Habitat complexity influences the growth rate of juvenile gadiformes (gadus morhua, gadus ogac, urophysis tenuis) in newman sound, Newfoundland

• Main Author: Renkawitz, Mark D.
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2008
• Subjects: Greenland; Hake; atlantic cod; Gadus morhua; Gadus ogac; Greenland cod; Newfoundland
• Online Access: https://research.library.mun.ca/8814/; https://research.library.mun.ca/8814/1/Renkawitz_MarkD.pdf

In Newman Sound, Newfoundland, juvenile fish settle in shallow near-shore waters and are often associated with eelgrass beds of intermediate structural complexity. Although it is well established that structurally complex habitats such as eelgrass provide a refuge for juvenile fish from larger predatory fish, little is known about the potential energetic reward associated with use of these complex habitats. The settlement and close association of age 0 and 1 juvenile fish (approximately 60-100 mm SL) with eelgrass habitat may be the result of an active compromise in which optimal foraging habitat is sacrificed for habitats with increased shelter from predators. In this study, I quantified the relative growth rates of fishes associated with three adjacent habitats of differing structural complexity (barren seafloor, eelgrass, and water column) at five sites in Newman Sound, Newfoundland. Juvenile Greenland cod (Gadus ogac), Atlantic cod (G. morhua), and white hake (Urophysis tenuis) were placed in 1 m³ enclosures positioned over eelgrass, barren seafloor, and water column habitats in 2002 and 2003. Changes in standard fish length (mm SL) and volume (ml) were measured, and specific daily growth rates were determined and compared. Stomach contents were examined for habitat-related differences in the type and quantity of items consumed by enclosed fish at the termination of each experiment. Zooplankton samples were also collected biweekly during summer and fall in 2003 to determine if differences in prey concentration differed among the habitats. -- Annual and seasonal variations in growth rates were documented among habitats and between the species. In fall 2002, there was no statistical difference in specific growth rates (SGR) of Greenland cod among the habitats (barren = 0.068 % SL·day⁻¹, eelgrass = 0.074 % SL·day⁻¹, water column = 0.064 % SL·day⁻¹). SGR of Atlantic cod during winter from 2002 to 2003 did not differ significantly either (barren = 0.129 % SL·day⁻¹, eelgrass = 0.151 % SL·day⁻¹, deep water = 0.116 ...