While there is a persistent inverse relationship between latitude and species diversity across ma... more While there is a persistent inverse relationship between latitude and species diversity across many taxa and ecosystems, deviations from this norm offer an opportunity to understand the conditions that contribute to large-scale diversity patterns. Marine systems, in particular, provide such an opportunity, as marine diversity does not always follow a strict latitudinal gradient, perhaps because several hypothesized drivers of the latitudinal diversity gradient are uncorrelated in marine systems. We used a large scale public monitoring dataset collected over an eight year period to examine benthic marine faunal biodiversity patterns for the continental shelf (55-183 m depth) and slope habitats (184-1280 m depth) off the US West Coast (47°20'N-32°40'N). We specifically asked whether marine biodiversity followed a strict latitudinal gradient, and if these latitudinal patterns varied across depth, in different benthic substrates, and over ecological time scales. Further, we subd...
Forage fish play a pivotal role in marine ecosystems and economies worldwide by sustaining many p... more Forage fish play a pivotal role in marine ecosystems and economies worldwide by sustaining many predators and fisheries directly and indirectly. We estimate global forage fish contributions to marine ecosystems through a synthesis of 72 published Ecopath models from around the world. Three distinct contributions of forage fish were examined: (i) the ecological support service of forage fish to predators in marine ecosystems, (ii) the total catch and value of forage fisheries and (iii) the support service of forage fish to the catch and value of other commercially targeted predators. Forage fish use and value varied and exhibited patterns across latitudes and ecosystem types. Forage fish supported many kinds of predators, including fish, seabirds, marine mammals and squid. Overall, forage fish contribute a total of about $16.9 billion USD to global fisheries values annually, i.e. 20% of the global ex-vessel catch values of all marine fisheries combined. While the global catch value of forage fisheries was $5.6 billion, fisheries supported by forage fish were more than twice as valuable ($11.3 billion). These estimates provide important information for evaluating the trade-offs of various uses of forage fish across ecosystem types, latitudes and globally. We did not estimate a monetary value for supportive contributions of forage fish to recreational fisheries or to uses unrelated to fisheries, and thus the estimates of economic value reported herein understate the global value of forage fishes.
Population viability analysis (PVA) to forecast extinction risk is a commonly used tool in decisi... more Population viability analysis (PVA) to forecast extinction risk is a commonly used tool in decision-and policy-making processes of governments and conservation organizations. A drawback to PVA is the high degree of uncertainty in these forecasts due to both population stochasticity and parameter estimation uncertainty. With sparse or noisy data, extinction probabilities frequently have 95% confidence intervals ranging from 0 to 1. To make stochastic simulation results more interpretable, we present a new metric, susceptibility to quasi-extinction (SQE), to assess whether or not a population is at risk of declining to a prespecified level (quasi-extinction). Following standard methods for diffusion approximation of extinction risk, we use a parametric bootstrap to determine the 95% CI for the probability of quasi-extinction. SQE is the proportion of this parametric bootstrap that indicates a high (defined as !0.90) probability of quasi-extinction, resulting in a point estimate that integrates both parameter uncertainty and stochasticity in extinction forecasting. We demonstrate the application of the metric with sea turtle nest census data, which have a high degree of year-toyear variance and represent only a small fraction of the total population. Using population simulations, we found that for these types of data a critical SQE value of 0.40 corresponds to populations that have a true risk of quasi-extinction. The metric has an accuracy of .80%, which can be increased further by lowering the 0.40 threshold and trading off Type I error (considering a population to be ''not at risk'' when it actually is) and Type II error (considering a population to be ''at risk'' when it actually is not), giving managers a flexible and quantitative tool for assessments of population status.
While there is a persistent inverse relationship between latitude and species diversity across ma... more While there is a persistent inverse relationship between latitude and species diversity across many taxa and ecosystems, deviations from this norm offer an opportunity to understand the conditions that contribute to large-scale diversity patterns. Marine systems, in particular, provide such an opportunity, as marine diversity does not always follow a strict latitudinal gradient, perhaps because several hypothesized drivers of the latitudinal diversity gradient are uncorrelated in marine systems. We used a large scale public monitoring dataset collected over an eight year period to examine benthic marine faunal biodiversity patterns for the continental shelf (55-183 m depth) and slope habitats (184-1280 m depth) off the US West Coast (47°20'N-32°40'N). We specifically asked whether marine biodiversity followed a strict latitudinal gradient, and if these latitudinal patterns varied across depth, in different benthic substrates, and over ecological time scales. Further, we subd...
Forage fish play a pivotal role in marine ecosystems and economies worldwide by sustaining many p... more Forage fish play a pivotal role in marine ecosystems and economies worldwide by sustaining many predators and fisheries directly and indirectly. We estimate global forage fish contributions to marine ecosystems through a synthesis of 72 published Ecopath models from around the world. Three distinct contributions of forage fish were examined: (i) the ecological support service of forage fish to predators in marine ecosystems, (ii) the total catch and value of forage fisheries and (iii) the support service of forage fish to the catch and value of other commercially targeted predators. Forage fish use and value varied and exhibited patterns across latitudes and ecosystem types. Forage fish supported many kinds of predators, including fish, seabirds, marine mammals and squid. Overall, forage fish contribute a total of about $16.9 billion USD to global fisheries values annually, i.e. 20% of the global ex-vessel catch values of all marine fisheries combined. While the global catch value of forage fisheries was $5.6 billion, fisheries supported by forage fish were more than twice as valuable ($11.3 billion). These estimates provide important information for evaluating the trade-offs of various uses of forage fish across ecosystem types, latitudes and globally. We did not estimate a monetary value for supportive contributions of forage fish to recreational fisheries or to uses unrelated to fisheries, and thus the estimates of economic value reported herein understate the global value of forage fishes.
Population viability analysis (PVA) to forecast extinction risk is a commonly used tool in decisi... more Population viability analysis (PVA) to forecast extinction risk is a commonly used tool in decision-and policy-making processes of governments and conservation organizations. A drawback to PVA is the high degree of uncertainty in these forecasts due to both population stochasticity and parameter estimation uncertainty. With sparse or noisy data, extinction probabilities frequently have 95% confidence intervals ranging from 0 to 1. To make stochastic simulation results more interpretable, we present a new metric, susceptibility to quasi-extinction (SQE), to assess whether or not a population is at risk of declining to a prespecified level (quasi-extinction). Following standard methods for diffusion approximation of extinction risk, we use a parametric bootstrap to determine the 95% CI for the probability of quasi-extinction. SQE is the proportion of this parametric bootstrap that indicates a high (defined as !0.90) probability of quasi-extinction, resulting in a point estimate that integrates both parameter uncertainty and stochasticity in extinction forecasting. We demonstrate the application of the metric with sea turtle nest census data, which have a high degree of year-toyear variance and represent only a small fraction of the total population. Using population simulations, we found that for these types of data a critical SQE value of 0.40 corresponds to populations that have a true risk of quasi-extinction. The metric has an accuracy of .80%, which can be increased further by lowering the 0.40 threshold and trading off Type I error (considering a population to be ''not at risk'' when it actually is) and Type II error (considering a population to be ''at risk'' when it actually is not), giving managers a flexible and quantitative tool for assessments of population status.
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Papers by Selina Heppell