Growth and Habitat Use by Juvenile Alewife in Windham, Maine

Sea-run alewife are currently undergoing population restoration in many lake/river systems in Maine. This work is part of an ongoing study that is trying to understand juvenile alewife behavior in Highland Lake. Using 13C and 15N stable isotopes, Dennison and Wilson (2019) found that larval fish fed in the open water and then, as they grew, fed on prey from shallow water. In this study we hypothesized that juvenile fish growth rates in 2019 would change when fish shifted feeding habitats. We used stable isotope analysis (13C and 15N) to determine feeding habitat and trophic level, and used otoliths (ear bones) from the same fish to determine age and growth through the summer. Fish growth/age can be determined by viewing the otoliths of the fish which is distinguished by the repeated ring pattern, much like aging a tree. We compared growth information with trophic level (as determined using 15N) to determine if changes in trophic level correspond to changes in growth rates. Preliminary results show that 2019 fish have similar patterns in length and stable isotope values to those studied in 2018, suggesting that patterns observed by Dennison & Wilson (2019) were not unique to 2018. Understanding how larval and juvenile alewife use lake habitats and the connection to growth will help with further restoration efforts