Recreational SCUBA diver interactions with the critically endangered Grey Nurse Shark Carcharias taurus

Grey Nurse Sharks Carcharias taurus are listed as 'Critically Endangered' along the east coast of Australia. Magic Point (off Maroubra) in Sydney is favoured by recreational SCUBA divers wishing to observe these sharks. This study was conducted to answer the question: do current recreational SCUBA diving practices at Magic Point have a significant impact on the aggregation behaviour of C. taurus? The study found that diver activity does temporarily affect the behaviour of C. taurus at this site, with a significant difference in the number of sharks and their distribution within the preferred area of occupation inside the cave between diver and non-diver treatments. Small dive groups (less-than-or-equal-to 4 divers) approached the cave closer than large groups, resulting in a greater impact on sharks than large groups positioned further back from the cave. Shark behaviour rapidly returned to pre-diver exposure levels once divers left the area. This study is the first to (a) monitor recreational SCUBA diver activities at a critical habitat site and (b) use a noninvasive behavioural technique to study the behavioural responses of C. taurus towards SCUBA divers in southern NSW. It contributes to improving C. taurus conservation measures along the east coast of Australia by highlighting current diver behaviour and its impact on Grey Nurse Sharks at this site. Results suggest that changes in the current code of practice regarding SCUBA diving at recognized and protected Grey Nurse Shark critical habitat sites should be considered by relevant management agencies.9 page(s

A Video and photographic study of aggregation, swimming and respiratory behaviour changes in the Grey Nurse Shark (Carcharias taurus) in response to the presence of SCUBA divers

The Grey Nurse Shark (Carcharias taurus) is a popular attraction for shark eco-tourism using SCUBA. The species is also 'globally Vulnerable' (IUCN 2008. List of Threatened Species. www.iucnredlist.org/. Magic Point (off Maroubra) in Sydney is favoured by recreational SCUBA divers wishing to observe these sharks. The objective of this study was to experimentally test the level of the activities of recreational SCUBA divers on shark behaviour. This study assessed the shark responses to diver group size (4, 8 and 12), time of day (am, noon and pm) and diver distance from the sharks (3m and 6 m). The study found that diver activity does affect the aggregation, swimming and respiratory behaviour of sharks at this site, albeit at shortterm levels. Diver group size had no significant effect on shark aggregation, but the proximity of divers to the sharks was crucial. Shark distribution in the cave changed significantly in the presence of divers at 3m distance from the cave, but stayed unchanged at 6m. This was particularly apparent in the presence of large groups of 12 divers at 3m distance when sharks increased their swim speed and ventilation mechanism from 'active' to 'RAM' ventilation. Such change coincided with a sudden decrease in ventilation frequency. Our research suggests that these effects are shortterm and that sharks resume their behaviour once the divers retreat. If divers abide by the current code of practice for diving at this site, it is unlikely that their activities will substantially impact Grey Nurse Sharks in the long term.18 page(s

Beach safety: Can drones provide a platform for sighting sharks?

CSIRO 2019 Open Access. Context: A series of unprovoked shark attacks on New South Wales (Australia) beaches between 2013 and 2015 triggered an investigation of new and emerging technologies for protecting bathers. Traditionally, bather protection has included several methods for shark capture, detection and/or deterrence but has often relied on environmentally damaging techniques. Heightened environmental awareness, including the important role of sharks in the marine ecosystem, demands new techniques for protection from shark attack. Recent advances in drone-related technologies have enabled the possibility of real-time shark detection and alerting. Aim: To determine the reliability of drones to detect shark analogues in the water across a range of environmental conditions experienced on New South Wales beaches. Methods: A standard multirotor drone (DJI Inspire 1) was used to detect shark analogues as a proxy during flights at 0900, 1200 and 1500 hours over a 3-week period. The 27 flights encompassed a range of environmental conditions, including wind speed (2-30.0 km h-1), turbidity (0.4-6.4 m), cloud cover (0-100%), glare (0-100%), seas (0.4-1.4 m), swells (1.4-2.5 m) and sea state (Beaufort Scale 1-5 Bf). Key results: Detection rates of the shark analogues over the 27 flights were significantly higher for the independent observer conducting post-flight video analysis (50%) than for the drone pilot (38%) (Wald P = 0.04). Water depth and turbidity significantly impaired detection of analogues (Wald P = 0.04). Specifically, at a set depth of 2 m below the water surface, very few analogues were seen by the observer or pilot when water turbidity reduced visibility to less than 1.5 m. Similarly, when water visibility was greater than 1.5 m, the detection rate was negatively related to water depth. Conclusions: The present study demonstrates that drones can fly under most environmental conditions and would be a cost-effective bather protection tool for a range of user groups. Implications: The most effective use of drones would occur during light winds and in shallow clear water. Although poor water visibility may restrict detection, sharks spend large amounts of time near the surface, therefore providing a practical tool for detection in most conditions

At-vessel mortality and blood biochemical status of elasmobranchs caught in an Australian commercial longline fishery

This study investigates mortality of sharks in a commercial longline fishery in Australia. To examine the rate and biological, environmental and technological factors contributing to at-vessel mortality, four setlines with 120 gangions possessing \u27hook timers\u27 were deployed daily (for 7h and 14h) using conventional gears from two commercial fishing vessels during 2013. A total of 689 animals across 22 species and including 18 elasmobranchs were landed. For the five species (Carcharhinus spp.), and one genus (Sphyrna spp) where there were sufficient numbers for analysis, generalised linear mixed models showed that species and the elapsed time spent on the line after hooking were the strongest predictors of at-vessel mortality, with spinner (Carcharhinus brevipinna), blacktip (C. limbatus) and hammerhead (Sphyrna spp) sharks exhibiting the highest death rates. The variables which best explained mortality, included: (i) sex of the caught sharks, and the interaction between species with (ii) capture depth, and (iii) the elapsed time spent on the line after hooking. For the subset of dusky (C. obscurus) and sandbar (C. plumbeus) sharks examined for physiological status at the point of capture, very few of the 13 chosen blood analytes varied significantly. Given the observed high mortality rates and stress associated with the time spent on the line after capture, operational changes to reduce these adverse impacts should be considered. Even simple changes such as shorter soak times could considerably mitigate these impacts

Temporal hooking variability among sharks on south-eastern Australian demersal longlines and implications for their management

An experiment was done to quantify species-specific variation in temporal hooking rates from demersal longlines targeting various carcharhinids off south eastern Australia, with a view to reducing the incidental catches of protected species, including the scalloped hammerhead Sphyrna lewini, great hammerhead Sphyrna mokarran and grey nurse Carcharias taurus. The longline comprised a 9600 m mainline, separated into four sections (termed lines) each with 120 gangions (20 m apart) rigged with hook timers and 16/0 circle hooks baited with either sea mullet Mugil cephalus or eastern Australian salmon Arripis trutta. The mainline was deployed on each of 17 nights (between 19:30 and 23:30 h), with two lines retrieved after 7 and 14 h respectively. From a total of 8160 hooks, 246 timers were activated without hooking fish. Twenty-two species comprising 684 individuals were caught, including 52 S. lewini, 12 C. taurus, 11 S. mokarran and 1 loggerhead turtle Caretta caretta. Several environmental factors, including water temperature, moon phase and depth had mostly homogeneous, positive effects on catches. The only identified variables that might be used to considerably reduce the catches of Sphyrna were soak time and/or diurnal gear retrieval, with most individuals hooked during daylight. Simply mandating shorter deployments and within nocturnal retrieval might limit exploitation, especially among juveniles (<150cm total length). For the studied fishery to approach sustainability, future research is required to investigate other gear modifications for improving size and species selectivity, and/or operational procedures for mitigating discard and escape mortalities. Keywords: Bycatch mitigation, Carcharhinids, Carcharias taurus, Hook timer, Selectivity, Sphyrn

Percentage of validated analogue sightings per aircraft with the relative contribution of different trial treatments.

<p>Open bars indicate fixed-wing data, closed bars indicate helicopter sightings. Hashed bars indicates contribution of trials using standard methodology (cruising speed, no orbiting), non-hashed bars indicates contribution of alternative trials (orbiting permitted (fixed-wing), 100 kts airspeed (helicopter)). Contribution of each treatment type has been scaled to account for differences in sample size.</p

Linear regression analysis examining the effects of aircraft type, shark analogue type, water depth, day and various environmental variables on sighting depth.

<p>Note the exact p-value for Water depth is 0.0497.</p><p>AIC = 121.6, BIC = 130.6.</p

Migrating humpback whales show no detectable response to whale alarms off Sydney, Australia

Migratory Group V (Stock E1) humpback whales Megaptera novaeangliae are at risk of entanglement with fishing gear as they migrate north and south along the east coast of Australia. This study investigated the effectiveness of 2 distinct tones for use as an alarm to acoustically alert whales to fishing gear presence and therefore reduce the chance of entanglement. We compared how whales responded in terms of changes of surface behaviour and changes in direction of travel in response to 2 acoustic tones and when there was no alarm. These 2 acoustic tones were a 5 kHz tone (5 s emission interval and 400 ms emission duration, similar to but higher frequency than the signal from a Future Oceans F3TM 3 kHz Whale Pinger®) and a 2-2.1 kHz swept tone (8 s emission interval and 1.5 s emission duration). A total of 108 tracks (focal follows) were collected using a theodolite at Cape Solander, Sydney, Australia, during the whales’ 2013 northern migration. Linear mixed effects models were used to determine the effect of the different acoustic tones on whale direction (heading), and behaviour (dive duration and speed). Whales showed no detectable response to either alarm. Whale direction and surfacing behaviour did not differ whether the alarm was ‘on’ or ‘off’. Although the response may have been different if the alarms were attached to fishing gear, the lack of measurable response suggests that the types of tones used are not likely to be effective in alarms intended to reduce entanglement of northward migrating Australian humpback whales.9 page(s

Depths at which shark analogues were sighted by fixed-wing and helicopter observers maintaining their position at 500 ft (∼150 m) around a known position.

<p>Overlaid are individual data points from each aircraft; open circles represent fixed-wing sightings, closed circles represent helicopter sightings.</p