Consideration of the Stable Age Distribution Assumption in "Analytical" Yield Models
The implications on the "analytical" yield model of deviations from the stable age distribution were investigated for stocks of five species with a range of life history characteristics, these being Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), pollock (Pollachius virens...
| Published in: | Canadian Journal of Fisheries and Aquatic Sciences |
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| Main Authors: | , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Canadian Science Publishing
1983
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1139/f83-016 http://www.nrcresearchpress.com/doi/pdf/10.1139/f83-016 |
| Summary: | The implications on the "analytical" yield model of deviations from the stable age distribution were investigated for stocks of five species with a range of life history characteristics, these being Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), pollock (Pollachius virens), Atlantic herring (Clupea harengus harengus), and Atlantic mackerel (Scomber scrombus). Recruitment variability for the stocks considered ranged from 21% for pollock to 104% for haddock. The comparison of the growth rates at age for the five species showed the expected continuum in relative growth rates from cod to mackerel. With the population in a stable age distribution without fishing there is also a continuum from cod to mackerel in the manner in which age-specific production decreases through the life span. It is thus to be expected that deviations from the stable age distributions for mackerel would have a much greater impact on population production than would a similar deviation for cod. Also, species whose growth rates decrease more rapidly with age tend to have a higher recruitment variability. To demonstrate the implications of deviations from the stable age distribution on the accuracy of model output, MSY yields (that would have been generated given historical estimates of population numbers-at-age) were compared to estimates of annual population production. Cod and pollock production deviate relatively little from the "analytical" model predictions. In contrast, annual production for haddock, herring, and mackerel deviate markedly from MSY yields as the age composition deviates in each direction from the stable age distribution. The analysis suggests that for some species the "analytical" model may contribute to growth overfishing.Key words: "analytical" yield models, stable age distribution, growth overfishing |
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