Drought - and a bit about Fisheries Management

If you have been paying the least bit of attention to the news, you know that the Colorado River and the states dependent upon the Colorado for their water are in a world of hurt. States dependent upon Colorado River water are being forced to reduce the amount of water they they use. While the first cuts are relatively minor - though Arizona may disagree with that assessment - more reductions are extremely likely without a good bit of luck.

U.S. Drought Monitor from mid-August (2022) - note that severe and prolonged drought in the Southwestern U.S.

And Europe is in a historic drought. The story I caught on public radio as I was driving back from Avalanche the other day (as you read this, now a few weeks ago) was about how Germany was importing coal to replace Russian natural gas but the Rhine River was so low that the ships were only carrying a quarter of their typical loads. The European heat wave and drought is exceedingly widespread and responsible for more than 1,500 deaths.

European drought map from mid-August.

Of course there have always been droughts - some of us remember back to the 1988-89 drought here in the Midwest - more on that later. And of course, climate change is making our weather more variable. Here in Wisconsin, we have seen an increase in flooding but also have had short-term droughts.

On our way to New Mexico's San Juan River - a tailwater fishery in an arid landscape.

Those of you that travel West to fish have likely had to deal with warm streams and restrictions on them ranging from total closures to "hoot owl" restrictions which allow only morning fishing. The lack of snow and snow melt is part of the reason for these restrictions as are increasing air temperatures and at least short-term droughts. And it it mostly occurring due to agricultural withdrawals that reduce stream discharge and make it easier for the sun to warm the water. But with more precipitation, those rather uniquely allocated water rights are more easily fulfilled. While Montana has drown the most attention for their hoot owl restrictions, most western states have had localized restrictions.

Lower Wisconsin River sandbars are extensive, particularly when the river is low.

Just a month or so ago, our trip to the Lower Wisconsin River was altered by a few much needed inches of rain in north-central Wisconsin. The river went from about 4,000 cubic feet - where navigation requires a lot of attention - to about 9,000 cubic feet where most of the sandbars are largely underwater (and navigation is still tough - but a bit easier).

Some of the effects of the historic 2018 floods are shallower and wider streams which are more prone to warming up the stream.

Floods and droughts have always happened but they are both happening more often and more severely in recent decades. Much of it is due to our alteration of the atmosphere but it is also due to our increasing population and all that comes with it - greater groundwater withdrawal, increased impervious surfaces and row crops. And one of the most interesting pieces of the puzzle are that drought make floods more severe. Dry ground does not allow hard rainfalls to soak in and without abundant vegetation to slow the overland flow of water; floods can be more drastic. We have seen this effect in the Las Vegas and Dallas areas this summer.

Late-1980's Drought

Raise your hand if you remember the drought in the late 1980's. I do but I was not yet a fly angler - other than messing around with my dad's fly rod to catch Creek Chubs in the creek by our house. However, I was playing baseball and what a crazy year it was. Brown as far as the eye could see. And a grounder down the line or a line drive to the gap was at least a triple if not an in the park home run. There was nothing in the outfield to slow a ball down. My own fly angling started on the heels of this historic drought in 1991 when I moved to Platteville for college and had a ton of streams nearby.

In response to the prolonged drought, the Wisconsin DNR required anglers to catch and release all trout in parts of the state. Wisconsin Trout's Winter 1990 issue's article, "Drought Creates Havoc with Inland Trout Fishery" is full of information about the drought and the data and quotes from fisheries managers are quite ominous. Jim Talley from the WDNR Black River Falls office estimated that Brook Trout were down 60-70%. Dave Vetrano then out of the La Crosse office saw great declines in category II and III streams while the better streams seemed to hang on - albeit with some drought effects. Gene Van Dyke, then out of the Dodgeville office, witnessed similar effects on category II and III streams and estimated that entire year classes were lost. Further north, Alan Huber noted that streams in the Wausau area were as low as he had seen in 17 years and spawning everywhere was poor. And Russ Heizer in the Marinette area showed up to 90% reductions in young-of-the-year trout and older fish to be down up to 50%.

From the Winter 1990 Wisconsin Trout newsletter about the early season closure.

The drought was having drastic effects, particularly on category II and II streams. The WDNR categorizes streams as category I - sufficient natural reproduction so that trout reach carrying capacity, category II - streams with natural reproduction but stocking may be required, and category III where there is no natural reproduction and trout are only present due to stocking. There are many reports of streams that once held trout in northern Wisconsin that have seen a total loss of their trout fisheries due to the 1980's drought. Additionally, the other effect noted by the biologists were that entire year classes from 1988 and 1989 were almost entirely missing.

Year class strength is an important idea in fisheries management. Although anglers do not always like hearing it, fish populations are quite variable and year-to-year fluctuations are to be expected. Each species is affected differently by abiotic conditions - floods, drought, timing of flood, barriers, etc. - depending upon their life history. Some fishes are flood spawners - like Northern Pike (Esox lucius) and Yellow Perch (Perca flavescens) - and their strong year classes coincide with spring floods whereas others - trout and Smallmouth Bass (Micropterus dolomieu) may have their nests destroyed by floods. Brook and Brown Trout are fall spawners so their hatch is largely depending upon winter water temperatures and floods that occur between late-October and March or April when they emerge from the gravel. Then, upon emerging, they face threats from a lack of food, floods and drought, predators, and other biotic and abiotic factors. Life as a young trout is tough and a relatively small percentage will ever make to to adulthood.

Particular year classes often drive fisheries and the loss of a couple of successive year class can be enough to crash a fishery. For Wisconsin, maybe the most famous and talked / written about example are Walleye (Sander vitreus) in the Lake Winnebago chain. A single strong year class can sustain a fishery for several years. Most stream trout in Wisconsin only live two or three years thus a loss of two consecutive year classes can be pretty significant.

From the Winter 1990 Wisconsin Trout newsletter

The effects of drought are several fold and often quite long-lived. Bob Hunt's quote was quite prophetic, many would argue that some streams never came back from the 1980's drought. Streams hardest hit were likely those streams which were not in connected cold-water stream networks. For example, isolated Brook Trout streams that are tributaries to warm-water rivers are more likely to have faced extirpation compared to a similar stream that occurs in a network of coldwater streams. For more about the importance of connectivity, I wrote four posts earlier this year (links to the first of the four posts).

I don't know - it seemed like time for a fish photo.

In addition to the effects on year classes, low water creates greater stream warming, though some streams are less affected as it means a greater proportion of the stream's water is from groundwater springs. However, most streams are negatively effected, particularly if the drought is long-lived. And high stream temperatures mean that the water can cold less dissolved oxygen leading to oxygen stress for trout, species that require more oxygen than most fishes. And lastly, habitat becomes more limiting in low water. This means that the pools are not as deep and trout are more susceptible to Great Blue Herons and there are fewer stream margins, the habitat used by most young-of-the-year trout.

Fisheries Management and Drought

The articles above provide a bit of the response by the Wisconsin DNR to a sustained drought in Wisconsin. And as mentioned above, individual stream closures and hoot owl restrictions are becoming more common in Western states. There really is no one-size-fits-all response to the issue. And there probably needs to be some flexibility for both long-term and short-term droughts. The effects of short-term droughts - the ones that last but a part of the season - may be mitigated by education. Since the significant late-1980's drought, we have had shorter and more localized droughts. In most years, a number of Driftless streams near me - the West Fork and the Kickapoo River itself, the North Fork of the Bad Axe, and some other larger streams - warm to a point where people should not be fishing them. Educating anglers about how they are unlikely to be successful as the streams warm and that they will cause increased mortality are probably more effective than closures and hoot owl restrictions. Western waters are fewer and it is easier for them to monitor temperatures on their streams. Additionally, much of their temperature issues are related to irrigation which reduces flow only in certain streams. What works out West is less likely to work here.

West Fork of the Kickapoo River was warm in June of 2021 - and this was below a series of riffles. Above that, the temperature was closer to 80F.

Another long-term drought may require more drastic action. However reports on how effective Wisconsin's restrictions were are variable and suggest that the restrictions had a minor effect. Without question, the biggest improvement came with heavy snowpack and increased rains by 1990 and 1991. Without getting too deep into the social and economic impacts, there are significant issues with restrictive regulations. Economically, Wisconsin is in a much different places than Western destination fisheries that face summer restrictions. A few closed streams would probably have little economic effect here as we have an abundance of streams. However the social impacts of placing regulations such as a temporary closure, catch and release only, and / or limiting anglers to artificial only is likely to be even more divisive than it was in the late-1980's and early-1990's.

Turbid water following a small August 2022 flood event.

While floods get most of the attention, I would suggest that the effects of drought are probably greater and longer lived. In fact you hear from many trout anglers that a good scouring flood is helpful as it cleans the spawning gravel of the fine sediments that limit the redd's success. An August or September flood is likely to have less impact that one when egg and alevins are still in their redds. Droughts, on the other hand, tend to occur over larger time frames and are almost always associated with the summer. Late summer can be one of the most physiologically stressful times for stream trout.

Drought Monitors

• United States

• Europe