wf4133 fisheries science - github pages · 4/1 group 3 group 4. lab today @ 1pm • bring – rain...
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WF4133‐Fisheries Science
Module 3: Harvesting biomassClass 15
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Housekeeping
• Now is the time to be looking for summer jobs!– State websites– USA jobs– Fisheries.org– Texas A&M
• Half way there
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Lab today @ 1pm3/18Group 1Group 2
4/1Group 3Group 4
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Lab today @ 1pm
• Bring– Rain gear– Sun screen– Bug repellent– Waders/boots
![Page 6: WF4133 Fisheries Science - GitHub Pages · 4/1 Group 3 Group 4. Lab today @ 1pm • Bring – Rain gear – Sun screen – Bug repellent – Waders/boots. BIOLOGICAL OVERFISHING Reduced](https://reader033.vdocuments.us/reader033/viewer/2022060901/609e8313ba87b65e0b3cc5c5/html5/thumbnails/6.jpg)
BIOLOGICAL OVERFISHING
Reduced yield with increasing fishing mortalityA combination of growth and recruit overfishing
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Biological overfishing
0.0 0.2 0.4 0.6 0.8 1.0
0
50
100
150
Fishing mortality
Yie
ld
Biological overfishing
Combination of growth & recruit overfishing
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GROWTH OVERFISHING
Occurs when fish are harvested at an average size that is smaller than the size that would produce the maximum yield per recruit
![Page 9: WF4133 Fisheries Science - GitHub Pages · 4/1 Group 3 Group 4. Lab today @ 1pm • Bring – Rain gear – Sun screen – Bug repellent – Waders/boots. BIOLOGICAL OVERFISHING Reduced](https://reader033.vdocuments.us/reader033/viewer/2022060901/609e8313ba87b65e0b3cc5c5/html5/thumbnails/9.jpg)
Growth overfishing
Harvest fish before they have time to growGrowth is a function of age, therefore we need to account for age structure
Example:
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Growth process in fish
The assimilation of food as biomass (i.e., tissue). Primarily refers to somatic tissue but also includes gonad tissue.
• Fish adding weight over time1. Relate time (age) to length2. Relate length to weight
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0 5 10 15 20 25 30
0.0
0.1
0.2
0.3
0.4
Total length (cm)
Wei
ght (
kg)
Length‐weight
3.020.0141 LengthWeight
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Weight for an age‐3 fish
0 1 2 3 4 5 6 7
5
10
15
20
25
30
Age
Tota
l len
gth
(cm
)
23.9 cm3.02
3.02
0.01410.014 4
821
20
WeightWeightWeig
Lengt
t
h
h
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Weight for an age‐6 fish
0 1 2 3 4 5 6 7
5
10
15
20
25
30
Age
Tota
l len
gth
(cm
)
3.02
3.02
0.01410.014 9
721
36
WeightWeightWeig
Lengt
t
h
h
28.6 cm
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Age‐weight
0 1 2 3 4 5 6 7
0.0
0.1
0.2
0.3
Age
Wei
ght l
engt
h (k
g)
23.9 cm
28.6 cm
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Age & timeYears
Age‐7
Age‐6
Age‐4
Age‐5
Age‐1
Age‐2
Age‐3 Age‐3
Age‐7
Age‐6
Age‐5
Age‐2
Age‐4
Age‐1
Age‐6
Age‐5
Age‐4
Age‐3
Age‐1
Age‐2
Age‐7
Age‐5
Age‐4
Age‐3
Age‐1
Age‐2
Age‐6
Age‐7
Age‐4
Age‐3
Age‐1
Age‐2
Age‐5
Age‐6
Age‐7
Age‐3
Age‐1
Age‐2
Age‐4
Age‐5
Age‐6
Age‐7
Age‐1
Age‐2
Age‐3
Age‐4
Age‐5
Age‐6
Age‐7
Age‐1
Age‐2
Age‐3
Age‐4
Age‐5
Age‐6
Age‐7
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Age & timeYears
Age‐7
Age‐6
Age‐4
Age‐5
Age‐1
Age‐2
Age‐3 Age‐3
Age‐7
Age‐6
Age‐5
Age‐2
Age‐4
Age‐1
Age‐6
Age‐5
Age‐4
Age‐3
Age‐1
Age‐2
Age‐7
Age‐5
Age‐4
Age‐3
Age‐1
Age‐2
Age‐6
Age‐7
Age‐4
Age‐3
Age‐1
Age‐2
Age‐5
Age‐6
Age‐7
Age‐3
Age‐1
Age‐2
Age‐4
Age‐5
Age‐6
Age‐7
Age‐1
Age‐2
Age‐3
Age‐4
Age‐5
Age‐6
Age‐7
Age‐1
Age‐2
Age‐3
Age‐4
Age‐5
Age‐6
Age‐7
Survival & growth
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Harvest process in fish
0 1 2 3 4 5 6 7
020
040
060
080
010
00
Age
Abu
ndan
ce
No harvest
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Harvest process in fish
0 1 2 3 4 5 6 7
020
040
060
080
010
00
Age
Abu
ndan
ce
No harvestHarvest of 4+ fish
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Harvest process in fish
0 1 2 3 4 5 6 7
020
040
060
080
010
00
Age
Abu
ndan
ce
No harvestHarvest of 4+ fishHarvest of 3+ fish
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Harvest process in fish
0 1 2 3 4 5 6 7
020
040
060
080
010
00
Age
Abu
ndan
ce
No harvestHarvest of 4+ fishHarvest of 3+ fishHarvest of 2+ fish
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Biomass
0 1 2 3 4 5 6 7
0.0
0.1
0.2
0.3
Wei
ght l
engt
h (k
g)
0 1 2 3 4 5 6 7
020
040
060
080
010
00
Age
Abun
danc
e
Combine the 2 to get yield
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Yield
0 1 2 3 4 5 6 7
010
2030
4050
60
Age
Abu
ndan
ce
Area under the curve is total yield
![Page 23: WF4133 Fisheries Science - GitHub Pages · 4/1 Group 3 Group 4. Lab today @ 1pm • Bring – Rain gear – Sun screen – Bug repellent – Waders/boots. BIOLOGICAL OVERFISHING Reduced](https://reader033.vdocuments.us/reader033/viewer/2022060901/609e8313ba87b65e0b3cc5c5/html5/thumbnails/23.jpg)
Trade off
1. Harvesting a lot of fish2. Harvesting fewer, but larger fish
Lets look at this
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Harvest related to size
http://www.mdwfp.com/media/218652/creel_limits_pt._3_chaper_1.pdf
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Flip the VBGF
Recall, the VBGF predicts length at age
Can rearrange equation to predict age given length
0( )(1 )K age tageLength Length e
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Proof0
0
0
0
(
(
( )
(
)
)
)
0
)
)
1
1
lo
(1
(1
(g 1 )
log 1
age
age
age
age
age
age
K age t
K age t
K age t
K age t
Length Length
LengthLength
LengthLength
LengthLength
LengthLength
Len
e
e
e
e
K
gthLength
age t
K
0
0
( )
log 1 ageLengthLe
age t
t agK
ngthe
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Example
Proposed minimumlength limit1. 8 inches (203 mm)2. 12 inches (304 mm)3. 14 inches (356 mm)4. 15 inches (381 mm)
0
4000.30.1
LengthKt
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8 inch limit
0
log 1
203log 1400.1
0.3
0.10.3
0.
0
3.05
10.2
1 16.46
ageLength
t ageK
age
age
ageage
Length
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12 inch limit
0
log 1
304log 1400
1.427
4.7574.
0.10.3
0
8
.10.3
0.157
age
t ag
L
eK
age
a
engthLength
ge
ageage
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Yield per recruit model!
![Page 31: WF4133 Fisheries Science - GitHub Pages · 4/1 Group 3 Group 4. Lab today @ 1pm • Bring – Rain gear – Sun screen – Bug repellent – Waders/boots. BIOLOGICAL OVERFISHING Reduced](https://reader033.vdocuments.us/reader033/viewer/2022060901/609e8313ba87b65e0b3cc5c5/html5/thumbnails/31.jpg)
Diagnosing growth overfishing
Growth overfishing
No growth overfishing
![Page 32: WF4133 Fisheries Science - GitHub Pages · 4/1 Group 3 Group 4. Lab today @ 1pm • Bring – Rain gear – Sun screen – Bug repellent – Waders/boots. BIOLOGICAL OVERFISHING Reduced](https://reader033.vdocuments.us/reader033/viewer/2022060901/609e8313ba87b65e0b3cc5c5/html5/thumbnails/32.jpg)
Diagnosing growth overfishing
Growth overfishing
No growth overfishing
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ASSESSING OVERFISHING?
Is there a way to evaluate the effects of fishing on a population?
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Total mortality (Z)
Z = F + MWhere,
F = Fishing mortalityM = Natural mortality
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0 1 2 3 4 5 6 7
020
040
060
080
010
00
Age
Abu
ndan
ce
Harvest process in fish
Fewer older fish with harvest.