603 research outputs found
Linking habitat mosaics and connectivity in a coral reef seascape
Author Posting. Ā© The Author(s), 2012. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 109 (2012): 15372-15376, doi:10.1073/pnas.1206378109.Tropical marine ecosystems are under mounting anthropogenic pressure from overfishing and habitat destruction, leading to declines in their structure and function on a global scale. While maintaining connectivity among habitats within a seascape is necessary for preserving population resistance and resilience, quantifying movements of individuals within seascapes remains challenging. Traditional methods of identifying and valuing potential coral reef fish nursery habitats are indirect, often relying on visual surveys of abundance and correlations of size and biomass among habitats. We used compound-specific stable isotope analyses to determine movement patterns of commercially important fish populations within a coral reef seascape. This approach allowed us to quantify the relative contributions of individuals from inshore nurseries to reef populations and identify migration corridors among important habitats. Our results provided direct measurements of remarkable migrations by juvenile snapper of over 30 km between nurseries and reefs. We also found significant plasticity in juvenile nursery residency. While a majority of individuals on coastal reefs had used seagrass nurseries as juveniles, many adults on oceanic reefs had settled directly into reef habitats. Moreover, seascape configuration played a critical but heretofore unrecognized role in determining connectivity among habitats. Finally, our approach provides key quantitative data necessary to estimate the value of distinctive habitats to ecosystem services provided by seascapes.This research was based on work supported by Award Nos. USA 00002 and KSA 00011 made by King Abdullah University of Science and Technology (KAUST). Additional funding was provided by Woods Hole Oceanographic Institution and an International Society for Reef Studies-Ocean Conservancy Coral Reef Fellowship. K. McMahon received support from the National Science Foundation Graduate Research Fellowship Program
Multiple small monthly doses of dicyandiamide (DCD) did not reduce denitrification in Waikato dairy pasture
The effectiveness of multiple small doses of the nitrification inhibitor dicyandiamide (DCD) to decrease denitrification under warm moist conditions was tested in a 1-year field trial on a grazed dairy pasture. DCD was applied approximately every 4 weeks as an aqueous spray onto ten replicate plots 3 days after rotational grazing by dairy cows. Each application was at the rate of 3 kg DCD haā»Ā¹, with a total annual application of 33 kg haā»Ā¹. Denitrification was assessed 5 days after each DCD application using the acetylene block method. At the end of the trial, the rate of degradation of DCD under summer conditions was measured. DCD significantly decreased the mean annual nitrate concentration by about 17%. Denitrification and denitrification enzyme activity were highly variable and no significant effect of DCD in decreasing denitrification was detected. In the summer month of December, DCD degraded rapidly with an estimated half-life of 5 Ā± 3 days (mean and standard deviation)
Inter-annual variability in isotope and elemental ratios recorded in otoliths of an anadromous fish
Author Posting. Ā© The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Geochemical Exploration 102 (2009): 181-186, doi:10.1016/j.gexplo.2008.10.001.Isotope ratios and elemental concentrations in otoliths are often used as natural tags to
reconstruct migratory movements and connectivity patterns in marine and
anadromous fishes. Although differences in otolith geochemistry have been
documented among geographically separated populations, inter-annual variation
within locations is less frequently examined. We compared otolith isotope (Ī“18O and
87Sr:86Sr) and elemental ratios (Sr:Ca and Ba:Ca) from several annual cohorts of
juvenile American shad (Alosa sapidissima) in three rivers. These four geochemical
signatures distinguished among river-specific populations of this species at both large
and small geographic scales, with Ī“18O and 87Sr:86Sr generating the majority of
multivariate variation. We found significant variation among years for all variables in
two to three rivers. However, the magnitude of variability differed among ratios, with
Ī“18O ratios showing substantial inter-annual shifts while 87Sr:86Sr ratios were
relatively stable across years. Sr:Ca and Ba:Ca ratios also varied among years. These
results imply that investigators using environmentally labile signatures must quantify
geochemical signatures for each cohort of interest in order to confidently identify
origins of migrants.Funding was provided by National Science Foundation grants to SRT
(OCE-0215905 and OCE-0134998) and grants by the American Museum of Natural
History Lerner-Gray Fund for Marine Research, SEASPACE, Inc., and the WHOI
Ocean Life Institute to BDW
Continental-scale variation in otolith geochemistry of juvenile American shad (Alosa sapidissima)
Author Posting. Ā© NRC Research Press, 2008. This article is posted here by permission of NRC Research Press for personal use, not for redistribution. The definitive version was published in Canadian Journal of Fisheries and Aquatic Sciences 65 (2008): 2623-2635, doi:10.1139/F08-164.We assembled a comprehensive atlas of geochemical signatures in juvenile American shad (Alosa sapidissima) to discriminate natal river origins on a large spatial scale and at a high spatial resolution. Otoliths and (or) water samples were collected from 20 major spawning rivers from Florida to Quebec and were analyzed for elemental (Mg:Ca, Mn:Ca, Sr:Ca, and Ba:Ca) and isotope (87Sr:86Sr and Ī“18O) ratios. We examined correlations between water chemistry and otolith composition for five rivers where both were sampled. While Sr:Ca, Ba:Ca, 87Sr:86Sr, and Ī“18O values in otoliths reflected those ratios in ambient waters, Mg:Ca and Mn:Ca ratios in otoliths varied independently of water chemistry. Geochemical signatures were highly distinct among rivers, with an average classification accuracy of 93% using only those variables where otolith values were accurately predicted from water chemistry data. The study represents the largest assembled database of otolith signatures from the entire native range of a species, encompassing approximately 2700 km of coastline and 19 degrees of latitude and including all major extant spawning populations. This database will allow reliable estimates of natal origins of migrating ocean-phase American shad from the 2004 annual cohort in the future.This work was funded by National Science
Foundation (NSF) grants OCE-0215905 and OCE-0134998
to SRT and by an American Museum of Natural History
LernerāGray Grant for Marine Research and a scholarship
from SEASPACE, Inc., to BDW
Regional Economic Implications of Water Allocation and Reliability
The understanding of how allocation decisions can maximise the economic returns to the community from water for irrigation has received little attention, but is a significant issue for regional councils, those interested in water allocation policy development, and for irrigated farmers. There is a tradeoff between the amount of irrigated area and the reliability with which it can be undertaken. Overseas studies have generated a curve with optimum levels of allocation which maximise the economic return to the community from the resource. The study on which this paper is based used a single case study to model the individual and regional economic outcomes for four scenarios of water allocation, using daily time step simulation models of the hydrological, irrigation, farm and financial systems over the 1973 ā 2000 period. The results show that there is an increasing return to the region as the allocation from the resource increases, at the expense of lower returns to existing users.Irrigation, reliability, regional economic impacts, Agribusiness, Agricultural and Food Policy, Agricultural Finance, Community/Rural/Urban Development, Environmental Economics and Policy, Farm Management, Financial Economics, Institutional and Behavioral Economics, Land Economics/Use, Resource /Energy Economics and Policy,
HMMoce : an R package for improved geolocation of archival-tagged fishes using a hidden Markov method
Author Posting. Ā© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Methods in Ecology and Evolution 9 (2018): 1212-1220, doi:10.1111/2041-210X.12959.Electronic tagging of marine fishes is commonly achieved with archival tags that rely on light levels
and sea surface temperatures to retrospectively estimate movements. However, methodological issues
associated with light-level geolocation have constrained meaningful inference to species where it is
possible to accurately estimate time of sunrise and sunset. Most studies have largely ignored the
oceanographic profiles collected by the tag as a potential way to refine light-level geolocation estimates.
Open-source oceanographic measurements and outputs from high-resolution models are increasingly
available and accessible. Temperature and depth profiles recorded by electronic tags can be integrated
with these empirical data and model outputs to construct likelihoods and improve geolocation estimates.
The R package HMMoce leverages available tag and oceanographic data to improve position estimates
derived from electronic tags using a hidden Markov approach. We illustrate the use of the model and
test its performance using example blue and mako shark archival tag data. Model results were validated
using independent, known tracks and compared to results from other geolocation approaches.
HMMoce exhibited as much as 6-fold improvement in pointwise error as compared to traditional light-level
geolocation approaches. The results demonstrated the general applicability of HMMoce to marine animals,
particularly those that do not frequent surface waters during crepuscular periods.This work
was funded by awards to C. Braun from the Martin Family Society of Fellows for Sustainability Fellowship at
the Massachusetts Institute of Technology, the Grassle Fellowship and Ocean Venture Fund at the Woods
Hole Oceanographic Institution, and the NASA Earth and Space Science Fellowship
Response of Otolith Microchemistry to Environmental Variations Experienced by Larval and Juvenile Atlantic Croaker (Micropogonias Undulatus)
Minor and trace elements incorporated into otoliths during growth may permanently record environmental conditions experienced by fishes. To determine the validity of this approach, we used laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) to assay sectioned otoliths from juvenile Atlantic croaker (Micropogonias undulatus) collected from each of three sites in the Neuse River, North Carolina, and the Elizabeth River, Virginia. Elemental concentrations at the center of the otoliths did not differ between locations, although both Mg : Ca and Ba : Ca were significantly higher at the edge of otoliths from the Neuse River than from the Elizabeth River. Three of the elements (Mg : Ca, Sr : Ca, and Ba : Ca) showed significant variation across otoliths. Sr : Ca, and to a lesser extent Mg : Ca, showed progressive decreases as the fish moved from offshore spawning sites to estuarine nursery areas. The opposite pattern was shown by Ba : Ca. We hypothesize that these patterns were related to the elemental concentrations within oceanic and estuarine water masses. Although both Sr : Ca and Ba : Ca seem to be useful tracers of offshore-inshore migration of estuarine-dependent species, the sensitivity of the technique to more subtle changes in water chemistry remains to be determined
The Potential Cost to New Zealand Dairy Farmers from the Introduction of Nitrate-Based Stocking Rate Restrictions
Introducing a stocking rate restriction is one possible course of action for regulators to improve water quality where it is affected by nitrate pollution. To determine the impact of a stocking rate restriction on a range of New Zealand dairy farms, a whole-farm model was optimised with and without a maximum stocking rate of 2.5 cows per hectare. Three farm systems, which differ by their level of feed-related capital, were examined for the changes to the optimal stocking rate and optimal level of animal milk production genetics when utility was maximised. The whole-farm model was optimised through the use of an evolutionary algorithm called differential evolution. The introduction of a stocking rate restriction would have a very large impact on the optimally organised high feed-related capital farm systems, reducing their certainty equivalent by almost half. However, there was no impact on the certainty equivalent of low feed-related capital systems.environmental regulation, dairy farms, whole-farm model, evolutionary algorithm, Environmental Economics and Policy, Livestock Production/Industries, Q12, Q52, C61,
Geochemical signatures in otoliths record natal origins of American shad
Author Posting. Ā© American Fisheries Society, 2008. This article is posted here by permission of American Fisheries Society for personal use, not for redistribution. The definitive version was published in Transactions of the American Fisheries Society 137 (2008): 57ā69, doi:10.1577/T07-029.1.Population connectivity is a critical component in the life history dynamics of anadromous fishes and in the persistence of local populations. We used geochemical signatures in the otoliths of American shad Alosa sapidissima to determine natal origins and estimate rates of straying among river-specific populations along the U.S. Atlantic coast. Stable isotope (Ī“13C, Ī“18O and 87Sr:86Sr) and elemental (Mg:Ca, Mn:Ca, Sr:Ca and Ba:Ca) signatures in otoliths of juvenile American shad from rivers from Georgia to New Hampshire varied significantly, allowing for an average of 91% cross-validated accuracy when classifying individual fish to their natal rivers. We also found significant interannual variability in the geochemical signatures from several rivers, due largely to differences in Ī“18O values among years. We then used the ground-truthed geochemical signatures in the otoliths of juvenile American shad to identify the natal origins of spawning adults in the York River system in Virginia. Approximately 6% of the spawning adults collected in the York River were strays from other rivers. Of the remaining fish, 79% were spawned in the Mattaponi River and 21% in the Pamunkey River. The combined results of this and other recent studies suggest that although most American shad spawning in the York River were homing to their natal river, there was much less fidelity to individual tributaries. Small-scale straying could allow fish spawned in the Mattaponi River to subsidize spawning in the Pamunkey River, which has experienced persistent recruitment failureThis work was
funded by National Science Foundation grants OCE-0215905 and OCE-0134998 to SRT and by the
WallopāBreaux Program of the U.S. Fish and Wildlife
Service through the Virginia Marine Resources Commission
to J.E.O
The Effects of Tree Density on Pasture Production Under Acacia Melanoxylon
Silvi-pastoral systems could contribute to greater total productivity and more sustainable land management of grazed pastures in New Zealand. Despite this potential, little is known of the interactions of tree species and environment on pasture growth. In this paper we report the effects of tree density on pasture yield in an Acacia melanoxylon silvi-pastoral system. The results show decreasing pasture yield with increasing tree density, although the extent of the reduction is less than would be expected under Pinus radiata. Results suggest that shade is the dominant factor causing yield decline in this study, while reduced N availability is clearly implicated in previous studies with pine trees. This study will provide more data on which a mechanistic model of tree-pasture interactions can be based
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