Image of Alewife herring. Photo by: cornell.edu
Image of Blueback Herring. Photo by: cornell.edu
Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science
Volume 4, Issue 1, 2012
Kevin Magowan, Joshua Reitsma and Diane Murphy
In this Journal Kevin Magowan, Joshua Reitsma and Diane Murphy were trying to assess their ability to use dual-frequency identification sonar (DIDSON) to capture migrating alewife, Alosa pseudoharengus and blueback, Alosa aestivalis. They did this research on the coast of Massachusetts. Two sites were used in this study to show how migrating herring were adapting to their environment. Herring River and the second location was located above a control dam at the outlet of Hinckley’s Pond. The crew processed each data using different techniques. One technique for using the DIDSON was using a software to determine how many migrating herring were swimming up the rivers. This one technique had multiple steps on using the DIDSON. One step was tally counting which involved manually counting the herring as they swam by the DIDSON. The second step was mark and measure. This step required the person to use the DIDSON software to count each fish in different time frames. Playback was important to reading how each fish was traveling and what type of species of herring was swimming up the river. The last step was using autocount. In autocount every fish was automatically counted regardless of the direction and species. This function was limited to good data because they were unable to discern species and direction of travel.
The data that they collected from site one which was at Herring River was processed using the fast-replay tally counting step. This took them 19.5 hours to look over and they concluded that out of 4,312 fish 4,134 were classified as the river herring. Using the mark and measure step it took them 33 hours to count. Out of those 33 hours of counting they figured 4,310 fish that passed the DIDSON only 4,119 were classified at the river herring. The autocount step took only 11 hours to process. They had over 2,300 river herring. The data collected at site 2 which was at Hinckley’s Pond. This was processed by a single observer using only fast replay tally counting and the mark and measure steps. The total number of fish spotted was only 1. Magowan et al states.” DIDSON is an effective type of sonar with which to count river herring in a small coastal stream, as is evident by the many clear images of river herring that they we collected during the day and at night”.