HASTINGS COLLEGE FACULTY LECTURES:
“THE SCIENTIFIC FISHERMAN”
“A Scientific Fisherman?” you say! “An oxymoron, for sure!” But there is a connection: Science, let us say, is a search for the possible (and at least the hoped for) discovery of truth; while a fisherman is one who searches for and possibly finds, hoped for fish. Picture, if you can, a solitary figure huddled in a little row boat, shrouded in the blackness of night and storm, writhing like a Laocoon in the coils of yards and yards of black snake-like hose, pumping black water from a blacker lake into frail looking flasks, bottles, vials, or a silken net, his work lighted occasionally by the feeble flicker of a flashlight or the glare of lightning. A lunatic you say? No! He’s just one of the scientific fisherman, determining factors that may mean more and bigger fish for the followers of Isaak Walton.
Age old is the question, “How are they biting?” More often today, with lake after lake being fished out, the question becomes “Where are they biting?” The accurate answer to this question has become the goal of a new science, the science of increased fish productivity in ponds and lakes, known as “Limnology.”
The foundation and development of this science occurred in Switzerland. Louis Agassiz, not only contributed to “Education,” co-education and the laboratory method of biological teaching, but as an ardent ichthyologist, laid the foundation for Limnology by identifying and studying the habits of fishes, both in his native Switzerland, and later, in his adopted home of Harvard University and the Marine Biological Station, which he founded. However, modern limnological science is based on the work on Lac Liman by another Swiss, Farel, whose experiments took place between 1870 and 1900. Although little was done in this country until the last few years, we cannot overlook the outstanding work of Dr. Stephen A. Forbes, on lakes in the Rockies, or that of Dr. H.B. Ward, formerly of the University of Nebraska, on Lake Michigan, or of Kofoid on the Illinois River. Also both in the past and present tenses, the work of Birge and Juday on the Wisconsin Lakes is important and especially interesting to us because of their studies of thermal stratification and of the penetration of sunlight into water – most important factors in the productivity of any lake or pond, as we shall subsequently see.
The practical significance of limnology, although early recognized by Germany and other European countries, is only now beginning to be appreciated in this country. Or perhaps I should say the need for increased fish production is just beginning to be felt in this country, where the fish population of ponds and lakes have been (until recently) relatively untouched. But with the rapidly decreasing unemployment and the W.P.A. the field of Limnology offers one of the most promising fields for young scientists.
Many are the factors which determine the productivity of a lake (the importance of each factor varying with geographical regions and even with each lake in the region). Consequently, I have chosen to discuss those factors which are common to most Nebraska ponds and lakes, as compared with those Minnesota lakes to which local fisherman migrate with the coming of each new fishing season.
Three things with which any body of water must supply its fish population are adequate breeding grounds, food, and oxygen. But even upon these basic requirements, different fish do not agree. For spawning, most of the common game fish, such as the bass, perch, sunfish, and crappie, scrape out a shallow nest (usually on a sandy bottom) in water two to six feet deep. However, the closely related pike, perch, or walleyed pike requires a stream environment, attaching its eggs to rocks in a stream where the current may keep them thoroughly and constantly aerated, or to rocks in a lake where wave action will accomplish the same purpose. As to food, these fish feed largely near the bottom on insect larvae, while the pike prefers a diet of smaller fish, and the common white fish of the northern lakes lives entirely on plankton – those small invertebrates floating or swimming in the open water. Oxygen requirements are much less variable. A notable exception to this is that unwelcome immigrant, the carp, which actually seems to prefer the low oxygen supply of almost stagnant water. The often reported experiment of Dr. (Ph.D.) Smith on his pet carp, “Ike,” – short for ichthyology – is illustrative of this. Dr. Smith is reported to have reduced the water in which his pet lived every few days, until the carp was perfectly at home in the little moisture of dew on the grass. Early one morning while the carp was out enjoying a dewy sunrise, a sudden shower came up and Ike drowned in a puddle. Such variability of fish requirement gives increased fish production a qualitative as well as a quantitative aspect.
No doubt many of you have heard it said: “That lake looks fishy.” Such a statement may have a sound though unconscious, scientific basis, because plants grow in much the same kind of area as those required by fish for breeding ground. But the relations of plants to fish life are much more far reaching than superficial observation can detect. They are indirectly the source of the fish’s food supply, by virtue of serving as food for the animals which are, in turn, “fish food”; green plants also furnish a large part of the necessary oxygen by releasing oxygen in the process of photosynthesis, by which they get their own food. Consequently, the observation that a body of water has extensive shoal areas with protruding or submerged beds of vegetation where fish may spawn, may rightly lead to the conclusion that its productivity is high.
This plant or photosynthetic zone is limited: first of all by the extent of the firm, but not rocky, bottom containing the necessary mineral salts (particularly phosphates and nitrates) and not being subjected to violent wave or stream action where the plants may become rooted. In most Nebraska lakes and ponds this is not an important factor. In Heartwell Lake, however, and perhaps also in Crystal Lake, when, and if, it becomes a reality, the notable absence of rooted plants caused by frequent violent stream action, is largely responsible for low fish productivity. Contrary to popular belief, the presence of sewage (if not too concentrated) may actually increase the productivity by increasing the phosphorus and nitrogen content of both the water and the bottom soil. Experiments on ponds at Fairport, Iowa, have shown that a one-to-one mixture of sheep manure and superphosphates, or even soy bean meal, used as fertilizers in amounts of five hundred to one thousand pounds per acre have most beneficial effects. No doubt many of the sand-hill lakes, such as Lake Erickson and Pibel Lake would be greatly improved by such fertilization.
Because sunlight is necessary to plants for the manufacture of food, the penetration of sunlight is the second limiting factor. Through the use of photographic plates and more recently the pyrlimnometer developed by Birge and Juday, light has been detected at 15,000 meters in the ocean near the Azores. But it is generally agreed that this light is neither of sufficient intensity nor of the proper quality necessary for plant metabolism. There are reports of green plants growing at depths of nearly 400 feet in Lake Superior, indicating effective penetration of light to that depth. In most small inland waters, however, essential red rays of sunlight penetrate from about sixty feet in relatively clear lakes to less than three feet in muddy streams and ponds. This difference may be attributed in part to the reflection of light by the water, to the absorption of the red rays by substances dissolved or suspended in the water, and/or to the shading of the underlying water by silt and microorganisms either in the upper layers or caught in the surface film. It is not difficult for Nebraskans to appreciate the fact that a large quantity of dust and silt on or in some of the local waters often completely prevents the penetration of adequate light to any appreciable depth. Such conditions, however, are usually temporary (except in years of drought) and in most Nebraska waters the blistering rays of the summer sun are entirely adequate for plant growth. However, this may not be true of these lakes being developed in connection with irrigation projects.
Rather surprising is the fact that one fish, the German carp – that bundle of bones wrapped in skin – is often a most serious menace to the abundant growth of water plants. Like most of our common fish, they are bottom feeders, but unlike the game fish they actually root in the bottom mud, tearing up the plants as they go, denuding the bottom, and so roiling the water that it becomes unfit for other fish life, with the possible exception of the mud cats. Consequently, the scientific fisherman advises against their introduction to waters where they are not now found.
Although the importance of an extensive photosynthetic zone cannot be overlooked, the scientific fisherman points to many lakes with little water vegetation that are productive of many fish—and big fish at that. At the other extreme, he sites lakes with abundant vegetation that produce few fish. Plants, like animals, must use oxygen, if they are not producing it. This obviously occurs at night, or when the red rays of the sunlight cannot penetrate to the plants because of clouds, dust in the surface-film of the water, or silt. Under such conditions abundant vegetation is then, by its own needs, or by the process of decay absorbing oxygen to such an extent as to choke out all fish life. This is most likely to occur in small plant-filled ponds or shallow lakes – particularly in dry years. Such was the case in 1935, when the fish from several small sand-hill lakes had to be seined out by the Nebraska Fish and Game Commission and transported to larger bodies of water.
Moreover, sunlight may have a destructive, as well as a constructive, effect. The ultraviolet rays of the sun at the opposite end of the spectrum from the red, have a definite lethal effect on microorganisms. For this reason, during the bright hours of the day, microscopic animals (which are indirectly the food of the game fish) are noticeably scarce in the upper three feet of open water and surprisingly concentrated at depths from nine to twelve feet. Adaptation to this factor is partially responsible for the perpendicular migration of many fish forms from deep water to the surface, or to shoals, as the sun sinks in the West. One of the most interesting of these migrations is that of the larva of the insect, Corethia, the so-called, “ phantom larva,” which lives in muddy bottom water at depths of eighty feet or more. At sunset, it starts its long wiggle to the surface, and by sunrise it has returned. Why many forms of aquatic life so migrate and what the migration’s practical effect may be are questions which have kept scientific fishermen up nights (myself included), as you may have guessed from the introduction. It is quite probable that fishing, best in early morning and in the evening, may be attributed to this phenomena. If the abundance of plant life or sunlight penetration cannot be taken as an index of productivity, where, then, does the answer to the question lie? Little has been said about the effect of size and depth relationships; less has been said about the production and circulation of oxygen other than its production by plants, and so far as I know, nothing has been mentioned concerning the importance of temperature relationships, although such factors markedly effect all animal life in any body of water. Furthermore, the mere physical nature of water, itself, has marked limnolofical significance when related to the other factors mentioned above.
Of these physical characteristics, density is one of the most important, especially as it is variable with changes in temperature. Ice forms at 0 degrees centigrade, and steam at 100 degrees centigrade; but of principal interest is the unique quality of its having its maximum density, that is, its greatest weight at 4oC (39.2oF). The fact that it becomes progressively lighter as it cools from 4oC to freezing, or as it warms up to the maximum temperatures in summer, is also unique. Closely related to its density is its mobility.
Water is an extremely mobile liquid, even though internal friction does make it viscid. The viscosity varies with the temperature — being about half as viscid at summer temperatures as it is at the freezing point. Since the mixing and stirring of water and the consequent distribution of oxygen is affected by the ability of the wind to move the water (it is quite apparent that the wind is most efficient in the summer and entirely powerless during the period of ice cover in winter). Further importance may be attributed to this phenomenon, when it is realized that wind, by creating violent wave action, not only distributes the oxygen produced by plants, but actually churns atmospheric oxygen into the water. This source of dissolved oxygen is often more than sufficient for all fish needs, and there are records of lakes in which the water actually became supersaturated with oxygen during severe storms. Lakes like Mills Lac, Winnebagoshish, Leech, and Cass Lake in Minnesota, because of their broad expanses of open water, have a rich oxygen supply from wave action. Moreover, winds commonly cause horizontal currents in lakes, sometimes of considerable velocity. A wind of about 10 miles per hour on Lake Okiboji, Iowa, produced a current flowing nearly three miles per hour. On Lake Superior and several of the other large lakes, the velocity of these currents is often nearly 5% of the wind velocity. Such currents, reaching the shore, return down the slope of the basin and set up a circulation throughout all the depths of the lake, thus distributing the warm surface water and oxygen uniformly, and preventing thermal stratification so characteristic of smaller deep lakes. Wind action is relatively unimportant in small lakes and in lakes where there are numerous islands. It is quite possible that the Kingsly Reservoir being developed in connection with the Tri-County Project, because of its relatively broad expanse — not expense — and the velocity of Nebraska winds may be similar in many ways to the famous fishing lakes of Minnesota.
From the foregoing discussion of density and mobility it becomes apparent that one of the most important factors — if not the most important factor of an aquatic environment — is temperature. The heat capacity of water at 15oC is taken as the value of one and the amount of heat necessary to raise one gram of water from 15 to 16oC is the standard calorie, so familiar to many of us! Needless to say, a lake must absorb a vast quantity of heat to raise its temperature 1oC and, likewise, must give off large amounts of heat in cooling its temperature to freezing. Obviously, changes in water temperature are far slower to affect than changes in air temperature.
Another peculiarity of water is the fact that in changing from its liquid form at the freezing point (that is, from 0oC to ice) it must give off a larger amount of heat in melting to the same temperature as that of the liquid surrounding it. To change one gram of ice to water at 0oC requires 80 calories of heat, an amount sufficient to raise the same amount of water 80 degrees. This heat, called “the heat of fusion” is, then, 80 times greater than the specific heat mentioned above.
A third peculiarity of water is its tendency to evaporate, not only in its liquid state, but also as snow or ice. To change to vapor, any of these forms of water requires a large amount of heat. The cooling effect of the evaporation of perspiration is a familiar expression of this phenomenon. Whereas it takes only one calorie of heat to raise a gram of water one degree C, it requires 5.3 calories to evaporate an equal amount of water. From this factor alone, it may rightly be concluded that a lake releases to the atmosphere vast quantities of the heat of fusion, and it is easily understandable why areas near large bodies of water have a much more uniform temperature than do Nebraska prairies! It should also be mentioned that water vapor from evaporation is the source of rainfall, as the advocates of water storage for irrigation point out. It is exceedingly unlikely, however, that the development of a few water storage reservoirs will noticeably increase our annual rainfall.
Dr. Welch, in his book entitled Limnology, has summed up the relationships between heat, water, and atmosphere in a very thought provoking manner: “It is interesting,” he says, “to speculate on the nature of that aquatic world which would have existed if specific heats, the latent heat of fusion and the latent heat of evaporation, were smaller than they are at present, or if density and temperature relations of ice were not as they are presently. Under present circumstances, water in nature is a great storehouse of heat without at the same time becoming a menace to the adjustments of life to temperature as they now exist.”
In the deeper lakes of the temperate zone there occurs a seasonal thermal phenomenon known as “thermal stratification.” A lake need not be over 20 feet deep for this stratification to develop, if protected by high banks or hills from the churning effects of wind, as will be the case of the Plum Creek Reservoir of the Tri-County Project. On the other hand, stratification does not occur in Winnebagoshish and similar lakes, except in their deeper parts, protected by islands from the wind — even though most of them are over 30 feet deep.
A vertical series of temperature readings taken at regular intervals from the lake surface to its bottom before the ice goes out, will show that the water gradually gets slightly warmer until temperatures near 4oC are reached at or near the bottom, at which temperature, water is at its maximum density. Thus, the colder, but lighter, water is on top of the warmer, but heavier, water. Were it not for this peculiarity of water, the colder water would settle to the bottom, until the lake was one huge cake of ice. As spring comes on and the atmosphere warms up, the ice gradually melts away and the surface water temperature rises to 4oC, producing heavier water on top of the lighter underlying water layers. This heavy water sinks, often aided by the winds, and the lighter water rises to the surface. A circulation pattern is thus set in motion, a pattern which continues until the whole lake is homothermous, that is, in possession of a uniform temperature throughout. The water, having a uniform density throughout, can thus circulate from top to bottom with its circulation being greatly aided by any amount of wind. This calendar period is designated as “the Spring Overturn,” and during this time oxygen and all other substances in the water become evenly distributed. Occasionally, when the weather is calm and warms rapidly, the Overturn is only partial and oxygen is distributed only to the upper layers of the water.
As the water continues to warm up, it becomes lighter and lighter and no longer exhibits any tendency to sink. When the surface water becomes 10oC warmer than the deeper water, then only, can wind currents force this oxygenated water into the colder deepwater. Shortly thereafter, stratification comes into existence. Vertical temperature readings will now show a definite layer of warm surface water fifteen to fifty feet deep, depending on the wind action (the temperature decreases gradually until the second layer is reached). This second layer is relatively thin — usually not over fifteen feet thick — and often ten feet or less deep. Throughout the entire layer there takes place a phenomenal drop in temperature — often over 2oC for each foot. Underlying this thermocline is a third layer, the hypolimnion, varying in depth as the depth of the lake varies. The temperature of the water is usually very close to 4oC, even though the surface water may be 20oC or higher and the air temperature 35 to 40oC. Because of the difference in temperatures, there is a corresponding difference in density and the warmer water of the upper layer (the epilimuion) being lighter, will not mix with the heavier water of the thermocline. This effectively stops all circulation from top to bottom, at which time the wind is rendered effective only in the upper layer. At this time, downward currents along the slope of the lake basin encountering the dense water of the thermocline are deflected parallel to the surface with the thermocline constituting a shearing plane. Most of the time the plane is parallel to the surface, but occasionally the wind (which is piling up surface water at one side of the lake) may temporarily tilt the plane.
The date at which definite thermal stratification becomes established varies with the geographical location and various meteorological differences. For instance, in lakes of comparable depths it occurs earlier in Nebraska than in Minnesota (except in western Nebraska, where wind sometimes completely prevents its formation). As the season progresses, the water becomes warmer and warmer and some of this heat is transported to the thermocline layer, decreasing the density of its upper layers, so that it decreases in thickness and approaches the upper level of the hypolimnion, varying in depth from 0 in the shoals to 50 feet in its deeper parts. The same stratification occurs in most deep lakes of the temperate zone and from a superficial study of the contours of the Plum Creek Reservoir, basis will, without doubt occur there. The significance of this condition is far-reaching. Because of the lack of circulation, oxygen is rapidly used-up by the forms living there; the water becomes stagnant; and the fish are forced to move into the surface waters. Although most of the common fish thrive in these warm surface waters, trout are an exception, requiring the low temperatures of deep water. Thermal stratification explains to a large degree their absence from many lakes. Birge has described the conditions most expressively, noting that, “Our typical northern lakes really consist of two lakes, one superimposed on the other: first, the lake above the thermocline, whose temperature is high and whose water is kept in active movement by the wind; and below this, the stagnant mass of water below the thermocline, having lower temperatures in which the products of decomposition are accumulating.”
More significance may attribute to this stagnation when it is remembered that the production of fish food is directly dependant on the area of the productive bottom. The establishment of a stagnant hypolimnion greatly decreases the available bottom area and thereby limits the supply of fish food. One investigator has suggested that one may find the relative productivity of any lake by dividing the volume of its epilimnion by the volume of its hypolimnion. It must be added, here, that even during the stagnation period it is possible for some animals to inhabit the deep areas of the lake. The Corethia larva, mentioned previously, is one of these, but it must make mighty migration into the surface waters to obtain its daily food supply. Also, it is quite well established that some of the fish can make extended journeys into this oxygenless realm, but in so doing they must use oxygen from their swim bladders.
With the advent of Autumn and with it, the cooling of the atmosphere, the water cools until conditions similar to those of the “Spring Overturn” exist. During this “Fall Overturn,” the surface water again sinks to the bottom, taking with it oxygen and thus giving the lake a uniform temperature, density, and chemical composition.
Then comes Winter. A practical immobile ice covers the lakes and ponds; the wind becomes an inconsequential factor; sunlight penetration is reduced to a minimum; and all those factors which have supplied water with oxygen and kept it distributed, become practically nonexistent. Then begins a most critical period for fish known as “the Winter Stagnation Period.” As long as the ice remains clear and uncovered by snow or, in Nebraska, dust, some photosynthesis may continue, but this period is usually relatively short. All forms of life begin to make inroads on the oxygen with which the water became charged during the Fall Overturn. In large lakes, the oxygen supply is usually more than sufficient to care for all needs except as regards wind action. In small bodies of water this stagnation may become very serious. Although chemical activity is reduced to a minimum, fish continue to breathe and the decomposition of dying vegetation continues to require oxygen. As a result in such ponds and lakes, smothering often occurs.
Those of you who have done ice fishing know how fish will often crowd around a hole in the ice simply to get oxygen. Often the thawing ice in the Spring yields up large numbers of fish dead of suffocation. Usually, these are the larger game fish — almost never catfish or carp, unless the lake is shallow or freezes deeply. There have been cases of lakes in which suffocation has killed the entire fish population.
From this discussion of the effect of seasons on the physical and chemical composition of lakes and ponds, two conclusions are obvious: first, that the size of both surface area and average depth of any body of water are of vital importance, not only to general productivity of fishes, but also to various individual fish species; and second, that wind and atmospheric temperature are equally fundamental considerations. To a Nebraskan it is especially encouraging to learn that the wind which harasses us so frequently is a constructive, as well as destructive, force and may actually be the most important factor in making some of the new lakes very productive.
It would seem that the scientific fisherman was a sublime combination of chemist and physicist with biology as a secondary interest, except where plant physiology was involved. In earlier research this was true to a large extent. But it must be recognized that chemical and physical features are easier to determine than biological ones because of the very nature of that unknown force called “Life,” with which the biological deals. Just how much one, or a dozen, tapeworms may effect the health and longevity of a fish no one has yet been able to determine. Neither has anyone yet devised any satisfactory method of determining the relative part played by such voracious fish as the pike and gar pike in preventing overcrowding of the fish population. Biologically inclined Limnologists are at present working on a theory that for each lake there is a total possible productivity which may be determined by weighing (usually after complete desiccation) all the animals of a certain area of bottom and its overlying water. The difficulties of such an undertaking are obvious. Another related theory maintains that the total dissolved and suspended nitrogen compounds limit the total weight of fish which a lake may produce. This would mean that a body of water might be limited to the production of 1,000 pounds of fish, either 1,000 fish, each weighing one pound, or 500 fish, each weighing two pounds. When, and if, these theories are established, the results may be far reaching. Already certain conservation departments are working on this basis seining out undesirable fish such as carp and garpike in order that the body of water may produce its maximum volume of game fish. Recognizing the importance of a proper proportion of aquatic vegetation, this too, is being controlled in many small ponds — particularly in those being created by the W.P.A. as the centers of recreational grounds. Although little can be done in larger lakes to increase productivity, spawning grounds are being carefully guarded.
The value of the scientific fisherman can best be illustrated by the experiences of the Canadian Pacific Railroad a few years ago. As part of a plan to establish a summer resort at a beautiful lake in the Canadian Rockies, time and time again it stocked the lake with trout, but without success. At last, one day a man walked into the office in Winnipeg and offered to make the lake one of the finest trout lakes in the country. He gave his name as, “Bikoff,” told them he was a Russian refugee, and that he had no references. In desperation he was hired, but with the provision that he would receive no remuneration if he failed. After considerable study he became convinced that the only factor lacking was fish food. He had can after can of insect larvae brought in and put into the lake. His conclusion proved correct and the lake is now noted for its fine trout fishing. Needless to say, he needed no further references.
I would close with a word of tribute to two men who will go down in the history of this young branch of science as the outstanding teachers of the age in limnology: Dr. Paul S. Welch of the University of Michigan and Dr. Sam Eddy of the University of Minnesota to both of whom I am indebted for much of the data included in this paper.