Growth Rate of Central British Columbia Pink Salmon (Oncorhynchus gorbuscha)

Abstract

Pink salmon were sampled at various stages, as fry and fingerling in enclosed waters, as juveniles and subadults in the ocean and as maturing salmon in the commercial fishery. On the basis of length frequency data and from recapture measurements of marked and tagged individuals the instantaneous growth rate in length (gl) for successive 30-day periods was computed. As a result three major growth stanzas were recognized. Following the entrance of fry into the estuary, growth was approximately exponential (gl = 0.559) during an initial 40-day period. Fish increased in length from 3.5 to 8.4 cm. Thereafter, the instantaneous rate of growth gradually declined to a minimum in March (gl = 0.076). During this time the length increased from 8.4 to 32.5 cm. The final growth period was marked by a rapid rate of increase in length in late April and early May (gl = 0.171), followed by a declining rate of increase in length which was finally terminated after the fish had re-entered the coastal waters and the commercial fishery (gl = 0.041). The length data were transformed to weight data from a generalized length–weight regression. During the initial 30-day period the instantaneous growth rate in weight, gw = 6.53. From a value of gw = 2.87 for late May and early June the instantaneous growth rate progressively fell to a low of gw = 1.28 for late March to early April. During late April to early May of the ultimate year, gw = 1.74. The instantaneous growth rate then fell to gw = 1.14 during mid July to early August. It was concluded that growth, in length and weight, of central British Columbia pink salmon is a continuing process with no period of complete cessation from the time the fry enter the sea until the time they re-enter the estuary as adults.