Rose K.A.,Louisiana State University |
Fiechter J.,University of California at Santa Cruz |
Curchitser E.N.,Rutgers University |
Hedstrom K.,University of Alaska Fairbanks |
And 13 more authors.
Progress in Oceanography | Year: 2015
We describe and document an end-to-end model of anchovy and sardine population dynamics in the California Current as a proof of principle that such coupled models can be developed and implemented. The end-to-end model is 3-dimensional, time-varying, and multispecies, and consists of four coupled submodels: hydrodynamics, Eulerian nutrient-phytoplankton-zooplankton (NPZ), an individual-based full life cycle anchovy and sardine submodel, and an agent-based fishing fleet submodel. A predator roughly mimicking albacore was included as individuals that consumed anchovy and sardine. All submodels were coded within the ROMS open-source community model, and used the same resolution spatial grid and were all solved simultaneously to allow for possible feedbacks among the submodels. We used a super-individual approach and solved the coupled models on a distributed memory parallel computer, both of which created challenging but resolvable bookkeeping challenges. The anchovy and sardine growth, mortality, reproduction, and movement, and the fishing fleet submodel, were each calibrated using simplified grids before being inserted into the full end-to-end model. An historical simulation of 1959-2008 was performed, and the latter 45. years analyzed. Sea surface height (SSH) and sea surface temperature (SST) for the historical simulation showed strong horizontal gradients and multi-year scale temporal oscillations related to various climate indices (PDO, NPGO), and both showed responses to ENSO variability. Simulated total phytoplankton was lower during strong El Nino events and higher for the strong 1999 La Nina event. The three zooplankton groups generally corresponded to the spatial and temporal variation in simulated total phytoplankton. Simulated biomasses of anchovy and sardine were within the historical range of observed biomasses but predicted biomasses showed much less inter-annual variation. Anomalies of annual biomasses of anchovy and sardine showed a switch in the mid-1990s from anchovy to sardine dominance. Simulated averaged weights- and lengths-at-age did not vary much across decades, and movement patterns showed anchovy located close to the coast while sardine were more dispersed and farther offshore. Albacore predation on anchovy and sardine was concentrated near the coast in two pockets near the Monterey Bay area and equatorward of Cape Mendocino. Predation mortality from fishing boats was concentrated where sardine age-1 and older individuals were located close to one of the five ports. We demonstrated that it is feasible to perform multi-decadal simulations of a fully-coupled end-to-end model, and that this can be done for a model that follows individual fish and boats on the same 3-dimensional grid as the hydrodynamics. Our focus here was on proof of principle and our results showed that we solved the major technical, bookkeeping, and computational issues. We discuss the next steps to increase computational speed and to include important biological differences between anchovy and sardine. In a companion paper (Fiechter et al., 2015), we further analyze the historical simulation in the context of the various hypotheses that have been proposed to explain the sardine and anchovy cycles. © 2015 Elsevier Ltd.
Asfaw S.,FAO of the United Nations |
Lipper L.,FAO of the United Nations |
Dalton T.J.,Kansas State University |
Audi P.,International Crops Research Institute for the Semi Arid Tropics ICRISAT
Environment and Development Economics | Year: 2012
This paper examines determinants of output and input market participation. It employs propensity score matching techniques to evaluate the impact of market participation on pigeonpea diversity and household welfare, using cross-sectional data of 333 households from Kenya. Results show that input and output market participation decisions are quite distinct. Output market participation is influenced by household demographics, farm size and radio ownership, while input market participation is determined by farm size, bicycle ownership and access to a salaried income. The findings reveal a positive and significant impact of output market participation on pigeonpea diversity, while input market participation had a negative and significant impact on diversity. The results indicate that output market participants have significantly higher food security status than non-participants, in line with the general findings of the literature. However, no significant impact is found between indicators of household welfare and input market participation. © Copyright 2012 Cambridge University Press.
Asfaw S.,FAO of the United Nations |
Shiferaw B.,International Maize and Wheat Improvement Center |
Simtowe F.,International Crops Research Institute for the Semi Arid Tropics ICRISAT |
Lipper L.,FAO of the United Nations
Food Policy | Year: 2012
This paper evaluates the potential impact of adoption of improved legume technologies on rural household welfare measured by consumption expenditure in rural Ethiopia and Tanzania. The study utilizes cross-sectional farm household level data collected in 2008 from a randomly selected sample of 1313 households (700 in Ethiopia and 613 in Tanzania). The causal impact of technology adoption is estimated by utilizing endogenous switching regression. This helps us estimate the true welfare effect of technology adoption by controlling for the role of selection problem on production and adoption decisions. Our analysis reveals that adoption of improved agricultural technologies has a significant positive impact consumption expenditure (in per adult equivalent terms) in rural Ethiopia and Tanzania. This confirms the potential role of technology adoption in improving rural household welfare as higher consumption expenditure from improved technologies translate into lower poverty, higher food security and greater ability to withstand risk. An analysis of the determinants of adoption highlighted inadequate local supply of seed, access to information and perception about the new cultivars as key constraints for technology adoption. © 2012 Elsevier Ltd.
Muscarella R.,Columbia University |
Uriarte M.,Columbia University |
Forero-Montana J.,University of Puerto Rico at San Juan |
Comita L.S.,Ohio State University |
And 7 more authors.
Journal of Ecology | Year: 2013
The transition from seed to established seedling (STS) represents a major bottleneck in plant demography with implications for community dynamics and the maintenance of species diversity. The relative strength of seed limitation versus seedling establishment limitation can reveal life-history trade-offs that contribute to the maintenance of community diversity. If seed limitation dominates, chance arrival to open sites may play a key role in maintaining diversity. If seedling establishment limitation dominates, however, species relative abundances may depend more on tolerance to environmental and biotic conditions during seedling establishment (i.e. species-specific regeneration niche). We used three years of seed rain and seedling recruitment data for 19 species of tropical woody plants collected in the Luquillo Forest Dynamics Plot in Puerto Rico to (i) examine a trade-off between seed and seedling establishment limitation and (ii) quantify the biotic and abiotic factors that mediate the STS transition. We did not find evidence of a life-history trade-off in the form of a negative correlation between seed and seedling establishment limitation. However, species varied considerably in the relative levels of seed and seedling establishment limitation they displayed. Seed mass correlated negatively with seedling establishment limitation but not with seed limitation. We found striking differences in STS transition between life-forms categorized as trees (including two palms) and lianas; lianas exhibited significantly higher STS transition rates than trees. The biotic and abiotic variables most strongly associated with successful STS transition differed between life-forms. For trees, conspecific seed density and temporal fruiting concentration had negative effects on seedling establishment, while seed mass had a positive effect. A significant interaction between leaf litter input at a plot and seed size suggested that large-seeded species had higher STS transition probability in plots with more leaf litter biomass. This effect was reversed for small-seeded species. For lianas, leaf litter had a negative effect on STS transition and temporal fruiting concentration had a positive effect. Synthesis. Our analyses demonstrate the multidimensional axes of regeneration niches and how they can be related to seed size. Long-term data sets are critical for understanding these relationships because the relevant factors vary along large spatial and temporal scales. © 2012 The Authors. Journal of Ecology © 2012 British Ecological Society.
Ye Y.,FAO of the United Nations |
Valbo-Jorgensen J.,FAO of the United Nations
Fisheries Research | Year: 2012
Sturgeon is the most valuable fish species because of the high demand for their roe. The sturgeon fishery was historically the most important fishery in the Caspian Sea, but the major sturgeon species have now been classified as " critically endangered" by the International Union for Conservation of Nature. Considering commercial importance and data availability, we focus this study on stellate sturgeon. By applying a Depletion-Based Stock Reduction Analysis to model the population dynamics of the stellate sturgeon in the Caspian Sea, we estimate that the current stock is only 16% of the biomass (B MSY) that can produce the maximum sustainable yield (MSY). If all fish removals are stopped and no more stock enhancement takes place in the future, the stock would recover to B MSY by 2035 on average, with a 50% probability of it occurring between 2029 and 2058. If stock enhancement continues at the 2010 level, the rebuilding process will be 5 years faster, reaching B MSY by 2030. In contrast, if IUU fishing continues at the current level and only legal fishing is stopped, the stellate sturgeon will fail to recover and become extinct by 2042 without stock enhancement. Therefore, the priority of conserving the stellate sturgeon stock in the Caspian Sea is to eliminate IUU fishing. Practical rebuilding plans need also to include a combination of reducing fishing removals and restoring the spawning potential of the stock that has been lost by human interruptions in the ecosystem such as destruction of spawning grounds and overfishing. © 2012 Elsevier B.V.