32 research outputs found
Selecting Indicator Portfolios for Marine Species and Food Webs: A Puget Sound Case Study
Ecosystem-based management (EBM) has emerged as a promising approach for maintaining the benefits humans want and need from the ocean, yet concrete approaches for implementing EBM remain scarce. A key challenge lies in the development of indicators that can provide useful information on ecosystem status and trends, and assess progress towards management goals. In this paper, we describe a generalized framework for the methodical and transparent selection of ecosystem indicators. We apply the framework to the second largest estuary in the United States – Puget Sound, Washington – where one of the most advanced EBM processes is currently underway. Rather than introduce a new method, this paper integrates a variety of familiar approaches into one step-by-step approach that will lead to more consistent and reliable reporting on ecosystem condition. Importantly, we demonstrate how a framework linking indicators to policy goals, as well as a clearly defined indicator evaluation and scoring process, can result in a portfolio of useful and complementary indicators based on the needs of different users (e.g., policy makers and scientists). Although the set of indicators described in this paper is specific to marine species and food webs, we provide a general approach that could be applied to any set of management objectives or ecological system
The spatial scale of competition from recruits on an older cohort in Atlantic salmon
Competitive effects of younger cohorts on older ones are frequently assumed to be negligible in species where older, larger individuals dominate in pairwise behavioural interactions. Here, we provide field estimates of such competition by recruits on an older age class in Atlantic salmon (Salmo salar), a species where observational studies have documented strong body size advantages which should favour older individuals in direct interactions. By creating realistic levels of spatial variation in the density of underyearling (YOY) recruits over a 1-km stretch of a stream, and obtaining accurate measurements of individual growth rates of overyearlings (parr) from capture–mark–recapture data on a fine spatial scale, we demonstrate that high YOY density can substantially decrease parr growth. Models integrating multiple spatial scales indicated that parr were influenced by YOY density within 16 m. The preferred model suggested parr daily mass increase to be reduced by 39% when increasing YOY density from 0.0 to 1.0 m−2, which is well within the range of naturally occurring densities. Reduced juvenile growth rates will in general be expected to reduce juvenile survival (via increased length of exposure to freshwater mortality) and increase generation times (via increased age at seaward migrations). Thus, increased recruitment can significantly affect the performance of older cohorts, with important implications for population dynamics. Our results highlight that, even for the wide range of organisms that rely on defendable resources, the direction of competition among age classes cannot be assumed a priori or be inferred from behavioural observations alone
The Nature Index: A General Framework for Synthesizing Knowledge on the State of Biodiversity
The magnitude and urgency of the biodiversity crisis is widely recognized within
scientific and political organizations. However, a lack of integrated measures
for biodiversity has greatly constrained the national and international response
to the biodiversity crisis. Thus, integrated biodiversity indexes will greatly
facilitate information transfer from science toward other areas of human
society. The Nature Index framework samples scientific information on
biodiversity from a variety of sources, synthesizes this information, and then
transmits it in a simplified form to environmental managers, policymakers, and
the public. The Nature Index optimizes information use by incorporating expert
judgment, monitoring-based estimates, and model-based estimates. The index
relies on a network of scientific experts, each of whom is responsible for one
or more biodiversity indicators. The resulting set of indicators is supposed to
represent the best available knowledge on the state of biodiversity and
ecosystems in any given area. The value of each indicator is scaled relative to
a reference state, i.e., a predicted value assessed by each expert for a
hypothetical undisturbed or sustainably managed ecosystem. Scaled indicator
values can be aggregated or disaggregated over different axes representing
spatiotemporal dimensions or thematic groups. A range of scaling models can be
applied to allow for different ways of interpreting the reference states, e.g.,
optimal situations or minimum sustainable levels. Statistical testing for
differences in space or time can be implemented using Monte-Carlo simulations.
This study presents the Nature Index framework and details its implementation in
Norway. The results suggest that the framework is a functional, efficient, and
pragmatic approach for gathering and synthesizing scientific knowledge on the
state of biodiversity in any marine or terrestrial ecosystem and has general
applicability worldwide
Assessing the Health of the U.S. West Coast with a Regional-Scale Application of the Ocean Health Index
Assessing trade-offs to inform ecosystem-based fisheries management of forage fish
Twenty-first century conservation is centered on negotiating trade-offs between the diverse needs of people and the needs of the other species constituting coupled human-natural ecosystems. Marine forage fishes, such as sardines, anchovies, and herring, are a nexus for such trade-offs because they are both central nodes in marine food webs and targeted by fisheries. An important example is Pacific herring, Clupea pallisii in the Northeast Pacific. Herring populations are subject to two distinct fisheries: one that harvests adults and one that harvests spawned eggs. We develop stochastic, age-structured models to assess the interaction between fisheries, herring populations, and the persistence of predators reliant on herring populations. We show that egg- and adult-fishing have asymmetric effects on herring population dynamics - herring stocks can withstand higher levels of egg harvest before becoming depleted. Second, ecosystem thresholds proposed to ensure the persistence of herring predators do not necessarily pose more stringent constraints on fisheries than conventional, fishery driven harvest guidelines. Our approach provides a general template to evaluate ecosystem trade-offs between stage-specific harvest practices in relation to environmental variability, the risk of fishery closures, and the risk of exceeding ecosystem thresholds intended to ensure conservation goals are met