Growth Analysis of Strait of Georgia Lingcod by Use of Length-Frequency and Length-Increment Data in Combination

Abstract

We estimated von Bertalanffy growth parameters for male and female lingcod Ophiodon elongatus in the Strait of Georgia, British Columbia, by use of length-frequency and length-increment data in combination. Although length frequencies can be an inferior data set if the overlap of year-classes obscures the modal structure, length-frequency data together with length-increment data provided a useful data set for analyzing lingcod growth. For determining growth and growth variance, length-frequency data were more useful for the younger year-classes, whereas length-increment data were more informative for older individuals. We used and extended Sainsburyˈs formulation of the von Bertalanffy growth model to incorporate a sinusoidal cycle of annual growth because we recognized such a pattern in our length-increment data. We concluded that male lingcod grew more slowly than female lingcod in the Strait of Georgia, and that the growth rates for both males and females were slower than rates determined from length-at-age data for lingcod off southwest Vancouver Island. Slower growth of male lingcod has been consistently observed in length-at-age analyses of British Columbia lingcod stocks, and slower growth for males and females in the Strait of Georgia relative to other regions has also been observed for the commercially important groundfishes Pacific hake Merluccius productus and walleye pollock Theragra chalcogramma.