Resumen del producto

Blacktip sharks are a semi-pelagic species that are associated with continental shelves and shallow coastal areas where they can form large aggregations. No-take marine protected areas (MPAS) offer spatial refuge for marine species that reside within them during all or part of their life-cycle. Cabo Pulmo National Park is a no-take MPA located on the eastern coast of the Baja California Peninsula, Mexico, in which aggregations of blacktip sharks have been observed close to shore. Due to advances in battery technology and wireless communications small UAVs are an emerging and invaluable aerial platform for the remote sensing of elasmobranchs. This study uses a small quadcopter UAV to determine the seasonal variations of blacktip shark abundance over a year period, throughout 2019. The UAV was piloted along a 1.5km long transect path, parallel to the shoreline, and over shallow sandy habitat. Flights were conducted weekly in the morning between 0830h and 0930h and in the afternoon between 1530h and 1630h. Blacktip sharks were observed on surveys between the months of January and April and in December, but they were not observed in warmer months when average sea surface temperature was above 25°C. Total abundance on each survey ranged between 7 and 1084 sharks (268 ± 59, mean ± SE). Average abundance was highest in January (529 ± 226, mean ± SE) but this was not significantly higher than other months that the sharks were present (Kruskal-Wallis chi-squared=2.48, df = 3, p-value=0.49) There were significantly more sharks in the survey area in the afternoon (433 ± 92, mean ± SE) than in the morning (135 ± 51, mean ± SE) (Wilcoxon test, w=88, p-value <0.01), likely using the shallow warmer water habitat as a refuge to conserve energy during the day before foraging offshore at night.

Palabras clave: Carcharhinus limbatus; Cabo Pulmo National Park; abundance

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