Faster juvenile growth with higher summer water temperature
The overall trend for the juvenile perch was that annual length
increment increased with summer water temperature and decreased with
relative density of perch in both Lake Vaggatem and Lake Skrukkebukta
(Fig. 4, Appendix Fig. S7-10). The combined length increment
(mm·year-1) from age 1 to age 4 year old perch
increased substantially with increasing 3-year-mean summer water
temperature and decreased similarly with an increase in 3-year-mean
relative density (Fig. 5a & 5b). The combined length increment (age 1
to 4 year) for Lake Vaggatem and Lake Skrukkebukta perch was
significantly related to temperature and density in a linear regression
model (p=0.004, adj-R2=0.28), increasing by 8.5 mm per
degree centigrade of temperature increment (t=2.481 on 31 d.f., p=0.019)
and decreased by 6.8 mm per 10 CPUE increment (t=-3.806 on 31 d.f.,
p=0.001) (Appendix Table S16). In addition, there was a difference in
intercept between the lakes, where the length increment was larger in
Lake Vaggatem compared to Lake Skrukkebukta (Appendix Table S16).
However, for the individual age groups, the effect of water temperature
and relative density on length increment varied. For the youngest age
group (1 year old) there was no significant change in length increment
(mm·year-1) with either increasing summer water
temperature or relative density of perch (Fig. 4, Appendix: Fig. S7,
Table S17 & S18). For all the other juvenile age groups (2 to 4 year
old), length increment (mm·year-1) increased
significantly with increasing summer water temperature in both lakes,
whereas only in Lake Vaggatem length increment decreased significantly
with relative density of perch (Fig. 4, Appendix: Fig. S6-S10, Table
S19-S24) (See Supplementary information for more detailed description of
results).