Spring Fish Kills

A lot of fish agency staff would like to have that proverbial nickel for every phone call they get about dead fish in the spring. Consultants get this too, and one can pretty much count on a couple of calls a week about dead fish in late May and June, but sometimes right after ice out. There are lots of things that can kill fish, including disease, angling mortality, toxic substances, low oxygen, and high temperatures, but the vast majority of fish-kills boil down to two main influences: low oxygen under the ice and spawning stress in late spring.

First, consider what defines a fish-kill. Two dead fish washing up on shore doesn’t really qualify; most agencies apply some number like 50 to a species or 100 to multiple species. It would be very wasteful to investigate every dead fish that shows up. If 50 fish (or whatever reasonable threshold is applied) of a species can be found at once, that is considered to represent some kind of event. Likewise, if 100 fish of multiple species are found in a short time span, that suggests something more than typical die off. So please don’t get on the phone to your fish agency or consultant when 5 dead sunnies float to shore. By all means, take a lap around the lake and see if this is a widespread phenomenon, in which case a call may be in order, but don’t panic over a few dead fish.

So if we do find enough dead fish to raise an alarm, what might this mean? The first conclusion that many jump to is that there is something undesirable in the water and fish are dying from it. Well, that may be true, but even if so, that doesn’t mean people will die from it if they go in the water, but that is a leap that many people make. If dead fish are plentiful after the ice goes out, it probably means that oxygen got too low and less healthy fish died. This could be one species that lives in the affected area (catfish on the bottom come to mind), or it could be multiple species that coincide in an isolated area (a shallow bay where thick ice met the bottom off shore and prevented them from leaving). These winter fish-kills may not be detected until the ice goes out, but the fish did not likely die after ice-out.

The other, and far more common cause of spring fish-kills is spawning mortality. Many species, most notably perch and sunfish, spawn in shallow areas in the spring. Perch tend to be earlier spawners, and the water is colder and better oxygenated, so they are less likely than sunfish to experience stress while spawning. Sunfish, on the other hand, start spawning in May in much of New England and may continue to do so well into summer. They make nests in shallow water subject to fluctuations in oxygen and temperature within and among days. They don’t eat but they do defend the nests against other fish. The energy balance just doesn’t work out in some cases, and some fish die. If we have extremely variable weather, the stress is often greater.

If a June fish-kill is one species, all of similar size, most commonly 5-6 inch sunfish, you can pretty much count on it being spawning mortality. If the kill involves multiple species or a wide range of sizes, then there might be something worth reporting. It should be noted that the timing of fish-kills in late spring often coincides with a period of herbicide application, leading to another leap to a conclusion that is rarely justified. Over 20 years of fish-kill investigation in Massachusetts, covering hundreds of investigated events, only a handful were linked to herbicides and these were almost always a function of low oxygen created by dying vegetation; toxicity to fish from properly applied herbicides is very, very rare.

Spring fish-kill

Two Main Plant Types

Plant taxonomy aside, there are really two main plant types when we are considering management: annuals and perennials. At this point all those whose eyes glaze over when the Latin genus names start rolling out should be paying attention, and gardeners and home landscapers probably already get it. Much of the decision about what to do rests on whether a plant reappears annually from seeds or other resting stages (propagules) or comes back from root stalks or stems (or never really dies back in winter). Perennial plants are easier to deal with (just like in your garden or lawn); if you kill the plant, it won’t return from its vegetative parts. For annuals, however, killing the plant just buys time; seeds, winter buds, turions, and other structures germinate and form new plants, usually in the following spring. Management strategies therefore have to consider whether the target plants are annuals or perennials, when they produce propagules, and when growth begins.

If one is applying drawdown, it can be effective on perennial plants like the milfoils, but will have little impact on annuals like naiad or most pondweeds. In fact, drawdown often stimulates propagule germination, so a shift from perennials to annuals can be expected over a period of years with continued annual drawdown.

If one is using herbicides, killing the plant before it can drop seeds is essential to eventually gaining control over an annual, but the seed bank may be large enough to allow recovery for years to come. If a contact herbicide is used, the root system of a perennial is usually unharmed and will allow plant regeneration. Systemic herbicides, which move throughout the plant and are intended to kill it all, can provide more lasting results with perennials, but are more expensive than contact herbicides and may be a waste of money for annual plant control.

Benthic barriers kill nearly all plants over which they are placed, but if the barrier is removed, propagules from annual plants are likely to sprout. Hand harvesting practitioners know that it is essential to get the whole plant out, roots included, if a perennial species is to be controlled by that means. Dredging may be the only all-purpose tool for rooted plants, removing the plant and the seed bank, but at a very high cost with a lot of permitting, so we don’t see this approach used much.

Some plants apply a mix of perennial and annual strategies, making them harder to manage. Bigleaf pondweed produces seeds but does not die back completely in most winters and survives many drawdowns and herbicide treatments. This is a native species in New England and is not a major nuisance plant in most cases, but it has created problems for swimming in some lakes. Many perennials do produce seeds, but viability tends to be low; they don’t depend on these for annual persistence, but it does mean that removing a stand of a perennial plant may not be a one-time job.

So be sure to know which plants apply which strategies when considering control; success may depend upon it.

Curlyleaf pondweed, an annual  

Eurasian water milfoil, a perennial

Invasive Species Statistics

Invasive species cost the USA over $120 billion annually, considering both management expenses and losses due to lack of management. The USA has experienced invasions by over 4000 plant species and 2300 animal species. About half of all pest species in the USA are exotic species, with nurseries, mail order, and the aquarium trade leading the way in new introductions. Just recently a shipment of an invasive snail not yet known in the USA was intercepted on its way to Hartford, CT. These are not trivial numbers.

We know about the impacts to agriculture and lake recreation, but often we get resistance to management from regulatory or private groups concerned over non-target impacts. This may be a valid concern in some cases, but doing nothing also has impacts on non-target species. About 30% of endangered species in the USA got on that list, at least in part, due to invasive species impacts. About 27 of 40 fish that have become extinct over the last century were eliminated by invasive species. After development, invasive species is the largest cause of loss of biodiversity. Doing anything represents risk to some component of an aquatic ecosystem, but so does doing nothing, and this needs to be recognized to get balanced decisions when considering possible management options.

Invasive species experts encourage managers to treat invasions like we do communicable diseases in medicine. Key steps include quarantine, assessment of damage, consideration of treatment options, and implementation of rapid response, rehabilitation, or maintenance. Prevention is important to avoid invasion in the first place or prevent re-infestation, but won’t reverse an invasion in progress.

Variable water milfoil

Zebra mussels

Celebrate Lakes Appreciation Month by telling us about your favorite

Whether it’s memories of idyllic summers spent in a cabin by the lake, learning how to swim or water ski, or morning coffee on the dock in your backyard we all have experiences we savor about our favorite lake. We’d love to hear about your favorite and what makes it so special.  Not only are those reflections fun to read about, but by sharing those experiences with decision makers, groups like NEC-NALMS and our national organization NALMS, can help make the importance of protecting those critical resources more apparent.

So why not leave us a comment to tell us about your favorite and what makes it so special?!


Where Drinking Water Comes From

Drinking water comes from the same places as all other water, it just tends to get treated differently to become potable supply. Treatment is required if specific source water conditions are not met. The risks from even natural sources of contamination (e.g., birds, wildlife, erosion) are substantial enough to necessitate treatment in most cases. Yet there is general recognition that drinking water sources need protection, even if that protection is not always provided. A study by the Nature Conservancy revealed that on average about 37% of the land in drinking water supply watersheds is protected from human–derived contamination sources. The other 63% is mostly in private ownership with varying degrees of development (8% on average) and agriculture (15% on average). There is geographic variation, with water supplies for west coast cities having a greater proportion of protected land than for eastern cities, and with northern New England having less developed lands but more agriculture than southern New England. Each case is to some extent unique, leading to differences in the level of treatment necessary.

About 85% of the population of the USA gets its water from public supplies, a percentage that has increased over decades from around 70%. About two thirds of that water is surface supply, a value that has been declining for years from a high of about three quarters. The remainder of the potable supply comes from wells, which have increased in use over the years. This is interesting in that public water supplies are fairly tightly controlled by law and regulation, and many wells are part of public supplies, but private well supplies experience minimal regulatory control. This suggests that an increasing portion of the population is less protected against water quality threats, although it is also true that water from wells is usually of acceptable quality.

About a decade ago 77% of surveyed people did not know where their drinking water came from. That is a scary statistic that suggests a low level of interest in this critical resource. Such lack of knowledge, and presumably concern, is very disappointing but is also consistent with the limited public support for water resource management. Education may not turn everyone into cooperating supporters of better land and water management, but it is a safe assumption that we won’t get more enlightened policy or greater support without such education.

The Breakdown of Water Use

As a society, we use water for drinking, washing, agriculture, industry, landscape watering, and carrying wastes. Overall, agriculture uses about two thirds of all the consumptive use water, but this varies quite a lot across the USA and is less in New England. Thermal cooling and power supply are also major uses of water, exceeding agriculture, but are generally non-consumptive (nearly all the water is put back into the system from which it came). Public supply water, used in residential, commercial and some industrial operations, accounts for about 11% of the total consumed; most of that is used for irrigating ornamental landscapes. Inside the house, water is used for drinking and cooking, but much more is used in bathtubs, washing machines, and toilets.

There is certainly variability over geographic areas, but most of the northern USA has a consumptive use of between 70,000 and 110,000 gallons per person per year. Arid southern areas can use as much as 200,000 gallons per person per day, but most of the difference is landscape watering. If a person used 5 gallons per day for drinking, cooking and washing, all uses where having very high water quality is important, that would equate to 1825 gallons per year, less than 2% of total consumptive use.

This raises some interesting questions. Should we be applying the same high level of treatment to meet stringent standards for the vast majority of water used in ways where that treatment is essentially wasted? The answer appears to be yes, but only because it all arrives at our homes in the same distribution system. Should we be pushing so hard for water conservation in the home when it represents such a small portion of water used? A yes answer is more philosophically satisfying than practical. If irrigation is the dominant use, why is so little effort expended on conservation of that use and so much attention paid to minor uses like bottled water? The answer may be that we have less apparent control, but there is technology to improve irrigation efficiency and we could do without some crops at some times of year to avoid all that water use in arid areas.

A truly comprehensive water policy at federal and state levels should demonstrate a clear understanding of how much water is used for what purpose and apply proper technology and restrictions to conserve a valued resource while recognizing economic limits. We should be pursuing multiple distribution systems that can carry water of the appropriate quality for corresponding uses. Landscape watering needs to be cut by a lot, or even eliminated. Irrigation water conservation should be a top priority. We have a long way to go to reach a sound water management position.

Irrigated cropland.