Secretary Island deer dradication

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Secretary Island Deer Eradication Scoping Document (PDF, 398K)

Summary

Secretary Island is part of Fiordland National Park, and is 8140 hectares in size.  It is a steep and rugged island, rising to 1196 m above sea level. It is separated from the mainland portion of Fiordland National Park by Thompson Sound to the east (minimum distance between the two is c 950 m), and by Doubtful Sound to the south. 

Secretary Island was until the late 1950’s or early 1960’s entirely free of introduced browsing or grazing animals, and was one of the largest and most significant areas of indigenous vegetation remaining free of the effects of such animal pests. Until that time, the stoat was the only introduced animal that had succeeded in crossing the gap between the mainland and the island. The spread of red deer into Fiordland inevitably meant that Secretary Island would be threatened by this species, a competent swimmer well capable of crossing either Sound to reach the island. 

A red deer stag was intercepted and killed as it was swimming to Secretary Island in 1959, and this was the first recorded evidence of red deer attempting to reach the island, though it is unclear whether individual deer had reached the island before this date. Deer were not present in the southern sector of the island during a visit in 1959/60 by an Otago University botanical team. However, deer could easily have been present on the island in low numbers, especially in the western/northern areas (now known to be favoured areas) where the botanical team never visited. 

Sporadic sign was confirmed from the southern end of the island from 1963, though it is unclear whether a resident breeding population was present. A fisherman reportedly saw and photographed a hind and fawn in Grono Bay some time prior to May 1966 (Brown and Evans, 1966) but incredibly the significance of the sighting appears to have been overlooked or dismissed (in one case it was suggested they were probably two stags minus antlers). 

By 1970 a small resident population was confirmed in the southern (Gut) area, where 4 adult females were shot and 2 more driven from the island around the ‘Gut’ area in April 1970 (Paulin, 1970). In all probability deer had extended over much of the island in low numbers by this date. This was confirmed by helicopter hunting and ground observers in 1973-74, when deer were shot in moderate numbers all over the island, with population large enough to have created tracks “over two feet wide and worn down exposing bare earth and roots” in some favoured areas (Evans, 1973). By 1975, deer were well established all over the island (Marks and Baylis, 1975) in sufficient number to have created very obvious tracking. 

Details of precisely when a breeding population established on the island will remain unknown. On the basis of the historical spread of red deer into the area, it is probable that deer most likely colonised the island from the east (across Thompson Sound) and could have remained undetected in the (still) favoured western areas for some years. (Note that a survey in 1973 showed no sign of deer, past or present, on Bauza Island). Access to the island at the time was almost exclusively by boat, and as a result field observations were largely confined to the southern sector.

Control measures were implemented between 1970 and 1987 but were never intensive enough or applied widely enough over the island to have major impact on the total population. Methods included aerial helicopter shooting, ground hunting, snaring, a capture pen, and 1080 gel baiting of palatable plants. Table1 summarises the available deer kill records from 1970-1985.

It became clear that ‘eradicating’ deer from Secretary Island was a massive task, and while considerable effort went into the control measures, questions were beginning to arise regarding the viability of the project. 

By 1985, the attitude was “even if extermination is unrealistic, it is possible to achieve an extremely low population at a level where animal damage to vegetation is regarded as insignificant” (Sanson and von Tunzelman, 1985).  By 1989, the attitude was more defeatist - “eradication of red deer from Secretary Island is not an option. The existing technology will not achieve this at any price. Even if it did, continuous control and monitoring would be required to prevent re-invasion by deer swimming across to the island from the mainland” (Chisholm, WAM options paper, 1989). 

The control budget was ceased in 1988/89. Some commercial aerial hunting continued into the 1990’s but its effect did not achieve a high level of control.  The island was largely ignored until 2001 when Munn (2001) put forward a proposal for restoration of the island through control of deer and stoats to low levels.

This scoping document has been prepared by Derek Brown in consultation with Department of Conservation staff, Te Anau Area Office and Southland Conservancy, December 2005.

The aim of this report is to present options for the removal of deer in the near future.  This report is by no means a final plan but a review of all the possible options to be considered for deer control on Secretary Island. Following feedback from interested parties we will collate this information and prepare a draft Operational Plan.

Publication information

Prepared by Derek Brown in consultation with Department of Conservation staff, Te Anau Area Office and Southland Conservancy.