Temporal and spatial distribution of common dolphins in São Miguel (Azores).

Abstract

The Common dolphin (Delphinus delphis) is one of the resident species of cetaceans in the Azores. The aim of this study is to look for intra and interannual differences in the temporal and spatial distribution of common dolphins. This is the first step to better understand the distribution of this species according to environmental features. The common dolphin is one of the species that enhances the whale watching activity all year long, improving economic incomes in the Azores. Data used in this study was gathered off the south coast of São Miguel (Azores) between 2009 and 2011 during the commercial trips of a whale watching company. We analyzed the temporal distribution of common dolphins and observed the relationship between their spatial distribution and sea surface temperature and depth. We registered 3090 sightings during the study period. From those, 530 were common dolphins, being therefore the most sighted species of the 18 registered ones. 58,7% of sightings occurred between February and June. 43,3% of sightings were registered within a sea surface temperature range of 16-17,5oC (typical winter sea surface temperature). Depths registered most frequently (77,4%) were under 700m. In 2009, the number of sightings and the size of the group were approximately double that of the following two years. Intra and interannual differences of temporal and spatial distribution could be due to several factors; fish stock, temperature changes or chlorophyll concentrations. Our investigation will continue studying these relationships to get a better understanding on cetacean distribution around Azores and its relationship with biotic and abiotic factors.

Full text

Laura González1,2 , Clara Sardà1 & Jesús Torres-Palenzuela2
1 Futurismo Azores Whale Watching, Ponta Delgada, São Miguel, Azores.
2 Department of Applied Physics, Vigo University, Vigo, Spain.
Corresponding author: lauragonzalez1986@hotmail.es
Data of dolphin sightings were collected off the south coast of
São Miguel during whale watching tours between 2009 and 2011.
We used GEBCO Bathymetry data set downloaded from
http://www.bodc.ac.uk, and sea surface temperature data
gathered from http://www.myocean.eu.
• 903 sightings between 2009 and 2011 (403, 227 and 273
respectively), becoming the most sighted species of the study
period.
• Recorded all throughout the year, with more sightings during
spring months (30% in March and April) (Fig.3).
• 43.4% of the sightings were recorded when sea surface
temperature was within 15.5ºC and 17ºC (Fig.1).
•77.4% of the sightings were recorded in depths under 700 m
(Fig.2).
• 41% of the sighted groups were formed by adults, juveniles
and calves. They were seen all year round, but mostly during
spring.
Laura González
Whale watching companies are increasingly providing useful
sources of information, even with some limitations, to
understand the ecological patterns of marine mammals.
In this study we want to assess the temporal distribution of
common dolphins (Common dolphin) off São Miguel (Azores),
looking as well at their preferences in depth and sea surface
temperature with data gathered between 2009 and 2011
during whale watching tours.
Rate of sightings of common dolphin decreases in summer just
when Atlantic spotted dolphin increase. It would be interesting
to assess if there is some niche competition between these
species (perhaps feeding competition?).
Fig.2. Sightings of common dolphins over the bathymetry map.
ISLANDS
DEPTH (m)
São Miguel
Santa Maria
Azores
Oriental
Group
Fig.1. Sightings of common dolphin off São Miguel according to SST.
25%
Fig.3. Sightings of common dolphin (Delphinus delphis) vs. Atlantic spotted
dolphin (Stenella frontalis).
530 m (SD=379.5)
18.66 ºC (SD= 2.63)
N= 903
1
754 m (SD=358)
21.98 ºC (SD=1.57)
N=384
fish stocks, temperature changes, fitoplanctonic blooms