Age and growth rates of a translocated chub Squalius cephalus chalk-stream population with comparison to indigenous riverine populations in England.

Abstract

Introduced fishes into lowland rivers can result in invasive populations establishing and then dispersing, where knowledge of their life history traits contributes to understandings of their invasion ecology. Here, the age and growth rates of a translocated chub Squalius cephalus population were assessed in the River Frome, alowland chalk-stream in Southern England, where chub was introduced approximately 15 years ago. The results were assessed in relation to 35 riverine indigenous chub populations in England. Across these populations, individual chub were present to lengths over 550 mm and aged to at least 19 years old. In samples collected from the River Frome, however, no fish were present over 300 mm and age 4+ years. Growth rate analyses of both the annual length increment produced between age 1 and 2 years (juvenile growth rate) and length at the last annulus (adult growth rate) revealed that both of these were relatively high in the River Frome population, being among the fastest of all sampled populations. It is suggested these fast growth rates were the response of the fish to their new environment, facilitating their establishment and colonisation through, for example, enabling reproduction at relatively young ages.