oa Mapping the path of the biggest fish: The whale shark from the Mexican Pacific side

Background Monitoring of animal populations is critical for proper management. To have a better understanding of the population dynamics and migratory pattern of the whale shark, data is required from locations close to key aggregation sites where hypothesized connections can be validated. Photo-ID is an effective marker for capture-mark-recapture studies. Underwater photographs of sharks, combined with photo-comparison software, are used to identify re-sighted sharks, which, in turn, contribute to estimations of population size, age structure, sex ratio, site fidelity, trends in abundance, and movement patterns Approach Since 2003 we have established and maintained a photographic identification research program in the Gulf of California, at Los Angeles Bay (LAB), La Paz Bay (LPB), Espiritu Santo Island (ESI) and Los Cabos (LC), and since 2010 at the Archipelago of Revillagigedo (AR, at the Mexican Pacific). Recently, we included Nayarit (Na, in the Mexican Pacific) to the study area, San Luis Gonzaga (SLG) and Coyote Bay (CB, Gulf of California) in order to address if connectivity exists in this region. Results The whale sharks appear to segregate by size. In coastal waters of LAB (n=501), LPB (n=380), SLG (n=51), Na (n=36), and CB (n=16) aggregations are exclusively juvenile sharks (<8 m). In the oceanic waters of ESI (n=20) and LC (32), pregnant adult females (>9 m) aggregate. At AR (n=11) both pregnant females and juveniles exist but are separated by time. From 2003 to 2014 we have identified 898 sharks over the course of the study; of these 841 were juveniles and 57 were adults, mainly pregnant females. Photo-identification showed the movements of 133 juvenile sharks between LAB, LPB, SLG, Na and CB and movement of 2 pregnant females between LC and AR. We found high levels of fidelity in the juveniles. For example in LPB up to 61% of the juveniles have been re-sighted between years. In contrast only one pregnant female has been re-sighted at the same locality after 7 years. Conclusions This study demonstrated the importance of a collaborative effort to have a better understanding of the population on a regional level. The connectivity data showed the necessity to generate a regional conservation strategy; of the eight localities where we study these gentle giants, currently three are protected, the other four require protection.