A New Paper From Marine Megafauna Foundation

Posted on: May 30th, 2013 by Hannah Darrin

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

ABSTRACT: 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.

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C. A. Rohner 1,2,3,*, S. J. Pierce 1,4,5, A. D. Marshall 1,5, S. J. Weeks 2, M. B. Bennett 6, A. J. Richardson 3,7,8

1 Manta Ray & Whale Shark Research Centre, Marine Megafauna Foundation, Praia do Tofo, Inhambane, Mozambique
2 Biophysical Oceanography Group, School of Geography Planning and Environmental Management,
The University of Queensland, St Lucia, Queensland 4072, Australia
3 CSIRO Marine and Atmospheric Research, EcoScience Precinct, Dutton Park, Queensland 4102, Australia
4 All Out Africa Research Unit, PO Box 153, Lobamba, Swaziland
5 ECOCEAN USA, Praia do Tofo, Inhambane, Mozambique
6 School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland 4072, Australia
7 Centre for Applications in Natural Resource Mathematics (CARM), School of Mathematics and Physics,
The University of Queensland, St Lucia, Queensland 4072, Australia
8 The Ecology Centre, School of Biological Sciences, The University of Queensland, St Lucia, Queensland 4072, Australia