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Integration and Synthesis of Georges Bank Broad-scale Survey Results, A Brief Overview. The principal objective of this project is to utilize the very comprehensive U.S GLOBEC broad-scale data sets that now exist to address two overarching questions:
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Georges Bank Broad-Scale Survey Results.
Principal Investigators and Their Institutions
Northeast Fisheries Science Center:
D. G. Mountain
J. R. Green
San Francisco State University:
University of Maine:
University of New Hampshire:
University of Rhode Island:
R. G. Campbell
Woods Hole Oceanographic Institution:
C. J. Ashjian
D. J. McGillicuddy
GLOBEC-01: Integration and synthesis of the Georges Bank Broad-Scale Survey Results.
Questions Guiding Research
What are the broad-scale distributions of the target species and their predators and prey in relation to physical variables, and how do these change from winter to summer conditions and year to year?
How are the broad-scale distributions of measurement/indices for growth, fertility, respiration, and starvation in the target species related to the distributions of food supply and environmental conditions?
How are predator populations spatially and temporally distributed with respect to their prey (target species) and environmental conditions?
How does the birth date and/or life stage frequency distribution of surviving individuals change during the drift around the Bank?
Is cohort mortality chronic or dominated by episodic events?
Is the probability of survivorship associated with individuals originating from discrete stocks?
Integration and Synthesis of Georges Bank Broad-scaleSurvey Results.
The grid spacing is 0.05 degrees in latitude and longitude. Also provided is the area represented by point. There are 2355 points in the grid.
Systematically map data to foster analyses, and
Produce a comprehensive atlas of physical, chemical, and biological fields
surveyed during the Program
Carbon (for 1999 only),
Currents1 (ADCP, Drogues),
Backscattering (BioS and
Satellite data (AVHRR, SeaWifs, Winds),
Species counts (e.g.
Calanus finmarchicus - by stage,
Pseudocalanus spp - by stage,
other inverts, cod, haddock),
predators (Invert, Vert [NMFS-COP]),
Derived rates such as productivity
Broad-scale egg samples for both cod and haddock have been processed to consider possible maternal influence on egg viability, assuming increased egg size may reflect better condition and overall viability.
There was no indication that interannual variation in egg
mortality rates was related to variation in egg size.
The eggs were also staged and seasonal egg mortality rates for both species were calculated for each year of sampling.
The mortality rates varied by a factor of two over the duration
of the program.
Comparisons with time series of the local wind stress suggest:
Variability in egg mortality was caused by variations in
wind-driven off-bank transport during the periods of peak
A particle tracking model, using the observed winds and the observed egg distributions, indicates:
A seasonal loss of eggs consistent with the calculated egg
mortality rates. Both the interannual variability in the winds
and in the egg distributions appear important in determining
the interannual variability in the egg mortality rates.
A 1 m2 MOCNESS (0.15 mm mesh) and a zooplankton pump (0.05 mm or 0.035 mm mesh) were used during the broad-scale surveys.
A comparison indicates that C1 and C2 of Calanus and all
C1-C5 of Pseudocalanus were under sampled by the
MOCNESS relative to the pump an average of 37%.
Overestimation of the volume filteredrelative to the
actual volume filtered is the likely cause.
Reproductive rates and mortality rates of target zooplankton species:
The reproductive rates of C. finmarchicus at broad-scale
stations have been calculated for all broad-scale cruises.
A modification of the procedure for estimating C. finmarchicus egg production rates from the preserved broad-scale samples has been developed that explicitly accounts for food limitation effects on clutch size.
Broad-scale patterns in the distribution of key species
produced by Ted Durbin
Calanus finmarchicus total copepodids. Monthly mean abundance (1995-1999), [log10(No m-2+1)].
Broad-scale biovolume and bioacoustic backscattering data are being compared to examine seasonal and the year to year variations.
The kriging technique and a newly developed wavelet/fractal
interpolation scheme is being applied to the acoustic and biovolume
data sets to obtain 3D volume renditions.
Work is being completed on data collected on cruises in the fall 1997, 1998, and 1999 to survey diapausing populations of Calanus finmarchicus and their predators in the Gulf of Maine using MOCNESS and BIOMAPER-II. Following the precipitous drop in the NAO index that occurred in
1996, colder and fresher water of Labrador Sea origin entered the
Gulf of Maine in 1998 after a lag of about two years.Coincidently,
the autumn diapausing C. finmarchicus abundance was much lower
in 1998 than in 1997 or 1999.
Despite the substantially lower Calanus abundance in 1998, overall zooplankton biomass levels as revealed by net catches and acoustic indices were comparable between the three years.
Potential competitors (other copepods, the pteropod Limacina
retroversa), and predators (euphausiids, decapods, medusae, and
siphonophores) had enhanced biomass and/or numbers, which may
explain the reduced Calanus in 1998.