Date of Award
Program or Major
Master of Science
Winsor H Watson, III
Aquaculture is one of the fastest growing food producing sectors of the world, with an annual compounding growth rate of 8.8% (since 1970). In spite of the rapid growth, scientific and public concerns have arisen about the sustainability and environmental impacts of the industry, including aquaculture's dependence on wild fish products, eutrophication from animal waste and uneaten food, and escapement of genetically altered farming stock. The use of behavioral studies may help refine commercial aquaculture by obtaining information to design operations that optimize growth, and feed utilization, while increasing production and animal well being. The goal of this study was to design and develop a system for monitoring fine-scale fish behavior in an offshore aquaculture net pen, using a combination of ultrasonic telemetry and underwater video. Additionally, 32 Atlantic cod, Gadus morhua, were studied, via ultrasonic telemetry, to provide a preliminary analysis of activity rhythms, cage utilization, and feeding behavior within a net pen.
The first chapter provides a detailed description of a self-contained data collection system designed to study cod at a scale previously unavailable. Ultrasonic telemetry was used to monitor individual cod while a video system monitored group dynamics. A preliminary evaluation of the telemetry system documented high signal retention capable of logging fish positions every two seconds. Laboratory studies showed no influence of transmitter implantation on swimming speed, behavior or feeding. Additionally, our data documented that sampling rates over 10 seconds per location caused significant error in calculations of activity.
The second chapter provided an analysis of cod movement, daily activity rhythms, behavior, swimming speeds and cage use. Individual cod behavior remained independent of conspecifics and consisted primarily of "milling" behavior. Cod exhibited clear diurnal rhythms, with activity highest during daytime hours. Analysis of cage utilization documented inefficient use of the net pen; with individual space use limited to small overlapping areas within the bottom half of the net pen. Additionally, operational stresses were documented to elicit dramatic changes in behavior.
The third chapter used feeding behavior, along with stomach content analysis, to assess feeding efficiency. Aggressive feeding behavior was displayed in 42.7 +/- 4.6% of cod daily, while 25.8 +/- 3.7% of cod displayed no interest in feeding during a feeding cycle. Additionally, 31.5 +/- 4.5% of cod displayed an intermediate feeding behavior whereby fish moved into the feeding area but did not make vertical movements toward the feed source. Stomach content analysis revealed that 77.6 +/- 14.1% of cod stomachs contained recently consumed pellets. The combination of stomach content and ultrasonic telemetry data results suggests cod displayed multiple feeding strategies: aggressive, non-aggressive and none feeding, or scavenging.
Rillahan, Christopher B., "The behavior of Atlantic cod, Gadus morhua, in an offshore net pen" (2008). Master's Theses and Capstones. 429.