| Summary: | Although the effects of mobile fishing gear on the habitat and productivity of the sea bottom has warranted attention for several centuries, recent concern has fueled an upsurge in research into the ecosystem effects of fishing over the last decade. This dissertation addresses the effects of mobile fishing gear disturbance on the benthic megafaunal productivity, scavenging amphipods and isopods, and benthic habitat-mediated survival of juvenile cod ( Gadus morhua). Using baited traps, scavenging amphipod and isopod populations were sampled at deep and shallow sites in disturbed and undisturbed areas on the northern part of Georges Bank and in the Great South Channel from 1996–1999. Multivariate exploratory statistics revealed the most important grouping variable for these populations was depth. Any long-term effects of disturbance associated with scallop dredging and fish trawling on this part of the benthic community was overshadowed by the influence of depth on the distribution of populations of these scavenging invertebrates. Laboratory experiments were conducted to assess the effects of habitat complexity on the survival of juvenile cod in the presence of an ambush predator, the sea raven (Hemitripterus americanus). Strike success was significantly lower in the intermediate complexity habitats versus the low and high complexity habitats. Some degree of habitat complexity confers a survival benefit on juvenile cod in the presence of this piscivorous ambush predator. The gravel pavement on the northern part of Georges Bank was sampled from 1994–2000 with a 1-m wide Naturalists' dredge to assess the effects of mobile fishing gear on benthic megafaunal production. Sidescan sonar surveys, fishing records, and photographic transects allowed us to identify and to sample disturbed and undisturbed areas. In addition, the closure of large parts of Georges Bank in late 1994 created recovering areas. At the shallow, recovering Site 17, production increased markedly from 1994 to 2000. Production remained comparatively static and low at the chronically disturbed Site 18 over the same sampling period. At the deep sites, production remained markedly lower at the disturbed Site 13 compared to the undisturbed Site 20 over the sampling period.
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