|
The
Dusky Dolphins of Kaikoura
Researchers
Study A Unique Population of Dolphins on the Far Side of the World
July 9,
2004
By
Jody Weir, Dusky Dolphin Research Assistant
Special
to AquaNews
 |
A dusky dolphin
performs a "backslap" in the waters off Kaikoura.
Like Pacific white-sided dolphins, dusky dolphins are known
for their displays of aerial acrobatics.
Photo:
Jody Weir |
KAIKOURA,
NEW ZEALAND - Twenty years ago, dolphin and whale expert Dr. Bernd
Würsig began studying dusky dolphins off the coast of Kaikoura,
a seaside settlement on the rugged East Coast of New Zealand’s
South Island. Dr. Würsig had previously studied dusky dolphins
in Argentina and wanted to see if his findings there could be attributed
to the dolphins in New Zealand.
Dusky dolphins
(Lagenorhynchus obscurus) are coastal dolphins found only
in the Southern Hemisphere. The populations that we know of are
found along the west, southern and southeastern coasts of South
America, along the coast of South Africa and Namibia, and all around
the South Island of New Zealand.
Dusky dolphins
look very similar to the Pacific white-sided dolphins (Lagenorhynchus
obliquidens) of the Northern Hemisphere, and are in fact of
the same taxonomic genus Lagenorhynchus. Like their Northern
Hemisphere cousins, dusky dolphins are most famous for their incredible
displays of aerial acrobatics.
A
Breed Apart
Dr. Würsig’s research showed that the Argentinian and
New Zealand dusky populations were almost identical, except for
the slightly smaller average body length of the New Zealand duskies.
When he looked at their behaviour, however, Dr. Würsig found
significant differences between the two populations.
Duskies in South America feed during the day by searching for schooling
anchovy in small, scattered groups. When a group comes across a
large school of anchovy, it performs a series of aerial displays
that involve a loud slapping of their bodies on the surface of the
water. This alerts the other dolphin groups, who immediately come
to the area, and together the group of dolphins herds and tightens
the school of fish into a tight “bait ball.” The dolphins
then take turns swimming into the bait ball and eating the fish.
| "As
I write this, the house is shaking so hard the monitor of my
computer is jiggling and my glass of water has some serious
wave action going on. These are the days for inside work!" |
The dusky
dolphins of New Zealand have two known foraging techniques. In the
Marlborough Sounds, on the northern bit of the South Island, dusky
dolphins hunt fish using the “fish ball” technique,
similar to those in South America.
In Kaikoura,
however, it’s a completely different story. Here, they feed
at night on a fantastic group of organisms that make up the Deep
Scattering Layer (DSL) of the ocean. During the day these organisms
stay deep in the water column to avoid being seen and eaten by predators.
At night, they rise much closer to the surface to feed.
Most predators
have a hard time finding and catching the DSL organisms because
it is dark, and many predators hunt by sight. Dolphins, however,
navigate incredibly well in the dark using a technique called “echolocation.”
By emitting frequent, high-pitched sounds that act as sonar, they
can dive and feed on the DSL for much of the night. In the morning,
they head back in closer to shore to rest and socialize.
Kaikoura’s
Secret World
 |
A dusky dolphin
performs a back flip - note the trail of water spray!
Photo:
Jody Weir |
This unusual
foraging behaviour may have developed in response to the unique
and ecologically important marine environment surrounding Kaikoura.
Just five
kilometres from the shoreline, a submarine canyon plunges to a depth
of 1,000 metres. Just a few kilometres north or south of the area,
the water at the same distance from shore is only 25-50 metres deep,
which is more typical for a coastal environment. To my knowledge,
the only other place in the world to have such a geological phenomenon
is Monterey Bay, California.
Why does
this matter to the marine critters that aggregate here? Well, as
it happens, the deepest water in the ocean is extremely rich in
nutrients. Ocean dwellers are messy eaters, and when bits of nutrient-rich
food sink from the surface to the bottom of the ocean, there fewer
things living in the deeper waters to eat the leftovers.
Usually,
this leftover food just accumulates at depth, except for certain
areas of the ocean where bathymetric features coupled with weather
patterns lead to an “upwelling” of these nutrient-rich
waters to the surface. The canyon off Kaikoura creates such an upwelling.
When deep-water currents bring nutrients closer to the surface,
they promote more plankton growth and hence more food for everybody.
In this
relatively small area, we see an incredible concentration of life
in comparison to the surrounding areas. It is home to thousands
of invertebrates, fish, seabirds, dolphins and whales.
The
Tourism Explosion
 |
| This
is me onboard our survey boat. I'm wearing a Mustang Suit
(meant for survival in Antarctic waters) and using our fancy
Nikon D1H digital SLR camera.
Photo:
Jody Weir
|
In the
past 20 years, Kaikoura has changed from a sleepy fishing village
to a booming hot spot for tourism. In the late 1980’s, only
20 years after the whaling industry in the area was shut down, whale-
and dolphin-watch operators appeared on the scene. Since then, the
industry has grown to be worth millions to Kaikourians, including
not only the tour operators and their employees but also hotel,
restaurant and shop owners.
The draw to swim with the dolphins is immense. People from all over
the world come to Kaikoura for the chance to be in the ocean next
to a dolphin. In the summer dozens of boats and hundreds of visitors
meet and follow the dolphin groups.
How much
is too much? Ongoing research in the area is key to monitoring the
response of dolphins to the growth and expansion of the industry.
Since the study of Kaikoura’s dolphins began before the tourism
explosion, we have some base-level data for comparison.
Research
At Sea
 |
| This
is an example of a distuinguishable dorsal fin, which gives
us the identity of the dolphin. The marks are caused by encounters
with sharks, orcas and other dusky dolphins. The skin on the
trailing edge of the fin is very thin, so it tatters easily.
Photo:
Jody Weir
|
Whenever
the wicked winds allow us, we head out in our boat and search for
dolphins. Sometimes this takes five minutes, other times it takes
hours, and sometimes we don’t find them at all. On a good
day, we find a group of dolphins that don’t appear to mind
our presence. It is very important to drive slowly and carefully
around dolphins so as to minimize disturbance.
As soon
as we find a group, we start recording data about the group’s
location, movement, distribution and composition. We also take photographs
of dolphins that have any kind of distinguishable markings on their
dorsal fins. Somewhere between 7,000-10,000 dolphins spend time
in the Kaikoura area throughout the year. Only 1 in 3 of these have
any kind of markings on their dorsal fin that distinguishes them
from the thousands of others.
Back at the lab, our data analysis consists of hours of looking
through digital photographs in an effort to identify individuals.
Have they been photographed before? If so, in what years, what months,
what area, with whom were they seen? This process takes a considerable
amount of time and is generally left to days when the rains poor
down in Kaikoura, or the gale-force winds threaten to shake the
house down. (As I write this, the house is shaking so hard the monitor
of my computer is jiggling and my glass of water has some serious
wave action going on. These are the days for inside work!)
By continuing
to monitor the behavioural and association patterns of the dolphin
groups that come to Kaikoura, we hope to be able to detect and possibly
prevent undue stress to the animals. The swim-with-dolphin operators
are very supportive of our work. They, too, believe that a healthy
dolphin population is essential for the health of the industry.
What can you do?
Every year, approximately 70 volunteers from around the world enroll
to help with this project through the Earthwatch Institute. If you
are interested in participating, visit the
Earthwatch Institute website and follow the expedition links
to New Zealand Dolphins.
If you
participate in animal viewing activities while travelling, you can
help by supporting companies that are sensitive to animal welfare
issues, such as ecologically responsible whale watching operations.
Jody
Weir is a Research Assistant with Dr. Bernd Würsig of Texas
A&M University. Volunteers and funding for the project are generously
provided by the Earthwatch Institute.
|
