At the request of the Niue Government a FAO-SPADP funded pilot-stock survey was conducted on Niue in 1988 to assess the status of the coconut crab population. The study found that the coconut crab was in all probability suffering from over-exploitation and that immediate remedial measures were necessary to ensure that stock levels did not decline further. The study recommended that an immediate detailed population study of the coconut crab be conducted to provide the data necessary for formulation of a resource management plan. An interim series of conservation measures, including protection of crab with eggs, closed seasons and cessation of crab exports, were also provided to assist the Niue Government in halting/slowing the decline of its coconut crab resource. The initial findings indicated that the decline of the coconut crab was the result of exporting large numbers to Niueans resident in New Zealand. Unfortunately the interim conservation recommendations were not acted upon. Fortuitously coconut crab exports declined dramatically from mid 1988 through to late 1989 as a result of a major disruption to air services linking Niue with New Zealand.
The detailed coconut crab population survey, which is the subject of this report, commenced in 1990 and ran for 71/2 months. The primary aim of the study was to gather detailed population data to enable the formulation of a viable coconut crab management strategy. In addition, educational materials (coconut crab poster and video movie) were to be developed for use in a public awareness programme.
Survey results revealed that the coconut crab population on Niue (259 km2) is quite small at only 181 440 individuals and is predominantly comprised of small individuals (mean male thoracic length= 32.5mm, mean female thoracic length= 26.9mm). Male and female coconut crab size frequency data are non-normally distributed and exhibit pronounced skewness and/or kurtosis - the result of intermittent recruitment and long-term over-exploitation.
Destruction and fragmentation of forested areas on Niue has drastically reduced the total area of suitable coconut crab habitat to such an extent that 76% of the crabs are now found in a narrow band of Coastal Forest occupying only 11.5% of the available land area.
It is probable that recruitment on Niue operates as a closed system whereby coconut crabs recruiting to Niue must be sourced from Niue. Given a 5 year cycle for successful recruitment, it is suggested that reproductive viability of the coconut crab population on Niue requires that females be able to produce at least 5 batches of eggs (1 batch per year) prior to their removal from the population as a result of natural mortality or hunting pressure. As such, a reproductively viable population must include individuals which have been sexually mature for at least 5 years (assuming that these sexually mature females will produce eggs each year). On Niue this corresponds to female crabs of approximately 11 years of age, which is equivalent to a female thoracic length of approximately 32mm.
At present only 10% of the female coconut crab population has a thoracic length in excess of 32mm. On this basis it is suggested that rates of exploitation have for many years been far in excess of recruitment-based replenishment, resulting in a population which is in serious decline and heading inexorably towards extinction in the short term. It is further postulated that the driving force behind the non-sustainable level of exploitation is not local consumption, but coconut crab exports. It is estimated that exporting of crabs to Niueans in New Zealand has increased exploitation rates 200-350% over the 'normal' levels required to meet local demand.
A series of management proposals were developed to ensure the continuation of the coconut crab on Niue. A summary of the recommendations follows:
No female coconut crabs with large orange-tinted abdomens or bearing external eggs to be taken or interfered with.
Introduction of a minimum legal hunting size of 36mm thoracic length for all coconut crabs (includes providing a size-guide for hunters to use in the field to size crabs).
Banning of all coconut crab exports.
Introduction of closed hunting seasons.
A comprehensive public awareness campaign (involving production of a large coconut crab conservation poster and educational video movie).
Establishment of formal coconut crab sanctuaries.
Banning use of dogs by coconut crab hunters.
Instigation of a coconut crab monitoring programme.
Preservation of coconut crab habitat.
Legislation developed using preliminary results from this study to ban coconut crab exports and to protect crabs carrying eggs was submitted to the Niue Cabinet in November 1991 for ratification but was rejected. The legislation is currently being amended and will be re-submitted to Cabinet at a later date. In the mean time it is hoped that the coconut crab video and poster will sufficiently increase public awareness of the need to protect the coconut crab that the hunting of small/female crabs and exports will be reduced voluntarily. This may be adequate in the short-term but a directed management plan in the form of coconut crab legislation is required for the long-term maintenance/growth of coconut crab stock on Niue.
It is essential that the coconut crab stock not be allowed to decline below current levels as this would greatly increase the possibility of a devastating recruitment failure. Regular monitoring of the coconut crab population is considered essential to ensure that any management/conservation measures instigated are having the desired effect.
A programme of future research/population monitoring has been developed as follows (summarised to point form):
Monitoring of Exploitation Levels (continuous monitoring by DAFF staff)
Monitoring of Coconut Crab Population Dynamics (annual survey)
Monitoring of Numbers of Egg-releasing Females (annual survey)
The majority of the proposed follow-up research, collection of exploitation data and conducting of transect surveys, can be accomplished by staff from DAFF. However overall co-ordination of the research, development of transect survey programmes and analysis/interpretation of results would require an external consultant versed in such procedures.