Resource Management

Red footed boobies

Starting in the late 1940s, Johnston Atoll played an important role in the United States' nuclear testing program. From the late 1950s to 1962, high-altitude nuclear testing was carried out at Johnston Atoll. Chemical munitions were also stockpiled on Johnston and subsequently incinerated in the Johnston Atoll Chemical Agent Disposal System, built in 1990 and disassembled in 2004 after completion of its mission. By May 2005, almost all of Johnston Island's infrastructure had been removed and the wildlife returned by the hundreds of thousands. 

Today, the emergent land at Johnston Atoll remains under the jurisdiction of the U.S. Air Force. Refuge staff occasionally visit and manage a remote camp of volunteers to monitor the status of its wildlife and specifically with the intent to eradicate an invasive ant.  While previously most of the seabirds and shorebirds were found on Sand, Akua (North), and Hikina (East) islands, they have now colonized Johnston Island, taking advantage of the shade and height of the trees and shrubs left behind by its former human residents.

Johnston Atoll has recently been a focus of attempts to improve our understanding of yellow crazy ant ecology and its impacts on wildlife while developing effective eradication techniques. In January 2010, an infestation of yellow crazy ants (Anoplolepis gracilipes) was found affecting approximately 130 acres of the 630 acre Johnston Island.  Not much is known about yellow crazy ants (YCA), including their native habitat, but they are referred to as “tramp ants” because they are highly mobile and easily invade new areas due to their aggression towards other ant species and large colony sizes. YCA were probably brought to Johnston by unwitting humans, but once established began to wreak havoc on the populations of nesting seabirds. YCA excrete formic acid as a defense mechanism and colonies can quickly reach such high population densities that they swarm over anything in their path. This is a devastating combination for nesting seabirds, who suffer skin irritation, blindness, and loss of reproductive success as a result of the ants’ invasion. Many species of seabird, including red-tailed tropicbirds and wedge tailed shearwaters, all but abandoned their historical nesting sites that were within the infestation area. 

By August 2010, a plan had been devised and the first Crazy Ant Strike Team (CAST) made up of a crew leader and 3 volunteers was assembled and deployed to the island.  The first team established a remote field camp on Johnston Island as a base of operations and began studying and attempting to eradicate the invasive ants. Since then, crews have been on an approximate six-month rotation schedule applying different baits and insecticides to the infestation area, the CAST members have been able to reduce YCA populations by 99%. Seabirds have begun to return to their former nesting sites within the infestation area, but as long as the YCA still persist on the island, continued monitoring and control are necessary.

Much of CAST’s time is still devoted to deploying bait, monitoring YCA population to determine how the ants are reacting to pesticide application and how populations change over time. Every week early morning ant surveys are conducted using, believe it not, Spam, as a bait to count ants and assess how they are distributed across the infestation area. Depending on the ant activity, bait slurry of cat food, karo syrup, or house-hold sugar and water added to diluted insecticide is applied to portions of the infestation area.

A bi-monthly ant survey at selected sites within the infestation area provides an idea of how ant species other than YCA are responding to insecticides and if their presence is increasing. Every six months the entire island is surveyed for ants and samples are taken at each monitoring point for later identification and counting. This helps get an overall picture of the ant population on Johnston and shows if YCA have managed to expand to other parts of the island outside of the regularly monitored infestation area.

Captive ant farms are maintained to study YCA life cycle and history characteristics. Even today, not much is known about this ant species, so the information gathered from the ant farms is extremely valuable. Biological assessment experiments are periodically conducted on some of these farms to determine things like the lowest effective concentration of an insecticide, or what bait matrix the ants will prefer.

One of the primary concerns with applying any sort of pesticide to the island is the potential negative impacts on the rest of the island’s wildlife. Weekly shorebird surveys performed by the CAST crew assess shorebird presence to determine if the birds are consuming insects that had been exposed to pesticides. As anticipated, no signs of impacts to shorebirds have been observed since the project was initiated.

With the reduction of YCA on the island, Johnston may be home to the largest nesting colony of red-tailed tropicbirds in the world. Now that the tropicbirds are coming back, nest productivity plots are monitored to keep a close watch on how well the birds are doing, both in and outside the YCA infestation area.  The CAST crews count and monitor nests within 10 plots and track the growth of chicks until they fledge.

Mean incubation count surveys for red and white-tailed tropicbirds, great frigate birds, and brown, masked, and red-footed boobies are all surveyed at an interval that corresponds with the average number of days it takes each bird species to incubate its eggs, which for these six species ranges from 43 to 55 days.  Using this interval ensure nests are not double counted and provides a picture of the overall seasonality and periodicity of nesting, as well as population census.

Equally important is the island vegetation that provides essential nesting habitat and cover for seabirds from the extreme heat and wind. In an effort to control invasive plant species a vegetation mapping project is currently underway to record the abundance and location of invasive plants. Unfortunately, most of the plants growing on Johnston are non-native, and the CAST crew is on constant watch for Klu (Acacia farnesiana) a particularly invasive species.

Just as the terrestrial portion of Johnston is thriving with nesting seabird populations, the waters surrounding Johnston are home to a diverse assemblage of marine life. Several dozen coral species and hundreds of different fish species reside in Johnston’s offshore reefs. To learn more about the fish in near-shore waters transects on the north and south shores of the island are surveyed biweekly, counting and identifying fish. A bi-weekly sea turtle survey is also conducted to get a general idea of the presence of threatened green sea turtles that visit the island’s south shore.

If that is not all enough to keep them busy, the CAST crew assists the University of Hawai'i with their data collection through maintaining a tide level monitoring station that tracks sea levels across the Pacific to monitor global climate change. And then of course there is always the organic garden (fresh vegetables are a real treat) and each power bar wrapper has to be individually washed and dried so as not to attract ANTS!