Evaluating Strategies to Promots Sea Turtle Conservation

Like many sea turtles worldwide (Figure 1), loggerhead sea turtle (Caretta caretta) populations are declining by approximately three percent annually and the species is currently provided federally threatened status. Two potentially beneficial strategies could boost loggerhead populations. First, conservation groups have successfully limited access to beaches during the time when females lay their eggs and have thereby lowered mortality of eggs and hatchlings. Second, the National Marine Fisheries Service has devised a technology, the Trawl Efficiency or Turtle Excluder Device (TED), that virtually eliminates juvenile and adult mortality due to incidental capture and drowning in shrimp and fish trawls. Each of these strategies requires effort and expense. Thus, it is essential to evaluate the relative merits of the two conservation measures. However, loggerhead turtles are large, long lived (maximal life span is approximately 54 years and reproduction begins around age 22) and require extensive areas of open ocean. Therefore, it is difficult to design and carry out short-term, controlled experiments to test hypotheses about the effects of management strategies on the long-term health of loggerhead populations. In cases where hypotheses might be difficult to test with experiments, dynamic simulation models are often used to explore predictions that follow from the hypotheses. Such models are based on an understanding of the underlying processes that control the variables of interest. For example in the absence of experiments designed to understand the effects of the two loggerhead management scenarios, biologists have developed population models that have been used to explore the consequences of the two strategies. In lab today, you will develop a dynamic simulation model of loggerhead sea turtle populations and you will explore the consequences of the two management options suggested above.