Evaluating the use of side scan sonar for improved detection and targeted retrieval of abandoned, lost, or otherwise discarded fishing gear

Abstract

Abandoned, lost, or otherwise discarded fishing gear (ALDFG) has surfaced as a significant conservation issue that continues to compromise the economic, social, and ecological aspects of the marine environment. To alleviate these concerns, methods of lost gear detection at the seabed can be applied to increase the precision of derelict gear retrieval and potentially improve the likelihood of success. Targeted in Canada's most productive American lobster (Homarus americanus) fishing area, a “hotspot” analysis was performed by mapping the density of reported lost gear at a 3 km × 3 km grid resolution. The hotspot analysis was used to target the collection of 27 side scan sonar (SSS) transects in Lobster Fishing Area (LFA) 34 over a 12-day survey period in Clark's Harbour, Nova Scotia, to evaluate the benefits of gear detection in large-scale retrieval missions. Following a comprehensive review of the SSS data post-processing, 114 potential ALDFG targets were visually identified, and only one item was confirmed retrieved. Despite this, a large volume of ALDFG was retrieved in areas where there was no SSS coverage based on fisher's local knowledge. The findings from this study demonstrate that retrieval of ALDFG based on SSS data can be difficult due to limitations of retrieval methods used, and that costs of SSS data acquisition may prohibit widescale use of this technology on an annual basis in spatially extensive fishing areas. Nonetheless, the use of SSS to identify ALDFG is recommended at smaller geographic scales in areas where the benthic environment may be sensitive. Although the use of fisher's local knowledge was not evaluated in this study, where the impacts of grappling for ALDFG are considered minimal, local knowledge can be extremely effective in the removal of lost fishing gear and other debris from the benthic environment.