Fishing News index> April 2008

Didymo decline in Motueka a real surprise

Nelson/Marlborough staff have been pleasantly surprised at the relative absence of Didymo in the Motueka River this summer.  It would appear that the two large floods the Motueka received over the 2007 winter effectively flushed the algae from the river. 

The river experienced two floods in close succession so was high and discoloured for a continuous period of 3 weeks or more over winter.  Being of a return period magnitude of around 1 in 5 years, the floods were large enough to scour the substrate completely clean of both native and the introduced Didymo algae. 

Fish & Game staff expected the algae would re-appear rapidly and bloom this summer but the organism has been notable by its near disappearance.  Apart from one or two small isolated sites in the lower river, Didymo is still essentially absent from the system.  This absence has been confirmed through drift diving of 10 sites throughout the lower river and discussion with fishing guides using the river. 

Whether the organism will grow to biomass capable of blooming by next summer remains to be seen.  It would appear the Motueka may receive enough flooding, or has some other characteristic unfavourable for proliferation of this organism, so that at worst it may  be merely an occasional seasonal nuisance in some summers.  It bodes well for the future of this phenomenal powerhouse river fishery. 

Drift dives in some sections of this river at times reveal trout numbers of up to 1000 fish (small, medium, & large) per kilometre of river, and as such it is a regional icon for both resident and non-resident anglers alike. 

Fishermen at times perceive the river to have few fish as fish activity and visibility is influenced greatly by river conditions and insect hatches, but drift dive information shows the Motueka to still be one of the most productive rivers in the Nelson/Marlborough region, or indeed the country. 

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