Sperm whales are drawn (back) to the shores of Terceira, the question is why?

Abstract

The waters around Terceira island in the Azores are a hotspot for cetacean diversity, particularly species foraging on deep-sea cephalopods. The largest of these deep-divers is the sperm whale (Physeter macrocephalus), capable of reaching lengths up to 19 meters and diving to depths over 2000 meters. Following the cessation of whaling in the 1980’s, sperm whales remained less common around Terceira than other Azorean Islands, but sightings have significantly increased in the past 3 years. Moreover, sightings are being made increasingly close inshore (<4km), at relatively shallow depths (< 500m). Here we use over a decade of systematic survey data to investigate what could be driving the return of sperm whales to Terceira’s shores. We examine changes in the number of sightings and group composition over time from visual surveys, as well as highlighting recent insights into the distribution and consumption of cephalopod prey by sperm whales in the area.

Full text

Sperm whales are drawn (back) to the
shores of Terceira , the question is why?
Increasing numbers
Sighting distributions
Spatio-temporal hotspots
Important unobserved processes
New puzzle pieces
*mark.rademaker@nioz.nl
Mark Rademaker*1, Machiel G. Oudejans2, Marie Guilpin1, Luis M.D. Barcelos3, Fleur visser1,2
1Royal Netherlands Institute for Sea Research (NIOZ), Department of Coastal Systems Texel, The Netherlands
2Kelp Marine Research, Hoorn, The Netherlands
3Universidade dos Açores, Centre for Ecology, Evolution and Environmental Changes, Azores, Portugal
38.50°N
38.55°N
38.60°N
38.65°N
38.70°N
38.75°N
38.80°N
27.6°W27.5°W27.4°W 27.3°W 27.2°W 27.1°W
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The waters around Terceira Island in the Azores are a global hotspot
for cetacean diversity, particularly species that feed on deep-sea cephalopds
The largest of these deep-divers is the sperm whale (Physeter macrocephalus),
reaching up to 19 meters in length and diving to depths over 2000 meters.
Sperm whales are tagged and their diving profiles,
positioning, and vocalizations are recorded.
Sperm whale sightings around Terceira are increasing. We used >10 years of
systematic summer survey data to begin answering the question, why?
We modelled trends in sighting numbers as a function of year, bathymetry, slope,
distance, angle and spatio-temporal autocorrelation (assuming a ZiP distribution).
Results suggest an important, yet unmeasured, spatio-temporal process influences
sighting patterns. Perhaps annual changes in resource distribution. This might
explain why the effects of other habitat variables (slope ,bathymetry) were found
to be Marginal or Not-significant. What are your thoughts? Let’s discuss!
Faeces are collected for genetic
analysis of prey content
Prey distributions are mapped using
echosounders and eDNA sampling
of the water column.
Prey are opportunistically collected
to analyze calorific content