Research on Sampling Protocols
Spill Sampling on Purse Seiners and the Estimation of Selectivity Bias
Monday, 11 October 2010 14:56

The species composition and size composition of the catch taken by purse seiners in the Western and Central Pacific Ocean can be determined from samples collected by observers. However, grab samples — wherein the observer grabs five fish per brail as the fish are transferred from the net to the vessel — are known to be subject to size selectivity bias. Spill sampling — wherein fish are spilt from the brail into a bin — was developed so that the observer does not select the individual fish.


    Sampling tuna onboard a purse seiner after spilling fish from the brail into a bin

Collection of Fish Weight Data Using Motion-Compensated Scales
Monday, 11 October 2010 14:55

The weight of fish collected in samples taken by observers on longliners and purse seiners is usually determined from the length of the fish, which can be a source of error. However, it may be possible to collect the weight of fish directly using scale that compensate for the motion of the vessel at sea. Trials are currently ongoing on purse seiners in Papua New Guinea with a Marel M1100 motion-compensated scale.


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