The good and bad news of long-term monitoring: an increase in abundance but decreased body size suggests reduced potential fitness in nesting sea turtles

Gouvello, Diane Z.M. Le; Girondot, Marc; Bachoo, Santosh

doi:10.1007/s00227-020-03736-4

Cited by 17 publications

(24 citation statements)

References 84 publications

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“…3). A similar increase in nest counts coinciding with a decrease in mean size has also been documented in a loggerhead nesting assemblage in the southwestern Indian Ocean (Le Gouvello et al 2020). However, Ceriani et al (2015) found no significant change in the relative contribution of foraging areas to the ACNWR loggerhead nesting assemblage between 2007 and 2012.…”

Section: Discussionsupporting

confidence: 75%

Long‐term trends in marine turtle size at maturity at an important Atlantic rookery

et al. 2021

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For species reaching maturity at a range of ages or sizes, factors that influence juvenile growth and size at maturity may have lasting impacts on overall fitness. Assessing when animals reach maturity is especially challenging for species which are difficult to follow through time as a result of highly migratory behavior, long life spans, or both. We examined nesting female size in a reproductive assemblage of green turtles (Chelonia mydas) and loggerheads (Caretta caretta) on the east coast of Florida, USA. We used a long-term dataset from 1982 to 2019 to estimate a minimum size at maturity interval on the basis of two standard deviations below mean female size for each species. The minimum size intervals for green turtles (81.4-89.3 cm) and loggerheads (68.1-79.1 cm) were lower than most previous estimates in the literature, many of which were simply the smallest individual ever observed. There was a significant decrease in the upper bound of the minimum size interval over the study period for both green turtles (1.6 cm) and loggerheads (4.1 cm). These shifts in size at maturity may be the result of changes in population demographics, habitat quality, and behavioral reactions to these changes. The development and periodic reassessment of robust estimators of maturity are an important part of programs centered around the monitoring and conservation of vulnerable wildlife populations.

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Section: Discussionsupporting

confidence: 75%

Long‐term trends in marine turtle size at maturity at an important Atlantic rookery

et al. 2021

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“…There are limited sites to test this prediction, since while many marked long-term increases in turtle nesting numbers have been described [ 8 ], the annual mean size of individuals is often not reported. Nevertheless, when both nesting numbers and mean size have been reported, a decrease in mean size accompanied an increase in the number of nests for nesting sites in the Atlantic (green turtles at Ascension Island [ 11 ], loggerhead and green turtles in Florida [ 22 ], the Pacific (green turtles in Hawaii [ 23 ]) and the Indian Ocean (loggerhead turtles in South Africa [ 21 ]).…”

Section: Discussionmentioning

confidence: 99%

“…In particular, relatively few turtles were tagged in proportion to the number of nests, largely due to the huge volume of nesting turtles and hence the logistic challenge of intercepting a high proportion of turtles while they were ashore. In other regions where populations are expanding and the mean turtle size decreasing [ 11 , 21 , 22 ], it may be possible to tag a greater proportion of nesting turtles and so, for example, more clearly identify the relative numbers of neophytes versus remigrants as well as any possible changes in breeding intervals.…”

Section: Discussionmentioning

confidence: 99%

Changes in mean body size in an expanding population of a threatened species

Hays

Taxonera²,

Renom³

et al. 2022

Proc. R. Soc. B.

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With some taxa, a reduction in the mean size of individuals may reflect over-harvesting and/or trophy hunting. However, we show that in sea turtles, a reduction in the mean size of breeding individuals may be part of the good news story of an expanding population. We describe a 70-fold increase in annual nest numbers on the island of Sal (Cape Verde, North Atlantic) between 2008 and 2020 (from 506 to 35 507 nests), making this now one of the largest loggerhead ( Caretta caretta ) nesting aggregations in the world. We use 20 128 measurements of the size of nesting turtles to show that their mean annual size has decreased by about 2.4 cm, from 83.2 to 80.8 cm. This decrease in the mean size of nesting turtles was not caused by the removal of larger turtles, for example by selective harvesting. Rather we develop a theoretical model to show than this decrease in mean size can be explained by an influx of first-time nesters, combined with a decrease in the size of those first-time nesters over time. A reduction in mean size of nesting turtles has been reported across the Atlantic, Pacific and Indian Oceans, and may be a common feature of population recoveries in sea turtles.

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“…In the 1990s and 2000s, studies in the region further increased and diversified, making use of satellite telemetry and genetics to gain insight into the connectivity of regional marine turtle populations (Broderick et al 1998, Mortimer & Broderick 1999, Pelletier 2003, Formia et al 2006, Luschi et al 2006, Bourjea et al 2007b, 2015b, Dalleau et al 2014, Vargas et al 2016. Concerted long-term nest monitoring efforts at the island rookeries and South Africa have continued (Bourjea et al 2007a, 2015a, Lauret-Stepler et al 2007, Dalleau et al 2012, Nel et al 2013, Derville et al 2015, Le Gouvello et al 2020.…”

Section: Introductionmentioning

confidence: 99%

Marine turtles of the African east coast: current knowledge and priorities for conservation and research

Geer

Bourjea

Broderick

et al. 2022

Endang. Species. Res.

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Although published literature regarding the 5 species of marine turtle found along the continental African east coast has grown substantially over the last decades, a comprehensive synthesis of their status and ecology is lacking. Using a mixed methods approach, which combined an exhaustive literature review and expert elicitation, we assessed the distribution and magnitude of nesting, foraging areas, connectivity, and anthropogenic threats for these species in Somalia, Kenya, Tanzania, Mozambique, and South Africa. A complex pattern of nesting sites, foraging areas, and migration pathways emerged that identified areas of high importance in all 5 countries, although significant data gaps remain, especially for Somalia. Illegal take, bycatch, and loss of foraging and nesting habitat were identified as the most serious anthropogenic threats. Although these threats are broadly similar along most of the coast, robust data that enable quantification of the impacts are scarce. Experts identified regional strengths and opportunities, as well as impediments to turtle conservation. Topics such as legislation and enforcement, collaboration, local stakeholders, and funding are discussed, and future directions suggested. Given the projected growth in human population along the continental African east coast and expected accompanying development, anthropogenic pressures on turtle populations are set to increase. Stronger regional collaboration and coordination within conservation and research efforts are needed if current and future challenges are to be tackled effectively.

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The good and bad news of long-term monitoring: an increase in abundance but decreased body size suggests reduced potential fitness in nesting sea turtles

Cited by 17 publications

References 84 publications

Long‐term trends in marine turtle size at maturity at an important Atlantic rookery

Long‐term trends in marine turtle size at maturity at an important Atlantic rookery

Changes in mean body size in an expanding population of a threatened species

Marine turtles of the African east coast: current knowledge and priorities for conservation and research

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