Where the Fish Are: A Science-Based Guide to Stalking Freshwater Fish - Brossura

Bagur, Daniel

Brossura

ISBN 10: 0071592911 ISBN 13: 9780071592918

Casa editrice: International Marine/Ragged Mountain Press, 2009

Riassunto

More science and less art leads to bigger fish and fewer tales

Most anglers rely on advice from fishing buddies or books by well-known but unscientific anglers. Here is a book that distills the science of fish behavior into easy-to-follow advice on how to catch fish in any situation. Describing how feeding behavior in fish changes in response to fluctuations in dissolved oxygen, turbulence, turbidity, temperature, light, noise, and other factors, Bagur advises you on how to respond, recommending specific flies, baits, rigs and tactics.

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Informazioni sull?autore

Daniel Bagur is a marine and freshwater biologist, an avid angler, and a regular contributor to the international angling press. He works for the UK Fisheries Department, promoting angling, advising on fish behavior, managing habitat restoration projects, and serving as press liaison. He is resident expert on fish behavior for a leading UK fishing magazine, writes regular columns for Canadian and English publications, and has published feature articles in dozens of magazines worldwide, including: Big Game Fishing Journal (US), Boating (US), Canadian Fly Fisher, Fish Alaska, Hawaii Fishing News, New Zealand Fish & Game, Bush & Beach (Australia), Today's Flyfisher (UK), and Angling Times (UK). He served as treasurer for the Institute of Fisheries Management; is an active member of the Marine Conservation Society, Wild Trout Trust, and Trout Unlimited; and serves as Chief Scientist for the Polish ‘save the pike’ campaign.

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WHERE THE FISH ARE

An Angler's Guide to Fish BehaviorBy DANIEL BAGUR

The McGraw-Hill Companies, Inc.

Copyright © 2009 Daniel Bagur
All right reserved.
ISBN: 978-0-07-159291-8

Contents

Chapter One

How Fish Work, Behave, and Think

Fish are highly evolved creatures that have adapted to the aquatic environment physiologically and behaviorally over millions of years. The significant differences between their aquatic and our terrestrial worlds mean that fish are influenced by factors we may not even consider.

Knowledge of fish behavior and physiology is a vital part of an angler's skill set. Understanding how a fish works and what environmental cues fish are likely to be attracted to or repelled by enables an angler to put him- or herself into the fish's world, making every angling decision a little easier and improving the chances of a catch.

Of course, a reasonably complete overview of either fish behavior or anatomy alone would require a textbook in itself. What follows, therefore, is limited to those factors that have the greatest influence on angling.

Breathing and Metabolism

People use lungs to breathe air that, at ground level, has a more or less fixed and steady oxygen content. Fish, on the other hand, experience huge fluctuations in the levels of available oxygen. To make matters more complicated these fluctuations occur over relatively short time periods. These changes are due in part to the relationship between the temperature of water and its ability to hold oxygen. The warmer the water, the less oxygen it can hold.

Freshwater fish experience much higher oxygen fluctuations than their salt-water counterparts because it takes longer to heat or cool a larger volume of water. Smaller bodies of water, such as streams and small lakes, warm up and cool down more rapidly in response to the warming and cooling of the air and land around them.

Fish are well adapted to cope with these natural changes as they occur. Such changes do, however, influence where fish choose to spend their time and when they feed.

Gills

There are two main problems associated with obtaining oxygen from water. First, water contains less oxygen than air, around one-thirtieth as much per unit of volume. Second, water is denser than air. This makes it more difficult for fish to extract oxygen from water than it is for air breathers to extract oxygen from air. Through evolution, fish have gotten around these challenges by increasing the surface area of their respiratory organs and by pumping larger volumes of water over their respiratory surfaces.

A fish's gills are designed to expose as much surface area as possible to passing water, thereby maximizing the exchange of gasses between the fish's blood and the water. Each gill arch is covered by a strip of gill filaments, each filament is folded into a V shape to increase its surface area, and the filaments are covered in folds to further maximize their surface area. The membranes of the gill filaments are very thin, which further aids gas exchange. Species that lead more active lives, such as trout and bass, tend to have a greater number of gill filaments than less active species, providing them with the greater volume of oxygen needed to generate more energy.

As in humans, the red blood cells of fish contain a respiratory pigment called hemoglobin, which enables the blood to transport oxygen. Once the blood has passed through the gills, it is transported through the fish's body, where it provides the organs with their required oxygen.

The surface area of the gills is also used by fish to purge unwanted by-products of respiration from their blood. Carbon dioxide in the blood passes through the gill membranes and is absorbed by the surrounding water, while oxygen from the surrounding water passes through the membranes and is absorbed by the blood.

Water is pumped over the gills in two ways. Fish gulp a mouthful of water and then pump it into their gill chambers, where it passes over the gill filaments and back out into the environment. Some of the more active fish species, like bass and salmonids (including salmon, trout, char, and grayling), supplement this mechanism with another called ram ventilation. While swimming slowly or hovering at rest, fish pump water over their gills as described, but when swimming at speed, they open their mouths and allow water to "ram" through their gills, increasing the volume of oxygen available to the blood. The gill structure of fish. The rakers filter out debris and keep it from damaging the filaments, where gas exchange between the fish's blood and the water occurs.

Metabolism

Wind strips heat from terrestrial animals in cold conditions much faster than cold air alone. In the same way, mammals swimming in fast-flowing water will lose heat faster than those in still water. For fish, this is not a problem, because fish are cold-blooded—that is, their body temperature rises and falls to remain in equilibrium with the surrounding water. This means that, unlike birds and mammals, fish do not need to expend energy maintaining their body temperature in a cold environment. This energy saving is highly advantageous, particularly in waters where temperatures fluctuate regularly.

During cold weather, fish simply reduce their activity levels. Since they do not need to waste energy maintaining their body temperature, they are able to feed less and keep still until temperatures return to more favorable levels. Because of this, fish seek out places that don't force them to waste energy during the winter. This often means moving into deeper water, where they can hide from predators and avoid currents that exist higher in the water column.

This behavioral pattern is mirrored somewhat by other species. Some aquatic insects, for example, burrow in pond mud when temperatures drop, enabling them to overwinter and survive for a number of years. Similarly, soil insects dig deeper, and tree beetles burrow beneath bark. The basic strategy used by these animals is to put as much distance and matter (be it mud, bark, or overlying water column) between themselves and the greatest extremes of cold. These creatures also move very little during the cold weather in order to conserve energy.

The range of temperatures fish can withstand is generally much smaller than that of terrestrial animals. This is because of the high rate of heat exchange between an aquatic animal and surrounding water. Terrestrial animals are surrounded by air, which has a lower rate of heat exchange, and can therefore survive low temperatures for longer.

Temperature further influences the feeding regimens of fish by determining the behavior of many of their prey species. This point can be illustrated in broad but graphic terms by considering the role of temperature in shark attacks on people. When the water is warm, people spend more time swimming and venture farther from shore. This behavior raises the encounter rate between human swimmers and sharks, and as a result, the number of mistaken attacks increases.

The situation is similar for freshwater fish. Temperatures affect the behavior of the invertebrates upon which these fish feed in a way that influences encounter rates between them and their food. As a general rule, the warmer the water, the greater the activity levels of invertebrates and the higher the level of feeding activity by fish, which in turn increases encounter rates between foraging fish and predatory ones.

The level of a fish's hunger can influence its position within the water column (the position of the fish vertically in the water). Hungry fish seek out water that is a few degrees cooler than that preferred by fish that have finished feeding, and of course, deeper waters tend to be cooler. Hungry fish also move around more looking for food and therefore take more risks than fish that are full.

Along the coast, mackerel tend to be more abundant when colder bottom layers are covered by warmer surface waters. This is because mackerel prefer feeding in colder, deeper layers during the day and rising into warmer layers at night, when they are not feeding. The warmer water aids their digestion.

In the middle and high latitudes of the Northern Hemisphere, the highest water temperatures occur in July, August, and September, and the lowest in February and March. Seasonal temperature changes tend to occur slowly, while daily changes in the weather can be much faster, reducing the time available for fish to adapt. Changes in water temperature follow several hours behind changes in the air. During rapid temperature changes in fresh water, fish often go deep, where temperatures are more constant.

Because of their reduced activity levels in cold temperatures, fish eat less, and in fact, trout stop growing below 6°C (43°F). Given the prevailing water temperatures in their normal habitats, this means that most wild brown trout spend about half their lives not growing. There is a chicken-and-egg aspect to this, for when fish eat less, they become less active in order to conserve energy and therefore need less to eat, so they forage less, which conserves energy, and so on.

Like humans, fish do "snack" between meals, but with less intensity than they show at mealtime. If the opportunity for an easy meal occurs, a fish will break its fast and take the morsel. When temperatures are low and fish are trying to conserve energy, they require a greater temptation to stir them from their torpor. Cold weather therefore calls for the use of larger baits, both to provide that additional temptation and to be visible from a longer distance to fish that are not moving much. When temperatures are higher, small baits should be used, as they are less likely to be inspected carefully and rejected during periods of high feeding activity.

Along ocean coasts during the summer, when the weather is good, shallow waters are warmed by the air then cooled by incoming tides. As the tide falls again, the waters are once again heated by the sun. In winter the reverse occurs. Freezing temperatures cool shallow waters, then the incoming tide raises them. As the tide ebbs once more, the shallow water begins to cool again. Coastal fish will almost always feed during a rising tide. This is because it quickly exposes new and plentiful feeding grounds. The advantages to be gained from feeding during the incoming tide generally outweigh the problems of fluctuating temperature and exposure to predators. Fish feeding on the incoming tide can be found just behind the tide line in very shallow water. In extreme cases, their backs will appear above the water.

Energy Budget

Each species of fish behaves in accordance with its characteristic energy budget, which is a calculation of the amount of energy a fish has available for growth and reproduction. It takes into account the quantity and quality of food consumed and the energy lost as heat through metabolic processes and in fecal pellets and other excretory products.

Although these calculations are of little direct use to anglers, they illustrate a highly useful concept: wild fish often behave in ways that conserve energy. They have evolved to instinctively balance the energy gain of a meal against the energy loss in terms of pursuing, catching, and consuming the meal (as well as the risk of predation while seeking the meal). Trout, for example, often hide behind rocks to shield themselves from stream flow, darting out into the full force of the current only when a large enough morsel of food passes by. As we shall see, this does not mean that larger flies, lures, and baits are always better. When food is abundant and fish have ample energy reserves, they can become fussy about what and when they eat, and a smaller, better-presented bait, lure, or fly may be a more favorable option. It is, however, important for anglers to consider how much energy fish are likely to have at any given time, and to fish accordingly. For example, in the cold of winter, fish try to conserve their energy and are less likely to travel for a meal. At these times, an angler must do the traveling and cover plenty of water to find fish.

The energy budget also highlights other important aspects of angling, such as speed of retrieval. When fish are conserving energy because of low temperatures, slower retrieves are more likely to get a bite because the lethargic fish will have more time to spot and intercept a passing hook.

One experiment done in 1984 clearly highlights the importance of the principle of energy conservation to anglers. Through an aquarium with curved sides to imitate a stream channel, water was recirculated to create an artificial current. The researcher placed stones in strategic positions and manipulated the sediment to create microhabitats, then he "stocked" the aquarium—first with coho salmon, then brown trout, and finally brook trout, clipping the fins of the fish to identify individuals.

In each case he left the fish in place long enough for growth to occur. One difference among the three species was that while the brown and brook trout used their pectoral fins to grip the bottom of the tank during periods of high water velocity, the coho salmon never rested on the bottom at any point. The subordinate (weaker) trout would hide, lodging themselves between the Plexiglas wall of the "stream" and the gravel. The dominant fish in all species would consistently retain the most profitable positions within the stream—that is, the positions requiring the least expenditure of energy (behind stones, for example) and with the best food supply (close to a fast current). Growth rates for fish corresponded to their positions. Those in the best positions grew fastest, those in less profitable positions grew more slowly, and some were forced to settle for positions in which they actually lost weight. Understanding where fish prefer to live will lead you to the biggest individuals.

Scales and Skin

A fish's skin, like human skin, is designed to protect the organism from the environment. Fish skin contains glands that cover the fish with a film of mucus, which helps protect the skin from disease and parasites. In any catch-and-release fishery, care must be taken to avoid removing this mucus and thus exposing the fish to potential illnesses.

A little-known fact about many fish is that they can change the color of their skin, camouflaging themselves against their background. Trout, for example, gradually release melanin into skin cells when swimming over a dark riverbed or in peaty water, making themselves darker. Over a light background, they reduce their melanin levels, and their skin becomes lighter. Paling of the skin is controlled by nervous impulses and occurs rapidly, while the darkening process is controlled hormonally and is there-fore slower. The trout's sense of sight is vital to these short-term color changes; blind trout are unable to make such alterations. It is useful for anglers to be aware of these adaptations when trying to spot trout in shallow water. It can help if you know what shade or color you are looking for.

Embedded within the skin are the scales, which provide physical protection. Fish scales grow slowly during the winter and more rapidly in summer. This leads to an increase or decrease in the calcium deposits laid down in ridges known as circuli on the scales. The comparatively thinly spaced circuli of winter can be used to count the number of years a fish has been alive, much like the annual rings of a tree. The thickness of these rings can also be used to assess growth rates at particular stages within a fish's life cycle.

Other calcified structures within the body of a fish can be used in much the same way. Otoliths are found in the inner ears of fish, each ear containing three. These structures show a daily cycle of periods when calcium is more rapidly deposited, as opposed to the seasonal one shown by scales. This daily cycle is of particular use in determining the age of very young fish. For catfish, the pectoral spines can also be used. The obvious disadvantage of utilizing otoliths and pectoral spines is that the fish must be killed in order for its age and growth rates to be determined. In contrast, a few scales can be removed from a live fish without causing too much damage. It is important to determine the age of a fish at a given size to discover the growth rate. In some fisheries fish grow slowly and in others they grow quickly. This can be due to many factors such as the availability of food, competition, temperature, and so on. This information is of use to anglers because fish grow much bigger in some waters than in others.

A fish scale. The mottled, pie-slice-shaped section is the visible part of the scale on the fish. The roughly concentric curves are circuli, indicating growth of the scale. Slow growth during winter results in tight spacing of the circuli, called an annulus, each annulus indicating one winter of the fish's life.

Moving in Three Dimensions

Fish live in a three-dimensional world, moving and holding position both horizontally and vertically. They use different mechanisms for these two axes of motion: their muscles for the horizontal and their swim bladders for the vertical.

Muscles and Skeleton

The swimming and fighting power of fish comes from their lateral muscle structures (called myotomes), which are situated along a fish's sides. As the muscles on one side contract, they shorten that side of the fish. The fish's skeletal system provides support so that the muscle contraction pulls the fish's tail toward the contracting side. By alternating contractions on one side with contractions on the other, the fish swishes its tail from side to side, and the fish swims. Depending on the species, these muscles can contribute the bulk of the fish's overall weight—as much as 70 percent in salmonids. It is these muscles that we eat when we catch fish for the table.

(Continues...)

Excerpted from WHERE THE FISH AREby DANIEL BAGUR Copyright © 2009 by Daniel Bagur. Excerpted by permission of The McGraw-Hill Companies, Inc.. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Dettagli dell'edizione

• Editore: International Marine/Ragged Mountain Press
• Data di pubblicazione: 2009
• Lingua: Inglese
• ISBN 10: 0071592911
• ISBN 13: 9780071592918
• Rilegatura: Copertina flessibile
• Numero di pagine: 176
• Contatto del produttore: non disponibile
• Persona responsabile: Ufficio Anagrafiche Messaggerie; 0039 0245774342; ufficio.anagrafiche@meli.it; ; Via Verdi, 8.; Assago Milano; 20090; Italia