H
handee
Guest
quote:Originally posted by agentaqua
Claire's assertion that: "sockeye migrating past the Discovery Islands are much larger than the threshold risk." is complete bunk</u> - NO salmon (including adults) are "much larger than the threshold risk".
We went over (in detail) how to assess that risk all through this thread, but that risk depends upon the size (weight) of the host fish, and the number of motile lice on that fish.
In fact, Johnson, Blaylock, Elphick, and Hyatt found that in 1990, huge numbers of returning adult sockeye salmon were killed by sea lice and the associated lesions due to delays in getting-up the Sproat River in Alberni Inlet.
Here's the citation, and the abstract:
Can. J. Fish. Aquat. Sci. 53(12): 2888–2897 (1996) S.C. Johnson, R.B. Blaylock, J. Elphick, and K.D. Hyatt. Disease induced by the sea louse ((Lepeophteirus salmonis)) (Copepoda: Caligidae) in wild sockeye salmon (Oncorhynchus nerka) stocks of Alberni Inlet, British Columbia
Abstract: The occurrence of the marine ectoparasitic copepod Lepeophtheirus salmonis and the prevalence of lesions caused
by its feeding activities were monitored on sockeye salmon (Oncorhynchus nerka) adults returning to the Sproat and Stamp
rivers through Alberni Inlet, British Columbia, in 1990 and 1992#150;1993. All sockeye examined were infected with L. salmonis
and had higher intensities of infection than previously reported. The presence of high numbers of early developmental stages
of L. salmonis suggests a high rate of infection for sockeye in coastal waters. Lesions attributable to L. salmonis ranged from
minor skin discoloration to large open lesions that exposed the musculature. In 1990, when escapement into these river
systems was delayed, sockeye holding in the inlet developed severe lesions and suffered high mortalities. High percentages of
fish with open lesions entered both river systems in 1990, but few fish with open lesions were observed on the spawning
grounds, suggesting additional prespawning mortality. In 1992 and 1993, when escapement patterns were more normal than in
1990, the severity of lesions owing to L. salmonis was reduced and no mortalities were observed. Throughout the study, fish
in the Sproat River escapement had more severe lesions than those in the Stamp River escapement.
Only a complete idiot would have made the statement Backman did about sockeye juvies being past the size that lice can damage them, as well as his other assertion that there is: "scant evidence that sea lice can cause population level declines of salmon".
silly agent, you got all confused again about cause and effect. you always had trouble with correlation vs causation, but this one too seems to cause you trouble.
ok was it the lice killing the salmon or were the high lice numbers a symptom of crowding, high salinity, high density, low DO, stress etc? When you see a moribund fish with lice on it, did the lice cause the morbidity or did the lice attach as a result of the fish's decline in health?
Well we dont have to guess. It is obviously the latter. Fron Simon Jone's we KNOW that the most vulnerable salmon, pinks under 0.3 grams, if healthy, in labs, can only succumb to death by sea lice if exposed to mega doses of sea lice at concentrations several magnitudes of order above any levels found in nature.
Phew, one less thing to worry about. The sea lice on the Sproat and Stamp salmon did not CAUSE the adult fish to die, they flourished on the fish BECAUSE the fish were dying. They were dying BECAUSEthey were close to spawning and there was no access to freshwater due to lack of rain.
Wet sidewalks do NOT cause it to rain.