Troutbert's question - depletion rates

[Mike]

What is the typical "Stockie Depletion Rate", or "Stockie Removal Rate" on stocked streams?

Suppose 1000 trout are stocked. At the end of Opening Weekend, how many have been removed, and how many are left?

At the end of 1 week?

2 weeks?

3 weeks?

Surely this has been studied.

And how does this compare to the situation on DH areas?

The removal rate from ATW's varies considerably. The older numbers from the early 1990's when there was less C&R generally ranged from thirty to ninety percent in the first nine days of the season, but I believe there were some lower numbers too on small, rural streams.The range, of course, was at least in part related to human population densities...urban, suburban, and rural, as well as public vs private waters, and a host of other variables, and the results influence today's stocking rates in various human population density, width, and recreational use potential classifications of streams. Angler use drives this and that is part of the reason why we continue to do opening day angler use counts in various classes of stocked waters (and we will be out again this year). You may be able to find more up to date numbers in the 2004 or 2005 statewide stocked trout angler use and harvest studies. Inseason stockings were generally harvested at lower rates, which makes perfect sense.

As for DH Areas, the loss during the C&R period in SE Pa (at least 6) was measured by us to be about 6.5 percent per week across a number of waters with various characteristics. That means that there was about a 40 percent loss in the avg 6.5 weeks between the preseason and inseason stocking with no legal harvest. Now a number of DH areas are stocked even earlier in the year than they used to be....up to two weeks earlier so losses between the pre and inseason stocking can be expected to be perhaps fifty percent on average, which makes the frequent blame aimed at poaching being the primary culprit a scape goat if there ever was one. To have that kind of harvest would make harvest obvious to everyone, including conservation officers. And remember, these losses are without the stressful water temps seen later in the C&R season. Once the water temp is consistently over 68 degrees, which is above the thermal optimum, rainbows, for instance, will be lost at up to a 75 to 80 percent rate in a month based on important peer reviewed scientific research published in 2008. When the water warms up, blaming such losses on perceived high harvest, even when some harvest is witnessed, ignores reality.

 

[charliepff]

I have wondered this myself. Last year I was fishing Pohopoco and I talked to a gentleman that fished this section of stream every day. I assumed that he just came thru and released everything. I watched him put every fish he caught on a stringer. He was out of there before I left.

So I though hmm, if this guy did this every day he could, what was it actually doing to that stream?

 

[JackM]

Did he seem hungry?

 

[Maurice]

Mike I would assert that many of those fish missing in the survey have moved to other parts unsurveyed within the Special reg area or moved out of the Special reg areas into open water. This is likely due to stocking rates greater than carrying capacity that the habitat provides where stocked and also stocked trout competition for food once they acclimate especially in larger stream systems.

We see this in our C&R area every year catching fish where we know were not stocked, and noticing larger pods of fish thinning over time.

Its no secret that special reg areas are allocated high stocking rates (although less than waters open to harvest) to provide a higher angler catch rate. Some angler mortality exists I am sure but its not like we find dead fish everywhere...or even anywhere. I am sure if that were the case people would be talking about it. Even single fish found dead. It is not the case. And I pretty sure that the predators would not get them all before being seen.

Fish move...I am not suggesting that the stocking rates are too great, only that they don't stay where you put them all the time. Also keep in mind that stocking rates have been reduced by the F&BC in Special Reg areas so I would find that 40% number suspect today.

Smaller systems I can see having a greater impact from angler mortality with heavy angler use and even predation. Still they are utilized multiple times by anglers until they expire from poor handling or thermal stress.

The same would hold true in the waters under general regulation if they were not subject to harvest thinning them.

When you do a residency study, how often do you select streams wider than 10 meters? Smaller streams have defined holding areas separated by stretches of thin sometimes long riffles that contain the fish for longer periods until harvested unless they have issues with residency of course.

 

[brookieaddict]

I thnk Charlie described stocking depletion to the nines.

 

[Mike]

Maurice,

Surveys were done well into or near the end of the C&R portion of the spring season. That would have given the fish plenty of time to move away from stocking points and fully occupy available habitat.

Half of the streams were greater than 10 m in avg width and half were less.

I see how you could interpret my response to mean that I thought the spring losses during the C&R season were only due to mortality since that is what troutbert was asking about. While my response looks as though that's what I was talking about, in my mind I was considering all forms of residency problems...delayed hooking mortality, movement out of the DH Areas, predation, disease, and a little poaching .

I reviewed the DH Area stocking rates in my region as a result of you comment. The DH Areas on Metro and Urban streams receive a lower stocking rate than adjacent standard ATW sections, but that is not the case in Suburban classified streams, nor do I believe that to be the case on Rural classified streams (no rural DH Areas in my region).

Higher stocking rates could result in more fish movement due to competition, but that has not been obvious in the great amount of trout residency work that we have done for a number of years that you are more familiar with.

 

[charliepff]

I hope he was hungry. I really wanted to see how many fish he had when he left. Its amazing when there is no WCO around what games people play.