Growth and Smolting in Lower‐Mode Atlantic Salmon Stocked into the Penobscot River, Maine

• Published in: North American Journal of Fisheries Management
• Main Authors: Zydlewski, Joseph, O'Malley, Andrew, Cox, Oliver, Ruksznis, Peter, Trial, Joan G.
• Other Authors: University of Maine, U.S. Geological Survey
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2014
• Subjects: Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1080/02755947.2013.866996; https://onlinelibrary.wiley.com/doi/pdf/10.1080/02755947.2013.866996; https://onlinelibrary.wiley.com/doi/full-xml/10.1080/02755947.2013.866996; https://afspubs.onlinelibrary.wiley.com/doi/pdf/10.1080/02755947.2013.866996

Abstract Restoration of Atlantic Salmon Salmo salar in Maine has relied on hatchery‐produced fry and smolts for critical stocking strategies. Stocking fry minimizes domestication selection, but these fish have poor survival. Conversely, stocked smolts have little freshwater experience but provide higher adult returns. Lower‐mode (LM) fish, those not growing fast enough to ensure smolting by the time of stocking, are a by‐product of the smolt program and are an intermediate hatchery product. From 2002 to 2009, between 70,000 and 170,000 marked LM Atlantic Salmon were stocked into the Pleasant River (a tributary in the Penobscot River drainage, Maine) in late September to early October. These fish were recaptured as actively migrating smolts (screw trapping), as nonmigrants (electrofishing), and as returning adults to the Penobscot River (Veazie Dam trap). Fork length (FL) was measured and a scale sample was taken to retrospectively estimate FL at winter annulus one (FW1) using the intercept‐corrected direct proportion model. The LM fish were observed to migrate as age‐1, age‐2, and infrequently as age‐3 smolts. Those migrating as age‐1 smolts had a distinctly larger estimated FL at FW1 (>112 mm) than those that remained in the river for at least one additional year. At the time of migration, age‐2 and age‐3 smolts were substantially larger than age‐1 smolts. Returning adult Atlantic Salmon of LM origin had estimated FLs at FW1 that corresponded to smolt age (greater FL for age 1 than age 2). The LM product produces both age‐1 and age‐2 smolts that have greater freshwater experience than hatchery smolts and may have growth and fitness advantages. The data from this study will allow managers to better assess the probability of smolting age and manipulate hatchery growth rates to produce a targeted‐size LM product. Received June 11, 2013; accepted November 11, 2013 Published online February 10, 2014