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Trapping smolts to assess predator damage The types of damage found - - PowerPoint PPT Presentation
Trapping smolts to assess predator damage The types of damage found - - PowerPoint PPT Presentation
Trapping smolts to assess predator damage The types of damage found on smolts are recorded by reference to a set of photographs Most of these types were identified at a smolt trap on the R. Ness ( Williams, K., 2007: Nutrient Transport
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Type I – Scales removed, including ‘rake marks’ / areas of parallel scale loss. Type II – Scales removed, including converging lines or ‘v’-shaped areas of scale loss
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Type III – Single, small, puncture wound Type IV – Single, large, puncture wound
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Type V – Multiple, small, puncture wounds Type VI – Multiple puncture wounds, including one or more large ones
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Type VII – General scale loss or other damage types
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ADDED : Type VIII – U-shaped bite from below ADDED : Type IX – Upper lobe of tail damaged ADDED : Type X – Lower lobe of tail damaged If any damage type occurs on the wrist of the tail, put a ring round its number when recording
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WHAT CAUSES THESE DIFFERENT TYPES OF DAMAGE ?
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Type I – Scales removed, including ‘rake marks’ / areas of parallel scale loss.
Smolts known to have been regurgitated by Goosanders
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ADDED : Type VIII – U-shaped bite from below Have also seen this type in a stream where only Eels and Trout are present, so must be the mark of one of these
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Heron ?
But not seen at smolt traps, only on Autumn traps for upstream migrants
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Damage rates
TYPES OF DAMAGE FOUND TOTALS % Damaged % Bird damaged (I & II) I II III IV V VI VII VIII IX X XI XII Damaged Smolts 2011 Salmon 4 12 24 5 1 2 8 56 509 11.00% 3.14% Trout none 52 0.00% 0.00% 2012 Salmon 8 12 1 2 1 2 1 27 359 7.52% 5.57% Trout 1 5 1 1 1 1 10 90 11.11% 6.67%
But are unsuccessful attacks a high or low proportion of all attacks made? How many survivors of unsuccessful attack die afterwards – and how might it take them to die?
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Damage on an adult: by what?
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Inter cohort competition apparent in downstream emigrants ?
5 10 15 20 25 50 80 110 140 170 200 230 PERCENT LENGTH 2003 n=3974 5 10 15 20 25 50 80 110 140 170 200 230 PERCENT LENGTH 2005 n=2224 5 10 15 20 25 50 80 110 140 170 200 230 PERCENT LENGTH 2007 n=890 5 10 15 20 25 50 80 110 140 170 200 230 PERCENT LENGTH 2002 n=1389 5 10 15 20 25 50 80 110 140 170 200 230 PERCENT LENGTH 2004 n=3114 5 10 15 20 25 50 80 110 140 170 200 230 PERCENT LENGTH 2006 n=1316 5 10 15 20 25 50 80 110 140 170 200 230 PERCENT LENGTH 2009 n=789 5 10 15 20 25 50 80 110 140 170 200 230 PERCENT LENGTH 2008 n=546
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5 10 15 20 25 50 80 110 140 170 200 230 PERCENT LENGTH 2011 n=655 5 10 15 20 25 50 80 110 140 170 200 230 PERCENT LENGTH 2010 n=329 5 10 15 20 25 50 80 110 140 170 200 230 PERCENT LENGTH 2012 n=238
Inter cohort competition apparent in downstream emigrants ?
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SMOLT AGES – No S3s ?
100 200 300 400 500 600 700 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 NUMBER LENGTH (5mm)
S1 S2 S3
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