This week's storm-related macroinvertebrate drift

[Mike]

Trap netting Blue Marsh Lake this week through the storm and all of the high water (lake rose 4-5 ft above recreational pool) revealed something that is probably seldom seen with respect to Ephemerellids (mayflies, that include sulphers) during floods. As my graduate advisor used to say, you learn a lot when most other biologists are not crazy enough to be out sampling. Nets set in the lake about 0.3-0.6 mi downstream from the mouth of Spring Ck, a Berks Co limestoner, had been set in the middle of the storm and fished overnight as the waters rose in creeks and in receiving lakes. The next morning as the nets were being lifted into the boat to remove the entrapped fish we noticed that the boat was covered with many hundreds of Ephemerellids that had been shaken from the netting. In over thirty years of trap netting lakes we have never seen this before. We always net at this time of the year and frequently at Blue Marsh during this period, but it is unusual to be netting during near-flood conditions. Given these experiences, it is highly unlikely that these nymphs came from the lake. Rather, they most likely became drift as Spring Creek and other small tribs became bank full and overflowed their banks. The timing may also have been critical in the life cycle of these insects as they were large in size and could have been in their final stage of development as a nymph. Floods at critical times such as a few weeks before a large "hatch" may be one of the reasons why anglers claim that a particular hatch was especially poor in comparison to other years on the same stream. Substantial numbers of macroinvertebrates may be transported downstream from the coldwater environment into a warmwater environment, either a lake or a warmwater stretch of a stream.

We also found a number of Tipulid larvae (cranefly) on the nets and most catfish caught were just gorged full (distended belles) of earthworms as noted when they "hurled" in the holding tub.

 

[Fishidiot]

Fascinating.
We often wonder and speculate here on this forum about downstream fish movement during floods but I had never heard of something like this: a large influx of nymphs from a trib into a lake due to high water. Mayflies certainly hatch off lakes - wonder if these ones will manage to complete their cycle(?). I suspect more of this macro drift during floods occurs than we realize and is likely just a natural adaptation to dispersal, much like upstream flight swarm during hatches.
And the ole adage about fishing with worms - or San Juan Worms - after a storm has long been seen effective by old timers. And the catties seem to agree. The number of nightcrawlers I saw just on parking lots the other day during the deluge was tremendous and similar numbers of 'em in waterways must have been an enormous protein boost to multiple fish species.

 

[outsider]

Very interesting Mike, but it does not surprise me that insects are scoured from their habitat during floods. People underestimate the power of moving water. I kind of doubt they came from the lake, knowing the temps, lack of moving water with good oxygen content, and the bottom structure of Blue Marsh Lake. Not good habitat for Eephemerellids in my opinion.

 

[geebee]

This is one other reason why inlets are good places to fish on lakes.

I'm sure fish fry were swept down too.

 

[Chaz]

Great stuff Mike, I'd be near certain the the mayflies are from the stream, because the lakes just don't have the same species as streams. Keep up the good work.