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Old March 10th, 2014, 11:50 AM   #1
Fish Manager
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Patagonia Lake Bass Population

I got a call from an angler last week asking about what is going on with the bass population at Patagonia Lake. He said he was seeing changes in the structure of the population since he begin fishing the lake back in the 90's and he was worried about it.

So I found some time to go back into my data and look and although I had never looked at it on such a large scale. Typically I'll only look at the last 3 to 5 years when I'm assessing the current condition of the population. What the anglers question forced me to do was go back over time, in some cases as far back as 1975 and look at this population over what basically amounts to my career (23 years) and then some. I was able to pull data together from the 80's, 90's, 00's and now 10's. What I found was pretty interesting in that what the angler was reporting is actually what the data was saying. He was thinking that he was seeing fewer small bass in the population and he was concerned about what that meant to the population overall. What I found was that he was correct. There are fewer small fish in the population however there are more larger fish in the population.

So why, I'll say right up front that this is just my gut instinct on this and that I don't have hard data to back it up but I believe it is directly related to an increase in the harvest of the these smaller fish stimulated by the reduction/loss of harvest at Pena Blanca and Arivaca due to the mercury advisories against consumption of warm water species.

I believe that the increased harvest has shifted the size structure of the population by reducing the number of smaller bass impacting the prey base meaning that there is an abundance of prey leading to better growth and larger fish.

In the attachment that I have included I have tried to lay it out so everyone can understand it. Hopefully I've done that, but if not I'll be happy to answer questions. Enjoy!
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File Type: pdf patagonia historical bass data.pdf (333.7 KB, 252 views)
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Old March 10th, 2014, 01:27 PM   #2
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Good info Don thanks for taking the time and writing the report. What i find interesting is why 2008 was such a great year or maybe it was 2007 that caused 2008 to be so good.

For what its worth I looked back at the tournament results over the years that Ri and myself ran and the weights are pretty consistent, but 2009 seemed to have the biggest bags and individual fish but over all it was pretty consistent over 6 years. if i have time i will put together all the data i have into a graph and spreadsheet and see what it shows.
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Old March 10th, 2014, 01:48 PM   #3
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Thanks for sharing those findings. I read a similar article about bed fishing for smallies, and they basically said the same thing. Less smaller fish and more larger fish due to the disruption of removing fish from beds during spawning season. I've only been to Patty once, so is it a lake that is easy to bed fish and would that play a decline in the number of smaller fish. This was only mentioned on ultra clear lakes, as most studies indicate that only 20% of the bed fish may get caught. I could see a higher percentage on lakes like Saguro (limited acreage clear water) an possibly see a decline on the number of smaller fish.

With the data you found, which shows there is a decline in smaller fish what sort of actions are you planning to do ensure a healthy population of fish for future generations.

Again thanks, wish we could get that kind of interest from the ones that manage the valley lakes.
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Old March 10th, 2014, 03:13 PM   #4
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Pspence, its going to cycle, that's why I never consider just 1 year. The good and the bad seem to even out over time and give you the best look at it over time. The problems come when the metrics drop and don't come back over time!

2Dogs, I'm not pointing at bed fishing as the cause, I'm pointing at harvest. Anglers that are catching and keeping largemouth bass.

To answer your question though Patagonia is not what I consider a clear lake. I'm not convinced one way or the other on the impacts of bed fishing. I mean consider what you said you've read for a second, only 20% of bed fish are caught, how many of that 20% don't actually spawn? And even if none of them did you still have 80% of the spawning population left unmolested and free to spawn. Those are pretty favorable odds for success and the impact of bed fishing is going to be dependent on the overall condition of the population.

I probably need to be a little clearer on fewer smaller fish in the population. I'm not suggesting there are problems with spawning success or recruitment as I'm not seeing any indication of that at this point, what I'm saying is I believe that harvest is removing what historically was an overabundance of smaller fish leading to a reduction in the impact on prey populations which is making it easier for remaining fish to find prey of the appropriate size leading to better growth.

At this point, what I have to do is keep surveying and keep watching it and as long as it continues on the path it is on and anglers are not complaining and happy there is no need for me to step in.
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Tucson, AZ. 85745
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Old March 10th, 2014, 04:33 PM   #5
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Pspence, its going to cycle, that's why I never consider just 1 year. The good and the bad seem to even out over time and give you the best look at it over time. The problems come when the metrics drop and don't come back over time!

2Dogs, I'm not pointing at bed fishing as the cause, I'm pointing at harvest. Anglers that are catching and keeping largemouth bass.

To answer your question though Patagonia is not what I consider a clear lake. I'm not convinced one way or the other on the impacts of bed fishing. I mean consider what you said you've read for a second, only 20% of bed fish are caught, how many of that 20% don't actually spawn? And even if none of them did you still have 80% of the spawning population left unmolested and free to spawn. Those are pretty favorable odds for success and the impact of bed fishing is going to be dependent on the overall condition of the population.

I probably need to be a little clearer on fewer smaller fish in the population. I'm not suggesting there are problems with spawning success or recruitment as I'm not seeing any indication of that at this point, what I'm saying is I believe that harvest is removing what historically was an overabundance of smaller fish leading to a reduction in the impact on prey populations which is making it easier for remaining fish to find prey of the appropriate size leading to better growth.

At this point, what I have to do is keep surveying and keep watching it and as long as it continues on the path it is on and anglers are not complaining and happy there is no need for me to step in.
Don't believe I said your were pointing a finger at bed fisherman, only asked a question if that could also have an impact. Found your finding almost verbatim as to what was happening due to bed fishing on some ultra clear lakes. For me the bigger the fish the merrier.
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Old March 10th, 2014, 04:57 PM   #6
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Thanks for the info Don. Personally I do believe people are keeping way more than allowed and I have stated that in a previous post. I have nothing against people keeping there share but there are laws and need to be followed. I have also noticed the decline in "smaller" fish, but as far as more bigger fish I agree with Patrick in that they've been about the same if not better in the years leading up to now and hopefully this what I call over harvesting doesn't affect fishing in the future years from now
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Old March 10th, 2014, 05:12 PM   #7
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Also thanks again Don it's good to get this information and to hear back from you
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Old March 11th, 2014, 07:21 AM   #8
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I originally contacted Don and had asked for the fish surveys for the last fifteen or twenty years, which is basically within the time frame that I started fishing Patagonia. I did this, because I do have concerns about the lake, and I just wanted to see if I could see any patterns. I related to him past observations that I wasn't seeing anymore. Basically, the large schools of one pound bass that were always present in the fall. When is the last time, in the fall, that you saw in excess of 100 one pound bass boil on a school of shad, when your boat scattered the school of shad, as you went into the main channel, out of the marina? Or catch one pounders one nearly every cast, off of reed point until you got bored with it. The last time I remeber it was '03 or '04. It also seemed to me that average size of big fish had increased, but it also seemed that there were fewer of them. Don was nice enough to go through the surveys and put together the data.
When looking at the data, you have to remember, this only relates to the ratios of fish size within the population, not the actual number of fish, or total population. I'm not sure if the surveys can quantify the total number of fish or fish per acre. That's a question that I have for you Don. One thing I did notice in the data right away, was how the PSD would spike somewhat, in years following major flood events. To me, the spike indicates a year class failure, which would raise the PSD ratio. The winter floods typically wipe out the weeds, and cattails in the east end of the lake, as well as bring in large amounts of silt. '05 seemed to me to have one of the most significant impacts on the lake, others have relayed the same to me. After '05, an area I referred to as the "hog pen", basically a stretch of shore line approximately a hundred yards long, was now 2 - 3 shallower at full pool and a large section of cattails were gone. I haven't caught a big fish or hardly any fish from that area since. Typically, you'll also see the lake would return to a more balanced population, the year after the spike. You'll also notice how the PSD and the Quality lines basically mirror themselves, until '10 where the trend in the PSD is upward and Quality and Memorable is downward, which I think is somewhat of a concern. Is the lack of smaller fish or poor year classes having having an effect on the lake?
I really don't think you can point your finger at one particular thing. There are just too many variables to consider, flooding, low water, water quality, available nutrients,an over population of shad (yes too many shad can be a bad thing), over harvest, bed fishing and etc.
Thanks again Don, for putting this together.
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Old March 11th, 2014, 08:24 AM   #9
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2Dogs, Sorry for the confusion, Yes, as you have read you can have the same impacts through bed fishing and disruption of the spawn. Your achieving the same results which is a reduction in small bass which is leading to a reduction in competition, which means small bass are having an easier time finding plenty of food during the early growth period.

And with fewer fish impacting the prey base, you're also allowing members of the prey base (sunfish at Patagonia) to grow to a larger size which supports the larger individuals in the bass population. The results are an abundance of larger prey items which provides the larger fish with an easier opportunity to maintain their body condition and continue to grow.

BStephans, I can't speak to whether or not there is over harvest occurring as I have no data on that. I will say that there are always that group of people that will bend and break the laws so it does occur but at what level I don't know.

DanW, There are ways to get the data on fish per acre, total population estimates, etc but not with my current survey methods.

Tying the data back to major flood events is something I have not done but I did think about that a lot when working on this and I did mention that when a lot of the changes begin happening was about the time we begin to see major weather changes. I just need to find the time to dig up the weather data.

A spike in PSD values is actually a strong year class not a failed year class. Keep in mind a fish that shows up in the PSD value is at least 12 inches long. I don't have age at length data, its something I'm working on now but PSD fish are likely going to be at least 1.5 to 2 years and older. So if you're looking for causation look back further than the previous year.
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Old March 11th, 2014, 10:40 AM   #10
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Ok so i was bored at work and put together some data. Now please take it for what its worth and considered i only had limited data that i have gathered over the years of running some of the tournaments down there. I put together some graphs that i thought could be informative. i did not go crazy and all scientific like Don. i am not trying to prove anything or over ride Don's data.
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File Type: pdf Patagonia Tournament Fish Data.pdf (384.9 KB, 203 views)
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Old March 11th, 2014, 12:24 PM   #11
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Pspence, That's some cool stuff right there! I'm going to have to dive into it a bit more and see what I can make out of it. Any chance I could get all of your raw data?

Also, I'm not trying to prove anything either. I simply want you guys to be informed about what is going on at the lakes you fish and try and help you understand how this all works.
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Old March 11th, 2014, 01:30 PM   #12
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Yeah Don i will send it over by email.
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Old March 11th, 2014, 05:14 PM   #13
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Really quite a blessing to fisherman to have Bio's on the level like you guys have down there. There was a very lengthy post on a forum up here (CO) about a specific Bio and his lack of transperency or feedback to anglers,... the post actually was titled "Our bio's could learn alot from Wayne" referencing Wayne up at lake powel, and all he does for anglers.

You are to be commended as well Don.

You guys are spoiled down there in AZ!
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Old March 11th, 2014, 07:38 PM   #14
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A spike in PSD values is actually a strong year class not a failed year class. Keep in mind a fish that shows up in the PSD value is at least 12 inches long. I don't have age at length data, its something I'm working on now but PSD fish are likely going to be at least 1.5 to 2 years and older. So if you're looking for causation look back further than the previous year.[/QUOTE]

After I posted, and got into my truck and was driving to work, I thought more about what I posted, and realized that I was looking at the data with a preconceived idea. I also assumed that a fish would reach at least 8' by fall of it's first year, which is a bad assumption. Although, with the equation that you are using, it can't be said that a spike in the PSD indicates a strong year class or a poor year class, only that the ratio between the larger and the smaller fish has increased.That equation is driven by the difference between the entire population 8" and over and the population 12" and over. So either an increase of fish twelve and over, or a decrease in fish between 8" and 12" could create the same spike in PSD value. You could double the number of fish in the lake or cut it in half, and as long as the ratio was the same, the PSD value would remain the same. Without real population numbers, it really can't be said that there are fewer small fish in the lake, only that the average size has increased.
I realize lakes are cyclical, and my concerns may be baseless, as I'm sure some of you think they may be. I only raised the question to Don, because I think my observations do have some validity and I really do care about the lake. The one thing that I do know is true, is it takes little ones to grow big ones.
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Old March 14th, 2014, 10:59 AM   #15
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Dan, I'm working on a response to your last post as I get time, I'll be out all next week and won't have time but I will get back to you when I return.

Great conversation so far I hope it's helping!
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