We present results of an international collaboration to survey American lobster Homarus americanus Milne-Edwards, 1837 nurseries in Atlantic Canada and the northeast United States from 2007 to 2009 under a standardized protocol involving two sampling methods, diver-based suction sampling and passive collectors. We surveyed young-of-year and older juveniles at 191 sampling sites over 39 sampling areas considerably expanding the known depth range and geographic limits of benthic recruitment. Young-of-year densities were strongly correlated in space with the abundance of older juveniles, signifying consistently strong settlement in the Gulf of Maine, lower Bay of Fundy, southwestern Nova Scotia and southern Gulf of St. Lawrence, and relatively weak settlement in southern New England, eastern coastal Nova Scotia and Newfoundland, a pattern consistent with commercial lobster harvests. Passive collectors elucidated bathymetric patterns of young-of-year recruitment in oceanographically contrasting regions. Although we observed young-of-year lobsters as deep as 80 m, they were most abundant above the thermocline in summer-stratified regions, such as the western Gulf of Maine and southern New England, and depth-wise differences were less extreme in thermally mixed waters of the eastern Gulf of MaineÁFundy region, a finding consistent with previous observations that postlarvae concentrate above the thermocline. Between the two samplers, we detected no sampling bias for young-of-year lobsters, although collectors may slightly underrepresent older juveniles entering from the surrounding sea bed. Finally, we found that interactions between juvenile lobsters and suspected predators or competitors in collectors, such as crabs and fishes, are weak and unlikely to bias collector results.
Development of mariculture in Canadian waters has outpaced the ability of regulators to adequately assess environmental impacts and coexistence with other resource users. In eastern Canada, suspended longline culture of blue mussels (Mytilus edulis) leads to depletion of seston and subsequent biodeposition of feces and pseudofeces. Based on the need to evaluate aquaculture effects over multiple farms, a model was developed to compare the rate of mussel egestion with the scale of culture and tidal flushing of particulate waste from estuarine waters. Egestion was calculated using a bioenergetic submodel, and tidal flushing was determined with a tidal prism method. A short-term field program of particle sensing and sediment trapping was undertaken in Tracadie Bay and Savage Harbour (Prince Edward Island) to examine model assumptions and for validation. A finite element model was used to verify tidal prism calculations. Expressing model output as sedimentation rate, predicted biodeposition in Tracadie Bay was less than that estimated from field results but within the range of estuary-wide variation. In Savage Harbour, the egestion model overestimated biodeposition, likely because culture density on leased areas was sparse. A ranking of sites based on susceptibility to culture impacts was devised for multiple culture sites.
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