FISHERIES - SALMON COUNTS |
4,000 3,500
3,000 2,500 2,000
1,500 1,000 500
0 1973 ’75 ’77 ’79 ’81 ’83 ’85 ’87 ’89 ’91 ’93 ’95 ’97 ’99 2001 ’03
was designed for smolt detection and operated at approximately 50% efficiency for adults. This will greatly improve the quality of the data that we collect on returning adults.
Parr We had excellent river conditions for our annual autumn parr tagging campaign with predominantly dry weather and a low river, yet we caught low numbers of salmon parr at most sites. This resulted in us tagging only half the targeted 10,000 salmon parr. Poor recruitment of salmon from the 2015/16 spawning season has been observed in many rivers across England and Wales so it appears to be a national, rather than a local, phenomenon. One thing of note during the 2015/16 spawning season was the warm weather during early winter. The high air temperature was reflected in very high water temperatures in the Frome where the average water temperature for December was 10.8°C. This was the highest December temperature recorded in the last decade, 3.4°C warmer than the average and 1.8°C warmer than the second warmest, recorded in 2006. The high water temperatures during spawning and early egg incubation may well have had a negative impact on egg survival and, therefore, parr recruitment. The true measure of freshwater productivity is the smolt output and as salmon in the Frome only spend one year in freshwater before smolting, the parr from the 2015/16 spawning season will smoltify in the spring of 2017. The proportion of tagged smolts in the 2017 smolt run will tell us whether the density of parr in the catchment was low or whether our catch efficiency was poor. If the density of parr was indeed low in 2016, then it is possible that there will be compensation in the form of higher over-winter survival due to lower competition. With the PIT systems on the Frome we can determine this by the redetection probability (survival) of the tagged individuals and we are therefore in a unique position to answer such questions.
KEY FINDINGS
Our new PIT-tag system of marking fish proved itself very efficient (90+%) at detecting returning adults as well as smolts. Parr densities recorded during 2016 tagging were very low indicating poor recruitment from the 2015/16 spawning despite good numbers of returning adults, a phenom- enon reported across the UK. However, on the Frome we are equipped to determine the smolt output and any effect of parr density on survival to the smolt stage, which we will report on in 2017.
Rasmus Lauridsen ’05 ’07 ’09 ’11 ’13 ’15 Figure 2
Numbers of returning adult salmon in the River Frome, 1973-2016
ACKNOWLEDGEMENTS
We thank Cefas for help with parr tagging and are grateful for financial support from the Environment Agency and Jock Miller for our salmon work.
Electro-fishing and tagging salmon smolts. © GWCT
www.gwct.org.uk GAME & WILDLIFE REVIEW 2016 | 15
Salmon count
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