Document Type

Honors Thesis

Publication Date

Spring 5-2015

Abstract

The depth and vertical movements of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) and shortnose sturgeon (Acispenser brevirostrum) at Bucks Ledge (river kilometer 21) in the Penobscot River were examined to investigate sturgeon depth preferences and jumping habits. The purpose of this project was to expand knowledge on the endangered and threatened sturgeon populations in Maine waters. Behavior of 20 individual sturgeon (6 Atlantic sturgeon and 14 shortnose sturgeon) was used to characterize fish depth as it varied with water depth, e.g., in relation to tidal periodicity or not (random). The study used depth data collected using acoustic telemetry between 2007 and 2014. A receiver on the bottom of the river recorded depth from fish tagged with acoustic transmitters and pressure sensors. Many of the recorded depths of all six Atlantic sturgeon and 11 of the 14 shortnose sturgeon fluctuated with the tide (tidal behavior), meaning they remained at the bottom of the water column, throughout multiple tides; on average, the proportion of the time the fish spent at Bucks Ledge doing tidal behavior ranged from 0.16 to 0.52 per season. There was a great deal of variability, with standard deviations ranging from 0.08 to 0.2, but depth observations of Atlantic sturgeon had more tidal periodicity while shortnose sturgeon depths were more random. Atlantic sturgeon also spent more time at Bucks Ledge than shortnose sturgeon did during the days they were present in this area. There were minimal seasonal differences in depth use for both species. Recorded depths of less than 0.5 meters were assumed to be jumping points. There were 14 sturgeons with depths of less than 0.5 meters, for a total of 33 data points. The majority, 73%, of the jumping points occurred during the flood tide, and 67% of jumping points occurred within three hours of low tide. These results indicate sturgeon may jump more commonly at certain stages of the tidal cycle, suggesting a link between gas bladder function and sturgeon jumping.

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