Inhambane, Mozambique
Inhambane, Mozambique

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Gleiss A.C.,University of Swansea | Norman B.,ECOCEAN Inc. Aust. | Norman B.,ECOCEAN United States | Norman B.,Murdoch University | Wilson R.P.,University of Swansea
Functional Ecology | Year: 2011

A primary determinant of movement strategies is travel speed, which modulates both power consumption and distance travelled and thus varies according to ecological circumstance. Many dense animals moving in 3D media face costs according to their movement trajectory and it should therefore equally be optimized according to circumstance. We investigated the power requirements (using dynamic body acceleration as proxy for power) in relation to movement geometry of nine whale sharks (Rhincodon typus) and discovered that movement geometry significantly affects power requirements in a manner similar to travel speed. Whale sharks dive repeatedly and use their negative buoyancy to glide during descents, while ascents were characterized by strong locomotory activity. Power requirements of ascents increased with the square of degrees pitch and were significantly greater than both level and descent swimming. The differences in geometry of five dive types are explored using four empirical optimality models based on minimum power based on our measurements. These models suggest that some dive types minimize the horizontal cost of transport, whereas others minimize the cost of vertical transport. Whale sharks are presumed to shift diving geometry with changing currencies and ecological context. The adaptive significance of appropriate diving geometry and associated power requirements is discussed with regard to current hypotheses for diving in gill-breathers: search, orientation and travel. Movement geometry significantly affects the cost of locomotion and is probably modulated by animals according to ecological circumstance. The in situ measurement of animal trajectory and locomotory activity via accelerometers now permits testing context-dependent movement geometry in free-ranging animals. © 2010 The Authors. Functional Ecology © 2010 British Ecological Society.

Rohner C.A.,Manta Ray and Whale Shark Research Center | Rohner C.A.,University of Queensland | Rohner C.A.,CSIRO | Pierce S.J.,Manta Ray and Whale Shark Research Center | And 8 more authors.
Marine Ecology Progress Series | Year: 2013

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. © Inter-Research 2013.

Marshall A.D.,Manta Ray and Whale Shark Research Center | Marshall A.D.,ECOCEAN United States | Pierce S.J.,Manta Ray and Whale Shark Research Center | Pierce S.J.,ECOCEAN United States
Journal of Fish Biology | Year: 2012

The use of photography to discriminate between individuals in a population using natural markings or aberrations is increasingly being utilized to support field research on elasmobranchs. This non-intrusive method has facilitated investigation of a wide variety of subjects including population composition, abundance estimates, residency and movement, demography and social behaviours. Here the first detailed review of photo-identification as a research technique for sharks and rays is provided, and its assumptions, current applications and potential highlighted. The limitations and practical considerations of photographic studies are also investigated with recommendations on initial survey design and ongoing data collection using current technology. Future directions are also explored with an emphasis on a move towards standardized approaches and automated recognition programmes to facilitate global collaborative work. © 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.

Fox S.,Utila Whale Shark Research | Foisy I.,Utila Whale Shark Research | De La Parra Venegas R.,Chooj Ajauil AC | Galvan Pastoriza B.E.,Chooj Ajauil AC | And 5 more authors.
Journal of Fish Biology | Year: 2013

There were 479 reported whale shark Rhincodon typus encounters between 1999 and 2011 at the island of Utila, which forms part of the Meso-American Barrier Reef System (MBRS) in the western Caribbean Sea. The majority of R. typus were found to feed on small bait fish associated with various tuna species. Ninety-five individual R. typus, ranging from 2 to 11m total length (LT), were identified through their unique spot patterns. A significant male bias (65%) was present. There was no significant difference between the mean±s.d. LT of female (6·66±1·65m) and male (6·25±1·60m) R. typus. Most R. typus were transient to Utila, with 78% sighted only within a single calendar year, although some individuals were sighted in up to 5years. Mean residency time was modelled to be 11·76days using maximum likelihood methods. © 2013 The Fisheries Society of the British Isles.

Couturier L.I.E.,University of Queensland | Couturier L.I.E.,CSIRO | Marshall A.D.,ECOCEAN United States | Jaine F.R.A.,CSIRO | And 9 more authors.
Journal of Fish Biology | Year: 2012

The Mobulidae are zooplanktivorous elasmobranchs comprising two recognized species of manta rays (Manta spp.) and nine recognized species of devil rays (Mobula spp.). They are found circumglobally in tropical, subtropical and temperate coastal waters. Although mobulids have been recorded for over 400 years, critical knowledge gaps still compromise the ability to assess the status of these species. On the basis of a review of 263 publications, a comparative synthesis of the biology and ecology of mobulids was conducted to examine their evolution, taxonomy, distribution, population trends, movements and aggregation, reproduction, growth and longevity, feeding, natural mortality and direct and indirect anthropogenic threats. There has been a marked increase in the number of published studies on mobulids since c. 1990, particularly for the genus Manta, although the genus Mobula remains poorly understood. Mobulid species have many common biological characteristics although their ecologies appear to be species-specific, and sometimes region-specific. Movement studies suggest that mobulids are highly mobile and have the potential to rapidly travel large distances. Fishing pressure is the major threat to many mobulid populations, with current levels of exploitation in target fisheries unlikely to be sustainable. Advances in the fields of population genetics, acoustic and satellite tracking, and stable-isotope and fatty-acid analyses will provide new insights into the biology and ecology of these species. Future research should focus on the uncertain taxonomy of mobulid species, the degree of overlap between their large-scale movement and human activities such as fisheries and pollution, and the need for management of inter-jurisdictional fisheries in developing nations to ensure their long-term sustainability. Closer collaboration among researchers worldwide is necessary to ensure standardized sampling and modelling methodologies to underpin global population estimates and status. © 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.

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