Sea turtle declines not all due to human impacts

Humans are pushing sea turtles to the brink of extinction by entangling them in fishing gear, tossing plastic garbage into their habitats, and building resorts on their nesting beaches. That's what everyone thinks, anyway. But a new study shows that humans’ evil doings are nothing compared to natural oceanic cycles for the loggerheads. These findings aren’t making up excuses for people, but they do provide new insight into the ways climate can shape turtle populations. From the 90s to 2006, loggerhead nests in Florida declined from about 55,000 per year to around 30,000. Numerous studies have shown that fishing bycatch kills a large number of sea turtles each year, but ecologists Kyle Van Houtan of the National Oceanic and Atmospheric Administration's Pacific Islands Fisheries Science Center in Honolulu and John Halley of the University of Ioannina in Greece wondered if other factors can contribute to this massive decline in population. In the new study, the two ecologists measured the effect of certain ocean conditions on loggerhead nesting. Specifically, they looked at two long-term warming and cooling cycles whose effect on sea turtles hadn't been investigated. They also looked at recent ocean conditions, in particular the temperature of the sea surface near Japan and Florida the winter before a given breeding season. Such conditions have been shown to influence whether females are robust enough to make the long migration to shore and produce hundreds of eggs. Van Houtan and Halley found a strong correlation between the nest counts in a given year and the state of the long-term oceanic cycles some 3 decades earlier. That's when most nesting females would have been in their first year of life, the researchers say. Van Houtan and Halley say favorable cycles bring food and good weather and the number of survivors seems to strongly affect the number of nests.

http://www.enn.com/wildlife/article/42644