Feeding ecology of early marine phase Atlantic salmon Salmo salar post-smolts.

Dietary analyses of Atlantic salmon Salmo salar post-smolt stomachs collected from 2001 to 2005 in Penobscot Bay, Maine, U.S.A., have yielded insights into the feeding ecology of early marine phase post-smolts from different rearing origins. Most stomachs contained only one or two prey types, suggesting active prey selection. Post-smolts that lived in the river longer (i.e. from naturally reared and parr-stocked origins) were smaller and consumed more fishes than invertebrates compared to larger post-smolts that emigrated immediately post-stocking (i.e. from smolt-stocked origins). Naturally reared S. salar consumed c. 84% fishes and 16% crustaceans and parr-stocked S. salar consumed 64% fishes and 34% crustaceans. Stocked smolts consumed 48% fishes and 40% crustaceans. Differences in the type and quantity of consumed prey may be indicative of behavioural differences among rearing origins that influence post-smolt survival.

Surface trawl survey for U.S. origin Atlantic salmon Salmo salar.

A surface trawl survey (2001-2005) in Penobscot Bay, Maine, U.S.A., and the nearshore Gulf of Maine waters was conducted to investigate early marine dynamics of a hatchery-dependent Atlantic salmon Salmo salar population from a severely modified river system. Data generated were used to evaluate the effect of stocking location and time on migration success and to describe the migratory pathways and environments that post-smolts traverse. Significant differences in early migration success were detected among different stocking groups, but subsequent marine survival was independent of stocking group. While the post-smolt population was primarily composed of hatchery origin smolt-stocked fish, other life-stage stocking strategies (i.e. parr stocking) represented a higher proportion of the population than previously assumed. Catch distribution suggests evidence of an initial marine migratory pathway out of the dynamic Penobscot Bay environment. The hypothesized benefits of a predator refuge based on the co-occurring species complex is considered minimal for emigrating post-smolts given a mismatch in the size overlap among species and low abundance of other co-occurring diadromous populations. These data can be used to modify current management actions to optimize S. salar recovery and inform future research agendas.