Effects of Marine-Derived Nutrients on Juvenile Atlantic Salmon Growth and Body Condition

Prior to construction of dams beginning in the early 1800s, Atlantic salmon (Salmo salar) and other anadromous species migrated from the ocean to spawn in Maine’s extensive rivers and streams. Spawning fish transported marine-derived nutrients to these systems in the form of metabolic expenditure and through decomposition of mortalities. These contributions may have strongly influenced productivity in otherwise nutrient limited systems, bolstering the growth and survival of young Atlantic salmon and other anadromous species and influencing other components of the stream communities. Today, much of the historic spawning habitat for anadromous species in Maine receives no such pulse of marine-derived nutrients, which may result in more nutrient deficient, less complex ecosystems. There is growing interest in reversing anadromous fish population declines through fisheries restoration. It is hypothesized that improved access to spawning habitat through dam removal and improved fish passage will enhance stream productivity and increase natural reproduction of Atlantic salmon and other anadromous fishes, but this is largely untested in this region.

We are investigating the influence of marine-derived nutrients on Atlantic salmon nursery streams in the Penobscot River watershed, Maine. We stocked four headwater streams with young-of-the-year Atlantic salmon in May 2009 and 2010.  We manipulated nutrient input with a salmon carcass analog placed at a density of 0.10 kg/m² in 300 meter treatment reaches in July and late October each year, timed to match sea lamprey and Atlantic salmon spawning. We lethally sampled Atlantic salmon during June – December each year. We are assessing Atlantic salmon growth and body condition with fish size, condition factor, otolith microstructure analysis, and total lipid extractions.  Preliminary data indicate that young-of-the-year Atlantic salmon lengths are 4-14% greater and masses are 22-69% greater in treatment reaches relative to control reaches one month after nutrient addition. In addition, we are analyzing Atlantic salmon muscle tissue for δ¹⁵N and δ¹³C to trace marine-derived nutrient uptake. Preliminary data indicate that young-of-the-year Atlantic salmon have incorporated marine-derived nutrients into their muscle tissue within one month after nutrient addition.

While removal of barriers in the Penobscot River drainage will increase access to much of the historic Atlantic salmon spawning range, implementation of a fertilization program with a salmon carcass analog may be a strategy to enhance survival of Atlantic salmon in their early life stages.