Author Oscar Sosa-Nishizaki introduces Journal of Applied Ecology’s June Editor’s Choice research article which was identified by Editors for proposing strong applied ecological guidance. Sosa-Nishizaki et al’s studied whale shark abundance through modelling and photo identification, suggesting that local authorities apply the model each spring.
Research conception
The foundations of this study began around 2007 with the efforts of the Pejesapo community group from the Bahia de los Angeles town led by Abraham Vázquez, co-author of this article. Each year, whale sharks (Rhincodon typus) aggregate in the northern Gulf of California at Bahia de los Angeles, a small coastal village that recently developed whale shark swimming as economic activity during the summer and autumn. The Pejesapo group set itself the objective of knowing in depth why whale sharks aggregate in the bay and thus be able to develop measures that would allow swimming with sharks sustainably.
Photo identification
One of our first actions was initiating individualized whale shark monitoring through photo identification. Therefore, in its bases, this study can be classified as Citizen Science. We photo-identified whale sharks while surface feeding in Bahia de los Angeles during a 13-year period, which allowed us to estimate a local abundance index per year through mark–recapture techniques.
Modelling
Later we joined them by Salomé Jaramillo, Oscar Sosa’s master’s student, complemented by the ecological-marine process modeler Mario Pardo and the connoisseur of mark and recapture models Jaime Bolaños. Since the number of animals using the bay fluctuates annually, we aimed to predict it 1 month before each whale shark season.
We then used a modelling approach based on the hypothesis that interannual warming conditions would spatially restrict whale shark habitats, triggering larger aggregations in areas that remain productive. We fit these abundances as a function of several competing model structures, based on means of sea surface temperature and chlorophyll-a, as well as their interannual anomalies from the linear trend, during spring, within the best-known range of the species in the northern Gulf of California.
Together we tried to answer the question: How can we strengthen the management of swimming with whale shark activities to ensure control of these activities by local authorities, especially those belonging to the Directorate of the Biosphere Reserve of Bahia de los Angeles? This protected natural area is eager for ecological sustainability and a robust management system. Therefore, the authors of this study believe that we have created a tool that will help in this goal.
Findings
The results of the ecological model showed that whale sharks visit Bahia de los Angeles in larger numbers during extreme warming conditions, with relatively high surface chlorophyll-a concentrations, which was especially evident during the 2014–2016 northeast Pacific Marine Heatwave and El Niño.
Presumably, the overall reduction in surface productivity associated with these events forced whale sharks to restrict their summer–autumn habitat to productivity hotspots, including Bahia de los Angeles.
Our model also allowed us to predict the number of animals visiting the site before each season starts, which has crucial proactive management implications, such as allowing authorities to regulate the ecotourism effort dynamically to reduce the probability of ship strikes and/or excessive stress to the animals.
We propose an abundance baseline from the prediction for neutral interannual conditions and recommend that local authorities apply the model described in this study during the late spring of each year to obtain predictions of the upcoming whale shark abundance, establishing the maximum ecotourism effort allowed accordingly.
Read the full article “Whale shark abundance forecast: The interannual hotspot effect” in Journal of Applied Ecology
