Benthic Habitats and the Effects of Fishing

Symposium Abstract: Impacts of Scallop Dredging on Marine Bottom Complexity and Juvenile Fish Habitat

F. Hartog, P. Archambault, and L. Fortier

doi: https://doi.org/10.47886/9781888569605.ch93

Dredging for scallops is known to reduce habitat complexity by homogenizing the sediments structure and by the removal of epibenthic organisms. Large bivalves such as scallops and their shells provide secondary substrate and physical structure adding to the complexity of the bottom. A complex habitat may enhance survival and growth of juvenile fishes by providing refuges from predation, abundance of prey and shelters from water flow. The Magdalen Islands shelf, in the Gulf of Saint- Lawrence, supports a fishery for Giant scallops (Placopecten magelanicus) and is believed to be a nursery area for juvenile Atlantic cod (Gadus morhua). Four scallop beds are still fished while three have been closed to fishing for 4, 10 and 12 years. During the summer 2002, three locations closed to dredging will be compared to three dredged locations in order to detect fishing impacts on epifauna and fish habitat. Bottom complexity and epifauna diversity and species abundances will be assessed from photographic sampling. Demersal fishes associated with the bottom will be sampled with fine mesh experimental nets. A complexity index will integrate sediment features, biogenic structures and patchiness values. Hypotheses are that unfished locations will be more complex and that juvenile fish and emergent benthic species will be more diverse and abundant at these locations. Epifauna diversity, abundances and assemblages will also be compared from fish and unfished sites. Differences in epifauna and fish assemblages will be examined.