Poseidon of the Bay, Nathan Pettigrew, talks stingrays.
Rain or shine. Winter or summer. There’s always one creature I see while I’m out venturing in my kayak. I’m of course talking about our local rays.
I think they are wondrous. There’s a tranquillity about the fish, thanks to their ability to ‘fly’ so gracefully. And I’m always astonished that something so wild is so easy for us to see in the ocean.
There are three types of ray in the Bay of Plenty; the short tail stingray, the long tail stingray, and the eagle ray. These rays (the eagle ray in particular) are so numerous in our region that they are considered to be kaitiaki, or guardians, by local Māori.
How to tell the difference? The eagle ray swims through the water by ‘flapping’ its wings like a bird in an up and down motion. The long and short tailed rays propel themselves with an undulating or ripple motion through their wings.
Rays are a close cousin to sharks, and feed on shellfish and small crabs. They play a large role in the food chain as they prey, and are preyed upon. I often see half eaten rays being brought to the surface by orca, and live rays leaping into the air to escape their predators. I was also once fortunate enough to witness a bronze whaler shark thrashing about in the shallows in an effort to grasp onto an eagle ray, which make up part of the shark’s diet. And these fascinating bottom feeders may also hold the key to the health of our harbours and give us clues to help improve marine life in the ocean.
Recently, I met up with good friend and PhD stingray researcher, Helen Cadwallader. She has a real passion for these underwater gliders and has spent many hours around the Tauranga Harbour, studying their feeding behaviour and distribution. The rays give away their favourite spots by leaving behind a feeding ‘pit’ which looks like a sunken bowl in the sand. It’s very recognisable when the tide is low. She also uses a tagging technique to find out where each individual travels to. But it’s the food chain that really interests her. She explains to me over a lesson in stingray barbs: “Knowing where the rays go and what they’re doing in different areas is important if we’re going to protect their essential habitat. Rays accumulate contamination from their food and their environment, and may end up with much higher levels of pesticides and heavy metals than the surrounding environment.”
This build up of toxins is then passed onto larger predators, such as our local orca, that feed on them. These orca are being hit with huge amounts of toxins, as they are at the top of the food chain.
But, there could be some answers on the way. Helen will be using muscle samples from two species of ray to work out if time spent in our increasingly urbanised waterways is affecting their heavy metal levels. Helen’s hard work, determination and skilled research will help us protect our endangered orca population. Like many of you ocean lovers out there, I look forward to finding out the results of her research.
FOR INFORMATION ON HELEN’S WORK, VISIT: apexpredator.co.nz