A look back

We poked our nose out beyond the Kaikoura Peninsula but it was far too windy to do fieldwork today. Plenty of paperwork needed to be done though, mainly processing the data from the last few days of fieldwork.

We saw lots of whales on Saturday. Will Rayment and Liz Slooten were tracking whales and doing photo-ID. The WHOI team tagged two whales and flew the hexacopter above the whales to get measurements of their body condition. We retrieved our last tag was after midnight. A really productive day!

HL.160 "Tutu" showing his fluke.
(Will Rayment, University of Otago)

We are already starting to analyze the data, and over the next few months will be very interested to find out how data from this field trip compare to the long-term Kaikoura dataset. In 1990, Liz Slooten and Steve Dawson from the University of Otago started a research project on sperm whales in Kaikoura, using photo-ID, sound recordings, and behavioral observations. Graduate students and post-docs who joined the project include Nathalie Jaquet, who studied seasonal changes in the distribution and behavior of the whales. Caron Chessum, Simon Childerhouse, and Miranda van der Linde determined that the number of whales in the Kaikoura area has declined significantly from almost 100 individuals in 1991 to about 50 individuals now. (We are not yet sure if this means a shift in their distribution, with fewer whales coming close to shore, or an actual decline in the population.) Christoph Richter carried out detailed studies on the effects of tourism on sperm whales. Olaf Jaeke and Lesley Douglas studied sperm whale sounds, and Abe Growcott and Quin Rhinelander used the whales’ sounds to estimate their size. Brian Miller used a hydrophone array to follow the whales underwater. The University of Otago team also built directional hydrophones and hydrophone arrays for finding whales, and a stereo-camera system to measure whales.

Dusky dolphin at play. (Will Rayment, University of Otago)

Background data from the long-term study provide the context for the joint WHOI–University of Otago project. For example, one of the whales we tagged on this trip, known as Tutu or HL.160, was first seen in 1991 and has been seen 127 times since then. This is clearly a mature male. Another whale seen on this field trip, LNL.160, has been seen 180 times since 1994. Repeated estimates of this whale, using the stereo-photography and acoustic length measurements show that it has grown from 14.6 meters to 15.1 meters. These data on age and growth will be very useful in interpreting the information gathered on this field trip.

Hector's dolphins. (Leigh Hickmott, Open Ocean
Consulting/University of St. Andrews)

If the data on diving behavior we get from the DTAGS turn out to be similar to the data from the hydrophone arrays, then information from the two methods can be combined to provide insight into the diving behavior of sperm whales. On the other hand, if the results are different this will lead to further questions about whether the differences are due to the different techniques, differences between the individual whales in the two data sets, differences in the locations, changes in oceanographic conditions this year compared to earlier years, or a combination of the above.

To provide a break from the database work today, we did some research on two of the sperm whales’ smaller cousins. We spotted some Hector’s dolphins and dusky dolphins in the calm water on the north side of the peninsula. The dusky dolphins were doing their usual leaping and bounding. The Hector’s dolphins were much less boisterous, but very approachable and curious. Two of the Hector’s dolphins had joined a group of dusky dolphins, which is unusual. We took photographs that will be added to long-term photo-ID catalogs for these two species.