68 research outputs found
Erratum: Opinion: Putting all foods on the same table: Achieving sustainable food systems requires full accounting (Proceedings of the National Academy of Sciences of the United States of America(2019)116(18152–18156)Doi: 10.1073/pnas.1913308116)
No full textCorrection to Supporting Information for “Opinion: Putting all foods on the same table: Achieving sustainable food systems requires full accounting,” by Benjamin S. Halpern, Richard S. Cottrell, Julia L. Blanchard, Lex Bouwman, Halley E. Froehlich, Jessica A. Gephart, Nis Sand Jacobsen, Caitlin D. Kuempel, Peter B. McIntyre, Marc Metian, Daniel D. Moran, Kirsty L. Nash, Johannes Többen, and David R. Williams, which was first published September 10, 2019; 10.1073/pnas.1913308116 (Proc. Natl. Acad. Sci. U.S.A. 116, 18152–18156). The authors note that the following datasets were missing from the published article: Dataset S1, Dataset S2, and Dataset S3. The datasets have been added online
A comparison of multispecies models with potential use for strategic fisheries management
No full textBig fish or small fish: size based methods to evaluate direct and indirect ecosystem effects of fishing
No full textLimited impact of big fish mothers for population replenishment
No full textA recent meta-analysis by Barneche et al. (Science 360(6389): 642) show that fish reproductive output scales hypergeometrically with female weight. This result challenges the common assumption that reproductive output is proportional to weight. The implication made is that current theory and practice severely underestimates the importance of larger females for population replenishment. Their example for cod shows that current practice makes an error of 149%. By properly accounting for fish demography we show that the error is maximally on the order of 10%, and in most other fish stocks likely much less
The Consequences of Balanced Harvesting of Fish Communities
No full textNo abstracts are to be cited without prior reference to the author. Balanced harvesting, where species or individuals are exploited in accordance to their productivity, has been proposed as a way to minimize the effects of fishing on marine fish communities and ecosystems. We use a size- and trait-based model where species interact through competition and predation to compare balanced harvesting with selective harvesting, where juvenile fish are protected from fishin
En revision af traditionelle koncepter i fiskeriet. Er balanceret fiskeri en mulig forvaltningsstrategi?
No full textThe consequences of balanced harvesting of fish communities
No full textBalanced harvesting, where species or individuals are exploited in accordancewith their productivity, has been proposed as a way to minimize theeffects of fishing on marine fish communities and ecosystems. This callsfor a thorough examination of the consequences balanced harvesting hason fish community structure and yield. We use a size- and trait-basedmodel that resolves individual interactions through competition and predationto compare balanced harvesting with traditional selective harvesting,which protects juvenile fish from fishing. Four different exploitationpatterns, generated by combining selective or unselective harvesting withbalanced or unbalanced fishing, are compared. We find that unselectivebalanced fishing, where individuals are exploited in proportion to their productivity, produces a slightly larger total maximum sustainable yield thanthe other exploitation patterns and, for a given yield, the least change inthe relative biomass composition of the fish community. Because fishingreduces competition, predation and cannibalism within the community,the total maximum sustainable yield is achieved at high exploitation rates.The yield from unselective balanced fishing is dominated by small individuals,whereas selective fishing produces a much higher proportion of largeindividuals in the yield. Although unselective balanced fishing is predictedto produce the highest total maximum sustainable yield and thelowest impact on trophic structure, it is effectively a fishery predominantlytargeting small forage fis
Comparing model predictions for ecosystem-based management
No full textEcosystem modeling is becoming an integral part of fisheries management, but there is a need to identify differences between predictions derived from models employed for scientific and management purposes. Here, we compared two models: a biomass-based food-web model (Ecopath with Ecosim (EwE)) and a size-structured fish community model. The models were compared with respect to predicted ecological consequences of fishing to identify commonalities and differences in model predictions for the California Current fish community. We compared the models regarding direct and indirect responses to fishing on one or more species. The size-based model predicted a higher fishing mortality needed to reach maximum sustainable yield than EwE for most species. The size-based model also predicted stronger top-down effects of predator removals than EwE.In contrast, EwE predicted stronger bottom-up effects of forage fisheries removal. In both cases, the differences are due to thepresumed degree of trophic overlap between juveniles of large-bodied fish and adult stages of forage fish. These differenceshighlight how each model’s emphasis on distinct details of ecological processes affects its predictions, underscoring theimportance of incorporating knowledge of model assumptions and limitation, possibly through using model ensembles, whenproviding model-based scientific advice to policy makers
The theoretical foundations for size spectrum models of fish communities
No full textSize spectrum models have emerged from 40 years of basic research on how body size determines individual physiology and structures marine communities. They are based on commonly accepted assumptions and have a low parameter set, which make them easy to deploy for strategic ecosystem oriented impact assessment of fisheries. We describe the fundamental concepts in size-based models about food encounter and the bioenergetics budget of individuals. Within the general framework three model types have emerged that differs in their degree of complexity: the food-web, the trait-based and the community model. We demonstrate the differences between the models through examples of their response to fishing and their dynamic behavior. We review implementations of size spectrum models and describe important variations concerning the functional response, whether growth is food-dependent or fixed, and the density-dependence imposed on the system. Finally we discuss challenges and promising direction
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