A bioenergetic approach to manage production and control phosphorus discharges from a salmonid hatchery

Abstract

The environmental effects of fish culture operations are important issues in Michigan as well as many other parts of the world. The State of Michigan Department of Natural Resources operates the Platte River State Fish Hatchery (PRSFH) located near Honor, Michigan (USA). This facility has a restrictive discharge permit that limits the input of phosphorus into the Platte River that subsequently drains into a downstream oligotrophic lake (Platte Lake). The permit has been violated on occasion in recent years. Hatchery managers and operators need to understand the cause of these violations and prevent them in the future; and at the same time meet production goals to satisfy fishery management objectives. This paper describes the development and application of models designed to quantitatively analyze these issues. First, a bioenergetic growth and consumption model is developed for juvenile coho (Oncorhynchus kisutch) and Chinook (Oncorhynchus tshawytscha) salmon to quantify the relationship between fish production and by-product phosphorus loads. Next, phosphorus mass balance equations are used to calculate the phosphorus discharge from the facility as a function of the by-product phosphorus load and the efficiency of various phosphorus removal equipment and processes. The accuracy and consistency of the energy and mass balance equations are verified using extensive measurements. The ability of the model to successfully match various aspects of system performance supports the contention that the bioenergetic modeling approach developed here can provide reliable estimates of salmonid growth and feed requirements for a variety of food compositions, rations, and temperatures. This capability, along with knowledge of the effectiveness of phosphorus removal equipment, forms the basis of a practical operational and management tool. An example of model utility is presented that analyzes the PRSFH phosphorus discharge and provides insights into why permit violations occurred in 2009 but not in 2010. The model demonstrates how to avoid food waste caused by over feeding, lower the food conversion ratio, and evaluate the effectiveness of phosphorus removal treatment processes. A steady-state version of the model can be used by managers to establish production goals that avoid future violations of the phosphorus discharge limits. Statement of relevanceThe environmental effects of fish culture operations are important issues in many parts of the world. This paper describes the development and application of models designed to quantitatively analyze the relationships among fish production, by-product phosphorus loads, and the phosphorus concentration of the discharge following treatment. The ability of the model to successfully match various aspects of system performance supports the contention that the bioenergetic modeling approach developed here can provide reliable estimates of salmonid growth and feed requirements for a variety of food compositions, rations, and temperatures. This capability, along with knowledge of the effectiveness of phosphorus removal equipment, forms the basis of a practical operational and management tool. The model demonstrates how to avoid food waste caused by over feeding, lower the food conversion ratio, and evaluate the effectiveness of phosphorus removal treatment processes. A steady-state version of the model can be used by managers to establish production goals that avoid future violations of the phosphorus discharge limits.