Maui's dolphins: project overview
Hector's dolphin: aerial survey (by: Will Rayment)
In January, WWF supported an ongoing survey of Hector's dolphin at Banks Peninsula to look at distribution and abundance. The survey took about 10 days, and involved many hours flying out from the coast searching for Hector's dolphins and recording sightings. Here Will Rayment, one of the research team, provides us with an inside view on what it's like to do an aerial dolphin survey.
Day 1
The aerial survey team assemble in Christchurch. The team consists of Drs Liz Slooten and Steve Dawson, both senior lecturers at Otago University, Simon Childerhouse from the Department of Conservation's Science and Research Unit and myself, Will Rayment, a PhD student in Liz and Steve's lab.
Day 2
First thing in the morning we call Canterbury Aero Club and chat to our pilot, Vaughn Richardson, who tells us that the plane is having some last minute safety checks done. We head to the airfield anyway to set up the cables for the GPS and palmtop computer in the plane which log our position when we are flying the surveys. By the time we have set up the plane, the gusty Canterbury nor'wester has arrived so it's too windy to fly today.
Before the actual survey begins we require a couple of training flights to allow the observers to get their eyes used to spotting the dolphins again and for the pilot to reacquaint himself with flying the survey flight lines. There is a light north-east breeze which is good for surveying. We fly at an altitude of 500 feet and a speed of 100 knots (185km/h).
This is quite a challenge for our pilot, but he copes admirably. Thorough training helps to ensure that the real survey data are as good quality as possible. We fly some practice survey lines on the south-west side of Banks Peninsula and see plenty of Hector's dolphin groups. The sea breeze picks up so we head back to base to check the data.
Day 4
Light north-east winds again so conditions are suitable for our second training flight. Everyone makes lots of Hector's dolphin sightings again, particularly Simon (a welcome newcomer to the team). Aerial surveys for Hector's dolphin work well because their distinctive grey and black markings stand out clearly against the blue or green background of the sea. The team is now ready to embark on the survey for real.
Days 5-6
Strong nor' west winds mean that we cannot do any work. We require light winds of less than 10 knots (18km/h) for survey work so that we can be sure we are giving ourselves the best chance of seeing the dolphins. Winds are so strong that the power lines joining the South and North Islands are blown down! On days like this we are glad that we have set aside plenty of time for the surveys. It also gives us a chance to plot the sightings we have seen so far.
Day 7
The winds have eased, so today we begin the first official day of the survey. On the first flight we complete 8 survey lines and make a good number of Hector's dolphin sightings. The observers measure the downward angle to each sighting and record this, along with the exact time, into a dictaphone.
Later we can use these details to precisely fix the position of each dolphin group sighted. So far, most of the sightings have been close inshore, as we would expect at this time of year. We are also lucky enough to see a group of 12 pilot whales and a group of about 50 false killer whales.
Back on the ground, we download the palmtop computer and GPS which record precisely where we have been, and transcribe the sightings information from our dictaphones.
Day 8
The winds are light at the 5am weather check so we get up and go. We finish the survey flight lines on the southern side of the peninsula and complete 3 lines to the north, before the sea breeze picks up and shuts down work for the day. It is disappointing not to get more done and we only see 6 Hector's dolphin groups.
Interestingly though, we do see some groups quite a long way offshore (between 6 and 9 nautical miles) and Liz sees a mother and calf just off Lyttleton harbour. Our survey lines extend to 15 nautical miles (27km) from the coast, well beyond the 4 nautical mile boundary of the marine mammal sanctuary.
Day 9
A strong southerly in the morning means we have no doubt we are sleeping in. The wind goes easterly in the afternoon but it is still too windy to work. There are not many survey lines left but we will have to wait at least another day to complete the survey.
Day 10
We're up at 4.45am and quickly get underway. Winds are light and the cloud cover means we can work very efficiently with no problems with glare from the sun impeding the sighting conditions. Many of the survey lines to be finished are a long way offshore, so it's not surprising that we do not see many Hector's dolphins.
Concentration becomes an issue on the long survey lines. It is actually hard work staring at the sea whizzing by, particularly when we are not seeing many dolphins. The weather holds and we are delighted to finish all the furthest offshore survey lines, some are as far out as 20 nautical miles (37km) from the coast.
After a fuel and coffee stop we're back in the air to complete the final offshore survey lines to wrap up the survey. We do not see any Hector's dolphins on these offshore lines but they will be very useful for comparison with the winter survey.
