Relating the swimming movements of green sturgeon to the movement of water currents

Abstract

Animals swimming in tidal environments continuously interact with water currents which may either hinder or aid their movement. It is difficult to observe the orientation of an organism relative to the current when it is swimming in the wild without specialized telemetry; however, using the total recorded movement vector and the current vector, one can use vector analysis to calculate the actual movement of the animal. Here, we apply this method to six tracks of green sturgeon (Acipenser medirostris) in the San Francisco Estuary, using current vectors derived from a hydrodynamic model. Three movements were near the surface in deeper, high-current regions of the bay and three were near the bottom in shallow, low-current areas. The total displacement over ground was faster at the surface (0.9 m sec −1 versus 0.5 m sec −1 ) and occurred in stronger currents (0.7 m sec −1 versus 0.4 m sec −1 ), but the swimming speeds of the fish were similar between surface and bottom movements (0.5 m sec −1 versus 0.6 m sec −1 ). All surface movements were in the direction of the current, and two of the fish also oriented closely to the flow. In contrast, none of the three benthic movements were in the direction of the current, and two were oriented opposite to the flow. It seems plausible that green sturgeon orient to and make use of water currents to efficiently move through tidal habitats, riding the flow in high-current areas, and moving independently of, or even into, the flow in slower currents.

Physiological preparedness and performance of Atlantic salmon Salmo salar smolts in relation to behavioural salinity preferences and thresholds

“…The apparent tidal modulation of acoustically tagged smolts in the Penobscot Estuary was indicative of selective tidal stream transport (STST; Forward & Tankersley, 2001). STST is a behavioural tactic that reduces energetic costs of migration for marine animals (Forward & Tankersley, 2001), and several examples exist in a number of invertebrate (Queiroga, 1998;Forward et al, 2003;Criales et al, 2011) and fish species (Barbin, 1998;McCleave & Arnold, 1999;Kelly & Kimley, 2012), including adult sockeye salmon Oncorhynchus nerka (Walbaum 1792) (Levy & Cadenhead, 1995). Changes in depth by S. salar smolts in the Penobscot Estuary suggested that fish were located deeper during incoming tides than outgoing tides, a behaviour that would result in increased, rather than decreased exposure to SW during tidal cycles as would be expected from the laboratory results.…”

Use of a hydrodynamic model to examine behavioral response of broadnose sevengill sharks (Notorynchus cepedianus) to estuarine tidal flow

“…Among these, there has been increasing recognition that external constraints in particular may play a larger role in shaping an organism's movement path than previously considered (Wilson et al 2012;Shepard et al 2013;Brownscombe et al 2017;Gallagher et al 2017). In estuarine habitats, one such external force is the seasonal and daily hydrological variance, which is generated by complex bathymetry and water flux from various inshore and offshore sources (Brodersen et al 2008;Anderson and Beer 2009;Forsythe et al 2012;Kelly and Klimley 2012). Due to the presence and variability of these currents, it is likely that different species that reside in or transit through estuaries will exhibit plasticity in their movement in response to the currents.…”

Activity patterns of Gulf Sturgeon (Acipenser oxyrinchus desotoi) in the staging area of the Pascagoula River during fall outmigration

“…Lunar and tidal cycles have long been shown to affect the movements of many fish species and decapod crustaceans (Forward & Tankersley 2001;Reebs 2002;Hare et al 2005;Keefer et al 2013) and generally are co-dependent on one another. Kelly & Klimley (2012) noted Green Sturgeon (Acipenser medirostris) swimming into the current while maintaining position just off the bottom which likely allows them to more efficiently maintain buoyancy while swimming. Thus, it is possible that flow conditions experienced during a rising tide caused Gulf Sturgeon to change their swimming behaviour in a way which made them more susceptible to capture in the anchored gear.…”