Trends in Observed
Mean Weight and Length of
Several Groundfish Stocks
GARM Maturity and Weight Working Group
Loretta O’Brien
National Marine Fisheries Service
Northeast Fisheries Science Center
Woods Hole, Ma.
Potential Mechanisms Influencing Growth
Maternal and Paternal Effects
Stock Density
Environment
Food Habits (prey abundance)
Selective mortality
1
Outline of Presentation :
Length – Weight Relationship
Trends in Length, Weight, Abundance
Possible Mechanisms for Trends
----------------------------------------------------Georges Bank:
Gulf of Maine:
Haddock
Cod
Cod
American plaice
Georges Bank Haddock
NEFSC Autumn Research Bottom Trawl Survey
1963 – 2005
2
G eorges Bank H addock
Autum n 1997
6
P redicted
O bserved
5
Weight increases with Length
Generally described by the equation
W=a*Lb
Weight (kg)
4
3
2
1
0
0
10
20
30
40
50
60
70
80
90
Length (cm )
6
Georges Bank Haddock
Predicted Length-Weight Curves
Fall 1992-2006
Weight (kg)
5
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
4
3
2
1
Relationship varies year to year,
Depending on environment
and available food
Greatest difference in wt.
at length is at larger sizes
0
0
10
20
30
40
50
60
70
80
90
Length (cm)
3
7
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
6
Weight (kg)
5
4
3
Georges Bank Haddock FALL
Shifts in weight at length
from 1992-1999 to 2000-2005
1973
2
Mean length of age 5 fish varies from 47-68 cm
2002
1
0
50
55
60
65
70
75
80
Length (cm)
80
Changes in the average length age 5 haddock
GB Haddock
Autumn
length age 5
Length (cm)
70
60
50
40
1960
1970
1980
1990
2000
2010
Year
4
80
Changes in the average
GB Haddock
weight and length of
Autumn
age 5 haddock, Georges Bank, 1963-2005.
4.0
length age 5
weight age 5
3.5
70
60
2.5
Weight (kg)
Length (cm)
3.0
2.0
50
1.5
W= a (mean L age 5) b
40
1960
1970
1980
1990
2000
1.0
2010
Year
Mean Length at ages 0 - 6
80
70
age 0
age 1
age 2
age 3
age 4
age 5
age 6
Georges Bank Haddock
Autumn
Length (cm)
60
50
40
30
20
10
0
1960
1970
1980
Year
1990
2000
2010
5
Haddock Autumn Length at Age
3
Remove the scale to compare across all ages
Age 1
Age 2
Age 3
Age 4
Age 5
Age 6
Age 7
2
Z-score
1
0
-1
-2
-3
1960
1970
1980
1990
2000
2010
Year
Haddock Autumn Weight at Age
4
Age 1
Age 2
Age 3
Age 4
Age 5
Age 6
Age 7
Z-score
2
0
-2
-4
1960
1970
1980
1990
2000
2010
Year
6
The Consumers Report Approach
ƒ Analogous to consumer product evaluations
ƒ Consider one or more attributes: average
weight, length, numbers caught
ƒ Bin data into quintiles based on rank value:
0-20, 2020-40, 4040-60, 6060-80, 8080-100%ile
ƒ Solid black= highest value, solid red = lowest
ƒ Look for patterns across ages and years
Length
Georges Bank
Row = age
Haddock
Column = year Fall
1963-2005
Number
7
Length
GB
Haddock
Autumn
1963-91
Weight
Number
Georges Bank
Haddock
Autumn
Length
1992-2005
Weight
Number
8
Haddock Summary
Fish slightly heavier at length
during 1990’s vs. 2000’s
Declining trend in length and weight
since 1990s
Length and weight lower
when abundance higher & vice versa
Georges Bank Cod
NEFSC Autumn Research Bottom Trawl Survey
1963 – 2005
9
Georges Bank Cod Autumn Length at Age
3
Age
Age
Age
Age
Age
Age
Age
Age
Age
2
Z-score
1
0
0
1
2
3
4
5
6
7
8
-1
-2
-3
1970
1975
1980
1985
1990
1995
2000
2005
Year
Georges Bank Cod Autumn Weight at Age
4
Age 0
Age 1
Age 2
Age 3
Age 4
Age 5
Age 6
Age 7
Age 8
3
Z-score
2
1
0
-1
-2
-3
1970
1975
1980
1985
1990
1995
2000
2005
Year
10
Length
Georges Bank
Cod
Autumn
1970-2006
Number
Georges Bank
Cod
Autumn
1992-2005
Length
Weight
Number
11
GB Cod Summary
Trend in length and weight
since mid-1980s
Mean length and weight highest during
1980’s
Since 1992, weak relationship of length
and weight to abundance
Gulf of Maine Cod
NEFSC Autumn Research Bottom Trawl Survey
1963 – 2005
12
Gulf of Maine Cod Autumn Length at Age
3
Age 0
Age 1
Age 2
Age 3
Age 4
Age 5
Age 6
Age 7
2
Z-Score
1
0
-1
-2
-3
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
Year
Gulf of Maine Cod Autumn Weight at Age
3
Age 0
Age 1
Age 2
Age 3
Age 4
Age 5
Age 6
Age 7
2
Z-Score
1
0
-1
-2
-3
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
Year
13
Length
Gulf of Maine Cod Fall 1970-2005
Number
Cod
Gulf of Maine
Autumn
1992-2005
Length
Weight
Number
14
GM Cod Summary
No overall long term trends
Cyclical trend (~ ~ decadal )
Gulf of Maine American Plaice
NEFSC Autumn Research Bottom Trawl Survey
1980 – 2004
15
American Plaice Autumn 1997
3.5
female
male
Weight (kg)
3.0
2.5 Females grow faster than males
2.0
1.5
1.0
0.5
0.0
10
20
30 40
Length (cm)
60
American plaice - Autumn
Age 5
42
38
70
0.7
female (length)
female (weight)
male (length)
male (weight)
40
Mean Length (cm)
50
0.6
0.5
36
0.4
34
0.3
Mean Weight (kg)
0
32
0.2
30
Average 11% difference
28
1990
1992
1994
1996
1998
2000
2002
2004
0.1
2006
Year
16
Gulf of Maine American Plaice Male Autumn Length at Age
3
Age 1
Age 2
Age 3
Age 4
Age 5
Age 6
Age 7
2
Z-Score
1
0
-1
-2
-3
1990
1992
1994
1996
1998
2000
2002
2004
2006
Year
Gulf of Maine American Plaice Male Autumn Weight at Age
3
Age 1
Age 2
Age 3
Age 4
Age 5
Age 6
Age 7
2
Z-Score
1
0
-1
-2
1990
1992
1994
1996
1998
2000
2002
2004
2006
Year
17
Gulf of Maine American Plaice Female Autumn Length at Age
3
Age 1
Age 2
Age 3
Age 4
Age 5
Age 6
Age 7
Age 8
Age 9
Age 10
2
Z-Score
1
0
-1
-2
-3
1990
1992
1994
1996
1998
2000
2002
2004
2006
Year
Gulf of Maine American Plaice Female Autumn Weight at Age
3
Age 1
Age 2
Age 3
Age 4
Age 5
Age 6
Age 7
Age 8
Age 9
Age 10
2
Z-Score
1
0
-1
-2
-3
1990
1992
1994
1996
1998
2000
2002
2004
2006
Year
18
Length
American Plaice
Gulf of Maine
Autumn
Males 1992-2004
Weight
Number
Length
American Plaice
Gulf of Maine
Autumn
Females 1992-2004
Weight
Number
19
Percent of Male GM American plaice by Age
NEFSC Autumn Surveys, 1992-2004
Percent Males
GM Am. Plaice
Autumn
1992-2004
1.0
0.6
age 1
age 5
0.5
0.8
0.4
0.6
0.3
0.4
0.2
0.2
0.1
0.0
1.0
0.0
0.6
Percent Male American plaice
age 2
0.5
0.8
age 6
0.4
0.6
0.3
0.4
0.2
0.2
0.1
0.0
0.6
0.0
0.7
0.6
age 3
0.5
0.5
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
0.7
0.6
age 7
0.4
0.0
0.6
age 4
age 8
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
1992 1994 1996 1998 2000 2002 2004 2006
0.0
1992 1994 1996 1998 2000 2002 2004 2006
Year
Year
Length
Combined Sexes
American Plaice
Gulf of Maine
Autumn
1992-2004
Weight
Number
20
Length
GM American Plaice
Fall Combined Sex
Ages 1-10 1980-2004
Number
GM American Plaice Summary
Overall declining trend both sexes
Possible density dependence
in females not males
Younger ages dominated by males;
Older ages all females
21
Preliminary Summary of Visual analysis
Potential Mechanisms Influencing Growth
Maternal and Paternal Effects
Density dependent growth
Environmental effect
Food Habits (prey abundance)
Selective mortality
Effect on Yield
Slower growth:
Total M greater prior to fishery/spwn
Lower productivity
Lower SSB if maturity also delayed
Delayed / reduced yield to fishery
22
Future Work
Evaluate plausibility of alternative
hypotheses ; statistical analysis
Consider oceanographic & biological effects
*temperature* salinity*depth*distribution
*habitat*food habits*predator*prey
Broadscale patterns:
GM vs. GB vs. SNE
flatfish vs. roundfish
groundfish vs. pelagics
23