Galapagos shark movement patterns and interactions with fishing vessels in the marine parks surrounding Howe Island
Jonathan D. Mitchell, Victoria Camilieri-Asch, Fabrice R.A. Jaine, Victor M. Peddemors and Tim J. Langlois
- Galapagos shark movement patterns and interactions with fishing vessels in the marine parks surrounding Howe Island
The abundance of Galapagos or ‘whaler’ sharks in the waters of the Lord Howe Island (LHI) Marine Park (NSW waters) and Lord Howe Marine Park (Commonwealth waters) is well-known to locals and visiting fishers. Fishers and this shark species regularly interact and they are sometimes inadvertently captured as bycatch and/or consume bait and hooked fish (depredation), leading to negative outcomes for both fishers (social and economic) and sharks (altered natural behaviour, injury or death). This species had not previously been studied in Australian waters, so research was needed to inform management decisions by marine park managers - NSW Department of Primary Industries and Parks Australia.
A four-year collaborative research program funded by Parks Australia with the University of Western Australia, NSW Department of Primary Industries and the Integrated Maritime Observing System has produced the final report, Galapagos shark movement patterns and interactions with fishing vessels in the marine parks surrounding Howe Island.
Galapagos sharks (Carcharhinus galapagensis) are an abundant species in the World Heritage listed marine parks surrounding Lord Howe Island (the Lord Howe Island Marine Park in NSW State waters and the Lord Howe Marine Park in Commonwealth waters), yet very little is known about their movement patterns or residency.
A combination of acoustic telemetry to collect data on shark movements and Vessel Monitoring Systems (VMS) to track fishing vessel activity, was used to identify how shark movements and fishing activity overlap and where key ‘hotspots’ of overlap occur.
To investigate Galapagos shark movements, 30 juvenile sharks were internally tagged with acoustic tags in January 2018 and 12 acoustic receivers were deployed around the Lord Howe Island and Ball’s Pyramid shelves. These acoustic receivers collected data on the movements of tagged sharks across a three-year period (January 2018 – January 2021). Between 2018 and 2021, acoustic receivers recorded 24,933 detections from 28 of the 30 tagged Galapagos sharks, with a substantial level of individual variation in the detection patterns.
Galapagos sharks were detected in every month of the three-year study period, with five individuals showing high and consistent numbers of detections all year round, indicating that at least part of the Galapagos shark population within the marine parks is resident.
One individual was detected by an acoustic receiver on a Fish Aggregating Device close to the Hunter Marine Park (Commonwealth) and Port Stephens – Great Lakes Marine Park (NSW) and approximately 30 km offshore from Port Stephens (32.78278°S, 152.41171°E) in mainland New South Wales, representing a distance of 653 km from the original tagging location.
A range of statistical techniques were used to investigate the movements and residency patterns of tagged sharks, how they overlapped with fishing vessel activity and how they were influenced by environmental factors. Residency index values varied from <0.01 – 0.57 with most individuals having a low residency index (i.e. <0.1). However, three sharks tagged at a site where fish waste is disposed had notably higher residency index values, possibly because this consistently available food source led to changes in their behaviour and movement patterns over time.
Space use areas of tagged sharks were highly variable, ranging from 0.28 km² – 217.65 km² (mean = 75 km2). Three sharks with the smallest space use areas were those that displayed high residency at the site where fish waste was disposed. Some of the sharks use core areas that closely overlapped with areas of highest fishing activity, particularly at shelf edges in the northeast and southeast LHI shelf and the northern Balls Pyramid shelf.
Four key ‘hotspot’ areas were identified where fishing activity and Galapagos shark habitat use overlapped. This key finding will enable fishers to make more informed decisions about where they can fish to potentially reduce shark interactions.
A survey of local charter and recreational fishers collected detailed information about shark-fisher interactions and mitigation/avoidance techniques currently being used by fishers. Results indicated that shark depredation resulted in the loss of 50.6 ± 26% of fish hooked per trip, with generally higher depredation rates in summer months. Lower levels of depredation were noted to occur in waters >150 m deep. Rates of Galapagos shark bycatch were 7.7 ± 4.2 sharks per trip.
Logbook catch data for sharks from 2015 to 2018 were also analysed to determine the overall shark catch per year, the percentage of sharks released and retained and the length distribution. Logbook data indicated that 4441 sharks were caught between 2015 and 2018, with a mean of 1114 ± 500 per year. Of those, 98% were released and 2% were retained by fishers. The length distribution of sharks caught ranged from 50 cm to 250 cm, with a mean of 92.86 ± 61.08 cm.
The combination of shark movement data, fishing vessel activity data and information collected from fisher surveys, has facilitated the development of best-practice guidelines to help fishers reduce negative shark interactions in the marine parks. Key recommendations for fishers include avoiding hotspots where shark movements and fishing activity were found to overlap, moving location regularly when fishing, avoiding fishing in the same area on consecutive days, fishing in deeper water (>150 m), using electric reels and handlines instead of rod and reel, jigs and lures instead of bait, diversifying target species and bringing back fish waste for disposal on land.
Overall, this collaborative research project has used a multi-disciplinary approach and worked closely with the LHI fishing community to provide detailed insights into the behaviour and movement ecology of Galapagos sharks and their interactions with fishing activity. This research represents a critical first step towards informing approaches to reduce negative shark-fisher interactions in the marine parks surrounding LHI.
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