Relationship between abundance, growth, egg size and fecundity in a landlocked population of longfin smelt, Spirinchus thaleichthys

Abstract

Sixteen year‐classes of longfin smelt, Spirinchus thaleichthys, show a consistent pattern of alternating year‐class strength between even (strong) and odd (weak) years. A recent (1989) odd year‐class grew as well as, if not better than, the late 1960s odd year‐classes. However, fish in the even year‐classes (1988 and 1990) were significantly smaller in size then the 1966 and 1968 cohorts. Associated with this reduction in growth of the even year‐class fish is a decline in fecundity. Fecundity of the odd year‐classes of smelt was also smaller than in the early 1960s. Mean egg diameter and gonadosomatic index were not statistically different between 1988 and 1989 year‐classes but the relative fecundity was higher for the 1988 year‐class than for 1989, suggesting a higher reproductive investment in the even year‐class. Reduction in growth and associated reproductive traits is considered to result from a reduction in the abundance of mysids, a preferred prey species.