GROWTH PROCESSES IN THE TWO SCOTTISH POPULATIONS OF POWAN, COREGONUS LAVARETUS (L.) (EUTELEOSTEI, SALMONIDAE) VOLUME I Elizabeth A. R. Brown A Thesis Submitted for the Degree of PhD at the University of St. Andrews 1990 Full metadata for this item is available in Research@StAndrews:FullText at: http://research-repository.st-andrews.ac.uk/ Please use this identifier to cite or link to this item: http://hdl.handle.net/10023/2772 This item is protected by original copyright This item is licensed under a Creative Commons License GROWTH PROCESSES IN THE TWO SCOTTISH POPULATIONS OF POWAN, COREGONUS LAVARETUS (L.) (EUTELEOSTEI, SALMONIDAE) by Elizabeth A. R. Brown Department of Biology and Preclinical Medicine University of St. Andrews A thesis submitted for the degree of Doctor of Philosophy June 1989 I dedicate this thesis to the memory of my father Allan Melville Brown (1.5.30 - 3.1.89) ACKNOWLEDGMENTS I am grateful to the many people who assisted in this research, including Mrs Flora Slack for the use of her home, the Yett of Ptarmigan, as a field base, also her boat for sampling Loch Eck. Rab McMath of the University Field Station allowed us to use the Field Station boat to sample Loch Lomond, often at odd hours and very short notice. Salar Properties Ltd. gave us permission to net powan in Loch Eck. Murdo McKenzie and the local angling club allowed us the use of their boat in the first winter on Loch Eck. Thanks are also due to the technical staff of the Department of Biology, and to Dr C. Muir for technical assistance in investigating methods of examining otoliths and bones. Dr P.S. Maitland provided scales and data of earlier Loch Lomond samples, P.P. Pomeroy and A.F. McCulloch made available the data for the first two Loch Eck samples, and Dr D.B.C. Scott provided the data of previous Loch Lomond samples, collected by himself and many postgraduate and honours students. Thank you to my mother, M.I. Brown, for entering these 1979-84 Loch Lomond field data into a computer database at the end of which she "never wanted to see another fish figure again!", also to my sister A.L.R. Brown for typing most of this thesis. The study was funded by a University of St. Andrews 'Janet Thomson Anderson Memorial Scholarship' for three years, with an additional grant from the Russell Trust Fund to help start the Loch Eck sampling. The work was supervised by Dr D.B.C. Scott. ABSTRACT ., The powan, Coregonus lavaretus (L.) is endemic to only two British waters, Loch Lomond and Loch Eck, Scotland. This thesis describes the seasonal and longer term growth processes of the two populations, concentrating on growth in length back-calculated from scales, factors affecting recruitment and mortality, reproductive cycles, and seasonal deposition and mobilisation of storage products, particularly lipid. The interrelationships of these cycles is discussed. The populations differ in their diet and duration of feeding, and it is shown that most of the inter- population differences in seasonal cycles of growth relate to these feeding differences. The Loch Eck population is the more variable. In addition to adult and immature powan, a third category is identified, termed adolescents. These are fish which are entering their first reproductive cycle. Immature and adolescent fish are analysed separately and compared with the adults. There are some differences in seasonal cycles between the juveniles and adults, mainly in relation to the presence or absence of the reproductive cycle. A preliminary histological study of the ovaries of adolescent females is carried out. Comparison of historical data with the results of the present study shows that there has been little change in the Loch Lomond powan in the past 200 years. Both lochs are coming under increasing human pressure, and conservational measures urgently need to be taken if the powan populations are to survive. TABLE OF CONTENTS VOLUME 1 Page 1. TELEOST GROWTH, POWAN, AND THE POWAN LOCHS 1.1 Introduction 1 1.2 General materials and methods 13 1.3 Results 17 1.4 Discussion 20 2. AGE AND SOMATIC GROWTH 2.1 DETERMINATION AND VALIDATION 2.1.1 Introduction 22 2.1.2 Materials and methods 30 2.1.3 Results 37 2.1.4 Discussion 44 2.2 GROWTH FROM YEAR TO YEAR 2.2.1 Introduction 70 2.2.2 Materials and methods 72 2.2.3 Results 74 2.2.4 Discussion 91 2.3 RECRUITMENT AND MORTALITY 2.3.1 Introduction 109 2.3.2 Materials and methods 111 2.3.3 Results 115 2.3.4 Discussion 118 3. REPRODUCTIVE AND STORAGE GROWTH PROCESSES 3.1 REPRODUCTION 3.1.1 Introduction 134 3.1.2 Materials and methods 137 3.1.3 Results 140 3.1.4 Discussion 146 3.2 WEIGHT CHANGES RELATIVE TO DEPOSITION AND MOBILISATION OF STORAGE PRODUCTS 3.2.1 Introdution 153 3.2.2 Materials and methods 157 3.2.3 Results 158 3.2.4 Discussion 164 3.3 LIPID ANALYSIS, WATER AND PROTEIN CONTENTS 3.3.1 Introduction 174 3.3.2 Materials and methods 178 3.3.3 Results 185 3.3.4 Discussion 194 4. JUVENILES 4.1 Introduction 206 4.2 Materials and methods 207 4.3 Results 208 4.4 Discussion 220 5. GENERAL DISCUSSION 5.1 INTERRELATIONSHIPS OF SEASONAL GROWTH PROCESSES 5.1.1 Feeding 231 5.1.2 Reproduction 234 5.1.3 Somatic growth 250 5.2 VARIATIONS IN GROWTH PROCESSES FROM YEAR TO YEAR 256 5.3 THE TWO POPULATIONS COMPARED 5.3.1 Summary 260 5.3.2 Feeding 263 5.3.3 Liver 267 6. THE POWAN, PAST, PRESENT AND PROSPECTS 271 REFERENCES 280 VOLUME 2 TABLES 1.1 - 6.5 APPENDICES 1 - 4 FIGURES 1.1 - 6.1 PLATES 1 - 45 1 CHAPTER 1 TELEOST GROWTH, POWAN, AND THE POWAN LOCHS 1.1 INTRODUCTION. (a) Growth 'Growth' is an oversimplification in that it actually involves a complex of distinct, yet interrelated, processes. These processes are sometimes categorised as: (i) somatic growth (ii) reproductive growth (iii) deposition and mobilisation of storage products (Shul l man, 1974; Weatherley & Gill, 1987). In practice, the categories are not as rigidly separable as this scheme implies; for example, although protein is essentially structural, and is therefore a component of somatic growth in teleosts, it is also drawn on as a storage product. All the growth processes are seasonal, reproductive and storage growth being characterised by cycles of accumulation and expenditure, which are often annual. The timing of the seasonal processes may be dependent on environmental cues (as in reproduction, Ch. 3.1), or by physiological triggers including feedback (as, perhaps lipid metabolism, Ch. 3.3). In this thesis, somatic growth (Ch. 2) is defined as growth which is progressive throughout the life of a fish, although it varies seasonally in its rate, periods of rapid growth alternating with periods of slow or no growth. In teleosts somatic growth refers mainly to the long term build up of skeleton and muscle and can be measured by changes in 2 length or weight. Length is used here as the main criterion of somatic growth because body weight is contributed to by both structural and mobilisable protein and by lipids, and the use of 'condition factors' (Le Cren, 1951; Bolger & Connolly, 1989) does not distinguish between these. Also, by the method of back-calculation from calcified tissues (Ch. 2.1), it is possible to assess the growth of fish in years other than those in which the samples were taken (Iles, 1974). Reproductive growth (Ch. 3.1) is here defined as including gametogenesis, the development of secondary sexual characteristics, and behaviour associated with reproduction. Reproduction accounts for a very high proportion of the resources available for growth. Ovaries may account for up to 40% of the total weight in some species, and testes, though often less in bulk, may be metabolically more expensive to produce (Ursin, 1979). Storage (Ch. 3.2, 3.3) in teleosts is mainly in the form of lipids, which may be present in very high concentrations (Shul l man, 1974). Dried specimens of candle- smelt, Thaleichthys pacificus (Richardson), were used as torches by Southern Alaskan Nishka Indians (Swan, 1880 cited by Miller, 1979). Protein may also be drawn upon, sometimes to a lethal extent as in Pacific salmon (Idler & Bitners, 1959; Love, 1980), but carbohydrates do not contribute significantly to storage (Elliott, 1976a; Craig, 1977). The pattern of storage and mobilisation depends on the extent to which the availability of food and metabolic requirements 3 coincide, and varies from species to species (Shul'man, 1974) and even from population to population (Chs. 3, 5). These growth processes depend ultimately on the food resources available, and how these resources are partitioned amongst them. Feeding, studied by Pomeroy (1987), will be discussed in this thesis as the primary factor controlling growth processes. There have been many studies of feeding, resource partitioning, and growth in teleosts (reviewed by Weatherley & Gill, 1987), but the value of many of these studies has been limited by a variety of factors. In some cases the fish have been studied under laboratory conditions with imposed feeding regimes (e.g. Brown, 1946a,b,c; Elliott, 1975a,b, 1976,a,b,c; Weatherley & Gill, 1981, 1983,a,b). In many cases only a few of the growth processes could be simultaneously studied, for practical reasons. Shullman (1974) wrote, "The morphological, physiological and biochemical aspects of growth may be studied, but this is practically impossible within the framework of a single investigation. It is also difficult to combine a study of growth connected with an increase of the animal's mass with a study of the growth of its reproductive tissue".