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Today we conducted a visual transect survey of our current study area to describe the distribution of blue whales. We covered approximately 80 nautical miles in fantastic sightings conditions and remarkably all the many blue whale sightings were concentrated in the first fifteen or so miles of the survey. Outside this hotspot sightings were few but included humpback, minke and southern bottlenose whales.
This survey will help us assess if the visual and acoustic data suggest a similar geographic distribution of whales. These data will also provide an indication of what proportion of the blue whales in an area are singing or calling at any one time.
Like the blue whales, the few krill balls detected with the echosounders were concentrated at the start of the survey. Although they appeared small on the sounder a very rough back-of-the-envelope calculation estimated one of these dense krill balls could represent about 400 tonnes of krill. To get a better estimate will require data on the size distribution of krill within the balls and this requires a trawled sample – but we have not had any luck with that yet.
Tonight the echosounder team and ship crew will attempt to sample krill and tomorrow we will return to the blue whale hotspot to conduct focal follows and collect more photo-identification images.
Map
A map showing Australia and Antarctica. The map shows the journey of one voyage that has occured in the season, with each route highlighted in a distinct colour.