Fish counter

Abstract: Introduction: The life history. Part 1 The homecoming: homing time of return and progress upstream pattern of return. Part 2 The freshwater face: fecundity the automatic fish counter egg deposition the juveniles. Part 3 Life in the sea: distribution at sea feeding migrational routes predation natural mortality the high seas fisheries assessment of the effect of fisheries at West Greenland and the Faroes migration in coastal waters and exploitation rates. Part 4 The fate of North Esk salmon derived from the 1978 spawning. Part 5 The fisheries: ownership of fishing rights management fishery methods and fishing economics. Part 6 Catches past and present. Part 7 Modelling Atlantic salmon stocks. Part 8 Salmon farming. Part 9 The future.

Abstract: Data on the migratory behaviour of salmonids were collected at a gauging weir by means of a restivity fish-counter which triggered a motor-driven 35 mm still camera to provide photographic records of passing fish. A clear bimodal seasonal pattern of movement was observed in three consecutive years with peaks during June–August and October–December. Daily variations in the rate of movement could not be correlated with changes in discharge or temperature. Salmonids tended to move at discharges lower than those generally available. This contrasts with other published work and was attributed to the more equitable flow-pattern of chalk rivers. There was no optimal temperature associated with movements. Some evidence suggested that the largest fish moved earlier in the year but this was not marked. In clear water most movement occurred during the hours of darkness but during floods, when the river was turbid, the diurnal pattern tended to be reversed with greatest movement during the hours of daylight. Most fish negotiated the weir close to the bottom, well below mean velocity, and took a central path through the flume. Although analysis of upstream migratory behaviour was hindered by the lack of data on the numbers of fish available below the counting point it was concluded that the basic pattern of migration is established by time (season). Changes in discharge, light intensity and other parameters may then play a secondary role in modifying the details of the pattern but attention is drawn to records of movements in regulated flows where a remarkably constant pattern is shown from year to year.

Abstract: Closed-circuit television was used to provide a visual record of the events associated with the counts recorded by a resistivity fish counter. The fish seen were classified as‘ large’fish > 50 cm length and‘ small’fish of < 50 cm. Some of the‘ large‘ fish escaped detection by the counter, some‘ small’fish were counted and some counts were registered when nothing was seen. The sensitivity of the counter varied inversely with water conductivity which varied inversely with discharge. Evidence was obtained suggesting that fish ascending a weir tend to swim closer to the bottom than do those descending. It was found that fish tended to move upstream just after sunset and downstream just before sunrise except when the water was turbid and when the fish were very close to spawning. The numbers of fish movements recorded increased during those periods when discharge was decreasing after a spate but when spawning activity was at its peak, increased activity occurred in the complete absence of any change in discharge. Instances of the same fish re-crossing the counting zone several times were recorded and the simultaneous passage of more than one fish through the counting zone was observed.