Graduate Thesis Or Dissertation
 

Fluctuations of year-class strength in petrale sole (Eopsetta jordani) and their relation to environmental factors

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  • The effects of potential parental egg production and environmental factors on year-class strength (YCS) of petrale sole (Eopsetta jordani) were investigated in two areas off Oregon and Washington (Pacific States Marine Fisheries Commission areas 2B: 42° 50'N - 44°18'N, and 3A: 45° 46'N - 47°20'N). Indices of YCS based on Summed-CPUE (summed catch rates of females for ages 6 + 7) and cohort analysis (numbers of females attaining age-6) tended to be significantly correlated within and between areas 2B and 3A (r ≥ 0.45, P ≤ 0.06). Since cohort analyses were deemed more reliable YCS indices than Summed-CPUE indices, only cohort analyses were used to determine the role of potential parental egg production and environmental factors on YCS variations. Large YCS fluctuations were evident from 1958 to 1977. Year-classes born from 1962 to 1965 and from 1973 to 1977 were intermediate to weak cohorts in areas 2B and 3A. In both areas, estimates of commercial catch rates suggested a substantial decline of abundance from the middle 1970's to the middle 1980's. The fact that the large decrease of YCS for cohorts born from 1973 to 1977 was not preceded by a decline in commercial catch rates, and that spawner-recruit relations were not detected, suggested that density-independent factors were more important than parental-stock size during the initial decrease of YCS in the 1970's and the subsequent decline of catch rates in the late 1970's. For cohorts born from 1958 to 1977, a regression model based on indices of offshore Ekman transport from January to March, and alongshore transport from December to February accounted for nearly 55% of the YCS variations in area 2B. For area 3A, sea surface temperature from December to February along with the previous environmental factors explained about 65% of the YCS variation. In a lower extent, winter salinity variations due to the Columbia River also appeared to be related to recruitment strength in area 3A. These findings suggested that YCS fluctuations of petrale sole from 1958 to 1977 may have been primarily forced by winter and early spring oceanographic conditions affecting distribution and/or survival of eggs and early larval stages.
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