Proceedings of the 27th Annual ISTS

Jennifer Laliberté, Andrew DiMatteo, Wallace J. Nichols and Andrew J. Read. 2008. Does the current reserve system in the Gulf of California and Baja, Mexico provide protection for a complex of migratory marine species? In: Rees, A.F., M. Frick, A. Panagopoulou and K. Williams., compilers. Proceedings of the Twenty-Seventh Annual Symposium on Sea Turtle Biology and Conservation. NOAA Technical Memorandum NMFS-SEFSC-569, 262 p.

The distribution of species in space and time is determined both by the natural history characteristics of a species as well as oceanographic and climatic factors that are often difficult or too time-consuming to reasonably quantify. However, the presence of a variety of taxa in a specific geographic location may indicate an important use area. Areas identified as valuable to a particular species or group of species based on their presence or absence may serve as a proxy for identifying important habitat where species-specific natural history information or relevant oceanographic data are not readily available. A cross-species approach is also more broadly applicable to marine conservation as a whole. By identifying areas that are useful to multiple species, we may implement the most protection for the least economic and spatial investment, factors particularly important in areas heavily reliant upon fishing, such as our study area in the waters surrounding the coastal states of northwest Mexico. The purpose of our study is to apply this cross-taxa approach for the conservation of migratory marine megafauna by mapping the distributions of several highly migratory species, including loggerhead (Caretta caretta) and green turtles (Chelonia mydas), in and around the Gulf of California, Mexico, to identify areas of overlap. We map species distribution using sighting data and establish a specific density threshold to determine whether the area is more valuable than other areas based on the presence or absence of individuals. Then using kernel analysis on telemetry data, we make a probabilistic determination of high-density areas which we term high-use, or “habitat” areas, for each of the species in order to differentiate between use areas and areas such as transitory corridors. Here we present the analyses for loggerhead turtles and green turtles in the waters of the Gulf and off the west coast of the Baja Peninsula. Loggerheads are not known to nest anywhere in the eastern Pacific and it is assumed that, within this region, their presence in a particular area indicates foraging behavior. The nearest nesting grounds for green turtles are over 1000km away, so their presence here is also assumed to be for foraging. In this area, loggerheads feed primarily on pelagic red crabs (Pleuroncodes planipes) and may come into conflict with local fisheries, creating the risk for bycatch. Green turtles are primarily herbivorous, but their presence in offshore waters makes them susceptible to bycatch as well. We map loggerhead and green turtle distribution in and around the Gulf to identify potentially important habitat. We then compare our habitat areas with the reserve system currently in place in the Gulf and along the west coast of the Baja Peninsula. The reserve system was not set up for the protection of migratory marine megafauna, with the exception of El Vizcaino Biosphere Reserve in Baja California Sur, but it may prove to be vital in protecting species such as marine turtles if the locations of the reserves are congruent with high-use habitat.