Area-restricted searching by manta rays and their response to spatial scale in lagoon habitats

Abstract

Animals may use a variety of search patterns to locate resources when the exact locations of those resources are unknown. Theoretical and empirical evidence suggests that the optimal type of random walk will vary based on the distribution of resources such as prey. Once resources are located, the animal may utilize a movement strategy that allows it to remain within a small area and maximize resource acquisition (area-restricted searching, ARS). Detecting the location of ARS zones is important, as it identifies profitable habitat to the animal, although such analysis is rarely conducted with fishes. We utilized correlated random walk (CRW), fractal, and first passage time (FPT) analysis to quantify the response of planktivorous manta rays Manta alfredi to spatial scale and identify locations of ARS within lagoons at Palmyra Atoll. Mantas used CRWs at small spatial scales to move between prey patches, but not at larger scales as they performed home-ranging behavior. One domain was located with straighter movements at scales <330 m, and more tortuous movements at scales >330 m. ARS was located adjacent to ledges with high abundance of plankton, or within channels. Fractal and FPT analyses suggest that mantas used patches that were 5 to 49% of the scale of their activity space over short time periods (days). Quantitative analytical tools help explain observed patterns of movements and demonstrate the importance of lagoon habitats to these macro-planktivores. © Inter-Research 2012.