The downstream movements of wild Atlantic salmon, Salmo salar L., from their established feeding territories in the River Itchen, Hampshire, UK, were logged continuously over an 11‐month period using a passive integrated transponder (PIT) antenna system. The time of these movements was then related to a number of monitored and calculated environmental parameters. Initial downstream movement of smolts in April was correlated with the onset of darkness, at which time salmon moved from their established feeding territories alone. No relationship was found between the number of smolts migrating and river flow or maximum daily water temperature. The timing of downstream movement of parr between October and March was random with regard to sunset and time of maximum daily water temperature, suggesting the environmental cue that initiates movement may be different outside the spring smolt period.
An Integrated Sediment Disturber (ISD) was developed to study the effects of repeated physical disturbances on sediment geochemistry and associated benthic fauna. The ISD is capable to generate a strong, more or less uniform mixing of surface sediments by three rotating fork-like disturber units of approximately 1 m in diameter. Perturbations can be set at different intensities and frequencies, e.g., on times scales of hours, days, or weeks, depending on the experimental design. The ISD carries an Autonomous Positioning Drive (APD) module, which allows the three-dimensional positioning of sensors by a programmable controller. The three circular disturbed zones and an undisturbed control area in-between can be monitored at specified frequencies using a microprofiler with microelectrodes for measuring various parameters (e.g., oxygen, pH, hydrogen sulphide). All operations are supervised by a digital stills camera. Sediment sampling at the start and end point using coring devices handled by divers (and potentially undertaken using a Remotely Operated Vehicle) provides material to study shifts in biodiversity of the small sedimentinhabiting biota and alterations in ecosystem functioning in response to perturbations and the changing geochemical characteristics of surface sediments.
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