AN ABSTRACT OF THE THESIS OF Siaurdur Gudjonsson for the degree of Doctor of Philosophy in Fisheries Science presented on May 17, 1990. Title: Classification of Icelandic Watersheds and Rivers to Explain Life History Strategies of Atlantic Salmon Abstract approved: 4 Redacted for Privacy Charles E. Warren A hierarchical classification system of Iceland's watersheds and rivers is presented. The classification is based on Iceland's substrate, climate, water, biota, and human cultural influences. The geological formations of Iceland are very different in character depending on their age and formation history. Three major types of formations occur: Tertiary, Plio-Pleistocene, and Pleistocene. These formations have different hydrological characters and different landscapes. There are also large differences in the climate within Iceland. Four major river types are found in Iceland: spring-fed rivers in Pleistocene areas, direct runoff rivers in Plio-Pleistocene areas, direct runoff rivers in Tertiary areas and wetland heath rivers in Tertiary areas. Eleven biogeoclimatic regions occur in Iceland, each having a different watershed type. The classification together with life history theory can explain the distributions, abundances, and life history strategies of Icelandic salmonids. Oceanic conditions must also be considered to explain the life history patterns of anadromous populations. When the freshwater and marine habitat is stable, the life history patterns of individuals in a population tend to be uniform, one life history form being most common. In an unstable environment many life history forms occur and the life span of one generation is long. The properties of the habitat can further explain which life history types are present. In the most stable and favorable rivers of Iceland resident life history forms are more common. Such a classification of a river habitat greatly aids the understanding of the habitat and how it enables and constrains thesalmonid populations within it. Consequently adaptations in life histories are better understood and conservation, utilization, and management of these valuablenaturalresourcesare made more coherent and efficient. Classification of Icelandic Watersheds and Rivers to Explain Life History Strategies of Atlantic Salmon by Sigurdur Gudjonsson A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Completed May 17, 1990 Commencement June 1991 APPROVED: Redacted for Privacy Professor Emeritus of Fisheries and Wildlife in charge of major Redacted for Privacy Head of Departm4nt of Fisheries and Wildlife Redacted for Privacy Dean of Gradte School Date thesis is presented May 17th, 1990 Typed for Sigurdur Gudjonsson ACKNOWLEDGEMENT I would like to express my deep appreciation to Dr. Charles E. Warren for his suggestions, encouragement, and support throughout the course of this study and also for spending his extra hours correcting manuscript and suggesting improvements. I would also like to thank other members of my committee; Dr. James D. Hall, Dr. William J. Liss, Dr. Charles L. Rosenfeld, Dr. GordonMatzke and Dr. FrankMoore for encouragements and helpful suggestions. I am grateful to Thor Gudjonsson and Arni Isaksson for giving me the opportunity to conduct this study at the Institute of Freshwater Fisheries in Iceland. I also thank my colleagues at the Institute of Freshwater Fisheries; Gudni Gudbergsson, Thorolfur Antonsson, Fridjon M. Vidarsson, Larus Kristjansson, Magnus Johannsson and Sigurdur M. Einarsson for their assistance and Dr.Tumi Tomasson for reviewing the manuscript. I am especially grateful to my wife, Gudridur, and my sons, Gudjon and Gunnar, for their encouragement and patience throughout this endeavour. Research funds were partly provided by a grant from the Icelandic National Science Fund. TABLE OF CONTENTS INTRODUCTION 1 Classification 1 Habitat view 1 Watershed as the fundamental unit 2 Contextualistic view 2 Capacity and performance 2 Hierarchy 3 Classification of stream systems 3 Adaptation 4 Present study 4 ICELANDIC WATERSHEDS AND RIVERS 5 Domains of Icelandic watersheds 5 Human population and geography 5 Vegetation 8 Geology 10 Earthquakes 13 Hydrogeology 16 Soil and loose sediments 18 Landscape 21 Climate and ocean condition 24 Temperature 26 Sunshine and global radiation 26 Precipitation 29 Forecast areas 32 Climate in the past 32 ICELANDIC FRESHWATERS 37 Surface hydrology 37 Geothermal water 37 Glaciers 39 Lakes 39 River types 40 Runoff characteristics 41 Influence of climate on flow pattern 43 Chemical compositions of river water 45 Electrical conductivity 47 CLASSES OF ICELANDIC RIVERS 50 Quaternary rivers 51 Spring-fed rivers 51 Direct runoff rivers in Plio-Pleistocene areas 55 Stability and productivity of the rivers in the Quaternary areas in Iceland 57 Tertiary rivers 58 Direct runoff rivers in Tertiary areas 58 Wetland heath streams 59 Stability and productivity of the Tertiary rivers 60 DISTRIBUTION AND ABUNDANCES OF SALMONIDS IN ICELAND 62 Icelandic freshwater fauna 62 Management of the freshwater fisheries 62 Habitat preferences of salmonid fishes 63 Distribution and abundance of salmonids in Iceland in relation to the classification 65 ADAPTATION OF SALMONIDS TO THE ENVIRONMENT - LIFE HISTORY STRATEGIES OF SALMONIDS 69 Review of ideas 69 Life history traits and their interaction 74 Incubation time 74 Time of spawning 75 Egg number and size 75 Freshwater age 76 Smolting 79 Time and size of seaward migration 80 Age at maturity 80 Life history strategies 87 LIFE HISTORY PATTERNS OF ICELANDIC SALMONIDS IN RELATION TO THE CLASSES OF ICELANDIC WATERSHEDS AND RIVERS 89 Life history data 89 Life history in spring-fed rivers 90 Spring-fed rivers in south Iceland 90 Spring-fed rivers in south-west Iceland 91 Spring-fed rivers in north Iceland 93 Lifehistory in Quaternary direct runoff rivers 94 Quaternary direct runoff rivers in south-east Iceland 96 Quaternary direct runoff rivers in south Iceland 96 Life history in Tertiary rivers 98 Direct runoff rivers in north-west Iceland 98 Direct runoff rivers in north Iceland 99 Direct runoff rivers in east Iceland 101 Direct runoff rivers in west Iceland 101 Wetland heath streams in north-west Iceland 104 Wetland heath streams in north-east Iceland 107 The life history strategies of Icelandic stocks of salmonids in relation to the classification 107 REFERENCES 113 LIST OF FIGURES Figure Page 1. Topography of Iceland 6 2. Inhabitated areas in 1980 7 3. Vegetation in Iceland 9 4. The mid-Atlantic ocean rift zone and Iceland 12 5. The age of geological formations in Iceland 14 6. Active volcanic systems in Iceland 15 7. Pleistocene formations of Iceland 19 8. Neovolcanic formations of Iceland 20 9. Sea currents around Iceland 25 10. Average temperature in Iceland in July 1931-1960 27 11. Average temperature in Iceland in January 1931-1960 28 12. Distribution of global radiation in Iceland 1958-1967 in July, expressed in cal/cm2 day 30 13. Average annual precipitation (mm) in Iceland 1931-1960 31 14. Distribution of potential evapotranspiration (mm) 1958-1967, annual values 33 15. Potential water balance (mm), annual values 34 16. Weather forecast areas in Iceland 35 17. A drainage map of Iceland, annual runoff in mm 38 18. Drainage patterns of Icelandic rivers 52 19. Classes of Icelandic watersheds and rivers 54 LIST OF TABLES Table Page 1. Amount of dissolved solids in mg/1 and specific conductivity in uS/cm (25 °C) for several Icelandic rivers 48 2. Distribution of salmonids in the rivers of Iceland 68 3. Several life historytraits of salmon stocks of spring-fed riversin south-west Iceland 92 4. Several life historytraits of salmon stocks of spring-fed riversin north Iceland 95 5. Several life historytraits of salmon stocks of Quaternary directrunoff rivers in south Iceland 97 6. Several life history traits of salmon stocks of direct runoff rivers in north-west Iceland 100 7. Several life history traits of salmon stocks of direct runoff rivers in north Iceland 102 8. Several life history traits of salmon stocks of direct runoff rivers in east Iceland 103 9. Several life history traits of salmon stocks of direct runoff rivers in west Iceland 105 10. Several life history traits of salmon stocks of wetland heath rivers in north-west Iceland 106 11. Several life history traits of salmon stocks wetland heath rivers in north-east Iceland 108 12. Summary of life history patterns of salmonids in Icelandic rivers in relation to the stability of river and oceanic environments 110 Classification of Icelandic Watersheds and Rivers to Explain Life History Strategies of Atlantic Salmon INTRODUCTION Rivers and streams and their biological systems are valuable resources and their value will without doubt increase in the future. Understanding of these ecosystems will help to insure their conservation and wise management. Classification In order to understand nature, humans classify natural systems.Habitat classification is one way of understanding ecosystems. Many attempts to classify rivers and streams have been based on various chemical, physical, and biological variables, either in combination or alone (Huet 1959, Illies and Botosanenu 1963, Pennak 1971, Hynes 1970, Hawkes 1975, Binns and Eisermann 1979, Oswood and Barber 1982). There have been, however,few attempts to integrate these major groups of variables. The suitability of selected habitat variables has often been doubtful, even though success or failure of the stream inventory depends on this