Cetacean occurrence off the west central Portugal coast from boat-based surveys 2007-2008

Escola de Mar

Throughout the years some researchers have dedicated their
efforts to the study of cetaceans’ occurrence off Mainland
Portugal. However, it is still missing a systemic scientific
methodology for studying the presence of coastal dolphins and
whales. This work intends to be a first approach on the occurrence of cetaceans off the west central coast of Portugal. Our objective was to contribute towards the compilation of relevant “forgotten science” such as whaling data and observations of opportunity, together with two years of boat-based surveys.
We found 1,313 occurrences of great whales captured off
Setúbal and Sesimbra (1925-1927 and 1944-1951) and a total
of 45 cetaceans in non-directed captures between 1976 and
1978. We accounted 45 dolphins and whales in sea-sightings
as a result of observations of opportunity, from 2002 to 2008.
In 2007 and 2008 a total of 63 boat-based visual surveys were
conducted from three different geographic locations, Nazaré,
Peniche and Sesimbra, and as a result 45 independent sightings
of cetaceans were recorded. The most frequent small dolphin
off the Portuguese mainland coast is the common dolphin
(Delphinus delphis) as shown by the three distinct approaches used in this study. Regarding whales the most common species is the fin whale (Balaenoptera physalus) as shown by whaling records. Overall, the small delphinid community along the central coast of Portugal is similar to the one that can be found along the Iberia shore.
This dataset contains only the boat-based sightings.

This work intends to be a preliminary approach on the
occurrence of cetaceans off the west central coast of Portugal.
Our objective was to contribute towards the compilation of
relevant “forgotten science”, namely 20th century whaling and
dolphin capture data and opportunistic observers’ reports on
whales and dolphins, in order to reduce the lack of knowledge
in central mainland Portugal. This information together with
boat-based surveys for obtaining new biological data is a
starting point for a new methodological approach.

Records did not have time recorded and were filled with 00:00:00. Records that did not have group size recorded were filled with 1. When an estimated range of animals was sighted, the median value (rounded down) was used as the observed count. Time and group size details are recorded in the [Notes] column.
Three opportunistic sightings of Delphinus delphis recorded for August 2007 were excluded because the day information was not available. One erroneous record of Delphinus delphis sightings on land was also excluded.

Overview

This section explains attributes included in the original dataset. OBIS-SEAMAP restricts the attributes available to the public to date/time, lat/lon and species names/counts only. Should you need other attributes described here, you are encouraged to contact the data provider.

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
oid	Unique ID number (generated by SEAMAP)
sp_obs	Species observed
sp_tsn	Species ITIS TSN
obs_time	Observed time
latitude	Latitude of observation
longitude	Longitude of observation
obs_date	Observed date
year	Year of observation
group_size	Estimated group size
obs_count	Number of animals observed
notes	Time was not recorded and 00:00:00 was used; observed count was the median when a range was recorded for group size; 1 was used for observed count when group size was blank