• Demographic components of philopatry and nest-site fidelity of Pacific black brant

      Lindberg, Mark Steven; Sedinger, James S. (1996)
      I investigated demographic components of nest-site fidelity and philopatry of Pacific black brant (Branta bernicla nigricans). My analyses included data I collected during summer 1990-1993, and also incorporated data obtained between 1986-1989. My studies of nest-site fidelity were limited to the Tutakoke River colony, Yukon-Kuskokwim River Delta, Alaska. Studies of philopatry and dispersal among colonies included observations at 7 breeding colonies of brant marked with tarsal tags (n = 20,147). I observed strong evidence that philopatry of brant was female biased. Probability of breeding philopatry, which was estimated with multi-state modeling techniques, was high (>0.9) and dispersal of adults among breeding colonies was rare. I developed an ad hoc estimator for natal philopatry that was unbiased by a confounding of homing, survival, and detection probabilities. Probability of natal philopatry for females was both age and density dependent. The density-dependent decline in natal philopatry may result from increased rate of permanent nonbreeding or increased probability of dispersal. Observed probability of natal philopatry for males was approximately equivalent to the relative size of their natal colony, suggesting that males pair at random with females from other colonies. Gene flow among populations of brant is largely male mediated, and I predict populations of brant will exhibit distinct mitochondrial DNAs if populations have been reproductively isolated for an adequate period of time. Probability of fidelity to previous nest sites for adults was high (>0.7). Probability of nest-site fidelity was affected by previous nesting success, age, and availability of nest sites. Phenology of nesting, nest-site selection, and clutch size of brant was affected by spring snowmelt. Dispersal of brant from traditional nest sites in years with late springs may represent a tradeoff between site fidelity and timing of nest initiation. Movement of young females from natal nest sites was a mechanism for colony expansion. I observed little evidence that site fidelity was advantageous, and concluded that quality of individual bird, environmental conditions, and demographic status may be more important determinants of breeding performance.
    • Forecasting catches of Pacific salmon in commercial fisheries of southeast Alaska

      Marshall, Robert Paul (1992)
      Data collections since 1911 and statistical methods from time series analysis are employed to forecast catches of pink, chum, coho, and sockeye salmon in Southeast Alaska. Knowledge of the spatial and temporal domains favored by Pacific salmon originating in Southeast Alaska is summarized to provide a basis for estimating environmental variation experienced by each species. Catches in northern, southern, and all of Southeast Alaska are forecast with univariate ARIMA, transfer function-noise (TFN), and vector ARMA models. Univariate models for catch in numbers and catch in weight yielded similar results for each species. Air and sea surface temperatures, freshwater discharge, and coastal upwelling enter TFN models for several species and areas. Environmental variables allow TFN models to explain a small amount of variation in the catches (average of 19%) above that explained by univariate models. Forecasts for most, but not all, species and areas are improved (average of 16%) by including environmental data in TFN models. Stock-recruit models with a parameter for density dependent mortality provide the best forecasts of pink salmon catch and are recommended for future forecasts. Winter air and sea surface temperatures enter stock-recruit models for pink salmon, and forecasts of catch and recruitment in northern and southern Southeast Alaska tend to oppose each other and cancel (1981-1985), which suggests that the salmon are caught in areas other than where they originated. Mean absolute percentage error (MAPE) for forecasts of pink salmon catch from stock-recruit models in Southeast Alaska, based on data for 1981-1990, is estimated at 49%, with first, second, and third quartiles of 10%, 23%, and 83%, respectively. Catches of Pacific salmon in Southeast Alaska are significantly correlated and are forecast jointly with good accuracy by vector ARMA models, except when effects believed to result from density dependent mortality are present in the data. Correlations indicate that coho salmon smolts might prey on young pink salmon. Also, recruitment of pink salmon in Southeast Alaska and British Columbia is correlated; regional environmental influences might thus affect catches in both areas. In Southeast Alaska, MAPE for forecasting coho and sockeye salmon catch with time series analysis is about 20%, and about 30% for chum salmon.
    • Martingales in mark-recapture experiments with constant recruitment and survival

      Humphrey, Patricia Buslee (1995)
      The method known as mark-recapture has been used for almost one hundred years in assessing animal populations. For many years, these models were restricted to closed populations; no changes to the population were assumed to occur through either migration or births and deaths. Numerous estimators for the closed population have been proposed through the years, some of the most recent by Paul Yip which make use of martingales to derive the necessary estimates. The independently derived Jolly-Seber model (1965) was the first to address the open population situation. That method as originally proposed is cumbersome mathematically due to the large number of parameters to be estimated as well as the inability to obtain estimates until the end of a series of capture events since some of the "observed" variables necessary are prospective. It also is cumbersome for the biologist in the field as individual marks and capture histories are required for each animal. Variations have been proposed through the years which hold survival and/or capture probabilities constant across capture occasions. Models based on log-linear estimators have also been proposed (Cormack 1989). This paper builds on the closed population work of Yip in using martingale-based conditional least squares to estimate population parameters for an open population where it is assumed recruitment of new individuals into the population is constant from one capture occasion to the next, and capture and survival probabilities are constant across capture occasions. It is an improvement over most other methods in that no detailed capture histories are needed; animals are simply noted as marked or unmarked. Performance of the estimator proposed is studied through computer simulation and comparison with classical estimators on actual data sets.