Gifford Dian J.

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Gifford
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Dian J.
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  • Preprint
    End-to-end foodweb control of fish production on Georges Bank
    ( 2009-05-06) Collie, Jeremy S. ; Gifford, Dian J. ; Steele, John H.
    The ecosystem approach to management requires the productivity of individual fish stocks to be considered in the context of the entire ecosystem. In this paper, we derive an annual end-to-end budget for the Georges Bank ecosystem, based on data from the GLOBEC program and fisheries surveys for the years 1993-2002. We use this budget as the basis to construct scenarios that describe the consequences of various alterations in the Georges Bank trophic web: reduced nutrient input, increased benthic production, removal of carnivorous plankton such as jellyfish, and changes in species dominance within fish guilds. We calculate potential yields of cod and haddock for the different scenarios, and compare the results with historic catches and estimates of maximum sustainable yield (MSY) from recent stock assessments. The MSYs of cod and haddock can be met if the fish community is restructured to make them the dominant species in their respective diet-defined guilds. A return to the balance of fish species present in the first half of the 20th century would depend on an increase in the fraction of primary production going to the benthos rather than to plankton. Estimates of energy flux through the Georges Bank trophic web indicate that rebuilding the principal groundfish species to their MSY levels requires restructuring of the fish community and repartitioning of energy within the food web.
  • Article
    Analysis of energy flow in US GLOBEC ecosystems using end-to-end models
    (The Oceanography Society, 2013-12) Ruzicka, James J. ; Steele, John H. ; Gaichas, Sarah K. ; Ballerini, Tosca ; Gifford, Dian J. ; Brodeur, Richard D. ; Hofmann, Eileen E.
    End-to-end models were constructed to examine and compare the trophic structure and energy flow in coastal shelf ecosystems of four US Global Ocean Ecosystem Dynamics (GLOBEC) study regions: the Northern California Current, the Central Gulf of Alaska, Georges Bank, and the Southwestern Antarctic Peninsula. High-quality data collected on system components and processes over the life of the program were used as input to the models. Although the US GLOBEC program was species-centric, focused on the study of a selected set of target species of ecological or economic importance, we took a broader community-level approach to describe end-to-end energy flow, from nutrient input to fishery production. We built four end-to-end models that were structured similarly in terms of functional group composition and time scale. The models were used to identify the mid-trophic level groups that place the greatest demand on lower trophic level production while providing the greatest support to higher trophic level production. In general, euphausiids and planktivorous forage fishes were the critical energy-transfer nodes; however, some differences between ecosystems are apparent. For example, squid provide an important alternative energy pathway to forage fish, moderating the effects of changes to forage fish abundance in scenario analyses in the Central Gulf of Alaska. In the Northern California Current, large scyphozoan jellyfish are important consumers of plankton production, but can divert energy from the rest of the food web when abundant.
  • Preprint
    Balancing end-to-end budgets of the Georges Bank ecosystem
    ( 2007-05-09) Steele, John H. ; Collie, Jeremy S. ; Bisagni, James J. ; Gifford, Dian J. ; Fogarty, Michael J. ; Link, Jason S. ; Sullivan, B. K. ; Sieracki, Michael E. ; Beet, Andrew R. ; Mountain, David G. ; Durbin, Edward G. ; Palka, D. ; Stockhausen, W. T.
    Oceanographic regimes on the continental shelf display a great range in the time scales of physical exchange, biochemical processes and trophic transfers. The close surface-to-seabed physical coupling at intermediate scales of weeks to months means that the open ocean simplification to a purely pelagic food web is inadequate. Top-down trophic depictions, starting from the fish populations, are insufficient to constrain a system involving extensive nutrient recycling at lower trophic levels and subject to physical forcing as well as fishing. These pelagic-benthic interactions are found on all continental shelves but are particularly important on the relatively shallow Georges Bank in the northwest Atlantic. We have generated budgets for the lower food web for three physical regimes (well mixed, transitional and stratified) and for three seasons (spring, summer and fall/winter). The calculations show that vertical mixing and lateral exchange between the three regimes are important for zooplankton production as well as for nutrient input. Benthic suspension feeders are an additional critical pathway for transfers to higher trophic levels. Estimates of production by mesozooplankton, benthic suspension feeders and deposit feeders, derived primarily from data collected during the GLOBEC years of 1995-1999, provide input to an upper food web. Diets of commercial fish populations are used to calculate food requirements in three fish categories, planktivores, benthivores and piscivores, for four decades, 1963-2002, between which there were major changes in the fish communities. Comparisons of inputs from the lower web with fish energetic requirements for plankton and benthos indicate that we obtained reasonable agreement for the last three decades, 1973 to 2002. However, for the first decade, the fish food requirements were significantly less than the inputs. This decade, 1963-1972, corresponds to a period characterized by a strong Labrador Current and lower nitrate levels at the shelf edge, demonstrating how strong bottom-up physical forcing may determine overall fish yields.
  • Dataset
    Extracted Chlorophyll and Phaeopigment data collected from R/V Endeavor cruises EN259, EN262, EN264, EN266, and EN267II in the Gulf of Maine and Georges Bank in 1995 as part of the U.S. GLOBEC program (GB project)
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-10-28) Gifford, Dian J. ; Manning, James P.
    Extracted Chlorophyll and Phaeopigment data collected from R/V Endeavor cruises EN259, EN262, EN264, EN266, and EN267II in the Gulf of Maine and Georges Bank in 1995 as part of the U.S. GLOBEC program. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/2416
  • Dataset
    Scanfish data from R/V Endeavor cruises EN321 and EN325 in the Gulf of Maine and Georges Bank in 1999 as part of the U.S. GLOBEC program (GB project)
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-10-31) Gifford, Dian J. ; Wishner, Karen
    Scanfish data from R/V Endeavor cruises EN321 and EN325 in the Gulf of Maine and Georges Bank in 1999 as part of the U.S. GLOBEC program. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/2432
  • Dataset
    CTD data collected during MOCNESS tows to Georges Bank and the Gulf of Maine on the US GLOBEC Georges Bank Broadscale and Process cruises, 1994-1999
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-01-30) Bollens, Steve M. ; Bucklin, Ann ; Garrahan, Peter ; Gifford, Dian J. ; Green, John ; Lough, Greg ; Miller, Charles B. ; Sibunka, John ; Taylor, Maureen ; Wiebe, Peter H.
    The MOCNESS is based on the Tucker Trawl principle (Tucker, 1951). The particular MOCNESS system from which these CTD data came is one of three net systems. The MOCNESS-10 (with 10 m2 nets)carries 6 nets of 3.0-mm circular mesh which are opened and closed sequentially by commands through conducting cable from the surface (Wiebe et al., 1976). In all three systems, "the underwater unit sends a data frame, comprised of temperature, depth, conductivity, net-frame angle, flow count, time, number of open net, and net opening/closing, to the deck unit in a compressed hexadecimal format every 2 seconds and from the deck unit to a microcomputer every 4 seconds... Temperature (to approximately 0.01 deg C) and conductivity are measured with SEABIRD sensors. Normally, a modified T.S.K.-flowmeter is used... Both the temperature and conductivity sensors and the flowmeter are mounted on top of the frame so that they face horizontally when the frame is at a towing angle of 45deg... Calculations of salinity (to approximately 0.01 o/oo S), potential temperature (theta), potential density (sigma), the oblique and vertical velocities of the net, and the approximate volume filtered by each net are made after each string of data has been received by the computer." (Wiebe et al., 1985) In addition, data were collected from four other sensors attached to the frame: the Transmissometer, the Fluorometer, the Downwelling light sensor, and the Oxygen sensor. A SeaBird underwater pump was also included in the sensor suite. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/2302
  • Dataset
    CTD data from R/V Endeavor cruises EN321 and EN325 to Georges Bank, 1999
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-01-30) Gifford, Dian J.
    CTD data from R/V Endeavor cruises EN321 and EN325 to Georges Bank, 1999 For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/2301
  • Dataset
    Chlorophyll data from R/V Endeavor cruises EN321 and EN325 to Georges Bank in 1999 as part of the U.S. GLOBEC program (GB project)
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-10-28) Gifford, Dian J. ; Manning, James P.
    Chlorophyll data from R/V Endeavor cruises EN321 and EN325 to Georges Bank in 1999 as part of the U.S. GLOBEC program. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/2417
  • Preprint
    Reconciling end-to-end and population concepts for marine ecosystems
    ( 2010-05-06) Steele, John H. ; Gifford, Dian J.
    The inherent complexities in the structure and dynamics of marine food webs have led to two major simplifying concepts, a species-centric approach focused on physical processes driving the population dynamics of single species and a trophic-centric approach emphasizing energy flows through broad functional groups from nutrient input to fish production. Here we review the two approaches and discuss their advantages and limitations. We suggest that these concepts are complementary: their applications involve different time scales and distinct aspects of population and community resilience, but their integration is necessary for ecosystem-based management
  • Preprint
    Construction kits or virtual worlds; management applications of E2E models
    ( 2011-10) Steele, John H. ; Aydin, Kerim ; Gifford, Dian J. ; Hofmann, Eileen E.
    We review briefly the diversity of modeling activity that comes under the rubric of end-to-end (E2E) models, but the focus of this paper – of joint concern to researchers and to managers - is on applications to management and decision making. The models and applications span a range from “construction kits” that identify particular management issues and use comparisons across ecosystems; to “virtual worlds” that immerse managers in the details of strategic evaluations for particular systems. The general conclusion is that “application” is not a straightforward transition from theory to practice but a complex interactive process.
  • Preprint
    Comparing species and ecosystem-based estimates of fisheries yields
    ( 2011-06) Steele, John H. ; Gifford, Dian J. ; Collie, Jeremy S.
    Three methods are described to estimate potential yields of commercial fish species: (i) single-species calculation of maximum sustainable yields, and two ecosystem-based methods derived from published results for (ii) energy flow and for (iii) community structure. The requirements imposed by food-web fluxes, and by patterns of relative abundance, provide constraints on individual species. These constraints are used to set limits to ecosystem-based yields (EBY); these limits, in turn, provide a comparison with the usual estimates of maximum sustainable yields (MSY). We use data on cod and haddock production from Georges Bank for the decade 1993-2002 to demonstrate these methods. We show that comparisons among the three approaches can be used to demonstrate that ecosystem based estimates of yields complement, rather than supersede, the single-species estimates. The former specify the significant changes required in the rest of the ecosystem to achieve a return to maximum sustainable levels for severely depleted commercial fish stocks. The overall conclusion is that MSY defines changes required in particular stocks, whereas EBY determines the changes required in the rest of the ecosystem to realize these yields. Species specific MSY only has meaning in the context of the prey, predators and competitors that surround it.
  • Dataset
    Event logs from the U.S. GLOBEC Georges Bank project, from 10 vessels and 104 cruises in the Gulf of Maine and Georges Bank area from 1994-1999 (GB project)
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-02-18) Ashjian, Carin J. ; Bollens, Steve M. ; Bucklin, Ann ; Campbell, Robert ; Davis, Cabell S. ; Durbin, Edward ; Gallager, Scott ; Garrahan, Peter ; Gibson, James ; Gifford, Dian J. ; Green, John ; Greene, Charles H ; Hebert, Dave ; Horgan, Erich ; Houghton, Robert W ; Incze, Lewis ; Irish, Jim ; Ledwell, James R. ; Lentz, Steven J. ; Limeburner, Richard ; Lough, Greg ; Madin, Laurence P. ; Miller, Charles B. ; Mountain, David ; Oakey, Neil ; Schlitz, Ronald ; Sibunka, John ; Smith, Peter C. ; Taylor, Maureen ; Weller, Robert A. ; Wiebe, Peter H. ; Williams, Albert J. ; Wishner, Karen ; Lee, Craig
    Event logs from the U.S. GLOBEC Georges Bank project, from 10 vessels and 104 cruises in the Gulf of Maine and Georges Bank area from 1994-1999. Event logs provide an overall summary of the sampling activities during a cruise. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/2321