Data from: Global decline in the size of sea turtles

Changes in mean adult body size may be a universal response to global
warming and sometimes lead to conservation concerns. We show that size
reductions in sea turtles are now the norm and have another explanation.
From 18,707 measurements of nester size (curve carapace length) spanning
30 years from Redang Island (Malaysia), where nearly all nesting
individuals have been tagged, we show that the mean size was initially
fairly stable and then decreased by 4.0 cm from 100.8 cm in 2005 to 96.8
cm in 2022, which likely translates to a change in mean mass from 120 kg
to 105 kg. At the same time, nesting increased from around 300 to 2,000
nests per year. Consistent with this finding of a size reduction in an
expanding population, at 27 of 31 sites across the globe where changes in
the mean size of nesting sea turtles have been assessed, mean size is
decreasing, and the most marked decreases are at sites where population
size is increasing most dramatically. Taken together, these focal and
global findings suggest that an important driver of size reductions in sea
turtles is an influx of small first-time nesters (neophytes) in expanding
populations, and hence, size reductions are partially a consequence of
successful sea turtle conservation measures and population recoveries. At
the same time, the focal observations in Malaysia show that the mean size
of neophytes has also been getting smaller over time: from 99.6 cm to 96.8
cm between 2005-2022, likely because of a change in foraging environments.
While smaller turtles have lower reproductive output, this negative
consequence of decreases in nest size will often be more than offset by
increases in nesting numbers that are occurring widely.