Changes in the density and growth of brown trout ( Salmo trutta) after intensive removal of sympatric Arctic charr ( Salvelinus alpinus) in the sub‐ Arctic lake Møkkelandsvatn, Norway

• Published in: Ecology of Freshwater Fish
• Main Authors: Svenning, Martin A., Hanssen, Øyvind K., Elliott, J. Malcolm
• Other Authors: The Norwegian Sea Ranching Program (PUSH)
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2014
• Subjects: Almo; Arctic; Arctic Lake; Norway; Arctic charr; Salvelinus alpinus
• Online Access: http://dx.doi.org/10.1111/eff.12172; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Feff.12172; https://onlinelibrary.wiley.com/doi/pdf/10.1111/eff.12172

Abstract This study tests the basic hypothesis that the removal of charr, S alvelinus alpinus ( L .), would cause an increase in both the growth and density of a sympatric trout population, S almo trutta L . The charr population was characterised by slow‐growing individuals, with a high proportion of mature fish, that is typical for so‐called overpopulated populations. A total of 31,000 charr was removed from the lake in the period 1990–1992, and the density of younger trout (1+, 2+), but not older trout (3+, 4+), increased. The growth of older trout (3+, 4+) increased, but the evidence for similar growth increases of younger trout (1+, 2+) was limited. From 1989 to 1990, the proportion of trout increased from 30 to only 40% of the total catch, but from 1991 to 1994, it was significantly higher (60–80%) than that of charr. Total trout biomass increased to a maximum in 1992 and then decreased so that the biomass of 1994 was nearly similar to that of 1989, that is before the start of the charr removal. Back‐calculated lengths of trout from otoliths showed that 2+ and 3+ trout caught in the pelagic were growing consistently faster over previous years than those caught in the littoral, while this was not the case for the 4+ fish. Therefore, the hypothesis was partially supported; the growth rate of trout increased (age groups 1+ to 4+), while the density of juvenile trout (1+, 2+), but not the older trout (3+, 4+), increased after the removal of charr.