A dolphin travels through the mirror-like waters of the Hauraki Gulf near Gannet Rock. Photo / Supplied
A dolphin travels through the mirror-like waters of the Hauraki Gulf near Gannet Rock. Photo / Supplied
In the first of a five-part series looking at Auckland University's research in the region's blue backyard, science reporter Jamie Morton looks at efforts to track and monitor resident creatures like sharks, rays, seabirds, dolphins and whales.
Here's an incredible statistic: in Auckland's Hauraki Gulf, you can find one quarter of the world's seabird species - and around 20 per cent of its whale and dolphin species.
Auckland residents also might not realise how many large shark species are found in the gulf, especially in the warmerwater months of summer and autumn.
Each year, scientists have recorded many sharks as long as three to four metres - including hammerhead, bronze whaler, dusky, mako and blue sharks - along schools of 20 or more smaller hammerheads.
They also often see groups of several hundred common dolphins in the gulf, swimming in the middle ground waters and feeding on small schooling fishes.
Under the sea surface, life is anything but the "silent world" that famed documentary maker Jacques Cousteau once called it.
It's extremely noisy, with a myriad of animals, such as dolphins, fish, crabs and sea urchins, contributing to the submarine racket; one of the stranger sounds comes from a tiny shrimp dubbed the pistol or snapping shrimp.
Researchers refer to the big animals - sharks, whales, dolphins, rays and seabirds - as charismatic megafauna.
A Bryde's whale in the Hauraki Gulf. Photo / File
Closely watching them - and trying to pick out any concerning changes in their behaviour or numbers - is the challenging task of a team of University of Auckland scientists, and one that's done using some intriguing methods.
"Listening" to sea creatures has been part of their work since a collaboration between Australian, UK and Kiwi researchers began investigating how larval fish use sound as a long range orientation cue to find reefs.
Scientists deploy instruments in the Hauraki Gulf. Photo / Supplied
From that point, the knowledge of how marine animals use underwater sound has increased remarkably, and led to work around the interactions between sharks and fish a decade ago.
And 10 years before that, research on whales and dolphins kicked off when scientists established a catalogue of Bryde's whale dorsal fins and began collecting images of bottlenose dolphins from the region.
These catalogues continue today with some animals seen in the gulf for more than 15 years. There are also multi-year seabird monitoring projects.
These long-term research projects provide immense value in our understanding of population trends, threats and conservation management measures required to tackle threats.
More recent advances in technology have allowed scientists to look at a range of factors like habitat use, behaviour, movement patterns and the relations of individuals within populations, along with factors in their environment such as water temperature, prey and underwater sound.
Seabirds flock over the Hauraki Gulf. Photo / Olivia Hamilton
The researchers draw on tools such as suction cup "D-tags" that are attached to whales and allow them to determine the animals' sub-surface behaviour, effectively "seeing" beneath the sea.
The tags are fitted with time-depth recorders to log swimming speed and depth, along with two hydrophones that record all sound the whales make and hear, and 3D motion sensors that measure all sub-surface movements.
A Bryde's whale breaks the sea surface in the Hauraki Gulf. Photo / Olivia Hamilton
"We can't see most of what the whales are up to once they dive below the surface as the Gulf is often green with phytoplankton, so these tags have been really valuable in determining the whales' behaviour and habitat use," said Associate Professor Rochelle Constantine, from the university's School of Biological Sciences.
Dr Craig Radford, a senior lecturer in the university's Institute of Marine Science, has deployed a complex array of acoustic loggers deployed throughout the gulf that record a wide array of biological sounds such as fish, shrimp and dolphin sounds through to man-made noise from boats - and even seismic noise from earthquake events and the sound of rain on the sea-surface.
A Brydes whale in the Hauraki Gulf. Photo / Olivia Hamilton
The distance that they can detect sounds over depends how loud the source of the sound is: large ships can be picked up tens of kilometres away, but the range of detecting animal sounds is limited to a few metres.
"Our acoustic research has really highlighted the diversity of biological sources in the gulf, and we've recorded fish that we have known to produce sound, but have never managed to record in the wild, such has john dory and two-spot demoiselles," Dr Radford said.
University of Auckland researchers conducting aerial surveys over the Hauraki Gulf. Photo / Olivia Hamilton
They've recorded a new species - the New Zealand paddle crab - and a few earthquakes some 700km away.
"We are also integrating recorded ship noise with ship movement data to correlate with the tag acoustic information, showing whales are almost constantly exposed to vessel noise in the gulf and then modelling the effect of anthropogenic noise on whales in the gulf."
In the air, they've also been flying a 430km-long transect (observation line) across the entire gulf, recording every mega-fauna sighting and also surface plankton and fish aggregations.
A Brydes whale in Auckland's Hauraki Gulf. Photo / Supplied
"We have four observers flying at a speed of 100 knots along several lines within these boundaries and recording the location, group size and distance from the plane of all sharks, rays, seabirds, potential surface prey, whales and dolphins," Constantine said.
"Our aerial survey research has shown clear niche separation between the different species of whales and dolphins which is probably the reason the gulf can support year-round populations of three main species in the region - they each use a different area and target different prey with only small amounts of overlap."
One new project used gene sequencing to pick up zooplankton changes throughout the year and whether these affected Bryde's whale diet.
Surprisingly, they found that the whales were actively seeking out plankton year-round, instead of behaving like seasonal foragers.
"All of these different projects are woven together to give us the most comprehensive understanding of what drives the great diversity and abundance of megafauna and how changes to the gulf environment will affect the future of these species and their ecosystem," Constantine said.
"In the past decade there have been a few major issues of concern, namely the Bryde's whale mortality rates from ship-strike - which has now mainly been resolved with a dedicated commitment by the shipping industry to slow vessel speeds - bycatch mortality rates of seabirds and we are beginning to see effects of climate change in this region."
A recording instrument set up on the seabed in the Hauraki Gulf. Photo / Supplied
The biggest risks facing the gulf were primarily through habitat degradation, as the number of people living around the region rapidly increased, along with climate change.
The gulf is increasingly vulnerable to man-made effects such as run off caused by farming practices and land development, fishing pressure and vessel noise that masks the communication of many marine species, from the smallest plankton that use sound to settle on reefs, through to large whales that communicate with sound.
Climate change had already resulted in changes to water temperature and rainfall, which affected the base of the food-chain, phytoplankton, which propagated up the food chain to large creatures that require large volumes of prey to survive.
"The extreme El Nino event we saw last summer resulted in quite dramatic shifts in prey and megafauna distributions due to the warm water temperatures affecting prey movements," Radford said.
"Our research has been able to map these changes and we have a few students currently analysing these data to measure the impacts on megafauna in the gulf and make predictions of what the region might look like in the future and map the resilience of species to these changes."
