Proposal for a Habitat Area of Particular Concern for Juvenile Atlantic Cod (Gadus morhua) in the Nearshore Waters of the Gulf of Maine.
Prepared by: EFH Technical Team (Excerpted from the 1999 Habitat Annual Review Report)

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inversely related to the index of rugosity. As a result, higher densities of age-0 cod were found in cobble and rock reef habitats than in eelgrass. However, the rugosity index could not account for the complexity of surface area that eelgrass offered. Higher survival in sites of cobble and rock reef was attributed to increased shelter that the more structurally complex habitats afforded coupled with decreased predator efficiency (Keats et al. 1987; Lough et al. 1989; Tupper and Boutilier 1995b; Gotceitas et al. 1997; Grant and Brown 1998a and 1998b).

Tupper and Boutilier's (1995b) and Grant and Brown's (1998a) in situ studies confirmed earlier and subsequent laboratory experiments on substrate preference and predator efficiency. Clearly, the presence of conspecifics may influence the distribution and food intake of age-0 cod in the wild. Both age-0 and 1 cod preferred finer grained substrate in absence of a predator, but when in the presence of an age-3 conspecific, young-of-the-year and age-1 either avoided the predator or selected the coarser substrate (cobble vs. gravel) where they hid in interstitial spaces (Gotceitas and Brown 1993; Gotceitas et al. 1995; Fraser et al. 1996).

Age-0 avoided the yearling conspecific resulting in a significant increase in use of gravel and cobble confirming the level of habitat segregation noted in the wild (Fraser et al. 1996). Also, age-0 cod avoided kelp (Laminaria) except when exposed to an actively foraging predator and cobble was unavailable. In this situation, kelp significantly reduced predation risk (Gotceitas et al. 1995). Both field and laboratory studies indicate that the association with coarse substrates, when coupled with behavior patterns that reduce predation risk, give young cod competitive advantage in avoiding detection or capture.

Eelgrass Habitat and Abiotic Factors
The presence of eelgrass beds or meadows appears to be a very important factor influencing the distribution of age-0 cod throughout the Canadian maritime provinces (Tupper and Boutilier 1995a; Gotceitas et al. 1997; Grant and Brown 1998a, 1998b). Grant and Brown (1998b) noted that cod were more highly concentrated in eelgrass beds with >65% submersed canopy coverage. Gotceitas et al. (1997) captured age-0 cod almost exclusively in eelgrass beds of Trinity Bay, Newfoundland, where their usage by 0-group cod was consistent spatially and temporally.

The eelgrass sites most sheltered to natural physical disturbance produced the highest catches; lower catches occurred at the shallowest and least saline sites (10.4-19.5 ppt). Salinities were usually high (>25 ppt) at most Newfoundland study sites (Methven and Bajkik 1994). Age-0 tolerate much lower salinities as was observed in coastal waters of Wales and England where catches occurred from 20-31 ppt (Riley and Parnell 1984).

Post-settlement cod may respond to environmental gradients in addition to substrate structure and salinity. For example, high water clarity may be important for feeding (Home and Campana 1989). Strong tidal currents may be beneficial for concentrating food in seagrass beds (Tupper and Boutilier 1995b; Grant and Brown 1998a). Water temperatures coinciding with age-0 collections in St. Margaret's Bay, Nova Scotia, ranged between 4-9°C from May to July (Tupper and Boutilier 1995b) while July to September temperatures in age-0 habitat of Trinity Bay, Newfoundland, were 12-16°C with a year-round range of 1.7-17.0°C (Methven and Bajdik 1994). Water temperature might displace 0-group and yearlings to slightly deeper waters south of Newfoundland, however (Methven and Schneider 1998).

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