Population Characteristics of the Red Porgy, Pagrus Pagrus, Stock off the Carolinas
Using recorded and estimated landings and size frequencies of fish from commercial, headboat, private recreational and charter boat fisheries from 1972–1986, we examined the age structure and population size of the stock of red porgy, Pagrus pagrus, off the coast of North and South Carolina. Combining annual age-length keys with length-frequency distributions, annual landings in numbers at age are estimated. Virtual population analysis (VPA) is applied to these data to estimate annual, age-specific population sizes and fishing mortality rates for three levels of natural mortality (M = 0.20, 0.28, and 0.35). On average 3% to 6% of the population (ages 1 and older) was landed annually from 1972–1978 compared to 16% to 23% from 1982–1986. Eleven to 21% of fully recruited red porgy (ages 5 and older) were landed annually from 1972–1978 compared to 40% to 50% from 1982–1986. For the intermediate level of natural mortality (M = 0.28), estimated population size in biomass declined from 2.6 million kg in 1978 to 0.6 million kg in 1986. Spawning stock (ages 2–10) in biomass ranged between 0.5 million kg in 1986 and 1.5 million kg in 1977. Recruitment to age 1 in numbers ranged from 0.6 million in 1986 (from the 1985 spawning stock) to 2.2 million in 1973 (from the 1972 spawning stocks, respectively). For the low exploitation period (1972–1978), spawning stock biomass declined to 69% to 86% of unexploited spawning stock (F = 0); while for the high exploitation period (1982–1986), spawning stock biomass declined to 38% to 53% of unexploited spawning stock. Between these two exploitation regimes, spawning stock biomass for the high exploitation period was reduced to 55% to 62% of the spawning stock biomass for the earlier low exploitation period. Yield per recruit based on age-specific fishing mortality rates increased by about 53% from 121.1 g for the low exploitation period to 184.8 g for the high exploitation period. Because age-specific fishing mortality rates (Fi, ages 1–9) increased by a factor of 3.7, most of the gains available by increasing F have been taken. With proportionately greater increases in Fi incurred by younger age classes (ages 1–4) between 1972–1978 and 1982–1986, small gains in yield per recruit may now be obtained by raising age-at-entry to the fishery above the current age-1.
No Supplementary Data.
Document Type: Research Article
Publication date: 1992-01-01
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