the importance of pelagic processes in determining habitat in the sea seascape meeting sandy hook...
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The Importance of Pelagic Processes in determining Habitat in the Sea
SeaScape MeetingSandy Hook
March 2, 2012Donald B. Olson
With major input from Jerry Ault, Ashley McCrea-Strub, Jing-Gang Luo, and William Harford
Regional Oceanography
Bathymetry & Currents Sea Surface Temperature1 June 2011
Bottom topography and SST
Retrograde fronts: Density surfaces are perpendicular to the bottom topography
Examples: Mid-Atlantic Bight
Prograde fronts: Density surfaces parallel to bottom topography.
Examples: Gulf Stream along U.S. coast or Kuroshio off China
See Mooers et al. 1978 or Olson 2001
Behavioral concentration in fronts under photo- or geo-taxis. (Olson and Backus, 1985, Olson, 2001, 2007)
Americas First and Foremost Fishery: Menhaden or Mossbunker• Early visitors to America came for cod; but the
early colonists were not fishermen per see.• Capt. John Smith noted on his first trip to
Virginia that a small fish formed massive shoals in the shallow bays.
• Squanto (Tisquantum) taught the Pilgrims to place these small fish in mounds of corn to act as fertilizer.
The Menhaden Industry
• Early Long Island and New England fishery involved groups of farmers covering their fields with fish.
• In 1850s this gave way to industrial trying and processing oil and meal separately.
• Meal becomes easily shipped fertilizer and later animal feed.
• Oil becomes prime replacement for whale oil following the fall of the whale fishery after the early 1860s.
Tracing large scale flows using salinity and oxygen isotopes. The water entering high latitudes is lighter, has less O18 and more O16, since the latter evaporates more easily.
Drowned river valleys: Also partially mixed estuaries except at high flow.
Shallow well mixed systems
Conditions in an estuary and the nature of drainage basins.
What factors determine the maximum flux, Qr, that a linear riverine plume can take?
What happens if this flux is exceeded?
Shortfin mako - Bluefish Interactions in the Western North Atlantic Ocean
• A large fraction (>80%) of mako diet consists of bluefish during part of the year;
• Food web model developed using Ecopath with Ecosim;
• Emphasis on indirect effects of fishing.
Shortfin mako Bluefish
Fishery FisheryIndirect Effects
William Harford
Multispecies Yield Surfaces
• Resource-driven control by bluefish was strongly evident;
• Mako fishery had little effect on bluefish (right), whereas bluefish fishery had notable effect on mako (left);
• Suggestive of competition for shared bluefish prey between mako & fisheries.
Model spatial grid resolution:5.5 km x 5.0 km in south5.5 km x 3.8 km in north< 3000 m; 136083 cells
Atlantic Coast Ecosystem Simulation Model
Factors affecting fish “spatial growth rate potential”
Wdt
dWcomponents of “essential habitat”.
max
)(
cos1),(~
)( max
maxt
b etaVX
max
)(
sin1),(~
)( max
maxt
b etaVY
AugustAge 0 Menhaden
AugustAge 4 Menhaden
n
(X,Y)
tX /
tY /
Bluefish
October 1
Transport and Movements of Predator & Prey
April 15
Spatial Ecosystem Models to Assess Multispecies Fisheries Risks from Exploitation and Environmental ChangesSpatial Ecosystem Models to Assess Multispecies Fisheries Risks from Exploitation and Environmental Changes
What are the effects of schooling affinities?
• Bakun’s Red fish/Blue fish hypothesis: Obligations to remain in schools shift fish populations towards different geographic locations based on metapopulation density within schools. Selection and genetics?
• The MacCall hypothesis: Fish make use of their ability to migrate as schools to exploit changes in mesoscale habitat linked to larger scale climate variations.
The process of predation:
• Predator/Prey encounters
• Handling times (satiation included)
• Explicit inclusion of schooling dynamics (Cosner et al., 1999)
Summary
• Fisheries habitat is at the highest level set by the physical factors: Climatological postions of front and circulations and their dynamics; seasonal progression of S, T,…
• Trophic interactions between species and the adaptation to each other and the environment.
• The use of habitat by fishermen is a crucial factor in terms of understanding fisheries.