<em>Abstract.—</em>Eighteen Gulf of Mexico sturgeon <em>Acipenser oxyrinchus desotoi</em> netted at the mouth of the Suwannee River, Florida, in February–April 2001, were tagged with ultrasonic transmitters to examine riverine and estuarine movements. In addition, 30 fish (11 carrying ultrasonic transmitters) were fitted with archival temperature-logging tags to record temperatures encountered by Gulf sturgeon over the course of a year, including both their riverine and estuarine residency. Movement rates of Gulf sturgeon in the Suwannee River were greatest during the upstream migration in March and April 2001 (4.8 km/d) and upon their emigration from the river in September 2001 (6.4 and 16.0 km/d for males and females, respectively). Mean maximum distance that fish were relocated upstream was significantly greater for male Gulf sturgeon (165 km) than for females (126 km). This may relate to female Gulf sturgeon not spawning annually and thus not migrating to putative spawning grounds upriver. In contrast, rates of upstream movement did not differ significantly between sexes. Movements in the nearshore regions of the Suwannee River estuary did not differ between males and females (0.8 and 2.2 km/d, respectively), and was much lower than in the river. Three Gulf sturgeon bearing archival temperature tags were recovered in subsequent netting activities in 2002. Data downloaded from the tags demonstrated that on average Gulf sturgeon were exposed to a 13°C annual flux in temperature, ranging from 26°C in the river during the summer to 13°C in the estuary in the winter, although individual fish experienced as much as a 20°C range (8.1–28.5°C) over the course of a year. Given the influence of temperature on the metabolism of ectotherms such as sturgeon, this broad fluctuation in temperature may have profound implications for the bioenergetics, and hence growth and reproduction, of Gulf sturgeon.
Exploring Impacts of River Discharge on Forage Fish and Predators Using Ecopath With Ecosim