The waters of PIPA contain a wide variety of fishes, including coral reef fish, tuna, billfish, sharks, and deep sea varieties, but even more than the diversity, the sheer numbers of fish are extraordinary. Fish that are seen rarely in other parts of the world still exist here in great numbers. Fish populations are abundant with, at locations featuring high currents and topographic complexity, large schools of jacks, barracuda, snappers, surgeonfish, and parrotfish, and abundant sharks. Both coral and fish communities show differentiation between windward, leeward and lagoon habitats.
Leeward outer reefs contained the highest fish diversity with an average of species per site. Other major habitats included windward outer reefs, passages, and lagoon reefs. Certain species were particularly common on Phoenix Islands reefs, occurring in much higher densities than at most localities in the Indo-Pacific region. These included various surgeonfishes (Acanthurus guttatus, A. nigricans, A. triostegus, A. xanthopterus, Naso literatus, and Zebrasoma veliferum) and parrotfishes (Hipposcarus longiceps and Scarus ghobban). All of these species were frequently sighted in extraordinarily large aggregations. The giant humphead wrasse Cheilinus undulatus, usually a good indicator of local fishing pressure, was seen in much greater numbers compared with other areas recently surveyed in the Indo-Pacific.
One of the most remarkable aspects of the Phoenix Islands are the large numbers of sharks. The habitat is ideally suited for them with the shallow atoll lagoons acting as nurseries and the gradient of the reef providing a varied feast of fish of all sizes. The isolation of the islands has helped to protect the sharks from the burgeoning shark fin trade as well as the threat of becoming fishing bycatch. These apex predators, while seeming invincible to those they encounter underwater, are actually quite vulnerable. Due to their status as apex predators they do not need to have many offspring. Consequently, females only bear a few pups every year. In contrast to the thousands (even millions) of eggs laid by many fish, it becomes apparent how quickly shark populations can be decimated and how long they will take to recover.
Sharks are an integral part of the reef system, as is demonstrated by the health of the phoenix reefs. They keep the fish populations in balance and help to reduce disease. In the Phoenix Islands, researchers described the sharks as curious and abundant which is amazing for the populations but a little intimidating for divers at times. In addition, deep-water camera deployments and images provided the first data on deep-sea fauna for the Phoenix group. These are new sighting records for six-gilled and Pacific Sleeper sharks and help to build our understanding of their worldwide distribution.
The Phoenix Islands are located in the heart of the famous 19th century sperm whaling ground. In these waters, whalers from North America came and hunted sperm whales in tremendous numbers in the 19th century. Despite these historical populations, recent observations indicate that populations of sperm whales, or other large whales, in the Phoenix Islands are not abundant today, at least at the time of year that the survey was conducted. There have been groups of bottlenose (Tursiops spp.) and common dolphins (Delphinus delphus) observed close to most of the islands and also several sightings of unidentified beaked whales (Mesoplodon spp.). These data are of concern and supports the need for the currently proposed International Whaling Commission South Pacific Sanctuary, which would protect all large whales in the region.
There are a significant number of turtles and turtle nesting sites in the PIPA. In many places in the world, turtle poaching is excessive and eggs are removed from the nest and eaten. However, due to the remote location of the Phoenix Islands these nesting populations have been spared the brunt of human interaction. The confirmed species that are nesting in PIPA are the Green Turtle and the Hawksbill Turtle.
There are four species of rays that have been observed by visiting scientists to the Phoenix Islands. Two species are bottom dwelling and spend the majority of their time on the sandy bottom. The two pelagic rays that have been documented in the Phoenix Islands are the Eagle Ray and the Manta Ray. The Eagle Ray feeds on mollusks and the Manta Ray feeds on plankton.
“The thing that impressed us most was the overwhelming numbers of individuals of many species. Fishes that we see rarely in places like Indonesia and the Philippines were visible in spectacular abundance. On most dives, we were greeted by swirling masses of black jacks (Caranx lugubris) and bigeye jack (Caranx sexfasciatus). There were also huge numbers of surgeon fishes, particularly at Nikumaroro Island.”
- Gerry Allen, Ichthyologist, Conservation International
“I saw several thousand surgeonfishes and over 500 buffalo parrotfish on his dive—numbers you don’t see in most places anymore. The way the parrotfish charged in a herd and grazed on coral, they looked just like buffalo.”
- Steve Bailey, Curator of Fishes, New England Aquarium