Survival rates for Cassin's and Rhinoceros Auklets at Triangle Island, British Columbia.

We estimated survival of Cassin's Auklet (Ptychoramphus aleuticus) and Rhinoceros Auklet (Cerorhincam onocerata) from recapture rates during 1994-1997. For both species, a two "age"-class model provided the best fit. Estimates of local adult survival were significantly lower for Cassin's Auklet (0.672 +/- 0.047) than for Rhinoceros Auklet (0.829 +/- 0.095). Our estimate of survival appears lower than that required for the maintenance of a stable population of Cassin's Auklets. The available information indicates that a low survival rate and a declining population at Triangle Island are plausible, particularly given the recent age scale oceanographic changes which have occurred in the North Pacific Ocean. Nevertheless, additional mark-recapture data and indexes of population size are required to rigorously demonstrate population declines at the world's largest Cassin's Auklet colony

Estimation of trade-offs with capture-recapture models: A case study on the lesser snow goose

SUMMARY Trade-offs between traits such as fecundity or survival are fundamental to much of our understanding of the evolution of life histories. There has been much renewed interest and controversy concerning methods for estimating trade-offs, in the wild or in captivity, and with or without experimental manipulations. In this paper, we assess the general question of the utility of modern capture ± recapture methods as a robust tool for estimating trade-offs in natural populations. We present results from analyses of two forms of trade-offs: the cost of present reproduction on future survival and the cost of present reproduction on the probability of breeding in the future. We apply the methods to data from a long-term study of a snow goose population, and generally discuss the advantages and potential problems with various approaches.

Site fidelity of Black Brant wintering and spring staging in the Strait of Georgia, British Columbia.

Site fidelity has important implications for population genetics and dynamics. In birds, most studies have dealt with breeding ground fidelity, ignoring the fact that waterfowl mainly pair in winter or early spring. We used multiple observation data from a mark-relight study of Black Brant (Branta bernicla nigricans) to estimate fidelity to wintering and spring staging areas in Boundary Bay and Parksville-Qualicum British Columbia. Site fidelity was low for winter residents but still indicated that Brant were faithful to Boundary Bay. Birds seen twice or more during any given winter had significantly higher site fidelity rates than those seen only once. The models for the spring period showed the presence of transients in both Boundary Bay and Qualicum. Birds seen for the first time in an area had a lower probability of returning to that area than birds seen in more than one year. Survival probability was significantly higher for Qualicum birds than for Boundary Bay birds. We concluded that prior knowledge of an area was an important determinant of site fidelity, and that low site fidelity levels were unlikely to lead to genetic sub structuring of the population

Applying the multistate capture-recapture robust design to characterize metapopulation structure

Population structure must be considered when developing mark-recapture (MR) study designs as the sampling of individuals from multiple populations (or subpopulations) may increase heterogeneity in individual capture probability. Conversely, the use of an appropriate MR study design which accommodates heterogeneity associated with capture occasion varying covariates due to animals moving between 'states' (i.e. geographic sites) can provide insight into how animals are distributed in a particular environment and the status and connectivity of subpopulations. The multistate closed robust design (MSCRD) was chosen to investigate: (i) the demographic parameters of Indo-Pacific bottlenose dolphin (Tursiops aduncus) subpopulations in coastal and estuarine waters of Perth, Western Australia; and (ii) how they are related to each other in a metapopulation. Using 4 years of year-round photo-identification surveys across three geographic sites, we accounted for heterogeneity of capture probability based on how individuals distributed themselves across geographic sites and characterized the status of subpopulations based on their abundance, survival and interconnection. MSCRD models highlighted high heterogeneity in capture probabilities and demographic parameters between sites. High capture probabilities, high survival and constant abundances described a subpopulation with high fidelity in an estuary. In contrast, low captures, permanent and temporary emigration and fluctuating abundances suggested transient use and low fidelity in an open coastline site. Estimates of transition probabilities also varied between sites, with estuarine dolphins visiting sheltered coastal embayments more regularly than coastal dolphins visited the estuary, highlighting some dynamics within the metapopulation. Synthesis and applications. To date, bottlenose dolphin studies using mark-recapture approach have focussed on investigating single subpopulations. Here, in a heterogeneous coastal-estuarine environment, we demonstrated that spatially structured bottlenose dolphin subpopulations contained distinct suites of individuals and differed in size, demographics and connectivity. Such insights into the dynamics of a metapopulation can assist in local-scale species conservation. The MSCRD approach is applicable to species/populations consisting of recognizable individuals and is particularly useful for characterizing wildlife subpopulations that vary in their vulnerability to human activities, climate change or invasive species

Control of structured populations by harvest

It has long been recognized that demographic structure within a population can significantly affect the likely outcomes of harvest. Many studies have focussed on equilibrium dynamics and maximization of the value of the harvest taken. However, in some cases the management objective is to maintain the population at a abundance that is significantly below the carrying capacity. Achieving such an objective by harvest can be complicated by the presence of significant structure (age or stage) in the target population. in such cases, optimal harvest strategies must account for differences among age- or stage-classes of individuals in their relative contribution to the demography of the population. In addition, structured populations are also characterized by transient non-linear dynamics following perturbation, such that even under an equilibrium harvest, the population may exhibit significant momentum, increasing or decreasing before cessation of growth. Using simple linear time-invariant models, we show that if harvest levels are set dynamically (e.g., annually) then transient effects can be as or more important than equilibrium outcomes. We show that appropriate harvest rates can be complicated by uncertainty about the demographic structure of the population, or limited control over the structure of the harvest taken. (c) 2006 Elsevier B.V. All rights reserved

Optimal control of Atlantic population Canada geese

Management of Canada geese (Branta canadensis) can be a balance between providing sustained harvest opportunity while not allowing populations to become overabundant and cause damage. In this paper, we focus on the Atlantic population of Canada geese and use stochastic dynamic programming to determine the optimal harvest strategy over a range of plausible models for population dynamics. There is evidence to suggest that the population exhibits significant age structure, and it is possible to reconstruct age structure from surveys. Consequently the harvest strategy is a function of the age composition, as well as the abundance, of the population. The objective is to maximize harvest while maintaining the number of breeding adults in the population between specified upper and lower limits. In addition, the total harvest capacity is limited and there is uncertainty about the strength of density-dependence. We find that under a density-independent model, harvest is maximized by maintaining the breeding population at the highest acceptable abundance. However if harvest capacity is limited, then the optimal long-term breeding population size is lower than the highest acceptable level, to reduce the risk of the population growing to an unacceptably large size. Under the proposed density-dependent model, harvest is maximized by maintaining the breeding population at an intermediate level between the bounds on acceptable population size; limits to harvest capacity have little effect on the optimal long-term population size. It is clear that the strength of density-dependence and constraints on harvest significantly affect the optimal harvest strategy for this population. Model discrimination might be achieved in the long term, while continuing to meet management goals, by adopting an adaptive management strategy