Penobscot Bay Watch

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Juvenile cod may utilize the intertidal zone for feeding purposes although there is no mention of this in recent studies. Earlier, an underwater television camera mounted on a herding fence recorded 423 "young" Atlantic cod (no size given), and Atlantic tomcod (Microgadus tomcod), which were sometimes indistinguishable from cod, as well as six, 30-40 cm (age-3 to 4) cod moving up and down a beach, either with or against tidal current, during daytime between June and October in Passamaquoddy Bay, New Brunswick (Tyler 1971). Of eight fish species observed undertaking these movements, the cod/ tomcod combination ranked third, behind only winter flounder (Pseudopleuronectes amercianus) and Atlantic herring (Clupea harengus) in their use of the intertidal zone.

Diel Differences in Abundance
Keats (1990) found one- and two-year-olds 16 times more abundant at night than during the day while making SCUBA transects at a depth of 5-9 m MLW. Methven and Bajdik (1994) were able to seine age-1 cod throughout the year but only at night in a cove of Trinity Bay, Newfoundland, whereas age-1 were caught both day and night by Grant and Brown (1998a) in a different cove of the same embayment. An explanation for the difference in catch of yearling cod between the two studies may be related to sampling techniques. The first study employed a 9 m seine pulled from a maximum depth of 1.2 m (no bridle). The second utilized a 30 m seine deployed by small boat 50 m from shore and pulled by towropes thereby encircling age-1 cod inhabiting a slightly greater depth range.

Researchers studying young cod recognized that gear avoidance occurred during daylight, but avoidance was secondary to diel activity in explaining abundance differences between day and night catches for both age-0 and the older juveniles (Methven and Bajdik 1994; Gibson et al. 1996; Methven and Schneider 1998; Grant and Brown 1998b). Abundance of age-1 peaked in the shore zone from August-November and again in April-June period, but was much reduced in winter (temperature <0°C) indicating withdrawal to deeper habitat. The offshore movement by young cod was also reported in Passamaquoddy Bay, Bay of Fundy (MacDonald et al. 1984).

Juvenile Winter Habitat and Activity Br>Juveniles inhabit progressively deeper water and associate with coarser substratum as they grow and mature, especially in winter (Keats et al. 1987). Age-1-4 cod were observed at 18 to 150.m. from submersible vehicles during April (-1 °C at 25-75m), Placenta Bay, Newfoundland (Gregory and Anderson 1997; Gregory et al. 1997). They found that 80% of two-to four-year- olds were associated with rock, boulders, and high bathymetric relief (cliffs) and often maintained fidelity to such features including crevices in rocks. They exhibited significant increases in swimming speed with increasing distance from structure.

Yearling cod showed no such connection, 59% of those observed were primarily over gravel and low relief with the fish appearing to rely on cryptic patterns to remain undetected. Macroalgae was neither avoided or preferred by either group. Age-1 and ages 2-4 co-occurred laterally and vertically throughout the study area most abundantly at depths of 60-120 m. Juveniles did not appear to undertake a diel movement shoalward during the winter/ early spring season. However, onshore movements may be initiated during March and April after ice break-up and coincident with nearshore water temperature of ;~,-2-3°C. The same temperature prompts offshore movements in late autumn (Methven and Bajkik 1994).