Monday, October 3, 2011

Okarito 1080

Personal assessment of the success of an aerial 1080 operation at Okarito to protect kiwi (rowi) from stoat predation.
By Ian James

Executive summary:

1.  Small mammal tracking data indicate successful control of rats and stoats.

2.  Seven tagged Kea losses is a serious problem.  Other native birds seem not affected and all will benefit from rat-free breeding season.

3.  Fresh possum sign post 1080 cast doubt on control success.  A few rabbits killed but hare numbers seem unaffected.

4.  The 1080 operation may have been done one year too soon as another rimu seed-fall is coming next year. Rat, then stoat, numbers may recover fast.

4.  Deer losses are unacceptable to local hunters.  Independent study of deer numbers, before and after 1080, suggest 45% of deer herd was lost.

5.  Deer losses could have been minimised had a deer repellant been used.  DOC policy and action does not recognise yet the change in legal status of deer to "game animals"  Lack of action is fueling the fire of opposition to 1080.


It's now four weeks since the Okarito 1080 operation, time enough for some conclusions.

The good news is that DOC reports success in achieving their goal of protecting kiwi. Their small mammal tracking index showed rat and stoat numbers declined from 29% and 48% respectively, before 1080, to 1% and 0% afterwards.

 On the negative side, DOC has recorded 7 kea losses from a total of 32 tracked birds. That is a serious loss as an unknown number of other kea, not tracked, were likely lost as well?   Kea are as threatened as kiwi.

 How did the other birds fare? As far as I can judge pretty well. Tui, bellbird, morkpork, falcon and pigeons remain around the village in the same numbers as before. Grey warbler, fantail, fernbird, brown creeper and tomtit can still be heard along bush tracks but numbers are desperately low.  But they were like that before 1080.  The status of kakariki, riflemen and robins is unknown.

 All birds should benefit from a breeding season without rats and stoats. It is a pity that early 5-min bird count data was not repeated as long-term small bird monitoring data is available for both north and south Okarito forests.  That would have demonstrated that the wider avian ecosystem benefitted, not simply kiwi.

I am not sure that possum numbers have been effectively controlled.  Live possums can still be seen at night along the Okarito road and there are fresh possum tracks along the beaches south of Okarito. Perhaps the low bait sowing rate (< 2kg/ha) allowed the rats to quickly hoover up the baits before some possums got the chance. Hares were largely unaffected and 3 rabbits were found dead.

I do have concerns that the 1080 operation was done one year too soon.  I understand that rat numbers were barely high enough to ensure a successful 1080 control after a rimu mast last autumn. Normally rimu has two concurrent mast years followed by 3 years with little or no seed.  This year is no exception as rimu seed is ripening on trees at the present time (see image above).  This means that surviving rats will have a stoat-free holiday in a coming mast year so numbers should rebound rapidly.  That in turn will facilitate a rebound in stoat numbers - not the result hoped for.

The "numero uno" for local hunters is number of deer poisoned.  Sadly, no data was collected, more than an oversight in my opinion, given the level of concern amongst local hunters.  Deer are now legislated as "game animals" but this change appears yet to be fully implemented in DOC policy, or practice.  

To rectify matters, I have made a personal study by visiting 16 localities (good hunting spots) pre-1080 and made an assessment of the number of deer using the area i.e. the level of tracks, droppings and browse. I then repeated the assessment three weeks post-1080.

While observational studies can never be as scientifically rigorous as collecting hard data, I made special effort to avoid bias. In cases of doubt I erred on the side that no change in deer numbers had occurred. To protect local hunter's favorite spots the areas are not described. The results of my study are tabled below:

 Area.       Deer numbers before.       Deer numbers after.

A                           1                                      2
B                           2                                      0
C                           1                                      1
D                           1                                      0
E                            1                                     0                          
F                            0                                     0
G                           0                                     1
H                           2                                     2
I                             2                                     1
J                             2                                     1
K                           2                                     1
L                            5                                     1
M                           1                                     0
N                           3                                     1
O                           3                                     3
P                            5                                     5

Totals                   31                                   17

The last two areas where deer numbers are the same may not have had been directly poisoned. P is near a major river and O is adjacent to the poisoned area. A few other records from after 1080 observations were tracks of indeterminate age but included as a positive.

The result indicate net 45% reduction in deer numbers. Comparative published information show red deer losses of between 5% to 93% (Technical Review of Sodium Monofluoroacetate, Table 5; Eason, 2002) ).

Why were so many deer killed at Okarito given the dense vegetation and low sowing rate?  It was not the result we expected.  The timing was not good coming at the end of winter just before the first spring grass growth. However, that time is ideal for maximizing the rat and possum kill.

The 1080 loading in individual baits is high given that the small size of the target animals.  DOC staff supplied the following commentary:

"One 12 gram 0.15% 1080 bait contains 18 mg of 1080. Deer require 0.5mg/kg body weight for a 50% chance of death. Therefore a deer weighing 36kg live weight needs one bait, a deer weighing 72kg live weight would need two, etc etc. So if an adult hind eats three full size full strength 1080 baits she is in trouble".

So few baits are needed to kill a deer so each bait contains many times the lethal doses for a rat or possum, the target species. That surely is an area DOC can reconsider. If it took 10 or more baits to kill a deer then less may be killed. 

These deer losses are unacceptable to the hunting fraternity and, in their eyes, are as bad as the kea killed.  For locals for whom venison is the main table meat, the deer losses are a serious disappointment and were avoidable.  Local hunters support the kiwi recovery as strongly as any folk but the cost to their sport is too high.

The deer numbers will recover over time.  However,  putting the same hunting pressure and natural mortality rates as inputs to a simple population model shows deer numbers will not fully recover for at least five years.  In the interim, 1080 may need to be used again if rats recover quickly.

The obvious need is for DOC to use a deer repellant as standard practice.  A successful repellant was developed and tested in New Zealand in 2003 (Speedy, 2005).  Why is it not used?  Deer are not a conservation problem in lowland South Westland.  DOC staff offer excuses such as patent problems, difficulty of application, cost, etc. But excuses simply imply inertia.  Deer repellants are used worldwide and many are blood based, a product available cheap from NZ freezing works.  Given the angst the department suffers and the legal status of deer a change of policy and action is way overdue. Their current inaction is fueling the fire of opposition to 1080.


  1. Deer repellent increases the cost of 1080 operations by $10-12 per hectare.

  2. $10 - 12 per hectare is ludicrous! All baits should have the repellant added at the time of manufacture. Easiest would be to add blood and bone into the grain pellets. It attracts rats and possums and repels deer.