Title:
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Predicting the impact of towed fishing gears on emergent epifauna
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In the context of an ecosystem-based approach to the management of marine resources,
fisheries managers have to consider the effects of fishing impacts on seabed habitats to
achieve sustainable use of marine resources. Bottom fishing, using mobile gears such
as scallop dredges or otter trawls, impacts benthic habitats directly due to the need to
maintain the gear in close contact with the seabed to maximize catches of target
species. In this thesis, the loss of emergent epifaunal biomass due to fishing disturbance
was quantified at the scale of an entire fishery. The results showed how fishing and the
physical environment, i.e. substratum type and the overlying hydrodynamic regime,
interact to determine the biomass and size composition of the resident emergent
epifauna. A novel method was used to track the spatial movement of fishing vessels in
the study and the implications of using alternate methods of fishing effort estimation to
describe fishing impacts were analyzed. The results show that analytical methods (track
reconstruction, density of position records) and the grid cell resolution used for the
analysis can lead to the underestimation of fishing impact on epifaunal communities.
This novel technique was then applied to enable the determination of the recovery of
benthic communities of hard substrates. The recovery of species abundance, species
composition and functional group structure was estimated to take from 1 to 4 years, and
was significantly influenced by the prevailing hydrodynamic conditions. Finally, the
application of a novel approach to monitoring habitat distribution and status was
investigated. The technique utilized underwater imaging of a laser line applied to the
seabed that allows the calculation of a habitat complexity index. Details of the
implications of the various methods developed in this thesis and of the key findings to
the implementation of an ecosystem approach to fisheries management were integrated
in the general synthesis.
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