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dec home > wsmd home > lakes & ponds > lake champlain long-term monitoring > zebra mussel monitoring > results graphs
Lake Champlain Zebra Mussel Monitoring - Results Graphs

Veliger Densities

zebra mussel veliger density in lake sections over time
zebra mussel veliger densities at south and central lake stations
zebra mussel veliger densities at northwest lake stations
Veliger graph

Veliger graph

Settled Juvenile Densities

zebra mussel settled juvenile densities at northeast nearshore stations


Seasoned Settled Juvenile Densities

Settled juveniles graph
Settled juvenils graph

Season plate densities from 1998-2009. Plates were missing at SH09 and WILL in 2009. In 2008, plates were missing at CHIP and BAHA . In 2006, sampling was discontinued at SH07 Grand Isle Ferry dock due to Homeland Security issues and plates were missing at WILL, SH09 and SH10. In 2007 plates were missing at SH09 and SH10

*Comparisons of veliger and settled juvenile densities between lake stations and/or between years were based on seasonal time-weighted mean density estimates. Simpson's integral was used to calculate the area under the density vs. time plots and the areas were divided by the duration of the sampling season. Seasonal weighted mean estimates were based on equal sampling season lengths of 150 days starting and ending with zero density values at the beginning and end of the sampling seasons.

Seasonal weighted mean densities were considered more appropriate than geometric means, arithmetic means, or single peaks because of the extreme within-season variation in veliger and settled juvenile densities. Veliger production and juvenile settlement occur during discrete time periods, causing densities to increase from zero upwards over several orders of magnitude within a short time interval during a season at some stations. Mean values would therefore be too strongly biased by the number of samples obtained during non-reproductive periods. Seasonal time-weighted mean density values provide a better index of the overall larval and juvenile production at each site.

Updated: May 2008

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