The Rainbow Smelt, Osmerus mordax, Complex of Lake Utopia: Threatened or Misunderstood?

Abstract

We report on the spawning ecology, genetic characteristics, and predation threats to spawning groups of rainbow smelt, Osmerus mordax, in Lake Utopia, New Brunswick where a dwarf morpho-type has been listed as a threatened species. Two spawning groups in three inlet streams had been previously identified; we observed three groups using four inlet streams. The earliest group was the largest in body size (12–29 cm fork length (FL)), lowest in numbers (∼1 000), and completed spawning approximately two weeks before the second group. The early spawners were previously identified as the normal morpho-type, but we now classify these as a giant morpho-type. The second group spawned in three different streams. They were intermediate in body size (10–15 cm FL) and numbers (∼10 000). The dwarf group began spawning as the intermediate group completed spawning and within the same three streams. The dwarfs were numerous (∼1 000 000), small in size (<12 cm), and with higher gill raker counts. Microsatellite analyses suggested that gene flow among groups occurred, but genetic divergence was high and genetic separation among populations of the same group among streams and within a stream occurred. Stable isotopes and stomach contents indicated the dwarf group were likely consumed by a variety of fishes, but they were not the sole food resource of any predator including a population of landlocked salmon. These are some of the complexities of smelt ecology, but there are clearly life history tactics that we do not yet understand.