Offshore pelagic shark and teleost surveys Objectives

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  To assess the biodiversity and composition of the pelagic shark and teleost assemblage in shelf slope and offshore regions of the GAB.
  
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  To determine the spatial and temporal distributions of pelagic sharks and teleosts in shelf slope and offshore regions of the GAB.
  
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  To identify key habitats of pelagic sharks and teleosts in the shelf slope and offshore regions of the GAB.
  
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  To collect dietary information for the pelagic sharks and teleosts in the shelf slope and offshore regions of the GAB to contribute to aligned trophodynamic models for the region.
  

Pelagic sharks and teleosts will be captured using tuna circle hooks (size 14/0 and 16/0) baited with blue mackerel attached to a short (1 m) stainless steel wire leader (2 mm). Tuna circle hooks will be used to minimise the chance of deep ingestion of hooks and harm to the animals. This hook pattern is designed to hook the jaw hinge which minimises injury and optimises the post-release survival probability. The leader will be attached to a 9 mm floating rope and suspended from a 70 mm diameter rubber buoy, or multiple leaders (200-400) will be attached to a set long-line that will be constantly monitored from a nearby vessel.

Once captured, sharks will be removed from the water using an aluminium chute or a soft rubber sling and restrained using a dense foam mattress. Circle hooks will be removed immediately using bolt cutters or pliers. The gills of each shark will be irrigated with saltwater using a deck-hose covered with PVC pipe. The eyes will be covered with a soft, black damp cloth and the mattress to minimise any potential capture related stress or eye damage. Sharks will be sexed, and length will be measured to the nearest 10 mm by total length (TL).

Conventional tags do not have an energy source, and are solely used to identify individuals if they are re-captured at a later date by commercial or recreational fishers. Sharks will be tagged using Hallprint stainless steel dart tags (SSD). Dart tags are inserted in the dorsal musculature near the first dorsal fin depending on the species. There is no automated mechanism to release conventional tags, but shedding can occur. Sharks with conventional tags are regularly recaptured after several years at liberty.

Dorsal fin mounted satellite tags, including the Wildlife Computers SPOT and Mk10A models, (position only), will be deployed on selected pelagic shark species (shortfin mako and white shark). These tags report to the Argos tracking satellite network. The tags are attached directly to the first dorsal fin of sharks by drilling two 3. 5 mm holes through the fin cartilage and affixing the tag using two stainless steel bolts, nylex locknuts and small lower grade stainless steel washers. These tags will not be retrieved from sharks, but the small lower grade stainless steel washers are expected to grow out of the fin over time. The small washers have been shown to grow out of the fin over time. The bolts are joined to the tags using a water-proof epoxy that is expected to break away from the tag as the fin grows in width, therefore allowing the sharks to shed the tag over time. Once each tag is fastened to the dorsal fin, the lock nuts will be loosened by two turns to allow for growth of the fin during the deployment period. The battery life of satellite tags (SPOT tags) is dependent on how the duty cycle of the tag is programmed (i.e. how many times the tag transmits data each day). SPOT tags deployed previously on shortfin makos have been shown to transmit data for up to 680 days. SPOT tags record and transmit Argos location estimates and temperature data. Shortfin makos have been recaptured following long-term (1 + yrs) satellite tag deployments in the NE Pacific Ocean and recently off Southern Australia have shown good healing responses at the tagging site. While this information has not been published, the PI has observed the dorsal fin of two shortfin makos that were satellite tagged. The drill holes used to fasten the satellite tags to the dorsal fin are small in diameter (4.5 mm). The tag dry weights of dorsal mounted tags is 0.1 % of the body weight of an average sized shortfin mako (2 m), and therefore it is expected that this would have little to no effect on individual motility or behaviour. When the tag is fastened to the dorsal fin each of the lock nuts are loosened by one to two turns to allow for growth of the fin in width during the tag deployment period. This is a standard technique that is also used by other leading fisheries research agencies. Stainless steel dart tags are also known for being shed.

Sharks will be attracted to the vessel using fish-based berley and a baited line. Vemco V16 coded acoustic and pop-up satellite archival tags will be inserted into the dorsal musculature using a tagging pole and modified spear-gun and stainless steel applicator. Tags are attached to a plastic dart head via 260 mm of 2 mm diameter, multi-strand, high grade (316) stainless steel wire trace.

If an animal requires euthanasia due to unforeseen circumstances, the procedure will be performed by Dr Paul Rogers by severing of the spine on the dorsal side adjacent to the first gill arch. This is the most suitable and humane method for euthanasing pelagic sharks.