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Table of contents:
|Chapter 2:||Diet and foraging ecology of northern bottlenose whales in the Gully: fatty acid and stable isotope analyses of biopsy samples|
|The influence of biotic and abiotic oceanographic features on the distribution of northern bottlenose whales in a submarine canyon|
|Chapter 4:||Diving and ranging behaviour of odontocetes: a methodological review and critique|
|Chapter 5:||Deep-diving behaviour of the northern bottlenose whale, Hyperoodon ampullatus (Cetacea: Ziphiidae)|
|Chapter 6:||Pattern and scale of northern bottlenose whale movements in the Gully: limited horizontal displacement in a profitable area|
|Chapter 7:||Acoustic behaviour of northern bottlenose whales - click characteristics and implications for foraging|
|Chapter 8:||Synthesis: bottlenose whale ecology in the Gully and potential implications for conservation and behaviour|
|Appendix:||Behavioural reactions of northern bottlenose whales to biopsy and tagging procedures|
Northern bottlenose whales (Hyperoodon ampullatus) show a concentrated distribution within the Gully, a submarine canyon off the coast of eastern Canada. Using data collected between 1988 and 1998, I have analysed the potential function of this local abundance in terms of foraging behaviour, movements and distributional preferences of these whales in the Gully.
Stomachs of northern bottlenose whales, which stranded in Nova Scotia and Quebec, contained a high proportion of the squid Gonatus steenstrupi. Fatty acid and stable isotope analysis of biopsy samples collected from free-ranging whales in the Gully were compared to results for samples of Gonatus fabricii. Results suggested that squid of this genus could form the bulk of bottlenose whale diet in the Gully. Isotopic nitrogen values suggest that bottlenose whales (mean 15.3 ‰ d15N) occupy a trophic level of approximately 4.4.
The abundance and distribution of bottlenose whales varied between years, with yearly distribution shifting primarily along the main axis of the canyon. Bottlenose whale distribution was investigated in relation to fixed physical parameters (depth and slope), surface environmental characteristics (sea surface temperature and water clarity), and mid-water environmental characteristics (sub-surface biomass, depth and thickness of deep scattering layer). The distribution of bottlenose whales was found to show strongest correlation with water depth and deep-water biomass.
Two deployments of suction-cup attached time-depth recorder/VHF radio tags on bottlenose whales demonstrated the whales' exceptional diving ability, with dives approximately every 80 min to over 800 m (maximum 1453 m), and up to 70 min in duration. Sonar traces of non-tagged, diving bottlenose whales suggested that such deep dives are not unusual. Many of the recorded dives were to, or close to, the sea floor.
Photo-resightings and radio-tracking follows were used to investigate the pattern and scale of whale movements within the Gully over time intervals up to their residency period (approximately 10 days). Bottlenose whales showed little daily movement (~4 km/day) and maintained ranges of ~20 km2 for time intervals between hours to days. This relative lack of movement is unusual for oceanic odontocetes and suggests that the canyon supports a profitable and stable food source for these whales. Geographic positions of individuals showed significant variation between years, but no range difference between whale age-sex classes. Within years, individuals showed some range separation particularly in years of highest whale abundance. Mature males showed consistent spatial orientation between years suggesting preferred relative locations.
Regular ultrasonic foraging clicks were recorded while whales were diving, and lower frequency, rapid and variable clicks were heard while whales were at the surface. The inter-click interval (0.4 s) and frequency (24 kHz) of clicks heard during dives were consistent with foraging at ranges of ~300 m on objects of diameter greater than 6 cm.
The estimated level of primary production required to support bottlenose whales in
the Gully was much greater than could be produced within this area, suggesting that there
must be significant energetic influx to the system. Identification of this input will aid
in the development of a comprehensive conservation plan for bottlenose whales. The
benthic nature of bottlenose whale foraging suggests that this foodweb would be especially
sensitive to threats to the seafloor in the Gully.