Trends in sightings and environmental influences on a coastal aggregation of manta rays and whale sharks

• Published in: Marine Ecology Progress Series
• Main Authors: Rohner, C. A., Pierce, S. J., Marshall, A. D., Weeks, S. J., Bennett, M. B., Richardson, A. J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Inter-Research 2013
• Subjects: GLM; Generalised linear model; Decline; Population trend; Seasonality; Environmental variability; Manta alfredi; Manta birostris; Rhincodon typus; North pacific-ocean; Remote-sensing data; Worlds largest fish; Rhincodon-typus; Ningaloo Reef; Western-australia; Satellite tracking; Mozambique Channel; Indian-ocean; Cetorhinus-maximus; 1104 Aquatic Science; 1105 Ecology; Evolution; Behavior and Systematics; 2303 Ecology; Indian; Pacific; Cetorhinus maximus
• Online Access: https://espace.library.uq.edu.au/view/UQ:304057

Sightings of planktivorous elasmobranchs at their coastal aggregation sites are often linked to biological, environmental and temporal variables. Many large planktivorous elasmobranchs are also globally threatened species, so it is necessary to try and separate population trends from environmentally driven, short-term fluctuations. We investigated the influence of environmental variables on sightings of 3 species of planktivorous elasmobranchs off Praia do Tofo, Mozambique: the reef manta ray Manta alfredi, giant manta ray M. birostris and whale shark Rhincodon typus. We used 8- (2003 to 2011) and 6-yr (2005 to 2011) logbook data for manta rays and whale sharks, respectively, and constructed a generalised linear model with animal sightings as the response. Predictors included temporal (year, month, time of day), biological (plankton categories), oceanographic (water temperature, time from high tide, current direction and strength and wave height) and celestial (moon illumination) indices. These predictors best fitted reef manta ray sightings, a coastal species with high residency, but less so for the wider-ranging giant manta rays and whale sharks. We found a significant decline in the standardised sightings time series for the reef manta ray (88%) and whale shark (79%), but not for the giant manta ray.