Origins of green turtle fishery bycatch in the Central Pacific revealed by mixed genetic markers

Longline fishing vessels, such as those that target tuna or billfish, also
unintentionally catch endangered marine turtle species on the high seas.
The stock composition of this bycatch is often unknown but potentially
complex, with individuals coming from many possible origins on an
ocean-basin scale. To better understand the stock composition of green
turtle (Chelonia mydas) bycatch, we obtained 46 turtles, 27–78 cm in
curved carapace length, caught by Hawaii- and American Samoa-based pelagic
longline fishing vessels across large areas of the North- and
South-central Pacific. We genotyped these at nine microsatellite loci and
one mitochondrial DNA marker and used a baseline of 1,043 nesting female
green turtles from beaches across the Pacific for population assignment
and mixed-stock analysis. By analyzing both marker types jointly we were
able to increase power and genetically resolve ten baseline stocks of
nesting females with mean self-assignment and simulated accuracies of
75–97%. Above the Equator, green turtle bycatch was composed mostly of
individuals from Hawaiian and Eastern Pacific stocks, with a small number
from the Western Pacific. Below the Equator, the most common stocks in the
bycatch were from Australia and the Coral Sea, American Samoa and French
Polynesia, and the Galápagos Islands. Overall, turtles originating from
East, West, and Central Pacific breeding populations were major components
of the bycatch, suggesting that the geographic ranges of these populations
overlap across large tracts of ocean during the pelagic life history
stages.