Timothy F. Sheehan

Visibility of Visual Implant Elastomer Tags in Atlantic Salmon Reared for Two Years in Marine Net-Pens

Abstract We evaluated detectability of visual implant elastomer (VIE) tags in individual Atlantic salmon Salmo salar reared from smolts to adults in commercial marine net-pens. A total of 9,000 individual smolts were marked (adipose eye, lower jaw, or both) with colored VIE tags. During the period from March 1998 to December 2000 (2–28 months after tagging) a total of 3,220 fish were visually inspected for VIE tags. Tag detection rates remained high (>90%) for the first 17 months after tagging but then declined sharply, particularly for VIEs in the jaw. Use of a UV light significantly increased detection of both eye and jaw VIE tags. We conclude that VIE tags are optimal for use in Atlantic salmon when recovery of fish occurs within 17 months of tagging.

Scale Pattern Analysis Discriminates Atlantic Salmon by River Reach Rearing Origin

Abstract Scale pattern analysis was used to discriminate among juvenile Atlantic salmon Salmo salar reared in different reaches of the Narraguagus River basin. Measurements of parr scales collected during 1990–1999 were used in a principal components analysis and to create linear discriminant functions for seven geographic strata and three river basin strata groups reflecting natural habitat breaks and Atlantic salmon management regimens. Discriminant functions were calculated with both pooled and annual data. Sufficient differentiation existed among rearing habitats of different reaches (or between geographically grouped reaches) in the Narraguagus River basin, particularly for tributary habitats, to allow discrimination to various degrees of possible use in management.

Using Hydroacoustics to Describe Pelagic Fish Distribution in the Penobscot Estuary, Maine

AbstractTemperate estuaries are inherently variable and productive ecosystems that provide nursery habitat, migration pathways, and forage areas for diadromous, estuarine, and marine fish. We used multifrequency scientific echo sounders (SIMRAD EK60 split-beam, 38 and 120 kHz) to describe the distribution of pelagic fish in the Penobscot River estuary, Maine, in 2012 and 2013. Differences in responses between frequencies were used to distinguish fish from other biota. Acoustic area backscatter from echo integration (sA [m2/nautical mile2], a common measure proportional to fish density) and target strength (TS; dB re 1 m2, an acoustic measure of fish size) distributions varied with season and salinity. Overall, the sA and TS distributions were similar in both years, with detectable spatial and temporal patterns. The highest value of sA occurred in July of both years, when dense schools of fish were detected in higher-salinity areas of the lower estuary. The middle estuary had high sA values in April both y...

Assessment of Early Migration Dynamics of River-Specific Hatchery Atlantic Salmon Smolts

AbstractMany Atlantic Salmon Salmo salar populations within the southern extent of the species’ range are at critically low abundances, while others have been extirpated. The focus of many ongoing recovery efforts is on maximizing the number of smolts that reach the ocean, where marine survival is low, primarily through hatchery supplementation and improvement of in-river hydropower system management. However, estuaries also are known to be sites of high mortality, although in many cases the correlates of this mortality are poorly characterized. We acoustically tagged hatchery smolts (n = 666) during 2001–2005 to evaluate migration performance through freshwater, estuarine, and bay reaches of the small but tidally dynamic Dennys River, Maine, USA, to investigate potential drivers contributing to low returns within the system. Migration behaviors (e.g., migration timing and tidal use) were typical for Atlantic Salmon smolts, but reversals during migration were observed upon entry into the estuary environme...