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Severity of summer drought as predictor for smolt recruitment in migratory brown trout ( Salmo trutta )
Author(s) -
Jespersen Henrik,
Rasmussen Gorm,
Pedersen Stig
Publication year - 2021
Publication title -
ecology of freshwater fish
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 55
eISSN - 1600-0633
pISSN - 0906-6691
DOI - 10.1111/eff.12569
Subject(s) - salmo , brown trout , fish migration , precipitation , emigration , biology , fishery , ecology , environmental science , zoology , fish <actinopterygii> , geography , meteorology , archaeology
The recruitment of anadromous brown trout smolt from a small Baltic stream, frequently exposed to summer drought, was quantified for 9 years, and the effect from drought on smolt number and age composition analysed. Drought was quantified by, (a) a newly developed index quantifying the severity of summer drought (Drought Severity Index—DSI—based on amount of precipitation, monthly mean temperature and number of hours with sun), and (b) the amount of precipitation. Both DSI and precipitation were measured 1 or 2 years prior to emigration. We found highly significant (negative) relations between DSI (1 year before emigration) and both the total number of smolt, and the number of age 1 smolt. In addition, precipitation was (positively) related to total number of smolt, but DSI proved to be a stronger predictor compared to precipitation. In addition to drought, our results support a negative influence from older parr on the survival of age 0 trout. Our results indicate that recruitment of brown trout smolt from streams, regularly affected by summer drought, may be predicted approx. 6 months before the actual emigration the following spring. This offers an opportunity for managers to adapt protective measures in accordance with local and temporal changes in recruitment.