Distribution of sperm whales (Physeter macrocephalus) off the south coast of São Miguel (Azores).

Abstract

off the south coast of São Miguel, Azores. Distribution and abundance of cetaceans are directly related with biological, anthropogenic and physical factors. They influence the ecosystem productivity and therefore the distribution of every level of the food chain. For marine mammals, the distribution of their preys is considered to be an important factor that determines their distribution.

Full text

Distribution of sperm whales (Physeter macrocephalus)
off the south coast of São Miguel, Azores.
Distribution and abundance of cetaceans are directly related with biological,
anthropogenic and physical factors. They influence the ecosystem productivity and
therefore the distribution of every level of the food chain. For marine mammals, the
distribution of their preys is considered to be an important factor that determines their
distribution.
Laura González García(1), Jesús Souza Troncoso(2) & Jesús Torres Palenzuela(1)
(1) Department of Applied Physics, Vigo University.
(2) Department of Ecology and Animal Biology. Vigo University.
Contact: 1986lauragonzalez@gmail.com
INTRODUCTION
To study the relationships between sperm whale’s sightings (Physeter macrocephalus) and bathymetry, slope and bottom
aspect off the south coast of São Miguel, Azores.
OBJECTIVE
Biological data were recorded in the framework of the MONICET project
(http://www.monicet.net) during 2010. The data were collected during commercial trips of
Futurismo Whale Watching (Ponta Delgada, São Miguel). We recorded sea state, visibility,
species, behaviour, size of the group, location (Fig.1), etc. Bathymetry data were
downloaded from GEBCO site
(http://www.gebco.net/data_and_products/gridded_bathymetry_data/).
Due to the high cost and effort necessary for in-situ monitoring of cetaceans, the knowledge
of their role in ecosystem dynamics is still limited. The global touristic development of whale
watching companies is a valuable information resource, even if in some cases there are some
limitations.
METHODOLOGY
Azores
Data were analysed using GIS (gvSIG; IDRISI Kilimanjaro and MapInfo). Firstly, a
bathymetry raster was created and land was masked. Sea-bottom properties were retrieved
from these maps. After vectorizing them, we overlaid the sighting points and multiplied
both layers to extract data.
RESULTS
BATHYMETRY
SLOPE
ASPECT
CONCLUSIONS
Bathymetry data agree with other studies carried out in the Azores(3, 4), and
also in the world(1, 2). Sperm whales were observed between 700 and 1300 m
according to their prey’s distribution (meso and bathypelagic cephalopods),
and to their feeding behaviour.
Main slope is between 5 and 10%. These high values are related to the
volcanic nature of the islands(4).
More sightings in summer because of the increase of the tourists and the
presence of more familiar groups of sperm whales in the area.
PROPOSAL: study longer temporal series, relate the sightings with other
variables (e.g. SST, productivity, …), study distribution differences between
adult males and familiar groups.
734 sightings were recorded in 349 trips. 78.6% of the sightings occurred
between April and September, 52% in July and September.
Fig.2. Sightings over the bathymetry map (m). 73.84% were recorded between 700
and 1300 m depth. From 192 to 2650 m, mean 1031.66 m (SD=315.88, n=734).
Fig.3. Sightings over the slope map (%). 50% were registered between 5 and 10%.
From 1.27 to 69.97%. Mean = 9.68% (SD=7.10, n=734).
BIBLIOGRAPHY
SIGHTINGS
1) Jaquet, N. & Gendron, D. (2002) Distribution and relative abundance of sperm whales in relation to key environmental
features, squid landings and the distribution of other cetacean species in the Gulf of California, Mexico. Mar. Bio. 141: 591-
601. 2) Mullin, K., Hoggard, W., Roden, C., Lohoefener, R., Rogers, C. & Taggart, B. (1991) Cetaceans on the upper continental
slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Department of the Interior, Minerals Management
Service, Gulf of Mexico OCS Regional Office, New Orleans, Louisiana. 108 pp. 3) Silva, M.A., Prieto, R., Magalhães, S.,
Cabecinhas, R., Cruz, A., Gonçalves, J.M. & Santos, R.S. (2003) Ocurrence and distribution of cetaceans in the waters around
the Azores (Portugal), Summer and Autumn 1999-2000. Aquatic Mammals. 29.1: 77-83. 4) Van Geel, N.C.F. (2007) Spatial and
temporal analyses of cetacean distribution off the south coast of Pico (Azores, Portugal) in relation to the bathymetric features
water depth and slope gradient. Amsterdam / Utrecht, University of Amsterdam / Utrecht University: 92 pp. Masters thesis.
Fig.1. Study area (São Miguel Island, Azores), field methodology (land and sea surveys) and map with sperm whales’
sightings, main land spotpoints and home port of the study.
Fig.4. Sighting over the aspect map (NNE, ENE, ESE, SSE, SSW, WSW, WNW y NNW).
80.57% were recorded southwards.
Fig.5. Number of sperm whales sightings recorded monthly.
AKNOWLEDGEMENTS
Depth (m)
Sightings Islands
Slope (%)
Islands
Bottom aspect (45⁰ each class, from 0 to 360⁰)
1- NNE
2- ENE
3- ESE
4- SSE 5- SSW
6- WSW
7- WNW
8- NNW
Islands
2
2
5
9
11
10
78
155
187
200
60
11
4
0
50
100
150
200
250
Nº of sightings
Depth (m)
Depht sightings
25
118
198
169
62
47
32
28
13
22
0
50
100
150
200
250
Nº of sightings
Slope (%)
Slope sightings
26
21
103
349
169
41
12
13
0
50
100
150
200
250
300
350
400
NNE
ENE
ESE
SSE
SSW
WSW
WNW
NNW
Nº of sightings
Bottom aspect
Bottom aspect sightings
0
2
17
2
55
94
207
42
177
97
33
8
0
50
100
150
200
250
Ene
Feb
Mar
Abr
May
Jun
Jul
Ago
Sep
Oct
Nov
Dic
Nº of sightings
Monthly sperm whales's sightings
AB12
Laura González