Aerial Survey as a Tool to Estimate Abundance and Describe Distribution of a Carcharhinid Species, the Lemon Shark,Negaprion brevirostris

Abstract

Aerial survey provides an important tool to assess the abundance of both terrestrial and marine vertebrates. To date, limited work has tested the effectiveness of this technique to estimate the abundance of smaller shark species. In Bimini, Bahamas, the lemon shark (Negaprion brevirostris) shows high site fidelity to a shallow sandy lagoon, providing an ideal test species to determine the effectiveness of localised aerial survey techniques for a Carcharhinid species in shallow subtropical waters. Between September 2007 and September 2008, visual surveys were conducted from light aircraft following defined transects ranging in length between 8.8 and 4.4 km. Count results were corrected for “availability”, “perception”, and “survey intensity” to provide unbiased abundance estimates. The abundance of lemon sharks was greatest in the central area of the lagoon during high tide, with a change in abundance distribution to the east and western regions of the lagoon with low tide. Mean abundance of sharks was estimated at 49 (±8.6) individuals, and monthly abundance was significantly positively correlated with mean water temperature. The successful implementation of the aerial survey technique highlighted the potential of further employment for shark abundance assessments in shallow coastal marine environments.

Surveying Wild Animals from Satellites, Manned Aircraft and Unmanned Aerial Systems (UASs): A Review

“…Furthermore, aerial imagery can be collected with significantly higher spatial resolutions, up to 2.5 cm [23]. Given the flight safety and the endurance time of aircraft, studies of terrestrial mammals distributed over smaller areas prefer to use helicopters [18,36,37], while those of plains, remote locations and marine environments prefer to use fixed-wing aircraft [2,17,[38][39][40][41]. One long-period study used a combination of helicopters and fixed-wing airplanes [42].…”

“…Aerial surveys of wild animals fall into two main categories: (a) Real-time surveys, in which the wild animals are counted in situ by trained observers, i.e., no imaging sensors are used during the surveys [2,17,[37][38][39]41], and (b) photographic surveys, in which wild animals are counted from still RGB images or video [36,42,[70][71][72][73]. Infrared thermography has also been tested for surveying wild animals with a significant temperature difference from the background environment, such as the Pacific walrus (Odobenus rosmarus) [63,74,75], and red deer (Cervus elaphus), fallow deer (Dama dama), roe deer (Capreolus capreolus), wild boar (Sus scrofa), foxes, wolves and badgers [76].…”

“…Manned aerial technology has been used for monitoring wild animals since the mid-1930s, when the US Bureau of Biological Survey used airplanes and dirigibles to survey waterfowl [70]. The early surveys were mainly real-time surveys that employed trained observers to survey terrestrial and marine animals with potentially low abundance in remote or large areas [38]. The terrestrial animals included polar bears in the Arctic [37]; red kangaroos (Megaleia rufa) and sheep [91]; buffalos (Syncerus caffer), elands (Taurotragus oryx), elephants (Loxodonta africana), and giraffes (Giraffa camelopardalis) in the African grasslands [41]; and pronghorns (Antilocapra americana) in two pronghorn pastures, Wyoming, USA, with vegetation communities dominated by mountain big sagebrush communities [2].…”

“…The terrestrial animals included polar bears in the Arctic [37]; red kangaroos (Megaleia rufa) and sheep [91]; buffalos (Syncerus caffer), elands (Taurotragus oryx), elephants (Loxodonta africana), and giraffes (Giraffa camelopardalis) in the African grasslands [41]; and pronghorns (Antilocapra americana) in two pronghorn pastures, Wyoming, USA, with vegetation communities dominated by mountain big sagebrush communities [2]. In marine environments, aerial surveys have typically focused on marine megafauna, such as cetaceans and elasmobranch [38,39], because these taxa are regularly visible at the surface and their large sizes make them highly visible. Aerial surveys have been widely used for decades to estimate the local densities and population sizes of walruses and other cetaceans [92].…”

Three decades of longlining in Bimini, Bahamas, reveals long‐term trends in lemon shark Negaprion brevirostris (Carcharhinidae) catch per unit effort

“…1). North Bimini and South Bimini partially enclose a shallow lagoon that forms a secondary nursery for sub-adult N. brevirostris (Chapman et al, 2009;Kessel et al, 2013). A high diversity of marine habitats allows Bimini to support a relatively abundant N. brevirostris population containing all life stages, from neonate juveniles to mature adults (Feldheim et al, 2002).…”