Mix of species KEPT on 1512 observed Trawl
trips, consisting of 20,420 tows, 2005
Trawl Kept (all meshes)
Am Plaice
Bluefish
yellowtail flounder
witch flounder
Black Sea Bass
cod
Butterfish
dogfish
fluke
winter flounder
windowpane
haddock
white hake
tilefish
halibut
skate
herring
silver hake
scup
scallop
red hake
redfish
Illex
Loligo
Pollock
Red crab
monkfish mackerel
Ocean Pout
Individual trips
are less
variable than
the aggregate
shown here.
However this
graph
illustrates the
wide variety of
species
routinely landed
in the New
England Region.
Proportions are
based on
weight.
Mix of species DISCARDED on 1512 observed
Trawl trips, consisting of 20,420 tows, 2005
Discards, Trawl Total
Am Plaice Butterfish
yellowtail flounder
witch flounder
windowpane
winter flounder
white hake
tilefish
Black Sea Bass
Bluefish
cod
dogfish haddock
mackerel
fluke
Loligo
halibut
herring
monkfish
Illex
Ocean Pout
Red crab
Pollock
redfish
red hake
scallop
scup
silver hake
skate
Discards are
driven by
market value,
permits (not all
fishermen can
land all
species), trip
limits (max wt
per trip) and
minimum size
limits.
Comparison of observed kept and discards
for 2005 from the total Trawl fishery
Trawl Kept (all meshes)
Discards, Trawl Total
Am Plaice
witch flounder
windowpane
winter flounder
Bluefish
yellowtail flounder
witch flounder
Am Plaice Butterfish
yellowtail flounder
white hake
Black Sea Bass
cod
Butterfish
dogfish
fluke
tilefish
Black Sea Bass
Bluefish
cod
dogfish haddock
mackerel
fluke
Loligo
halibut
herring
monkfish
Illex
Ocean Pout
Red crab
Pollock
redfish
red hake
scallop
winter flounder
scup
windowpane
silver hake
haddock
white hake
tilefish
halibut
skate
herring
silver hake
scup
scallop
red hake
redfish
Illex
Loligo
Pollock
Red crab
monkfish mackerel
Ocean Pout
skate
Is the environment changing or are we seeing
the long term genetic effects of fishing?
Calm conditions prevail during typical sea day
Witch flounder mean weights at age in the catch
0.8
Mean weight (kg) at age
0.7
0.6
Age 8
0.5
Age 7
0.4
Age 6
0.3
Age 5
Age 4
0.2
0.1
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008
Year
Changes in Average Weight at Age
• Reductions in average weight at age are evident for a number of
stocks
– Georges Bank Cod and Haddock
– Gulf of Maine Winter flounder, Plaice, and Witch flounder
• Appear for stocks at both high and low abundance levels
• Causal mechanisms unknown but could include
–
–
–
–
Environmental change
Density dependence
Earlier maturation/genetic selection
All of the above and more
• Implications if patterns persist
– Lower yields
– Slower rebuilding
– Possible changes in rebuilding targets when re-evaluated in
2008
Total Closed Area:
20,187 km2
CA-I = 3,960
CA-II = 6,927
NLS = 6,275
WGOM = 3,025
1996
Does space matter?
WGOM
Canada
CA-I
New England
Closed Areas
CA-II
NLS
USA
1994:
CA-I
CA-II
NLS
“Rolling Closures”
June
In addition to
Year-round
closures
May
April
OctNov.
March
May
“A committee has been called a
cul-de-sac into which ideas are
lured to be quietly strangled.”
George Will
4000+
Observed
Trawl Tows
20012002
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0 lbs.
0.1-500 lbs.
501-1000 lbs
1001-3000 lbs.
3001-7500 lbs
Haddock
kg/haul
How Much Catch & Effort is Proximate to CA-I?
Cumulative Distribution Function
1.0
0.8
0.6
Haddock Catch
Total Hours Towed
All Species Catch
0.4
0.2
0.0
0
20
40
60
80
100 120 140 160 180 200
Distance to Closed Area I
Jensen’s Inequality
• Function of the mean is less than or equal to the mean of the
function
• Relevance—fishermen focus on highest concentrations of
fish that can be found, subject to cost constraints and
regulations
• Gradients
– Space –closure areas
– Target of age classes
– School effects
• Mixture of populations
– Open area with refuge
– Closed area with leakage
– Try to describe with an average population
Jensen’s Inequality: Application to a spatial fishery
G ( x )   G ( x) pdf ( x) dx
where
x   x pdf ( x) dx
Suppose x is the average relative density at some location y and G(x) is
the amount of fishing effort expended to catch x at location y. Total
landings are proportional to the product of fishing effort and local
concentration so that the total yield is
Landings1    x G ( x) pdf ( x) dx
Where α is a proportionality constant that scales the relative
density x to true population size.
Jensen’s Inequality: Application to a spatial fishery
If we incorrectly assume that landings have been extracted
from a population whose relative size is defined by xbar,
Landings2   ' x G( x )
Since landings and relative density are an observed quantities,
then Landings1=Landings2. This means that α’>α to compensate
for the fact that
G ( x )   G ( x) pdf ( x) dx
Therefore a non-spatial treatment of average density COULD lead
to an overestimate of the population size.
A Scallop Example
• The reopening of Closed Area
II in 1999
• Had been closed for since
December 1994
• Vessel Monitoring Systems for
entire fleet
• High observer coverage
• Scallop fishery subjected to
– Individual trip limits (10 k lb)
– Overall yellowtail flounder
bycatch cap
-74
-68
-66
42.5
41.2
41.2
39.9
39.9
MAY 1999
38.6
38.6
May 1999
37.3
36.0
-76
37.3
-74
-72
-70
Longitude
-68
36.0
-66
Latitude
Latitude
-76
42.5
Longitude
-72
-70
-74
-68
-66
42.5
41.2
41.2
39.9
39.9
JUN 1999
38.6
38.6
Jun 1999
37.3
36.0
-76
37.3
-74
-72
-70
Longitude
-68
36.0
-66
Latitude
Latitude
-76
42.5
Longitude
-72
-70
Area II Reporting Locations: Weeks 25-26
41.5
> 2500 lb/day
1850-2500 lb/day
1500-1850 lb/day
1100-1500 lb/day
< 1100 lb/day
41.4
41.3
41.2
41.1
41.0
-67.50
-67.25
-67.00 -66.75
Longitude (deg)
-66.50
-66.25
-74
-68
-66
42.5
41.2
41.2
39.9
39.9
JUL 1999
38.6
38.6
Jul 1999
37.3
36.0
-76
37.3
-74
-72
-70
Longitude
-68
36.0
-66
atitude
Latitude
-76
42.5
Longitude
-72
-70
Area II Reporting Locations: Weeks 31-32
41.5
> 2500 lb/day
1850-2500 lb/day
1500-1850 lb/day
1100-1500 lb/day
< 1100 lb/day
41.4
41.3
41.2
41.1
41.0
-67.50
-67.25
-67.00 -66.75
Longitude (deg)
-66.50
-66.25