SCUBA diver observations and placard tags to monitor grey reef sharks, Carcharhinus amblyrhynchos, at Sha'ab Rumi, The Sudan: assessment and future directions

Abstract

Establishing baseline data on the abundance of threatened shark species is critical for monitoring site- and region-specific population tends over time. This is of particular importance for monitoring sharks at remote locations or in regions where there are no reliable data on shark numbers, fishing effort and current population status. Through establishing a standardized recreational SCUBA diver observation programme, this study examined the number, size and sex-composition of grey reef sharks, Carcharhinus amblyrhynchos, on a remote coral reef system off the Red Sea coast of Sudan. In addition, placard tags were attached to individual sharks to examine coarse scale residency and movement patterns and to determine the effectiveness of this technique. Over a 4.5 month period (December 2007–April 2008), a mean (±SE) of 5.9 ± 0.3 grey reef sharks were observed per diving day with peak numbers of sharks associated with temperatures of 26–26.9°C and strong currents. Estimated mean (±SE) total length of observed sharks was 1.9 ± 0.03 m identifying that most animals were mature. Female sharks were dominant on the site and pregnant females were recorded. Placard tagged sharks (N = 4) were observed by recreational SCUBA divers throughout the study period (23.1%, 20.0%, 16.9% and 3.1% of total observation diving days) indicating sporadic site attachment. The placard tags remained intact and were free of fouling for a total of 175 days. The numbers of grey reef sharks seen on this Red Sea coral complex suggest a healthy, relatively unexploited population. This study demonstrates that the recreational diver community, which forms a large pool of skilled volunteers, can generate baseline data on shark numbers at regularly dived sites and provide insights into the ecology of the observed species. Modification of placard tags, including attachment to the dorsal fin and time corrodible release systems may provide an inexpensive and accepted tool for monitoring individual shark residency and movement patterns. Engaging the recreational SCUBA diver community in a standardized scientific monitoring programme has the potential to monitor trends in shark populations over large spatial and temporal scales.

Effectiveness of recreational divers for monitoring sea turtle populations

“…In the marine realm, volunteer recreational divers have been involved in collection of data for biodiversity assessments and coral reef fish (Darwall & Dulvy 1996, Hodgson 1999, Pattengill-Semmens & Semmens 2003 and flora abundance surveys (Chou 1994, Schmitt & Sullivan 1996. In addition to these broadly scoped programmes, volunteer divers are also involved in focal species programmes focused on seahorses (Goffredo et al 2004), sea turtles (Bell et al 2008b) and elasmobranchs (Hussey et al 2011. Although such data collection programmes are generally designed to test specific hypotheses or undertake routine monitoring, a key tenet is that participants are not required to have formal training in scientific survey techniques.…”

“…Conscientious long-term record-keeping by recreational divers has been shown to have considerable scientific value (Goffredo et al 2010, Jaine et al 2012, particularly when there are reliable records of the presence and absence of the focal species coupled with environmental data (Goffredo et al 2004, Hussey et al 2011. Divers can facilitate continuous temporal monitoring of large areas where resources and either traditional academic or government research interest are low (Goffredo et al 2010, Lorenzo et al 2011.…”

Habitat use and abundance of goliath grouper Epinephelus itajara in Brazil: a participative survey

“…Recreational divers represent a potentially large community of skilled and often highly motivated volunteers (Hussey et al, 2013). This approach has proven to be valuable in structuring consistent largescale geographic databases encompassing marine system properties such as diversity and dynamics at multiple scales (Goffredo et al, 2010;Holt et al, 2013).…”

Uso de hábitat de Triaenodon obesus (Carcharhiniformes: Carcharhinidae), Rhincodon typus (Orectolobiformes: Rhincodontidae) y Manta birostris (Myliobatiformes: Myliobatidae) en el Parque Nacional Natural Gorgona, Pacífico colombiano

“…En cuanto a esta práctica con tiburones y rayas, se destacan aquellas realizadas con Rhincodon typus, Manta birostris y algunas especies arrecifales como Carcharhinus perezi, Gynglimostoma cirratum o Dasyatis americana, las cuales son la base de actividades turísticas como avistamiento, alimentación y buceo. Esta cercanía con la industria del turismo, ha facilitado el desarrollo de investigaciones sobre diversos temas como patrones de movimiento (Graham & Roberts, 2007;Brooks, Rowart, Pierce, Jouannet & Vely, 2010;Heupel, Simpfendorfer & Fitzpatrick, 2010), estimaciones poblacionales (Meekan et al, 2006;Theberge & Dearden, 2006;Holmberg, Norman & Arzoumanian, 2008;Hussey, Stroh, Klaus, Chekchak & Kessel, 2013) y estudios focales en especies como Orectolobus spp. (Huveneers, Luo, Otway & Harcourt, 2009), Carcharias taurus (Bansemer & Bennett, 2008, Stegostoma fasciatum (Dudgeon, Noad & Lanyon, 2008) y Manta birostris (Luiz, Balboni, Kodja, Andrade & Marum, 2009), entre otras.…”

“…La mayoría de estos estudios se han realizado en áreas geográficas como Australia (Meekan et al, 2006;Holmberg et al, 2009;Huveneers et al, 2009;Speed et al, 2011), indonesia y Tailandia (Theberge & Dearden, 2006;Stacey, Karam, Dwayer, Speed & Meekan, 2008), el Mediterráneo (Canese et al, 2011), el Mar Rojo (Hussey et al, 2013), el Atlántico y el Caribe (Luiz et al, 2009;Cárde-nas-Palomo, Herrera-Silveira & Reyes, 2010;de la Parra-Venegas et al, 2011). Por su parte, en el Pacífico Oriental dichos trabajos se han iniciado recientemente y las publicaciones disponibles se restringen a poblaciones de Manta alfredi y M. birostris en Hawaii (Clark, 2010;Deakos, Bajer & Bedjer, 2011) y Sphyrna lewini en la isla Malpelo (Bessudo et al, 2011).…”