ASSESSING BENTHIC ECOSYSTEM RECOVERY FOLLOWING HYDRAULIC DREDGING FOR ARCTIC SURFCLAM (MACTROMERIS POLYNYMA)
Date
2024-12-13
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
This study aims to characterize benthic ecosystems on Banquereau Bank, NS, and assess long-term recovery following hydraulic dredging for Arctic surfclam (Mactromeris polynyma). A combination of acoustic multibeam echosounder (MBES) data, seafloor imagery, sediment grab samples, and fisheries catch data were used to produce a surficial sediment map and a species distribution model for surfclam. These thematic maps informed the design of a survey to assess ecosystem recovery post-dredging. Hydraulic dredging, a method for harvesting infaunal bivalves, causes significant local disturbance to the benthic environment. Physical seafloor recovery was evaluated through acoustic sidescan sonar and MBES data, revealing spatially variable degrees of remnant dredge track visibility. Biological recovery was assessed using diversity indices and non-metric multidimensional scaling (NMDS) to compare communities at control and fished sites. Results showed recovery extent and rate were highly spatially variable, and influenced by both time since fishing and local environmental conditions.
Description
This study aims to characterize benthic habitats on Banquereau Bank, NS, and assess the long-term recovery of biotic and abiotic components of seafloor ecosystems following hydraulic clam dredging for Arctic surfclam (Mactromeris polynyma). Geospatial modelling techniques were applied to characterize the distribution of surfclam and sediment types across Banquereau. A combination of acoustic multibeam echosounder (MBES) data, seafloor imagery, sediment grab samples, and fisheries catch data were used to create fine-scale thematic maps of the bank. Object based image analysis (OBIA), and Maximum Entropy (MaxEnt) modeling approaches were used to produce a surficial sediment map of the Banquereau Bank and a species distribution model for Arctic surfclam. The resulting maps provide insights into the spatial distribution of suitable Arctic surfclam habitat, offering guidance for targeted fisheries management. This spatial data was used to design a post-fishing recovery survey to assess physical and biological recovery across various timeframes following hydraulic dredging. Hydraulic dredging is a specialized fishing practice used to harvest infaunal bivalves in soft sediments, creating high levels of disturbance affecting benthic faunal communities and physical characteristics of the seafloor. Physical recovery was evaluated through analysis of sidescan sonar and MBES bathymetric and backscatter data, which revealed spatially variable degrees of remnant dredge track visibility. Biological recovery was assessed using diversity indices and non-metric multidimensional scaling (NMDS) ordinations to compare community structure at control sites and those impacted by fishing at multiple replication areas across the bank. Results indicated that the extent and rate of ecological recovery was variable and influenced by both the time since fishing and local environmental conditions. While some sites exhibited significant shifts in benthic diversity or community structure, recovery patterns were ambiguous and highly spatially variable. This thesis provides valuable insights into the recovery potential of benthic ecosystems on Banquereau Bank, and the findings underscore the importance of incorporating fine-scale spatial data and long-term monitoring into ecosystem-based fisheries management.
Keywords
Seafloor Mapping, Fisheries Management, Benthic Ecology