Physical and chemical temporal variations in two spawning areas with contrasted sedimentation dynamics and preliminary results on the early life survival of brown trout (Salmo trutta).
F. Massa et al., Physical and chemical temporal variations in two spawning areas with contrasted sedimentation dynamics and preliminary results on the early life survival of brown trout (Salmo trutta)., B FR PECHE, (350-51), 1998, pp. 359-376
Citations number
36
Categorie Soggetti
Aquatic Sciences
Journal title
BULLETIN FRANCAIS DE LA PECHE ET DE LA PISCICULTURE
The effects of fines and water quality on incubating salmonid embryos were
studied in two tributaries of the river Oir (Normandy, France) with differe
nt fish populations. Brown trout are very abundant in la Roche stream and t
heir density is low in le Moulinet stream. We collected suspended and depos
ited sediments circulating within and sealing the substrate of two reproduc
tive areas every 8 to 15 days in 1996 and 1997. Incubators were buried in t
he streambed to estimate the survival from egg to fry in 1996, and from fer
tilization to hatching and from hatching to emergence in 1997. The characte
ristics of the interstitial water (oxygen, pH, nitrates, nitrites and ammon
ia) were measured once a week in 1997. This was performed with sampling tub
es buried in the substratum and with a sample collected in each incubator a
t hatching time.
Preliminary results indicated that the amount of sediment in the spawning a
rea was higher in la Roche stream during the incubation period. The particl
e size distribution was mainly sandy while it was silty in le Moulinet stre
am. No survivors were collected in fry traps at emergence in 1996 and betwe
en 0 and 11% (mean : 3.3%) were found in 1997 in le Moulinet stream. The su
rvival in one fry trap was 20% in 1996 in la Roche stream, between 0 and 23
% in 1997 (mean: 7.7%). The hatching-to-emergence survival was high in the
two rivers (83.6 and 82.3%), with no rain falling during this period. Disso
lved oxygen concentration of the interstitial water was significantly lower
in le Moulinet stream (P = 0.01) during the second part of the incubation
period while it remained quite high in la Roche stream (minimum value of 5
mg/l). Nitrate concentration is significantly different from that in the su
rface water (P = 0.01) in le Moulinet stream and equivalent in la Roche str
eam. Concentrations of nitrites and ammonia were low in the interstitial wa
ter of the two streams (maximum values : 12.9 mu g/l N-NO2 and 240 mu g/l N
-NH3 in le Moulinet stream, 11.4 mu g/l N-NO2 and 1.4 mu g/l N-NH3 in la Ro
che stream). The higher mortalities observed in le Moulinet stream could be
caused by a synergism of unfavourable factors such as low concentrations o
f oxygen and nitrites.