Observer-based study of targeted commercial fishing for large shark species in waters off northern New South Wales.
|Observer-based study of targeted commercial fishing for large shark species in waters off northern New South Wales.
Targeted commercial fishing for large sharks is a significant industry in the coastal waters of northern New South Wales (NSW) and is managed as part of the Ocean Trap and Line (OTL) fishery. The annual total catch from the line fishing component of the OTL fishery is estimated to be worth approximately $A10 million. Large sharks are caught mainly using ‘setlines’ and ‘trotlines’, which are long, horizontally-oriented fishing lines that have hundreds of hooks attached. These fishing gears are positioned on or near the seabed, or suspended well below the surface. Although caught primarily for the high value of their fins, the bodies of the sharks are also retained (as required by law) and sold.
An increase in targeted shark-fishing effort and tripling in the total catch of sharks in the OTL fishery in northern NSW waters over a two-year period between 2004/05 and 2006/07 raised serious concerns over the potential impact of such an expansion on populations of the species being targeted and also non-target species such as the threatened grey nurse shark and protected great white shark. This highlighted the urgent need for a much greater understanding of targeted shark fishing in NSW waters and, therefore, an observer-based research project to collect scientific information and biological samples onboard shark-fishing vessels within a relatively short period of time. In addition to implementing considered management strategies to gain appropriate control over the quantities of large sharks being retained by the shark fishers, I&I NSW collaborated with the Northern Rivers Catchment Management Authority (NRCMA) to fund much-needed observer-based research in the shark fishery of northern NSW during 2008/09. Observers were placed on 81 targeted shark-fishing fishing trips between 1 September 2008 and 30 June 2009, providing an overall level of observer coverage for setlining and trotlining combined of just over 40% of the total shark setlining done in those waters during that time.
The results showed that around 85% (by number) of the overall total catch (i.e. all retained and discarded organisms) during the observed shark-fishing trips was comprised of the targeted species of whaler, hammerhead and mako shark. Whaler sharks dominated catches, with sandbar shark (35% of overall total catch), dusky whaler (15%) and spinner shark (11%) the main species observed, although the dominant species in catches depended primarily upon the time of year and how far north the fishing was being done. Lesser numbers of common blacktip shark and tiger shark (both whaler sharks), smooth hammerhead, scalloped hammerhead, bronze whaler and shortfin mako were also recorded. A total of around 30 non-target species were recorded in catches, with around 43% of those non-target individuals retained as byproduct (saleable product) and the rest released back to the water, in most cases alive. Interactions with threatened and/or protected species were rare, with overall totals of six great white sharks, five grey nurse sharks and two green turtles hooked during observed trips - all of which were alive upon capture and subsequent release. There were no observed interactions with marine mammals, seabirds or other marine reptiles.
This study has provided a considerable knowledge base regarding targeted shark fishing in northern NSW waters, and has demonstrated the value of concentrated, observer-based research in obtaining large amounts of reliable information within a short timeframe. The information gathered during the project will assist the formulation of management strategies that ensure the stocks of whaler and hammerhead sharks in NSW waters are harvested sustainably in future.