Murder Mystery!!!

[chipmunk]

OK so technically it might not count as murder but it's defiantly a mystery: 

I have caught bait in the local creeks with a minnow trap for many years.  I almost never have to buy bait.   So a few years ago my grandfather buys a farm to retire to.  I see an opportunity in all the small cattle ponds on the property so I load them up with fathead minnows.  Those lil things reproduce like crazy so I soon had ponds full of bait ready to go.  My go to way to get them out; the minnow trap.  For the first year everything went awesome, but here recently I have started to have a confusing pattern develop.  When I check my traps, I find ONLY DEAD MINNOWS INSIDE!!!   I only leave the traps out for a few hours at a time so I know it's nothing like they were trapped to long.  They don't look eaten so I know nothing tried to eat them.  The only thing that is wrong is that they are dead. 

Anyone have any ideas?  I'm stumped! 

[DDZ]

Chipmonk

My Family has had a pond for 40 years. When we were kids we stocked the pond with Bluegills, crapie, perch and bass. The fish thrived in the pond for many years, untill a couple of years ago. One day all the fish in the pond were dead. We did a lot of research as to why this happened. The only thing that we came up with is lack of oxygen. Its something that can happen on hot summer days with cloud cover, and its caused by dying plant life.  When sunlight is blocked by snow and ice cover or clouds, photosynthesis is reduced, which is a biologic process during which plant life releases oxygen. Plant and leaf litter decay robs oxygen from the water.

There was always at differant times algie on the pond and we would kill it with a diluted coper-sulfate and water mixture. This never had killed a fish. A few years ago a plant life called duck weed was introduced to the pond. Its a lime green plant life that compleatly covers the pond. It was introduced from chicken manure pellets being spread on a field near the pond. We think that the duck weed contributed to the lack of oxygen in the pond that killed the fish. We are in the process of killing the duck weed which is kind of costly.

Maybe your ponds have a low amount of oxygen, and when the minnows are confined to a trap thier movement is liminted, in turn are not able to get enough oxygen from the water by moveing around.  I'm not sure if this is the cause, just a guess. If you wanted to know for sure you could place a small aerator under your trap. If they still come up dead, its something else thats killing them.   

[Chilachuck]

One of the local farmers used to let Boy Scouts camp at his cattle pond and we drank out of it and fished in it. Then he started fertilizing the fields around the pond and water started tasting horrible. The number of fish in the pond also dropped.

That might not be your problem, but you might check the cooperative extension service about getting the pond water checked. There might be something in there that's not good for cattle, either. (That means lighter beef carcasses and less milk.)

DDZ might be onto something. Try dropping the traps at different depths and see if you can catch some alive. The ponds might be stratifying with hypoxic zones so you still have some live minnows, but they have to look in the hypoxic zone for food. You are probably going to be out of minnows soon if that's the case.

I've stumbled over different ways to stir the ponds up and equipment you can buy or make to aerate the ponds, but didn't pay any attention to the subject. There's several forums around, both the city people with fancy Koi ponds ($$$$$) and farmers with aquaculture ponds. The more information you take to them, the better the advice you get, faster.

[DDZ]

Chilachuck, We thought about the possiblity of fertilizer causeing the problem, but the field above the pond was fertilized with 10-10-10 etc. ever since the pond was there. The fertilizer never had a negitive effect on the fish. The fertilizer did aid the growth of algie. Untill my relative that farms the field decided he was going to go organic to increase the price of his milk. He started useing chicken pellet manure as fertilizer. We are positive that this introduced the duck weed. Which in turn created the atmosphere for reduced oxygen in the pond.   

[chipmunk]

Low oxygen is my number one thought too.   I'll play with the trap some to see if it can be figured out.  Thing is, one of the ponds has an aerator in it and I still catch dead ones in there.  It is one of those aerators that is just a motor with a prop that throws a ton of water a couple of feet in the air.  Really moves some water.  The other ponds would have aerators too but they are too far from the electric.  It's not feasible.  I played with floating the trap on the surface today and the results seem good - no dead ones so far.  It will take some time to be sure though.   I sometimes catch them fine on the bottom too.

My only other thought is related to the soft muck on the bottom of the pond.  It is so soft that I wonder if the trap is maybe sinking into it some.  Also I seem to catch an oddly high number of tadpoles when I catch dead minnows.  Can't imagine that has anything to do with it though.  I catch tadpoles all the time; even with live minnows.

[outdoorlover]

Maybe the pond has been lacked of oxygen or there is a problem with the water, the best thing you can do now is you should let the water be checked by some specialist I'm pretty sure this will be very useful for you.