What are the biggest threats facing Hawaiian odontocetes?
A pantropical spotted dolphin with a wound from a vessel propeller. Photo by Annie Gorgone
The most well-publicized threat to Hawaiian odontocetes is the issue of harassment and potential displacement of spinner dolphins from their resting areas by swimmers, snorkelers, and small boats. Spinner dolphins are the only species of cetacean that rests near shore in protected bays around the main Hawaiian Islands, and this behavior puts them at risk from usually well-intentioned people that will follow groups of dolphins for extended periods. While some individual spinner dolphins, particularly juveniles, may show interest in swimmers or bowride on vessels, even when the majority of the group is resting, interacting with spinner dolphins in their resting areas may result in them moving out of their preferred resting areas, potentially exposing them to greater risk of attacks by sharks and disruption of their daily cycles. But is harassment the biggest conservation threat to Hawaiian odontocetes? A list of threats, some of which are more important to certain species than others, is below.
| Threat | Species most likely to be affected |
|---|---|
| Hook ingestion | false killer whale, bottlenose dolphin, rough-toothed dolphin |
| Navy sonar | beaked whales, dwarf sperm whales, melon-headed whales, possibly others |
| Vessel collisions | short-finned pilot whales, sperm whales, pantropical spotted dolphins, possibly others |
| Reduction in prey base | false killer whales, possibly bottlenose dolphins |
| Deliberate shooting | rough-toothed dolphins, melon-headed whales, possibly others |
| Vessel/human disturbance | pantropical spotted dolphins, spinner dolphins, short-finned pilot whales, probably other species |
| Line injuries/hooking | pantropical spotted dolphins, dwarf sperm whales, pygmy killer whales,others |
| Persistent organic pollutants | false killer whales, probably others |
| Entanglements in nearshore nets | bottlenose dolphins |
Some of these threats may cause the immediate death of individuals, and some may cause injuries that could later lead to death. Other threats could make it harder to "make a living" (e.g., reduction in prey base), or could increase an individual's susceptibility to infection or disease (e.g., persistent organic pollutants).
What puts a species most at risk?
Of the 18 species of odontocetes in Hawaiian waters, only one is listed as Endangered under the U.S. Endangered Species Act (the sperm whale). But is it the most at risk? Sperm whales were listed as Endangered because of large reductions in abundance world-wide due to commercial whaling. Although there is no recent abundance estimate available for the North Pacific, "on the basis of total abundance, current distribution, and regulatory measures that are currently in place, it is unlikely that this stock is in danger of extinction" (Allen and Angliss 2009). The species of toothed whale most at risk in Hawai‘i is currently proposed for listing as Endangered - Hawaiian insular false killer whales. False killer whales have the lowest known abundance of any of the 18 species in Hawaiian waters, are divided into at least two discrete populations (an open-ocean or pelagic population and the insular population around the main Hawaiian Islands), is slow to reproduce, is known to be threatened by a number of different anthropogenic activities, and is very high on the food web.
But many other species face a diversity of threats which could be impacting their populations in Hawaiian waters. Much of our research is focused on studying the factors that put species at risk in Hawaiian waters.
Bottlenose dolphin with hook in mouth (trailing a monofilament line) off the west coast of the island of Hawai‘i, July 5, 2009, evidence that this population does interact with local fisheries. Photo by Deron Verbeck/Iamaquatic.com. The reddish-brown material at the corner of the mouth is encrustring stalked barnacles and algae growing on the hook.
Small fishing vessels in Hawai‘i regularly "fish" spotted dolphins, repeatedly trolling through groups to try to catch associated tuna. Photo by Annie Douglas
A pantropical spotted dolphin with line injuries on the dorsal fin, most likely caused by interactions with fishing gear. Photo by Kira Goetschius.
A false killer whales with an ‘ono. This species feeds primarily on large game fish, and thus may injest hooks by consuming free-swimming fish that have hooks in them, or take fish off the lines of fishermen, potentially getting entangled or killed as a result. In addition, many game fish populations have declined due to overfishing and habitat degredation, potentially affecting false killer whale populations. Photo by Daniel Webster
Pygmy killer whale with healing injury on mouth-line, probably due to an interaction with a line fishery. Photo by Russ Andrews.
References on Hawaiian odontocetes with more information on threats
Photos on this page taken under NMFS Scientific Research Permits (Nos. 731-1774 and 774-1714). All photos are copyrighted and should not be used without permission.
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