Shellfish collapse in New Zealand
Shellfish fisheries in NZ collapsed, a bad omen
by Dr J Floor Anthoni
in-depth logo Floor Anthoni


    Shellfish are found in the near-coastal zone, close to where people live. It stands to reason then that they will be the first to show that the sea is in a serious condition. Furthermore, shellfish cannot swim away temporarily to avoid occasional bad conditions. This article raises alarm about what has been happening and what will happen next. The consistent collapses of our shellfish stocks brings an important message. No longer can we say that we were not warned!
  • introduction: an introduction to a new threat in the sea
  • the fate of the Toheroa: the Toheroa vanished in 1977, the coalminers' canary of worse things to come.
  • Cheltenham Beach: after a decade of full protection, the pipis and cockles vanished for good.
  • disappearing scallops: scallop beds in the outer Hauraki Gulf collapsed and vanished.
  • emaciated mussels: the West Coast mussels are no longer edible.
  • the big picture: official fisheries statistics show how all our shellfish are threatened.
  • collapsing fish stocks: finfish are next, and already the data is in.
  • Maui dolphin: can this subspecies of Hectors dolphin be saved?
  • further reading: stimulate your curiosity
The Seafriends Marine Conservation and Education Centre in Leigh was established in 1990 because as early as 1987 all the symptoms were in place of serious things to come as Dr Floor Anthoni documented rampant degradation in the coastal seas around New Zealand, affecting all species over huge areas (the entire continental shelf). The Seafriends web site is testimony to this fact, and now over 20 years later, new scientific data shows that Dr Anthoni's observations were right and that much worse is to be expected.

The degradation of the sea is accompanied by loss of quality and quantity of life. Because one species replaces another and because it happens slowly, most people won't be able to recognise it. But underwater photography helps as it records the seascape faithfully, later enabling one to travel back in time. Most photographers, however, take pictures of the beautiful creatures only while diving exclusively in the best of dive spots, thereby missing the slow decay happening everywhere. The two photos below show two ends of the scale, one rich and diverse, the other degraded and poor. For more examples visit our decay section.

a healthy rock face, standing room only
f032601: in healthy seas the rock face is so precious that a great variety of organisms vie for a place to stand on. This photo was taken at the Poor Knights Islands, some 30km out in sea.
a severely degraded environment
f035907: a highly degraded environment which not long ago supported a vibrant community of seaweeds and grazers. Now it has invasive alien species.

the fate of the Toheroa
Some 40 years ago the toheroa was New Zealand's most loved icon, not only unique to our country but also big, and one could catch and eat it. The toheroa (Paphies ventricosa) is a large clam that lives in wave-washed beaches along NZ's west coast from Wellington to North Cape. In the late 1970s it became protected by a reduced harvest season of only two days per year. Then it became fully protected. It was expected that its populations would recover within a few years but they did not. Instead their numbers dwindled further until today, it remains economically extinct.
New Zealanders did not realise that the toheroa was the first coal miners canary (whistle blower) to warn of something terrible happening to our seas. For if total protection could not save it, neither could marine reserves or any other fisheries regulation. It heralded the beginning of a new era, that of dying seas, culminating most likely in the extinction of Maui's dolphin and the loss of most of our coastal fisheries.
toheroa and tuatua ecology Paphies spp
On left the native toheroa (Paphies ventricosa) (1) in the act of digging, and next to it the much smaller but similarly shaped tuatua (Paphies subtriangulatum) (2) and the small tawera or morning star (Tawera spissa), each having  its place and depth on the beach. The toheroa is found from Ninety Mile beach down to Auckland, around Levin and a pocket in the very south of the South Island. It burrows at mid tide, the best place to be for abundant plankton. By comparison the tuatua is found between low and spring low tide. Tawera burrows well below low tide in calmer sandy bottoms. Both tuatua and toheroa are active burrowers, capable of keeping up with the turbulent sand under waves.

beach polluted by dense plankton and bacteria
0608147: a dense plankton bloom looking like an oil slick, on a toheroa beach near Bayleys Beach. Associated with such slicks are dense concentrations of decomposing bacteria that form a threat to life. Toheroa life in the midst of it.

Cheltenham Beach
Cheltenham Beach on Auckland's North Shore was an excellent place to gather shellfish for a meal. Not surprisingly, the numbers of pipis and cockles declined. The community responded by declaring the local beach a protected area under Maori customs, a rahui. Thus since 1995 the shellfish were allowed to recover. But what happened? They declined further until almost none could be found by 2006. If it was not caused by fishing, then what caused their continued decline?
Cheltenham Beach is an eastward facing sheltered beach where both cockles and pipis thrive. Boat traffic produces waves that favour the pipi (Paphies australe) whereas cockles (Austrovenus stutchburyi) favour flat muddy sediment. The curves show chronic decline of cockles (red), while pipis (green) appeared to be reacting positively to protection (just one year class), then declining likewise. Particularly striking was the disappearance of juveniles (not shown here). Thus it appears that the young are most affected by the 'dying seas' syndrome.
volunteers counting shellfish
0606073: volunteers are counting pipis and cockles at Cheltenham Beach. A box is placed on the beach and all shellfish large and small removed, washed and counted by their size classes.  Following a rope (transect line) extending from high tide level to low tide, a day's work ends up with much data.
collapse of cockles and pipis
The graph shows how cockles (red) declined chronically but that pipis (green) appeared to react positively to protection, then also declined.

disappearing scallops
The scallop (Pecten novaezelandiae) is another NZ icon on the way out. Only twenty years ago, scallops were numerous and easy to gather but now entire scallop beds have disappeared (red marks on map) and some are not even recognisable. The shells have become small, stunted and empty of their delicious gonads (roe). The burrowed scallop photographed under water (picture below) has not reached legal size, even after ten years of growth. It takes normally 2-3 years to reach legal size. Its margins are stunted (blunted) and it has no content to eat.

It must be noted that the scallop fishery is poorly managed, insensitive to the damage it causes. Scallops are caught by towing a heavy steel toothed dredge with a cage on it, over the sand. It scoops up everything including the scallop's predatory seastars. These are dumped overboard, ready to feast on the broken shells and small scallops. In the wake of a scallop dredge swim opportunistic scavengers such as snapper who finish off whatever survives. Because male and female scallops reproduce best when sitting close together, a scallop dredge easily diminishes densities to the point of preventing effective fertilisation of eggs by sperm. GPS navigational systems now enable a fishing boat to trawl one swath overlapping another, leaving no large adults in patches dense enough for reproduction. It is a fishery that can easily be overfished and mismanaged. To make matters worse, scallop stocks gyrate up and down because scallops mature fast and can reproduce profusely.

So if scallops appear to be overfished, a small rest period should revive the stock, such as held in 1998/1999 (see white graph). The problem now is that the stocks did not recover. Apparently fisheries measures prove unable to revive a collapsed stock. If they are ineffectual, then our entire Quota Management System must be questioned. Seafriends' own measurements of the health of the water have shown that the water has become unhealthy for scallops and that they cannot recover for this reason (see DDA map). But even as we write this, fisheries research scientists don't know what is happening.

old scallop grows too slow
f050810: this scallop is over 10 years old, yet not large enough to be harvested because the poor water quality prevented it from growing fast enough.
old scallop with blunt margin, empty inside
f050919: this scallop shows that its margin is blunt rather than sharp. It is also empty inside, devoid of large gonads. It is just not worth harvesting.

emaciated mussels
On the west coast of the North Island, wherever one finds a rocky outcrop, the first ten metres are covered in a dense carpet of mussels, too numerous and fast growing to overharvest. Now the mussels are still there, but people leave them alone. Why?
Because they are empty inside and not worth harvesting. The top photo shows green-lipped mussels (Perna canaliculus) at the entrance to the Manukau Harbour near Auckland. Notice that they are not pointed and 'sharp' but rounded and 'blunt' because their growth has stalled, and so has their insides (picture below).
f221826: green-lipped mussels at the entrance to the Manukau Harbour have blunted margins. They are not harvested because they are empty inside.
0703084: these green-lipped mussels from outside the Hokianga Harbour, have blunted margins and are empty inside. They also taste disgusting.

But the mussel saga does not end here. In the good old times when mussels spawned copiously, it was easy to catch mussel spat on ropes laid in the sea (near 90-mile beach). Nowadays this is no longer possible, which would have meant the end of commercial mussel farming who depend on spat obtained from elsewhere. Fortunately science has come to the rescue by growing mussel spat artificially in large tanks. Even so, everywhere mussel farms are being abandoned after a few successful years followed by mysterious decline and diseases.
the big picture
Ironically, we are experiencing collapsing fish stocks without them being fished. So there must be a new threat, one bigger than that of fishing, resulting in fish starving in seas full of food (plant plankton), their young not being born or when they do, dying prematurely. It is a threat affecting all species, from zoo plankton to table fish and dolphins, and also includes sessile plants and animals. What kind of threat could do all this? What kind of threat could be so large, yet so invisible and impossible to measure, so overlooked by the world's scientists? It is therefore hard to believe that Dr Floor Anthoni found this threat and invented a new scientific method to measure it (2003-2005) and that it is really quite simple. In the sea live very large numbers of bacteria that decompose dead plankton, converting it to nutrients for living plankton. When their numbers increase, they 'steal' solar energy from the food chain, which starves. Because they break down biomatter, they are a constant threat to all sea life. 

shellfish fishery collapses in New Zealand
The composite graph of shellfish harvests was obtained from the Ministry of Fisheries web site for each of the fisheries listed. It shows how all of our shellfish fisheries have collapsed to near extinction and that cockles are soon to follow. Note that most of the fisheries have been managed under tight control, but even so, collapsed. Note also that some fisheries have had respite which didn't result in a recovery. Ask yourself why a nation would allow its most precious fisheries to collapse like this? Obviously there is a new and unexpected threat at work. You and I now know what that is, but the fisheries scientists don't.

collapsing fish stocks
chronic fish decline at Poor KnightsSo far we've seen species getting in trouble while also being fished (except for Cheltenham Beach which was protected). But what is the situation with marine reserves where all species are protected? This would  increase fish numbers and make them bigger too, resulting in larvae leaving the reserve in quantities much higher than elsewhere. This would in turn restock the outside areas as larvae drift away on ocean currents, it is thought. However, fish counts inside marine reserves show the same decline as those observed in fished areas. The important graph on right was obtained from fish counts before the Poor Knights became a fully protected marine reserve (1998), and the four years following immediately. Surprisingly, the resident populations of the species that live and reproduce there, showed a steep chronic decline that continued from the unmeasured decade before.
These fish declined by 50-95% in a mere four years! Only one species, the grey maomao or sweep (Scorpis lineolatus) increased in numbers (as did mature snapper which had been fished before protection) but these are happy to live in the more polluted waters of the coast. The data suggests that coastal pollution has now reached the Poor Knights, our best marine reserve by far. If protection doesn't work here, what can we expect from all our other coastal reserves?

f051520: a female butterfish passing by for a good look at the photographer. Butterfish are shy and their numbers have decreased almost 30-fold at the Poor Knights, where their food, the stalked kelp and other sea weed, is plentiful.
f051128: a leatherjacket is a generalist feeder, biting a little from many kinds of life. Here it is seen nibbling at a red encrusting sponge, but in our aquariums it quite happily demolishes kelp. So there is plenty of food. Yet their numbers have dwindled precipitously at the Poor Knights.

Mauis dolphin
Mauis dolphins are the northernmost subtribe of the native Hectors dolphin which is mainly found around the South Island. It is a small dolphin with rounded fins and a fat belly, which makes it really cute. Hectors dolphins have high frequency echolocation for detailed 'vision' in murky water. It enables them to hunt small fish in darkness, in open water and over the seafloor. These small dolphins can be found several kilometres from shore, but will usually be found closer to the coast, which brings them in frequent conflict with people.
It has been shown that they are easily caught in unattended setnets. Because they reproduce slowly, their populations can soon be affected this way. However, what is easily forgotten is that all our dolphin species are in steep decline, and these are not known to die in set nets and trawl nets. Of the few Hectors dolphins washed up dead, only very few have actually drowned, which is what a net would do. So nets are not their main cause of death. But what is?
f026418: Hectors dolphins are very playful, forever cavorting and cajoling, pushing and chasing, as shown here. This is the New Zealand dolphin, a much better name.
f026417: a Hectors dolphin balancing its tail against the bow wave of a boat. They enjoy the push, the difficulty and the free ride.

Mauis dolphins are the northern subspecies of Hectors dolphin but are visually indistinguishable from their southern cousins. They are rare, counting no more than 100 and counting down year by year. It is a near-coastal dolphin that once thrived in the rich waters fertilised by the Waikato river, teeming with grey mullet and yellow-eyed mullet. Today the water of the Waikato river carries much higher nutrient loads, thereby overfertilising the coastal sea and overnourishing it (eutrophication). We have discovered that this gives rise to high concentrations of harmful bacteria that also diminish the food chain. Mauis dolphins are now being killed by the same waters that used to provide rich takings. Their food is no longer abundant, they die sooner, produce less offspring and when born, baby dolphins are more likely to die from infections.

In our wisdom we are trying to save Mauis dolphin by banning set nets and by applying severe restrictions on fishing in the large area where it occurs. This won't help. Mauis dolphin is just the next in line for extinction after the toheroa and those who followed, as shown above. Perhaps when it becomes truly extinct, will the scientific community begin to ask why, and perhaps they may discover that the fisheries collapses are no isolated incidents; that fishing regulations no longer deliver; that there is something wrong with the sea and that this was already evident before 1990, indeed before 1980.

Only by saving the land can we save the sea!

Further reading on this web site:
Decaying seas: many examples of degradation and its principles, complete with scientific explanation. The sea is seriously ill and all species are dying.
DDA for dummies: a simple explanation how eutrophication in the sea works, a discovery made by Dr Floor Anthoni.
Marine reserves: their promise and why they disappoint.

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