Thursday, January 7, 2010

What Happens When You Stop Planting Hatchery Fish?

Wild fish get alot more productive. Hatchery fish have lower fitness when spawning in the wild. When they spawn with wild individuals they reduce the overall productivity of the wild population. This is true even for resident trout, check out this redd count data following ODFWs 1995 decision to stop planting trout in the Metolius. The number of redds has increased about 5 fold since they stopped stocking the river. Figure from the NFS Dechutes River Steward Tom Davis.

6 comments:

okeanos said...

i really wish the ODFW would apply this type of data and knowledge- and manage our fisheries/waters in a responsible manner...
keep up the good work NFS!

the nutman said...

what was the drop from in 2006? just wondering but this is an interesting report

Osprey said...

Populations tend to fluctuate naturally. depending on environmental conditions the number of fish that survive to spawning age in a given cohort can go up or down. In resident populations where only freshwater conditions regulate survival it tends to be more consistent however in anadromous stocks abundance can fluctuate dramatically depending on ocean survival. What is instructive is that this population is resident and abundance hasn't dipped anywhere near the pre 1995 levels since the program was discontinued.

Jon said...

What was the count effort like each year? I found that redd count data, and spawner count data is usually with a high margin for error since count effort is inconsistent and comes with a degree of subjectivity in determining what is and isn't a redd.

Osprey said...

Data was collected by ODFW I believe. there is definitely error associated with using redd count data as an index of population abundance but it is certainly not enough to explain a more than 5 fold increase in redds observed after stock was discontinued. Especially since the pattern of increased abundance has more or less persisted since then.

Jon said...

I once found in some DFO analysis you could overlay DFO funding and subsequent count effort with the redd and spawner counts and they correlated quite closely! However, I agree, the data is way too significant. I'm curious to see if others have found similar results after removal of monoculture hatchery fish.