Veliger Densities

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