Collie Jeremy S.

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Jeremy S.

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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.

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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.

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The colonial ascidian Didemnum sp. A: Current distribution, basic biology and potential threat to marine communities of the northeast and west coasts of North America

2006-10-09 , Bullard, Stephan G. , Lambert, Gretchen , Carman, Mary R. , Byrnes, J. , Whitlatch, R. B. , Ruiz, G. , Miller, R. J. , Harris, L. , Valentine, Page C. , Collie, Jeremy S. , Pederson, J. , McNaught, D. C. , Cohen, A. N. , Asch, Rebecca G. , Dijkstra, Jennifer A. , Heinonen, K.

Didemnum sp. A is a colonial ascidian with rapidly expanding populations on the east and west coasts of North America. The origin of Didemum sp. A is unknown. Populations were first observed on the northeast coast of the U.S. in the late 1980s and on the west coast during the 1990s. It is currently undergoing a massive population explosion and is now a dominant member of many subtidal communities on both coasts. To determine Didemnum sp. A’s current distribution, we conducted surveys from Maine to Virginia on the east coast and from British Columbia to southern California on the west coast of the U.S. between 1998 and 2005. In nearshore locations Didemnum sp. A currently ranges from Eastport, Maine to Shinnecock Bay, New York on the east coast. On the west coast it has been recorded from Humboldt Bay to Port San Luis in California, several sites in Puget Sound, Washington, including a heavily fouled mussel culture facility, and several sites in southwestern British Columbia on and adjacent to oyster and mussel farms. The species also occurs at deeper subtidal sites (up to 81 m) off New England, including Georges, Stellwagen and Tillies Banks. On Georges Bank numerous sites within a 147 km2 area are 50-90% covered by Didemnum sp. A; large colonies cement the pebble gravel into nearly solid mats that may smother infaunal organisms. These observations suggest that Didemnum sp. A has the potential to alter marine communities and affect economically important activities such as fishing and aquaculture.

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Feeding habits of the yellowtail flounder and production of its invertebrate prey on Georges Bank

1985-09 , Collie, Jeremy S.

As part of the Georges Bank Benthic Infauna Monitoring Program, size-frequency analysis was used to study the life history and production of three benthic amphipod species: Ampelisca agassizi, Unciola inermis and Ericthonius fasciatus. Abundant over large areas of Georges Bank, these amphipods are important prey of yellowtail flounder. From benthic grab samples collected quarterly during 1981 to 1983, over 200 individuals of each species were measured for each sampling date. The computer program NORMSEP separated the length-frequency distributions into cohorts. Growth and mortality rates were determined by following cohorts through time; production was calculated as the sum of growth increments. Differences in the population dynamics of the three species were exemplified by annual production-to-biomass ratios (P/B). E. fasciatus had the highest P/B (2.8 to 4.1), followed by U. inermis (1.3 to 2.7) and A. agassizi (1.3 to 1.4). These results, the first direct production estimates for benthic macrofaunal species on Georges Bank, are compared to production estimates for other marine amphipod species. Amphipod production rates on Georges Bank are as high as production rates of related near-shore species with similar life-spans. The Northeast Fisheries Center sampled yellowtail flounder stomachs at three sites on four quarterly dates from August 1982 to May 1983. As closely as possible, stomach sampling coincided with the dates and locations of benthic monitoring to enable direct comparison between ingested and available food. Stomach contents were sorted and weighed and important prey species were measured. Yellowtail flounder feed mainly on benthic macrofauna; amphipods and polychaetes are the most important prey groups. Although the diet composition varied among stations and dates, in each case a few prey species constituted the bulk of the diet. Selection indices were calculated to compare the species composition of the stomach contents to that of the benthic macrofauna. Food selection by yellowtail flounder is explained on the basis of prey life history and prey size. The species- and size-selection indices account for most of the variability in diet composition. A log-normal curve was fit, by least squares, to the size-selection indices; according to this fit, the optimum prey weight for yellowtail flounder is 21 mg. The rate of food consumption by yellowtail flounder was calculated by two methods. The bioenergetic method sums the food required to satisfy the energetic requirements of the fish. The second method is based on the weight of stomach contents and the rate of food evacuation from the stomach. The bioenergetic method gave consistently higher results (1.4 to 1.6 kg fish-l yr-1) than the stomach-content method (0.5 to 0.8 kg fish-l yr-1). Yellowtail flounder abundance was estimated by a method that uses the commercial catch data to standardize the survey, relative-abundance index. These abundance estimates were divided by the appropriate areas to obtain yellowtail flounder density estimates for fall 1982 of 20.0 and 41.3 fish per hectare for Georges Bank and Southern New England, respectively. Consumption rates per fish were multiplied by flounder density to obtain estimates of consumption per unit area, which range from 1.2 to 6.3 gww m-2 yr-l. Annual production of six important prey species was calculated. Yellowtail flounder consumption as a percentage of prey production was 6 to 12%, 2 to 5%, and 1 to 3%, for the amphipods Unciola inermis, Ericthonius fasciatus and Ampelisca agassizi, respectively; 11 to 34% and 7 to 21% for the polychaetes Chone infundibuliformis and Nephtys incisa, respectively; and less than 1% for the sand dollar, Echinarachnius parma.

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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.