By Aaron DeLonay, Kimberly Chojnacki and Chad Vishy
Scientists from the U.S. Geological Survey and their partners have been successful in using telemetry to track adult sturgeon to their spawning locations on the Missouri and Yellowstone Rivers for several years (see previous blog entry A Spawning Recorded in the Yellowstone River). Despite locating spawning locations at a relatively fine resolution (10’s to 100’s of m), we continue to struggle to observe spawning and egg deposition in the swift turbid water. The definition of spawning habitat suitability and functionality is dependent upon adequately identifying quality spawning habitat (see previous blog entry Spawning patches on the Yellowstone River.) Scientists at the Columbia Environmental Research Center (CERC) are conducting studies to adapt new methods and technology to study spawning behavior and more precisely locate and characterize areas selected by pallid sturgeon for egg deposition. These studies will hopefully allow scientists to assess what characteristics of functional spawning habitats attract adults and result in the survival of developing embryos. This would help to both understand why sturgeon are having difficulty reproducing successfully and provide guidance for enhancing or creating functional spawning habitats.
One way in which scientists at CERC do this is to work with the closely related shovelnose sturgeon. We have implanted test shovelnose sturgeon with miniature acoustic transmitters and release them into specially constructed experimental mesocosms at CERC (see previous blog entry We Just Wanna See What Happens Down There!). Circulators in the mesocosm provide a continuous current that simulates conditions in the Missouri River. Scientists can manipulate the substrate in the mesocosms to provide patches of either gravel or cobble where sturgeon may spawn. We map fish locations using an array of 8 to 16, precisely arranged hydrophones connected by cables to a telemetry receiver. The hydrophones detect the acoustic pulses of the transmitters in the sturgeon. The telemetry receiver records each transmitted pulse and uses the signal detected by the array of hydrophones to calculate the precise position of each sturgeon in the pond, as often as once per second. In some trials an ARIS multibeam acoustic camera has been placed in the center of the pond to allow researchers to record sturgeon behavior.
The spawning trials begin when female and male sturgeon are primed with hormone injections and released into the pond to let nature take its course. Scientists can then evaluate the performance of the miniature transmitters by watching the tracks of individually tagged fish as the males and females move, come together, and finally spawn by releasing eggs and milt. Comparing the ARIS sonar imagery with the precise tracks from the telemetry system allows scientists to identify movement patterns that indicate spawning and egg deposition. If the transmitters perform well in the mesocosm and spawning behavior can be identified through patterns of movement, then the transmitters could be used in the wild fish in the river to determine the precise timing and location of spawning, and the habitat characteristics where egg deposition occurs. Scientists can then better study if these spawning patches are functional, and whether the quality of the patches used by sturgeon is limiting embryo development and survival.
Video 1. Video of ARIS Sonar imagery showing a female and two male shovelnose sturgeon over an egg deposition location recorded during controlled experiments to study spawning behavior.