Details of this species in Raoul Is. Status: Alien
Invasiveness: Invasive
Occurrence: Eradicated
Source: Parkes 1984; West, 2002 Arrival Date: before 1836
Introduction: Species Notes for this Location:
Feral goats (Capra hircus) were recorded on the island as early as 1836 by captain W.B. Rhodes (Parkes 1984). Estimates of the population size of the goats in the past have varied greatly and include “4000 to 5000” (Venables 1937, in Parkes 1984) and “3000 plus” (Clark 1974, in Parkes 1984). The narrow coastal strips and shores around the beaches are a favourite habitat of the goats (Sykes 1969). Management Notes for this Location:
This case study illustrates the feasibility of removing large, established goat (Capra hircus) populations from large islands - as of 1990 this was the largest island in New Zealand on which goats had been successfully eradicated (Parkes 1990). Since 1937 at least 15 000 goats have been killed intentionally. Since 1972 annual hunting expeditions have been sent to Raoul Island. In addition to hunting, alternative methods such as helicopter gunships, natural bait poisoning and snaring have been tried with “varying success”. By 1983 the hunters had difficulty finding any sign of goats despite intensive efforts.
According to Parkes (1990) the total direct cost of the campaign from 1972 was about $1 million (or $339/ha). In retrospect the long period of low intensity control worked against the projects efficiency. Early culling of the population resulted in regeneration of the forest, which would have provided extra food sources for the remaining population - allowing it to increase its breeding rate from 0.96 kids/female/year in 1972 (Rudge and Clark 1978, in ) to 1.7 in the 1980s –higher than those recorded for other feral herds in New Zealand (Parkes 1984). Location Notes:
Raoul Island is the northernmost and largest island (2959 ha) of the Kermadec group, which lies at a latitude of 29° and is of equidistance between New Zealand and Tonga. It is an active volcano which erupted in 1964 and consists of three steep walled calderas that rise up to 520m above sea level. The climate is subtropical with a maximum monthly temperature of 22.4° in February and a minimum monthly temperature of 16.0°C in August. The mean annual rainfall of 1 470mm is spread throughout the year, although the period from October to January is usually drier than the rest of the year. The island is largely forested, with the endemic Kermadec pahutukawa (Metrosideros kermadecensis) being the dominant canopy tree. The native flora on Raoul Island contains some tropical elements but is mainly associated with New Zealand flora. Eighteen taxa of vascular plants are described as endemic (Sykes 1977, in Parkes 1984). Impacts:
Habitat alteration: Browsing of native vegetation by goats on Raoul Island has caused changes in the vegetation structure of the forests because of the unpalatability of the two main understorey trees, Myrsine kermadecensis Chessem. and Ascarina lucida var. lanceolata (Hook. f.). Allan (Sykes 1969). These species were probably more common in 1966-67 than previously and were found to form dense pure stands in the dry and wet forests (respectively). The fern Pteris comans, also reportedly unpalatable to the goats, was also thought to be more common on the island due to its selective advantage (Sykes 1969).
Interaction with other invasive species: The introduced terrestrial aroid Alocasia macrorrhiza (L.) Schott., is unpalatable to the goats, a trait which is thought to have given it a selective advantage on the island, allowing it increase markedly in number to dominate large areas of the forest (Sykes 1969). This large-leaved plant restricts light reaching the forest floor and inhibits the regeneration of woody species. In addition to Alocasia a number of other introduced plants increased at the expense of indigenous flora due to their unpalatability to goats (Sykes 1969).
Modification of successional patterns: The forests of Raoul Island are mainly dominated by the Kermadec pohutukawa (Metrosideros kermadecensis W.R.B. Oliver) (Sykes 1969). Sykes (1969) reported that this is a favoured species by goats and in most areas observed on the island (before goat control) little or no young seedlings of this species were observed. As this is the main canopy tree, its disappearance over large parts of the island would obviously have resulted in drastic changes to the rest of the vegetation as well. (A similar effect to this has been realised on Cuvier Island near the New Zealand coast). The Raoul forests are noted also for their large tree ferns (belonging to two endemic species of Cyathea). Sykes (1969) hypothesised that these had became notably less common because of the inhibition of regeneration by the goats. Seedlings of the endemic Coprosma acutifolia Hook. F. were also reported to be reduced by the goats; the plant is a principal component of the understorey layer in dry forests and the canopy in wet forests (Sykes 1969).
Reduction in native biodiversity: The destruction of indigenous flora by goats was noted in 1908 (Oliver 1910, in Parkes 1984). A botanical survey conducted in 1966/67 and reported by Sykes (1969) revealed that at least one endemic species, Hebe breviracemosa, which is very palatable to goats, was nearly extinct. The survey also made light of the following points. Homalanthus polyandrous, Boehmeria dealbata and Pseudopanax kermadecense were reported to be uncommon due to the browsing activity of the goats. Whilst the mature trees were relatively unaffected, the regeneration of these species appeared to be inhibited. Regeneration of the endemic Kermadec nikau, Rhopalostylis cheesmanii, wharangi, Melicope ternate and karaka, Corynocarpus laevigatus has also probably been kept in check by goat browsing. Other palatable species, such as the karo (Pittosporum crassifolium) and the endemic Kermadec taupata (Coprosma petiolata), were mainly confined to the cliff faces. The Kermadec ngaio, once a characteristic of the coastal scrub, had also been greatly reduced in many parts of Raoul Island. Olivier (1910) noted that goats barked parapara trees (Heimerliodendron brunonianum) and they seemed to be nearly extinct by 1967. Goats have also been known to climb Kermadec pohutukawa and mahoe Melicytus ramiflorus to browse epiphytic ferns (particularly Asplenium). The ice plant Disphyma australe, abundant on the coast, was also browsed by the goats. Last Modified: 22/05/2006 10:02:46 a.m.
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