Documenting en route mortality and carcass sampling
With the help of local residents with deep-time knowledge of the Koyukuk
River, we surveyed approximately 250 km via jet boat, beginning at the
village of Hughes (66.05 N, -154.28 W) and traveling downstream to the
community of Huslia (65.69 N, -156.38 W). While traveling we counted the
number of carcasses floating in the river and those that were clearly
visible along sandbars and shore banks. On an ad hoc basis and as time
allowed, we stopped and surveyed along the river banks where we,i ) counted the number of carcasses along approximately 0.5 km
upstream and downstream of the landing site and noted characteristics of
carcasses including external signs of scavenging or disease (e.g. fungal
growth on fins or gills), ii ) recorded the sex and maturation
status of dead fish confirmed through internal examination, iii )
recorded water temperature and dissolved oxygen (mg/L) using a handheld
YSI PRO 2030 model multimeter, and iv ) measured the body length
of carcasses to the nearest millimeter between the middle of the eye and
fork of the tail. Due to decomposition of the tail on 36 individuals,
length was measured between the middle of the eye and the hypural
flexure and adjusted to mid-eye fork length using the equation derived
from the data (r2= 0.92)\(:\)
\begin{equation}
\ {\text{\ \ }\ \text{MEF}}_{\text{est}}=1.00*\text{MEH}_{\text{obs}}+52.5\nonumber \\
\end{equation}Where MEFÂest is the estimated middle eye to fork (mm)
and MEHobs is the observed middle eye to hypural
measurement (mm).