Presence and Distribution of Sperm Whales (Physeter macrocephalus) and Cuvier’s Beaked Whales...
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Presence and Distribution of Sperm Whales (Physeter macrocephalus ) and Cuvier’s Beaked Whales (Ziphius cavirostris) South West of Crete and along the Hellenic Trench in the Eastern Mediterranean Sea V. Burgener 1 , A. Frantzis 2 , M. Bouzelboudjen 3 1 Animal Behaviour Laboratory, University of Neuchâtel, Switzerland; 2 Pelagos Cetacean Research Institute, Greece; 3 GIS Neuchâtel, Central Computing Facilities, University of Neuchâtel, Switzerland We investigated and compared the distribution of sperm whales and Cuvier’s beaked whales according to three physiographic variables: bathymetry, slope and distance to shore. For sperm whales, we have distinguished social units and solitary individuals. Furthermore, we made a first approach of the short- term movement of solitary sperm whales South West of Crete. Study area : South West of Crete and Hellenic Trench, Eastern Mediterranean Sea Period : June-October 1998 to 2003 Field effort : visual and systematical acoustical surveys Data analysis : Geographic Information System (ArcInfo 8.1 and ArcView 3.3, ESRI 1996, 2002), classical univariate (Mann-Whitney) and multivariate (GLM, LDA) analysis, circular statistics (Rayleigh). Sperm whales were seen 97 times, from which 58 observations were defined as solitary individuals and 24 as social units. It represents a total of more than 248 individuals. The mean number of animals per sighting is 2.6 and the maximum is 12 individuals. The mean group size is 6.7. Cuvier’s beaked whales were seen on 34 occasions, which accounts for 66 individuals. The mean number of animals per sighting is 1.9 and the biggest group was of 5 individuals. Intraspecific comparison : Univariate and multivariate analysis showed no significant difference between the distribution of sperm whale’s social units and solitary individuals regarding to bathymetry, slope and distance to shore. Interspecific comparison : our results suggest that sperm whales and Cuvier’s beaked whales share the same habitat regarding to bathymetry, slope and distance to shore, eventhough a logistic regression model shows that bathymetry plays an important role in the distribution of these two species. Both species are deep divers that feed on meso- and bathypelagic cephalopods: in the case of competitive interaction, other factors associated with bathymetry, particularly those depending on the ecology of the prey, may play a significant role in the distribution of the two species. Intraspecific comparison : distribution of solitary individuals and social units do not appear to differ significantly depending on the three afore-mentioned variables. It is probable that there is a “vertical” segregation rather than a “horizontal” one: males seem to feed near or at the bottom, close to continental shelves, whereas females tend to feed higher in the water column. This behaviour may be a response to the intraspecific competition, as well as a specific social behaviour linked to the sex. Short-term movement : solitary sperm whales South West of Crete move back and forth along the continental shelf to forage. They rarely head North or South, they rather stay on an East-West axis. Sperm whale’s movement : we established that solitary sperm whales South West of Crete prefer moving on an East-West axis, parallel to the coastline. # # # # # # # # # ## # ## # # # # # # # # # ### # ## # # # # # # ## # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # $ $ $ $ $ $ $ $ $$ $ $ $$ $ $ $ $ $ $ $ $ $ $ $ $ $ $$ $ $ $ $ $ N # Physeterm acrocephalus ( N = 97) $ Ziphius cavirostris ( N = 34) 0 200 km A spatial database was created using the GIS: Interspecific comparison : we found no significant difference between the distribution of sperm whales and Cuvier’s beaked whales according to bathymetry, slope and distance to shore with the classical statistics and the discriminant analysis. However, a logistic regression model (GLM) based on a presence – absence database showed a significant tendency for beaked whales to be found in shallower waters. Other factors need to be investigated in order to define the sperm and Cuvier’s beaked whale’s habitat, particularly those concerning the ecology of their preys. At our scale, we could observe no significant difference between sperm whale’s social units and solitary individuals regarding to bathymetry, slope or distance to shore, which suggest a trophic specialization between males and females. Future studies in this area will be based on population’s size estimates and sperm whale’s mid- and long-term movement. Introduction Materials and Methods Results Discussion Conclusions 0 1000 2000 km N # C rete H e l l . T r e n c h S tudy area Bathym etry(m ) P rob.ofpresence (p) 500 1000 1500 2000 2500 0.0 0.1 0.2 0.3 0.4 Ziphius N = 196 Sperm W hale N = 196 X m ax1 = 828 m X m ax2 = 1065 m Bathym etry(m ) P rob.ofpresence (p) 500 1000 1500 2000 2500 0.0 0.1 0.2 0.3 0.4 Ziphius N = 196 Sperm W hale N = 196 X m ax1 = 828 m X m ax2 = 1065 m r= 0.34 St.D eviation = 65.8 ° n = 96 0° 90° 180° phi = 105.5 ° 0 100 200 300 0 5 10 15 20 25 Azim ut(°) r Frequency N r= 0.34 St.D eviation = 65.8 ° n = 96 0° 90° 180° phi = 105.5 ° 0 100 200 300 0 5 10 15 20 25 Azim ut(°) r Frequency N r= 0.34 St.D eviation = 65.8 ° n = 96 0° 90° 180° phi = 105.5 ° 0 100 200 300 0 5 10 15 20 25 Azim ut(°) r r= 0.34 St.D eviation = 65.8 ° n = 96 0° 90° 180° phi = 105.5 ° 0 100 200 300 0 5 10 15 20 25 Azim ut(°) r Frequency N Thanks to: A. Frantzis, Pelagos Cetacean Research Institute’s members and volunteers, M. Bouzelboudjen, J. Moret, C.Mermod, IFAW, V. Valavanis, R. Swift, S. Airoldi, J. Landron.
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Transcript of Presence and Distribution of Sperm Whales (Physeter macrocephalus) and Cuvier’s Beaked Whales...
Presence and Distribution of Sperm Whales (Physeter macrocephalus) and Cuvier’s Beaked Whales (Ziphius cavirostris) South West of Crete
and along the Hellenic Trench in the Eastern Mediterranean Sea
V. Burgener 1, A. Frantzis 2, M. Bouzelboudjen 3
1Animal Behaviour Laboratory, University of Neuchâtel, Switzerland; 2Pelagos Cetacean Research Institute, Greece; 3GIS Neuchâtel, Central Computing Facilities, University of Neuchâtel, Switzerland
We investigated and compared the distribution of sperm whales and Cuvier’s beaked whales according to three physiographic variables: bathymetry, slope and distance to shore. For sperm whales, we have distinguished social units and solitary individuals. Furthermore, we made a first approach of the short-term movement of solitary sperm whales South West of Crete.
Study area: South West of Crete and Hellenic Trench, Eastern Mediterranean Sea
Period: June-October 1998 to 2003Field effort: visual and systematical acoustical surveysData analysis: Geographic Information System (ArcInfo 8.1 and ArcView 3.3, ESRI 1996, 2002), classical univariate (Mann-Whitney) and multivariate (GLM, LDA) analysis, circular statistics (Rayleigh).
Sperm whales were seen 97 times, from which 58 observations were defined as solitary individuals and 24 as social units. It represents a total of more than 248 individuals. The mean number of animals per sighting is 2.6 and the maximum is 12 individuals. The mean group size is 6.7.
Cuvier’s beaked whales were seen on 34 occasions, which accounts for 66 individuals. The mean number of animals per sighting is 1.9 and the biggest group was of 5 individuals.
Intraspecific comparison: Univariate and multivariate analysis showed no significant difference between the distribution of sperm whale’s social units and solitary individuals regarding to bathymetry, slope and distance to shore.
Interspecific comparison: our results suggest that sperm whales and Cuvier’s beaked whales share the same habitat regarding to bathymetry, slope and distance to shore, eventhough a logistic regression model shows that bathymetry plays an important role in the distribution of these two species. Both species are deep divers that feed on meso- and bathypelagic cephalopods: in the case of competitive interaction, other factors associated with bathymetry, particularly those depending on the ecology of the prey, may play a significant role in the distribution of the two species.
Intraspecific comparison: distribution of solitary individuals and social units do not appear to differ significantly depending on the three afore-mentioned variables. It is probable that there is a “vertical” segregation rather than a “horizontal” one: males seem to feed near or at the bottom, close to continental shelves, whereas females tend to feed higher in the water column. This behaviour may be a response to the intraspecific competition, as well as a specific social behaviour linked to the sex.
Short-term movement: solitary sperm whales South West of Crete move back and forth along the continental shelf to forage. They rarely head North or South, they rather stay on an East-West axis.
Sperm whale’s movement: we established that solitary sperm whales South West of Crete prefer moving on an East-West axis, parallel to the coastline.
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$$$$$$$$$$ $$$$$$$$$ $$$$ $$
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N
# Physeter macrocephalus ( N = 97)
$ Ziphius cavirostris ( N = 34)
0 200 km
A spatial database was created using the GIS:
Interspecific comparison: we found no significant difference between the distribution of sperm whales and Cuvier’s beaked whales according to bathymetry, slope and distance to shore with the classical statistics and the discriminant analysis. However, a logistic regression model (GLM) based on a presence – absence database showed a significant tendency for beaked whales to be found in shallower waters.
Other factors need to be investigated in order to define the sperm and Cuvier’s beaked whale’s habitat, particularly those concerning the ecology of their preys. At our scale, we could observe no significant difference between sperm whale’s social units and solitary individuals regarding to bathymetry, slope or distance to shore, which suggest a trophic specialization between males and females.
Future studies in this area will be based on population’s size estimates and sperm whale’s mid- and long-term movement.
Introduction
Materials and Methods
Results
Discussion
Conclusions
0 1000 2000 km
N
#
Crete
He ll. Trench
Study area
Bathymetry (m)
Pro
b. o
fpre
sen
ce(p
)
500 1000 1500 2000 2500
0.0
0.1
0.2
0.3
0.4
Ziphius N = 196Sperm Whale N = 196
Xm
ax1
= 8
28
m
Xm
ax2
= 1
06
5 m
Bathymetry (m)
Pro
b. o
fpre
sen
ce(p
)
500 1000 1500 2000 2500
0.0
0.1
0.2
0.3
0.4
Ziphius N = 196Sperm Whale N = 196
Xm
ax1
= 8
28
m
Xm
ax2
= 1
06
5 m
r = 0.34
St. Deviation = 65.8 °n = 96
0°
90°
180° phi = 105.5 °
0 100 200 300
05
1015
2025
Azimut (°)
rF
requ
ency
N
r = 0.34
St. Deviation = 65.8 °n = 96
0°
90°
180° phi = 105.5 °
0 100 200 300
05
1015
2025
Azimut (°)
rF
requ
ency
N
r = 0.34
St. Deviation = 65.8 °n = 96
0°
90°
180° phi = 105.5 °
0 100 200 300
05
1015
2025
Azimut (°)
r
r = 0.34
St. Deviation = 65.8 °n = 96
0°
90°
180° phi = 105.5 °
0 100 200 300
05
1015
2025
Azimut (°)
rF
requ
ency
N
Thanks to: A. Frantzis, Pelagos Cetacean Research Institute’s members and volunteers, M. Bouzelboudjen, J. Moret, C.Mermod, IFAW, V. Valavanis, R. Swift, S. Airoldi, J. Landron.
