PIFSC Sea Turtle Longline Research EA June 1, 2009
incidental capture in various kinds of fisheries (coastal and high-seas); loss and degradation of nesting and foraging habitat; and predation on nesting beaches by feral and domestic animals (especially dogs and pigs). Increased environmental contaminants and hazards, such as marine debris, and sewage and industrial discharges, adversely impact nearshore sea grass and coral reef ecosystems on which some species of sea turtles depend for food and shelter. Anchoring beaches with walls, which prevent sea turtles from reaching the nesting beaches, and lights associated with human activity inland which cause hatchlings to move toward land rather than the ocean upon hatching, also reduce nesting success. In addition to direct and indirect human activities that affect the survival and recovery of sea turtle populations, other factors also contribute to declining populations, such as coastal erosion, seasonal storms, predators, temperature variations, rising sea and temperature levels from climate change, diseases such as fibropapillomatosis and spirochidiasis, and phenomena such as El Niño (Kaplan 2005, Beverly and Chapman 2007, Gilman et al. 2007, NMFS 2008a, Hermsmeyer 2008).
At present, all species of sea turtles are categorized by the International Union for Conservation of Nature and Natural Resources (IUCN 2004) as “critically endangered” (hawksbill [Eretmochelys imbricata], Kemp’s ridley [Lepidochelys kempii] and leatherback), “endangered” (loggerhead, olive ridley, and green), or “vulnerable” (Australia’s flatback turtle [Natator depressa]). Under the U.S. Endangered Species Act (ESA), leatherback, hawksbill, Kemp’s ridley, the populations of olive ridley turtles nesting in Mexico, and the populations of green turtles in Florida and the Pacific coast of Mexico are listed as endangered; loggerhead, other Pacific populations of olive ridley turtles, and the Hawaii subpopulation of green turtles are listed as threatened. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) identifies all sea turtle species excluding the flatback as threatened with extinction, and prohibits the international trade in sea turtles and sea turtle products.
The shallow-set fisheries in the north Pacific and Atlantic Oceans interact primarily with juvenile loggerhead turtles and adult leatherback turtles, primarily during their migratory stage (Watson et al. 2005). Due to their deep-diving behavior, the deep-set fishery interacts primarily with olive ridley turtles (Polovina et al. 2003, NMFS 2008a).
Most sea turtle species are highly migratory, traveling over broad expanses of open ocean between land-based nesting areas and pelagic foraging areas. In order to comprehensively address population decreases, the harvesting of adults and eggs for food, habitat degradation from pollution, and loss of nesting beaches and habitat are issues that must be addressed concurrently with attempts at reducing bycatch in ocean marine fisheries. Sea turtle conservation, therefore, cannot be implemented by a single nation, but rather requires international cooperation in alleviating all of the primary threats to their recovery. Therefore, a holistic integrated management approach appears to have the highest chance of success in solving the problem of declining sea turtle populations (Lewison et al. 2004, Kaplan 2005, Gilman et al. 2006, Beverly and Chapman 2007, Gilman et al. 2007). Kaplan (2005) calculated that, for leatherback turtles, land-based mortality may have a stronger effect on mortality than longline fishing and, therefore, addressing losses on nesting beaches may provide a more substantial contribution to species recovery. However, with most sea turtle populations in an increased rate of decline, all contributing factors to mortality must be addressed, including interactions with domestic and foreign longline fisheries.