Stochastic simulation model for the Hawaiian monk seal by Albert Lively Harting, Jr A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biological Sciences Montana State University © Copyright by Albert Lively Harting, Jr (2002) Abstract: The Hawaiian Monk Seal (Monachus schauinslandi) is an endangered marine mammal that lives almost exclusively in the remote Northwestern Hawaiian Islands. Recent trend estimates suggest that the species is declining in abundance due to a number of mortality sources, including starvation, intraspecific aggression, shark predation, and disease. The primary objective of this project was to develop a comprehensive stochastic simulation model to aid in understanding how certain natural perturbations and management alternatives influence the monk seal population. The model uses the data on demographic rates, migration rates, and other life history components acquired through long-term investigations by the National Marine Fisheries Service. The model is specific to the life history of the monk seal, and was designed to be highly flexible so that a broad array of simulation scenarios could be structured. The core sequence of steps in the model is survival (with options for multiple rate schedules and inter-atoll correlation in survival), reproduction, and migration. Each of these life history components is stochastically implemented, with the fate of individual seals determined by binomial sampling. All demographic parameters are specified as distributions, with simulation-specific values drawn from those distributions. Options available in the model include density dependent regulation, natural perturbations (shark predation, single or multiple male aggression, birth catastrophes, and survival catastrophes), and management intervention (removal of aggressive males, capture and captive rearing of females, translocation of females, and short-term captive maintenance of pups). Trial simulations were performed to explore specific phenomena and demonstrate the power of the model. The simulations indicated that age structure anomalies would likely lead to further decline at French Frigate Shoals over at least the next 10-12 years. This atoll was largely insensitive to management intervention targeted at improving pup survival because poor survival of juveniles negated the positive effects of those actions. Density dependent regulation acted to homogenize simulation trajectories, often masking the effects of other perturbations. Uncertainty regarding the correct form of density dependence in the monk seal makes long-term projections (> 25 years) tenuous until those uncertainties are resolved. The expected outcomes from natural or management-induced perturbations are best explored through shorter-term projections in which various different density dependence modes are employed. STOCHASTIC SIMULATION MODEL FOR THE HAWAIIAN MONK SEAL by Albert Lively Halting, Jr. A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Biological Sciences MONTANA STATE UNIVERSITY Bozeman, Montana . August 2002 j)3K 4 \ V U 5 APPROVAL of a dissertation submitted by Albert Lively Halting, Jr. This dissertation has been read by each member of the dissertation committee and has been found to be satisfactory regarding content, English usage, format, citations, bibliographic style, and consistency, and is ready for submission to the College of Graduate Studies. Daniel Goodman (Date) Jay J. Rotella (Date) Approved for the College of Graduate Studies Bruce McLeod '< ? (Signature) (Date) Z 'l iii ) STATEMENT OF PERMISSION TO USE In presenting this dissertation in partial fulfillment of the requirements for a doctoral degree at Montana State University, I agree that the Library shall make it available to borrowers under rules of the Library. I further agree that copying of this dissertation is allowable only for scholarly purposes, consistent with “fair use” as prescribed in the U.S. Copyright Law. Requests for extensive copying or reproduction of this dissertation should be referred to Bell & Howell Information and Learning, 300 North Zeeb Road, Ann Arbor, Michigan 48106, to whom I have granted “the exclusive right to reproduce and distribute my dissertation in and from microform along with the non-exclusive right to reproduce and distribute my abstract in any format in whole or in part.” Signature Date 7 / /? / o3 Z / ACKNOWLEDGEMENTS I would like to express my gratitude to all of the staff at the Honolulu Laboratory of the National Marine Fisheries Service who have helped with this project in countless ways. In particular, I wish to thank Jason Baker, Brenda Becker, and Thea Johanos, both for providing the core data used in the monk seal simulation model and also for aiding in the proper interpretation of those data. Chad Yoshinaga deserves special thanks for persevering during my first (sometimes bungling) field season in the Northwestern Hawaiian Islands. Each of these veterans provided insights into the ecology of the monk seal, borne from years in the field and long hours wrestling with the data, which were invaluable in developing the model. I also wish to thank George (Bud) Antonelis for taking the risk to support this project when I first approached him as an unknown quantity in the marine mammal world. My major professor, Dr. Daniel Goodman, has been a constant source of stimulation and sage guidance throughout this process. The success of this modeling effort is due in large part to his vast experience in marine mammal demography and stochastic modeling. He has been a mentor and a friend. I also wish to thank the other members of my Graduate Committee: Steve Cherry, Scott Creel, Michael Gilpin, Bruce Maxwell, and Jay Rotella. They provided a great deal of constructive guidance to help direct model development and improve this document. I was fortunate to have had the collaboration of such a stellar lineup. I must extend a special thanks to Dr. Tim Ragen of the Marine Mammal Commission in Washington, D.C. (formerly with NMFS, Honolulu). His work provided the foundation for the current monk seal model, and a great many lines of his code still lurk within the subroutines that are the core of the model. I have been privileged to inherit such a fine piece of work. Finally, I thank my family: my wife Jill Harting, my sons Aaron, Quinn, and Lucas, and my mother Betty Ann Harting, for their patience while I earned this degree. They have endured many sacrifices over the last several years, and I cannot overstate my appreciation. TABLE OF CONTENTS LIST OF TABLES.............................................................................................................. LIST OF FIGURES........................................................................................................ xv ABSTRACT..................................................................................................................xxi 1. INTRODUCTION......... ........ I Background on the Hawaiian Monk Seal...................................................................I Primary Objectives for the Project............................................................................... 3 Why a Species-Specific Simulation Model?............................................................... 4 Salient Issues in Simulation Modeling and PVA........................................................7 Overview of PVA................................................................................................... 8 Difficulties in Conducting Formal PVA............................................................ .'.10 PVA Issue I : Parameter Uncertainty............................................................... 11 PVA Issue 2: Unpredictability of Catastrophic Perturbations......................... 12 PVA Issue 3: Managing Uncertainties in Key System Processes (Density Dependence)......................................................... 14 PVA Issue 4: Failure to Incorporate Key Ecological Processes in PVA Models...............................................................26 PVA Issue 5: Failure to Validate PVA Models Using Empirical Data.......................................................................... 27 Further Considerations in the Design of Simulation Models: the Role of Stochasticity and Uncertainty............................................. .29 History and Core Structure of the Monk Seal Simulation Model.............................. 35 Introduction...........................................................................................................35 History of the Model.............................................................................................35 Overview of the Current Simulation Model (Model Type and Complexity).............................................................................. 36 Model Inputs.........................................................................................................41 Key Components of the Simulation Model..........................................................44 Annual Cycle (Each Simulation Year).............................................................44 Management Options.......................................................................................49 Stochastic Elements in the Simulation Model.............. 49 Output from the Simulation Model.................................................................. 50 2. METHODS................................................................................................................52 Programming Tools Used in Model Development................................................;.. 52 Analyses External to the Simulation Model.............................................................. 53 Specification and Application of Survival Rates.................................................. 53 Overview.......................................................................................................... 53 Field Data Collection for Survival Rate Analysis............................................ 55 Jolly-Seber Survival Analysis............................ 56 Fitting an Appropriate Multi-Parameter Survivorship Curve to the Jolly-Seber Estimates............ .............................................. ......63 Model Options for Survival Rate Schedules................ .................................. 66 Senescence in Monk Seal Survival Rates: Further Considerations................68 Solution I : Fitting an Idealized Lifetable to the Monk Seal Rates............ 68 Solution 2: Augmenting the Data with Non-Cohort Tagged Seals............ 70 Maximum Survival Rates by Size Class.......................................................... 71 Age-Specific Reproductive Rates......................................................................... 72 Inter-Island Migration Rates................................................................................. 76 Starting Age/Sex Structure......... ..........................................................................78 Lifetable Analysis................................................................................................. 81 Sensitivity and Elasticity Analyses....................................................................... 85 Non-Stochastic Population Projections...................................................... 86 Description of Algorithms within the Simulation Model......................................... 87 Applying Survival Rates in the Simulation Model............................................... 87 Overview..................................................... 87 Runtime Stochasticity in Survival Rate Schedule: Handling Parameter Uncertainty...................................................................... 88 Density Dependent Variation in Survival Rates.............................................. 92 Additional Options for Perturbing Survival Rates (Survival Catastrophes).......................................................................... 92 Stochastic Survival of Individual Seals....................................................... 93 Applying Birth Rates in the Simulation Model.................................................... 94 Density Dependence in the Simulation Model................................................ ,...95 Overview................................................................................ 95 Options for Density Dependence Models......................... i..... .......................98 No Density Dependence............... :............................................................ 98 . Linear Density Dependence.................................................................... „.98 Linear Density Dependence with Threshold............................................... 99 Theta-Logistic Density Dependence Model.............................................. 100 Annual Variation in Carrying Capacity....................................... 103 Enacting Density Dependent Changes in Demographic Rates.......................107 Moderating the Strength of Density Dependence in the Model....................112 Management Options and Special Scenarios...................................................... 113 Overview.............................................................................. 113 Multiple Male Aggression (Mobbing) Scenario..................... 114 Shark Predation/Management............................................................... 117 Overview .......................................................... 117 Shark/Seal Interaction: Modeling the Predation Event............................. 118 Probability That Predating Animals Will be Present............................ 119 Proportion of Pups in the Atoll That are Vulnerable to Shark Predation.............................................................. 120 vii Probability That a Single Vulnerable Pup Will Have a Predacious Encounter with Each One of the Predating Sharks..............................121 Probability That a Predatory Encounter Will Result in Death............122 Management Response to Shark Predation.......................................... . 122 The Detection Function.......................................................................122 Removal of the Shark..........................................................................125 Latent Period for Shark Recovery After Removals.............................127 Adjusting Survival Rates to Avoid Double-Counting Shark Mortalities.........................................................128 Aggression by Single Adult Males...............................................................129 Capture, Captive Rearing and Release of Female Monk Seals.....................131 Capture and Translocation of Female Monk Seals.......................................132 3. RESULTS............................................................. '.............................................. . 134 Input Data............................................................................................................... 134 Reproductive Rates............................................................................................ 134 Pre-Senescent Reproductive Rates................................................................ 134 Extrapolating Reproductive Rates to Other Atolls........................................ 136 Senescent Reproduction................................................................................ 138 Survival Rates.................................................................................................... 139 Parameter Estimation for the Siler Survivorship Model............................... 139 Migration Rates.................................................................................................. 144 Starting Age/Sex Distribution............................................................................ 146 Life Table Analysis................................................................................................. 150 Introduction........................................................................................................ 150 Intrinsic Lifetable Descriptors........................................................................... 159 Lambda.................................................... ..................................................... 159 Net Replacement Rate (RO).......................................................................... 162 Age-Specific Reproductive Value (vx)......................................................... 163 Theoretical Stable Age Distribution.............................................................. 165 Evaluating the Significance of Current vs. Stable Age Distribution............. 168 Per-Capita Reproductive Value.................................................................. . 170 Non-Stochastic Population Projections...!.......................................................... 171 Overview....................................... ........•.............. ........................................ 172 Changes in Abundance and Realized Growth Rate...................................... 172 Variance in Per-Capita Pup Production........................................................ 181 Sensitivity of Lambda to Changes in Demographic Rates............................ 184 Simulation Results................................................................................................. 188 Overview of Core Scenarios........................................ ..................................... 188 Comparing Simulation Results.......................................................................... 189 Baseline Projections (No Perturbations)............................................................ 191 Scenario a l : 25-Year Projection With No Perturbations Other Than Stochasticity In Vital Rates........................................................ 191 viii Scenario a2: I O-Year Projection With No Perturbations Other Than Stochasticity In Vital Rates....................................................... 193 Projections Testing Sensitivity to Survival Rates.......................... ................... 193 Scenario h i : 25-Year Projection With No Senescence In Survival Rates (Survival Rates From All Data Years, With No Senescence In Survival)............................................................................193 Scenario b2: 25-Year Projection Using Survival Rates Computed From Recent Data..............................................................195 Scenario b3: 25-Year Projection Using Survival Rates Computed From Recent Data With No Senescence In Survival Rates .......... :............. 197 Scenario b4: 25-Year Projection With No Constraints On Maximum Attainable Survival Rates...................................................... 197 Scenario b5: 25-Year Projection With Maximum Attainable Survival Rates From Recent Years.................................................................199 Projections Testing Sensitivity to Inter-atoll Migration.................................... 202 Scenario c l : 25-Year Projection With No Inter-Atoll Migration Allowed...................... 202 Projections Testing the Influence of Density Dependence................................203 Scenarios dl and d2: Non-Density Dependent Projections Using All-Year Survival Rates (25 Year And 10 Year Projections).......................203 Scenario d3 and d4: Non-Density Dependent Projections Using Survival Rates From Recent Years (10-Year And 25-Year Projections).....206 Scenarios d6 and d7: Non-Density Dependent Projections With No Migration...................................................................... 208 Scenario d8: Projection With Density Dependent Adjustment Allowed Via Pup/Juvenile Survival Rates Only............................................ 210 Projections Testing Effects of Correlation in Carrying Capacity..................u.. 211 Scenario e l : Scenario Testing Effects of Correlation in Carrying Capacity................................................................... 211 Projections Incorporating Survival and Birth Catastrophes................................ 213 Scenario fl: Moderate Survival Catastrophe............... '................................. 213 Scenario f2: Severe Survival Catastrophe...................................................... 215 Scenario £3 and 14: Longer Duration Survival Catastrophes......................... 216 Scenario £5: Moderate Birth Catastrophe....................................................... 218 Scenario f6: Severe Birth Catastrophe........................................................... 219 Scenarios Tl and f8: Combined Birth And Death Catastrophe, Severe And Extreme................................................................. 220 Projections with Specific Natural Perturbation (Shark Predation)....................222 Scenario g l : Moderate Shark Predation With No Management, Control......222 Projections with Management Intervention (Translocation and Headstart)......230 Scenario h i : Translocation OfFemales From FFS To MID.......................... 230 Scenario h2: Translocation OfFemales From LAY To FFS......................... 235 Scenario h3: Headstart OfFFS Pups.............................................................. 237 Projections to Test Tolerances to Loss of Adult Females................................... 238 Scenario i l : Tolerance To Loss OfFemales.................................................. 238 4. DISCUSSION/CONCLUSIONS............................................................................ 242 Salient Observations' from the Simulation Scenarios............................................. 242 What scenario features or perturbations were most influential in altering the trajectories? .............................................................. 242 General Observations on Simulation Results................................................ 242 Scenarios Dealing with Sensitivity to Survival Rates................................... 244 Scenarios with No Migration......................................................................... 246 Scenarios Dealing with Density Dependence and Correlation in Carrying Capacity........... ........................ 246 Simulations with Catastrophes....................................................................... 247 Shark Predation Scenarios.............................................................................. 249 Management Scenarios............................... !................................................ 250 Scenarios Pertaining to Loss of Adult Females............................................ 252 Management Interventions Most beneficial to the Long-Term Welfare of the Monk Seal?................................................................... 253 Using the Model for Long-Term Projections or PVA............................................ 254 Model Deficiencies Associated with Uncertainties in Environmental Stochasticity............................................................................... 255 Coping with Uncertainties in the Form and Mechanisms for Density Dependence in the Monk Seal Model .................................. 259 Other Data Uncertainties and Shortcomings in the Modeling Effort................264 Does the Model Properly Handle All Uncertainties Important for PVA?........ 266 Suitable Applications of the Monk Seal Simulation Model ......<...........................274 Suggestions for Model Maintenance and Further Development ............................ 275 Conclusions.............................................................................................................. 278 REFERENCES CITED......... ........................ ...........................:.................................281 APPENDIX A : TRAJECTORY PLOTS FOR THE CORE SIMULATION SCENARIOS............................................................ . 295