Although ecosystem-based fisheries management is often associated with trade-offs between conflicting demands for ecosystem services, the holistic ecological considerations the approach promotes may sometimes lead to novel solutions that benefit both conservation and fisheries. Directed fishing on large piscivorous fish can reduce predation on prey and thereby benefit those populations, but incidental take of prey species in these fisheries may negate or even reverse the benefit. Whether benefits from reduced predation outweigh the costs of increased fishing will depend on the relative strength of each mortality source and the sensitivity of the population to mortality at different life stages. In the California Current, predatory lingcod (Ophiodon elongatus) populations recovered rapidly from fishing exploitation over the past two decades, while recovery of some rockfish species (Sebastes spp.) has been slow, mainly because of low natural productivities. One management tool has been the adoption of rockfish conservation areas (RCAs) that prohibit bottom contact fishing gear. Because lingcod also inhabit RCAs, fishers have been unable to catch their sustainable lingcod quotas. Therefore, we explored the conditions under which opening RCAs to a selective lingcod fishery might permit rockfish recovery despite the potential bycatch. We developed a joint equilibrium model of the two populations and analysed scenarios to assess the sensitivity of the model's predictions to key uncertainties. The model suggests a wide range of fishery and ecological conditions under which a lingcod fishery may not harm rockfish populations. However, a sensitivity analysis indicated that the range of fishing scenarios where rockfish are not harmed is highly sensitive to assumptions regarding the nature of the trophic linkage between lingcod and rockfish. We conclude that consideration of trophic interactions may reveal new fishing opportunities that meet both ecological and human goals, but precise predictions of the outcomes will require more detailed models and adaptive management.

Predation can play an important role in population, community and ecosystem processes. When predator guilds are diverse, fluctuations in individual predator populations may have small influences on the guild at large, suggesting that predator diversity stabilizes the amount of predation prey experience. The strength of this phenomenon depends on how synchronously populations within predator assemblages vary and whether all predators are equally important consumers. We utilized a database of biomasses of fish species across ten temperate marine ecosystems paired with diet composition and feeding rate information from mass-balance food web models to develop a predation index that weights the importance of predators on a prey based on predator feeding habits. Using the index, we asked how diverse sources of predation in these ecosystems are and how much diversity stabilizes variability in predation. Predator assemblages displayed a wide range of diversity; in one-third of assemblages, a single predator group accounted for over half of all predation. Abundances of predator populations within assemblages generally varied independently of one another (neither synchronously nor asynchronously), implying an intermediate stabilization on predation intensity by predator diversity. Accounting for interaction strength (versus mere presence) is critical for interpreting the predator landscape; doing so led to a wider range in predator assemblage diversity and less synchronous assemblages. This work challenges conventional notions that marine food webs are diverse and therefore less susceptible to predator control. Future work should consider the temporal variability of the predator assemblages and account for differences in mortality induced by each predator population.

The potential of predation to structure marine food webs is widely acknowledged. However, available tools to detect the regulation of prey population dynamics by predation are limited, partly because available population data often aggregate a population's age structure into a single biomass or abundance metric. Additionally, many food webs are relatively complex, with prey species subject to different assemblages of predators throughout their ontogeny. The goal of this study was to evaluate the extent to which stage-structured predation could be reliably detected from time series of total biomass of predators and prey. We simulated age-structured populations of four mid-trophic-level fish species with distinct life-history traits, exposed them to variable predation at different life stages and fit production models to resulting population biomass to determine how reliably the effects of predators could be detected. Predation targeting early life history and juvenile life stages generally led to larger fluctuations in annual production and was therefore more detectable. However, ecologically realistic levels of observation error and environmental stochasticity masked most predator signals. The addition of predation at a second life stage sharply decreased the ability to detect the effect of each predator. We conclude that the absence of detectable species interactions from biomass time series may be partly due to the interactive effects of environmental variability and complex food web linkages and life histories. We also note that predation signals are most robust for predator-prey systems where predators primarily act on mortality of submature life-history stages. Simulation testing can be applied widely to evaluate the statistical power of analyses to detect predation effects.

BACKGROUND:Accounting for carbon gains and losses in young-growth forests is a key part of carbon assessments. A common silvicultural practice in young forests is thinning to increase the growth rate of residual trees. However, the effect of thinning on total stand carbon stock in these stands is uncertain. In this study we used data from 284 long-term growth and yield plots to quantify the carbon stock in unthinned and thinned young growth conifer stands in the Alaskan coastal temperate rainforest. We estimated carbon stocks and carbon accretion rates for three thinning treatments (basal area removal of 47, 60, and 73 %) and a no-thin treatment across a range of productivity classes and ages. We also accounted for the carbon content in dead trees to quantify the influence of both thinning and natural mortality in unthinned stands. RESULTS:The total tree carbon stock in naturally-regenerating unthinned young-growth forests estimated as the asymptote of the accretion curve was 484 (±26) Mg C ha-1 for live and dead trees and 398 (±20) Mg C ha-1 for live trees only. The total tree carbon stock was reduced by 16, 26, and 39 % at stand age 40 y across the increasing range of basal area removal. Modeled linear carbon accretion rates of stands 40 years after treatment were not markedly different with increasing intensity of basal area removal from reference stand values of 4.45 Mg C ha-1 year-1to treatment stand values of 5.01, 4.83, and 4.68 Mg C ha-1 year-1 respectively. However, the carbon stock reduction in thinned stands compared to the stock of carbon in the unthinned plots was maintained over the entire 100 year period of observation. CONCLUSIONS:Thinning treatments in regenerating forest stands reduce forest carbon stocks, while carbon accretion rates recovered and were similar to unthinned stands. However, that the reduction of carbon stocks in thinned stands persisted for a century indicate that the unthinned treatment option is the optimal choice for short-term carbon sequestration. Other ecologically beneficial results of thinning may override the loss of carbon due to treatment. Our model estimates can be used to calculate regional carbon losses, alleviating uncertainty in calculating the carbon cost of the treatments.

Quantifying the impacts of disturbances such as oil spills on marine species can be challenging. Natural environmental variability, human responses to the disturbance (e.g., fisheries closures), the complex life histories of the species being monitored, and limited pre-spill data can make detection of effects of oil spills difficult. Using long-term monitoring data from the state of Louisiana (USA), we applied novel spatiotemporal approaches to identify anomalies in species occurrence and catch rates. We included covariates (salinity, temperature, turbidity) to help isolate unusual events. While some species showed evidence of unlikely temporal anomalies in occurrence or catch rates, we found that the majority of the observed anomalies were also before the Deepwater Horizon event. Several species-gear combinations suggested upticks in the spatial variability immediately following the spill, but most species indicated no trend. Across species-gear combinations, there was no clear evidence for synchronous or asynchronous responses in occurrence or catch rates across sites following the spill. Our results are in general agreement to other analyses of monitoring data that detected small impacts, but in contrast to recent results from ecological modeling that showed much larger effects of the oil spill on fish and shellfish.

Climate change is altering habitats for marine fishes and invertebrates, but the net effect of these changes on potential food production is unknown. We used temperature-dependent population models to measure the influence of warming on the productivity of 235 populations of 124 species in 38 ecoregions. Some populations responded significantly positively (n = 9 populations) and others responded significantly negatively (n = 19 populations) to warming, with the direction and magnitude of the response explained by ecoregion, taxonomy, life history, and exploitation history. Hindcasts indicate that the maximum sustainable yield of the evaluated populations decreased by 4.1% from 1930 to 2010, with five ecoregions experiencing losses of 15 to 35%. Outcomes of fisheries management-including long-term food provisioning-will be improved by accounting for changing productivity in a warmer ocean.

Szuwalski argues that varying age structure can affect surplus production and that recruitment is a better metric of productivity. We explain how our null model controlled for age structure and other processes as explanations for the temperature-production relationship. Surplus production includes growth, recruitment, and other processes and provides a more complete description of food production impacts than does recruitment alone.

Forage fish support the largest fisheries in the world but also play key roles in marine food webs by transferring energy from plankton to upper trophic-level predators, such as large fish, seabirds, and marine mammals. Fishing can, thereby, have far reaching consequences on marine food webs unless safeguards are in place to avoid depleting forage fish to dangerously low levels, where dependent predators are most vulnerable. However, disentangling the contributions of fishing vs. natural processes on population dynamics has been difficult because of the sensitivity of these stocks to environmental conditions. Here, we overcome this difficulty by collating population time series for forage fish populations that account for nearly two-thirds of global catch of forage fish to identify the fingerprint of fisheries on their population dynamics. Forage fish population collapses shared a set of common and unique characteristics: high fishing pressure for several years before collapse, a sharp drop in natural population productivity, and a lagged response to reduce fishing pressure. Lagged response to natural productivity declines can sharply amplify the magnitude of naturally occurring population fluctuations. Finally, we show that the magnitude and frequency of collapses are greater than expected from natural productivity characteristics and therefore, likely attributed to fishing. The durations of collapses, however, were not different from those expected based on natural productivity shifts. A risk-based management scheme that reduces fishing when populations become scarce would protect forage fish and their predators from collapse with little effect on long-term average catches.

Permafrost soils currently store approximately 1672 Pg of carbon (C), but as high latitudes warm, this temperature-protected C reservoir will become vulnerable to higher rates of decomposition. In recent decades, air temperatures in the high latitudes have warmed more than any other region globally, particularly during the winter. Over the coming century, the arctic winter is also expected to experience the most warming of any region or season, yet it is notably understudied. Here we present nonsummer season (NSS) CO2 flux data from the Carbon in Permafrost Experimental Heating Research project, an ecosystem warming experiment of moist acidic tussock tundra in interior Alaska. Our goals were to quantify the relationship between environmental variables and winter CO2 production, account for subnivean photosynthesis and late fall plant C uptake in our estimate of NSS CO2 exchange, constrain NSS CO2 loss estimates using multiple methods of measuring winter CO2 flux, and quantify the effect of winter soil warming on total NSS CO2 balance. We measured CO2 flux using four methods: two chamber techniques (the snow pit method and one where a chamber is left under the snow for the entire season), eddy covariance, and soda lime adsorption, and found that NSS CO2 loss varied up to fourfold, depending on the method used. CO2 production was dependent on soil temperature and day of season but atmospheric pressure and air temperature were also important in explaining CO2 diffusion out of the soil. Warming stimulated both ecosystem respiration and productivity during the NSS and increased overall CO2 loss during this period by 14% (this effect varied by year, ranging from 7 to 24%). When combined with the summertime CO2 fluxes from the same site, our results suggest that this subarctic tundra ecosystem is shifting away from its historical function as a C sink to a C source.