Seasonal cycles and long-term trends in abundance and species composition of sharks associated with cage diving ecotourism activities in Hawaii

Abstract

SUMMARYShark cage diving is both popular and controversial, with proponents citing educational value and non-extractive use of natural resources and opponents raising concerns about public safety and ecological impacts. Logbook data collected 2004–2008 from two Oahu (Hawaii) shark cage diving operations were analysed to determine whether such voluntary records provide useful insights into shark ecology or ecotourism impacts. Operators correctly identified common shark species and documented gross seasonal cycles and long-term trends in abundance of Galapagos (Carcharhinus galapagensis), sandbar (Carcharhinus plumbeus) and tiger sharks (Galeorcerdo cuvier). Annual cycles in shark abundance may indicate seasonal migrations, whereas long-term trends suggest gradual exclusion of smaller sandbar sharks from cage diving sites. Numerically dominant (> 98%) Galapagos and sandbar sharks are rarely implicated in attacks on humans. Negligible impact on public safety is supported by other factors such as: (1) remoteness of the sites, (2) conditioning stimuli that are specific to the tour operations and different from inshore recreational stimuli and (3) no increase in shark attacks on the north coast of Oahu since cage diving started. Tracking studies are required to validate logbook data and to determine whether sharks associated with offshore cage diving travel into inshore areas used for in-water recreation.

No persistent behavioural effects of SCUBA diving on reef sharks

“…BRUVs have become the standard tool for monitoring large-bodied, potentially cautious reef fish including sharks (Meekan & Cappo 2004, Malcolm et al 2007). BRUVs are non-invasive, repeatable, and allow the collection of data on the relative abundance and distribution of the marine faunal community (Harvey et al 1996(Harvey et al , 2001, particularly for motile fauna.…”

“…BRUV surveys were conducted simultaneously (within 30 min of each other) in a paired design so that one system was at a dived site and one was in an adjacent, undived site. To precise ly assess the distance travelled by a bait plume, Cappo et al (2004) developed an equation that considers current speeds and tidal movements; however, currents on Palmyra's forereefs are highly variable and unpredictable and we were unable to use this equation to inform our study design. Previous studies have demonstrated that distances of 100 m (Ellis & Demartini 1995) and 450 m (Cappo et al 2004) be tween simultaneously deployed BRUV systems were adequate to ensure independence.…”

“…To precise ly assess the distance travelled by a bait plume, Cappo et al (2004) developed an equation that considers current speeds and tidal movements; however, currents on Palmyra's forereefs are highly variable and unpredictable and we were unable to use this equation to inform our study design. Previous studies have demonstrated that distances of 100 m (Ellis & Demartini 1995) and 450 m (Cappo et al 2004) be tween simultaneously deployed BRUV systems were adequate to ensure independence. Evidence from Palmyra also suggests that sharks limit movement within small core areas during the day (largely remaining around single acoustic receivers with a 300 m range), with larger-scale movements made primarily at night (Y. P. Papastamatiou unpubl.…”

“…For example, over relatively short time scales, provisioning caused changes in daily vertical space use, activity budgets, and metabolic rate of whitetip reef sharks Triaenodon obesus (Fitzpatrick et al 2011, Barnett et al 2016, increased residency in sicklefin lemon sharks Negaprion acutidens (Clua et al 2010), and increased local abundance in bull sharks Carcharhinus leucas (Brunnschweiler & Baensch 2011). Over longer time scales, provisioning had no effect on residency and space use in Caribbean reef sharks Carcharhinus perezii (Maljkovi & Côté 2011) and tiger sharks Galeocerdo cuvier (Hammerschlag et al 2012), and had only minimal behavioural effects that decreased with time in white sharks Carcharodon carcharias (Laroche et al 2007), but resulted in significant changes to the relative abundance of several shark species at a multi-species shark feeding site in Fiji (Brunnschweiler et al 2014) and to shark communities in Hawaii (Meyer et al 2009). There is some evidence that SCUBA diving activity, absent provisioning, can also lead to short-term changes in shark behaviour, with sharks both evading and approaching groups of recreational divers (Quiros 2007, Cubero-Pardo et al 2011) and changing activity budgets while in the presence of SCUBA divers (Smith et al 2010, Baronio 2012.…”

Determining the Role of Hand Feeding Practices in Accidental Shark Bites on Scuba Divers

“…The most common technique for allowing tourists to see Great White sharks (Carcharodon carcharias) and pelagic sharks such as the Silky (Carcharhinus falsiformis), Galapagos (C. galapagensis), Sandbar (C. plumbeus) and Tiger sharks (Galeorcerdo cuvier), either from boats or through scuba (and cage) diving, is known as 'chumming' [4,5,6]; it is also known in Australia as 'berleying' [7,8]. Chumming or berleying involves placing blood and/or liquidized tiny fish parts in the water to create an oily slick that sharks can sense and follow to the boat (or the divers) [5].…”