Hector’s Dolphin Research; Best Summer Day So Far……

World leading marine mammal experts Professors Steve Dawson and Liz Slooten are currently in Akaroa carrying out Hector’s Dolphin research. They have given us an exclusive sneak peak into what daily life is like for them on the peninsula….

”After a summer of unstable weather, the day has dawned calm and sunny, and promised to stay that way. We hit the water soon after seven, and head out of the harbour towards Birdlings Flat, where Banks Peninsula meets the Canterbury plains.

Our aim is to cover the south coast, so we barely slow for the dolphins we see in Akaroa harbour. Once at the heads, we’re “on effort” travelling at a slow planing speed in our 6.6m rigid-hulled inflatable, and stopping for any dolphins we see.

It’s flat calm. Virtually no swell, and perfect sighting conditions. The first group, off Squally Bay, is diffuse – spread over a couple of hundred metres. They’re busy – feeding, but still coming over to the boat occasionally. With them is a large bunch of spotted shags. The dolphins and shags are diving steeply, probably for the same prey. There’s a dark mark on our echsounder showing a dense prey aggregation at 15-20m deep. The dolphins prey mostly on small fish – surprisingly small, in fact most fish taken are only a few cm long.

Identifying Hector’s Dolphins

We are here to photograph dolphins that have individually distinctive natural marks – usually nicks from the dorsal fin. We use these like tags, they tell us who is who, and of course who goes where, with whom. More importantly resightings tell us how often females breed (every 2-3 years), and how long the live (25-30 years). Indeed monitoring change in survival rate is the main way that we keep tabs on whether the poplation is doing okay. These dolphins had a very tough time in the 1970s and 80s, when many hundreds were caught in gillnets and trawls. Thanks to inshore restrictions on these fishing methods, they are doing much better now, but still too many are caught for the population to recover. The population is about a third of its original size.

The next few groups also have shags in attendance, and are busy feeding. There have been only a few marked dolphins so far, but we manage to get their pictures. Dolphin photo-ID is a bit like photographing sport. The dolphins move quickly and erratically, and the dorsal fin is above the surface for about a second. If you haven’t had your coffee, you’ll miss the shot.

Since the dolphins are often found very close inshore, we go into each of the small bays. In one of the bays, we find a shag behaving oddly. Mostly, they fly off when you get close. But this one was preoccupied. It had caught a decent-sized banded wrasse, and spent the next several minutes trying to swallow it. Successfully! Noteably, it didn’t fly off, instead it slowly swam to shore. I doubt it could have flown at all.

 

The next few dolphin groups are harder to work with. They’re in stealth mode, not really very interested in the boat. When close, they seem to like to surface at bad angles – we need our pictures to be side-on. Our strategy here is to stop, and have a break. Often, they’ll get curious and come over. So far we have pictures of several individuals with rather subtle marks, but this way we get the picture of the best ID of the day. It’s a dolphin we’ve known since 2007, when we noted (from its size) that it was then at least 2 years old. So it’s 12 or 13 years old now – about 40 in human years. We don’t know what caused the large cut in its dorsal fin, but this mark has not changed in a decade.

The number of dolphins we see on these alongshore surveys is very variable. Small changes in distribution, as they follow their food around, mean that some days we can see 200 or so, but the next day, just a few. While Hector’s dolphins have small home ranges for a dolphin, they still move around over tens of kilometres. That’s why we measure population change via measuring survival rate.

We eventually get to Birdlings Flat, at the base of the Peninsula. We turn for home, about 19 nautical miles away (35km). It’s still flat calm. It’s been a great day. Now we go back to sort out the data and get prepped to do it all again.”

Prof Steve Dawson & Prof Liz Slooten