Swans’ role in ecosystem studied by Masters student
Another day at the office - swan researcher Henry Dixon on the mudflats at White Pine Creek. Photo: Supplied.
Collingwood resident Henry Dixon has spent the last 18 months studying the role of black swans in the tidal ecosystem of western Golden Bay as the subject of his Masters of Science through Massey University.
Anywhere between 10,000 and 15,000 swans are seasonally present around the inside of Farewell Spit, and Henry’s findings have generated much local interest. Last Tuesday evening he gave a public talk and PowerPoint presentation at the Golden Bay Community Centre.
It has been known for some time that the number of knots visiting Farewell Spit has been declining (around 60 per cent over the last 25 years), whereas numbers have remained constant in other parts of the country. Henry’s Massey supervisor, ecologist Phil Battley, did a survey in 2003 that raised suspicion that the swans were reducing the quality of the feeding habitat at the Spit. This encouraged Henry to do the follow-up study.
“We knew that swans impact on the eel grass from their grazing—up to a kilogram a day they can crop off—but I was more interested in finding out why they were turning the most luxuriant patches of seagrass into patches of bare sand.”
Swans not only graze, but dig for the seagrass roots and rhizomes. Henry’s nutrient analysis revealed that while the shoots were full of nutrients, the roots and rhizomes were full of sugary carbohydrates. “This explains why they are such active diggers; this carbo-loading gives them all the fuel and energy they need, plus some.” Despite this, Henry pointed out that there hasn’t been a significant increase in the swan population in recent years.
“Fish and Game have been tracking them for 30 years with an annual flyover every summer to count them, and there’s been no big increase. It’s a vast inter-tidal area; in reality there’s little more than one swan for every hectare.”
While the swans can certainly influence the habitat and dramatically alter seagrass beds on a localised scale, it is too early to say whether they are negatively affecting shorebird numbers, says Henry. He plans to hand in his report to his supervisor shortly.
Initially, Henry planned to do all his research around Farewell Spit, but because of the sheer logistics of getting around, confined it instead to the mudflats off Puponga, around Te Rae, and over at Westhaven Inlet (mainly the White Pine Creek area).
“There was hardly a day I wasn’t out there on the tidal flats over the whole late 2007 - early 2008 period. Since then it’s been once every few days. I got to really know the place, all its subtleties; it grew on me immensely.” Along with the weekly counting of swans, Henry also managed to investigate the density and distribution of 50 of the many invertebrate species—mainly worms and snails— found in the area and eaten by shorebirds. Henry also looked at biomass turnover rates and nitrogen levels in quantities of swan droppings, potentially useful in determining the swans’ possible contribution to the contamination of cockle beds. Two years ago, Alistair MacDonald of Westhaven Shellfish called for a swan cull. Consequently, Fish & Game granted several permits to shoot swans at Pakawau, where cockles are harvested.
Henry, now 26, attended Golden Bay High School until the fifth form before completing his high school education in Wellington. Working stints followed—apple-picking, tree pruning, café work, a hospitality course—and of course helping out at the Mussel Inn, owned by his parents Jane and Andrew. Scoring a six-month job on the assembly line of the Suzuki car factory at Hamamatsu, outside Tokyo, Japan, not only gave him some extra money but “the aspiration to get into something I was really passionate about.” Ironically, he met his Japanese wife-to-be, Emi, in Wellington before he left for Japan. They now have three children: Tane (5), Kiki (3), and Summer (1).
Henry completed his initial Bachelor of Science at Victoria University, specialising in Ecology before completing a year-long Masters of Conservation Biology course at the University of New South Wales in Sydney. In effect, he will soon have two Masters after his name.
As for his career: “I have a strong feeling my future lies in wetland conservation. I’m enjoying getting involved in the Streamcare group and Friends of Mangarakau Swamp, two neat local grassroots projects. Wetland conservation is an important issue globally and there are all kinds of amazing initiatives that people have started all over the world. I would like to travel and put my skills to use overseas for a while, but in the end Golden Bay is home and it’s where I’d like to end up eventually.”
Gerard Hindmarsh
