2.4.1 | Calculating variables
The infection level (prevalence, intensity, and mean intensity) was
calculated following Bush et al.’s (1997) method. The estimated charr
abundance in each section was calculated using the removal method
implemented in the program CAPTURE (White et al., 1978; available
at http://www.mbr-pwrc.usgs.gov/software/index.html). The host density
in each section was calculated from estimated charr abundance, and each
section area (m2) calculated from mean stream width
and section length (i.e. 25 m or 11 m). For the accurate evaluation of
the host body condition, we used the residual index (Jakob et
al., 1996): we calculated residual distances of individual points from
the regression of ln (BW) with ln (FL). As fish body condition is
assumed to be different among seasons in salmonids (e.g. Morita et
al., 2011), we calculated residuals in each capture session (i.e. June
2020, July 2020, October 2020, and July 2021). We also calculated the
growth rate (mm / day) for each host individual for each
capture-recapture interval.