Composition of Hawaiian green turtle foraging aggregations: mtDNA evidence for a distinct regional population

Abstract

To examine the stock composition of Hawaiian foraging populations and evaluate current life-history hypotheses, mtDNA control region sequences from immature and adult green turtles that forage around the Hawaiian Islands were compared to potential source nesting populations across the Pacific. We examined the stock composition of the feeding ground (FG) populations at 5 index sites across the Hawaiian Archipelago, as well as animals stranded in areas outside these index sites. Six haplotypes, based on mtDNA sequences, were observed among the 788 green turtles sampled around the Hawaiian Islands. Stock mixture analysis shows that the Hawaiian FG populations comprise one genetic stock derived from the nesting population at French Frigate Shoals (FFS), based on a mean estimate of 99.9% from FFS as opposed to other potential source stocks. We identified only 3 turtles with haplotypes not found at FFS, indicating that Hawaiian FGs might occasionally, albeit rarely, be visited by animals from rookeries outside the Hawaiian Archipelago, both in the eastern and western Pacific. These findings lead us to conclude that the numerous foraging aggregations around the Hawaiian Islands can be considered part of a distinct regional population for management. The finding that FGs scattered across a distance of over 2400 km belong to one genetic stock is unique among sea turtles, and allows Hawaiian green turtles to be assessed separately from other Pacific stocks with respect to risk. We explore the unique population ecology of Hawaiian green turtles with reference to the complex life history of this marine megaherbivore.

Estimating carrying capacity at the green turtle nesting beach of East Island, French Frigate Shoals

“…Given the genetic and ecological importance of the Hawaiian stock (Chaloupka & Balazs 2007, Dutton et al 2008, the ongoing debate on the reinstatement of indigenous hunting rights in the Hawaiian Archipelago (Chaloupka & Balazs 2007), and the ambiguous impacts of climate change (Baker et al 2006, Hawkes et al 2009), an ecosystem-based assessment of the population is needed to understand the adaptability and resilience of the green turtle population within a fluctuating ecosystem. This is particularly important for devising meaningful and adaptive ecosystem-based conservation and management strategies.…”

“…Evidence from tagging and radio telemetry work indicates that females nesting on East Island maintain strong nesting fidelity and rarely nest on any of the other islands (Balazs 1980, Dizon & Balazs 1982. Green turtles migrate from throughout the Hawaiian archipelago to French Frigate Shoals to breed (Balazs 1976(Balazs , 1980, and the numerous foraging aggregations are composed of one genetic stock and form a distinct regional population (Dutton et al 2008). With increased nesting on East Island and decreased observations of turtles that have not been previously tagged, it has been suggested that the population may be approaching carrying capacity in the coastal foraging habitats (Balazs & Chaloupka 2004a, Chaloupka & Balazs 2007).…”

Kemp's Ridley Sea Turtle Saga and Setback: Novel Analyses of Cumulative Hatchlings Released and Time-Lagged Annual Nests in Tamaulipas, Mexico

“…Despite the genetic differences, sea turtles from separate nesting origins are commonly found mixed together on foraging grounds throughout the species' range. Such mixing occurs at extremely low levels in Hawaiian foraging areas, perhaps making this central Pacific population the most isolated of all green sea turtle populations occurring worldwide (Dutton et al 2008 (Doughty 1984;Hildebrand 1982;Shaver 1994), the Gulf of Mexico off Florida from Yankeetown to Tarpon Springs (Caldwell and Carr 1957;Carr 1984), Florida Bay and the Florida Keys (Schroeder and Foley 1995), the Indian River Lagoon system in Florida (Ehrhart 1983), and the Atlantic Ocean off Florida from Brevard through Broward Counties (Guseman and Ehrhart 1992;Wershoven and Wershoven 1992). The summer developmental habitat for green sea turtles also encompasses estuarine and coastal waters from North Carolina to as far north as Long Island Sound (Musick and Limpus 1997).…”

Trends and variability in demographic indicators of a recovering population of green sea turtles Chelonia mydas

“…Green sea turtles in Hawaii were recently categorized as a distinct population segment based on mitochondrial DN A, anatomical features, and migratory patterns (Dutton et al 2008, NOAA & USFWS 2015 Dizon & Balazs 1982, Bowen et al 1992. Females generally will not nest in the year immediately following a nesting year (i.e.…”