The biology and fishery of American plaice (Hippoglossoides platessoides [Fabricius]) with special reference to the Grand Bank

Pitt, Thomas Kenton (1975) The biology and fishery of American plaice (Hippoglossoides platessoides [Fabricius]) with special reference to the Grand Bank. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

American plaice (Hippaglossoides platessoides) is widely distributed throughout the Northwest Atlantic with the Grand Bank supporting the largest population. Meristics indicated possibly considerable intermingling during pre- metamorphosis stages, but on the Grand Bank, at least, tagging and growth data suggested little intermingling beyond the early life-history stages. -- Length-age comparisons, indicated considerable differences between localities and also gave positive correlations between average length at ages 5 and 15 and probable bottom temperature. -- Peak spawning occurred from early April on Flemish Cap to early June off Northeast Newfoundland and Labrador. Fifty percent (50%) sexual maturity for different localities occurred at 7.8-12.2 years for females and 5.3-7.6 years for males. -- Log-log relationships were established between fecundity and fish length, gutted and gilled weight and age for Grand Bank samples. No differences were found between fecundity- length relationships for different parts of the Grand Bank. -- Although invertebrates, principally benthic forms occurred most frequently in plaice stomachs from the Grand Bank capelin and lance made up a major part of the total food weight and were especially important for the southern Grand Bank. -- Landings of Grand Bank plaice increased from the early 1950’s and reached a peak in 1966-68 with a subsequent gradual decline. Increased exploitation was reflected in declines in catch per hour, stock abundance and fishing mortality rates. Stock assessments suggested that removals in the immediate future may be lower than in previous years. However, because of non-reporting of discards of plaice, prediction of yield is difficult. -- Average length at age increased from the early 1950’s to the 1970’s apparently-because of increased rate of growth in the early years of life and coupled with this was a decline in age at sexual maturity. Significant correlations were found between stock size ,asymptotic length and size at age 5 and 10 years for the northern half of the Grand Bank.

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