Production of Fish and Benthos on Georges Bank

• Estimates of benthic biomass and production• Preliminary estimates of energy flow• Dynamic fish population models

Jeremy Collie, Allison DeLong, and Richard Bell

Graduate School of Oceanography

University of Rhode Island

Benthivorous Fish

Pelagic Invertebrate

Predators

Micro-Phytoplankton

(>20m)

Seabirds

Deposit-feedingBenthos

Suspension- feeding Benthos

Detritus Ammonia

Fishing

R

Micro-Zooplankton(2-200m)

Meso-Zooplankton

(>200m)

Nitrate

Nano-Phytoplankton

(<20m)

PlanktivorousFish

Piscivorous Fish

Pre-recruits Pre-recruits Pre-recruits

MarineMammals

spawning

recruitment

Time period Location Biomass P:B Production

1960s Entire Bank

Suspension 19 0.9 16

Deposit 64 1.5 86

Total 83 1.2 102

1977Southern Flank

Suspension 54 1.0 54

Deposit 20 1.7 39

Total 74 1.3 93

1983Southern Flank

Suspension 30 1.0 30

Deposit 31 2.0 56

Total 61 1.4 86

1990sNorthern Edge

Suspension 113 0.5 45

Deposit 89 0.7 60

Total 202 0.5 105

Benthic macrofaunal biomass (kcal m-2) and production (kcal m-2 yr-1) on Georges Bank

Benthic Production on Georges Bank

DEPOSIT

SUSPENSION

unfished

fished

closed

open

0

50

100

150

200

250

300

1994 1997 1998 1999

kcal

m-2

yr-1

Suspension feeders

Deposit feeders

0

50

100

150

200

250

300

1994 1997 1998 1999

kcal

m-2

yr-1

Benthic production on the northern edge of Georges Bank is significantly lower in fished areas compared with unfished areas at the same depth

Fished area, depth 79 m

Unfished area, depth 84 m

From Hermsen et al. 2003, MEPS 260:97-108

0

50

100

150

200

250

1994 1995 1996 1997 1998 1999 2000

kcal

m-2

yr-1

Suspension feeders

Deposit feeders

0

50

100

150

200

250

1994 1995 1996 1997 1998 1999 2000

kca

l m

-2 y

r-1

Suspension feeders

Deposit feeders

Benthic production has increased in the northern part of Closed Area II relative to an area just outside the closed area that remains open to fishing

Inside closed area, depth 48 m

Outside closed area, depth 47 m

From Hermsen et al. 2003, MEPS 260:97-108

Area closed

P: Production (Kcal m-2 yr-1)

available for next consumer

Functional Guild NameB: Biomass (Kcal m-2)

C: Consumption (Kcal m-2 yr-1)

Key to Preliminary Energy Budget

MarineMammals

C: 7.8

P: 2.2Benthivores

B: 4.4, C: 17.8

Pelagic Invertebrate

Predators

P: 1197Micro-

Phytoplankton

SeabirdsC: 0.1

P: 55.5 DepositFeeders B: 31

P: 30 Suspension- Feeders B: 30

P: 1034Detritus

P: 3374Ammonia

FishingC: 2

R

P: 285Micro-

Zooplankton

P: 202Meso-

Zooplankton

P: 741Nitrate

P: 2793Nano-

Phytoplankton

P: 5.7Planktivores

B: 10.9, C: 54

P: 4.9Piscivores

B:8.3, C: 39

P: 5.4 RecruitsB: 0.4, C: 15.9

spawning

recruitment

P: 10 RecruitsB: 0.8, C: 30.1

P: 13 RecruitsB: 1.1, C: 39.5

Dynamic models of the upper trophic levels

Fishing

Benthivorous Fish

Piscivorous Fish

Planktivorous Fish

Pre-recruits

Pre-recruits

Pre-recruits

BenthosZooplankto

n

rB

rb

rh

rP

rp

FB FH FP

cP

cpcbdb dpgb gp

predationspawningrecruitment

bottom-up forcing

Top-down control

)()()()()(1)(

)()()()()(1)(

tptHctPgtpdKtprtp

dtdp

tPFtPtHctpdKtPrtP

dtdP

Ppp

p

PPpP

P

Equations for fish model - Planktivore

P (t ) = Planktivore post-recruitp (t ) = Planktivore recruitH (t ) = Piscivore post-recruit

r = intrinsic growth K = carrying capacityd = recruit to post-recruitg = recruitment to recruitsF = harvest ratec = predation rate

Bottom-up forcing

Top-down forcing

Deterministic Simulation

0 10 20 30 40

0100

200300

400

BenthivoresPiscivoresPlanktivores

Year

Bio

mass

(K

T)

1960’s biomass

1990’sbiomass

Planktivore Bottom-up ForcingSimulate autocorrelated growth rates

0 20 40 60 80 100

0100

300

500

BenthivoresPiscivoresPlanktivores

Year

Bio

mass

(K

T)

Bio

mass (

KT)

Historic harvest patterns1960sHigh: Planktivore & PiscivoreLow: Benthivore

0 20 40 60 80 100

0100

300500

BenthivoresPiscivoresPlanktivores

Year

1970sHigh: BenthivoreLower: Planktivore & Piscivore

1980-90Lower: Planktivore

On-going work

• Refine estimates of benthic production• Balance the entire energy budget• Account for energy imports and exports• Statistical parameter estimation of

multispecies biomass-dynamics models