Southern Southeast Regional Aquaculture Association, Inc.
Enhancing and Rehabilitating Salmon Production in Southeast Alaska

Research and Evaluation Studies Chum Production Techniques and Returns Spanning over a 20 Year Period

An exhaustive study of SSRAA's production techniques and returns across more than 20 years shows some indicators of how to maximize salmon survival and run strength. 

No production scheme fits all fish.  For some, size does matter, others timing is everything. 

Susan Doherty, SSRAA's assistant manager for research and evaluation, is about three years into a detailed examination of fish production variables and salmon returns.  The statistics go back as far as 1980.  Her analysis of an ocean of data is boiling down to preliminary but striking guidance for the association. 

"Take Neets Bay chums," Doherty said.  "We looked at release weight versus survival for all release sites, summer and fall chums.  Does size have something to do with survival?  The numbers are all over the place,  There's nothing universally striking there."
 

But for one fish, release timing is crucial.  "Some Neets Bay summer chum survival was down when the release weight was greater," she said.  "But we looked at release dates. Survival was about twice as good if we release the smolts before May 1.  Now we have data that tells the production manager that size is a factor, but not to the extent of going past the release date. Neets Bay summer chum survival since 1982 averages 3.7%." 

Neets Bay fall chum, on the other hand return in greater numbers if they leave home at larger sizes.  "Release timing doesn't look like an influence there," said Doherty.  "But fish bigger than 1.5 grams survived about four times better.  That weight was our goal, but we found out how critical it is. Neets Bay fall chum survival since 1980 averages 2%."

Nakat Inlet statistics since 1982 pose puzzles.  Fall chum survive and return at slightly better rates than summer chum.

"Why are fall chum surviving better?" Doherty asked.  "Everywhere else, it's summer chum that survive better.  Some of this just lead to more questions."

Does the timing of Nakat Inlet summer chum releases subject smolts to greater predation?  Is less food available to them than to their fall counterparts?  Releases of summer and fall chum smolts overlap for a matter of days; do dual releases tax the ocean's ability sustain the smolt releases? 

Doherty blended data for summer and fall Nakat chum and found that returns were better for fish released in greater numbers. 

"It doesn't appear to be a carrying-capacity issue, " she said.

Doherty's long-term study also looks at net-pen density.  SSRAA has increased net-pen capacity for years and salmon fry are already getting benefits. 

Chinook culturing variables aren't so easily read, but kings released at 30 grams seem to have an edge.  In 18 years at Whitman Lake, king release sizes have ranged from 20 to 80 grams.

SSRAA is now trying a production wrinkle:  overwintering king fry and coho fry without feed in the raceways and lakes - replicating the their natural "dormant" state. 

"Early indications are that this gives us the best survivals ever," said Doherty.