Mussels: more, fresher, better


You might have noticed – your supermarket’s seafood counter has got bigger, there’s a lot more variety, a constant supply and hardly anything pre-packaged. It’s changed because you’ve changed.

You go to the supermarket more often, you’re more likely to pick up a basket than push a trolley, and you want your goods super fresh in quantities that you can specify. You welcome ideas on what to make for dinner, especially if it comes with cooking advice.

And you’re eating more seafood than ever, says David Jose.

He is the seafood manager at Foodstuffs, the company that runs New World and Pak’nSave supermarkets.

Why we’re eating more seafood

More people eating more seafood, he says, can be attributed to three things. Firstly, there’s those changing shopping habits, then there’s the enduring marriage between television and cooking competition shows.

Masterchef and Our Kitchen Rules are in your face, showing you how to cook. The competitors use seafood quite often and they show you that it’s pretty easy, that it’s healthy and good for you and looks trendy at the same time. That’s where the biggest change has come from.”

The third factor is New Zealand’s evolving ethnicity. Jose says Asians, in particular, view seafood as their main protein, in the same way we have traditionally viewed red meat.

Live mussels are a huge part of that, particularly at Pak’nSave. While many people traditionally regarded them as a snack, Jose says mussels are now more often bought by the kilo, sometimes up to three or four kilos at a time.

That means that getting them through the supply chain quickly is crucial, as is consistency.

“We’re very spoilt here. We can collect seafood at the beach and we expect to buy product as good as those we collect ourselves. We want the best, as fresh as we can possibly get.”

Foodstuffs NZ seafood manager David Jose. [Foodstuffs]

A bumper year for mussels

This season, as it happens, mussels are better than ever.

Mussel farmer Graeme Clarke says it’s been “20 odd years or more” since he’s seen mussels as big as the ones he’s harvesting in the Marlborough Sounds this year.

 “It’s amazing, the growth rate has been incredible.”

Fellow farmer John Young agrees: “I haven’t seen mussels this fat in a long time. We’re having a wonderfully productive season, it’s phenomenal.”

The wet spring and plenty of nor'west winds have been good to mussel farmers in the Sounds. It’s brought more food for their crop to help boost growing conditions. El Niño, the weather pattern that brings the threat of drought to eastern areas, and this year is being compared to the horror drought of 1997–98, is, ironically, a welcome visitor here.

Almost 700 mussel farms in under 40 years

Commercial mussel farming began in New Zealand in the late 1970s and expanded rapidly over the next decade. Today, there are almost 700 mussel farms operating, most of them in Marlborough. It is a multi-million dollar export business that underpins the ambitious plan of Aquaculture New Zealand to achieve $1 billion in overseas sales for the sector by 2025.

But it is also an industry that continues to face fluctuating harvests and a raft of environmental issues that need a combination of science, ingenuity, cooperation and courage to address.

John Young is a strong advocate of the need for science in the mussel industry. He has farmed in the Marlborough Sounds for more than 40 years and ridden the waves of prosperity and heartbreak, misinformation and bias that have come with the territory.

“What I do know is that as a farmer you’ve got to move quickly when something isn’t right, otherwise you go broke.”

More science welcome to commercial mussel farmers

He remains grateful for the evidence provided by science that has helped grow the industry, but cautions that the business is “notoriously difficult”.

“Weather mechanisms are critical, any research that can look into that is very valuable. So would be knowing the complete hydrology of Golden Bay and its relationship to the biology – I’d love to see that full scientific picture and it would help immensely with management of the farms.”

NIWA is spearheading several research projects that are beginning to unlock some of the triggers that drive mussel production – from the reliability of spat (settled larvae) production to whether the strength of the shells influences the quality of the flesh.

NIWA’s Jeanie Stenton-Dozey and John Zeldis measure shell strength in the 'Mussel Crusher'. Variations in fatty and amino acids, sex, shell dimensions, and body weight are also recorded at NIWA's site in Christchurch. [Joseph Johnson]

Combining climate and ecology research to help the mussel industry

One of those projects is a combination of NIWA’s climate and marine ecological science capabilities.

Each month NIWA releases its Seasonal Climate Outlook, which forecasts weather probabilities around New Zealand for the next three months. The rural sector uses these outlooks to help them prepare – especially this year with
El Niño threatening to ramp up its intensity.

Now, NIWA Principal Scientist Marine Ecology, Dr John Zeldis, is developing something similar specifically for the mussel industry in the Marlborough Sounds, based on his collaborative research with the industry. Farmers could use such forecasts to more accurately determine the best time to harvest, or whether to harvest at all, or seed new lines, as well as gain a far better understanding of how climate affects their business.

One of the key elements that has enabled Zeldis to develop this capability has been a detailed set of data on mussel meat yield in Pelorus Sound collected by seafood company Sealord between 1997 and 2005.

“Every time a line was harvested, they took 20 mussels off and weighed their meat.” There were 13,000 individual records in this data set, giving a detailed picture of variation in meat yield per mussel.

Two years into this data collection, mussel meat yield began to drop, until it was 20 per cent below normal. The industry was worried that they had over-stocked the Sounds with mussels. The slump in production lasted for three years before the crops recovered in 2002.

Fortuitously during this period another data set, this time documenting water quality, was also being collected in a collaboration between an industry consortium (Marlborough Shellfish Quality Programme) and NIWA. These data included information on the amount of phytoplankton and seston available. Seston is suspended organic matter (including phytoplankton) that floats in the water, which constitutes mussel food.

Production changes are caused by climate, not intensity

Zeldis discovered that by relating mussel meat yield fluctuations to a number of climatic factors, he could see a useful relationship between climate and the supply of food for mussels. Furthermore, the meat yield fluctuations observed between 1997 and 2005 occurred independently of farm stocking rates. In other words, mussel yield is driven by the climate and not related to farm stocking rates.

“Changes in production aren’t caused by the intensity of farming; they are caused by climate.”

What also became clear to Zeldis was just how crucial the occurrence of upwelling in Cook Strait was to the mussels. This upwelling, strongest in El Niño summers, supplies nitrogen-rich water from the Strait into Pelorus Sound, enabling the seston to proliferate.

“Upwelling is related to winds and is often detected as cool sea temperatures. Westerly winds drive the upwelling, and that’s when we see cold water in western Cook Strait and near the entrance of Pelorus Sound. In terms of bringing nutrients toward the surface, upwelling is most effective between October and March and almost completely disappears over winter.”

In winter, however, the mussels’ food supply is influenced by winter rain and increased flow rates of the Pelorus River feeding into the Sound.

What Zeldis wanted to know was whether it was possible to use that information to forecast seasonal production.

Marlborough Sounds mussel farm. [AquacultureNZ]

Predicting mussel production in Pelorus Sound

“It looks very encouraging – our studies show it may be possible to predict mussel production in Pelorus Sound for time periods of three to six months into the future.”

The process is complex – wind and river flows are not forecastable and had to be substituted with equivalent variables to make the forecast model work. But testing using historic yield and climate data has produced some outstanding results. “The predictions were just as good, if not better, and we are pretty confident we have the variables that are forecastable to predict mussel yield.”

There is still some work to be done on some “fuzzy” areas in the model. But Zeldis says they should know by early next year what level of confidence can be ascribed to the forecasting.

It will then be up to the industry to decide how to use it – but the benefits seem obvious: the ability to forecast growing conditions for the next six months, information about the longevity of good or bad conditions and, ultimately, improvements to the bottom line.

Pintpointing the best times to harvest

While Zeldis is focused on climate parameters, colleague Dr Jeanie Stenton-Dozey is taking a close look at the mussels themselves.

The marine ecologist knows that one good season of fat, juicy mussels isn’t always followed by another, and she is applying her science to find out why.

The catalyst for her research was the harvest in the Firth of Thames in 2011, 2012 and 2014 – yield declined, the mussels themselves were skinny and the flesh wasn’t in good enough condition for the food market.

Debate in some parts of the industry centred on whether to leave the mussels on the lines to fatten up or harvest them and look for other markets.

Fortunately, if a mussel can’t meet the standards for the export food market, it can be processed for the nutraceutical market – provided the omega and fatty acid contents are retained.

Greenshell™ mussels are purported to have anti-inflammatory properties that are easily absorbed by humans as omega-3 fatty acids, amino acids, minerals and carbohydrates. Freeze-dried mussel powder, taken as an oral dietary supplement, has found a steady market, particularly in Germany and the US. In the year to April, $9.2 million of powder was exported along with $23 million of mussel oil.

Stenton-Dozey wanted to know if she could identify trends in the condition of mussels that would enable farmers to pinpoint the best time to harvest and maximise the value.

This year she began a new three-year monitoring project – every two months mussels arrive at her Christchurch base from the Firth of Thames, Marlborough Sounds and Stewart Island for analysis. Body dimensions are measured, along with flesh weight, gonad weight and reproductive conditions. The fatty and omega acid profiles are measured, seasonal variation is assessed, and from that a library of mussel data is beginning to grow.

“At the same time we are collecting information on the environmental parameters such as water temperature, turbidity, nutrient levels and chlorophyll-a levels, to get a better handle on the relationship between the mussels and their growing conditions.”

It is early days, but Stenton-Dozey believes a food supply issue is most likely to be the key factor in poor mussel production.

“It’s not the stock. But it could be combinations of low food supply, long sustained high temperatures which affect metabolic rates, and long periods of stratified water preventing nutrients reaching the light-filled surface waters where plankton need to grow.”

Ellie Kerrisk from SPATnz examines a flask of microalgae grown as mussel food in the hatchery. [Tim Cuff, SPATnz]

Spat survival continues to be an issue

However, there is no mussel industry without spat, and that too is something of an enigma. There are three sources of spat in New Zealand. Currently, most of the spat is harvested from the wild, with up to 90% harvested from Ninety Mile Beach in Northland, where small pieces of algae, sponges, and other marine debris on which mussel spat have settled (referred to as Kaitaia spat) wash up onto the beach in particular weather. The spat, along with all the seaweed and debris they are attached to, are collected and transported to mussel farms around the country. Exactly where the Northland adult mussel beds are is a mystery. The spatfalls happen in late spring and through the summer, although NIWA marine scientist Dr Ken Grange says over the past couple of years, spat hasn’t come ashore as often or in as much volume as previously.

Wild spat is also harvested from the mussel culture regions of Marlborough Sounds and Tasman/Golden Bays where farmers hang out hairy ‘Christmas tree’ ropes that mimic the settlement surfaces preferred by the larvae. The most recent development is a state-of-the-art hatchery, SPATnz, which opened in Nelson this year aiming to supply 30% of the industry’s spat needs by 2020.

Having several sources of spat is a smart strategy for ensuring sustainable production, but not all the spat survive the journey to the grow-out areas and Ken Grange is keen to build on previous NIWA research to find out why. Would mussels ultimately fare better if they were transported under different conditions? Are they getting enough oxygen as they are trucked south? Should the spat be stripped off the seaweed before farmers get it?

“There is not a lot of research into issues such as oxygen depletion at the moment. We want to take some of the spat to our Northland Marine Research Centre at Bream Bay (near Whangarei) where we can keep it for a couple of weeks and fatten it up. Or maybe we will try to encourage it to leave the seaweed so we can get it to farmers in better condition with no debris, which would mean farmers getting more spat for their money.”

Dr Grange intends to compare the success of spat handled in these novel ways with spat handled as it is now, with the aim of improving the existing guidelines on spat handling that would cover temperature, oxygen rates, humidity and optimum harvest times. This research will take another season to complete.

Life for the spat once they have been seeded onto the culture ropes in the mussel farms continues to be challenging because there they have to compete for food with other marine creatures, including each other, are preyed on by fish that take advantage of the delicious smorgasbord prepared for them by hard-working mussel farmers, and have to deal with the changing environment that Mother Nature serves up. It is these processes that are the focus of Dr Barb Hayden, NIWA's Chief Scientist, Coasts and Oceans, who knows from many years working with the industry that improving the ‘retention’ of spat on the mussel ropes will make a significant difference to farm productivity.

A sustainable growth story

This research is helping to build a more robust industry that is increasingly important to New Zealand’s brand and to the diets of New Zealanders. If there’s any evidence needed of that fact, it can be found at this year’s South Island Farmer of the Year competition – won for the first time by a member of the aquaculture industry – John Young, Managing Director and part owner of Clearwater Mussels and a New Zealand aquaculture pioneer.

Need more evidence? Take a look at the industry’s sustainable growth story, below.

New Zealand Aquaculture: A sustainable growth story [PDF 1.5 MB]

And next time you’re at the supermarket, take a look at the seafood display – it’s changed.

Fish counter. [Dave Allen, NIWA]