quote:
Originally posted by cuttlefish
Sager1 wrote;
quote:
This channel was maintained in the summer of 2007, so it was in its worst state in the fall of 2006 which was the time when the 2008 stock were eggs. Was this 1.5 km spawning channel a death trap for returning adults in the fall of 2006?
FYI;
DFO estimated 2006 Glendale adult pink returns = 182,000
DFO estimated Glendale juvenile out-migration, spring 2007 (after severe high water conditions and before maintenance) = 7,694,454 juvenile pinks
DFO estimated 2007 Glendale adult pink returns = 264,000
DFO estimated Glendale juvenile out-migration, spring 2008 (with normal water conditions and after maintenance) = 4,585,434 juvenile pinks
DFO estimated 2008 Glendale adult pink returns = 18,000 (and counting?)
Thanks for the work digging these data out, cuttlefish.
When you compare the 2006 returning adult #'s with 2008's (i.e. 182,000 verses 18,000) - it's apparent that the 2008 even year broodstock is only 10% of the 2006 #'s.
In other words, we lost 90% of the run, somehow.
If you then compare the smolt output from 2006 even-year broodstock that outmigrated in spring/summer 2007, with the 2007 adults and 2008 smolts -
1/ each female of the 91,000-strong 2006 even-year broodstock contributed 84 juveniles to the outmigrating #s (on average, assuming a 50/50 male/female ratio), for a total juvenile outmigration of 7,694,454 juvenile pinks.
2/ while the 132,000-strong 2007 odd-year broodstock females contributed an average of 35 juveniles each for a total juvenile outmigration of 4,585,434 juvenile pinks. This is after the "
channel was maintained in the summer of 2007, so it was in its worst state in the fall of 2006 which was the time when the 2008 stock were eggs" as sauger stated above.
If you went back until the first salmon through the Glendale spawing channel - the #'s would be more informative - and you could follow trendlines and upper limits of the channels capacity (as expressed as # smolts released per female) through time.
But, even though DFO built a spawning channel 2.6 km upstream of the mouth to enhance the pink salmon run, way back in 1987 - the Glendale Creek juvenile out-migration has been enumerated by mark recapture of out-migrating fry using a rotary screw trap (RST) only since 2003, and in 2004 the enumeration project did not operate. The 2005 and 2006 RST programs experienced significant trap efficiency issues, compromising the ability of the program to produce abundance estimates. Due to those issues, information from 2003, 2005 and 2006 can only provide a relative index of production as well as timing information.
So unfortunately, we don't have much data to look at the density-dependent capacity of the spawning channel - but it does seem that the 2006/2007 overwintering eggs that came back this year had a higher in-stream survival rate than the eggs overwintered during 2007/2008 when one compares smolts produced per female spawner - as I did above (84 for 2006/2007 verses 35 for 2007/2008
AFTER gravel cleaning).
The suggestion that the 1.5 km spawning channel was "
a death trap for returning adults in the fall of 2006" appears unsupported.
However, what we do know is that at least 7,694,454 juvenile pinks escaped their natal stream (i.e. the Glendale spawning channel)
in spring of 2007; and that run would be expected to return this fall, 2008.
Even if we assume something like a 2% marine survival (which is a little on the low side, but more "normal" in the past few years), we would expect something like 154,000 pinks to return this year. Instead we got something like 18,000, or only 12% of what would be expected.
The ocean survival rates for pinks in Alaska is normally something like 1.2-3.2%, but the 2002 ocean survival rate was 9.7%. We got a 0.2% marine survival rate for the Glendale River this year.
I would very strongly suggest that the data indicates that the problem is marine survival for outmigrating juvenile pinks, although one would want to index interception from all sources of marine fisheries to compare between years.
It's my understanding that the commercial fleet caught reduced #s of returning pinks this year - definitely not a 9-fold increase in exploitation rates that might be an alternative explanation for the interception.
So, the suggestion that the : "
1.5 km spawning channel a death trap for returning adults in the fall of 2006" seems highly improbable.
Okay then, what are the most likely alternative suggestions for a large decrease in marine survival rates for outmigrating juvenile salmon?
Answers:
1/ Global warming effects,
2/ increased predation, and/or
3/ impacts from fish farms.
What's the most likely?
the effect of #1 also effects #2, where warming water may affect not only food availability, but also allows more predators, like mackerel, hake or other more southern-based stocks to invade more notherly waters.
This effect could be determined by comparing marine survival rates of more southern stocks (like the Broughtons) to those of:
1/ other southern stocks, and then
2/ comparing southern stocks to northern stocks (like northern BC and Alaska).
In other words, the Broughton's decreases in smolt marine survival would echo and be similar to other southern stocks; and on average - southern stocks would all be affected the same way when compared to northern stocks.
I'm not sure if this is true. Does anyone have any data on this?
If it were effects from fish farms - then only the Broughton #s would show such dramatic effects.
It would take a bit of digging - but I think we could figure it out.
If we do get the data - I'll bet It's likely a combination of all 3 effects, with the Broughton being affected more than other areas.
