Solving the whale shark mystery: How do we save the fish we can't find?
Authors: Pierce Simon J. 
Published: July 2019

Background Whale sharks have received significant research attention in recent years, yet key questions on their biology and ecology remain unanswered. This continues to hamper the conservation assessment of the species. The critical mass of whale shark researchers at IWSC4 presents an opportunity to collaboratively develop strategic research initiatives to close these knowledge gaps. Approach Thispresentation is intended to promote discussion, and eventual consensus, on key research questions and approaches. Accompanying this presentation will be a discussion document. My aim is to publish a multi-author manuscript outlining a framework for achieving medium-term (the next five years, to 2020) applied research objectives for whale sharks. Results Mykey questions are: (1) How many whale sharks are there? Movement models applied at single sites consistently point to transience, with a degree of site fidelity in some individuals. Some mark-recapture models are better-suited than others to modelling this reality. A more existential challenge is that, at most aggregations, we are disproportionately sampling juvenile male sharks. We need to understand habitat use of other life stages and incorporate them into population models. (2) Are regional populations present? Two major genetic subpopulations exist, in the Atlantic and Indo-Pacific, respectively. Further genetic/genomic studies, along with the expansion of photo-ID studies and medium- to long-term electronic tag deployments, will be vital in clarifying smaller-scale divisions. Biochemical studies are also showing promise. This work is vital, as the human threat profile differs between regions. (3) Are regional populations, if they exist, increasing or decreasing? Whale sharks are highly mobile. Even studies that have attempted to control for biophysical variation, such as in Mozambique, have documented declines in sightings that are steeper than can be explained by known human pressures. On the other hand, in at least some areas where whale shark sightings are on the increase, such as in the Azores, changes in the long-term ocean climate is a likely contributor. An improvement in our ability to relate local sighting trends to broader abundance is necessary. More data on whale shark demographic parameters, such as age at maturity and reproductive periodicity, are also required to understand the potential timeframe for recovery. (4) How can human impacts be mitigated? Some clear threats to large whale shark aggregations remain, such as the active whale shark fishery in southern China, ship strikes off the Quintana Roo coast in Mexico and in the Arabian Gulf, and the inadequate management of purse-seine bycatch. These examples, and others, require specific examination. (5) What is the best overall strategy for ensuring population recovery? Broadly, large juvenile and adult females are the most important individuals to the species' rebound potential. Identifying human threats to these life stages, and mitigating them, will be the most efficient means of reversing population decline. Regionally, identifying high-priority threats (i.e. the most significant impact on the largest number of sharks) will help with the development of practical mitigation strategies. Conclusions Effectivemanagement requires good data. I hope that the discussions we start at IWSC4 will go a long way towards aligning our regional research objectives towards answering these global questions in the shortest possible timeframe.