Effectiveness of recreational divers for monitoring sea turtle populations

Five sea turtle species, all globally threatened, are found in southern Mozambican waters. Illegal hunting of foraging turtles, nest raiding and modification of coastal habitat are assumed to affect local sea turtle populations, but a lack of capacity and resource constraints hamper monitoring and compliance activities. Enlisting the recreational SCUBA diving community to report sea turtle sightings is a potential solution for population monitoring. The effectiveness of recreational divers as monitors was tested through the review of 2 approaches: the use of a routine dive logbook with sightings, and data from a dedicated survey. These approaches provided 37 consecutive months of data between 2008 and 2011 from dive sites in Inhambane Province, Mozambique. A total of 317 sightings of loggerhead Caretta caretta, green Chelonia mydas, hawksbill Eretmochelys imbricata and unidentified turtle species were reported from 918 dives. While the dedicated survey collected more detailed behavioural data (e.g. response to divers and feeding behaviour), independent logbook records provided a more robust data set for analysis of sighting trends. Useful data on sea turtle species composition, size and distribution were obtained from both approaches, although there were concerns with regard to species identification and size estimates. With refined methodology, particularly the incorporation of photographic verification of species identification, reports from divers can provide cost-effective and useful data for monitoring foraging turtle populations.