Bongo Bonanza

17 November 2013
Sunday evening finds us steaming southeast of Nantucket Shoals towards Georges Bank.  We spent most of the weekend working the shelf of southern New England.  This morning we had a nice sunrise over Great South Channel.  We sampled a lot of stations with our main gear, the 60-cm and 20-cm bongo nets.  The 60-cm bongo nets are used to collect quantitative samples.  The nets have flow-meters in the mouth that allow us to calculate the volume of water sampled during a tow.  This allows use to standardize the number of zooplankton or ichthyoplankton (fish eggs and larvae) in each net, then we can estimate the abundance of different species and compare all the stations we sample on the cruise.  We are also collecting samples on this cruise that will be used to genetically identify the fish eggs and some of the different zooplankton species.  These samples need to be preserved differently than the samples used to estimate abundances.  The 20-cm bongos, or “baby bongos”, can fish at the same time as the 60-cm net, allowing us to collect more samples without spending extra time on more tows.  The nets are washed down and preserved for later analysis.
bong net laumch

Bongo net launch. Photo by Jerry Prezioso, NEFSC/NOAA

Often visual analysis of the plankton samples can give you a quick idea of the variation of zooplankton abundances and types across the stations sampled.  Samples from the two regions we’ve collected in so far, Middle Atlantic Bight and southern New England, demonstrate this.  The samples from the Middle Atlantic Bight have lower biovolume than those from the southern New England.  Biovolume is the amount of plankton collected at a station, and can give a rough measure of production.  The southern New England samples have greater biovolume than the Middle Atlantic Bight stations.  However, the samples from the Middle Atlantic Bight have more Atlantic menhaden larvae (long skinny white fish floating in the sample on the left from Middle Atlantic Bight).  Estimates of menhaden larval abundance will be calculated after the samples are processed later in the lab.

Everyone on the ship has been enjoying the clam sunny weather of the past weekend, especially in light of the storms forecast for the beginning of the week.  We hope to be able to stay out in the Georges Bank region and ride out the worst of the winds and waves.
Harvey Walsh, Chief Scientist
GU-13-05 Northeast Integrated Pelagic Survey

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