Steele John H.

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Steele
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John H.
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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.
  • Preprint
    Productivity and linkages of the food web of the southern region of the western Antarctic Peninsula continental shelf
    ( 2013-11-23) Ballerini, Tosca ; Hofmann, Eileen E. ; Ainley, David G. ; Daly, Kendra L. ; Marrari, Marina ; Ribic, Christine A. ; Smith, Walker O. ; Steele, John H.
    The productivity and linkages in the food web of the southern region of the west Antarctic Peninsula continental shelf were investigated using a multi-trophic level mass balance model. Data collected during the Southern Ocean Global Ocean Ecosystem Dynamics field program were combined with data from the literature on the abundance and diet composition of zooplankton, fish, seabirds and marine mammals to calculate energy flows in the food web and to infer the overall food web structure at the annual level. Sensitivity analyses investigated the effects of variability in growth and biomass of Antarctic krill (Euphausia superba) and in the biomass of Antarctic krill predators on the structure and energy fluxes in the food web. Scenario simulations provided insights into the potential responses of the food web to a reduced contribution of large phytoplankton (diatom) production to total primary production, and to reduced consumption of primary production by Antarctic krill and mesozooplankton coincident with increased consumption by microzooplankton and salps. Model-derived estimates of primary production were 187 – 207 g C m-2 y-1, which are consistent with observed values (47-351 g C m-2 y-1). Simulations showed that Antarctic krill provide the majority of energy needed to sustain seabird and marine mammal production, thereby exerting a bottom-up control on higher trophic level predators. Energy transfer to top predators via mesozooplanton was a less efficient pathway, and salps were a production loss pathway because little of the primary production they consumed was passed to higher trophic levels. Increased predominance of small phytoplankton (nanoflagellates and cryptophytes) reduced the production of Antarctic krill and of its predators, including seabirds and seals.
  • Preprint
    Constructing end-to-end models using ECOPATH data
    ( 2011-03) Steele, John H. ; Ruzicka, James J.
    The wide availability of ECOPATH data sets provides a valuable resource for the comparative analysis of marine ecosystems. We show how to derive a bottom-up transform from the top-down ECOPATH; couple this to a simple NPZD web with physical forcing; and use the end-to-end model (E2E) for scenario construction. This steady state format also provides a framework and initial conditions for different dynamic simulations. This model can be applied to shelf ecosystems with a wide range of physical forcing, coupled benthic/pelagic food webs, and nutrient recycling. We illustrate the general application and the specific problems by transforming an ECOPATH model for the Northern Californian Current (NCC). We adapt results on the upwelling regime to provide estimates of physical fluxes and use these to show the consequences of different upwelling rates combined with variable retention mechanism for plankton, for the productivity of fish and other top predators; and for the resilience of the ecosystem. Finally we show how the effects of inter-annual to decadal variations in upwelling on fishery yields can be studied using dynamic simulations with different prey-predator relations. The general conclusion is that the nature of the physical regimes for shelf ecosystems cannot be ignored in comparing end-to-end representations of these food webs.
  • 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.
  • Article
    Why compare marine ecosystems?
    (Oxford University Press, 2009-08-30) Murawski, Steven A. ; Steele, John H. ; Taylor, Phillip ; Fogarty, Michael J. ; Sissenwine, Michael P. ; Ford, Michael ; Suchman, Cynthia
    Effective marine ecosystem-based management (EBM) requires understanding the key processes and relationships controlling the aspects of biodiversity, productivity, and resilience to perturbations. Unfortunately, the scales, complexity, and non-linear dynamics that characterize marine ecosystems often confound managing for these properties. Nevertheless, scientifically derived decision-support tools (DSTs) are needed to account for impacts resulting from a variety of simultaneous human activities. Three possible methodologies for revealing mechanisms necessary to develop DSTs for EBM are: (i) controlled experimentation, (ii) iterative programmes of observation and modelling ("learning by doing"), and (iii) comparative ecosystem analysis. We have seen that controlled experiments are limited in capturing the complexity necessary to develop models of marine ecosystem dynamics with sufficient realism at appropriate scales. Iterative programmes of observation, model building, and assessment are useful for specific ecosystem issues but rarely lead to generally transferable products. Comparative ecosystem analyses may be the most effective, building on the first two by inferring ecosystem processes based on comparisons and contrasts of ecosystem response to human-induced factors. We propose a hierarchical system of ecosystem comparisons to include within-ecosystem comparisons (utilizing temporal and spatial changes in relation to human activities), within-ecosystem-type comparisons (e.g. coral reefs, temperate continental shelves, upwelling areas), and cross-ecosystem-type comparisons (e.g. coral reefs vs. boreal, terrestrial vs. marine ecosystems). Such a hierarchical comparative approach should lead to better understanding of the processes controlling biodiversity, productivity, and the resilience of marine ecosystems. In turn, better understanding of these processes will lead to the development of increasingly general laws, hypotheses, functional forms, governing equations, and broad interpretations of ecosystem responses to human activities, ultimately improving DSTs in support of EBM.
  • 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.
  • 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
    Dividing up the pie : whales, fish, and humans as competitors
    ( 2013-04-29) Ruzicka, James J. ; Steele, John H. ; Ballerini, Tosca ; Gaichas, Sarah K. ; Ainley, David G.
    Similarly structured food web models of four coastal ecosystems (Northern California Current, Central Gulf of Alaska, Georges Bank, southwestern Antarctic Peninsula) were used to investigate competition among whales, fishes, pinnipeds, and humans. Two analysis strategies simulated the effects of historic baleen and odontocete whale abundances across all trophic levels: food web structure scenarios and time-dynamic scenarios. Direct competition between whales and commercial fisheries is small at current whale abundances; whales and fisheries each take similar proportions of annual pelagic fish production (4 - 7%). Scenarios show that as whale populations grow, indirect competition between whales and fish for zooplankton would more likely impact fishery production than would direct competition for fish between whales and commercial fisheries. Increased baleen whale abundance would have greater and broader indirect effects on upper trophic levels and fisheries than a similar increase in odontocete abundance. Time-dynamic scenarios, which allow for the evolution of compensatory mechanisms, showed more modest impacts than structural scenarios, which show the immediate impacts of altered energy pathways. Structural scenarios show that in terms of energy availability, there is potential for large increases in whale abundance without major changes to existing food web structures and without substantial reduction of fishery production. For each ecosystem, a five-fold increase in baleen whale abundance could be supported with minor disruptions to existing energy flow pathways. However, such an increase would remain below historical population levels for many cetaceans. A larger expansion (20X) could be accommodated only with large reductions in energy flow to competitor groups. The scope for odontocete expansion varies between ecosystems but can be restricted because they feed at higher, less productive trophic levels.
  • 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.
  • Technical Report
    Biological/physical modeling of upper ocean processes
    (Woods Hole Oceanographic Institution, 1994-09) Davis, Cabell S. ; Steele, John H.
    To enhance collaboration between researchers who model upper ocean biological/physical processes, a workshop was held at WHOI on June 7-12, 1993. The workshop was part of our on-going URIP project entitled "Modeling Biological-Physical Interactions: A Population Biological Approach" sponsored by ONR (Grant N000l4-92-J-1527). The two principal goals of the workshop were to: 1) identify critical problems related to mixed-layer biological-physical models, and 2) develop approaches for solving these problems. The workshop was organized into two parts to address these goals. The first part, held over the first day and a half, included three overview presentations given in plenary followed by working groups, organized along disciplinary lines, to identify critical issues. The second part of the workshop consisted of working groups, organized across disciplines, using "hands-on" modeling to address critical aspects of coupled biological-physical models. Several coupled models were presented and/or developed at the workshop addressing specific aspects of both the biological and physical dynamics. These aspects included the different mixed-layer formulations, a structured grazer population model, and an allometric food-web model including microbial-loop dynamics.
  • Preprint
    Are there eco-metrics for fisheries?
    ( 2005-11-03) Steele, John H.
    Ecosystem based management of marine resources is a worthy ideal. At present, however, the science is unable to measure and relate the fundamental concepts of diversity, productivity and resilience required for management decisions. Further, we do not have legal or fiscal measures that would allow us to allocate these resources to reserves, fishing quotas or fish farms. A proper appreciation of these shortcomings is needed.
  • Technical Report
    Report of the Fisheries Ecology Meeting, June 8-11, 1981
    (Woods Hole Oceanographic Institution, 1982-06) Rothschild, Brian ; Clark, Colin W. ; Sissenwine, Michael P. ; Steele, John H.
    An Ad Hoc Group of the Ocean Sciences Board of the Assembly of Mathematical and Physical Sciences, National Research Council, was formed in 1980 to study the constraints that impede advances in the understanding of fisheries ecology. In order to continue the discussions of the Ad Hoc Group and plan strategies or actions that might be taken to resolve the critical questions of fisheries ecology, the Woods Hole Oceanographic Institution and the National Oceanic and Atmospheric Administration sponsored a Fisheries Ecology Meeting at Woods Hole, June 8-11, 1981. The Woods Hole meeting addressed various topics related to a) fisheries ecology: the point of view of management, b) regional experience, c) fish and their environment, d) population dynamics, e) socioeconomics, f) the national environment for conducting fisheries ecology research, and g) actions that need to be undertaken.
  • Article
    Understanding patterns and processes in models of trophic cascades
    (John Wiley & Sons, 2013-12-16) Heath, Michael R. ; Speirs, Douglas C. ; Steele, John H.
    Climate fluctuations and human exploitation are causing global changes in nutrient enrichment of terrestrial and aquatic ecosystems and declining abundances of apex predators. The resulting trophic cascades have had profound effects on food webs, leading to significant economic and societal consequences. However, the strength of cascades–that is the extent to which a disturbance is diminished as it propagates through a food web–varies widely between ecosystems, and there is no formal theory as to why this should be so. Some food chain models reproduce cascade effects seen in nature, but to what extent is this dependent on their formulation? We show that inclusion of processes represented mathematically as density-dependent regulation of either consumer uptake or mortality rates is necessary for the generation of realistic ‘top-down’ cascades in simple food chain models. Realistically modelled ‘bottom-up’ cascades, caused by changing nutrient input, are also dependent on the inclusion of density dependence, but especially on mortality regulation as a caricature of, e.g. disease and parasite dynamics or intraguild predation. We show that our conclusions, based on simple food chains, transfer to a more complex marine food web model in which cascades are induced by varying river nutrient inputs or fish harvesting rates.