Variations in Biological Characteristics of Rainbow Smelt in the Gulf of Maine and Relationships to Genetic Distinctions and External Stressors

Rainbow smelt (Osmerus mordax) populations have declined precipitously since the late 1800s. We studied 17 spawning runs geographically spanning the US Gulf of Maine to document current population characteristics. Concurrently, we collected habitat and water quality information. Smelt are fully recruited to the spawning run at age-2, though some age-1 fish participate in the spawning run. The age class composition varied between sites but displayed geographical patterns. Age-1 smelt were common in Massachusetts and, in some years, were the dominant age class. Higher levels of mortality were found at Massachusetts and New Hampshire sites, where water quality and habitat characteristics were of poorer quality. We compared length at age among age-2 males as a consistent variable with low intra-site variability. The largest age-2 males occurred in Massachusetts runs, indicating a faster growth rate at lower latitudes. At New Hampshire sites, age-2 males were smaller compared to Massachusetts and Maine sites. This trend may be evidence of stressed populations due altered habitat, however, this pattern is also consistent with the genetic stock structure of rainbow smelt reported by Kovach et al. (2013). Further study is necessary to determine if genetics or environmental variables are responsible for these patterns.