Muc Mhara Ireland's Smallest Whale - Marine Institute Open Access ...

Pinger spacing
Next BIM set out to establish what number of pingers would be required on fishing gear. European
legislation required pingers to be deployed at a maximum spacing of 200m, but the maximum
effective spacing had yet to be determined and the sound characteristics of specific pinger models
suggested that the spacing could be higher. The advantages of using less pingers include reductions
in pollution from lost or damaged pingers, noise pollution and associated potential porpoise habitat
limitation, and of course cost and handling for fishermen. Further trials on fishing vessels were
carried out and by-catch rates in nets with pingers deployed at 200m, 600m and in control hauls
with no pingers attached were compared. Aquamark 100 pingers supplied by Aquatech in the UK
were deployed according to these categories on individual strings or stations of gear approximately
4 km in length and careful watch was maintained when hauling gear to check for porpoise by-catch.
As by-catch rates were low, the data were supplemented with control hauls from the pinger
assessment trials during 2005 in order to take advantage of incidences of porpoise by-catch and to
boost the power of analyses.
Spacing results
A total of 152 hauls/stations measuring 637km were carried out over 13 trips to sea for a total bycatch
of 7 porpoises. No porpoises were caught in 27 stations with 600m spacing or in 22 stations
with 200m so these groups were obviously not statistically different. A total of 7 porpoises were
caught in 103 control stations but this group was not statistically different from either of the groups
with pingers (Two sided Fishers exact chi squared test: P = 0.27). So although it appears that
pingers do work at higher spacings, due to relatively low levels of porpoise by-catch it was not
possible to scientifically prove this in Irish waters. A similar trial was carried in 2006 by the Danish
Institute for Fisheries Research (DIFRES), in the Danish North Sea hake fishery where higher
porpoise by-catch rates produced clear and conclusive results. A 100% reduction in porpoise bycatch
rates was observed in nets with 455m spacing and a 78% reduction in by-catch in nets with
585m spacing with no significant difference between pinger spacing groups (Larsen and Krog
2007). Based on the research carried out by BIM and DIFRES the Irish government issued a
derogation in June 2007 permitting an increase in the maximum spacing from 200m to 500m.
Figure 2. Position of 152 hauls used in pinger spacing analysis. Porpoise by-catch points are
represented by clear squares.
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Proceedings of the 2 nd IWDG International Whale Conference: Muc Mhara - Ireland’s smallest whale
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