CNMI Wildlife and Vegetatio,N Surveys and Feral Animal Control
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2003 Technical Report #10 CNMI Wildlife and Vegetatio,n Surveys and Feral Animal Control ANATAHAN 2002·2003 Conducted by CNMI Division of Fish and Wildlife, CNMI Northern Island Mayor's Office, and US Fish and Wildlife Service Justine de Cruz Laura Williams Nathaniel Hawley Jacob Esselstyn Curt Kessler Ortwin Bourquin Anatahan Feral Animal Control Project 2002-2003 CNMI Wildlife and Vegetation Surveys and Feral Animal Control ANATAHAN 2002-2003 This report is dedicated to the memories ofHappy Gideon and Joseph Ogumoro (former Mayor of the Northern Islands) who contributed their sound judgement, good humor, versatility, and hard work to many of the Northern Island projects conducted by our combined agencies. They were good friends to us all and are greatly missed. 2003 Technical Report #10 2 Anatahan Feral Animal Control Project 2002-2003 CNMI Wildlife and Vegetation Surveys and Feral Animal Control ANATAHAN 2002·2003 EXECUTIVE SUMMARY To attenuate the impact of feral animals on Anatahan's ecology, the CNMI and the US Fish and Wildlife Service (USFWS) are cooperating on a US Navy funded project to remove feral pigs and goats as an emergency measure to put a stop to the destruction of the island. This report covers the feral animal removal activities, faunal and vegetation surveys conducted by CNMI-Division of Fish and Wildlife (DFW), the Northern Island Mayor's Office (NIMO), and USFWS from April 2002 - April 2003. Wildlife surveys to assess species diversity and abundance were conducted from 25 April - 2 May 2002 for birds, skinks, geckos, lizards, rodents, bats, invertebrates, goats, and pigs on the eastern side of Anatahan. Two vegetation surveys were conducted: a point-center quarter survey to establish forest species diversity and a baseline survey of long-term vegetation plots (with fenced and unfenced plots) to monitor habitat recovery with the removal of feral animals. The vegetation plots established in May 2002 were reassessed in November 2002 to evaluate the impact of removal on vegetative recovery. Feral animal removal strategies, logistics, and activities were planned by the agencies involved during September 2001 - January 2002. Goats and pigs were removed systematically from 4 - 16 May 2002 on the south, east, and north sides of the island and in the volcanic crater, where most of the removal was conducted from a helicopter. Feral animals were removed opportunistically until 31 August 2002 on the western end of the island, near the village, mostly by capture or hunting on the ground. Following the major removal effort in 2002, trips were made monthly to Anatahan beginning in 2003 to control feral animals until a fence could be built across the island to separate subsistence hunting zones from no-ungulate zones. Eight goats were radio collared and released on the island to act as "judas" goats, leading the hunters using telemetry to herds of remaining animals. Shooting from an aerial platform was scheduled to occur monthly through calendar year 2003 while ground hunting was to continue from May through August 2003, rounding out the reduction phases of the project. Survey Results In May 2002, forest birds appeared to be densely packed into the small amount of forest remaining on Anatahan. We crudely estimated that less than one-third of the island remained forested (about 1,050 ha out of the island's 3,230 ha) and birds were most numerous in the forests remaining on the eastern end. Only four species of forest birds occurred on Anatahan (the Micronesian Honeyeater, Micronesian Starling, White throated Ground-dove, and Micronesian Megapode), or fewer species than on any of the other northern islands. Honeyeater and starling densities appeared to be quite high, but megapode and ground-dove densities were low. The diurnal hawks on Anatahan 2003 Technical Report #10 3 /' Anatahan Feral Animal Control Project 2002-2003 may be depressing these last two populations. However, as the forest recovers from the negative effects of feral animals and once again provides cover for ground-foraging species, we expect to observe an overall rise in bird numbers, especially of the endangered Micronesian megapode. Herpetofauna surveys have just begun to establish a base-line inventory for Anatahan so it is not surprising that the April - May 2002 survey found the Rock Gecko (Nactus pe/agicus) for the first time on the island. Mariana Fruit Bat surveys in May 2002 and subsequent observations by goat hunters until April 2003 identified several major roosting sites for bats on the island. Aggregations of bats dispersed and reformed over this period, with colony sites located mostly in the southern, northern and eastern coastal areas. Nearly simultaneous counts from the helicopter of several of the colonies, combined with survey observations, indicate that fruit bats on Anatahan during this period numbered at least 1,200 individuals. The invertebrate survey in April - May 2002 was one of the most extensive conducted in recent decades on the northern islands of the CNMI. The list of 144 previously recorded invertebrate species on Anatahan was increased by an additional 117 species during this collection trip, of which 10 were new records for the CNMI and one, a click beetle, is considered to be a new species and has been sent to a specialist for naming. A number of new distribution records were found including a dragonfly which had not previously been recorded from the CNMI, and a robber fly, a tick, a praying mantis and a scorpion not previously recorded from Anatahan. A fly index technique was developed during the April - May trip that was simple, fast, and required a minimum of equipment. The method appears to have merit as an easily applied index technique. In May 2002, the number of tree species present in both the point center-quarter survey and the vegetation monitoring plots was very low and lacked diversity. The size and therefore age structure of the tree population was skewed heavily towards the larger and older tree classes, with virtually no juvenile recruitment. Additionally, several tree species that are known to occur on Anatahan and that are important to wildlife were not found during either survey. Without drastic and consistently maintained reductions in the feral animal population, the lack of recruitment will eventually lead to loss of the forest and the development of unpalatable grasslands. The re-survey in November 2002 of the vegetation plots established to monitor habitat recovery showed that seedling recruitment had improved in both fenced and unfenced vegetation monitoring plots, as had ground cover, suggesting that even six months of feral animal suppression had a positive effect on forest recruitment. However, fenced plots that excluded ungulates entirely were acquiring more species and greater ground cover at a faster rate than unfenced plots, indicating that feral animal control had not reached levels sufficient to minimize the remaining ungulates' negative impact on the island's vegetation. If the goats and pigs are not eliminated as uncontrolled feral populations, there is a real danger that plant and animal species native to the island could be lost, that soil erosion will continue, and that overall natural productivity will be further reduced. 2003 Technical Report #10 4 Anatahan Feral Animal Control Project 2002-2003 Feral Ungulate Removal Aerial and ground hunting effectively reduced the population of goats on Anatahan in May - August 2002. A total of 2,561 goats out of the estimated population of 4,604 were removed. Of the methods used (capture and live removal, aerial gunnery, and ground hunting), aerial gunnery was the most efficient method of removal, considering the cost per unit removed, and the number of man-hours involved for each type of removal effort. However, ground hunting is most effective in ferreting out goats that hide in caves or do not move into open areas where aerial targeting is possible. Live capture was the least efficient method employed and did not result in removal of large numbers of animals. Feral ungulate removal efforts were renewed in January 2003 with monthly trips to Anatahan focused on removing animals using telemetry and aerial gunnery. Between January and April 2003 over 824 feral goats and 52 feral pigs were eliminated from the island. The number of goats removed has diminished with each of these monthly trips, indicating that the method has been effective in reducing the number of goats on the island, thus making them harder to find. A combination of both aerial gunnery and ground hunting efforts will be necessary to reduce goat numbers further toward eradication. Postscript On May 10 2003, the eastern volcano on Anatahan erupted sending steam, ash and rocks over the majority of the island. The feral animal control project is currently postponed until it is safe enough to approach the island again. 2003 Technical Report #/0 5 Anatahan Feral Animal Control Project 2002-2003 CNMI Wildlife and Vegetation Surveys and Feral Animal Control ANATAHAN 2002·2003 INTRODUCTION Anatahan is the closest of the volcanic Northern Islands to Saipan (120 km north). It is large (approximately 3,230 ha) and long (9 km) with a maximum elevation of 788 m. Over the last half-century, large numbers of feral goats and pigs have inflicted incredible damage on Anatahan that will be hard to remedy. Overgrazing has left the upper ridges as largely swordgrass (Ohbra 1994) with the native forest common only in ravines, on the eastern slopes of the island, and in a few pockets in the large crater. By 1995, Marshal et al. (2001) reported that much of the native vegetation had been destroyed by ungulates, with little remaining understory and severe erosion on the steep slopes. Several permanent vegetation stations established in 1995 along the western slopes and re-surveyed in 2000 document the loss of whole tree groves to feral ungulate damage (Kessler 2000).