A recurring pattern of declining mean trophic level of fisheries landings, termed ''fishing down the food web,'' is thought to be indicative of the serial replacement of high-trophic-level fisheries with less valuable, low-trophic-level fisheries as the former become depleted to economic extinction. An alternative to this view, that declining mean trophic levels indicate the serial addition of low-trophic-level fisheries (''fishing through the food web''), may be equally severe because it ultimately leads to conflicting demands for ecosystem services. By analyzing trends in fishery landings in 48 large marine ecosystems worldwide, we find that fishing down the food web was pervasive (present in 30 ecosystems) but that the sequential addition mechanism was by far the most common one underlying declines in the mean trophic level of landings. Specifically, only 9 ecosystems showed declining catches of upper-trophic-level species, compared with 21 ecosystems that exhibited either no significant change (n ؍ 6) or significant increases (n ؍ 15) in upper-trophic-level catches when fishing down the food web was occurring. Only in the North Atlantic were ecosystems regularly subjected to sequential collapse and replacement of fisheries. We suggest that efforts to promote sustainable use of marine resources will benefit from a fuller consideration of all processes giving rise to fishing down the food web.ecosystem-based management ͉ fisheries ͉ marine conservation
Many of the world's most vulnerable and rapidly changing ecosystems are also among the most data-poor, leading to an increased interest in use of local ecological knowledge (LEK) to document long-term environmental change. The integration of multiple knowledge sources for assessing species abundance and distribution has gained traction over the past decade as a growing number of case studies show concordance between LEK and scientific data. This study advances the use of quantitative approaches for synthesizing LEK by presenting a novel application of bootstrapping and statistical modeling to evaluate variance in ecological observations of fisheries practitioners. We developed an historical record of abundance for 22 marine species in Puget Sound, Washington (USA), using LEK, and we quantified variation in perceptions of abundance trends among fishers, divers, and researchers. These individuals differed in aspects of their information environments, which are characterized by how, when, and where an individual has acquired ecological information. Abundance trends derived from interviews suggest that populations of long-lived rockfishes (Sebastes spp.) have been in decline since at least the 1960s and that three rockfishes protected under the Endangered Species Act were perceived as relatively less abundant than other species. Differences in perception of rockfish abundance trends among age groups were consistent with our hypothesis that the reported magnitude of decline in abundance would increase with age, with younger respondents more likely to report high abundance than older individuals across all periods. Temporal patterns in the mean and variance of reported rockfish abundance indices were qualitatively similar between fishers and researchers; however, fishers reported higher indices of abundance than researchers for all but one rockfish species. The two respondent groups reported similar changes in rockfish abundance from the 1940s to 2000s, except for two recreationally valuable species that fishers perceived as having undergone greater declines than perceived by researchers. When aggregated at appropriate spatial-temporal scales and in a culturally appropriate manner, observations of resource users are a valuable source of ecological information. Continued development of creative analytical tools for synthesizing multiple knowledge sources will be essential for advancing the formal use of LEK in assessments of marine species.
Individuals relying on natural resource extraction for their livelihood face high income variability driven by a mix of environmental, biological, management, and economic factors. Key to managing these industries is identifying how regulatory actions and individual behavior affect income variability, financial risk, and, by extension, the economic stability and the sustainable use of natural resources. In commercial fisheries, communities and vessels fishing a greater diversity of species have less revenue variability than those fishing fewer species. However, it is unclear whether these benefits extend to the actions of individual fishers and how year-to-year changes in diversification affect revenue and revenue variability. Here, we evaluate two axes by which fishers in Alaska can diversify fishing activities. We show that, despite increasing specialization over the last 30 years, fishing a set of permits with higher species diversity reduces individual revenue variability, and fishing an additional permit is associated with higher revenue and lower variability. However, increasing species diversity within the constraints of existing permits has a fishery-dependent effect on revenue and is usually (87% probability) associated with increased revenue uncertainty the following year. Our results demonstrate that the most effective option for individuals to decrease revenue variability is to participate in additional or more diverse fisheries. However, this option is expensive, often limited by regulations such as catch share programs, and consequently unavailable to many individuals. With increasing climatic variability, it will be particularly important that individuals relying on natural resources for their livelihood have effective strategies to reduce financial risk. diversity-stability relationship | Bayesian variance function regression | income variability | natural resource management | ecological portfolio effects I t can be difficult for individuals to sustain a livelihood from natural resource extraction. These livelihoods tend to have high annual variability in income relative to other professions (1, 2). In addition to income variability from economic sources, such as changes in demand or prices, individuals dependent on natural resources are also subject to biological and environmental variability (3). For example, drought and flooding are a major source of risk for agricultural food security and farmers' incomes (4), and catastrophic disease outbreaks and wildfires increase risk for the logging industry (5).Individuals who rely on natural resources for income develop strategies to reduce income variability. For example, farmers may diversify their crops or include off-farm income sources to buffer against environmental and market shocks, as well as longterm climatic trends and seasonality (6-8). However, otherwise well-intentioned regulations may limit how individuals diversify, or may incentivize against diversification. For instance, crop subsidies in the United States may incentivize some farms ...
Glaciers have shaped past and present habitats for Pacific salmon (Oncorhynchus spp.) in North America. During the last glacial maximum, approximately 45% of the current North American range of Pacific salmon was covered in ice. Currently, most salmon habitat occurs in watersheds in which glacier ice is present and retreating. This synthesis examines the multiple ways that glacier retreat can influence aquatic ecosystems through the lens of Pacific salmon life cycles. We predict that the coming decades will result in areas in which salmon populations will be challenged by diminished water flows and elevated water temperatures, areas in which salmon productivity will be enhanced as downstream habitat suitability increases, and areas in which new river and lake habitat will be formed that can be colonized by anadromous salmon. Effective conservation and management of salmon habitat and populations should consider the impacts of glacier retreat and other sources of ecosystem change.
Pulsed resources create an influx of energy that can provide individual and population level benefits to their consumers. As consumers, Sablefish Anoplopoma fimbria experience strong seasonal pulses in prey resources during their critical period of juvenile growth in the nearshore marine environment. This study described temporal patterns in diet composition of Sablefish (N = 1,081) ranging in size from 226 to 455 mm FL during July and September in St. John Baptist Bay, Alaska. Juvenile Sablefish exploited a large variety of prey taxa characteristic of a generalist predator and experienced significant diet shifts among sampling periods revealing seasonal and interannual variation in resource use. Diets appeared more diverse in 2012 when more invertebrate taxa were consumed compared with 2013 when diets were dominated by herring and salmonid offal. In September of both years, spawning Pink Salmon Oncorhynchus gorbuscha were observed within the study area and juvenile Sablefish capitalized on this high energy subsidy, and salmon carcasses were among the top contributors to their diets by weight. However, Sablefish also exploited in situ prey of lower energy, such as benthic invertebrates, suggesting that Sablefish are not entirely reliant on seasonally pulsed, high‐energy prey. This study further emphasizes the significance of salmon as a vector of energy across ecosystems and is one of the first to document a marine teleost species scavenging on adult salmon carcasses in coastal marine waters.
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