Using an ocean model to predict likely drift tracks of sea turtle carcasses in the north central Gulf of Mexico

Abstract

From March through July 2011, an increased number of Kemp's ridley sea turtles Lepidochelys kempii were reported stranded on the islands, beaches and shorelines of Louisiana, Mississippi and Alabama. Members of the National Sea Turtle Stranding and Salvage Network responded, documenting the location and physical condition of each turtle. This report describes an ocean physical model-based analysis of the spring and summer 2011 Mississippi stranding events. Included within this group of strandings was 1 satellite-tagged moribund Kemp's ridley turtle, initially alive and tagged by the Institute for Marine Mammal Studies for a site fidelity study. Data from this tracking event provided an accurate time sequence of 58 h, during which the animal was presumed to be drifting, based on observed characteristics that were typical of a floating carcass. Turtle drift data were combined with output from the America SEAS (AMSEAS) hydrodynamic model to provide an estimate of leeway. The AMSEAS model was then applied to an additional 247 stranded turtles to produce 5 d Lagrangian backtrack drifts to derive mortality source location probability maps. Based on the model presented in this study, the majority of mortalities appeared to have occurred in eastern Louisiana state waters.

On simulating cold stunned turtle strandings on Cape Cod

“…After validating the model 23 using satellite-tracked drifters and local temperature moorings, ocean currents were 24 examined in the Cape Cod Bay in an attempt to explain stranding locations as 25 observed by volunteers and, for some years, backtracking was conducted to examine 26 the potential source regions. The general finding, as expected, is that sub 10.5 o C 27 water temperatures in combination with persistent strong wind stress (>0.4Pa) will 28 result in increased strandings along particular sections of the coast dependent on the 29 wind direction. However, it is still uncertain where in the water column the majority 30 of cold stunned turtles reside and, if many of them are on the surface, considerable Introduction 35 Kemp's ridley is the smallest and the most endangered sea turtle in the world and 36 shows little sign of recovery [1,2,3].…”

Characterizing watercraft‐related mortality of sea turtles in Florida

“…Although we could only conclude that a VSI occurred perimortem based on this finding, it is unlikely that many sea turtles would happen to be struck by a vessel within hours of death from another cause. Furthermore, sea turtles tend to sink when they die and do not float until decomposition generates enough gas within the carcass, which takes up to several days (Koch et al , Nero et al ). The supravital reactions evident in the stranded turtles of the current study would not occur in these floating carcasses.…”

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

“…As a first step toward examining the utility of this model, we compared predicted abundance to a long-term timeseries of sea turtle strandings in the coastal regions of the Gulf of Mexico. Strandings represent a complex interaction among anthropogenic and environmental conditions that influence mortality, the probability of washing ashore and the probability of being reported (Nero et al 2013, Santos et al 2018. Nonetheless, we presume that the more turtles present in an area, the more likely it is that one will wash ashore and be reported; thus, annual differences in the number of strandings are likely to be related to turtle abundance across that region (Hart et al 2006).…”