Sea Turtle Diving Patterns

Green Sea Turtle

Green Sea Turtles (Chelonia mydas) live in coastal waters in tropical and subtropical areas.  Their name comes from the color of their skin, which is an olive green.  They can reach lengths of 5 feet, can weigh up to 700 pounds and live up to 80 years in the wild.  Unlike most sea turtles, they are herbivores and mainly feed on sea grasses and algae.  They are an endangered species, declining in number because of human hunting, boat propeller accidents, and accidental fish net drowning.  Like most turtle species, Green Sea Turtles will dive to different depths of the ocean.  They can stay under water for up to 5 hours and their heart rate can slow to one beat for every 9 minutes.  Diving patterns of sea turtles are unique to each species and scientists have been conducting experiments that focus on the diving patterns of turtles, Green Sea Turtles included.  Knowing more about sea turtle diving patterns can help people understand how to conserve them better and to stop their population declines.

 

One study followed three Green Sea Turtles, two males and one female, during their migrations.  All three of them showed diurnal diving patterns.  They would do shallow, short dives during the day; only going down about 4 meters and staying under for a maximum of 18 minutes.  Around 7pm each night, they would start to dive deeper and for longer periods of time.  On average the dives were 45 feet and they stayed down there for 40 minutes or so.

In another study, the diving patterns in 2004 and 2005 of 5 Green Sea Turtles were observed and compared.  They found that U dives (deep dives) were more common at night than during the day, but there were still some U dives during the day.  This matches up with previous studies that have suggested that sea turtles are more active during the day and rest at night.  The average depths of those dives were between 16 and 20 meters for 2004, while in 2005 the average depths were between 10 and 13 meters.  When the turtles were nearing their nesting grounds, they had fewer U dives and stayed more towards the surface.  

The more time and energy efficient depth to travel at for sea turtles is between 1.5 and 4 meters, so why were the turtles diving so deep at night?  What purpose does that serve them?  Scientists have come up with many possible solutions but none of them have been proven.  Do they dive to avoid predators?  To check for shallow water?  Are the deep dives ‘resting dives’?  Is there a source of food at that depth?  Is it because they want to be in cooler water?  These questions have yet to be answered.

Article References

• http://journals.ohiolink.edu/ejc/pdf.cgi/Rice_Marc_R.pdf?issn=00220981&issue=v356i1-2&article=121_dbothgtmdom
• http://journals.ohiolink.edu/ejc/pdf.cgi/I-Jiunn_C.pdf?issn=00220981&issue=v381i0001&article=18_cidbdtipbgt
• http://journals.ohiolink.edu/ejc/pdf.cgi/Hochscheid_S.pdf?issn=00220981&issue=v450inone_c&article=118_wwmstuotsodb

 Website References

• http://animals.nationalgeographic.com/animals/reptiles/green-turtle/
•  http://marinebio.org/species.asp?id=51