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cheferson · 04-13-2004, 05:08 PM

Stock size and fishing mortality were estimated utilizing a Murphy Virtual Population Analysis (VPA) for two data sets, one with just the reduction fishery landings, and one that combined the reduction and bait landings into a combined catch at age matrix. The reference points contained in Amendment 1 were then recalculated based on the combined data.

Combined Reduction and Bait Fishery Data:

* Based on a combined catch at age matrix, the VPA-generated estimate of fishing mortality for 2000 (F 2000 = 0.6) was below both the revised overfishing threshold (F = 1.1) and target (F = 0.9).

* The estimate of spawning stock biomass for 2000 (SSB = 90,100 t) was above both the revised threshold (27,500 t) and target (50,000 t) values.

Reference Point
Target or Threshold
Value
Current
Stock
Status
Evaluation
Fishing Mortality Target (F target) 0.9 0.6
Stock Healthy
Fishing Mortality Threshold (F threshold) 1.1 0.6
Stock Healthy
Spawning Stock Biomass Target (SSB target) 50,000 mt 90,100 MT
Stock Healthy
Spawning Stock Biomass Threshold (SSB threshold) 27,500 MT 90,100 MT
Stock Healthy

Based on the revised biological reference points, the Atlantic menhaden population is not overfished and overfishing is not occurring. However, the spawning stock biomass is declining due to a series of years with poor recruitment (to age-1). There is no evidence that recent low levels of recruitment have been caused by overfishing. The poor recruitment appears to be the result of poor survivorship of age-0 fish prior to their entry into the fishery at age-1.

Due to the decline in reduction fishery landings coupled with increased and improved reporting of the bait fishery landings, the relative importance of the bait fishery landings has increased. Because the bait fishery tends to harvest older and larger menhaden, the combined catch at age matrix implies that more older and larger fish were removed relative to the younger and smaller fish. By relying solely on the reduction fishery landings, the previous assessments appear to contain some level of bias. Since the older fish were under-represented, the assessments underestimated the abundance of older fish. Using the combined reduction and bait fishery data removes any bias inherent in relying on the reduction fishery data only, and provide a more accurate picture of the total menhaden population.

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04-13-2004, 05:08 PM	#5
cheferson Registered User iTrader: (0) Join Date: Nov 2003 Location: MA Posts: 3,630	Stock size and fishing mortality were estimated utilizing a Murphy Virtual Population Analysis (VPA) for two data sets, one with just the reduction fishery landings, and one that combined the reduction and bait landings into a combined catch at age matrix. The reference points contained in Amendment 1 were then recalculated based on the combined data. Combined Reduction and Bait Fishery Data: * Based on a combined catch at age matrix, the VPA-generated estimate of fishing mortality for 2000 (F 2000 = 0.6) was below both the revised overfishing threshold (F = 1.1) and target (F = 0.9). * The estimate of spawning stock biomass for 2000 (SSB = 90,100 t) was above both the revised threshold (27,500 t) and target (50,000 t) values. Reference Point Target or Threshold Value Current Stock Status Evaluation Fishing Mortality Target (F target) 0.9 0.6 Stock Healthy Fishing Mortality Threshold (F threshold) 1.1 0.6 Stock Healthy Spawning Stock Biomass Target (SSB target) 50,000 mt 90,100 MT Stock Healthy Spawning Stock Biomass Threshold (SSB threshold) 27,500 MT 90,100 MT Stock Healthy Based on the revised biological reference points, the Atlantic menhaden population is not overfished and overfishing is not occurring. However, the spawning stock biomass is declining due to a series of years with poor recruitment (to age-1). There is no evidence that recent low levels of recruitment have been caused by overfishing. The poor recruitment appears to be the result of poor survivorship of age-0 fish prior to their entry into the fishery at age-1. Due to the decline in reduction fishery landings coupled with increased and improved reporting of the bait fishery landings, the relative importance of the bait fishery landings has increased. Because the bait fishery tends to harvest older and larger menhaden, the combined catch at age matrix implies that more older and larger fish were removed relative to the younger and smaller fish. By relying solely on the reduction fishery landings, the previous assessments appear to contain some level of bias. Since the older fish were under-represented, the assessments underestimated the abundance of older fish. Using the combined reduction and bait fishery data removes any bias inherent in relying on the reduction fishery data only, and provide a more accurate picture of the total menhaden population. <