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CROSS Carriers

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Ernest Yakovlev
Ernest Yakovlev

Green Sea(2020)


Climate change poses a threat to species with temperature-dependent sex determination (TSD). A recent study on green sea turtles (Chelonia mydas) at the northern Great Barrier Reef (GBR) showed a highly female-skewed sex ratio with almost all juvenile turtles being female. This shortage of males might eventually cause population extinction, unless rapid evolutionary rescue, migration, range shifts, or conservation efforts ensure a sufficient number of males. We built a stochastic individual-based model inspired by C. mydas but potentially transferrable to other species with TSD. Pivotal temperature, nest depth, and shading were evolvable traits. Additionally, we considered the effect of crossbreeding between northern and southern GBR, nest site philopatry, and conservation efforts. Among the evolvable traits, nest depth was the most likely to rescue the population, but even here the warmer climate change scenarios led to extinction. We expected turtles to choose colder beaches under rising temperatures, but surprisingly, nest site philopatry did not improve persistence. Conservation efforts promoted population survival and did not preclude trait evolution. Although extra information is needed to make reliable predictions for the fate of green sea turtles, our results illustrate how evolution can shape the fate of long lived, vulnerable species in the face of climate change.




Green Sea(2020)



Typically, the Pacific Islands Fisheries Science Center deploys field teams during the spring and summer to the Papahānaumokuākea Marine National Monument. There, they conduct research and rescue activities for threatened green sea turtles and endangered Hawaiian monk seals at five key breeding sites: French Frigate Shoals, Laysan and Lisianski Islands, Pearl and Hermes Reef, and Kure Atoll. The teams also conduct surveys during short visits at the Nihoa and Mokumanamana (Necker) Islands and Midway Atoll. Due to the uncertainties created by the COVID-19 pandemic, NOAA Fisheries decided to cancel this survey and field effort in 2020. Fortunately for the conservation of these species, our partners were able to step up and salvage part of the 2020 field season. Data are also coming in from satellite tags on a handful of monk seals and a green turtle.


We have conducted field studies in the Northwestern Hawaiian Islands for 47 years for sea turtles and 36 years for monk seals. These islands and atolls are nesting habitat for more than 90 percent of Hawaiian green sea turtles and home to 75 percent of the Hawaiian monk seal population (about 1,100 seals). These invaluable long-term datasets provide current population statuses and trends and insight on how climate change is affecting these animals and their habitat. Combined, this information guides management and recovery actions.


We consider marine debris and fishing gear entanglements the top threat for Hawaiian green sea turtles, causing almost 45 percent of strandings in the main Hawaiian Islands. Hawaiian monk seals become entangled more than most pinnipeds (seals, sea lions, and the walrus). More than 95 percent of the entanglements occur in the Northwestern Hawaiian Islands.


In addition to the three seals, we deployed a satellite tag on a basking green turtle on Oʻahu before the pandemic quarantine started. On March 12, the turtle team set out for the North Shore of Oʻahu. They wanted to perform an ultrasound to try and find a turtle in the early stages of egg development. Just like last year's success with Motherload, they were able to find one and attach a satellite tag to track her migration to her nesting ground.


The green sea turtle is the largest hard-shelled sea turtle. They are unique among sea turtles in that they are herbivores, eating mostly seagrasses and algae. This diet is what gives their fat a greenish color (not their shells), which is where their name comes from.


Green turtles are found throughout the world. They nest in over 80 countries and live in the coastal areas of more than 140 countries. Historically, green turtles were exploited for their fat, meat and eggs, causing global population declines. Many countries, including the United States, prohibit the killing of sea turtles and collection of their eggs. However, in some areas, the killing of green turtles for their meat or to supply shells to the wildlife trafficking trade remains a threat to their recovery. Bycatch in commercial and recreational fishing gear, vessel strikes, loss of nesting habitat from coastal development, and climate change are the biggest threats facing green turtles.


NOAA Fisheries and our partners are dedicated to protecting and recovering green turtle populations worldwide. We use a variety of innovative techniques to study, protect, and recover these threatened and endangered populations. We engage our partners as we develop measures and recovery plans that foster the conservation and recovery of green turtles and their habitats. And we fund research, monitoring, and conservation projects to implement priorities outlined in recovery plans.


Green turtles nest in over 80 countries, but in the United States, nesting green turtles are primarily found in the Hawaiian Islands, U.S. Pacific Island territories (Guam, the Commonwealth of the Northern Mariana Islands, and American Samoa), Puerto Rico, the Virgin Islands, and Florida. Nesting also occurs annually in Georgia, South Carolina, North Carolina, and Texas.


Green turtles are the largest of all the hard-shelled sea turtles, but have a comparatively small head. A typical adult is 3 to 4 feet long and weighs 300 to 350 pounds. They have dark brown, grey, or olive colored shells and a much lighter, yellow-to-white underside. Their shells have five scutes running down the middle and four scutes on each side. Other distinct characteristics of the green turtle are their serrated beak on the lower jaws and two large scales located between the eyes.


The life history of green turtles involves a series of stages of development from hatchling to adult. After emerging from the nest, hatchlings swim to offshore areas, where they live for several years in pelagic habitat. Juveniles eventually leave the open ocean habitat and travel to nearshore foraging grounds in shallow coastal habitats, where they mature to adulthood and spend the remainder of their lives. Adults migrate every 2 to 5 years from their coastal foraging areas to the waters off the nesting beaches where they originally hatched to reproduce.


In U.S. Atlantic and Gulf of Mexico waters, green turtles are found in inshore and nearshore waters from Texas to Maine, the U.S. Virgin Islands, and Puerto Rico. Important feeding areas in Florida include the Indian River Lagoon, the Florida Keys, Florida Bay, the Dry Tortugas, Homosassa, Crystal River, Cedar Key, and St. Joseph Bay.


In the eastern North Pacific, green turtles have been sighted as far north as southern Alaska, but most commonly occur from southern California to northwestern Mexico. Elsewhere in the U.S. Pacific, green turtles occur in Hawaii, American Samoa, Guam, and the Commonwealth of the Northern Mariana Islands.


Green turtles are long-lived and could live for at least 70 years or more. Female green turtles reach maturity at 25 to 35 years. Every 2 to 5 years they undertake reproductive migrations and return to nest on a beach in the general area where they hatched decades earlier.


A primary threat to sea turtles is their unintended capture in fishing gear which can result in drowning or cause injuries that lead to death or debilitation (for example, swallowing hooks, or flipper entanglement). The term for this unintended capture is bycatch. Sea turtle bycatch is a worldwide problem. The primary types of gear that result in bycatch of green turtles include trawls, gillnets, longlines, hook and line, and pot/traps.


Historically, green turtles were killed in extraordinarily high numbers for their fat, meat, and eggs. This led to the catastrophic global decline of the species. While illegal in the United States, killing green turtles and collecting their eggs remains legal in some countries and this can disrupt regional efforts to recover this species.


Coastal development and rising seas from climate change are leading to the loss of nesting beach habitat for green turtles. Shoreline hardening or armoring (e.g., seawalls) can result in the complete loss of dry sand suitable for successful nesting. Artificial lighting on and near nesting beaches can deter nesting females from coming ashore to nest and can disorient hatchlings trying to find the sea after emerging from their nests.


Various types of watercraft can strike green turtles when they are at or near the surface resulting in injury or death. Vessel strikes are a major threat to green turtles, in particular large juveniles and adults near ports, waterways, and developed coastlines throughout their range. High boat traffic areas such as marinas and inlets present a higher risk to green turtles. Adult green turtles, in particular nesting females, are more susceptible to vessel strikes when making reproductive migrations and while they are nearshore during the nesting season.


For all sea turtles, a warming climate is likely to result in changes in beach morphology and higher sand temperatures, which can be lethal to eggs or alter the ratio of male and female hatchlings produced. Rising seas and storm events cause beach erosion, which may flood nests or wash them away. Changes in the temperature of the marine environment are likely to alter the abundance and distribution of food resources, leading to a shift in the migratory and foraging range and nesting season of green turtles.


Fibropapillomatosis is a disease that causes external and internal tumors in green turtles. These tumors can significantly affect their ability to swim and feed and can lead to death. The disease is most prevalent in green turtles and some evidence has linked the disease prevalence to degraded marine habitats. 041b061a72