Sustainable Whale-Watching for the Philippines: A Bioeconomic Model of the Spinner Dolphin (Stenella longirostris).

We report here the first bioeconomic model designed to optimize whale-watching effort for sustaining a spinner dolphin (Stenella longirostris) population in the Philippines. The model is based on the maximum sustainable yield (MSY) concept. Whale-watching can negatively impact the behavior, habitat use and life history of cetaceans. To sustain a population under whale-watching, operators still need to make a profit. We investigated the bioeconomics of unrestricted whale-watching in one of the more popular whale-watching cities of the Philippines. We evaluated annual cost and revenue of operators and modeled a population of spinner dolphin under different levels of whale-watching effort. For the years 1995–2013, 12 of the 16 vessels lost an average of $4,000 yr-1. Sensitivity analysis showed that operators lost money when depreciation rate was set as low as 1%. Under current effort (n=16 vessels), the dolphin population is predicted to decrease by 94% in 25 years. Under high levels of effort, more cetaceans are exposed to vessels and fail to reproduce. Our model showed that since operations began, the abundance of spinner dolphin fell below the MSY as effort increased. We recommend a fixed number of permits, in which all operators cooperate to limit vessels out on the ocean. Even with as few as 4 vessels, the population declines. However, if effort is reduced to 3 vessels per day, our model predicts that the population will increase by 75% in 27 years. Our results indicate that the spinner dolphin population is overexploited by current whale watching and can be expected to decline.