Development of a Kemp\u27s Ridley Sea Turtle Stock Assessment Model

We developed a Kemp’s ridley (Lepidochelys kempii) stock assessment model to evaluate the relative contributions of conservation efforts and other factors toward this critically endangered species’ recovery. The Kemp’s ridley demographic model developed by the Turtle Expert Working Group (TEWG) in 1998 and 2000 and updated for the binational recovery plan in 2011 was modified for use as our base model. The TEWG model uses indices of the annual reproductive population (number of nests) and hatchling recruitment to predict future annual numbers of nests on the basis of a series of assumptions regarding age and maturity, remigration interval, sex ratios, nests per female, juvenile mortality, and a putative ‘‘turtle excluder device effect’’ multiplier starting in 1990. This multiplier was necessary to fit the number of nests observed in 1990 and later. We added the effects of shrimping effort directly, modified by habitat weightings, as a proxy for all sources of anthropogenic mortality. Additional data included in our model were incremental growth of Kemp’s ridleys marked and recaptured in the Gulf of Mexico, and the length frequency of stranded Kemp’s ridleys. We also added a 2010 mortality factor that was necessary to fit the number of nests for 2010 and later (2011 and 2012). Last, we used an empirical basis for estimating natural mortality, on the basis of a Lorenzen mortality curve and growth estimates. Although our model generated reasonable estimates of annual total turtle deaths attributable to shrimp trawling, as well as additional deaths due to undetermined anthropogenic causes in 2010, we were unable to provide a clear explanation for the observed increase in the number of stranded Kemp’s ridleys in recent years, and subsequent disruption of the species’ exponential growth since the 2009 nesting season. Our consensus is that expanded data collection at the nesting beaches is needed and of high priority, and that 2015 be targeted for the next stock assessment to evaluate the 2010 event using more recent nesting and in-water data

Additional file 1: of First record of Antarctic minke whale, Balaenoptera bonaerensis, in the northern Gulf of Mexico

Supplementary Tables S1–S3. (PDF 93 kb

Demographic clusters identified within the northern Gulf of Mexico common bottlenose dolphin (Tursiops truncates) unusual mortality event: January 2010-June 2013.

A multi-year unusual mortality event (UME) involving primarily common bottlenose dolphins (Tursiops truncates) was declared in the northern Gulf of Mexico (GoM) with an initial start date of February 2010 and remains ongoing as of August 2014. To examine potential changing characteristics of the UME over time, we compared the number and demographics of dolphin strandings from January 2010 through June 2013 across the entire GoM as well as against baseline (1990-2009) GoM stranding patterns. Years 2010 and 2011 had the highest annual number of stranded dolphins since Louisiana's record began, and 2011 was one of the years with the highest strandings for both Mississippi and Alabama. Statewide, annual numbers of stranded dolphins were not elevated for GoM coasts of Florida or Texas during the UME period. Demographic, spatial, and temporal clusters identified within this UME included increased strandings in northern coastal Louisiana and Mississippi (March-May 2010); Barataria Bay, Louisiana (August 2010-December 2011); Mississippi and Alabama (2011, including a high prevalence and number of stranded perinates); and multiple GoM states during early 2013. While the causes of the GoM UME have not been determined, the location and magnitude of dolphin strandings during and the year following the 2010 Deepwater Horizon oil spill, including the Barataria Bay cluster from August 2010 to December 2011, overlap in time and space with locations that received heavy and prolonged oiling. There are, however, multiple known causes of previous GoM dolphin UMEs, including brevetoxicosis and dolphin morbillivirus. Additionally, increased dolphin strandings occurred in northern Louisiana and Mississippi before the Deepwater Horizon oil spill. Identification of spatial, temporal, and demographic clusters within the UME suggest that this mortality event may involve different contributing factors varying by location, time, and bottlenose dolphin populations that will be better discerned by incorporating diagnostic information, including histopathology

Magnitude of numbers of stranded common bottlenose dolphins (<i>Tursiops truncatus</i>) above the upper baseline limit (1990–2009) in the northern Gulf of Mexico during the ongoing unusual mortality event (January 2010-June 2013).

<p>From west to east; A) Texas, B) Western Louisiana C) Barataria Bay, Louisiana, D) Northern Louisiana, E) Mississippi, and F) Alabama, G) Florida Panhandle, and H) Western Florida. The solid box marked ‘Pre-spill’ represents time before the <i>Deepwater Horizon</i> oil spill in the northern Gulf of Mexico.</p

Predicted distributions and abundances of the sea turtle ‘lost years’ in the western North Atlantic Ocean

International audienceOceanic dispersal characterizes the early juvenile life‐stages of numerous marine species of conservation concern. This early stage may be a ‘critical period’ for many species, playing an overriding role in population dynamics. Often, relatively little information is available on their distribution during this period, limiting the effectiveness of efforts to understand environmental and anthropogenic impacts on these species. Here we present a simple model to predict annual variation in the distribution and abundance of oceanic‐stage juvenile sea turtles based on species’ reproductive output, movement and mortality. We simulated dispersal of 25 cohorts (1993–2017) of oceanic‐stage juveniles by tracking the movements of virtual hatchling sea turtles released in a hindcast ocean circulation model. We then used estimates of annual hatchling production from Kemp's ridley Lepidochelys kempii (n = 3), green Chelonia mydas (n = 8) and loggerhead Caretta caretta (n = 5) nesting areas in the northwestern Atlantic (inclusive of the Gulf of Mexico, Caribbean Sea and eastern seaboard of the U.S.) and their stage‐specific mortality rates to weight dispersal predictions. The model's predictions indicate spatial heterogeneity in turtle distribution across their marine range, identify locations of increasing turtle abundance (notably along the U.S. coast), and provide valuable context for temporal variation in the stranding of young sea turtles across the Gulf of Mexico. Further effort to collect demographic, distribution and behavioral data that refine, complement and extend the utility of this modeling approach for sea turtles and other dispersive marine taxa is warranted. Finally, generating these spatially‐explicit predictions of turtle abundance required extensive international collaboration among scientists; our findings indicate that continued conservation of these sea turtle populations and the management of the numerous anthropogenic activities that operate in the northwestern Atlantic Ocean will require similar international coordination

Map of the U.S. Gulf Coast showing county groups used in analysis of regional monthly baseline common bottlenose dolphin (<i>Tursiops truncatus</i>) stranding numbers.

<p>Baselines for Texas and Western Florida were determined by combining multiple regions outlined below. Gulf Florida includes the Florida Panhandle and the Western Florida combined region.</p

Comparison of demographics for common bottlenose dolphins (<i>Tursiops truncatus</i>) stranded in Mississippi and Alabama during shared large-scale mortality years (LSMY) 1990 and 2011.

<p>Louisiana 2011 was compared to Mississippi and Alabama 2011 due to Louisiana’s relative longevity of high stranding rates. The ongoing dolphin Gulf of Mexico (GoM) unusual mortality event (UME) includes years 2010 and 2011.</p><p>Comparison of demographics for common bottlenose dolphins (<i>Tursiops truncatus</i>) stranded in Mississippi and Alabama during shared large-scale mortality years (LSMY) 1990 and 2011.</p

Baseline historical stranding numbers of common bottlenose dolphins (<i>Tursiops truncatus</i>) in the northern Gulf of Mexico, fitted values, and the upper 95% confidence limit from negative-binomial regression model for regions with statewide annual increases during the ongoing northern Gulf of Mexico unusual mortality event; A) Texas, B) Western Louisiana, C) Barataria Bay, Louisiana D) Northern Louisiana, E) Mississippi, F) Alabama, G) Florida Panhandle, H) Western Florida.

<p>Baseline historical stranding numbers of common bottlenose dolphins (<i>Tursiops truncatus</i>) in the northern Gulf of Mexico, fitted values, and the upper 95% confidence limit from negative-binomial regression model for regions with statewide annual increases during the ongoing northern Gulf of Mexico unusual mortality event; A) Texas, B) Western Louisiana, C) Barataria Bay, Louisiana D) Northern Louisiana, E) Mississippi, F) Alabama, G) Florida Panhandle, H) Western Florida.</p

Prevalence comparisons of lesions detected using histologic examination for fresh dead, stranded common bottlenose dolphins (<i>Tursiops truncatus</i>) among 1) UME cases from Louisiana, Mississippi, and Alabama, 2) Barataria Bay, Louisiana UME subset, 3) all reference dolphins, and 4) slide-reviewed and standardly scored reference dolphin subset.

<p>Denominators varied based upon information available, tissues collected from, and tests conducted on individual UME and reference dolphins.</p><p>¹Barataria Bay, Louisiana UME dolphin subset values different (<i>P</i> < 0.05) than standardly scored reference dolphins.</p><p>²UME dolphin values different (<i>P</i> < 0.05) than full reference group.</p><p>³Represents encephalitis, meningitis, or meningoencephalitis.</p><p>C:M = adrenal corticomedullary ratio. CNS = central nervous system.</p><p>Prevalence comparisons of lesions detected using histologic examination for fresh dead, stranded common bottlenose dolphins (<i>Tursiops truncatus</i>) among 1) UME cases from Louisiana, Mississippi, and Alabama, 2) Barataria Bay, Louisiana UME subset, 3) all reference dolphins, and 4) slide-reviewed and standardly scored reference dolphin subset.</p