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Wednesday <strong>January</strong> <strong>10</strong> <strong>2018</strong> News Latest Christchurch news at www.star.kiwi BAY HARBOUR Local News Now PAGE 7 Fire rages, homes at risk Impact of taking estuary shellfish Little is known about who is harvesting shellfish from the Avon-Heathcote Estuary and what impact, if any, this is having on the sustainability of the beds and bird feeding grounds. Environment Canterbury councillor and Avon- Heathcote Estuary Ihutai Trust member Cynthia Roberts is hoping new research will shed light on what’s happening. Sarla Donovan reports ANYONE WHO regularly drives along the McCormacks <strong>Bay</strong> causeway can’t help but notice them. Groups of people dotted over the sand at low tide, with their trousers and skirts hitched up and buckets nearby. They are collecting shellfish from the sandbed and there seems to be an increasing number doing it. But how safe is the practice? And how sustainable is it? That’s what a research project aims to find out. Canterbury University third year biological science student Stephanie Hampson has been brought on board this summer to try and shed some light on an area in which there are “gaps in our knowledge,” admits Cynthia Roberts. Both the university and the Avon-Heathcote Estuary Ihutai Trust have contributed to the costs of the summer research project, which will be supervised by Associate Professor Islay Marsden, an aquatic ecophysiologist from the School of Biological Science. Prof Marsden has been a member of the trust for <strong>10</strong> years and is currently its chairwoman. The trust manages the ecological welfare of the estuary and is working to update its management plan, said Dr Roberts. “As part of that, we realised there are gaps in our knowledge, and one of those was shellfish and harvesting. We’re particularly interested because you regularly see people harvesting at the end of the causeway in spite of signs saying it’s not healthy – it is still quite contaminated after the earthquakes and after high rainfall.” The level of contamination varies, with the signs only put up when there are concerns, but Dr Roberts said people continue even then. “Signs were up pretty well continuously during the heavy winter rains. The estuary is a receiver for all the contaminants coming down from rooftops, roads, pathways. Stormwater carries high contaminants, such as dog faeces and so on, and this is the receiving basin of all the stormwater off quite a large catchment.” One of the aims of the plan is for people to be able to resume shellfish harvesting, she said: “But we want to make sure if they are – they’re not poisoning themselves.” Miss Hampson said she was looking forward to the project. “I think it will be very interesting. I haven’t done much social science and I’m learning a lot about how people perceive the environment. A lot of people know about the bad – like smell, murky water – but something like the sea lettuce for example, they don’t know if it’s good or bad.” One of her tasks will be asking estuary users to complete a questionnaire including what they are collecting shellfish for and how often they come. There’s also a bit of citizen science involved. People who have been regular collectors over the years may have insight into how the abundance of shellfish has changed. And there’s also the small matter of the health and density of the shellfish beds themselves, and whether harvesting is really sustainable. Dr Roberts compares them to kidneys. “Wonderful filters of any waterway; they’re a very important part of an estuary eco-system. We want to maintain a healthy population, so will be doing RESEARCH: Dr Cynthia Roberts on the mud flats beside Mt Pleasant causeway, with cockle shells, crabs and barnacles. some sampling and looking at the health of those by doing some quadrant surveys.” Research will be based at the end of the causeway but may be extended to two other sites on the Southshore side of the estuary. There has been work done on the health of shellfish over the past 30 years, but not in the postearthquake period. “We’re intrigued that so many groups are out there harvesting,” said Dr Roberts. “Are they using it for bait? . . . we don’t know. One of the things that’s happened around the country is these things creep up on us and all of a sudden we’ve wiped out a whole area of paua or crayfish and have lost the ability to replenish it because it’s too late. “And we have one of the biggest populations of godwits and there are many other estuary bird feeders such as pied stilts, spoonbills and herons, for example – which are very dependent on the food in the estuary. “There could be a trophic cascade (where an alteration in the food chain triggers changes in the ecosystem). Over harvesting in any environment could upset the balance.” Does she think the influx of people into the city helping with the rebuild has anything to do with it? “The answer to that is one of the reasons we want to do this research. I think full stop there’s been an increase in population in Christchurch and we have more people coming in who love fishing and catching their food. “This is a lovely, free resource and there’s all sorts of reasons people might be out there. Maybe those people haven’t been through our school system where we put such an emphasis on the environment so it’s part of our challenge to educate them.” The research findings should be published by the end of March. ECO-SYSTEM: The estuary at low tide near Southshore. Research may be carried out on the Southshore side of the estuary.
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