Summary of recent research on threats to Hector's dolphins
- Hector’s dolphin is endangered and only found in New Zealand
- It is one of the best studies dolphin species in the World, with 25 years of research data on their ecology and conservation threats
- Mortality in fishing gear is the main threat, with 110-150 Hector’s dolphins killed each year in the commercial gillnet fishery alone (plus an unknown number in trawl fisheries and recreational gillnets)
- The level of bycatch needs to be reduced to below 10 dolphins per year to avoid further population decline
- Protecting Hector’s dolphins will benefit fisheries, tourism, other bycatch species such as seabirds and reef fish and would protect New Zealand’s reputation as an environmentally responsible nation
- Hector’s dolphin is endemic to New Zealand. Therefore, their protection is a national and international issue. The North Island Hector’s dolphin population has recently been proposed as a separate subspecies and is also known as Maui’s dolphin. The species as a whole is listed (by DOC and the IUCN) as Endangered. Maui’s dolphin is listed as Critically Endangered.
- After 25 years of intensive research on the species there is a wealth of published, peer-reviewed data on their ecology, population biology and threats. This research has involved staff from three New Zealand universities, DOC, MFish, NIWA and overseas researchers from the US National Marine Fisheries Service, New England Aquarium, Dalhousie University in Canada, among others. Key results from more than 140 peer-reviewed papers, published in NZ and international journals include:
- Total population size is small at 7,270 individuals (CV = 0.16) around the South Island and 111 (CV = 0.44) off the North Island
- Hector’s dolphins range out to 100m water depth and have a very small range of alongshore movement (average 31km) with less than 1% per year movement of individuals between adjacent populations
- Hector’s and Maui’s dolphins range into very shallow water, including harbours and bays, and are commonly seen in water of only one or two metres deep
- Survival, reproductive rates, social organisation, sounds, diet and other aspects of their ecology have been studied in populations around the North and South Island of New Zealand over the last 25 years
- Research in existing protected areas shows that small protected areas are not effective. Survival rates at Banks Peninsula are still too low to allow population growth
- All of the available research data consistently show that human impacts on Hector’s and Maui’s dolphin are not sustainable. Populations have declined substantially from an estimated 21,000-29,000 individuals in 1970 to about a third that number today
- This has caused reductions in the range of Hector’s dolphin and in their genetic diversity
- Under current management, populations are predicted to continue declining
- If fisheries mortality is reduced to zero, the species is predicted to recover to about 15,000 individuals over the next 50 years
Hector’s dolphin is now one of the best studied dolphin species in the world. As pointed out by the Cetacean Specialist Group of the IUCN in its submission on the Threat Management Plan as well as recent comments from the Society for Marine Mammalogy, the NZ government is in a very strong position because a great deal more is known about Hector’s dolphin than about most other dolphins and porpoises.
- The Threat Management Plan identifies gillnets and trawling as the two most serious impacts on Hector’s dolphin. Unlike impacts on many of our other endangered species, this problem is simple and easy to solve. Changing to selective and sustainable fishing methods would be relatively painless. Most fishing boats in NZ that use gillnets already use other methods as well, including trawling, fish traps, craypots, longlines and handlines. Economically, gillnet fishing is worth much less than 1% of the total New Zealand fishery (not including aquaculture). A very small proportion of recreational fishers use gillnets. Most recreational fishers regard this method as “unsporting”.
All science involves uncertainties. Not surprisingly, uncertainties in the science have been emphasized repeatedly by people with a vested interest in the continued use of gillnets. “We need more information” is of course a standard catch-cry from industries causing health and environmental impacts, and sometimes echoed by management agencies failing to manage those impacts.
A closer look at the research data shows that there is actually very little disagreement or uncertainty about the overall results. There are uncertainties about whether the total number of Hector’s dolphins killed in fishing per year is 110 or 150 or somewhere in between. However, all of the studies estimate that bycatch exceeds 100 Hector’s and Maui’s dolphins per year. Likewise, there is very good agreement on the probability of population increases and decreases for current management and the most effective management option in the TMP (Option 3). For example, the risk of population decline under current management has been estimated at 86% by the latest published risk analysise and at 82% by the only competing model (developed by NIWA and the fishing industry). The risk of decline drops to 14% if gillnetting is restricted to 6, 12 and 18 nautical miles offshore (Option 3 in the draft TMP) or 2% if dolphins are completely protected from fisheries mortality.
Other results from the two latest risk analyses are also very similar. For example, by 2050 populations are predicted to decline to 5,475 or 5,631 if current management continues and recover to 14,650 or 15,411 if fisheries mortalities are reduced to zero. Current Hector’s dolphin populations are estimated at 27% or 34% of 1970 population size, both falling well within the IUCN criteria for Endangered (reduction to <50% over 3 generations, 39 years for Hector’s dolphin.
- Another, independent benchmark is the Potential Biological Removals method developed in the US which was used to develop management goals for the Hector’s dolphin Threat Management Plan. PBRs of 0, 2, 7 and 0 for the North Island, South Island east, west and south coasts respectively, were calculated by the Expert Panel appointed by DOC and Mfish and it was agreed that total human impact should not exceed these levels. The most recent estimate of bycatch in commercial gillnets off Canterbury is more than ten times the PBR for the whole South Island east coast. Likewise, the nationwide PBR is less than 10 and the total number of dolphins caught is more than 100 per year. This is a clear indication that current management is not effective.
It is clear that Option 1 in the Threat Management Plan would result in continued population declines. Option 2, at best, is likely to result in holding populations at their current depleted levels. The piecemeal nature of Option 2 would make it very difficult if not impossible to monitor and police, would result in shifting impacts from one area to another and would result in further population fragmentation. Option 3 is the only option that is consistent with NZ and overseas guidelines for marine mammal conservation and stands a realistic chance of resulting in population recovery.
Option 3 needs to be seen in the context of the full range of options, which would include for example options 4: Remove fishing impacts throughout the current range of Hector’s and Maui’s dolphin, 5: Remove fishing impacts throughout the current and past range of the species, 6: Remove all human impacts throughout the current and past range.
- Protecting Hector’s dolphins will have economic as well as conservation benefits. The conservation benefits include not only Hector’s dolphin, but many other species that also have been impacted by the use of non-selective, unsustainable fishing methods. Any short term, economic costs would be substantially outweighed by economic benefits accruing to tourism and the fishery itself. Switching to selective, sustainable fishing methods will result in more and bigger fish in the sea for all of us. Sustainable fishing is also consistent with the government emphasis on being a world leader in sustainable management.
As highlighted in a recent article in Nature by Andrew Rosenberg, research on unsustainable fishing practices is usually challenged by fishing industry representatives. Rosenberg’s description of a typical response “the science was wrong, the rules wouldn’t work and everyone would go out of business” accurately describes public statements by the New Zealand Seafood Industry Council. He notes also that scientists are usually up-front about the uncertainties in their work. This is in stark contrast to claims made by the fishing industry, which generally sound as if they are utterly certain.
To enable science-based decision making in such adversarial situations, Rosenberg recommends asking questions like “what do we know” and “what does that mean we should do”. In this case, we know that Hector’s dolphin populations have been seriously depleted since the early 1970s due to mortalities in gillnet fisheries and that trawling poses an additional risk. All risk analyses carried out for the species (by scientists from universities, government, the fishing industry and NIWA) predict continued population declines to about 5,500 under current management and recovery to around 15,000 individuals in 50 years’ time if fishing impacts are removed. In other words, if fishing impacts are not managed, almost 10,000 dolphins will be lost over the next 50 years (200 per year).
For more information, please see:
Bräger S, Dawson SM, Slooten E, Smith S, Stone GS, Yoshinaga A (2002) Site fidelity and along-shore range in Hector’s dolphin, an endangered marine dolphin from New Zealand. Biological Conservation 108: 281-287
Burkhart SM, Slooten E (2003) Population viability analysis for Hector's dolphin (Cephalorhynchus hectori): A stochastic population model for local populations. New Zealand Journal of Marine and Freshwater Research 37: 553-566
Cameron C, Barker R, Fletcher D, Slooten E, Dawson S (1999) Modelling survival of Hector’s dolphins around Banks Peninsula, New Zealand. Journal of Agricultural, Biological and Environmental Statistics 4(2): 126-135
Davies NM, Bian R, Starr P, Lallemand P, Gilbert D, McKenzie J (2008) Risk analysis for Hector’s dolphin and Maui’s dolphin subpopulations to commercial set net fishing using a temporal-spatial age-structured model. Ministry of Fisheries, Wellington, New Zealand, www.fish.govt.nz/en-nz/Consultations/Hector+new/default.htm
Dawson SM, Slooten E, DuFresne S, Wade P, Clement D (2004) Small-boat surveys for coastal dolphins: Line-transect surveys for Hector's dolphins (Cephalorhynchus hectori). Fisheries Bulletin 201: 441-451
DOC & Mfish (2006) Management objectives for Hector’s dolphins. Department of Conservation and Ministry of Fisheries
DOC & Mfish (2007) Hector’s dolphin draft threat management plan. Department of Conservation and Ministry of Fisheries, www.doc.govt.nz, www.fish.govt.nz
du Fresne S (2004) Conservation biology of Hector’s dolphin. PhD Thesis, Otago University
Fletcher D, Dawson S, Slooten E (2002) Designing a mark-recapture study to allow for local emigration. Journal of Agricultural, Biological and Environmental Statistics 7(4): 1-8
Pichler FB, Baker CS (2000) Loss of genetic diversity in the endemic Hector's dolphin due to fisheries-related mortality. Proceedings of the Royal Society London, B 267:97-102
Rosenberg AA (2007) Fishing for certainty. Nature 449:989
Russell K (1999). The North Island Hector’s dolphin: a species in need of conservation. Unpublished MSc thesis, University of Auckland.
Slooten E (1994) Behavior of Hector’s dolphin: Classifying behavior by sequence analysis. Journal of Mammalogy 75: 956-964
Slooten E (2007) Conservation management in the face of uncertainty: Effectiveness of four options for managing Hector’s dolphin bycatch. Endangered Species Research 3:169-179
Slooten E, Dawson SM (1994) Hector's Dolphin Cephalorhynchus hectori (van Beneden, 1881). In: Ridgway SH, Harrison R (eds) Handbook of Marine Mammals Vol V, The First Book of Dolphins. Academic Press, New York, p 311-333
Slooten E, Dawson SM, Rayment WJ (2004) Aerial surveys for coastal dolphins: Abundance of Hector’s dolphins off the South Island west coast, New Zealand. Marine Mammal Science 20: 117-130
Slooten E, Dawson SM, Rayment WJ and Childerhouse SJ (2005) Distribution of Maui’s dolphin, Cephalorhynchus hectori maui. New Zealand Fisheries Assessment Report 2005/28, 21p. Published by Ministry of Fisheries, Wellington
Slooten E, Dawson SM, Rayment WJ, Childerhouse SJ (2006) A new abundance estimate for Maui’s dolphin: What does it mean for managing this critically endangered species? Biological Conservation 128: 576-581
Slooten E, Dawson SM, Whitehead H (1993) Associations among photographically identified Hector's dolphins. Canadian Journal of Zoology 71: 2311-2318
Slooten E, Fletcher D, Taylor BL (2000) Accounting for uncertainty in risk assessment: Case study of Hector's dolphin mortality due to gillnet entanglement. Conservation Biology 14: 1264-1270
Slooten E, Lad F (1991) Population biology and conservation of Hector's dolphin. Canadian Journal of Zoology 69: 1701-1707
Slooten E, Rayment WJ, Dawson SM (2006) Offshore distribution of Hector’s dolphins at Banks Peninsula: Is the Banks Peninsula Marine Mammal Sanctuary large enough? New Zealand Journal of Marine and Freshwater Research 40: 333-343
Wade PR (1998) Calculating thresholds to the human-caused mortality of cetaceans and pinnipeds. Marine Mammal Science 14(1):1–37
Key researchers: Liz Slooten, Steve Dawson, Trudi Webster, Will Rayment, Judy Rodda, Silvia Scali, Elanor Hutchinson, Andrew Gormley