Historical versus Contemporary Climate Forcing on the Annual Nesting Variability of Loggerhead Sea Turtles in the Northwest Atlantic Ocean

<div><p>A recent analysis suggested that historical climate forcing on the oceanic habitat of neonate sea turtles explained two-thirds of interannual variability in contemporary loggerhead (<i>Caretta caretta</i>) sea turtle nest counts in Florida, where nearly 90% of all nesting by this species in the Northwest Atlantic Ocean occurs. Here, we show that associations between annual nest counts and climate conditions decades prior to nest counts and those conditions one year prior to nest counts were not significantly different. Examination of annual nest count and climate data revealed that statistical artifacts influenced the reported 31-year lag association with nest counts. The projected importance of age 31 neophytes to annual nest counts between 2020 and 2043 was modeled using observed nest counts between 1989 and 2012. Assuming consistent survival rates among cohorts for a 5% population growth trajectory and that one third of the mature female population nests annually, the 41% decline in annual nest counts observed during 1998–2007 was not projected for 2029–2038. This finding suggests that annual nest count trends are more influenced by remigrants than neophytes. Projections under the 5% population growth scenario also suggest that the Peninsular Recovery Unit could attain the demographic recovery criteria of 106,100 annual nests by 2027 if nest counts in 2019 are at least comparable to 2012. Because the first year of life represents only 4% of the time elapsed through age 31, cumulative survival at sea across decades explains most cohort variability, and thus, remigrant population size. Pursuant to the U.S. Endangered Species Act, staggered implementation of protection measures for all loggerhead life stages has taken place since the 1970s. We suggest that the 1998–2007 nesting decline represented a lagged perturbation response to historical anthropogenic impacts, and that subsequent nest count increases since 2008 reflect a potential recovery response.</p></div

Remigration interval effects on loggerhead sea turtle (<i>Caretta caretta</i>) nest counts on Florida index beaches.

<p>Observed nest counts (A) were filtered into two (B), three (C), and four (D) year data series to evaluate remigration interval effects on interannual variability in nest counts and model performance. Data series orders for panels B–D were assigned as follows: first (red), second (dark blue), third (green), fourth (light blue). The multi-decadal shift between high (1998) and low (2007) annual nest counts was a common feature to the original and the filtered data series; however, inconsistencies in the interannual signal among the filtered data series within each remigration interval demonstrate the importance of contemporary environmental conditions on annual sea turtle nest counts.</p

Associations between climate indices and loggerhead (<i>Caretta caretta</i>) sea turtle nesting on Florida index beaches.

<p>Percent similarity (y-axis) between the NAO (blue line) and annual nest counts at 15 Florida index beaches (1989 to 2012) peaked a year prior to nesting; however, percent similarity for the AMO (red line) and the ENSO (green line) and annual nest counts peaked at 32 and 33 years prior to nesting, respectively.</p

Projected (2020–2043) loggerhead (<i>Caretta caretta</i>) sea turtle nest counts on Florida index beaches.

<p>Age 31 neophyte nest counts during 2020–2043 were extrapolated from observed nest counts (grey bars) at 15 Florida index beaches during 1989–2012 under the assumption of consistent stage-based and age-based survival across all cohorts. Remigrant nest counts were evaluated for three scenarios in which nest counts in 2019 were unchanged from 2012 (scenario A, blue line), 258% greater than 2012 (scenario B, green line), and 79% less than 2012 (scenario C, red line). Under these three scenarios, which are also based on 5% annual population growth, projected annual nest counts for these 15 beaches would exceed the demographic recovery criteria for the entire Peninsula Recovery Unit of 106,100 nests per year (black line) by 2020, 2026, and 2041, respectively.</p

Fitted (A,B) and predicted (C) loggerhead (<i>Caretta caretta</i>) sea turtle nests on Florida index beaches.

<p>Annual nest counts predicted by contemporary NAO only (blue line), historical AMO only (red line), or both parameters combined (green line) were not statistically different. In all panels, observed annual nest counts for loggerhead (<i>Caretta caretta</i>) sea turtle at 15 Florida index beaches during 1989–2012 are displayed as black lines.</p

An overview of cohort survival to age 31, whereby columns denote a range of survival probabilities during three gauntlets in the first year of life (i.e., hatchling emergence, hatchling frenzy, and survival at sea) and rows denote a range of annual at-sea survival probabilities during the next 30 years.

<p>Cell values were computed as the column header to the third power multiplied by the row header to the 30^th power.</p

The relative importance of neophyte (A) and remigrant (B) nesters.

<p>Neophyte recruitment at 15 Florida index beaches during 2020–2043 was computed using observed nest counts at these beaches during 1989–2012 and assuming consistent stage- and age-based survival through age 31 across cohorts. Remigrant population size for the same period was evaluated under a range of scenarios contingent upon nesting in 2019. In scenario A (blue lines), nesting in 2019 was assumed to be the same as in 2012. In scenario B (green lines), nesting in 2019 was 258% greater than in 2012 following 20% annual increases after 2012. In scenario C (red lines), nesting in 2019 was 79% less than in 2012 following 20% annual decreases beginning in 2013.</p

Descriptive statistics for predictions of loggerhead sea turtle (<i>Caretta caretta</i>) nest counts at 15 Florida index beaches during 1989 to 2012 based on historical (AMO) and contemporary (NAO) environmental influences.

<p>Statistics provided include model equations and their corresponding coefficient of determination (r²) and correlation coefficients (r), as well as parameter significance (P-value; *if <0.05) and the percent sums of squares (%SS) associated with each parameter as a function of model term entry order.</p

Chronic debilitation in stranded loggerhead sea turtles (<i>Caretta caretta</i>) in the southeastern United States: Morphometrics and clinicopathological findings

<div><p>Chronically debilitated loggerhead sea turtles (<i>Caretta caretta</i>) (DT) are characterized by emaciation, lethargy, and heavy barnacle coverage. Although histopathological findings associated with this condition have been reported, only limited data is available on health variables with clinical application. The objectives of this study were to 1) to compare morphometrics, clinicopathological variables, and immune functions of DTs to a group of apparently healthy loggerhead turtles to better understand the pathophysiology of the condition and 2) to assess health parameters in live debilitated turtles as they recovered during rehabilitation in order to identify potential prognostic indicators. We examined and sampled 43 DTs stranded from North Carolina to Florida for 47 health variables using standardized protocols to further characterize the condition. DTs were grouped into categories of severity of the condition, and those that survived were sampled at four time points through rehabilitation. All groups and time points were compared among DTs and to clinically healthy loggerhead turtles. Compared to healthy turtles, DTs had significantly lower body condition index, packed cell volume (PCV), total white blood cell (WBC) count, lymphocytes, glucose (Glc), total protein, all protein fractions as determined by electrophoresis, calcium (Ca), phosphorus (P), Ca:P ratio, potassium (K), lymphocyte proliferation, and greater heterophil toxicity and left-shifting, uric acid (UA), aspartate aminotransferase, creatine kinase, lysozyme, and respiratory burst. From admission to recovery, hematology and plasma chemistry data improved as expected. The most informative prognostic indicators, as determined by correlations with a novel severity indicator (based on survival times), were plastron concavity, P, albumin, total solids, UA, lymphocyte proliferation, WBC, K, Glc, Ca:P, and PCV. The results of this study document the wide range and extent of morphometric and metabolic derangements in chronically debilitated turtles. Monitoring morphometrics and clinicopathological variables of these animals is essential for diagnosis, treatment, and prognosis during rehabilitation.</p></div

Diagram of severity indicator with five case examples of debilitated loggerhead sea turtles.

<p>Images show turtles at time of admission.</p