A re-evaluation of swimming performance in juvenile salmonids relative to downstream migration

Abstract

It has been hypothesized that downstream migration of juvenile salmonids is initiated by physiological changes that occur during smoltification, which render the fish unable, or unwilling, to swim against currents that exceed 2 body lengths per second (BL ·s-1). This decline in ability, coupled with the increase in flow rate generally associated with the spring run-off, is thought to result in passive downstream displacement. To test this hypothesis, we measured holding ability of wild Atlantic salmon (Salmo salar) parr and swimming ability of wild, migrating Atlantic salmon smolts in the field under ambient environmental conditions. Atlantic salmon parr (fork length 4.8-13.1 cm) used their pectoral fins to anchor themselves for indefinite (i.e., >200 min) periods in water speeds up to 0.86 m ·s-1. Atlantic salmon smolts (fork length 12.4-21.1 cm) swam indefinitely against currents up to 1.26 m ·s-1, maintained velocities as high as 1.64 m ·s-1 for short periods (2-10 min), and made short bursts at speeds up to 1.95 m ·s-1. These findings indicate that absolute swimming performance is not impaired after smoltification and that wild Atlantic salmon smolts are capable of swimming at speeds much greater than 2 BL ·s-1, making it unlikely that they are involuntarily carried to the sea by river currents.

Rainbow trout display a developmental shift in red muscle kinetics, swimming kinematics and myosin heavy chain isoform

“…comm.). In another study, there was reportedly no change in the maximum sustained swimming speed at PST in Atlantic salmon Salmo salar L. (Peake & McKinley, 1998).…”

Main stem movement of Atlantic salmon parr in response to high river temperature

“…Laboratory analysis of Atlantic salmon swimming velocities suggests that parr (fork length % 100 mm) are able to comfortably swim (or hold station) at flow velocities approaching 0.90 ms À1 (Arnold et al 1991;Peake et al 1997;Peake & McKinley 1998), more than sufficient for traversing the 1.60 km between the upstream PIT antenna and the cool tributaries in the~2.25 h between detection at the reach boundary antennas and the aggregation midpoint occurrence. First, the earlier mean detection occurrence at the reach boundary antennas compared to the thermal refuge aggregation midpoint suggests that, as hypothesised, parr movement is detected in the main stem several hours before the thermal refuge aggregations reach their peak size.…”

Response of downstream migrating adult European eels (Anguilla anguilla) to bar racks under experimental conditions

“…Time taken to approach the racks was greater than expected if fish had moved passively with the flow. The high susceptibility of eels to become impinged on screens and bar racks was attributed to their elongated bodies and relatively weak burst swimming capabilities [maximum c. 1.35 mAEs )1 , Solomon & Beach 2004;vs. 1.95 mAEs )1 for Atlantic salmon (Salmo salar) smolts, Peake & McKinley 1998]. No impingement or passage through the racks occurred, and passes per approach were high (98.3%), when vertical racks were angled 15°, 30°or 45°relative to the flow.…”