The Relationship Dynamics of Lagrangian Coherent Structures and Predator Interactions

• Ella McNeece, Marine Science, University of Delaware

• Matt Oliver, College of Earth, Ocean, and Enviormnet, University of Delaware

The circulation of the ocean provides the basic materials to sustain nutrient and prey field dispersion. Within the South Pacific Ocean, the South Pacific Gyre thrives and is the largest subtropical gyre in the world. Additionally, within the subtropical gyre, there is low productivity rate, making survival difficult. Lagrangian Coherent Structures (LCS) are fluid pathways of passive particles. LCSs are quantified using Finite-Time Lyapunov Exponents (FTLE) and dilation rate (delta). FTLE is the movement and measurement of the separation of two particles, while delta focuses on the particle cluster measurement. It is hypothesized that organisms who encounter LCS faster have a higher chance of finding food. The purpose of this study is to examine if predator speed influences encounter rate with LCSs in this biological desert. We simulated a model using turn angles and shark speeds, which generated the imitation of shark tracks within a set box in the South Pacific Gyre. This created a mathematical model, known as a correlated random walk (CRW). CRW are influenced by Brownian motion, and are step-by step- processes where the previous step impacts the location of the next turn angle, thus giving a local directional bias. Other various statistical tests, such as decorrelation analysis, were used to analyze this predator encounter with LCS as well. By analyzing the frequency of these interactions depicted in tests over a year long period (2004), it is observed that on average, a faster shark will encounter LCS at a higher rate than a slow shark. These findings indicate that shark speed is positively correlated with new LCS interactions, which may provide insight into the role speed plays in predatory species.