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Author Topic: Sockeye salmon adult populations in widespread decline  (Read 3523 times)

aquapaloosa

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Sockeye salmon adult populations in widespread decline
« on: July 03, 2012, 04:00:07 PM »

Sockeye salmon spawning on the rivers and streams of Washington state, British Columbia and southeastern Alaska have been producing fewer and fewer adults over the last six decades, a new study suggests.

http://www.cbc.ca/news/canada/british-columbia/story/2012/07/03/sockeye-salmon-productivity.html

I would have posted this in one of the other threads but it was pointed out to me that it is hijacking, at least when I do it anyways. ???
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skaha

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Re: Sockeye salmon adult populations in widespread decline
« Reply #1 on: July 03, 2012, 04:25:24 PM »

--I would really like to see some comparative studies of Sockeye and kokanee populations.. in particular where they share spawn and early rearing.
--It seems stream spawning kokanee such as those from Okanagan Lake are similarly in decline...
--Skaha soon to have sockeye returning.

--Skaha and Okanagan would be excellent candidates for comparative studies.
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dnibbles

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Re: Sockeye salmon adult populations in widespread decline
« Reply #2 on: July 03, 2012, 04:51:51 PM »

Ummm, yeah. No kidding. Will their next study tell us that southern BC coho productivity has changed a little since the 80's?

Given the broad declines observed, it's fairly clear that the mechanism responsible for this decline occurs in the marine residency stage. Coho and many Fraser Chinook stocks have seen the same decline. I would say that we have seen a uniform decrease in all Fraser salmon productivity, but it seems that different life history variants seem to be performing in a divergent fashion when it comes to marine productivity. For example, the Harrison River sockeye salmon population has seen an off-the-charts increase in productivity over the past decade or so. The common denominator across all populations that have bucked the trend and done well lately seems to be an immediate migration to sea (Harrison sockeye, Shuswap Chinook, Fraser pinks etc).

I think the gist of this is nothing surprising to us: the ocean ain't as friendly as it used to be, so getting more fish back to spawn is key i.e. reduce exploitation rates. IT's dropped on Fraser sockeye from the 80-90% seen in the past, but we still have 40-50% some years, which doesn't work when you're only getting 2 fish back for each spawner.
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skaha

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Re: Sockeye salmon adult populations in widespread decline
« Reply #3 on: July 03, 2012, 09:57:43 PM »

--Yes but.... kokanee population's have also been fluctuating some to near extinction and they don't got to the ocean. We've found different excuses for why this has happened. Maybe it is part of a longer term population cycle
« Last Edit: July 03, 2012, 09:59:35 PM by skaha »
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dnibbles

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Re: Sockeye salmon adult populations in widespread decline
« Reply #4 on: July 07, 2012, 05:59:05 PM »

--Yes but.... kokanee population's have also been fluctuating some to near extinction and they don't got to the ocean. We've found different excuses for why this has happened. Maybe it is part of a longer term population cycle

Sorry, I'm not familiar with kokanee population dynamics in BC, so can't really comment too much.

What I can comment on is that if the mechanisms responsible for kokanee and sockeye population productivity were the same, we would expect to see declining freshwater productivity for sockeye as well. IN the systems that are assessed, the opposite has been observed in recent years. This continues to point to something in the marine environment that is responsible for declining productivity in sockeye.

Once again, I don't know much about kokanee populations and productivity. In my experience, spawning habitat for kokanee and sockeye in systems that they co-inhabit differs somewhat. Rearing capacity of the nursery lake would be a definite concern. It's interesting to note that gene exchange between the two life histories occurs, as demonstrated in the "re-anadromization" of the Alouette kokanee/sockeye stock. Introduced sockeye fry in hanging lakes in the Stikine system has also resulted in residual kokanee populations, indicating that life history is not genetically hardwired in these animals.
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skaha

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Re: Sockeye salmon adult populations in widespread decline
« Reply #5 on: July 08, 2012, 10:25:36 AM »

--I have no doubt there are significant issues in the open ocean phase and that it is difficult to analyze. One benefit of a comparative study would be the elimination of the ocean phase in the kokanee population.  By studying similarities and differences we may be able to isolate causes of fluctuation that are not related to the ocean phase. If we intend to interfere it is most likely we could affect spawn and early rearing habitat to a greater extent than the ocean.

--Wood lake near kelowna touted just last year as the best kokanee fishery in Canada today hardly any kokanee.
--Is it the trait of this schooling fish that makes it susceptible to being significantly affected by single events.
   
   
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dnibbles

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Re: Sockeye salmon adult populations in widespread decline
« Reply #6 on: July 10, 2012, 07:15:36 PM »

--I have no doubt there are significant issues in the open ocean phase and that it is difficult to analyze. One benefit of a comparative study would be the elimination of the ocean phase in the kokanee population.  By studying similarities and differences we may be able to isolate causes of fluctuation that are not related to the ocean phase. If we intend to interfere it is most likely we could affect spawn and early rearing habitat to a greater extent than the ocean.

--Wood lake near kelowna touted just last year as the best kokanee fishery in Canada today hardly any kokanee.
--Is it the trait of this schooling fish that makes it susceptible to being significantly affected by single events.
   
   

I agree, a comparative study would be interesting. Biggest problem: kokanee aren't worth anything commercially, so no one would play for this study.

Cyclical fluctuations in kokanee populations (much like the Adams) may possibly be responsible for this Wood Lake phenomenon?
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