. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. MORTALITY RATES FOR STRIPED BASS 169 Chadwick's method depends on the mean expectation of natural death for prior years when bass were tagged. Sommani's method is more sophisticated in that it utilized the mean instantaneous natural mortality rate calculated from tags actually returned in the non- tagging years to deyelop the other rates for those years. However, newly recruited fish are not represented in non-tagging years, so return
. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. MORTALITY RATES FOR STRIPED BASS 169 Chadwick's method depends on the mean expectation of natural death for prior years when bass were tagged. Sommani's method is more sophisticated in that it utilized the mean instantaneous natural mortality rate calculated from tags actually returned in the non- tagging years to deyelop the other rates for those years. However, newly recruited fish are not represented in non-tagging years, so returns from older fish bias Sommani's estimates eyen more than in years when bass are tagged. The harvest rate declined from 1958 to 1962, while the catch rate in the partyboat fishery reached its 16-year peak (Figure 3). If catchability was relatively constant, this relationship would indicate that the bass population increased during this period. The harvest rate increased 40% from 1962 to 1963. After 1963, the catch rate, harvest rates, and fishing effort all declined, (Figures 3 and 4) suggesting a decline in population. < o < a. X UJ. -o Bass Per Angler Hour -- — --0 Exploitation Rate -L. 40 IT o X —' o Z CD T3 UJ c V) CO < m 1956 57 58 59 60 62 63 64 YEAR 65 66 67 68 69 70 71 FIGURE 3. Comparison of striped bass exploitation rates and partyboat catch per angler hour. (Data from McKechnie and Miller, 1971 and Stevens, unpublished). The decline in harvest rates is probably an indirect effect of a decline in success which likely caused the reduction in fishing effort. The significant correlation between angler success and effort as meas- ured in the partyboat fishery supports this viewpoint (r = ; Figure 4). The decline in mortality rates suggest that harvest rates can be increased greatly with little reduction in yield. For example, based on Chadwick's (1969) equilibrium yield model a four-fold increase in harvest rate will increase the numbers of bass caught
Size: 2538px × 985px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorcaliforniadeptoffishandgame, bookauthorcaliforniafish
