fishing industry's proposals to protect North Island Hector's dolphin are
totally inadequate, the Forest and Bird Protection Society said today.
Society spokesperson, Barry Weeber, said the industry proposed banning
gill nets in only part of the dolphin's range. "They propose only
weak controls north of Manukau Harbour and no controls south of Aotea Harbour."
Mr Weeber, said gill nets must be banned throughout the entire range of Hector's dolphin on the West Coast of the North Island if this population is to survive.
"Around 100 Hector's dolphin are estimated to be left on the West Coast of the North Island between Mokau and Dargaville."
Mr Weeber said, "Hector's dolphin was one of only two endemic marine mammals found in New Zealand waters and was internationally recognised as a threatened species and is highly susceptible to being caught in gill nets. A recent survey for the Ministry of Fisheries confirmed that Hector's dolphin are caught in gill nets on the West Coast of the North Island along with other dolphins and seals."
Mr Weeber said the Society is calling for a prohibition on gill netting in areas where the dolphins live. He also said the North Island population was one of at least three genetically distinct populations of the dolphin. The other two are on the western and eastern coasts of the South Island.
"Given the level of gill netting off the West Coast of the North Island and the small size of the dolphin population there, it was critical that action be taken this year. It should be a priority to establish a marine mammal sanctuary on the West Coast of the North Island between Dargaville and Mokau extending 10 km off the coast. The removal of gill nets from this area would be a major advance in the protection and rebuilding of the critically endangered dolphin population."
For further information contact Barry Weeber (04)385-7374 or (025)622-7369.
Background information on Hector's
Hector's dolphin is the world's smallest and possibly the rarest marine dolphin with a population of 3000 - 4000. They occur only in New Zealand's inshore waters and are rarely found more than 8 km from the coast. Hector's dolphin was gazetted late last year by the Minister of Conservation as a threatened species under section 2(3) of the Marine Mammals Protection Act 1978.
The dolphin is classified as a vulnerable threatened species in the most recent IUCN-World Conservation Union listings of globally threatened animal species (1996) . This listing is based on its small population size and the large number of dolphins drowned in gill nets since at least 1980. The Cetacean Specialist Group of the Species Survival Commission of IUCN, the world scientific experts on cetacean conservation, have assessed Hector's dolphin as a threatened species of vulnerable status using the agreed threatened species criteria.
The dolphins mainly occur around the South Island but an additional population lives on the West Coast of the North Island between the Kaipara Heads and near New Plymouth. The main populations are found between Motunau and Timaru on the East Coast of the South Island, on the West Coast of the South Island, and in Foveaux Strait -Te Waewae Bay area in Southland.
Genetic work carried out by Auckland University indicates there are at least three relatively distinct populations of Hector's dolphins (Pichler et al 1998) - East Coast South Island, West Coast South Island, and West Coast North Island. This means that each population must be managed separately when considering human impacts. The West Coast of the North Island population has been reduced to around 100 individuals between Taranaki Bight and the Manukau Harbour. Current research indicates that the west coast populations have been declining due to gill nets deaths (Martien et al, 1999). A survey by the Ministry of Fisheries of commercial gill netters confirmed they catch Hector's dolphin, as well as other dolphins and seals. A workshop in May agreed that for the North Island population to recover, less than one dolphin per five years would have to drown in gill nets.
About 95 percent of the population is found around the South Island. Dolphins live to around 20 years old with females calving at 7-9 years old and males reaching sexual maturity from 6-9 years old. Females appear to calve only once every two to four years. Hector's are probably the world's smallest dolphin with a mature length of 119-145 cm and weighing up to 58 kg.
Hector's dolphins have been recorded drowned in both gill nets and trawl nets but the vast majority of the reports are from gill nets. Around Banks Peninsula gill nets were estimated to drown over 230 dolphins between 1984 and 1987 (Dawson and Slooten, 1993). Both commercial and recreational fishers have failed to report Hector's dolphin deaths in gill nets, a legal requirement of the Marine Mammal Protection Act. It wasn't till a scientific observer programme was undertaken of gill net and trawl vessels off the Canterbury coast that the true level of dolphin deaths was confirmed. As the previous Minister of Conservation, Nick Smith, said "What makes me particularly angry is that fishermen have for years failed to report fatalities and denied there was a problem".
In the 1997-8 a Department of Conservation observer programme on commercial vessels recorded the deaths of six Hector's dolphins. Observers covered only 89 of 351 fishing days. "I remain cynical that fishermen claim there were no deaths during the 262 days when observers were not present," former Conservation Minister Nick Smith said. It is clear that neither commercial nor recreational gill netters are reporting deaths of Hector's dolphin.
Past Management Action:
Banks Peninsula: In response to dolphin deaths in the 1980s the Banks Peninsula Marine Mammal Sanctuary was established late in 1988. It covers an area of 1140 km2 around Banks Peninsula from Rakaia River to Sumner Head. The Sanctuary extends 4 nautical miles offshore and commercial gill-netting is banned all year round and recreational fishing is prohibited between 1 November and the end of February.
This restriction on gill netting has almost eliminated gill net deaths in the sanctuary but dolphins are still being killed north and south of the Sanctuary. Forest and Bird considers the sanctuary should be extended to include the area from Motunau to Timaru where a significant number of dolphins have been drowned in gill nets.
Other areas: Dolphins have been reported drowned with marks attributed to gill nets around Taranaki and on the West Coast of the North Island. No management action has been taken to protect Hector's dolphin in these areas.
More gill nets?
The Minister of Fisheries has agreed to an increase in the rig and elephant fish catch on the East Coast of the South Island. Both species are caught by gill nets. The proposed limit of seven animals is arbitrary and was agreed without consultation with the Minister of Conservation as required by section 15 of the Fisheries Act 1996.
The fishing industry is arguing that the use of pingers (noise generating devices) on nets can reduce dolphin deaths. To work pingers must not fail (they are battery powered), the right frequency must be used, the dolphins must not habituate to them and many pingers must be used per net. It is unclear whether they will work and it could take 6 years of independent observation to confirm this during which up to 100 dolphins could drown if used on the East Coast of the South Island.
This would require a dedicated observer programme. A recent International
Whaling Commission (IWC) Sub-committee meeting on cetaceans raised concern
at "pingers being deployed without any apparent attempt to either test
their efficacy nor to monitor their effects". They noted that "harbour
porpoises and short-beaked common dolphins are the only cetacean species
for which properly designed studies .. have been conducted to evaluate
pinger effectiveness. Nevertheless, some bycatch has occurred in
nets with active pingers during experiments and sea trials".
The IWC Committee was also concerned that dolphins could become habituated to the pingers so that, while there may be an initial drop in deaths, the rate may increase over time as dolphins get used to the pingers. This seems to have occurred with harbour porpoises where the main trial has taken place.
Previous work has indicated that the dolphin population at Banks Peninsula can only withstand around 1 individuals a year being killed by gill nets from both recreational and commercial fishers (Dawson and Slooten, 1993). For the smaller West Coast North Island population no gill nets deaths can be accepted.
Urgent management Action Needed:
Given these uncertainties and the risk to the dolphin, in particular the West Coast North Island population, Forest and Bird see only one option, that is banning gill nets where Hector's dolphin live. Urgent management action should be taken to reduce Hector's dolphin deaths from gill nets by:
1. Establishing a marine mammal sanctuary on the West Coast of the North Island to protect the critically endangered and genetically isolated population found there. This should run from Mokau to near Dargaville and extend 10 km offshore.References:
2. Expanding the Banks Peninsula Marine Mammal Sanctuary to include the area from Motunau to Timaru with a total ban on commercial and recreational gill netting in the extended sanctuary.
3. Further research by the Department of Conservation aimed at developing more marine mammal sanctuary's and a ban on gill netting to protect the dolphin populations on West Coast of the South Island and in Southland.
Department of Conservation (comp) (1992) Banks Peninsula Marine Mammal Sanctuary Technical Report, July 1992. Canterbury Conservancy Technical Report Series 4. 84p.
Dawson S M and Slooten E (1993) Conservation of Hector's dolphins: The case and process which led to establishment of the Banks Peninsula Marine Mammal Sanctuary. Aquatic Conservation: Marine and Freshwater Ecosystems Vol 3: 207-221.
Dawson S M and Slooten E (1996) Down-under dolphins - the story of Hector's dolphin. Canterbury University Press. 60p.
Dawson S M, Read A and Slooten E (1998) Pingers, Porpoises and Power: Uncertainties with using Pingers to reduce bycatch of small cetaceans. Biological Conservation 84: 141-146.
Martien, K K, Taylor B L, Slooten E and Dawson S (1999) A sensitivity analysis to guide research and management for Hector's dolphin. Biological Conservation 90:183-191.
Pichler F B, Dawson S M, Slooten E and Baker C S (1998) Geographic isolation of Hector's dolphin populations described by Mitochondrial DNA sequences. Conservation Biology 12:676-682.
Slooten E and Lad F (1991) Population biology and conservation of Hector's dolphin. Canadian Journal of Zoology 69: 1701-1707.
Barry Weeber, Senior Researcher, Royal Forest and Bird Protection Society
PO Box 631; Wellington; New Zealand
Phone 64-4-385-7374. Fax 64-4-385-7373. www.forest-bird.org.nz
A threatened population of the rare Hector's dolphin along the west coast of the North Island is about to get help. The Northern Inshore Fisheries Company, which looks after the interests of local fishers, is about to launch a conservation mission to reduce the impact of commercial fishing on one of New Zealand's most endangered marine mammals. The move anticipates, and therefore may influence, eventual regulation by Government agencies for greater protection of this dolphin.
The population has fallen to a dangerously low level of about 100 individuals. Most dolphin species are far ranging and cruise the open seas, but Hector's is confined by its natural behaviour to shallow coastal waters, especially the slightly turbid areas around harbour entrances. It is therefore more vulnerable to threats associated with human activities in these busy seaways.
Most threatening is the risk of drowning if they become entangled in gill nets set by commercial or recreational fishers, although it is also suspected that some, especially juveniles, are killed by boat strikes and that their health and fertility are affected by industrial and agricultural chemicals flowing from harbours.
Hector's dolphin is special because it is found only in New Zealand waters
and is the smallest dolphin in the world. Adult females reach 1.5m and
males are smaller. Their attractively marked, grey, white and black bodies
are unusual in having short, rounded dorsal and pectoral fins rather than
the longer, curved, pointed fins of most other dolphins.
The Hector's dolphin has other peculiarities, some of which may be contributing to its decline. They live for about 20 years but females do not start breeding until they are 7 to 9 years old and then, at best, produce a single calf only every two to three years. A local dolphin population of 100 dolphins would therefore do well to increase by just four a year if none was killed in nets, by boat strikes or by shark predation.
The Hector's dolphin is also unusual in being residential. The dolphins do not migrate along the coast, are seldom seen more than 10km from land and about half of each population is always found within 1km of the shore.
The plight of the Hector's dolphin became better known in the late 1980s
when set netting restrictions were enforced around Banks Peninsula, where
most of the population reside. The action has helped reduce dolphin deaths
there, and the new code of pratice for commercial fishers as well as management
proposals for the North Island west coast between New Plymouth and the
Kaipara Harbour mouth are aimed at reducing bycatch kills to a minimum.
The industry initiative requires fishers to keep more detailed logs of
fishing effort and catch results, along with reports of sighting of dolphins.
It also establishes new closed and controlled fishing areas. In addition
to closed areas of 2 nautical mile radius around each harbour mouth, inshore
waters out to 4 NM from the entrance to Manukau Harbour to Taranaki Pt
near Aotea Hr, will be closed to set netting. From the Manukau Hr north
to South Kaipara Head, restrictions on net height and deployment are proposed
that will eventually include the attachment of sonic warning devices (known
as 'pingers') to nets, to alert dolphins to their presence.
Anyone fortunate enough to have seen a live northern Hector's dolphin (Cephalorhynchus hectori), would have difficulty recognising the northern subspecies, even though it is a little larger and has a different colour pattern. Fact is that the two subspecies don't interbreed. We need to act as if we are about to lose another major-sized animal from this world. Like its southern relatives, the northern Hector's dolphin is thought to reproduce late in life (age 7-9), with only 4-5 offspring for each female, but nothing is sure about this. How do we relate this to fishery-caused mortalities?
If a dolphin produces a calf at years 8, 10, 13, 16, 18 and dies at 20, then it takes 2 x 20 = 40 dolphin years to produce 5 offspring (males are needed too, or at least they are produced in the same numbers). Two are replacing their parents, so three remain to increase the size of the population, if none die from other causes. If the average age of a dolphin increases to 22, another calf may be had, resulting in 6 calves in 44 dolphin years. But if the average age decreases to 18, then only 4 calves are born for every 36 dolphin years. With 100-150 dolphins existing today, the number of calves born each year (equals to 100-150 dolphin years), to expand the population is 8 - 14. As one can see, the average life span of a dolphin is rather critical to the number of newly borns. As the dolphins live shorter still, it becomes even more critical. So early mortality is not just reducing their numbers but also critically affects new calves, which affects numbers. It is an unintuitively critical relationship. Mortality from fishing is particularly detrimental to species that naturally grow old.
From the above quick estimates for best and worst cases, the scientist's
claim of maximally one fisheries-induced death in five years, is hard to
substantiate. The number of calves born to increase the population in five
years is 40-70, according to the above estimates. Any natural population
of wildlife as sensitive as claimed, does not deserve to survive. In the
end, we must also acknowledge that extinction is a natural process. Is
the North Island Hector's Dolphin destined for natural extinction? According
to the scientists' claims, yes.
|Marine mammal scientist
Steve Dawson retorts (19 Nov 2004). For the complete letter see /say/opinion.htm
One specific example is your statement (made about Maui's dolphin) that "the scientist's claim of maximally one fisheries induced death in five years, is hard to substantiate". Frankly, you are not equipped to say. This result comes from a model by Dr Paul Wade (1998. Calculating limits to the allowable human-caused mortality of cetaceans and pinnipeds. Marine Mammal Science 14, 1-37.) It doesn't sound l ike you'd read the paper. Your criticism here is way off beam. It should have been that this model is not applicable, as it is intended for populations that are MUCH bigger. There is no such thing as a calculable sustainable take from a population this small, simply because at small population sizes demographic problems such as sex ratios, environmental change and Allee effects could cause extinction even in the absence of the fishery. We do know that these dolphins are taken surprisingly often in gillnets. Therefore it only makes sense to get rid of the gillnets.
(19 Nov 2004)
Your extensive criticism relates to the use of a computer model which produces an unrealistic result. I am familiar enough with computers and models to know that what they produce depends on the assumptions and rules put in it. Most computer models therefore are not reliable, so the result must be weighed against common sense. To say that a population of 110 cannot sustain one unnatural death in five years (against 40-70 natural births in five years), is poppycock. Death is death, whether natural or unnatural. You then state that a sustainable take cannot be calculated for such a small community, but what is the difference between sustainable take and unnatural death? Your answer cannot convince thoughtful readers.
You simply close your eyes to landbased degradation, which is rather high in the area where Maui dolphins are found. A good scientist would take this into account and prove that this is not the invisible but major cause of their demise, before attacking gillnets, the deaths of which are highly visible.
It could also mean that the dolphin's main problem is not that of dying
in nets, but of a high mortality without a recompensing rate of reproduction.
In the entire discussion about their survival, nothing was mentioned about
the fishing down of their food supply, which could make their lives very
difficult, and even leave insufficient food for survival. Although a dolphin
is very efficient at catching its food in murky waters and during the night,
human technology is even more successful. It is not difficult for the fishing
fleet to out-compete these animals. According to the laws of ecology, the
most efficient species, the fisherman, then survives while the others go
Another factor has been missing from the debate, that of the deteriorating quality of our coastal waters, resulting in recruitment failure, disease, poisonous plankton blooms and so on. Undoubtedly, this too must have an effect on the population of Hector's dolphins. The mysterious deaths of lion seal pups on the Auckland Islands, may serve as reminder.
The main point here is that if these two factors are the main causes of their decline, which the scientist's figures suggest, then the proposed limitations on fishing, simply won't work to save this little dolphin. The dolphins would then be better served with an increase in fish stocks, which can be achieved by adapting fishing quotas until a higher residual biomass is achieved. Ironically, a higher level of fish stocks will also lead to fewer fishing days at sea, and an equally reduced chance of accidentally catching dolphins. Furthermore, it may well be that dolphins are more attracted to the high concentrations of food in a net, when they are hungry than when they are well fed. Raising the stock levels in the sea may thus add up to a considerable benefit in the dolphin's favour.
Why would these dolphins have evolved such a critical reproduction mechanism? Wouldn't it be better for their species to reproduce profusely instead? Why do other dolphin species do better? Four reasons can be found:
Living with these serious limitations, it does not pay to reproduce fast with populations bouncing between boom and bust. Being a top predator, Hector's dolphin has instead evolved a gentle reproductive strategy, which has served it well for millions of years. But humans have changed the situation, bringing this species (and many others) under stress. The dolphin's very solution for survival has now become its downfall.
But why do these dolphins not interbreed with their southern cousins? In the end, nature is not much interested in the survival of an animal, a population or even a subspecies, but more so in preserving their genetic material. This is done more successfully, if there is a large degree of variability (diversity) in the genes of a species. The northern individuals would thus be better placed for survival, if they interbred with the two other subspecies, forming a larger pool. Then again, if all sub species interbred, the variability in their combined gene pool would be less. The natural formation of subspecies, is thus one of nature's ways to increase biodiversity, and increase the chance of survival of the genes under changing environmental conditions (ice ages, e.g.). But it entails that by natural selection, one or more subspecies will eventually be 'unfit' to survive, making room for the surviving ones. Is this the fate of the northern subspecies? It is also true that the genetic variability is larger in a larger population, and that it reduces rapidly as the population reaches critically low levels, which places this small population in an evolutionary disadvantaged position.
With only some 100-150 individuals left in the wild and no chance of captive breeding, effective and decisive action is now the only solution, although it may eventually fail. New Zealanders like to think that God's Own Country is one of sustainability; that all species will still be here in a thousand years from now. Our people unanimously endorse this idea, but many don't realise that it comes with a sacrifice, sometimes temporarily, sometimes permanently. For the last remaining Hector's we obviously need to make a sacrifice. For once, it does not matter how big, but only that it works, and fast - that this subspecies may survive.