Where have all the scallops gone?
It's a question that has puzzled commercial and amateur fishermen for years. The answers are coming, writes Bill Moore:
Look out across Tasman Bay on a calm spring day and it's a picture of loveliness: sparkling blue water lapping the grey sand on one side and the golden beaches on the other, perhaps a distant sail or two and snow-capped peaks as a backdrop. What lies beneath isn't nearly so attractive.
There are many opinions on what's wrecked the scallop fishery but a consensus on one thing: Large parts of Tasman Bay's bottom and now Golden Bay's are coated with a thick layer of murk that makes it impossible for scallops to survive.
Filter-feeders, they like to partially bury themselves on a firm sand or mud bottom and eat what is found in that bottom layer of water. If it's full of suspended sediment, they die. That's exactly what's happened to many millions of fingernail-sized scallop spat in Tasman Bay in the past seven years and now it's happened in Golden Bay too.
Commercial diver Kevin Primmer, with 15 years of benthic survey work in both bays behind him, has seen the sea floor change.
"In areas where scallops lived in the past, what we'll call a firm bottom, those areas are definitely either a thick mud settlement or a mud slurry," he says. "In a lot of those areas you think you're about to touch the bottom and you sink down into this mud slurry that's half a metre to 800mm deep. There's not a lot that you'll find that'll live in that."
It's a far cry from a decade ago when the scallop enhancement programme seemed to be a recipe for rich harvests of the sought-after shellfish in perpetuity, and was frequently hailed as one of the region's greatest success stories.
A short history: From their "discovery" by commercial fishermen in 1959, the Tasman Bay scallop beds were shamelessly exploited to collapse. Two tonnes of "meat weight" the first year, 78 tonnes a decade later, and then a steep increase to the all-time peak of 1246 tonnes in 1975. That was when around 250 boats were dredging, some of them double-crewed so that they could work around the clock.
It couldn't last. By 1980 the catch had fallen to 41 tonnes and the Government, which must share the blame for what had gone on - it kept issuing licences - closed down scalloping.
After a two-year hiatus, the fishery was reopened, this time with the beginnings of scallop seeding - collecting the tiny spat in bags as they drift about after the adult shellfish spawn, and depositing them when they'd grown to around thumbnail size in various parts of Tasman Bay, Golden Bay and the Marlborough Sounds.
There were also strict new controls. The free-for-all was over, with a limit of 48 licences to cover 49 boats in the southern scallop fishery.
The recovery was initially encouraging and then spectacular. The 1983 catch was 225 tonnes and by 1994 this had grown to 850 tonnes. That was when it peaked, though. With some seasonal ups and downs, the trend has been going south ever since.
This year the projected harvest is just 53 tonnes, virtually all of which is coming from Queen Charlotte and Pelorus Sounds, mostly from just two locations, Ship Cove and Guards Bank. There's been no commercial harvest in Tasman Bay since 2005 and this year, for the first time, Golden Bay is also almost entirely ruled out.
The hordes of amateurs have also given up in Tasman Bay and most of the previously reliable Golden Bay beds, some only minutes from Port Tarakohe, are just a dimming memory. This season the amateurs are pretty much restricted to two areas, Squally Cove outside Okiwi Bay, and Ketu Bay in Pelorus Sound. Despite an entitlement to fish in both places, the commercial boats are leaving them alone.
What was allowed to happen in the 1970s is indefensible. The shameless plundering of a magnificent natural fishery through sheer greed must go down as one of the worst examples of fisheries mismanagement New Zealand has seen - and the fact that it took place in plain view of Nelson makes it even more reprehensible.
However, it was followed by the development of the seeding programme, the formation of the Challenger Scallop Enhancement Company to gather, nurture and seed the spat, and what was for nearly two decades a highly successful management regime that divided the two bays into "paddocks" that could be harvested or fallowed, and made sure the amateurs were kept happy with areas voluntarily left to them.
But from 2002, it all went wrong again.
The enhancement company brings together the remaining fishermen and the quota holders - mainly Talley's and iwi, along with an amateurs' representative. Its goal has been to ensure a sustainable catch. At one time it had 14 employees and in its biggest year it collected and seeded 120 million scallop spat.
Now it has two workers and has cut spat collection right back. The spat dies when it settles and in any case, the company isn't making enough from its levies to do much work. Last year it collected and seeded 18 million spat in Golden Bay. Its surveys have shown that few survived.
Scallop company chairman Buzz Falconer has an association with the industry going back to the 1970s and in retirement is still a keen amateur.
"We've learnt a lot over the years about catching, handling and looking after spat," he says. "We're probably top of the world for knowledge of that, but of course once you put it on the sea floor you come under mother nature's control."
He says the company's rotational fishing plan, refined with the use of satellite navigation and close monitoring of boat movements and catches, is "exactly the same" as a farmer on land rotating his crops to ensure good yields.
But in practice it's more complicated. Scallops have to be taken within roughly two years of reaching maturity. Shifting currents and variable natural spat falls can mean a mixture of age ranges in one "paddock" - and there aren't any fences on the sea floor.
"It becomes a real problem in a practical sense," Mr Falconer says.
Even so, it worked extremely well in Tasman Bay until 2003, was still producing good results in Golden Bay for several years after that and is still used in the areas of the Sounds that are dredged each year. Not only is the total catch controlled, but also precisely where it is taken.
The most frequent criticism is that the heavy dredges the boats tow - not forgetting the hundreds of light ones used by amateurs - plough up the sea floor, disturbing not only the scallops but also everything else that lives in the complex seafloor communities.
Mr Falconer accepts that dredging is probably "a small contributing factor". But he says it has only taken place for a few months each year and not at all in Tasman Bay for several years, yet the scallop population hasn't recovered.
Sedimentation has emerged as the main driver of the decline. That's shown, Mr Falconer says, by the fact that Golden Bay's problems have only shown up since the severe floods in the past few years, while Tasman Bay, with more forestry harvesting contributing to what's flushed from the rivers, has been suffering a lot longer.
Plus, the zone devoid of scallops is inside a depth of 27 metres, the area most subject to the river plumes.
Coastal and marine scientist Paul Gillespie shares that view. He has worked at Nelson's Cawthron Institute for 40 years and much of his work has been around water quality and aquaculture, particularly in the top of the south.
His research into scallops has led him to believe that both bays are in the grip of a natural process of change caused by gradual sedimentation entering from the rivers, and that man's activities have accelerated it.
"Initially, while we may have had ideal seabed habitats for scallops, that's changed over time," he says.
Scallop enhancement provided a temporary boost to the industry, with spat kept until it had grown enough to have a better survival rate.
"But that whole process has still been continuing all this time, and now I think we've reached another threshold. We've gone beyond that point where it's just inhibiting spat fall and settlement, it's the next stage, a drastic effect on the feeding ability of scallops."
Dr Gillespie says the process is taking longer in Golden Bay because it has higher nutrient levels and phytoplankton growth, and has a slightly coarser, more sandy and less muddy seabed than Tasman Bay.
However, he says it's on the same trajectory towards increasing fine sediments as Tasman Bay, "it's just that it's taken a little longer".
He notes that a century of bottom trawling and dredging has flattened the three-dimensional structure of the seabed, making it more liable to the movement and suspension of fine material.
Without those fishing methods, living reefs of horse mussels and greenshell mussels with other organisms growing on them would provide a barrier to this "tidal re-suspension" which he believes is a greater problem than irregular floods.
"My original opinion was that instead of having the whole of Tasman Bay managed for the scallop industry and fishing, so that the whole of the bay was affected by dredging and trawling, it would be far better to break it up into different uses, and keep some of the bay protected from physical disturbance. I still hold to that view."
So do the environmental lobby groups. Forest & Bird includes scallops on its 2012 "red list" of seafood to avoid, saying that dredging is a highly destructive fishing method that results in a high by-catch and dramatically alters seabed ecology.
Long-time member of the environmental group Friends of Nelson Haven and Tasman Bay, Green Party list MP Steffan Browning, says the best way forward for the entire scallop fishery would be to rule out dredging and replace it with harvesting by divers. He suggests the increased labour cost could be covered by the ability to take only scallops perfectly suited for market from a truly sustainable fishery.
"Dredging is a bad way of harvesting scallops," he says. "There are some areas that are more resilient because of the nature of the seabed, but the fact is that it effectively rotary hoes the bottom, it destroys habitat and alters the composition of the seabed. That's not a good thing."
Combine that with large quantities of forestry sediment and other sediment from the land, add in other pollutants that are "harder to put your finger on" and the decline of the scallops and their habitat is explained, he says.
Mr Browning connects the retreat of scallops from the inner Sounds - something the enhancement company has also noted - to "huge amounts of murk" washing into the bays from what he says are poorly managed forests.
"We shouldn't just look at what's happening in the sea, we should look at what's happening on the land as well, treat it as a whole and put the rules and regulations around that," he says.
Chris West sits at the sharp end of the industry. A Motueka man, he's been scalloping since 1983 and hasn't missed a year. But he's watched the seasons grow shorter and more constrained.
This year, the 53-tonne meatweight total is being spread over 14 boats, mostly fishing for Talley's, and will be wrapped up inside three weeks.
Mr West remembers seasons that lasted four months.
In those days scallops were most of his earnings. Now they are about a quarter, but still "crucial to our yearly income".
Interviewed while his boat the Okarito was unloading its Ship Cove catch at one of Picton's wharves on Monday night, he said he and his two crew had done about 25 tows in 11 hours of fishing to fill four large bags with around 2.2 tonnes of scallops, "a pretty reasonable day's fishing".
A scallop enhancement company board member, Mr West has also carried out surveys in Golden Bay for four years, this year towing a fine mesh liner to bring up spat seeded in Golden Bay.
It had been a really good spat catch the previous summer but the small shellfish all came up dead, along with "silt and pure sludge" that wouldn't show up in regular dredging.
"It's quite alarming and enlightening to see what I've seen," he says.
"There's been a lot of questions and we haven't understood it, but I'm seeing it now, the runoff from the rivers and these big storms we're having; it's just having a killing effect."
He doesn't believe scallops will do well in Tasman Bay or Golden Bay "until the rain stops falling and the rivers stop flooding".
His hope is that good management will sustain the Sounds scallop beds so there will be work for this and the next generations.
The scallop gold rush days are "well in the past", he says.
"Now we're fully aware that we need to have a future and with the quota system it's being managed, and we're working in-house to take more control." But like Mr Falconer, he says that "mother nature has the final call".
"When we were reseeding things were going so well, it looked like we could catch as much spat as we wanted, we could put it where we wanted. One part of it [nature] provides the spawn, another part says no, we're taking it away. You've got to get your head around that."
The Crown research institute Niwa has been a science provider for the scallop company and the fisheries ministry (now part of the Primary Industries Ministry) since the 1980s.
It is engaged in a series of workshops with scallop fishery stakeholders, including the company and fishermen and other science providers, aiming to build a bigger knowledge base, share information and set further research priorities.
The project is led by Niwa scientist Keith Michael, who has been involved with the fishery since the beginnings of the enhancement programme.
Dr Michael says not only scallop but also oyster and mussel populations have declined to low levels in both Tasman and Golden bays over the past decade.
Scallop populations have a high natural variability year to year. There are many intricacies around sediments and the causes of decline might be due to a number of factors with complex interactions, he says.
"There may be some potential to mitigate or remedy some of these factors, and these measures may be beyond the sole control of the fishing industry."
Like Dr Gillespie, Dr Michael emphasises the need for more science.
"We do not at present have the information required to make a robust assessment of the factors involved, how they interact, and how that interaction may vary over space and time," he says.
For Mr Falconer, that's grounds for optimism.
The enhancement company chairman says neither fishermen nor quota holders can make a living from the fishery in its current state, but he doesn't believe it's a sunset industry.
"I've always said it can never come right in terms of the high tonnages until we get Tasman Bay operating again.
"It will return, I hold no qualms about that, but it's going to be a while."