Beneath the Surface > August 2014 > Thursday Analysis Update - 21.08.2014

Thursday Analysis Update - 21.08.2014
This week I continued to look at the scale damage observed in the smolts captured by the screw trap sited at Brabourne's pool on the River Carron.

One of the things that the project would like to do going forwards is to monitor the numbers of piscivorous birds on the river as this seems the most likely cause of the damage seen in these small fish (damage by seals or otters would be much more devastating to the fish). As there are no records of bird sightings or numbers to date it is impossible to try and relate the two factors to each other a this time, except to say that adult and juvenile birds have been seen on the river and smolts are getting damaged.

Examples of smolts from the screw trap with scale damage.

What I was able to do was explore whether the smolts might have been being damaged in fast-flowing water. By comparing the levels of damage to the strength of the water flow it's possible to estimate the likely impact of the flows on the smolts.

For a larger image of this graph click here.

For a larger image of this graph click here.

Bearing in mind that the data for the screw traps is incomplete due to the need to remove it from the river when the flow is very high to prevent it from being damaged; the graphs actually seem to show that there are less damaged smolts when the flow rate of the river is high. This can be seen in the examples above where the flow rate (green line) peaks either side of the peak incidence of scale damage.

However, this data does support Bob's observation that the damage is greater in lower, calmer flows and may even bear out his idea that piscivorous birds on the river have an easier time catching fish in these water conditions. If we could get collect the quantitative data on bird numbers/ sightings on the Carron and match this up with the damage and flow data, the three things together could perhaps tell us exactly what's going on...
Posted: 8/22/2014 2:26:43 PM by Matthew Curran | with 0 comments

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