Survival of the smallest

[popriveter]

For some time now, I've had a theory that could be a million miles off base.

Here goes:

If you want to breed a species to bring out a certain trait (we'll use small dogs as an example), you breed the littlest ones from each generation and remove the big ones from the blood line. Eventually, a wolf has been bred into a chihuahua.

If larger, faster growing sunfish are the easiest to catch (because they have to eat more), we will catch them. They taste so good that we will eat them.

If the largest, fastest-growing members of a species are consistently caught and removed from the breeding population over generations, eventually, what remains could be a fish who is genetically programmed to grow more slowly and cap off at a smaller size.

This would create a stunted sunfish population like we see in the TC Metro.

Has anyone seen studies, articles addressing this question?

I have read many articles on fish stunting and none that I've seen deal with the idea that these conditions produce a competitive advantage for genetically smaller panfish.

Might we need to consider reclaiming some small lakes and introducing a larger strain bluegill?

[mainbutter]

Has anyone seen studies, articles addressing this question?

A bit of googling on this exact subject sometime last year resulted in me coming across a referenced study on the exact thing. Basically, in as little as 3 generations of removing the top.. 5%? 15%? (I forget the exact reported number, but it was something close) largest fish from an aquarium effectively caused significant tendencies toward slower growth rates and smaller fish.

[popriveter]

BTW- I should mention that I support eating moderately sized sunfish and releasing the bulls, but I say "we" including all fishermen. They are called panfish, after all, because they end up in the pan. Also, I won't ever fault anyone who harvests and eats fish within their legal rights.

[goblueM]

there is considerable academic work on this subject

i dont have the reference off the top of my head, but channel cats in an exploited fishery actually started reaching sexual maturity at much earlier ages (coincidentally, just below the minimum length limit...)

some other papers...

http://departments.oxy.edu/biology/gnorth/fishsizeevolution.pdf and http://rspb.royalsocietypublishing.org/content/276/1664/2015.full

(ocean fishery)

http://www.pnas.org/content/104/40/15799.full.pdf (northern pike)

if you're so inclined, you could probably find a lot more (look for some of their referenced papers)

but i gotta get stuff done before the football game in 30 mins!

[popriveter]

The MN DNR basically explains that it could be A- overpopulation (the big fish we've eaten gets replaced by 2 small ones and there isn't enough forage for them to grow as big and fast as she did)or B-bad conditions for growth (not enough predation, too much weed cover protecting runts, etc.)

I'd like to follow some links and read some articles about this subject if any of you are able to share something you found insightful.

Thanks

P.S. I wrote this, then broke off to watch the game before sending so I'll follow up on any existing links if they're already there.

[Dale_Gribble]

Well i might not be a biologist or anything but this is my main theory (simplified). Bigger fish eat bigger things, if theres not as many big things for them to eat they have to eat more smaller things. Smaller fish happen to be faster, giving an advantage to smaller fish catching smaller things. This causes in increase in the passing of the "small" gene from generation to generation. Pretty much natural selection. As far as fixing a stunted population by introducing an unstunted strain wouldnt solve the problem as the pop. was stunted from a lack of sustainable forage for the larger fish and an abundance of forage for smaller fish. And one last thing, the average angler isnt pulling up 9" sunnies or 12" crappies, i think sometimes people forget this and over estimate the dent we can put in an average lake (notice i said average lake).

[Jack Peterson]

Oh yeah, this is definitely common.

Take some of the lakes up north for example. I can't remember which ones, but I'm thinking in the Crow Wing chain.

A certain lake was full of large bluegills. It was fished out over a couple years, because the fish were so plentiful and large. Nowadays, all of the bluegills only get up to about a 1/2lb. This is getting more common.

Take out the big bluegills, and the result is: a ton of smaller bluegills, and not-so-good fishing!

Just release the big bulls. You can pull out the females, but make sure you leave in the males, because there are plenty of females to breed.

[popriveter]

While reading the studies GoBlueM posted, I was struck by how quickly this change can take place.

I wonder if regulations and education will ever be able to successfully bring sunfish sizes around the metro back to what they were 25 years ago when my dad and I could catch limits of 8 inchers a couple times a year.

It also makes me wonder how the Wisconsin lakes I occasionally visit manage to produce large sunfish with the intense pressure they get. 2 winters ago, I went fishing on a lake near New Richmond with a buddy. He set up his house in a cluster of 10+ houses. We caught 2 or 3 big sunfish and 2 or 3 crappies. By the time we packed up, all the other portable houses were gone and the ice was scattered with 8 inch sunnies and 10 inch crappies. Apparently, the other fishermen hadn't caught enough to bother filleting, so they threw the fish on the ice and left. We collected them all and put them to good use. Ended up with about 20 sunfish and a dozen or so crappies.

I have to think this approach to harvest is likely to turn lakes like this straight into runt factories.

Sad.

[Chode2235]

There was an article in National Geographic, and I think it even made it into the politics section that detailed this trend occuring in mountain sheep.

Since hunters were constantly shooting the biggest rams the overall size of the species was diminishing.

[T.S128]

this post thread is kinda dead but oh well... the other day in my fish population and ecology class my professor was just talking about stuff like this. there are two types of bluegills. the big bulls we all want to catch and then the small males known as sneakers.they are called sneakers because since they selected for a small size and cant fertilize a whole batch of eggs from a female without being chased away by a big bull they literally sneak to the spawn site and fertilze portion of the eggs. the sneakers grow faster and reach sexual maturity at and earlier age then the big ones.

Fishing for bull bluegills when they are on their beds also reduces chances of the offspring to live beacause the fish can not always find its way back to its bed if pulled off. but when people start keeping a large quant. of large males this obviously reduces the population of those type of bluegills. resulting in more and more "sneakers". once a lake has started to lose the big guys and have higher numbers of "sneakers" it will be hard for that lake to produce quaility size males.

This was kind of a long post and maybe nothing new to you guys but i thought it was cool my teacher brought it up in lecture not too long ago. I'm sure if a guy looked he could find numerous scientific articles on topics similar to this.

[OnAFly]

I really wish more people would understand more things like this. Some people just don't understand that they can have an effect on the world around them.

Sounds like a cool class.

[Tom7227]

There are a lot of reports published by the DNR that provide some interesting concepts. They are doctoral type reports and so can get to be a bit dry but with some effort you can read them and at least begin to see the various factors that can have an impact on a lake.

http://www.dnr.state.mn.us/publications/fisheries/investigational_reports.html

[half-dutch]

One of the hidden facts here is that when fishing pressure goes away, it takes about 10 years for the bluegill population to recover its size structure. Sometimes not that long. But that can be destroyed very quickly by overfishing.

The prime bed sites for best fry survival in bluegills go the biggest males, and those are normally in the middle of a spawning colony. Virtually all of the surviving fry from any particular nesting colony come from the center nests. The edge nest have almost complete mortality. So it is natural for the biggest available males to sire most of the next generation providing an almost constant pressure to increasing size in coming generations. Bluegill males tend not to sex out until they can compete with something around the size of those central fish. They don't grow much after that.

Bluegills are not the only Lepomis sunfish with sneaker males either, and by and large the sneakers do not get in far enough to fertilize the bigger male's nests. Sneakers are a backup strategy to get early restoration of reproduction following some sort of catastrophe. In normal populations they have little effect, even in those overfished, since most males sex out normally in every bluegill population, and the sneakers have always been there from well before the first fish hook.

What this fish is very good at is reproduction. Most small nesting males are young. Most real bulls have been juveniles for 6 or 7 years at least. It takes that long and longer in this part of the North Country to grow a true bull. Regardless of what we take out, they have a portion of the population that will reproduce if it is at all possible. Reduce the harvest of the top sizes and the whole size structure shifts up automatically until it reaches the potential of the particular water. There are certainly different genetic potentials for different strains, but harvest and quality of the water involved are far more important limiting issues overall. They work directly on maximum life expectancy which if less than 7 or 8 years cannot produce true bulls regardless of the strain.

[Chode2235]

Not to open the whole can of worms, but why are there not more regulations (closed season, smaller limits) on panfishing?

Heck, I can't even shoot a buck without counting its points to ensure it's got 4, but I can go out and keep a whole bucket of sun fish.

[OnAFly]

I've been beating that drum for years...how about a middle ground...enforcement of our current laws! I've never been checked for limits. I've never seen anyone checked for limits. I guess this is just one guy, but it really seems like there is very little enforcement of laws when it comes to outdoor recreation (littering, limits, behavior).

[Chode2235]

I've been beating that drum for years...how about a middle ground...enforcement of our current laws! I've never been checked for limits. I've never seen anyone checked for limits. I guess this is just one guy, but it really seems like there is very little enforcement of laws when it comes to outdoor recreation (littering, limits, behavior).

But enforcement is expensive. You would have to hire a lot more COs to check limits, so your license would end up being like $250/year.

I think the better way to do this is to instill/build a better selective harvest ethic with panfisherman. Look at the way bass fisherman have done it for the past 30 years, but even the walleye guys are coming around.

Panfish need to be elevated to the level of a sportfish.

How many of you would never keep a 20" walleye, but would throw a 12" crappie in the bucket?

The DNR should work to publish better guidelines around selective harvest, lower limits (one of the better examples of the regs working are the panfish regulations on the Miss. down near Winona), and to not be afraid to try special regulations.

I do think that Panfisherman do have a more important part to play. We need to encourage CPR and selective harvest. We need to start putting more of those bigger fish back, and chastising our buddies when they put a big one in their bucket.

[Scott M]

Good topic. It's one that has been researched and thought of over the years, but the first fish studied are often fish with commercial values and that is not bluegills. Fishing can be a size selection pressure that creates (un)natural selection. In fisheries populations classes, one topic covered is overexploitation. Looking at entire stocks of fish over time can give you an idea of whether overexploitation has happened. Since the pulse of the fishery are the parameters of the stock (reproduction, recruitment, growth, and mortality), you are going to be taking weights, lengths, gender, and deciphering ages for fish through the years to get at those parameters. If you do so, you can find a couple important values. You'll know length at age, you'll know growth, and you'll know when fish are sexually mature by looking at gonads. In exploited stocks of fish, you'll see smaller length at age, slower growth, and earlier sexual maturation. It only makes sense; fish have to compensate for being cropped off at certain sizes by producing succeeding generations earlier and since more fish are crammed into fewer age and size classes, they will grow slower and reach smaller sizes. (This is my one paragraph oversimplification)

This is probably the best bluegill example. Maybe we should start a campaign called "Save the Bulls"

this post thread is kinda dead but oh well... the other day in my fish population and ecology class my professor was just talking about stuff like this. there are two types of bluegills. the big bulls we all want to catch and then the small males known as sneakers.they are called sneakers because since they selected for a small size and cant fertilize a whole batch of eggs from a female without being chased away by a big bull they literally sneak to the spawn site and fertilize portion of the eggs. the sneakers grow faster and reach sexual maturity at and earlier age then the big ones.

Fishing for bull bluegills when they are on their beds also reduces chances of the offspring to live because the fish can not always find its way back to its bed if pulled off. but when people start keeping a large quant. of large males this obviously reduces the population of those type of bluegills. resulting in more and more "sneakers". once a lake has started to lose the big guys and have higher numbers of "sneakers" it will be hard for that lake to produce quaility size males.

This was kind of a long post and maybe nothing new to you guys but i thought it was cool my teacher brought it up in lecture not too long ago. I'm sure if a guy looked he could find numerous scientific articles on topics similar to this.

Gross, M .R. 1982. Sneakers, satellites and parentals : polymorphic

mating strategies in North American sunfishes . Z .Tierpsychol. 60 : 1-26.

[Acemac]

I feel that for something like size limits on pan fish to be passed there needs to be proof that a healty large population helps the walleye fishery. Untill you put the panfish population in comparison with a large game fish I dont think we will see any regulation.

[popriveter]

I hadn't checked back on this thread in quite a while, but I am really happy to read this discussion.

I hope we see some tactical approaches and some mindset changes that lead to the return of the big sunfish in the metro. I fear it is a long time coming. That said, it is encouraging to see that there are fisherman who care enough to learn about it and adjust their personal approach.

My favorite sunfish lake is the little neighborhood lake I grew up fishing. As a kid, we'd keep a ton of nice bluegills from that little lake. It would occasionally winterkill. After one winterkill, it didn't bounce back. The sunfish were puny for 15 years. This has finally changed over the last 5 years. The lake's water clarity management has included use of an aerator and trapping/removal of bullheads and sunfish for several years now. It has very limited fishing pressure. Their are nowhere near as many sunfish as there were 10 years ago, but most sunfish I've caught this winter are 6.5-7 inches. It sure took a long time to get to this point, and I really don't want to see it regress so I will harvest responsibly and won't put out the word, but it is a matter of time before fishing pressure becomes an issue.

I wonder how much impact the "runt removal" approach could have on other small, manageable neighborhood ponds and lakes. Maybe some of the FIN resources would be better spent removing tiny fish to free up forage and spawning grounds rather than stocking moderately sized fish.