How to preserve and how to exploit natural populations to be sustained for the future. Plain questions without equally plain answers

Applied freshwater biology An introduction to methods of research and management

Arne N. Linløkken, ass. professor Inland University of Applied Sciences

Arne N. 1

CONTENT INTRODUCTION ...... 3 Prehistory and evolution ...... 3 Short on construction and function ...... 4 Morphology ...... 4 Anatomy and physiology ...... 5 European freshwater fish species ...... 6 Immigration and distribution of freshwater fish in western Scandinavia ...... 7 Western immigrants ...... 8 Southeastern immigrants to Norway ...... 8 Northeastern immigrants to Scandinavia ...... 9 Biotops and habitats...... 23 Streams and rivers ...... 23 Lakes...... 24 Clear water lakes ...... 27 Boreal lakes and tarns ...... 27 Eutrophic lakes ...... 28 Acidification affecting aquatic life ...... 29 Fish management ...... 30 Issues and action ...... 31 Reducing density/biomass to increase individual growth ...... 31 Stocking ...... 32 Habitat Enhancement ...... 33 Fish Surveys ...... 34 Test fishing ...... 34 Sampling in running water ...... 35 Sampling in lakes ...... 36 Calculations ...... 40 Length and weight relationship ...... 40 Back calculation of length...... 41 Growth rate ...... 42 Hydroacoustics ...... 47 Age distribution and mean age ...... 48 Survival and mortality ...... 49 Nutrition and prey species of fish ...... 51 Genetic surveys ...... 54 Pollutants and contamination ...... 55 Fish parasites and diseases ...... 56 Creel surveys ...... 60 2

CURRENT TOPICS ...... 61 Temperature increase ...... 61 EU’s habitat directive ...... Feil! Bokmerke er ikke definert. Water framework ...... 62

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INTRODUCTION

This is a short introduction to freshwater fish biology and applied research, with a presentation of freshwater fish species in Norway, their immigration, distribution and ecological roles. It is based on Norwegian and Scandinavian conditions, with an environment characterized by pronounced seasonal variation, with annual ice cover and cool summer temperatures. Due to topography and postglacial history of freshwater organism invasion, the number of species is actually low, and a lot of lakes and streams have only one or two fish species. This makes them especially vulnerable to introduction of new species, like or other cyprinids which may affect the native population dramatically.

PREHISTORY AND EVOLUTION

Life on Earth originated in the sea, about 3 billion years ago, with living organism defined as "something" with combustion and an ability to multiply. After additional one billion years, some organisms developed ability to harness energy from sunlight and build organic molecules of carbon dioxide and water, with oxygen in molecular form (O2) as a byproduct. The first bacteria to have photosynthesis, the basis for most of what we know of life on the planet today, started the "oxygen revolution".

The sea slowly received oxygen from these organisms, and environmental conditions were changed perpetuity. This meant disaster for organisms that do not tolerate oxygen (the strictly anaerobic), being forced to retreat to oxygen free areas in sediments of oceans and lakes. For others, this offered new opportunities and future success. Most multicellular and advanced forms of life are depending on oxygen, produced by algae and plants. The oldest known multicellular organisms are left in 600 million year old fossils, some of them with living descendants, but numerous forms have emerged in the meantime. The earliest fish, known until now, is an almost 500 million years old fossil. These were the first provided with vertebra for attachment of limbs and muscles and for protection of the important spinal nerve. The first skeletons were of cartilage, which is still found in sharks. Sharks have inhabited the world's oceans for 400 million years, and they were from the beginning a 4 success having existed with minor changes since then. The bony fish appeared concurrently but the modern ray finned bony fish developed during the last 200 million years.

After Michael Benton: Vertebrate palaeontology (1st edition, 1990; 2nd edition, 1997; 3rd edition, 2005; 4th edition, 2014)

SHORT ON CONSTRUCTION AND FUNCTION

MORPHOLOGY

Bony fish have their skin covered by scales and a protective slime layer, a tailfin, (s), anal fin and the paired pectoral and pelvic fins, pairs pointing towards the more advanced vertebrates, the tetra pods with two pairs of limbs, the amphibians, reptiles, birds and mammals. Design of fins, with or without rays, spiny fins or soft fins, and location relative to each other characterize species and groups, as do the shape of scales, and the shape and location of the mouth (length of jawbones). Bony fish have opercula used to pump water 5 over the gills when the fish is at rest, different from sharks. The number and design of the fish’s teeth is adapted to its way of life, predatory fish such as pike with a jaw filled with sharp teeth, not only in the jaws but also in the groom, for grasping and holding its prey before swallowing, without chewing. Plankton-eating fish, however, like the salmonids whitefish and vendace and many Cyprinids, have no teeth. An exception here is the small (< 15 cm) plankton-eating salmonid, the smelt (Osmerus eperlanus), with the predator’s teeth and an ability to develop piscivory and grow large (>25 cm). Cyprinids have their pharyngeal teeth in the roof of the pharynx with which it can crush food items like shells of mollusks.

ANATOMY AND PHYSIOLOGY

The pharynx leads to the esophagus, further to the stomach and to the intestine continuing to the anus (Fig.). Close to the stomach a varying (with species) number of pylorus tubes are attached to the intestine. Glands are the liver, spleen and gall bladder, the latter partly translucent with characteristic greenish color, the others are typically dark red. The heart has a pyramidal dice form, dark red, and situated in the bottom of the belly. It has a ventricle and an atria. Blood is pumped forward and up through the gill filaments to emit carbon dioxide and absorb oxygen before being pressed backward in a dorsal vein, and distributed to the body vascular system, being collected again and lead to cardiac atrium. Freshwater environment has different requirements to organisms than the marine environment due to its low salinity creating an osmotic pressure that attempts to squeeze salt out of the fish and water into it to equalize the concentrations. To live with this, fish must conduct an active salt uptake (e.g. sodium and chloride) and an active fluid transport out. This takes place in different organs of the fish. Monovalent ions (such as sodium Na+ and Cl- chloride) over gills and divalent ions (such as calcium Ca2+) are absorbed in the intestine. Water is excreted in urine from the kidney (in the roof of the body cavity). Sharks are lacking excretion organ, and body fluids have approximately the same salinity as seawater. This makes it fit for a life in the ocean, but the low salinity of freshwater makes it an unsuitable habitat for sharks. There are exceptions, however. Fish, as vertebrates, have a nervous system with the center of the brain in the head’s upper part, which is associated with the spinal nerve connected to the smaller nerves in the body. In the fish brain there are some small bones, the otoliths, located in slime bags and tell the fish 6 it’s horizontally orientation. The largest pair of these, the Sacculus otoliths, are used for age determination of many species. Some special features of bony fish are sidelines and swim bladder. The sideline is a channel filled with mucus and nerve receptors, running along each side edge of the body wall, actually through the shells (Fig. ). Nerves register when the mucus canal is subjected to pressure changes. The swim bladder is an elongated “balloon” on top of the abdominal cavity, against the kidney and backbone. The pressure is adjusted to the pressure outside the fish, that is, after which depth the fish is situated and the present atmospheric pressure. In some species the swim bladder is connected to the pharynx (physostome species), whereas in other species (physocliste species) the pressure in the bladder is regulated by the blood that can emit or capture gas from thin veins at two locations in swim bladder. Gonads, male milt and female roe, developing prior to the breeding season, are located along the swim bladder (Fig. ). In most species, there are two gonads. Color, length, thickness and grain size (roe size) in females tell whether it is male or female and whether the fish is mature. In percids the females have only one gonad situated posterior in the body cavity.

As poikilothermic , the body temperature of fish vary as a consequence of the ambient surrounding environmental temperature. Due to this, physical activity, swimming activity and speed, as well as internal body processes, metabolic processes increase with temperature, but within certain intervals depending on species adaptation and individual acclimatization.

EUROPEAN FRESHWATER FISH SPECIES

The freshwater fish species in represent 26 families, of which yy are restricted to freshwater. Number of species is a matter of discussion as this vary with the species concept (Hausdorf, 2011, Cowx, Fisher & Broughton, 1986, Cowx, 1991). Kottelat & Freihof (2007) define approximately 525 freshwater fish species of Europe, of which numerous species are endemic in small locations, and some may be regarded as ecotypes or morphological variants due to isolation, by other biologists. Nevertheless, the definition of species is crucial as it is a management unit and of great importance in conservation work. Endemic species in small, restricted areas will appear as threatened and subject of protection, whereas a local population of a widely distributed species will not. The Cyprinids (with six subfamilies) and Salmonids 7

(with x subfamilies) are two of the most species rich families, and are important to human as well as they play important ecological roles in freshwater ecosystems. They both include species represented in most of Europe, often in high densities, whereas some species have very limited distribution and some are threatened. Others occur as alien species in new areas, brought there by humans. Management of these species therefor demands very different strategies. and pike represent two families of few species, but are both paid much interest from both managers and anglers. In the following, some selected European freshwater fish families and species are presented alphabetically, focusing on Norwegian and Scandinavian species.

IMMIGRATION AND DISTRIBUTION OF FRESHWATER FISH IN WESTERN SCANDINAVIA

The distribution and assumed immigration history of the 32 naturally occurring freshwater fish species in Norway is based on a fundamental work by Huitfeldt-Kaas from 1918 (Huitfeldt-Kaas, 1918), which still holds, with some exceptions mostly due to human induced changes. The number of species is low, due to the location at the sea, the topography and glacial history, with consequences for availability for fish to water courses and parts of them.

The western immigrants comprise the anadromous salmon, brown trout and Arctic charr, spawning in freshwater and migrate to the sea for a number of years to seek nourishment before maturation and returning to . All species can carry out their life cycle in freshwater, although only exceptionally for Atlantic salmon populations. Eels do it the opposite way, spawning in the sea (Saragasso), spending much of their young stages in freshwater - it is catadromous. The eastern immigrants, divided in southeastern species that entered from the Lake Ancylus, once covering parts of the current Southern and Central , and northeastern immigrants that entered from the current and . Among those, we find the (obligate) freshwater fish species that were dependent on continuous freshwater systems to immigrate.

Some species were introduced by humans the last 100 – 150 years. Three species, rainbow trout, Canadian brook trout (first time in 1876) and Lake trout, introduced deliberately and legally during the 19th and the 20th century, while two species, sunbleak (Leucaspius 8 delineatus) and gudgeon (Gobio gobio) are introduced to some locations illegally during the past 30 years. Minnow (Phoxinus phoxinus) is a naturally occurring species in southeastern parts of Norway, but has been spread for a long time, probably by anglers using it as bait. Other species are spread by people who later want to fish on them. Lately, carp seem to be spread by people with interests of modern bait fishing.

WESTERN IMMIGRANTS

Salmon, brown trout, Arctic charr and three-spined stickleback spawn all in freshwater, but can live in salt water as adults. Of salmon, there are only exceptionally freshwater resident stocks (Vänern salmon in River Trysi (River Klara in Sweden), småblank in river Namsen and blege in Lake Byglandsfjorden). Brown trout and Arctic charr are commonly freshwater resident, especially Arctic charr, which in Norway is found anadromous only in northern Norway, with some exeptions in Mid-Norway.

SOUTHEASTERN IMMIGRANTS TO NORWAY

Lake Ancylus covered for more than 10,000 years ago, the Gulf of Bothnia and coastal areas that are currently dry land in Sweden, Finland, the Baltics and Northwest Russia. This freshwater sea, named after the freshwater snail species Ancylus fluviatilis, recorded by the Swedish geologist Henrik Munthe as fossils in ancient sediments on Gotland, and still existing within the area previously covered by the Lake Ancylus. The lake drained westward from current Lake Vänern and River Göta. From this freshwater sea, freshwater fish and other freshwater organisms descended north- and westward to southeast Norway, through the River Glomma which until 8000-9000 years ago drained to Lake Vänern. Freshwater fish entered the River Glomma until the river turn to the west, collecting the tributary from Lake Mjøsa, and ended in Oslofjorden in the present city of Fredrikstad. This opened a new immigration pathway to the lower parts of Glomma from the Oslofjord, which was brackish due to freshwater from the melting. Among the species that came from the east, there were 9 grayling, , vendace, whitefish, perch, ruffe, pike, burbot, nine-spined stickleback and ten cyprinids. Some species can tolerate brackish water, and entered coastal areas in the western side of the Oslofjord, and some even reached the southernmost Norway (perch) and the southwestern Norway (whitefish), whereas the cyprinid distribution is limited to coastal area around Oslofjorden, lower and middle parts of the Glomma river system and river systems draining eastwards to Sweden.

NORTHEASTERN IMMIGRANTS TO SCANDINAVIA

Perch, pike, burbot, grayling and whitefish are present in rivers in the eastern part of the northernmost part of Norway, the county of Finnmark. Grayling is also present in some rivers in the counties Trøndelag, Nordland, Troms and western part of Finnmark. This group also include brown trout and Arctic char, the two most widespread freshwater resident species in Northern Norway, and beside salmon, also forming anadromous stocks in all rivers in the region. In addition to natural immigration, humans have introduced species important livestock; brown trout, grayling, whitefish, perch, to lesser extent vendace, to locations outside the species natural occurrence. Burbot may have been stocked in the mountain lakes. It has a large vitamin rich liver and may have been an important source of vitamins to humans.

It would be a simple matter to carry ripe brown trout upstream a waterfall giving it the opportunity to spawn and establish in river stretches upstream falls, but carrying live fish over a long distance in the mountains requires more insight, skills and equipment. They may have been caught on the ice, and transported at cool temperature, which increased the chances of survival transport.

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NATURALLY OCCURING FISH SPECIES IN NORWAY

BURBOTS (COD ORDER)

Burbot (Lota lota) is the only cod relative in fresh water. It dwells to the bottom of lakes, but also in rivers and streams. It is widespread in eastern water systems in east Norway and in Sweden. It is brown with dark spots, light 0n the belly, typically disguised for a life on the bottom, and can be up to 7-8 kg, but 0.5-1.5 kg is the usual. It has a club- or tube-like body shape with a slightly flattened head and wide mouth and is a distinctly predatory. They matures at 3-4 years of age and spawning takes place from December to March over bottom of sand, gravel or solid clay, in shallow or deep water. Several places there are traditions of “clubbing” burbot when it comes into the shallow waters to spawn under the ice. It may be visible under the ice, and a powerful punch on ice with a mallet or a cane will at least stun fish until the ice is cut open and the fish can be retrieved.

BULLHEAD ()

Alpine (or Siberian) bullhead ( poecilopus) of the Cottidae family, with most of its relatives in marine environments, is relatively widespread in Scandinavia, contrasting the other two freshwater cottidae. C. poecilopus is present in the Trysil watercourse to Lake Femunden and in the Glomma river system up to a waterfall downstream Lake Aursunden. Tributary rivers to Glomma are the Rena watercourse with the Lake Storsjøen, River Atna with the Lake Atnsjøen, both harboring . In river Lågen it is present up to the waterfall Harpefossen in Sør-Fron municipality. It is present in the county of Finnmark and in some rivers in the county of Troms. Bullheads have a characteristic broad and slightly flattened head (giving to English name), two dorsal fins and large pectoral fins. In Norwegian, there are several local names, one is “stein-purke” = “stone-sow”. It is usually 10-12 cm long and live in both standing and running water and is always dwelling to the bottom. It has internal fertilization and eggs are deposited nests in spring, and is guarded by the male until hatching. It feeds on insect larvae and other benthic animals and can catch eggs and fish fry. It can be a competitor of small brown trout, but also a prey for brown trout. It is also used as bait for trout fishing.

European bullhead (Cottus gobio) is much like the Alpine bullhead but is less widespread in 11

Scandinavia. The biology of the two species is also quite similar, and the difference appear in that the has a sideline that goes backwards to the tail fin and ventral fins that do not reach as far back as to the anus, and misses the transverse stripes on the fins that the common bullhead have. It is 12-15 cm long and spawn in the spring. It has internal fertilization.

Four-horn (Triglopsis quadricornis) are found in the Lake Mjøsa and some other large lakes in Scandinavia, where it lives on > 90 m depth. It has long tail set and it gives it a sleeker look than the other sculpins. It is also larger, up to 20 cm and in the brackish waters of the are lengths of 30-35 cm not uncommon. The name has been given by four legs nodules on the head, but these are lacking in freshwater populations. Spawning biology is little known but it is believed that it spawns in late autumn or winter in the lake. From elsewhere it is known that it has internal fertilization and that the eggs are spawned in nests on the bottom where they are guarded by the male.

CYPRINIDS ()

The most species-rich family of freshwater fish in Europe. Many species have large, silvery scales, some may be difficult to distinguish from each other. We can count the scales along the sideline and dissect the pharyngeal teeth, a special trait of the cyprinids, used crush and grind food items, and have species specific shape. Number of scales along the sideline varies within species and may overlap between some, and do not always provide definitive answer. Experienced persons recognize species on body height, width and color shades not easily described by words. Size, location and shape of fins are also important characteristics for some species. There is a digital base of fish species:

(http://www.fishbase.org/identification/SpeciesList.php?genus=Rutilus) naming nine species of the Rutilus , whereas Kottelat & Freyhof (2007) name 13 species.

Roach (Rutilus rutilus) is clearly the most widespread cyprinid species, but in Norway it is naturally present only in the southeastern part of the country, but far more prevalent in Sweden and Finland, and are present in the north, near the coast of the in Russia. As cyprinids usually occur in highest density in eutrophic water where it stands up well in 12 competition with other species, for several reasons. It is an effective plankton feeder but can also feed on benthos and even algae, macro vegetation and sediments. It can also live at oxygen concentrations lower than what perch and trout can withstand. Roach resemble several other cyprinids with its silvery exterior and large circular shaped scales. It has reddish color in the fins, and it has red eyes, which is the simplest characteristic of a living any recently dead roach. Roach matures usually as two or three year old, at length 12-15 cm, and spawn in May, one to two weeks later than perch. The eggs are sticky and are deposited on rock or vegetation in running water and in lakes, above the bottom surrounded by oxygenated water, and they hatch within 10 days, faster at higher temperatures.

The common dace ( leuciscus) is relatively widespread, with a body shape and musculature that makes it a more proficient swimmer than most other cyprinids we know. It has a nice silvery color and large scales. Sexually mature at 12 to 14 cm length, at age 2-3 years, and spawn on sand and gravel bottom in running water in May-June. It can be more than 30 cm but commonly 15 to 25 cm.

The bleak (Alburnus alburnus) has a prevalence as dace, is silvery in color and have large scales. It is higher in body shape and more laterally flattened than dace and roach, and it is rarely more than 20 cm long. Sexually matures at 10 cm length and age 2-3 years, and spawn in the water in June-July.

The (Leuciscus idus) is one of the cyprinids that grow large, up 4 kg. It is powerful, with not particularly high body shape, but wide across the back, with large scales, tawny at the sides and gray on the back and the belly. Sexually mature at 3-4 years of age and spawn in April-May, on rocks and gravel in both standing and running water.

The common rudd ( erythrophthalmus) have a very limited distribution in Norway, up to Dark falls in Glomma and in the lower parts of the Drammen River and rivers in Telemark. Present in some coastal waters in southeastern Norway. Body shape is high, compressed from sides, and the color is silvery interspersed with green and red fins. Sexual maturation after 2-3 years at 10-12 cm and spawn in May-July by land into lakes.

The chub () is present in lower parts of rivers in southeast Norway, the River Tista, in River Glomma to Lake Øyeren and the tributaries River Nitelva and River 13

Leira, and in the lowest part of the River Drammenselva. The chub is more powerful than most other cyprinids with a broad back and otherwise slim body shape, often 30-40 cm long, sometimes up to twice of that, so it is a popular species to anglers. Large individuals are piscivorous. It spawns in running water in April-June and the sticky eggs are deposited on rocks and vegetation.

The asp (Aspius aspius) is present in River Glomma up to Lake Øyeren and lower parts of the tributary River Nitelva. Asp is sleek, with silvery sides, darker on its back, and the belly has a sharp keel between abdominal and anal fin. It is over 50 cm long and as adult it is the predominant predatory, which is unusual among cyprinids. It spawns in running water in April-May and the eggs from sticking to gravel, stone and vegetation. It is tasty and is also popular to anglers because of its size, but it is not easy to get off the hook.

White bream or silver bream (Blicca bjoerkna) have a very limited distribution in Norway, in river Glomma up to Lake Øyeren, some locations east of the lowest parts of river Glomma, and some few locations in coastal areas in southeast Norway. It has a high body shape, ventrally compressed, resembling a small bream, but with relatively larger eyes and may have a reddish tinge. It is usually up to 20 cm long and live in shallow lowland lake with rich vegetation, eating planktonic and benthos; insects and mollusks, and fish fry. It becomes sexually mature at age 3-5 years, and spawns in June-July in vegetation in flooded shorelines where the sticky eggs are attached to vegetation.

The crucian carp (Carassius carassius) is a special species in several ways, and is a close relative to prussian carp (Carassius gibelio), and goldfish (Carassius argentus argentus), the goldfish probably descending from the prussian carp, which is not present in Norway. The crucian carp was probably stocked by humans in Norway, and has a limited distribution, whereas the other two are not present. The introduction was possibly done during the Catholic times (before 1536) by monks and pilgrims, and this was a fairly easy process as crucian carp can live for quite some time without getting oxygenated water over the gills. Body shape varies, it often have higher body shape in water with predator fish such as pike. In small ponds crucian carp rarely exceds 15 cm of length, but may become several kilograms in other circumstances, such as in Lake Øyeren. Crucian carp stores sugar in the brain by access to oxygen and food, and it can draw on this in periods during periods when neither is 14 available. The combustion is set to a minimum in a hibernation state, and it can for example survive in mud on lakes and ponds where water is oxygen free, for example under the ice in the winter. Crucian carp can thus be absolute ruler in such water as most other species die under such conditions. In diverse fishing communities, which often means multiple carp species present, it is not so much to see the carousel for it is not particularly competitive strong. Crucian carp becoming sexually mature at 2-5 years of age and approximately 10 cm length and spawn in May-July in vegetation belt in ponds / lakes where the sticky eggs attach to vegetation.

Tench (Tinka tinka) is introduced by human in Norway and found in some lakes in the counties of Østfold, (southern part of) Hedmark, Akershus, Vestfold and Aust-Agder. Tench has a high body shape and the tawny and brown color and small scales differ it from the other cyprinid . In addition, it has two small barbells that distinguishes it from all other Norwegian freshwater fishes. It is usually up to 40 cm long and becoming sexually mature at 3-4 years of age. Spawning takes place in several stages in June-July in vegetation belt, where the sticky eggs attach themselves to plants.

Minnow (Phoxinus phoxinus) is naturally widespread in eastern, from Numedalslågen in the west to Dovre in the north of southern Norway, and in some places in the County of Trøndelag in Mid-Norway. used as bait by anglers, also as live bait even if it is not allowed, and it has been spread to new areas of anglers. It lives in both standing and in running water, albeit not in the toughest rapids, and are rarely much longer than 10 cm. It has small scales and the yellow and brown color varies with the environment they live in. Those who live in humus colored water have darker color, but the characteristic in all environments is a dark stripe on light / yellowish bottom along the sides. It eats partly same food items as trout fry and is therefore regarded as an important competitor to this. Spreading of minnows to new areas where trout dominate from before is very undesirable and illegal. Minnow becoming sexually mature after 1-2 years and spawn in shoals in June-July. Spawning over rocky bottom and the eggs from sticking to the bottom.

EELS - ANGUILLIDAE

European eel (Anguilla anguilla) is (like American eel) special in both appearance and life 15 history. A snake-like body shape and a coherent fin from back to haul and forward belly makes it easily recognizable. In freshwater, only the even more special lampreys may resemble. The eel is also known for its migration in different stages. The fry emerge from the Saragasso-ocean, partly with ocean currents, towards the shores of Europe as glass eels, and enter the rivers as elvers. They live in rivers and lakes until they become sexually mature, when it becomes shiny under the belly and called silver eels in the venturing back to Saragosso. This will take a long time, for males 4-10 years (35-45 cm) and for females 6-25 years (40-150 cm), which means that they can be fished upon for many years, before they migrate to spawning areas. Eels are caught in traps and had economic significance before the stock decreased and the species was characterized as threatened in many areas.

PERCH FAMILY

Perch (Perca fluviatilis) is the clearly most prevalent of these species, and the most widespread. In Scandinavia, perch immigration was restricted by topography and its low tolerance to sea water. The natural occurrence therefor does not include the western part of Norway, neither the middle and northern Norway, except the far north east, where perch immigrated from the east. In south Norway the perch is supposed to have immigrated from the Ancylus lake which once covered the Bothnic sea and parts of South Sweden.

Perch with its high body shape and rigid body is not a fast swimmer. It exists in the slow running stretches of river in large rivers, but is primarily associated with small lakes and tarns where it often dominates the fish community numerically. Perch spawn in the spring, usually in the 2nd and 3rd week of May in the lowlands, at water temperature 8-10 C. The eggs are spawned in a mucus tube that swells in water to form protection for the eggs. They must be deposited on submersed objects preventing them from ending up on the bottom sediments. After 10-14 days, depending on water temperature, the eggs hatch and fry with little yolk sac eat small food animals like rotifers and small plankton crustaceans. Perch gradually begins to eat larger food animals, and insect larvae (mayfly, caddis fly, alderfly, chironomids) are important for adult perch. Growth is stagnating between 15 and 20 cm, in small nutrient-poor ponds at 12-14 cm, but some individuals turn to piscivory. These do not stagnate in growth and with an annual length increment of 2-3 cm, they can become one kilogram or more, in some cases over two kilograms, but it is rare.

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Pikeperch (Sander lucioperca) is the big brother of the perch family, and can reach a weight of 8 kg, but commonly from 1 to 3 kg. This species is limited to the southeastern part of Scandinavia, and has a very limited distribution in Norway. It is distinctly predatory and thrive in nutrient-rich lakes, where it hunts in open waters, complementing the pike that primarily occupies the littoral zone. Pikeperch has been introduced in nutritious lakes to reduce dense populations of cyprinids and perch to reduce the fish predation on herbivorous zooplankton. It provides higher density of zooplankton that feed on algae that can otherwise affect the water quality negatively. Light transparency is limited in eutrophic water due to excessive algae density and pikeperch is adapted to this with their specially developed eyes. The area between the photosensitive cells in the retina is light-reflecting, and works as a night binoculars. This gives the pikeperch eyes shiny look.

Males becoming sexually mature at age 2-4 years, females one year later. Spawning takes place in May at 10-14 ˚C in the water, in shallow bays in lakes or slow flowing rivers and is a bit special. It builts nests on the bottom and after spawning, eggs are guarded by either male or female. The female has approximately 200,000 eggs per. kg body weight, which tells about high mortality at early stages. The size and strength of the pikeperch make it a popular sport fish, and in addition, the meat is tasty.

Ruffe (Gymnocephalus cernuus) is the smallest of the percid family, rarely more than 14 cm long, and has a limited distribution in Scandinavia. It is present on the eastern side of Oslofjorden, in Lake Mjøsa and the tributary river Lågen to Harpefoss and in river Glomma up to Rena. It is a distinctly benthic fish, and has a brownish gray color and relatively large eyes. It is found often in humid water where there a small amount of light reaches the bottom. On the head it has many small pits where mucus is excreted. The sideline is designed to locate prey. Ruffe mature after one or two years. It spawns in May-June and the female spawns eggs in portions throughout the season. Total egg number is 1000-6000.

SALMONID FAMILY

Arctic charr (Salvelinus alpinus) was probably the first immigrating freshwater fish after glaciation, and it is the only freshwater fish species in Svalbard. It live well in the mountains and in the northern counties because of its adaptation to low temperature. It is found, however, in Southern Scandinavia, where it seeks cold water in the deep layer of lakes in 17 summer. The southernmost anadromous charr is in Trøndelag in Mid-Norway. The charr’s body shape varies with growth and condition, and when food availability is good, charr get a tall and broad body shape. It has reddish yellow color in the abdomen and the redness is stronger in the spawning season. There are stunted charr originated in deep layers in some larger lakes, and these are uniformly yellow-gray, but usually with white dots on darker background, a sure sign to distinguish charr and trout. The charr mature at 2-3 years of age, and spawn in the fall on rocks and gravel bottom in lakes, although some stocks spawn in running water. The size at spawning varies widely, depending on environmental conditions and growth rate, from about 20 cm to the double of this. Spawning period varies geographically and in terms of altitude. Hatching occurs in May.

Brown trout (Salmo trutta) remain the most popular fish to anglers, among the freshwater resident fishes in Norway, and it is the same species as the anadromous sea trout. It is widespread because it is both an eastern and a western immigrant and it is, thanks to its importance for livestock and sport fish, and its adaptability, been spread wide over by humans. Most brown trout stocks spawn in running water, even in small streams where it is easy to observe and capture during the spawning season. It is no difficult task to catch spawning trout in a stream and help it upstream a waterfall, and this was done from prehistoric times. Age and size at spawning varies widely, as in charr, and brook living brown trout can spawn at 2 years of age and 12 to 15 cm of length, whereas large sized brown trout in big lakes may grow for five and six years, to 50 and 60 cm before maturation. Spawning takes place in September and October on the gravel bottom where spawners dig pits for eggs and covering over it after spawning. The eggs hatch in May and larvae (yolk sac fry) live the first couple of weeks in the gravel until the yolk sac is digested, and the fry emerge from the gravel. Normal growth for brown trout is approximately 5 cm per year for the first two years, then growth often will slow down and maturation occurs if there is a stream resident type. For lake living specimens, turning piscivour, the annual growth increases, doubling and even more from one year to the next. Brown trout living the entire life in the river, which Glomma, may also go through growth shift, associated with a shift to piscivory (e.g. bullheads and minnow).

Grayling (Thymallus thymallus) is present in the eastern part of southern Norway and widespread in some rivers in Middle and Northern Norway, as an eastern invader. It exists in 18 both lakes and rivers and streams with clean water. It is grayish brown to gray colored, reddish fin edges in the breeding season, and the scales are large with three tags. Muzzle is slightly compressed from above and wider than for example in the whitefish. It is usually one-half to three-quarter kilo (30-40 cm), but it may be several kilograms. The sex mature as 3-4 years old and spawn in the spring in running water or lakes, sand and gravel bottom and fry leaves spawning creek during the summer or autumn. This allows grayling to reproduce in small streams, where winter flow is too small for fish, like immature brown trout, to survive winter. The grayling is sensitive to pollution, and is due to this threatened in many locations. It is popular among anglers, and fly fishing for grayling is very popular in Glomma river system attracting fishermen from home and abroad. A more special way of fishing by most local anglers in Glomma is "spræle" fishing on the river ice in late winter, a handline fishing where fish are lured to whole with stone fly nymphs (called the Grindal fly), whiich is also sampled from a hole in the ice (attracted by the light to hatch).

Salmon (Salmo salar) with few exceptions, anadromous, spawn in most Norwegian rivers up to migration barriers in the form of natural waterfalls or dams. There are a few freshwater resident salmon populations. In Norway there is Blege in Lake Bygglandsfjord and småblank in River Namsen (above the waterfall of Lower Fiskumfoss). Salmon persists in the nursery river until smoltification as it gets ready for life in saltwater. Smoltification starts when the salmon has reached a size that gives the chance of survival in a new habitat. The size varies from river to river, and age at migration is largely determined by the growth rate. Growth is two to three times as fast in the sea as in freshwater, and this is easy to see by scale analyzes. After 2-5 years in the ocean, with a size of 50-200 cm, salmon migrate back to the birthplace river to spawn. Ascent occurs from June to August and spawning takes place in October. Atlantic salmon spawn several times unlike totally seven species of Pacific salmon that die after the first spawning.

Smelt (Osmerus eperlanus) has a limited distribution in Norway, in water systems crossing the boarder to Sweden, like the Halden river system, in the river Glomma up to Kongsvinger, in the Lake Mjøsa and its inlet river Lågen up to Hunderfossen. In the Drammen River to Lake Randsfjoden and some water courses on the western side of Osloforden. Its length is 12 to 15 cm, with a slender body with large scales and the color is light gray to silvery with darker color on its back. Some individuals turn piscivorous and grow to 30 cm. It is a shoal 19 fish and constitutes an important part of nutrition for lake trout, including lake and Tyrifjord, as well as for large perch. It spawns in May and shoal along the shores at the spawning grounds a day or two before it pulls out again. Anglers use smelts as bait and it is captured easiest on spawning grounds.

Vendace (Coregonus albula) have an even more limited distribution than grayling in Norway, best known in the Lake Mjøsa and the inlet river Lågen (giving the Norwegian name “Lågåsild”) where it spawns in the lower part of the river and it operated a traditional fishing with splash in the stream in autumn. Vendace has similarity with the herring, it is silvery with large shells and the body is slender and compressed from sides and the lower jaw excides the upper (unlike whitefish). It may grow rapidly until maturation after 2-3 years of age, but the size varies between populations, from less than 15 cm to more than 25 cm. It is primarily related to the pelagic zone feeding on planktonic crustaceans with greater efficiency than, for example whitefish.

Whitefish (Coregonus lavaretus) has a southeasterly and northeasterly distribution, but found as far west as to the county of Rogaland. It can live in brackish water, but is primarily related to larger lakes. It is silvery with large shells, and it lives both in open waters and benthic areas. In beach and benthic areas are often the major subjects, while younger fish are more plankton-eating, and living in open waters. Whitefish occur in several different forms, and growth, habitat selection and nutrition varies between with delights of whitefish form. There may be several forms in the same lake, utilizing different niches. This may be considered as an incipient speciation and separation probably happened after immigration by glaciation. Such division in various forms, like in Lake Femunden with three forms, in Isteren there are two. Both these lakes drain to River Trysilelva and Lake Vänern. In Mjøsa however, we only know one form, but there are also vendace and smelt occupying niches that may have some overlap with the whitefish niche. In the lakes Femunden and Isteren however are neither vendace, smelt nor cyprinids (except minnow). Whitefish sex mature as 2-3 years old and spawn in October to December on the gravel bottom in Lake Osensjøen, River Northern Rena to Lake Storsjøen in Rendalen and inlet River Tufsinga to Lake Femunden, in River Dokka, a tributary to Lake Randsfjorden in the county of Oppland and River Storelva that runs into the Lake Tyrifjord in Buskerud. The eggs hatch when the ice thaws in April / May and growth is rapid for the fast 2-3 years. Whitefish continue to grow rapidly when food 20 availability is good, i.e. at low or moderate density of fish, and it eats both plankton and benthos, to some extent, fish eggs and larvae / fry. It is in all a very efficient producer of fish meat. As a food resource it has therefore been of great importance, and has, due to this, also been spread by humans, though not as popular in recent years compared to in the old days. Reduced exploitation has resulted in increased density and stunted fish in several places. In many lakes are whitefish heavily infected by the cestoda (tapeworm) Trianophorus crassus, the pike worm. This parasite has a larval stage that are seen as white treads in the dorsal muscle of the whitefish. It is not dangerous to humans, and it disappears by freezing, but it gives the fresh fish meat a very undelicate look.

INTRODUCED SALMONID SPECIES

Rainbow trout (Oncorhynchus mykiss) (ca. 1908), Lake trout (1971) and Canadian brook trout (1876) derives all of North America and is introduced to Norway. The first two are known for rapid growth, and Lake trout can grow very large, in North American lakes up to 50 kg. Canadian brook trout (Salvelinus fontinalis), as the name tells, is found primarily in small waterways, and it can withstand acidic water better than trout and European char. Rainbow trout used in fish farming can be hosts of the parasite Gyrodactylus salaris which has more or less wiped out salmon in several Norwegian rivers. Rainbow trout, which unlike most salmonids spawn in spring, have established breeding populations in some Norwegian rivers, and unlike most salmonids spawn the spring. Brook trout are stocked in several watercourses and have established populations in some few locations in Norway.

GASTEROSTEIFORMES

Three-spined stickleback are widespread in coastal areas and up to the upper marine limit throughout Norway, as it is a western imigrator. It is 5-7 cm long, silvery with brown spots and three spines on the back. In the breeding season males have red throat and belly. It thrives in shallow bays in freshwater and saltwater, and may also occur in open waters, then as schooling fish. It spawns in May-June, and the eggs are laid in nests which the territorial male builds of plant parts and pebbles at the bottom. Several females may spawn with the same male and add eggs in the same nest. Stickle backs often host parasites, especially tapeworms, and the belly may look bursting because of this. Nine-spined stickleback has a more eastern distribution than the three-spined, and is present 21 along the coast and in coastal areas of waterways from Østfold to South Western Norway, in Trøndelag and Finnmark. It is found among others in the Lake Mjøsa. It is slightly less than three-spined sticklebacks, 5.4 cm long, and has silvery ventral side and brown back side, and the nine pins on the back is smaller than those of the three-spined stickleback. Live in streams, lakes and brackish water, to a lesser extent in saltwater than the three-spined stickleback, and it is more related to the vegetation zone. It spawns in May-June and the eggs are deposited in the nest which the male builds of plant parts in water vegetation, not at the bottom, and several females may spawn in the same nest.

AILIAN SPECIES IN NORWAY

Sunbleak or belica (Leucaspius delineatus) is a silvery, shoals forming cyprinid, 6-10 cm long with its natural range in Central Europe and Russia. It is present in several locations in southern Sweden and in 1997 it was recorded in Norway for the first time, in the southern county of Aust-Agder. Belica is used as bait by anglers. Gudgeon (Gobio gobio) is also a cyprinid with natural propagation further south in Europe, naturally occurring in both and Southern Sweden. It is usually up to 15 cm long, less usual up to 20 cm. It is recorded in River Numedalslågen in west central Norway and in the Nesheim watercourse in Farsund in southernmost Norway, and is probably spread by anglers using this species as bait. It should be noticed that Kottelat and Freyhofs (2007) eminent book describes the natural occurrence of this species as, seriously erroneous, including parts of southernmost Norway.

JAWELESS FISHES – THE LAMPREYS

These species belong to a primitive group, with a cartilaginous skeleton, and as the name tells without jaws. In fishes' evolutionary development were the two foremost of a total of nine gill arches developed to jaws (in sharks and bony fish) and in bony fish are another couple of gill arches become opercula. The jawless mouth is just a round opening with wreaths of pointy chitin teeth, which can neither bite nor chew. Conversely, it may be sticking to the substrate, like a stone in running water, or it can suck itself firmly to a larger fish, like salmon, to hitch hike and be transported to a river. It can also do it to eat at a fish, dead or 22 alive. In Norwegian, they are called nine-eyes because, seen from the side, it seems to have nine eyes. They have, however, like others, only one eye on each side, seven are gill openings (a primitive trait) and the foremost is the nares, otherwise just an opening as opposed to more advanced fish and other vertebrates that have two or four (i.e. paired nose openings). Lampreys also lacks paired fins (breast and pelvic fins) and they have a coherent fin from back to tail and belly. We have four species that mostly separated by size and habitat, but with some overlap.

European brook lamprey are 10-15 cm long and live in rivers and streams. It is common in the rivers Glomma and Lågen up to Harpefoss. It spawns in April-June, and spawning takes place in groups where a female spawns with several males and die shortly after spawning. The eggs are buried in gravel and hatch after 10-14 days, and the larvae live buried in 3-6 years eating dead organic material before they mature, emerge from the gravel. They then vestigial digestive system and does not take nourishment before they spawn and die shortly afterwards.

River lamprey (Lampetra fluviatilis) is up to 50 cm long. It is anadromous, but can also be freshwater resident in rivers near the coast north. Spawning in coastal rivers in April-June where it excavate spawning beds in sand and gravel bottom. The eggs hatch after 10-14 days and the larvae live down in the sediment in 3-6 years before they become adults and emerge. Predate other fish species for living.

Sea lamprey (Petromyzon marinus) grow up to 120 cm long. Anadromous form that live their adult lives in the ocean. Spawn in fresh water, on rock and gravel bottom, and the larvae feed buried in 6-8 years. Live by sucking blood and body fluids of other fish species (cod fish, salmon, also whales).

The Arctic lamprey (Lethenteron camtschaticum) is widespread from Passvik, Northeastern Norway, eastwards to the Bering Strait and the Pacific. Spawn in freshwater and live parts of life in the sea, the size is the somewhat between brook and river lamprey, 18-35 cm long, resembling river lamprey, but found only in the Arctic, and in Norway only River Passvikelva. Breeding migration up rivers take place in the autumn, while spawning occurs in spring. Feed on other fish species; salmonids, flounder, cod and herring. 23

BIOTOPS AND HABITATS

In natural ecosystems, several food chains form the total food web. The basis of a food chain are the producers, or primary producers, performing photosynthesis to build organic material (sugar) and produce oxygen from light, water, carbon dioxide and inorganic nutrients. These are cyanobacteria, algae and higher plants preyed on by the first order consumers, in turn preyed upon by the second order consumers, i.e. predators. Most freshwater fish species are consumers of the second order or higher, though some cyprinids are facultative herbivorous, such as roach, eating algae and macrophytes, and even sediment. Sediments have varying content of dead organic matter, detritus, and the latter is the basis for a separate detritus chain consisting most of such as insects, crustaceans and microorganisms; fungus and bacteria. The detritus chain brings substances back to mineral form that can be absorbed by the photosynthesizing organisms. Several species of insects and crustaceans in the detritus chain are important prey species to fish, like several species of mayflies, stoneflies and the crustaceans asellus, gammarus, water flies and copepods.

We divide freshwater habitats roughly in running and stagnant water, and divide these further according to size; streams and rivers, fast and slow running. Similarly for stagnant water; ponds, tarns and lakes. Puddles defined as temporarily water bodies, periodically drying out. Ponds are small and shallow, allowing higher vegetation to grow over the bottom. Due to environmental instability and oxygen deficit throughout the year, fish do not exist in such habitats.

STREAMS AND RIVERS

Running water drains a catchment, and starts as a well in the uppermost part of the catchment, easily observable in drainages that include bare mountains. The discharge is a function of catchment size and the specific runoff (precipitation minus the evaporation and what goes to groundwater) in the area, and specific runoff and catchment area can be used to estimate the mean discharge of a stream. Imagine a stream starting in the mountains, running 24 through lichens covered rocks and boulders, further through marshlands with sedges and willows along the banks. This vegetation is important, especially for running water where aquatic algal and plant production is negligible due to physical instability (current). Higher life in the stream dependt on organic material supplied from the catchment, allochthonous material. Leaves from autumn fall is the most important source because this happens annually, in predictable amounts, and the matter is readily degradable for bacteria, fungus and vertebrates, insects, crustaceans and oligochaetas. This detritus fauna forms the basis for organisms on the next step in the food chain, especially insect nymphs like mayflies and stoneflies, also important prey species for fish. A stream must have a minimum runoff to hold a fish stock through the year. Ice cover and low discharge in winter and drought in summer hurdle in the smallest streams. Brown trout is the species most frequently present in the watercourse upper parts, sometimes as the only fish species (allopatric). If the mountain stream culminates in a mountain lake, the brown trout in some cases live in sympatry with Arctic charr. Charr also occur occasionally in streams, but it spawns with very few exceptions only in the lake and is primarily lake dwelling.

Streams downstream lakes are fed both dead and living material produced in the lake, and this provides an increased production in the outlet river that is referred to as the outlet effect. The number of naturally occurring fish species increases down the watercourse. The grayling also occurs in streams and rivers, but not in the most rapidly flowing sections, where the trout dominate. Grayling and brown trout can compete for both space and nourishment. Sculpins is another group of fish found in streams and rivers, being closely linked to the bottom, and they are competitors to the brown trout. Small (young) individuals of burbot and pike are also found in stream stretches that are available from lakes or slow running rivers. In the lowland, species diversity increases, and cyprinids like dace and bleak occur, often in high densities. Brown trout are rare in small streams with diverse fish stocks, whereas it may live and grow big in larger rivers, recruited from tributaries upstream, predating on former competitors like perch and roach.

LAKES

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Lakes are divided into several physical habitats; from the water surface and beyond, and along the bottom we find the littoral zone with macro vegetation, and at depth below the vegetation we have the profundal zone. Open waters, with organisms living independent of the bottom surface, the pelagic zone, at least in periods of the year. During summer, the warm upper layer (epilimnion) is divided from a cooler water layer at greater depths (hypolimnion) by the metalimnion, where the temperature drops by more than 1 C per meter from epilimnion to hypolimnion. When the air temperature drops and solar radiation decreases in autumn, the water temperature in the surface water gradually drops to 4 C. At this temperature, water has its highest density and surface water begins to sink down towards the depth. Waves and currents cause the entire water mass to circulate vertically, the autumn stirring, and the temperature is 4 C throughout the water column for a short while. The surface water cools down further, and eventually to zero and less than zero C and ice settles. Bottom water will be 4 C all winter, unless the sea is very shallow. After ice break up in spring, solar insolation raises the temperature of surface waters to 4 C, the surface water sinks, and is replaced by water with lower temperature rising to the surface and is warmed to 4 C. The entire water column again reaches 4 C and the spring mixing occures. The two circulation period are of crucial importance for the chemical and biological conditions in the lake, supporting the deep layers with oxygen and the upper layers (the photolytic zone) with nutrition, especially phosphorous, normally the minimum factor of production in freshwater.

Nutrients which are concentrated in the deep water during stagnation periods, and are mixed in the water coulomb by spring and autumn circulation, and oxygen lacking in the deep layers are mixed from the photolytic zone as it becomes. The oxygen is consumed by the living organisms in the water, including detritus organisms both in the water column and in the sediment surface. Temperature preferences of fish species determine their vertical distribution, and for those who prefer cool or cold water, oxygen deficit in depth layers may exclude them from their preferred temperature and thereby exclude them from lakes with eutrophication and increasing temperature.

Water bodies are also divided according to water quality, primarily a result of the geology of the catchment but also affected by human activity. Calcareous rocks (containing carbonate 2- CO3 ) provides high pH and often relatively high phosphorus, since these often occur together. The rock type apatite contains calcium and phosphorus and is especially beneficial 26 for productivity and buffer capacity, otherwise are rocks from the Cambrosilurian period favorable, gabbro which are remnants of ancient volcanoes, is also relatively readily soluble and provides a better buffer capacity than harder and less calcareous rocks such as granite, gneiss and sparagmite. Climate varies with altitude, distance from the coast and latitude, and along with bedrock, is essential for the kind of vegetation type found in the catchment area. Areas with weak buffer capacity is dominated by coniferous forests contributing humic acids and gives the water brown color and low pH, as opposed to foliage and vegetation of the tree line.

When two species that utilize the same resources occur in the same habitat, they will seek to avoid direct competition (encounter) by utilizing the resources somewhat different. This can lead to habitat segregation, i.e. the species prefer different habitats for which they are best suited. Activity and distribution at depth can be determined by the species temperature preference; salmonids prefer relatively cold water, living well in 12-15 ˚C, while perch, pike and carp thrive at higher temperature, often above 20 ° C in epilimnion. By summer stagnation in lowland, we find therefore often salmonids in deep layer and hypolimnion, while warm water species prefer epilimnion. In shallow lakes, salmonids may have difficulties in stagnation periods if the oxygen content is too low in the deeper water layers. This is especially the case in nutritious lakes.

Fish seek nourishment at the bottom, in the water column and at the surface. At the bottom are benthic insects, both nymphs/larvae, pupae and adults, mollusks (clams and snails) and worms. Some crustaceans also live near the bottom and shoreline and is important for example for perch and roach. Benthic animals are the main sources for brown trout, grayling, large whitefish, perch and roach, though roach may feed on algae and macrophyts. In open waters, there are many planktonic crustaceans of varying size. Large waterflies with species of the genus Daphnia are important, but also some copepod species is important. In some water the larvae of mosquito tissues important. These can live in water with very little oxygen, and remains at depths in daytime to avoid predation by fish. In twilight and darkness they wander higher up in the water column to graze. Plankton-eating fish in large lakes is primarily whitefish, vendace and smelt where these species are found, but several cyprinids are also effective plankton feeders. Charr is a plankton specialist compared with, for example, 27 brown trout, but will lose in competition with whitefish and vendace.

CLEAR WATER LAKES

When the contribution of organic matter from the lake's catchment is minor, the water becomes clear. Exceptions are in areas where glaciers add inorganic material as clay particles from glacial sediments, give the water a greenish color. The apparent green color is caused clay particles diffusing light in the water, and the blue and green light waves (short-wave, high frequency light) are spread most and giving the water a seemingly green color. The water itself does not have blue or green color. The same applies clear water that looks blue, it has no color, but the water molecules diffuse light, and the blue light is scattered more and gets visible. Both these types of lakes are primarily above the tree line. The tree line runs at varying heights, depending on distance from the coast and latitude. Coniferous belt is narrow at western and northern Norway, and also lakes in the lowlands may have clear water.

The topography surrounding a lake often gives an indication of the lake morphometry. In areas with high and steep mountains, lakes normally are deep. Clear water provides great light transmission and algal and plant production can occur at great depths. Fish community in such lakes often consists of few species, commonly brown trout and Arctic char, in some cases with newly introduced minnow. The management of such stocks is simple in principle, if the exploitation is controlled. Recruitment conditions and nutrition determine the density, growth and size of the fish. A widespread problem is large spawning areas providing high density resulting in fierce competition and slow growth.

BOREAL LAKES AND TARNS

Coniferous forest adds humus, colour and low pH to the water, but the effect depends on the bedrock, soil thickness and quality. Calcareous rocks and soil and/or thick deposits neutralize acid and the water is less colored. Humus is organic matter, where the substance lignin is an important ingredient. This substance is degraded by fungi, but not of bacteria. The fungus needs oxygen, and as there is little of this in the bottom sediments the lignin does not biodegrade in the lake sediments. Depletion of other organic substances is also slow without 28 oxygen. Lignin is also produced by sphagnum in the bogs, and in addition, mosses produce acid and lower the pH. Strong color of humus absorbs much light and the thickness of the trophogenic layer, where photosynthetic production exceeds decomposition, is reduced. Humus particles are however nutrients that can be utilized by certain detrivorous, which again can be exploited by zooplankton. Lakes in marshlands are surrounded by peet, and this is converted sphagnum slowly filling up bog lakes and marshes. The shores are more or less vertical edges, often caving inwards below the rim. In this lake type perch is a characteristic species. Roach and pike are also common, though roach is sensitive to acidification, unlike perch and pike that are among the species most tolerant to acidic water. In some lakes, roach are present in low numbers or is absent due to acidification (pH < 5.5). All three species spawn in the lake unlike trout, which may occur sympatric with perch in forest lakes, but rarely when roach and pike are present. The trout depends on spawning streams to reproduce, and this is an obstacle for the species in isolated ponds and lakes.

EUTROPHIC LAKES

These are primarily found in the lowlands, often in catchments influenced by runoff from human activities. Since the 1970s, however all runoff from household and agricultural is reduced by the construction of sewage treatment plants and various agricultural measures. Runoff from farmland have been reduced through changes in soil treatment and fertilization practices, such as reduced autumn plowing and spreading of manure shortest possible time before it can be plowed down. The eutrophic lakes have a green or yellow-green color in summer when algae production peaks. High abundance of algae reduce light transmission and the trophogenic zone, but plentiful supply of nutrients allows high production. Algae production can be so high that shortage of carbon dioxide occurs, and pH is always high in these lakes, both because nutritious lakes normally indicates a geology rich in lime and nutrients, and because the rapid uptake of carbon dioxide reduces the concentration of carbonic acid. Such lakes are productive, but are dominated by fish species not so popular to anglers, and oxygen depletion in stagnation periods is a limiting factor, especially for salmonids.

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In Eastern Norway cyprinids, especially roach, are a dominant element in eutrophic lakes and these are sought by dedicated bait anglers. In lakes outside the distribution area of these species there may be high trout production, especially if it is the only species in the lake. Perch can also live well in eutrophic lakes, commonly in competition with cyprinids. These competitors are also potential prey items and can contribute to increase the proportion of large grown perch.

ACIDIFICATION AFFECTING AQUATIC LIFE

From late 19th century, burning of fossil material, mainly coal in the early days, deposits of sulphuric and nitrous compounds from the fossilized material started to affect nature, first observed in aquatic systems. The combustion frees sulphuric and nitrogenous oxides, turning to sulphuric acid and nitrous acid when mixed with water. These are strong acids, different from naturally occurring organic acids and carbon acid. Carbon dioxide in water, like in rain water, in equilibrium with the atmospheric carbon dioxide, gives pH = 5,7, whereas sulphuric and nitrogenic acids may give pH < 4.0 in the rain water. The lowered pH also solutes aluminum, which is a very abundant metal in nature, but heavily bound to other minerals. The solubility of aluminum decreases rapidly when pH increases from 5.0 to 5.5, which means that the weaker carbonic acid cannot solute the aluminum. When acidification added the stronger acids, aluminum concentration increased, and the aquatic life was not adapted to this. Therefore, great changes, massive die offs and recruitment failure, was observed in numerous freshwater systems, and aluminum and its characteristics was supposed to have a key role.

Fish are organisms of great importance to human, and are relatively easy to observe. Massive salmon die offs in River Frafjordelva, River Dirdalselva and River Helleelva in Southwest Norway in 1920 was the first events observed and related to acidification (Huitfeldt-Kaas, 1922). This happened in the autumn, after melting of an early snowfall, assumed to be exceptionally acid. Later acidification surveys revealed that salmon is one of the most vulnerable species to acidification. Arctic charr, whitefish, vendace, roach and other cyprinids are also vulnerable to acidification. Perch and pike are the most tolerant, and brown trout is also fairly resistant, though it may vary between populations, probably a question of adaptation. 30

Though, the most striking effect of acidification is massive fish death, less observable events may occur gradually. Fish populations may become more short lived, leading to juvenilization, i.e., lack of old specimens, probably due to toxic effects from aluminum when pH varies between < 5.0 and > 5.5, causing precipitation of aluminum, which binds to the fish gills and cause slime clogging and choking. Low abundance of large specimens favor recruitment and the population may look healthy until, eventually, the pH decreases further, to chronically < 5.0. Then the eggs and larvae are injured, even of the most tolerant species (perch and pike), and recruitment fails. For the most vulnerable species, the recruitment failure occurs at pH < 5.5 (roach and other cyprinids) and even at pH < 6.0 (salmon and Arctic charr). Brown trout tolerance is somewhere between this, varying across populations.

When perch and roach coexist they are competitors, so when pH decreases to 5.0-5.5, roach is exterminated, and the perch benefits from this by increased growth and abundance. N Fish management

FISH MANAGEMENT

The aims of fish management have traditionally been to increase the proportion of large individuals of one or a few target species in a lake or a stream. Fish communities and populations are studied to explore abundance, recruitment, individual growth, mortality and exploitation of economical and ecological important species. These factors are estimated and evaluated to consider eventual need for action to “enhance” the fish stock, usually according to a human interests. When planning measures, the following should ideally be known:

- The number of fish present in the lake or stream

- Age distribution of the target fish populations

- How many individuals die naturally within a year

- Annual recruitment

- Annual growth of each age group

- Annual catch of each species

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This is too ambitious, usually, but methods exist to at least give realistic approaches to answers of the questions. Though each fish cannot possibly be counted, useful methods exist for estimating approximate numbers, sufficiently precise to decide whether the density is higher or lower than optimal (for the purpose), concerning conservation or exploitation of the population(s). A test fishing with nets including a proper choice of mesh sizes, length measuring, weighing, and age determination of the fish catches, give crucial information about aging, mortality, growth and recruitment to be used in future management. The number of fish caught per gillnet or m2 gillnet night can be a useful measure of the relative density of fish, but not necessarily. Mark-recapture experiments and successive removal are laborious methods, but on the other hand, they are far more reliable, and confidence intervals may be calculated. Modern equipment for hydro-acoustic acquisition may count and describe the size of pelagic fish, but not littoral or bottom dwelling fish.

ISSUES AND ACTION

When monitoring a fish population, age and growth can be determined routinely, though it is not necessary. If length distribution of the population remains unchanged from year to year, recruitment and growth may also be assumed unchanged, but this should be checked from time to time, like at every third survey. If catches in large meshes of the gillnets diminish whereas the catches in small-meshed nets increase, it indicates increasing recruitment, for example due to high exploitation or high adult mortality due to other causes. If such a trend continues, the fish stock will become "overcrowded" with increased competition for food and reduced individual growth. Conversely, lower catch rates in small-meshed nets suggests recruitment decline. This has often been observed in acidified waters, due to mortality of eggs and larvae. Overexploitation will result in a population dominated by young specimens, or slow growing individuals may be favored, if the fast growing individuals are caught in a particular gillnet mesh size, before maturity, it favors early maturation.

REDUCING DENSITY/BIOMASS TO INCREASE INDIVIDUAL GROWTH

High abundance of non-target species, often cyprinids, may provide need for density reduction or biomass removal. Increased exploitation may have an effect, but it is laborious. 32

In diverse fish communities, one or a few species usually dominate by numbers, and biomass removal must be operated selectively on some species and sparing others. A species that commonly occurs in high density is perch, allopatric or sympatric with pike and cyprinids or brown trout. Arctic charr is another species, often forming overcrowded populations, allopatric or in sympatry with brown trout. Populations of brown trout or Arctic charr, stunted due to strong recruitment compared with available production areas, are easier to handle as density is lower than of perch and roach, and spawning sites are restricted to areas of specific environmental conditions, current velocity and bottom substrate.

Perch can be removed with traps during the spawning in May, and can be caught by benthic nets in spring and summer. Roach can be caught selectively (avoiding perch) with gillnets on spawning sites in May, with pelagic nets and baited traps during summer. Roach can also be caught selectively with nets in autumn after the water temperature has ceased, as perch are less active and less catchable in passive gears at low temperature (< 10 C) (Linløkken & Haugen, 2006, Linløkken, Bergman & Greenberg, 2010). Arctic charr can be caught selectively with pelagic nets in summer and benthic nets on spawning sites in autumn and with baited traps in winter and spring. Heavy exploitation of Arctic charr through ice fishing (jigging) may also have an effect on stunted Arctic charr.

Stocking

Stocking, primarily brown trout and salmon, as the most common target species of anglers, is performed in several ways. In habitats harboring natural populations, it is required to breed on local strains for supportive stocking. A less common method, is to put fertilized eggs into spawning gravel in rivers and streams and let embryo and larvae develop as naturally as possible, letting the natural selection favor the most fitted individuals for the local environment. When stocking hatchery reared fish, various age and size groups may be used. The most common have been to stock fry, one-summer, one-year or two-summers and two- years old fish. Large juveniles, less vulnerable to predators, are commonly used in waters where predatory perch and, especially, pike and burbot are present. Beside that unit price of the large hatchery fish is high, large (2 – 3 years old) hatchery the fish have for several years been fed artificial food, added at the surface in a breeding tank, and may have difficulties 33 with capturing living items which are doing their best to hide on the bottom of a lake or river. Stocking smolt (2-3 years old and 12 to 25 cm long) of anadromous strains is quite different, as the fish will emigrate almost immediately, without feeding on stream living benthic fauna competing with indigenous conspecifics. Still, it is supposed to return to the “home” river to spawn, mostly, providing a stock for angling when they return. In landlocked systems, the emigration to downstream river stretches or lakes is not that straight regular, as the freshwater residents may reside in the stocking area for some time, and may potentially affect the natural occurring conspecifics through competition for territories.

Habitat Enhancement

The purpose may be two-fold; to increase recruitment to the population by improving spawning conditions and habitat for juveniles and immature fish, or it may be to improve conditions for larger fish for angling. Salmonids in running water are territorial, and fish abundance will increase if new territories are created. The individual territories are limited by sight, and boulders on the riverbed limit the territory size and may increase the number of territories. Spawning gravel and small pools will enhance reproduction, whilst excavating larger pools provide habitats for larger and mature fish. The latter is also important for wintering of stream dwelling fish. The measures are in brief, to vary the flow rate by narrowing the width of the stream by placing boulders located in groups or in a weir. Such a constriction increases the flow rate and form a rapid. Below this, a pool is constructed with a small threshold placed downstream, and the distance between rapids and threshold, i.e. the length of the pond depends on discharge, the catchment size of the stream, and the terrain slope. Slope and discharge determine the depth, current velocity and particle size of the sediment. The increased flow velocity in rapids helps to maintain the depth conditions in the pond downstream by "flushing" out sand and silt sediments in periods of high flow. Otherwise, the pools will gradually be filled up by sediment. The constructions should be supported by blasted, flat rocks. If the weirs are constructed solely of boulders and gravels from the river bed (material that mostly was brought there by the river), high flow will gradually move the boulders out of its position. Together with the gravel, they will be transported further downstream, and the weir is deteriorated and the pool filled up.

34

FISH SURVEYS

When exploring fish populations, assessment of density and species composition of a fish community is crucial for managing angling or commercial fishing, as well as ensuring preservation of threatened populations and species. It is of special interest to consider recruitment, growth and survival of populations in locations that are susceptible to water pollution or physical interventions. By physical interventions, such as constructing a hydropower plant, surveys are normally performed before and after the intervention to identify and describe possible changes. Fish surveys usually are conducted by means of test fishing in one form or another, but there are other methods that can be useful, often in combination with test fishing. Fish density can be determined by 1.) mark-recapture experiments, 2.) successive capture and 3.) hydroacoustic acquisition (in lakes). In addition, the public's use of fish resources may be studied (Cowx, 1991, Cowx et al., 1986): Who are the anglers, how much do they fish (number of trips, duration of a trip), what do they catch and what is their opinion about the angling quality, what is the target species? This can be mapped with various types of surveys providing useful information for further management, by means of catch reports, postal surveys or interviews.

Test fishing

Species identification of the sample is the first step, then: length measuring, weighing, determining sex and maturation stage, and collecting structure(s) for age determination, stomach content for analysis, samples for determining concentration of pollutants, stable isotopes (distribution of different isotopes of carbon and nitrogen at different steps of the food chain). The sampling usually involves killing a sufficient number of fish (minimum 30 or 50 specimens of the target species) to collect the necessary data, but species identification, length, weight and scales (for age analysis) may also be recorded from anesthetized fish. It is practical to store scales and otholits of each specimen in a small envelop, with notes of recorded data (date, location, species, length, weight, sex, maturation). Later, data are punched in a spreadsheet like OpenOffice Calc or Microsoft Excel, installed on most laptops. Both programs are user-friendly and flexible. Eventually, data are further loaded into a statistical software like the R program (R, 2012), which has numerous program packages for 35 special analysis, some of them specially for fish data, and even a textbook is available for treating fish data in R (Ogle, 2015).

Sampling in running water

Grayling, salmon, brown trout and salmon spawn in running water, and recruitment in small streams can easy be investigated with a portable electric fish apparatus. The device located in a backpack is equipped with an eight to ten meters long uninsulated cable of woven steel or copper wire, pulled behind the apparatus as one pole in the water, and the other pole is one or several rings of iron attached at the end of a rod (the performer wears waders). The stick with the ring is put in the water on spots where fish is expected to reside, and the current is switched on for short periods (seconds) by means of a switch on this rod. The fish are anesthetized by the electrical current, and caught in a splash by the performer or by one or two cooperators with splashes. The equipment is not harmless in use, neither for fish nor for the performer, and should not be used without proper training and accreditation. Improper use can injury and even kill fish. Use of such gear is also in violation of the law and requires special permission from the environmental management authorities.

The power source in appliances used in Norway is a 12 volt battery with a limited operating time before recharging is needed. There are also electric fish appliances powered by a generator on land. A cable, necessary to connect the device to the power source can be somewhat inconvenient, and requires at least one person helping to move the cable as the person with the apparatus moves upstream. An advantage of the aggregate operated apparatus is that voltage and current is constant, while the effect of a battery ceases during use and appliance becomes progressively less effective. It is important to have at least one newly charged battery available at the beginning of the fishery. In larger streams an electro fishing boat can be used, a flat-bottomed motor driven vehicle with multiple electrodes in the form of bare wires suspended in the water and in principle operates in the same way as the backpacked fish apparatus. The effect is much more powerful and work in rivers, although deep water is limiting also for this equipment.

Standardized methods are developed for surveys with electric fishing apparatus, and is described in EVS-EN 14011:2003 and Norwegian Standard (2003), in compliance with 36

European standards. This method requires in short that: Water course that is up to 5 m wide should be sampled in its full width along a stretch of at least 20 m. Streams with width up to 15 m should be sampled in its the full width along a stretch of at least 50 m. In larger streams, with parts of the cross section too deep for sampling with this method, a stretch of at least 50 m length should be sampled along one or along both banks. Sampling should be performed on at least three sites in a waterway and it can be done in two different ways:

- One sample at each site, and the number of fish caught per 100 m or m2 is calculated - The site is sampled by three runs, removing the fish of each run, and density and catchability are estimated.

The removal method is time consuming, but it makes it possible to estimate the number of fish and the catchability, both with confidence limits. This is based on the number of fish caught by each run. Fish is either killed or removed temporarily, kept in a tank for example, until the last sampling is conducted, and the fish can be released where they were caught. Then the fish may also be checked for potential injuries before it is returned to the stream.

Population estimates from mark-recapture experiments, marking fish by fin clipping or PIT tagging may be compared with estimates based on subsequent sampling. For the tagging- recapture methods, it is important that marked and unmarked fish have the same catchability (and mortality meanwhile) when fishing for recaptures, and it is then customary to wait for an hour or two from the first to the second sampling. If marked fish migrate out of or into the study area during the period between sampling/marking and the recapture sampling, it will of course affect the estimate. Emigration or increased mortality of tagged fish lead to lower number of marked fish in the population, biasing the population estimate upward.

Sampling in lakes

Survey nets consisting of a mix of selected mesh sizes, often linked together in gangs of two or more mesh sizes. Nordic survey nets with 12 different mesh sizes are now standard in test fishing. Multi-mesh nets consist of sections of different mesh sizes tied together as in one net. Mesh sizes range from 5 mm to 46 mm, which normally cover all relevant length groups of fish. Thread thickness ranges from 0.10 to 0.20 and more. Each mesh (section) is 2.5 m long, 37 making the multi-mesh net series totally 32 m long. There are benthic multi-mesh nets of 1.5 m depth and 4 or 6 m deep pelagic nets. Large salmon, brown trout, Arctic charr and pike are too large for this net series, and when needed, nets of 52 mm and larger meshes may be added. The modal length of a mesh size (the fish length caught most efficiently in a mesh size) is roughly 8 – 10 times the knot to knot mesh size (Jensen & Hesthagen, 1996, Jensen, 1976, Linløkken, 1984), depending on the fish species (actually body height).

According to standard methods of test fishing with nets (BS EN 14757:2015; Standard Norway 2005), three gillnet series should be placed at every 3 m depth interval: < 3 m, 3-6 m, 6-9 m, 9-12 m etc. for benthic nets, and a manual for this by Morgan and Snucins (2005) is available on the internet. Catches of each species is evaluated for each depth interval and catch per. effort is calculated (Catch per unit effort, CPUE) for species and depth. Units of effort can be a gillnet series, or 100 m2 net in 12 or 24 hours. This method gives an expression of spatial distribution of species; littoral or benthic areas or in the pelagic, and at which depth they occur.

Alternatively, gangs of gillnets in series of selected mesh sizes, may be used, depending on what kind of fish communities there are to be examined. It should nevertheless, be selected mesh sizes that are included in the Nordic series to make it comparable with other studies. Small mesh sizes are less effective than large, and especially catches in mesh sizes smaller than 10 mm compared with catches in larger mesh sizes, are not representative of the population (Jensen & Hesthagen, 1996). The small-meshed nets is also very expensive to purchase. A series may therefor start from mesh size 10 mm and continue with 12.5, 16.5, 19.5, 24 mm etc. When fishing in populations of stunted perch and roach, catches in 24 mm, and even in 19.5 mm, are sparse. In most perch lakes there are however some large, piscivorous individuals which are of particular interest. These are few in number, and should be spared, if possible, from survey fishing. A large perch may be removed from the net and put back again, after recording an approximate length. These predators are important to reduce the recruitment of stunted perch, roach and others.

Fish can swim along the shore, in the littoral zone, near the bottom at different depths, or it may move in the pelagic zone, and move between habitats. Behavior varies between species, with size and age, season and temperature, and must be accounted for when gillnetting is planned. In the littoral zone and at the bottom at deeper water (profundal zone) benthic nets 38 are used (usually 1.5 m deep, though some are 2 m), equipped with a sinking line that is heavier than the floating ability of the upper line so they sink to the bottom, standing as a “soft” wall. Pelagic nets for use in open waters has a floating line with greater fluidity, but most are slightly sinking, so without anchoring and floaters (floats, plastic jugs or polystyrene/frigo bits) at the ends and distributed along floating line, they will slowly sink to the bottom.

Catches from different mesh sizes and from each net is treated separately, put in plastic bags with location, mesh size, depth and date added with a marker on the bag (alternatively on a paper with pencil written markings inside the bag), and recorded in the field notes. Further sampling should be done from fresh fish, but this is not always possible. The catch can be frozen and processed later, and it is important that the fish are stored in sealed bags with the least possible air in the bag. Freezing causes dehydration and weight loss, and leakage in the bags makes the fish lighter after a few days and weights and length-weight relationship, condition factor, will be biased.

SAMPLING

When catches from a test fishing are brought ashore, fish species must be determined. This may be easy when few species are present and the fishermen are familiar to the area and the lake. Lack of this familiarity and presence of several cyprinid species make it different. Data of fish length in mm or cm, weight in grams, sex and maturity stage (spawner this season or not), should be recorded as soon as possible. Enumerate each fish and the recorded data on a small envelope with scales and otoliths inside, eventually opercular bones (Fig.). Otoliths are used for age determination of most species of salmonids, cyprinids and perch, but also scales, mainly for back-calculating of length. Opercular bones are used for back-calculating length of perch, ruff and pikeperch, whereas for pike, the metapterygoid bone (Fig. ) is recommended (Sharma & Borgstrøm, 2007). The latter requires more work, but is the best structure for age determination of pike. Mucus and skin must be removed from the structures by soaking the pike head in hot or boiling water, before rinsing and storing in paper envelopes (this smells).

Nutrition and food selection are studied by sampling stomach content, emptying it by cutting the esophagus and squeezing out the content. It can be stored in alcohol or put in a freezer. 39

Analysis of heavy metals (like mercury and lead) which are water soluble, and organic compounds (like dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyl (PCB) and others) which are fat soluble, and samples to analyze for stable isotopes to explore trophic levels in the food web, are all performed on tissue cut from the dorsal muscle, and eventually the liver, hart, brain, kidney. This samples must be kept in absolute sealed wrapping as small leakages of fluid or evaporating water will bias the weight of the sample to be analyzed, and in the next bias the estimation of the target element, usually given as part per million (ppm) of wet or dry weight.

For genetic analysis, small tissue samples, often a small (< 1 cm2) part of a fin, eventually the adipose fin (salmonids) are collected. This may be stored frozen, but the most convenient way in the field, is to add the piece on a 1.5 ml eppendorf tube with 96% ethanol.

AGE ANALYSIS

Winter zones, i.e. the narrow hyalin rings (Fig. ) are counted and give the number of years (actually winters) the fish has lived (in tropical areas this is not so easy). Age determination is most accurate with otolith for most species, but for pike the metapterygoid bone is the best. When fish length growth stagnates, the winter zones of scales and opercular bone are

Opercular bone and cross section of the otolith of a perch, showing 9 year of age.

40 deposited so narrow they are difficult or even impossible to count. In otoliths, however, checks are also deposited by increasing its thickness, and even when length increment are neglible, the winter zones can be counted so otolith age provides total age. Back calculation of length is done by measuring distances Ri from a center (specific for the structure selected) of the structure to each zone i (R1, R2, R3, etc.), and to the outermost edge (RT) of the structure (total scale or opercula radius). It is nevertheless important to know the age of the fish, so scale and opercula analyzes should always be compared with otolith age. The annual growth can be interrupted of environmental events, such as a temperature fall for a period in the summer, forming false checks.

Otoliths are read under a binocular microscope, and the quality of the microscope is important. Quality generally follows the price, but before ordering equipment, try it on the kind of objects you intend to study. It is very important to choose magnification suitable for the objects size, and 10x ocular and 40X objective may be a good choice for otoliths, 10X and 5 to 10X for opercula, depending of fish size.

Scale of a seven years (winters) old brown trout caught in South Imsdalsjøen in Hedmark county, pretty easy to read, with easily detectable winter zones due to proper winter conditions at 616 m a.s.l.

CALCULATIONS

LENGTH AND WEIGHT RELATIONSHIP 41

Length (L) weight (W) ratio (BMI) can tell us whether the fish is "in good fit" or not. A common way to describe this relationship is by Fulton’s condition factor K:

K = (W, g) x 100 /(L, cm)3

Normal good condition for brown trout and Arctic charr is considered to be 1.0 or slightly above this. A fish that measures 25 cm and weighing 156 grams, will have condition factor K = 156/253 = 1.0. In populations with good access to nutrients, K will increase with fish length, i.e. the growth is allometric, unlike isometric growth, which means that K is constant with length. Allometry can also mean that condition factor decreases with increasing length, which is not a good sign. "Normal" condition factor will vary between species due to different body shape. The perch, for example, with its higher shape compared with brown trout, will naturally get a slightly higher condition factor than trout, without being more "fat" for that reason, especially large specimens.

Length-weight ratio can be calculated by means of a regression analysis to achieve a mathematical model describing the relationship between length (L) and weight (W). The best regression model (i.e. with the highest coefficient of explanation r2) is usually obtained by analyzing the log transformed length and weight. This can be done easily in a spreadsheet and used to calculate the average fish weight and condition factor at a selected fish length within the length groups of fish we analyze.

Log W = b • Log L + a, where W is given in gram and L in mm and a is a constant (intercept), and W can be written as: W = a • Lb and b = 3 means isometric growth. The condition factor K for a fish of length L is

K = a • 105 x Lb-3

BACK CALCULATION OF LENGTH 42

Back-calculation of length is best when based on structures that are relatively large, such as scales and opercular bones, because the larger structures are easier to measure precisely. Annuli (winter-checks) in an otolith from a slow growing fish may be difficult to count accurately by commonly used instruments and even worse to measure. Width or radius (R) of winter zones in a scale are relatively easy to measure, for example by using a microfilm reader or a microscope, marking the checks on a graph paper. Opercular bones must be read in a binocular microscope and zone width (R) measured by means of a ocular with scale or a drawing mirror on the microscope (Fig ). The calculations can further be performed in two ways. It can be assumed direct proportionality between the fish length (L) and the structure being measured (R), the proportional hypothesis method (Francis, 1990):

Lt /Rt = LT /RT => Lt (LT • Rt) /RT

where LT is fish length, RT is the total radius of the structure being measured, for example, a scale, and Lt is fish length at age t calculated by scale radius Rt at age t. The method is claimed to be more acurate than the regression method described below (Francis, 1990). The relationship between the length of the structure and the fish length may be described by means of a regression model. This model is then used to calculate the previous year's length:

L = b • R + a

Natural logarithm Ln (L) and Ln (R) is used when it provides a better model (higher r).

GROWTH RATE

Growth is defined as weight increase, and increase pr. unit time is growth rate. By back calculation of length, transformed to weight by the estimated length weight relationship, the growth rate can be calculated for previous years. 43

The length-weight regression model combined with back-calculated length are used to calculate previous years weight (Wt-1). The natural logarithm (ln) of the relationship between the fish weight (Wt) and back-calculated weight in the previous year (Wt-1) then gives the instantaneous growth rate Gt = ln (Wt/Wt-1), providing a rate of weight increase; G = 0 at no growth and G = ln (2) = 0.69 if the fish has doubled its weight. It demonstrates at which age growth slows, normally at sexual maturation. Access to other prey species, often associated with habitat change, may increase the growth rate. This happens when brown trout recruits leave spawning/nursing stream, and enter a lake where other food animals are available. The brown trout of Lake Mjøsa is a good example, entering Lake Mjøsa at size 15 – 25 cm (Fig. ), where smelt are an abundant prey species. Perch live their entire life in the tarn or lake but shifting diet as it grows, and when some switch to piscivory, and increase its growth (Fig. ).

POPULATION ESTIMATES

Reliable population estimates require much work, and precision, often expressed in confidence intervals, is closely related to effort. By mark-recapture experiments, the number of marked fish has the largest impact on confidence intervals, and is usually the most demanding part. Hydro acoustic acquisition is less labor intensive than mark-recapture experiments, but the estimates are based on records of something we do not see, and includes only fish occupying habitats where they may be spotted by the echo sound beam. The precision is not so high, but can be increased by increasing the number of transects. This takes time, and if the fish has an uneven horizontal distribution, the confidence intervals nevertheless are large. Gillnet or trawl sampling in addition, is necessary to determine species and age distribution of the counted fish.

MARK - RECAPTURE

Fish tagging of groups can be done by several methods to explore migrations, the effect of stocking or to estimate the number of fish, based on fraction of marked fish in the sample. The easiest way is to remove the pelvic fin (which does not grow back) of salmonids, of other species other fins are selected (a pelvic fin), but only a little bit of those fins may be removed. 44

These fins regenerate but breaks in the fin rays witness the history. Since adipose fin clipping is commonly used to mark hatchery fish before stocking (to monitor the stocking success), it should be avoided for wild fish within the same area. It must be noted that cutting fins or parts of fins of living fish, demands permission from veterinary authorities.

The number of fish in a population, for example in a lake, can be estimated by the fraction of marked fish in the sample (Petersen, 1896). For example, M = 1,000 fish were marked, and C = 2,000 fish are caught when sampling for recaptures, of which R = 200 (10%) proves to be marked. Then we can calculate that the 1,000 tagged fish accounted for 10% of the total population (under certain conditions), and the population can be calculated by N = 2000x (1000/200) = 10,000 fish.

R /M = C /N => N = C • M/ R

This simple formula has been adjusted to avoid downward bias, especially at low R (Ricker, 1975):

N = [(M+1) • (C+1)]/(R+1) - 1

This is supposed to be unbiased when R > 8 or M • C /N > 4.

Variance of the estimate is given by:

V(N) = [N2 (N - M) • (N - C)]/M C • (N - 1)

when catch C is not returned (drawing without replacement, most common)

Whereas when catch C is drawn one fish at a time and put back alive (drawn with replacement) it is:

V(N)=M2 • C • (C - R)/R2 45

The method is implemented in the r package “fishmethods” with the command: mrN.single(M=948,C=421,R=167,alpha=0.05)

for a given example of M, C and R, applying S.E. and 95% C.I. Confidence level 95% is applied as a default option which can be left out, but for the alternative 99 % C.I., adding alpha=0.01 is necessary. The C.I. estimate is based on assuming the recaptures R, as counting data, to be Poisson distributed. The proportion fin clipped juveniles in test fishery catches tells whether fish stocking program is success or failure.Repeated marking and capture, releasing recaptures alive, during a period of time, for example trapping perch during the spawning period of perch, giving a multiple census, was developed by Schnabel (1938). This is an example:

Date Ct Mt ∑Mt Ct • ∑Mt ∑(Ct • ∑ Mt) Rr ∑Rt ∑Ct •Mt/Rt 11.06 342 342 15.06 140 134 342 47 880 47 880 6 6 7 980 23.06 99 77 476 47 124 95 004 15 21 4 524 30.06 244 240 550 134 200 229 204 4 25 9 168 08.07 113 - 790 89 270 318 474 17 42 7 582 09.07 17 - 790 13 430 331 904 1 43 7 718

The final estimate is N = ∑ (Ct • Mt)/∑Rt = ∑ (Ct • Mt)/R = 7 718 specimens, and the variance and confidence interval is computed like for the single census case (above).

INDIVIDUAL TAGGING

Individual tagging, like PIT tagging, opens for quit different methods of population estimation by repeated encountering, catching without killing, recording individual numbers of tagged specimens. Software like MARK (White, 1996, White & Burnham, 1999) and the RMark package (Laake, 2015) in the r software package.

Earlier, the Carlin tags were used, with low rate of tag losses, but time consuming tagging processes. Now, Floy tags and Pit tags both inserted by using a handy brand pincers, can be inserted much faster than Carlin tags, the first one with some tag loss, depending on the execution, other latter with no tag loss.. 46

Individual tagging also allow exploration of fish migration. Pit tags are needle or nail formed, inserted in the peritoneum, and recorded by means of a portable hand reader, eventually by an antenna mounted in the creek or river, and connected to a recorder that stores the data for later downloading to a pc.

SUCCESSIVE REMOVAL

Population number N may be estimated from sequential catches if catchability remains constant through the experiment, unaffected of density. This method is commonly used with electro fishing in running water, but can be used also with traps or nets. There are two slightly different methods to be used: Leslie method (Leslie & Davies, 1939) which is based on decreasing catch per effort in successive captures (assumes removal of significant numbers of specimens in each sampling), and Moran-Zippin method (Moran, 1951, Zippin, 1956, Zippin, 1958) which is based on capture and cumulative catches. At least two, but preferably three or more sampling occasions are necessary. Trap- or gillnet sampling must be performed more than three times. Catches from each sampling (C1, C2, C3, eventually C4 and more) are removed, killed or kept in isolation until the last the sampling is completed. This method requires that the capture probability is equal at each occasion, which is not always the case. Estimation by these methods can be performed in the r program package FSA. The example below shows results from the FSA package performed on data from two locations. The results of B, based on three sampling occasions, gave large C.I., due to the difference between the relationships C1/ C2 and C2/C3, but by performing one more sampling, the C.I. was reduced and N increased.

Sampling location A B B’ C 1 64 27 27 C 2 33 20 20 C 3 19 8 8 C 4 - - 3 N 136.5 54.1 65.4 95 % C.I. 98.7 - 174.3 -108.4 – 216.6 40.2 – 90.5

47

By the use of nets and fish traps, this is particularly difficult because this is passive gear and catchability depends on the activity of the fish. Withdrawals of large catches reducing density significantly, affect fish activity and thus catchability. In addition, gillnet saturation at large catches will reduce the catches and underestimate the density. The same applies to a trap full of perch, hardly with room for one fish more. By successive captures, it is easy to check whether fish size is important for catchability. Number of large fish caught will normally decrease faster from one sampling occasion to the next, compared with smaller sized fish, due to higher catchability.

HYDROACOUSTICS

Sonar registration is primarily suited for lakes, especially lakes with trough-shaped basin, with limited shallow areas and pelagic fish. An echo transceiver consists of two units, and is operated from a boat. The main unit produces signals emitted via the second unit, the transducer submersed beside the boat and submits audio signals vertically towards the bottom or horizontally in the upper water layers (Fig. ). The transducer can also be placed stationary on the bottom and transmit signals towards the surface. The latter method is suitable to detect fish that are so near the surface that it is spooked by the boat. Echo signals are returned from fish encountered in the water and from the bottom, and received by the transducer, which forwards it to the main unit where it is recorded with echo strength and counted. Based on the time it takes from transmitting and till receiving the echo of a fish, the depth of the fish is calculated, and the size is determined from the echo strength, adjusted for depth. The size of the fish's swim bladder is important for echo strength. The signals are recorded on a PC based software for later analysis. Audio signals transmitted vertically in the water covering a cone shape with a top angle of 7, 9, 11 or 29 degrees, depending and equipment type. The area covered therefor increases with distance from the transducer (i.e. with depth), so the registration covers a small water area/volume close to the surface. The analysis software SONAR 5 calculates the number of fish in the pylon, and divide this by the area of the cone base midway between top and bottom of the selected segment. The program can analyze segments of the pylon, for example of 0 to 10 m (in practice 2 to 10 m), 10 to 20 m depth, etc. It is an advantage if the majority of the fish are located at depth > 10 m, not too close to the bottom (> 1 m), since that makes it difficult to separate the fish from the bottom signals. 48

Sonar Registration combined with pelagic gillnetting or trawling, gives a good picture of the density and biomass of pelagic fish species like vendace, whitefish, Archtic charr, smelt and cyprinids. The registration should be conducted when a largest possible fraction of the fish stock is “countable”, that means at leats one meter above the bottom, > 5 m below the surface, and preferably in areas of > 10 m. Alternativ ely, the signals may be transmitted horizontally or vertically from the bottom and towards the surface.

Echogram produced by a Simrad EK15 echosounder showing a transect in Lake Mjøsa, an evening in early December. Analysis in SONAR 5 gave 1127 fish > 10 cm per ha and 79 fish > 25 cm per ha. 30 % were recorded as single fish, and 70 % was integrated from shoals.

AGE DISTRIBUTION AND MEAN AGE

Results from age analysis presented in a table or a bar graph, show when the fish is recruited in the sampling gear, and the distribution age groups fully recruited. If the age distribution shows a steady decrease to the right in the diagram, it suggests that recruitment and mortality is stable from year to year. Often it is not so, and recruitment fluctuate from year to year suggesting varying cohort strength. Many fish species form strong year-classes in summers of high temperature. One explanation may be that high temperature increases the production of prey animals for the larvae, and perhaps more important, high temperature provides high 49 feeding activity and consumption for larvae and juveniles. It leads to faster growth and larger juveniles at the end of growing season, and winter survival of fry is positively related to size. Winter is, on high altitudes, a period of low activity and nutrient consumption. The fish spend their energy reserves from the summer and fall, and mortality can be high.

SURVIVAL AND MORTALITY

Survival S, commonly on annual base, is the relationship between the number of specimens alive Nt at a time t and the number of fish present a year before Nt-1.

S = Nt-1/ Nt => Nt = Nt-1/S

Variance is given by:

V(S) = S • (1 – S)/Nt

Mark and recapture can also be repeated after one year to estimate annual survival S:

S = R12 • M2/M1 • R22

Where M1 and M2 are the number of fish marked in year 1 and 2, respectively, and R12 and R22 are the number of recaptures of fish marked in year 1 and 2, respectively, recorded in year 2. The variance V of the estimate is:

V(S) = S• (1/R12 + 1/R22 – 1/M1 – 1/M2) and standard deviation S.D.(S) = √(V(S))

If reliable estimates of N are available, this is a simple calculation. Population estimates are not always available, and they are laborious to achieve. Survival and mortality can be estimated based on age distribution in a fish sample, though the assumption of constant annual recruitment and mortality, i.e. a steady state population. Chapman & Robson’s method (Chapman & Robson, 1960), implemented in the r program package “fishmethods”. Murphy (Murphy, 1997) raised some objection to the method.

S = T/(n + T – 1)

V(S) = S (S – (T – 1)/(n + T – 2))

Where n is the sample size and T is a statistic, estimated as follow:

T = (0 x n0) + (1 x n1) + (2 x n2) + (3 + n3) + (4 + n4) + ….. (t + nt) 50

Where n is coded age, staring with 0, the youngest age group fully recruited in the catches, and n1 is the age group one year older. An example:

Age Coded age nAge 2 11

3 0 n0 = 34

4 1 n1 = 21

5 2 n2 = 14

6 3 n3 = 8

7 4 n4 = 3

Age group 3 is the youngest recruited (notice the increase of n from age 2 to 3). The recruitment age can be checked by:

2 2 2 Χ 1 = (S – (n - n0)n) / (T(T-1)(n-1))/(n(n+T-1) (n+T-2)

2 and when this is significantly larger than expected (i.e. Χ 1 => P < 0.05), the chosen n0 group is not fully recruited in the catches, and should be replaced by n1.

By means of the FSA package in the r-programt:

(input) > age <- c(2,3,4,5,6,7) > ct <- c(11,34,21,14,8,3)

> cr3 <- chapmanRobson(age,ct,3:7) #i.e. n0 = n3, omitting n2 = 11 > summary(cr3) (output) Estimate Std. Error

S = 51.83 (0.5183) and S.E. = ± 3.91

Z = 0.652 and S.E. = ± 0.0879

> To find the instantaneous mortality rate Z we use the relationship:

S = e-Z => Z = - lnS

Z is the instantaneous natural mortality M, if no fishing mortality F occurs, but when fishing occurs, the instantaneous natural and fishing mortalities are additive: 51

Z = F + M

Instantaneous rates are needed to calculate exploitable stock at a specific time of the year, for example at the beginning of the fishing season, let us say 6 months after the population estimate was achieved. We use S= 0.5 and transformed to natural logarithms, the instantaneous annual mortality rate Z = - ln S = 0.693. Instantaneous mortality rate of half the -0.347 year is: 0.5∙ Z = -0.347 and survival rate during this time is S0.5 = e = 0.71, saying that 71 % of the stock will survive for the next 6 months, whereas 50 % that are expected to survive for the next year. This calculation assumes constant mortality rate through the year, which is most probably not thru, but calculation of monthly rates are laborious, and most often not needed. Recruitment studies may be exceptions. In management of exploited stocks, instantaneous fishing mortality during the fishing season, must be accounted for. The instantaneous mortality rate then is Zx = Mx + F, the sum of natural mortality M during the fishing period and mortality due to fishing F, during the period x. This could be during four months, that means Mx = 0.25 ∙ M. F is calculated by catchability (probability of being caught) q = C/Nx and Fx = - ln(1 - q), whereas the rest of the year, M1-x = M0.75 = Z – F – Mx, is working (Fig. ).

NUTRITION AND PREY SPECIES OF FISH

With few exceptions, freshwater fish feed on other animals, primarily invertebrates; insects, crustaceans and mollusks. Fish preference of food is related to fish size, its mobility and speed, and its equipment in the form of gap size, teeth and gill rakers, and generally small fish feed on smaller sized food items than larger fish of the same species. The smallest prey, plankton, are three groups, rotifers are very small and are eaten by larvae and small juveniles of lake spawning fish (whitefish, perch and cyprinids). Solmonids like vendace and smelt, with numerous long gill rakers, are typical planktivorous throughout their life. Whitefish also have many gill rakers, and the number may vary between populations even within the same lake. In Sweden four to six different types are described, in Russia eight? types are described within lakes, like Lake Ladoga. Plankton feeding populations of whitefish have more and denser gill rakers than whitefish who tend to be more benthivorous. Crustaceans represent the majority of plankton species and are divided into water fleas (Cladocera) and copepods. Water fleas include species with very different varieties of appearance, but the "classic" water 52 flea shape may be represented by the Daphnia sp., a genus including several species that are ecologically important herbivorous and also important prey species when occurring in quantity. The smaller species of the genus Bosmina, not looking too different from the Daphnids, are also important to many fish stocks, and there are several genera closely related to those mentioned. Other water fleas, like Bytothrephes longimanus, Polyfemus and Leptodora, looking quite different from Daphnids and Bosminas, are also important prey animals. Copepods are most important to the more specialized planktivorous, due to small size (most of them) and probably their jumping way of moving, but they are more available during winter than the water fleas, and they are hosts of many nematodes and represent a major source of parasitic worms in fish. Amphipod (Gammarus) and isopod (Assellus) crustaceans, benthic insect nymphs, larvae, pupae and adult insects are important food items, as well as annelids, mollusks; snails and clams. Fish diet is common in several species of fish, especially after having reached a certain length, commonly an ontogenetic shift take place of fish between 12 to 15 cm of length. Perch may become piscivorous between 15 and 20 cm long, brown trout at about 25 cm long, but there are variations.

STUDYING NUTRITION

Sampling to study fish nutrition, once you got the hand on the fish and recorded adequate data, starts with cutting the esophagus close to the stomach and expel the stomach content. Cyprinids have no stomach, so a portion of the intestine must be cut out and examined. Samples are stored in tubes with ethanol or in small plastic bags and frozen. Stomach sample analyzes are done under a stereo microscope. Fish nutrition may be divided broadly into four groups; items caught on the surface, plankton, benthos and fish. Many fish species go through several ontogenetic niche shifts during life, often starting with plankton as the smallest, then shifting to benthos and some end up as piscivorous. The stomach content may be a mix of plankton and benthos. Plankton, i.e. water fleas, copepods and phantom midge larvae, for fish larvae also rotatoria), and benthos, i.e. commonly mayflies, caddis flies, stoneflies (running water), chironomids and alderflies (forest lakes and ponds). Cyprinids have pharyngeal teeth and powerful digestive fluids and stomach samples may be difficult to analyze. Many fish species eat fish larvae, which immediately after hatching are not much larger than a 53 zooplankton, whereas preying upon larger fish is more demanding. Perch and pike predate other fish from rather small size, commonly when <15 cm, whereas brown trout start from a length about 25 cm. Small individuals of brown trout, perch, roach, pike and cyprinids are common in pike and perch stomachs, i.e. often cannibalistic, whereas large brown trout predate smelt, vendace and whitefish when available.

The stomach contents may be presented as frequency of fish with major food items present in the stomach. It may be presented as mean volume percent of each food item in each fish, or as mean percent of weight. A review of methods is given by Hyslop (1980). Further analysis are performed to evaluate importance of different food items and compare food selection between species or between cohorts or size groups of species. Stomach content data may be analyzed for dominance of species or groups in the stomach of one species or size group, and it may be analyzed for overlap in food selection.

In a dense allopatric population, a pronounced competition between conspecifics is expected, and individual specialization on different kinds of food items may be observed, expressed as low variance in individuals and high variance between individuals. Bolnick et al. (2002) reviewed four different methods, all with approximately the same result on a given data set, and one of them, Roughgarden’s index (Roughgarden, 1972) is given here:

Total niche width TNW = Var(xij)

Within-individual component WIC = E[Var(xj |i)]

Between-individual component BIC = Var[E(xj| i)]

The relative degree of individual specialization can be measured as the proportion of TNW explained by within-individual variation, WIC/TNW. As this value approaches 1, all individuals utilize the full range of the population’s niche, whereas smaller values indicate decreasing inter-individual overlap and hence higher individual specialization. Roughgarden’s WIC/TNW is limited to continuous data. To carry this approach over to discrete data such as the frequency of alternate prey taxa in the diet, Roughgarden (1979:510) proposed a measure that uses the Shannon-Weaver index as a proxy for variance. The following formulae are equivalent to Roughgarden’s formulation. Let nij represent the number (or mass) of diet items of category j in individual i’s diet. This raw data matrix is then transformed into a proportion matrix P, with elements pij describing the proportion of the jth resource category in individual i’s diet. Then, 54

Within individual component WICS = ∑i pi •( -∑j pij • ln pij )

Between individual component BICS = ∑i pi • ln pi) - {∑j qj •[-∑i γij ln(γij)]}

Total niche width TNWS = -∑j qj • ln qj)

To explore niche overlap between size groups or species, or feeding habits between different time periods the following formula may be used (Schoener, 1970)

Cxy = 1 – 0.5 • (∑ | pxi – pyi|)

Where pxi is the frequency of food item i in group x (species 1) and pyi is the frequency of the same item i in group y (species 2). The more different frequencies of food items, the lower

Cxy, i.e. the less niche overlap.

If relative abundance of prey items is known, a selection index may be calculated (Pearre, 1982):

Va = [(ad * be)-(ae * bd)]/sqrt[(ad+ae)*(be+bd)*(ad + bd)*(ae+be)] Where ad = relative abundance of prey type i in the diet be = relative abundance of all other prey ae = relative abundance of prey type i bd = relative abundance of all other prey in the diet

This describes the food selection of species or size groups of a species, and adds information about the niche occupied by a species.

GENETIC SURVEYS

Analysis of microsatellites (MS) and single nucleotide polymorphism (SNP) are modern tools, as compared to the formerly used allozyme electroforeses, to explore and describe population genetics. Genetic diversity expressed as number of alleles per locus, proportion of heterozygotes and even the theoretical effective population size, as well as number of siblings, parent-offspring relationships and genetic differentiation between population, genetic structure within and area. 55

A number of software packages for the purpose are available on the internet for free, including manuals. The softwares require input files of different formats. The input file format for the GenPop software is used by several programs, and among them the packages Convert, GenAIEx and MicrosatelliteTool all have the ability to convert the GenPop format files to the formats of other softwares, like Fstat, Arlequin and Structure, the latter two work nicely with both MS and SNP data.

POLLUTANTS AND CONTAMINATION

With pollutants we understand substances, somehow with toxic effects that spread through the environment resulting from human activity. They can be divided into two groups, heavy metals and organic contaminants. Metals are naturally occurring, but usually in very low concentrations. Manufacturing concentrates up some metals, as actual products or as waste from production. Mercury is well known in that regard. This is a highly toxic metal, occuring in low concentrations in most minerals. It has been used to make wood and grain stocks accomplished against microorganisms, precisely due to its toxicity. It was used from 1940 - century until the 1970s when the adverse effects of this was proven in many contexts, and it was abounded. Instances in nature, such as the atmosphere, will be there for many years yet, spread by air currents far from the original sources. Organic toxins, organic molecules consisting primarily of carbon, hydrogen and oxygen, often with halogens, are substances produced by humans, for example in the form of insecticides (insecticides) as DDT and brominated flame retardants used in the textile industry. These are digested by microorganisms, but this takes time, and on the way to the complete breakdown to carbon dioxide, water and other elements such as nitrogen and sulfur compounds, or halogens such as chlorine, bromine and fluorine in a somewhat unpredictable sequence. These intermediates may themselves be very toxic. When toxins are ingested by organisms the concentration will be higher in the organism than in the surroundings, and this is called bioconcentration. It is absorbed in the organism at a certain rate, a capture rate which depends on intake, mostly through food. Some part of it is not absorbed in the organism, whereas a certain part is bound in the tissue. If the capture rate is higher than the separation rate, there will be an accumulation with time, called bioaccumulation. When the poison has entered the food chain, it will be transferred from one trophic level to the next, and it will be more concentrated in the higher trophic level. Due to 56 this, predators will have a larger intake and higher concentrations in the body than herbivores. This is called biomagnification.

FISH PARASITES AND DISEASES

To explore the parasitic fauna in a fish population, veterinary expertise should be engaged. Samples should be handed over as living or fresh material, if possible, to keep the all parasitic microorganisms detectable. If this is not possible, samples should be preserved in ethanol or formaldehyde (not preferable of health regards). If the fish biologist is left to undertake the examinations, some multicellular organisms are pretty easy to record. Some examples are given below.

LEECHES

Acanthobdella peledina is an echtoparasite on brown trout, Arctic charr, grayling and whitefish in cold water. Usually we find the firm sucked on the ventral side of the fish, especially around the pelvic fins. It is < 2 cm long, but can occur in a large numbers on individual fish, and cause major external injuries.

PARASITIC CRUSTACEANS

Lices on fish occur in two species in Norway, Large (Argulus coregoni) and Small fish lice (). Fish lice are spherical and flat, adapted to life as exterior parasite in fish, living on blood and other body bag. Large sea lice can be up to 1 cm, and due to the size it influences fish welfare and behavior. Typical of brown trout with sea lice is that it often performs high jumps, attempting to get rid of lice. When trout are jumping with good clearance to the surface, it is very likely that the lake has a dense population of both fish and fish lice.

Parasitic copepods on fish are found in several forms and stages of development. It is proven 57 a few species in Norway, and one of these species, Salmincola edwardsi, is a gill parasite on Arctic charr. The parasite is a blood sucker, about 5 mm long, and the female has two distinctive egg sacs as appendages on the abdomen. The parasite is found especially in lakes with high density of Arctic charr, and it is shown that powerful attacks can cause bleeding and mortality. Perch has a separate species, Achtheres percarum, which also parasite pikeperch.

NEMATODES

Nematodes are everywhere, free-living and parasitic forms, and are very numerous, both in terms of number of species and individuals. We can find nematodes in brown trout and Arctic charr, where the red field threadlike worm is coiled in a bag. Generally, with minor effect on the fish.

FLUKES

Gyrodactylus is a monogenic fluke, i.e. it has only one host, and it is echtoparasitic at the mucus of the surface of the host skin, especially close to the fins. The most famous is G. salaris, parasiting salmon and rainbow trout. Species like brown trout and grayling also have their Gyrodactylus species (respectively G. truttae and thymalli), but live better with them than the Norwegian salmon do with G. salaris. Salmon populations in the Baltic region and rainbow trout can host G. salaris because they are adapted to the presence of the parasite. The parasite was accidentally introduced to Norway with salmon smolt from the Baltic Sea region, with disastrous effects in many Norwegian salmon rivers.

TAPEWORMS

There are several species of tapeworm, and several species spend larval stages in copepods, entering the fish with its prey. Plankton-feeding fish can be eaten by birds or other fish, and the parasite enters its next host on its way back to the main host and reproduction. The main host where they have their reproductive stage, often gave the named to the parasite. 58

The genus Diphyllobothrium, with D. ditremum hosted by loons, herons and fish predating ducks, is widespread even in high altitude areas. White yellowish cysts can be seen on the outside of the stomach of brown trout, charr, whitefish and vendace, resembeling cysts of D. dendricum, hosted by seagulls, with smaller, more spherical and with a more blueish white than yellowish compared with those of D. ditremum. D. latum is another species which may infect freshwater fish and even humans, when eating raw or undercooked freshwater fish. This tapeworm is regarded as the largest parasite that may infect humans.

Triaenophorus robustus is a cestode with pike as its main host, and is also called the pike worm. Whitefish is a common intermediate host, feeding on infected copepods. The larvae migrate into the meat of whitefish, where they are converted into liquid-filled, thin-walled cysts. These cysts are no appetizing, and in lakes with pike, whitefish may be heavily infected and is not popular as food. Vendace may also be subjected to pike worm, but have a low degree of infection, probably due to greater resistance. As plankton specialist vendace is more susceptible to infection, but this may have made it more resistant to the parasite. Freezing kills the parasite, and makes it also difficult to detect. Examination for pike worm should be performed on fresh material.

Cyathocephalus truncatus is a tapeworm that might develop in the intestine of many different freshwater fish, and its only known intermediate host is Gammarus. Will waterspiders eaten by a trout, puts battlefield jammed inside the intestinal wall, especially in pylorus sacs, where it is sitting the rest of your life. The worm affect river fish general condition, and gammarus must not be transferred from lakes that are infected to lakes where the parasite has not been proven.

Brown trout and Arctic charr worms, Eubothrium crissum and E. salvelini, respectively, are tapeworms living in the fish intestine (primary host) as adults, while small copepods are the intermediate host. It can be found in large quantities without seeming to affect the quality of the fish, and this type of tapeworm is not considered to be as harmful as f. ex. seagull worm. Other fish species have similar types of tapeworms.

59

UNICELLULAR ANIMALS (PROTOZOA)

The three groups of protozoa contemplated in terms of parasites in freshwater fish, flagellates, ciliates and Sporozoa. Here we mention the sporozo Henneguya zschokkei, which providing abscesses with an off-white, thin liquid content in muscles. The flagellate Costia that can cause problems to fish in aquariums, but also on wild fish in natural environment. It is an external parasite and massive attacks are deadly, fish species are affected differently.

WHIRLING DISEASE (MYXOBOLUS CEREBRALIS)

Myxobolus cerebralis is a disease, which is provoked by a unicellular organism with a stage in the life cycle of asexual reproduction by rutting. It attacks the cells forming bones and cause abnormalities, including the spine so that it tends to spiral shape. This is a common parasite in Norway and Europe, but not in America. Transfer of European trout to North America have brought the parasite with them to an environment that was previously unfamiliar with the parasite and therefore lack the resistance as European fish stocks have, and the parasite has caused great damage. The parasite is a possible reason why the American rainbow trout with only a few exceptions, do not establish wild populations in Norway, despite the fact that it has been stocked many places.

Fish are, like other wild animals, regularly in contact with bacteria of various types. Wild animals normally have an ability to resist infections potential harmful, but an impaired general condition can have serious consequences. Natural occurrence of potentially harmful organisms are not easily observed before an outbreak of disease resulting in mortality in a population.

FUNGI

Fungus parasiting fish are not really fungus but belong to the phylum Oomyceta, representing many species, and Sapprolegnia spp. is one genus. It is typical for Oomyceta, as for fungus, 60 that they reproduce and spread with spores that are small and highly resistant to physical stress, and they can spread with fishing gear and anything else that moves between locations. Crayfish plague is one such example, although not affecting fish. Oomyceta, like fungus, need oxygen, and thrive in moist environments. Moisture is not limiting in water, and high temperature has a favorable effect on growth and proliferation. Fish are most vulnerable to attack at places where slime or skin is injured, and farmed fish are particularly vulnerable if they live cramped and get abrasions on the nose or fins (Johnsen & Ugedal, 2001).

VIRUS

Virus is detectable through their symptoms. Several types of virus cause diseases, especial in fish farms, due to high fish densities, and also the fact that outbreaks of diseases are observed more easy that in the wild.

CREEL SURVEYS

To explore the angling quality of a given area, lake(s) or stream(s), it is a good idea to ask the anglers about their experiences and points of view. Fishing licenses may be sold with a table to fill out catch report and return to the fishing association. In recent years it has become common with license sales and catch reporting over the internet or mobile phone. In some areas, the anglers are checked for license by fish controllers, and this can be combined with a creel survey, and give tips and advice to unexperienced anglers. A somewhat more laborious method is postal surveys, sending out a questionnaire after the season to people who have bought license. The most important information is: how many fish of different species and how much they weighed, and were any tagged fish caught? It may be numbered/individual tags or removed adipose fin. Number of fishing trips and average number of hours per fishing trips is of interest. If the permit covers several localities, as they often do, it must be noted where it was fished. This provides information about where the angling activity is high and low, i.e. what is the most popular area, the most popular target species? The catch per effort, number and grams of fish per fishing trip or per angling hour may be negatively correlated with number of angling trips/hours, suggesting over exploitation, too many anglers or too 61 many fish removed. The number of anglers may be reduced by increasing the license price, to reduce the number of fish removed. The latter is also achieved by regulation of minimum or maximum size of fish allowed to be removed, or by catch release practice.

CURRENT TOPICS

Freshwater fish are of less economic importance than marine fishes, though repercussions of angling of anadromous salmonids are important in some local communities. Freshwater fish species are important as idicators of environmental changes in nature management, like direct physical or chemical effects caused by human activities or as results of climate changes. As mean temperatures increases and winter time becomes shorte, wether this is man made or not, life in water will be affected. Temperature is a crucial factor to all living organisms, espscially poikilothermic organisms like fish and all invertebrates. Activity and energy demands depend on temperature, and shortened winters combined with higher summer temperature must be expected to affect recruitment of fish populations as well as individual growth. Fish species are evolutionary adapted to different climatic conditions, and some species, especially some salmonids are adapted to low temperatures and will be more affected than others. Through this, species composition and lake ecology will be affected as results of altered competion and predation, and not least altered parasitic fauna and eventual enterence of new species.

TEMPERATURE INCREASE

Effect of temperature on perch recruitment was suggested already in th 1920ties by the Finnish researcher Silverstjerna, and LeCren developed this explanation further from the 1940-ties. LeCren also found correlation between indvividual growth and temperature. This has later been repeated in numerous surveys. Based on this, perch density may be expected to increase, though temperature increase will also affect intra- and interspecific interactions, i.e., competition and predation. The final outcome is therefore unpredictable, and high temperature during winter is shown to reduce egg quality of yellow perch. In systems with few species, it may seem easier to predist. Brown trout is often allopatric in alpine lakes, sometime coexisting with Arctic charr, and the limiting factor of recruitment is shown to be 62 the langth of growth season, i.e., roughly the time from ice break/snow melt and icecover. Shortened winter time therefor will make it possible to reproduce at higher elevation and increase the area of brown trout.

INVASIVE AND ALIEN SPECIES

Species may invade new areas as temperature increases and makes habitats closer to the poles suitable. “Successful” new species are called alien, and often cause detoration of local, natural species. Invasive species may host parasites, new to the area and the existing species, and may have a devastating effect.

INTERNATIONAL AGREEMENTS

The European Union (EU) is consern about habitats and environmental management on general, is focusing on conservation of species and their natural environments (EU’s habitat directive). To preserve species in the long run, the availability of natural habitats is a prerequisite, as the alternative is artificial environments, i.e. keeping populations more or less in captivity. This will make it difficult and even impossible to maintain the natural or original population structures and gene pools.

EU’S Water framework consentrate on environmental conditions in streams and lakes, i.e. algea, zooplankton and fish, as well as phisical characteristics, especially related to human impact, regulation of rivers and lakes, pollution and toxicants. It rest a commitment on each nation to bring a description of the present state, and preparing for restauration of affected habitats, back to natural state. This has opened financial sources to hardly needed surveys of streams and lakes, and laying a groundwork for future monitoring work.

MOLECULAR BIOLOGY AND SPECIES CONSERVATION

Though gentic analysis of wild animals has been done for many decades, a standardization of methods is yet to be seen, in part because new and improved methods are steadily appearing. Microsatellite analysis followed the isozyme analysis as a tool to decribe genetic diveristy in populations and differentiation between populations. Development of ststistical methods and software packages, mostly downloadable for free, has opened a new word to population studies. Relatedness, siblings/halfsiblings, parants/offsppring, may be calculated with an 63 estimated probility. Further, detection of genes under selection and effective population size may be estimated. These methods produce indices well suited for monitoring purposes. In conservation concern, basic questions will be: is the genetic diversity constant, is the differentiation between nabouring populations constyant, i.e., is the genetic structure constant, and is the effectiv population size constant? Routinly analysis of 30 or 50 specimens of a populations, for exemple of each generation, can answer these questions with a limited economic effort. Sampling can I most cases be done without killing anaimals, for fish, scales or a small part of a fin is enough. The use of scales open the oportunity to historical records as scales have been sampled for more than hundred years.

Uncategorized References

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