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:

What controls inter-annual variability in the abundance of the target species (cod and haddock larvae, Calanus finmarchicus, and Pseudocalanus spp) on Georges Bank (e.g., bottom up or top down biological processes, or physical advective processes)?

How are these processes likely to be influenced by climate variability?

Integration and Synthesis of Georges Bank

Broad-scale Survey Results,A Brief Overview

Began with 38 Stations in 1995

Added station 39 in 1996

Added stations 40 in 1997

Added station 41 in 1998

GLOBEC-01: Integration and synthesis of the

Georges Bank Broad-Scale Survey Results.

Northeast Fisheries Science Center: D. G. MountainJ. R. GreenP.L. Berrien

San Francisco State University: S.M. Bollens

University of Maine: D.W. Townsend

University of New Hampshire: A. BucklinJ. Runge

University of Rhode Island: E.G. DurbinR. G. CampbellB.K. Sullivan

Woods Hole Oceanographic Institution: P.H. WiebeC. J. AshjianL.P. MadinD. J. McGillicuddyJ. Quinlan

U. S. GLOBEC

NW

ATLANTIC/GEORGES BANK STU

DY

Principal Investigators and Their Institutions

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 project involves work in two coordinated efforts.

1) Data Completion and Data Management.

2) Data analysis, Integration, and Interpretation

A. Hydrographic-biological Relationships

B. Integration of Rate Processes and Broad-Scale-Distribution Data Sets

C. Building Climatology using Objective Mapping or Kriging

D. Modeling

Georges Bank Broad-Scale Standard Grid.

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.


Standard grids used to: Systematically map data to foster analyses, and

Produce a comprehensive atlas of physical, chemical, and biological fields surveyed during the Program

Bathymetry, Temperature, Salinity, Density, Chlorophyll, Fluorescence, Nutrients, Carbon (for 1999 only), Currents1 (ADCP, Drogues), Backscattering (BioS and HTI, ADCP)

Satellite data (AVHRR, SeaWifs, Winds), Meteorological data, Zooplankton biomass, 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 and mortality.

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 egg abundance.

A particle tracking model, using the observed winds and the observed egg distributions, indicates:

A seasonal loss of eggs consistent with the calculated eggmortality rates. Both the interannual variability in the windsand 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 allC1-C5 of Pseudocalanus were under sampled by theMOCNESS relative to the pump an average of 37%. Overestimation of the volume filtered relative 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-scalestations 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

January February March

April May June

Calanus finmarchicus total copepodids. Monthly mean abundance (1995-1999), [log10(No m-2+1)].

• Absence from the bank in January, but higher numbers in the Gulf of Maine (mostly Go C5). • Advection of animals onto the NE Peak and along the Southern Flank in February. • A build-up of the population in April and May and a decline on the bank in June.• A persistent region of low abundance in the shallow, tidally mixed crest of the bank.

Integration and synthesis of the nutrients and chlorophyll data. Effort involves re-plotting and re-contouring the data sets on phytoplankton chlorophyll and nutrient distributions on Georges Bank. Budgets are now being constructed, which include some of the organic nitrogen and carbon measures.

The 10-m2 MOCNESS data on the distribution and abundances of the major macrozooplankton and micronekton predators is being used:

1) To examine the relationships between these biota and various environmental conditions, especially hydrography and Slope Water intrusions.

2) To study the overall community structure within the Georges Bank macrozooplankton and micronekton using multivariate analyses.

3) To integrate the distribution and abundance data with various rate process data derived from GLOBEC process cruises and the literature to generate broad-scale distributions of specific predation mortality rates for each target (prey) taxon.


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/fractalinterpolation scheme is being applied to the acoustic and

biovolumedata 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, andsiphonophores) had enhanced biomass and/or numbers, which

mayexplain the reduced Calanus in 1998.


Chronology

integration and synthesis of georges bank broad-scale survey results, a brief overview

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