geom	definition not provided
oid	Unique ID number (generated by SEAMAP)