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Saturday, May 26, 2012

May 23rd - Hatchery Salmon

There are distinguishable differences between wild and hatchery salmon such as size, condition of health and behavior. This prompted me ask what is the impact from hatchery fish on the wild populations and just how many hatchery fish are we (people around the world) releasing every year?

As it turns out the hatchery fish may actually be hindering wild salmon recovery according to an article by the State of the Salmon.  A study by Zhivotovsky et al. 2012 shows how hatchery chum in Russia are beginning to replace wild chum within native streams.  Another study by Brenner et al. 2012, Grant 2012 reports that hatchery pink salmon are beginning to show up much higher within streams then ever before and that this has caused high hatchery spawning populations.  However, these studies do not conclusively prove that hatcheries have a negative impact but that there is potential.

Below is a diagram depicting where within the Northern Pacific hatchery salmon are being released, in what numbers and what species per region.


The website I referenced and where this graph is located is: http://www.stateofthesalmon.org/hatcheries/#study

Wednesday, May 23, 2012

May 21 - Shiner Perch

As we approach the end of May we begin to see fish who use the estuary intermittently as a breeding ground.   Among the fish who stay briefly in the estuary the shiner perch has shown up in the thousands, along the main estuary a typical seine will net several dozen.  The shiner perch prefer warm temperatures (14C) and very shallow water for breeding.



An interesting fact about shiner perch is that stress due to beach seining can cause them to give birth in the net. They produce live young and will give birth to tens of juvenile perch that are essentially fully functional fish.

 File:Cymatogaster aggregata female.jpg
http://en.wikipedia.org/wiki/File:Cymatogaster_aggregata_female.jpg

Sunday, May 13, 2012

May 9th - Coho Runs

It is very interesting to see the different salmonid life history patterns.  As the last of the chum leave the estuary we are seeing a surge of Chinook and coho sub-yearlings, as well as yearling coho (wild and marked).  The wild yearling coho predominately leave the the estuary beginning in April through June, while the sub-yearlings will stay within the estuary.

The below graph shows fork lengths of coho hatchery and wild yearlings, as well as sub-yearlings.  A "marked" salmon is a hatchery fish "marked" by the removal of the adipose fin.  The hatchery salmon are released in April-May and by June have already left the estuary and surrounding rivers.   A interesting point to make is the difference in behavior between wild and hatchery coho. The hatchery coho immediately leave the estuary whereas the wild coho remain through June.  This illustrates that while the fish are genetically similar their behavior and responses to environmental stimuli are different then their wild counterparts.

 
Graph obtained with permission from the WFC 2011 Annual Report