How to Drink From a Fire Hose

Since 2009, larval sampling efforts have focused on capturing newly hatched and drifting larvae immediately downstream of a suspected pallid sturgeon spawning site (see previous posts “Searching for a needle in a haystack” and “Panning for biological gold”).  In 2012 Comprehensive Sturgeon Research Project (CSRP) biologists initiated systematic sampling for larval, free-embryo pallid sturgeon to assess fluxes of larvae from the Missouri to the Mississippi Rivers.  Biologists have been stationed in St. Charles, Missouri conducting weekly larval sampling since mid-April.  This task of the CRSP will focus on a single channel cross-section through September to provide some relative indication of the importance of the Mississippi River as nursery habitat for shovelnose and pallid sturgeon young of year.

Larval samples collected near the confluence of the Missouri and Mississippi Rivers. Sturgeon collected in the samples ranged from recently hatched larvae to larvae more than two weeks old.

Given the size of the Missouri River, trying to catch the small larvae as they drift past is a little like trying to drink from a fire hose.  Drifting larvae are collected using a pair of ichthyoplankton sampling nets that are deployed in the water column on either side of the boat for 5 to 15 minutes.  One-hundred pound lead weights hold the fine mesh nets in the swift current while samples are taken in the middle of the water column and within inches of the bottom.  Small meters with propellers are mounted at the openings of the nets to measure the amount of water strained by the nets. The samples collected in the nets are emptied into pans and sorted.  All sturgeon and paddlefish larvae collected are preserved in alcohol and transported back the office.  The individual fish are then measured, identified, and aged based upon their developmental stage.  The date the fish was collected, along with its age can help to determine when and where adult sturgeon are reproducing.  To date, 322 larval sturgeon and 343 larval paddlefish have been captured at the study site.

Sturgeon larva captured near the confluence of the Missouri and Mississippi Rivers. This young sturgeon has used all its yolk reserves and must settle to the bottom and search for food on its own.

With contributions from Aaron DeLonay

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