This Document Is Made Available Electronically by the Minnesota Legislative Reference Library As Part of an Ongoing Digital Archiving Project
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This document is made available electronically by the Minnesota Legislative Reference Library as part of an ongoing digital archiving project. http://www.leg.state.mn.us/lrl/lrl.asp (Funding for document digitization was provided, in part, by a grant from the Minnesota Historical & Cultural Heritage Program.) Minnesota Department of Natural Resources lnvestigational Report 414, 1992 EVALUATION OF BIOENERGETICS MODELING IN THE STUDY OF PREDATOR-PREY DYNAMICS IN MINNESOTA WATERS OF LAKE SUPERIOR1 Mary T. Negus Minnesota Depanment of Natural Resources Section of Fisheries 10029 Nonh Shore Drive Duluth, MN 55804 1 This project was funded in part by Federal Aid in Sport Fish Restoration (Dingell-Johnson) program. Completion Report, Study 642, D-J Project F-26-R Minnesota. Table of Contents Abstract 1 Introduction 1 Study Area 2 Literature Review and Data Compilation . 4 Lake trout . 4 Chinook salmon . 6 Coho salmon . 7 Steelhead ............................................... 8 Kamloops ............................................... 10 Atlantic salmon . 11 Sea lamprey . 12 Forage species ........................................... 13 Bioenergetics Methods . 14 Model Simulations . 14 Sensitivity Analysis . 16 Bioenergetics Results . 16 Model Simulations . 16 Sensitivity Analysis . 18 Discussion . 18 Data Compilation . 18 Model Simulations . 20 Sensitivity Analysis . 22 Information Needs . 23 References . , . 25 Appendix A - Temperature data . 30 Table A 1 - Lake Superior water temperatures . 30 Table A2 - Lake trout temperature data . 31 Table A3 - Chinook salmon temperature data . 32 Table A4 - Coho salmon temperature data . ·. 33 Table A5 - Rainbow trout temperature data . 34 Table A6 - Atlantic salmon temperature data . 35 Table A 7 - Temperature inputs for bioenergetics model . 36 Appendix B - Length and weight data . 37 Table Bl - Lake trout length and weight data . 37 Table B2 - Lake trout length-weight relationships . 38 Table B3 - Chinook salmon length and weight data . 39 Table B4 - Coho salmon length and weight data . 40 Table B5 - Steelhead trout length and weight data . 41 Table B6 - Kamloops and Atlantic salmon length and weight data . 42 Table B7 - Weights used in model simulations . 43 Figure Bl - Lake trout length-weight relationships . 44 Figure B2 - Chinook salmon length-weight relationships . 45 Figure B3 - Coho salmon length-weight relationships . 46 Figure B4 - Steelhead trout length-weight relationships . 4 7 Figure B5 - Steelhead trout and Kamloops length-weight relationships . 48 Figure B6 - Atlantic salmon length-weight relationships . 49 Appendix C - Diet and prey caloric densities . 50 Table C 1 - Lake trout diet . 50 Table C2 - Chinook salmon, coho salmon, rainbow trout and Atlantic salmon diets . 51 Table C3 - Prey caloric densities . 52 Appendix D - Population abundances and mortalities . 53 Table Dl - Numbers of salmonines stocked . 53 Table D2 - Native lake trout and coho salmon population . 54 Table D3 - Mortality rates, all species . 55 Appendix E - Sensitivity analysis . 56 Table El - Sensitivities of simulation models . 56 Appendix F - Simulation model outputs ..................._. 58 Table F 1 - Total cumulative consumption, all species . 58 Table F2 - Cumulative consumption at equal stockings . 59 Table F3 - Age of greatest impact on forage base . 60 Table F4 - Relative cost of individual salmonines . 61 Appendix G - Forage base . 62 Table G 1 - Forage fish populations . 62 Appendix H - Ration and growth evaluation . 63 Table H 1 - Baseline ration (P) values . 63 Figure Hl - Lake trout growth at various ration levels . 64 Figure H2 - Chinook salmon growth at various ration levels . 65 ii Abstract.--Lake Superior's fish community has undergone dramatic changes since the mid-1950's, with major shifts in the forage base, invasion of exotics, and the decline of lake trout. Predator species have been introduced, and many of the predator stocks are maintained by stocking. The impact of these stocked fish on the forage base, and the ability of the forage base to sustain projected stocking levels are unknown. The most current information on fish populations in Lake Superior has been collected by biologists in three states, several tribes, the province of Ontario, and the U. S. Fish and Wildlife Service. Much of the information, however, is unpublished or in publications with limited distribution. Bioenergetics modeling can use basic population data for answering research and management questions about predator-prey dynamics, stocking quotas, and forage requirements. The objectives of this study were: 1) to compile data on the major salmonines in Minnesota waters of Lake Superior, as input for a bioenergetics model; 2) to estimate salmonine predation on prey populations in Minnesota waters through modeling simulations; 3) to conduct sensitivity analyses of the bioenergetics model; and 4) to prioritize data requirements for input to the bioenergetics model. Estimates of consumption by predator stocks in 1989 totaled 2,814 metric tonnes of rainbow smelt and 249 metric tonnes of coregonines, which greatly exceeded biomass plus production estimates of forage species (about 100 metric tonnes of rainbow smelt and 85 metric tonnes of coregonines). Discrepancies could be due to underestimates of forage fish biomass or inaccuracies in data on predators. Predator consumption estimates in the bioenergetics simulations were most influenced by values used for predator population abundance, weights, diets, and prey caloric densities. Further data acquisition should focus on the forage base biomass and production, predator age and growth, periodic diet monitoring, predator population abundances, and mortality rates. Introduction maintained without the high level of risk previously encountered. Lake Superior's fish populations are sup Bioenergetics modeling is a powerful plemented by extensive salmonine stocking, tool for answering questions about preda but quantitative information about existing tor-prey dynamics, stocking quotas, and the stocks and community interactions is incom forage requirements of predators (Christie et plete and difficult to obtain. Traditional al. 1987; Hewett and Johnson 1987). Bio management strategies, aimed at one species energetics modeling uses fish physiology, or game species only, were inadequate in temperature, growth (weight at age), diet this dynamic ecosystem. Efforts focused on composition, prey caloric content, and popu rehabilitating fish stocks when populations lation abundance data to estimate food con showed signs of distress, emphasizing the sumption (Kitchell 1983; Hewett and John trial-and-error nature of fisheries science at son 1987). Sensitivity analysis (Kitchell that time. The increased stocking desired by 1983) can be used to evaluate existing data, anglers sometimes conflicted with managing and identify and prioritize future data needs. toward a renewable and stable fish commun Variation in number and strain of stocked ity (Spangler et al. 1987). Christie et al. salmonines, and the unknown extent of (1987) and Spangler et al. (1987) recom natural reproduction has made standing stock mended a community analysis to predict the estimation difficult in Lake Superior. How effects of management actions on the species ever, estimating the forage requirements of assemblages. Management strategies are Minnesota-stocked fish is a manageable now focusing on this community approach, goal. Results can be used to adjust stocking so that healthy fish communities can be 1 quotas and harvest regulations to ensure a forage base (Hansen 1990). The small size stable fishery. and inshore distribution of rainbow smelt A review of the recent history of the fish may make them of lower value than lake community in Lake Superior emphasizes herring as forage for lake trout (Jacobson et many changes and interactions. , The fish al. 1987). Lake herring were historically a community has undergone dramatic changes preferred lake trout forage, with pelagic since the mid-1950's beginning with the lake-wide distribution. Since the resurgence invasion of the sea lamprey Petromyzon of lake herring populations, however, lake marinus, and the decline of lake trout Salve trout have shown a reluctance to return to linus namaycush and lake herring Coregonus lake herring as a forage base (Hansen 1990). artedii. Rainbow smelt Osmerus mordax, Fish population information from Lake which invaded in the mid-1950's and Superior has been collected by biologists in boomed in the 1960's, replaced declining three states, several tribes, the province of lake herring as the principal lake trout for Ontario, and the U. S. Fish and Wildlife age (MacCallum and Selgeby 1987; Busiahn Service. Because of agency differences, 1990; Hansen 1990). Subsequent lake reha data sets are sometimes inconsistent and bilitation programs included harvest restric difficult to compare. Lakewide impacts tions on lake herring and lake trout, sea from different management strategies are lamprey control, and lake trout stocking difficult to evaluate because the effects are (Lawrie and MacCallum 1980; Walters et al. cumulative and stocks are poorly defined. 1980; Busiahn 1990). Rainbow smelt stocks Rapid assessment methods and prioritizing have fluctuated and are now in a severe data acquisition are paramount, given the decline lake-wide, while lake herring are size and complexity of Lake Superior. making a strong comeback (Schreiner and Objectives of this study were: 1) to Morse 1990). The primary method of har compile available