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White Bass Die-off

I know this is not new news by any means, but I have heard a bunch of chatter and rumors still floating around.  So, as I often do, start with the news release:

Lake Maloney white bass die-off not caused by disease

LINCOLN, Neb. – The die-off of white bass May 26 at Lake Maloney was not the result of any infectious diseases, according to the Nebraska Game and Parks Commission. The cause can be attributed to the fish being concentrated in a localized area of the lake, stress due to spawning and a brief period of poor water quality.

Samples were collected and submitted to a fish health laboratory following the die-off. Results from tissue samples indicated several possible causes, but no single cause could be isolated.

The samples indicated poor water quality could have been a contributing factor in the die-off. The white bass were spawning over an extended time this year due to the unusual weather during their normal spawning period. This would result in the fish expending more energy over a prolonged time, making them more susceptible to any additional stressors, such as poor water quality.

Rocky Hoffman photo, NEBRASKAland Magazine

Now let me offer some comments:  First of all, yes, it took awhile to get results back from the diagnostic lab.  There are only a handful of places in the country that specialize in this type of work, so when you send samples in, sometimes it takes some time to get results.  Ain’t no government conspiracy, ain’t no one not doing their job, were not any broken promises, that is just the way it is.

Secondly, I commented a couple of times this spring that we had more reports of fish die-offs than usual.  Now, when I say that it implies that we often have reports of at least some dead fish from waters around the state every year in late spring.  This year it seemed to be more than usual and we suspect that the cold spring followed by a rapid warm-up was part of the reason for that.  Coming out of the winter and on into spring fish can be stressed and wild temperature swings like we can see in Nebraska can add to that stress.  Furthermore, annual spawning rituals are another stressor for fish.  Then some poor water quality, maybe for only a short amount of time, and at some point stress upon stress finally results in a die-off.  Any one stressor by itself probably would not even have been noticed, but add it all together at just the right time and some fish died.

Putting that in perspective, yes, some white bass in Lake Maloney died this spring.  So what?

From a biological perspective, natural mortality occurs in every fish population, every year, all the time.  Depending on the species and year, that natural mortality can be significant, maybe approaching 50% or more.  That is a fact of life, and death, in the wild.  No, those fish do not get to go home to someone’s frying pan, but there is no waste in nature and those populations always experience natural mortality.  What is more important is that fish survived, in fact the vast majority of the population.  They were biting then, are biting now.

It is not unusual that there is no “smoking gun”.  I know everyone always assumes there is some pollutant or some evil cause when dead fish are observed, but most of the time it is not like that at all!  In this case it was an accumulation of stressors that resulted in a die-off.  In many cases we never know for sure the exact cause of die-offs.  We may have a very good idea of what caused a fish kill, but unless conditions are documented at the time the fish start dying, unless samples are taken as soon as they start dying, it is impossible to know for sure.  In my days working in a field office I checked out a fish kill or three, and can count on one hand the times there was one thing, event, or person that was responsible.  Most of the time, natural events or a series of natural events were the cause.

Lastly, poor water quality, at least for a short period, was a factor in the Lake Maloney white bass die-off.  Again, just because gill tissue examination indicated that was a factor, do not assume that there was some horrible pollution event.  That may not have been the case at all.  Tissue analysis indicated that the fish had experienced poor water quality, it did NOT indicate what was the poor water quality.  Now, this is only speculation, we have not been able to go back and document exactly what happened, but it may have been something as simple as some extra sediment or trash coming down the canal into Lake Maloney for a short period of time.  White bass congregate in the inlet area and would have been right in something like that for a short period if that is what occurred.  It may not have been a big deal and by the time the water reached the rest of the reservoir, it may not have even been noticeable.  Because of the location of the white bass at that time, they may have been the only fish exposed enough to cause tissue damage and eventually a die-off.


About daryl bauer

Daryl is a lifelong resident of Nebraska (except for a couple of years spent going to graduate school in South Dakota). He has been employed as a fisheries biologist for the Nebraska Game and Parks Commission for 25 years, and his current tour of duty is as the fisheries outreach program manager. Daryl loves to share his educational knowledge and is an avid multi-species angler. He holds more than 120 Nebraska Master Angler Awards for 14 different species and holds more than 30 In-Fisherman Master Angler Awards for eight different species. He loves to talk fishing and answer questions about fishing in Nebraska, be sure to check out his blog at outdoornebraska.org.

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