Mapping lobster habitat in the Northumberland Strait using multibeam echosounders to assess juvenile lobster conservation zone placement

Abstract

The Northumberland Strait, located in the southern Gulf of Saint Lawrence, is an important area for scallop and lobster fishing. To mitigate the negative ecological effects of fishing, marine management strategies in the form of scallop fishing buffer zones are in place, and informed through dive surveys and fishing data aim to protect juvenile lobster habitat. Current scallop fishing buffer zone locations (shoreline to 1km offshore) align with where hard bottom is expected to be. There are multibeam datasets covering this area, but our understanding of the benthic ecosystem composition and marine conservation strategies could be greatly improved by creating benthic habitat maps of the area using multibeam echosounder (MBES) technology. Using a combination of bathymetry and backscatter collected by MBES, and drop camera footage, substrate distribution maps and habitat suitability maps for adult lobster were created using Random Forest and Maximum Entropy modelling respectively. The sediment was classified into three substrate categories using a modified Folk 5 classification: mud to muddy sand and sand, mixed sediment, and rock & boulders. The placement of the scallop fishing buffer zones from a species conservation standpoint is discussed based on the modelled habitat suitability and distribution of bottom type. Patterns of habitat suitability for adult lobster were spatially compared against the various bottom types. The sediment distribution results showed that there was a higher proportion of rock & boulder and mixed sediment within the scallop fishing buffer zones than outside of the protected zones. From the observed higher proportion of rock & boulders and mixed sediment inside the buffer zones, it can be inferred that substrate distribution inside the buffer zones is suitable for adult lobster conservation. There is however suitable habitat outside of the conservation zones that could be further protected. The observed adult lobster habitat preference can then inform juvenile lobster juvenile lobster habitat preference from what is known about juvenile lobster and adult lobster behaviour. Increased understanding of the distribution of bottom type and of adult lobster habitat suitability will allow for more informed juvenile lobster conservation decisions in the Northumberland Strait based on relationships that have been observed in order studies to work towards meeting Canada’s 2030 marine conservation goals.