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5th International Billfish Symposium

Taipei, Taiwan, 4-8 November 2013
Many of the world’s 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. Results from the New Zealand marlin ID project led by Clive Roberts and Lara Shepherd from Te Papa were presented. This project has been well supported with many sportfishing clubs and motivated individuals collecting detailed measurements and samples of muscle and external parasites for genetic analysis. This was one of 50 presentations in Taipei spanning the latest in billfish genetics, stock structure, habitat utilisation, aging, modelling and more.

With support from the NZ Sport Fishing Council and Whangamata Ocean Sports Club

The New Zealand marlin ID project found several measurements that were useful for separating the three marlin species across the whole size range, however no
single characteristic separated all three. 
The branchiostegal membrane or frill covering the gills is shorter in blue marlin (16% to 19% of body length) than in black and striped marlin. Black marlin have a shorter dorsal fin than striped marlin.  While size, body shape and pectoral fins are still useful, a few quick measurements can confirm species where there is doubt. These species IDs were backed up by genetic analysis. 

Of interest to sport fishers is the way marlin, broadbill and sailfish seek out the edge of warm water eddies.  A Japanese research vessel capable of recording ocean conditions and fishing several gear types at once showed that prey species also favour the edge of eddies where water masses converge. These eddies are not always visible in the  SST plots but are revealed by sea surface height and models which look at areas of warm sub surface water.  A number of studies found that in the “transition zone” between areas of high and low sea surface height, currents are higher, and billfish catch rates are higher

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