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5th International Billfish Symposium, Taipei, Taiwan. 4-8 November 2013.

Many of the worlds leading players in the field of billfish research as well as a good number of up and coming scientists gathered in Taipei to focus on the global conservation and sustainable management of billfishes.

5th Billfish Sym

With support from the NZ Sport Fishing Council and Whangamata Sport Fishing Club John Holdsworth attended to present the early results from the marlin ID project lead by Clive Roberts, Lara Shepherd from Te Papa and Blue Water Marine Research.  Many sportfishing clubs and motivated individuals have collected detailed measurements and samples of muscle and external parasites for genetic analysis.  This was one of 50 presentations spanning the latest in billfish genetics, stock structure, habitat utilisation, aging, modelling and more.

Off interest to sport fishers is the way marlin and sailfish seek out the edge of warm water eddies.  As Mark pointed out they like it on the edge of “spicy” water (hot and salty).  These eddies are not always visible in the SST plots but are revealed with sea surface height and models which look at concentrations of sub surface warm water.

Also worth noting was the timely recovery of Atlantic swordfish following quota reductions and closed areas in the mid 2000s.  A period of good recruitment also helped.  John posed the question “good luck or good management, it seems it was a bit of both.  John highlighted some of the difficulties getting effective international management action in place.  When effective cuts were made Atlantic swordfish were able to recover due to some special biology that has allowed then the wider global distribution than other fishes.  They are adapted to deep cold water with special eye and brain heaters which give them an advantage over prey, the largest females tend to feed in high latitudes where fishing pressure is generally less, and there is an extended spawning season in tropical waters.  There is some hope that swordfish in NZ will continue to improve after a reduction in fishing effort in northern waters.

Striped marlin featured in a number of papers.  Spawning and habitat utilisation in Central America where a highlight.   Again spawning was spread over several months with a preference for 26 to 28deg C  SST.  But the warmer water was not often preferred when feeding, the temperature fronts on the edge of large eddies where favoured. These can show up in satellite SST maps but at times the eddy is around warm sub surface water with is detected by oceanographic buoys and sea surface height.  Satellites detect small changes in surface height using radar, which is possible even through cloud cover.  The eddies off Central America are fleeting, but off eastern Australia and NZ they can last for several days or weeks.  Japanese research vessels capable of recording ocean conditions and fishing several gear types at once showed that prey species also favour the edge of eddies were water masses converge and current is stronger.

Julian Pepperell presented a summary of 40 years of conventional tagging in Australia. Apart from black marlin many of their billfish show north south movement between spawning grounds in the Coral Sea and foraging grounds of NSW and QLD.  A breakdown of recaptures by species and decade clearly slowed that conventional tagging was  still adding to our knowledge of long term movements of billfish.

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