Is wild food safe to eat?

Is wild food safe to eat?

This article has been written exclusively for Food New Zealand by the New Zealand Food Safety Science & Research Centre.

Who am I?

This is not science fiction. We have in our midst a dark and mysterious creature that travels a vast distance across the Pacific, with a faultless sense of direction, to some remembered place in Aotearoa. It glides, mostly unseen, beneath fern-cast shadows, can live for over 100 years and grow up to 25 kg, and is able to survive long enough out of water to take shortcuts across land. When some inner prompt calls ‘time’, it changes appearance and swims all the way back to its secret subtropical spawning ground to breed and die. Even now, no one knows exactly where that place is or for how many millions of years these epic journeys have been part of this awe-inspiring lifecycle. For a long time these special creatures were disregarded, undervalued and even, in the 1930s, classified as vermin and exterminated in huge numbers to stop them competing with the newly introduced trout. But tuna/eels have always been a taonga/treasure for Māori - once a main source of protein and no doubt essential to sustain inland expeditions. Māori smoked eels too, which meant they could be safely consumed for a long time after being caught.

Eels as food

Attitudes to many things, including the value of eels, have changed over the last century. Their commercial potential was exploited fairly recently, and this put a stop to their extermination. Smoked eel has become a gourmet delicacy at a gourmet price. A family of entrepreneurial Dutch immigrants, the Tecklenburgs, set up a company in Te Kauwhata in 1964 – NZ Eel Processing Company Ltd - to process and market eels, which were a traditional food in Holland. And now there are niche companies like Apatu Aqua in Northland, smoking eels to order for restaurants. The Ministry for Primary Industries manages the population closely under the quota management system. The quota is currently 400 tonnes per year (for long- and short-finned eels combined), most of which is exported to China, the UK, Europe, and Australia, either live or smoked. They must be larger than 250 g and under 4.0 kg. Harvesting company, Southfish Ltd, says the feedback from the individuals around the country who catch the eels, is that the stock is healthy and plentiful. But eels have a major problem – dams and other barriers which stop

Cawthron Scientist, Dr Jonathan Puddick is an expert on freshwater cyanobacteria and the toxins they produce

Eels under threat

Whakakī Lake Trustee chair, Richard Brooking

A remote shallow lake near Wairoa on the East Coast of the North Island, close to the sea, south of Māhia Peninsula, has a population of particularly fine-tasting eels (according to the locals), routinely harvested by Māori for hundreds of years. Unfortunately Whakakī Lake is now, like many other New Zealand lakes and rivers, polluted by agricultural run-off and silt, and this leads to high numbers of cyanobacteria, which thrive on the surplus nutrients – nitrates and phosphates. Under certain conditions, the cyanobacteria in the Lake produce particular toxins, called nodularins, which accumulate in the eels. There are other cyanobacteria that produce different toxins but these are not presently observed in Whakakī Lake. If people eat the contaminated flesh in high enough quantities (yet to be determined), the poisons can lead to liver cancer, even death. As well as poisoning the eels, and potentially people, cyanobacteria en masse starve other lake creatures of oxygen. Although they absorb carbon dioxide and emit oxygen during the day, at night time they switch to using oxygen to ‘burn’ sugars for energy, and instead emit carbon dioxide.

Can we fix it?

The NZ Food Safety Science & Research Centre (NZFSSRC) learnt about the community’s problem, and linked with the relevant experts at Nelson’s Cawthron Institute, and concerned locals, to put in a joint bid to MBIE’s Vision Mātauranga Capability Fund. The bid, led by NZFSSRC, was successful, receiving $227,000 for work to monitor and

determine safe cyanobacteria levels. Dr Jonathan Puddick is an expert on freshwater cyanobacteria and the toxins they produce. His Cawthron colleague, Dr Tim Harwood, is an analytical chemist specialising in the accumulation of toxins in food gathered from land and sea, and is also deputy director of the NZFSSRC. Together with NZFSSRC chief scientist, Massey University Distinguished Professor Nigel French, there is much confidence that whatever can be done, will be done. The project will be dynamically driven by NZFSSRC manager, Wendy Newport-Smith, who organised the bid, and has previously won substantial funding for East Coast restoration projects. The locals, represented by Whakakī Lake Trustee chair, Richard Brooking, will eventually do all of the water measuring and monitoring, and become masters in cyanobacteria biology. Basically, they want to know when the eels are safe to eat – cyanotoxin levels can vary widely throughout the year. The local team will provide information on harvesting and consumption practices, which together with the eel toxin level information will allow scientists to determine safe levels. On-site toxin measurements using technology similar to a COVID RAT test, will be checked against measurements made in the Cawthron lab using high precision analytical chemistry instrumentation. This will tell them how reliable on-site testing instruments are and whether they can be trusted. It will take decades to clean up our lakes – even if all pollutants stopped immediately - so in the short term, we need to make sure the eels are not going to make people sick, and manage the eel population, which was declining for a long time. Locals estimate that the number of eels at Whakakī Lake is about a quarter of what it was in the 1950s. The Lake trustees and volunteers have planted thousands of natives to stem future run off, but the legacy of nutrients lying on the lake floor in the form of sediments is more problematic. Though suffering much like any other waterway, Whakakī Lake is particularly important regionally, nationally and internationally, because of its special characteristics. The 500 hectare body of water is an intermittently closed and open lake (ICOL) that has to be vented to the sea several times a year. It is surrounded by extensive wetlands, hosts a huge variety of bird life, has supported local Māori for centuries as a major food sources (kapata kai), is the largest body of freshwater on the East Coast of the North Island, and was recipient of a Ramsar Wetland Conservation Award.

Be aware of risks from wild food

Without putting a damper on the fresh enthusiasm for wild food gathering among other sectors of the population, there are some food safety risks to be aware of. For example, watercress may be growing in polluted water. NZFSSRC, with partner Plant & Food Research, have another project on the East Coast, at Uawa/Tolaga Bay, to investigate the safety of wild watercress and the possibility of growing it hydroponically, thus guaranteeing the purity of the water and opening commercial opportunity. In 2017, there was a rare and extreme case of food poisoning in New Zealand, apparently from curried wild boar. Three of the unfortunate Waikato family collapsed immediately after eating it, were in serious danger, and took a very long time to recover. The cause could not be proven. Scientists and health professionals suspected botulism, but tests for this and 1080 came back negative. While cooking kills most microorganisms, some bacteria produce toxins that are heat proof. Tim Harwood says we need to continually consider the food safety risk that comes from gathering and consuming shellfish, which are filter feeders, sieving and retaining whatever is present in the water column. This can include myriad dissolved pollutants and various other natural toxins that are produced by some microscopic algae. Like all marine and freshwater animals, they are susceptible to whatever “comes down the pipe”. After heavy rain – an increasing occurrence – cow, sheep and dog faeces can wash into rivers and sea, and sewage systems can overflow. Hunter-gatherers should check MPI and Regional Council websites for advisories. And people should use their observational common sense to assess the likelihood of pollution – is the catchment area a low or high intensity agricultural area? How big is the human population? Is there riparian planting to protect the waterway? Are there cribs and baches with old septic tanks of doubtful integrity? Does the water look clean, or is there a lot of visible algae? Does it contain healthy signs of life? Sanitary surveys are regularly carried out in commercial shellfish growing areas to check possible pollution sources like septic tanks. As well as human waste, a lot of pharmaceuticals, agrichemicals, paints and other unmentionables go down the drain and end up in our ocean. Harwood says there needs to be more education about sewage and waste water, “It’s a case of out of sight, out of mind”. Another scientist at Cawthron Institute, Dr Louis Tremblay, is measuring exactly what chemicals are ending up in our rivers – one test site runs through industrial Auckland, the other through farmland and light industry in Southland. The list of chemicals he has found is very long, though many are present in tiny amounts. His presentation to NZFSSRC members (and many others of interest to food professionals) is at https://www.nzfssrc.org.nz/events/annual-symposium/#/ Says Harwood, “The harvest of healthy food is critical to all New Zealand, whether customary harvest or commercial. It’s the backbone of our economy, and it all comes back to clean water.” The eel population is a proxy for the health of our freshwater. These marvellous creatures have been around for 50 million years and may surely lay claim to permanent residency. They deserve sanctuary in our lakes and rivers after their epic journeys.