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MEPS 700:145-159 (2022)  -  DOI:

Demographics and dynamics of the world’s largest known population of oceanic manta rays Mobula birostris in coastal Ecuador

Kanina Harty1,2,*, Michel Guerrero2,3, Anna M. Knochel1,2, Guy M. W. Stevens1, Andrea Marshall4, Katherine Burgess4, Joshua D. Stewart1,5

1The Manta Trust, Catemwood House, Norwood Lane, Corscombe, Dorset DT2 0NT, UK
2Fundacion Megafauna Marina del Ecuador (Proyecto Mantas Ecuador), Calle F y Calle A, Lote 19 Urb El Eden, Collaqui, Tumbaco, Quito 170902, Ecuador
3Galapagos Science Center, Universidad San Francisco de Quito and University of North Carolina at Chapel Hill, San Cristóbal 200101, Galápagos, Ecuador
4Marine Megafauna Foundation, 7750 Okeechobee Blvd, Ste 4-3038, West Palm Beach, FL 33411, USA
5Marine Mammal Institute, Department of Fisheries, Wildlife and Conservation Sciences, Hatfield Marine Science Center, Oregon State University, Newport, OR 97365, USA
*Corresponding author:

ABSTRACT: Information on the life history and demographics of oceanic manta rays Mobula birostris remains scarce. Using photo-ID data, we describe the demographic structure, population size, and possible environmental drivers of the seasonal occurrence of M. birostris at Isla de la Plata and Bajo Copé, Ecuador. We identified a total of 2803 individuals from 3322 encounters over a period of 14 yr (2005-2018). The population sampled at these sites was significantly biased towards males (sex ratio 1F:1.67M) and only 12.9% of individuals were resighted. We used mark-resight models to estimate demographic parameters of the population, including superpopulation size, survival probability, entry/recruitment probability, and detection probability. We also evaluated how these parameters were related to environmental predictors, such as El Niño-Southern Oscillation (ENSO), sea surface temperature (SST), and chlorophyll a (chl a). Mark-resight analyses indicated that SST, chl a, time, and sex, but not ENSO, were important predictors of estimated population parameters. Entry probability peaked in 2012, which coincided with the lowest SST and highest chl a concentrations. The best-fit mark-resight model estimated a superpopulation size of 22316 individuals, with annual estimated abundances of 949-7650 females and 5226-9340 males. Localised sampling of this highly mobile species limits the interpretations of mark-resight analyses, but provides lower bounds for total abundance that indicate the population of M. birostris in coastal Ecuador and Peru is likely the largest in the world.

KEY WORDS: Population modelling · Mark-resight · Photo-identification · South America

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Cite this article as: Harty K, Guerrero M, Knochel AM, Stevens GMW, Marshall A, Burgess K, Stewart JD (2022) Demographics and dynamics of the world’s largest known population of oceanic manta rays Mobula birostris in coastal Ecuador. Mar Ecol Prog Ser 700:145-159.

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