Restoration programs for anadromous alewives in several Maine river drainages are based on trapping of adult alewives in lower river reaches and stocking the captured spawners in historic lentic spawning and nursery habitat farther upstream. Previous studies explored juvenile alewife production at certain adult escapment densities. However, no work has been done at the 15-alewives-per-lake-surface-hectare stocking rate currently used in the alewife trucking program.
This study examined the production of juvenile alewives in lakes stocked at 15 alewives per hectare and 30 alewives per hectare. The primary study waters were 288-ha Pattee Pond and 70-ha Nehumkeag Pond, both eutrophic lakes. Additional data were collected from 136-ha, mesotrophic Lake George, at 15 alewives per hectare. A pilot study to determine the plausibility of using weirs on the study lake outlet streams to count juvenile alewife emigrants was conducted in 1996 at Pattee Pond stream, the outlet of Pattee Pond, which was stocked with 15 alewives per hectare. Based on the success of this preliminary study, weirs were placed on Pattee Pond and Nehumkeag Pond outlet streams in both 1997 and 1998. Stocking rates varied, with Pattee Pond receiving 15 alewives per hectare in 1997 and 30 per hectare in 1998. Nehumkeag Pond received 30 alewives per hectare in 1997 and 15 in 1998.
Juvenile production responded positively to an increase in adult alewife wtocking density in Pattee Pond, although the increase was not proportional to the increase in the stocking rate. The elevated stocking rate at Pattee Pond produced at 27% increase in emigrating juveniles from 1996 (at 15 per hectare) to 1997 (at 30 per hectare).
Growth of juvenile alewives suffered as a result of increased stocking density and increased intraspecific competition. The growth rate of juveniles was much lower at the higher stocking density in Pattee Pond in 1997, compared to both 1996 and 1998 at the lower stocking density, suggesting intraspecific competition for limited food resources.
The timing of juvenile alewife emigration was examined in relation to stream water temperature and stream level (a surrogate for discharge). Water temperature seemed to play a minimal role, but juvenile alewife movement was strongly influenced by stream level, as measured by staff gauges located on the weirs. Peaks in juvenile movement out of both ponds in 1998 closely followed peaks in stream discharge. The magnitude, timing, and duration of juvenile emigration was strongly influenced by flow in the outlet stream