Yield per recruit for Summer Flounder
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Benjamin Gibson 11/14/14 BIO 332 Data assignment #4 1. In the summer flounder fishery, fisheries scientists strive for a fishing mortality rate of F 0.1 because it is much more sustainable than F max which allows much more prolonged exploitation of the fishery. One might look at the differences F max and F 0.1 have and think that F 0.1 is worse than F max due to the decreased yield per recruit, however, where it lacks in yield per recruit it gains in spawning stock biomass (table 1). If the yield per recruit is decreased enough, the spawning stock biomass will increase, allowing that stock to remain at relatively healthy levels (fig. 1). 2. Age is used as a proxy for size, which means the older the recruits are, the large they are. If the age at first capture is lower, they will have a lower yield per recruit, however they start out with a larger spawning stock biomass. If the fishing mortality increases to 0.8, the yield per recruit of the fishery with an age of first capture set at 5 will decline past the yield per recruit of the fishery whose age at first capture was set at 2. This indicates that the fishery whose age at first capture is 2, is more sustainable even if the yield per recruit is less than the fishery whose age at first capture is 5 (fig. 1). 3. The yield per recruit is lower at a fishing mortality rate of 0.4 due to growth overfishing, which is when fish are harvested at a size that is smaller than the size that would produce the maximum yield per recruit, decreasing the overall yield per recruit (fig. 1).
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Transcript of Yield per recruit for Summer Flounder
Benjamin Gibson
11/14/14
BIO 332
Data assignment #4
1. In the summer flounder fishery, fisheries scientists strive for a fishing mortality rate of F0.1 because it is much more sustainable than Fmax which allows much more prolonged exploitation of the fishery. One might look at the differences Fmax and F0.1 have and think that F0.1 is worse than Fmax due to the decreased yield per recruit, however, where it lacks in yield per recruit it gains in spawning stock biomass (table 1). If the yield per recruit is decreased enough, the spawning stock biomass will increase, allowing that stock to remain at relatively healthy levels (fig. 1).
2. Age is used as a proxy for size, which means the older the recruits are, the large they are. If the age at first capture is lower, they will have a lower yield per recruit, however they start out with a larger spawning stock biomass. If the fishing mortality increases to 0.8, the yield per recruit of the fishery with an age of first capture set at 5 will decline past the yield per recruit of the fishery whose age at first capture was set at 2. This indicates that the fishery whose age at first capture is 2, is more sustainable even if the yield per recruit is less than the fishery whose age at first capture is 5 (fig. 1).
3. The yield per recruit is lower at a fishing mortality rate of 0.4 due to growth overfishing, which is when fish are harvested at a size that is smaller than the size that would produce the maximum yield per recruit, decreasing the overall yield per recruit (fig. 1).
tc = 2 Y/R (kg) SSB/R (kg) Fmax 0.19 0.49 3.17 F0.1 0.13 0.47 4.10 tc = 5 Y/R (kg) SSB/R (kg) Fmax 0.23 0.52 2.81 F0.1 0.16 0.48 3.68
Table 1. Stock data for a population of summer flounder at set ages at first capture (tc; years), including the fishing mortality rate that maximizes yield per recruit (Fmax), the fishing mortality where Y/R is 1/10th of the origin’s slope (F0.1), the yield per recruit (Y/R; kg), spawning stock biomass (SSB; kg).
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.0 0.2 0.4 0.6 0.8
Y/R (kg)
F
Tc = 2 Tc = 5
0
2
4
6
8
10
12
0.0 0.2 0.4 0.6 0.8
SSB/R (kg)
F
Tc = 2
Tc = 5
A
B
Figure 1. (A) Yield per recruit (Y/R; kg) as a function of fishing mortality (F) in a population of summer flounder comparing two different ages at first capture (tc; 2 and 5 years). (B) Spawning stock biomass (SSB; kg) as a function of fishing mortality (F) in a population of summer flounder comparing two different ages at first capture (tc; 2 and 5 years). Recruitment ages when 2 is the age at first capture (tc = 2), stock contained 2-16 year old summer flounder, and recruitment ages when 5 is the age at first capture (tc = 5), stock contained 5-16 year old summer flounder.
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