Trawling the seafloor: the Northumberland Strait multi-species survey

By Natalie Asselin, Aquatic biologist

What lives on the seafloor in Northumberland Strait? Driving along the coast in New Brunswick, P.E.I. or Nova Scotia, it is clear this area is prime lobster habitat: it sustains a prosperous lobster fishery. But what other creatures swim or crawl along the depths of this waterway?

Since 2000, DFO scientists have used a multi-species survey to study the benthic (i.e. bottom) species found in Northumberland Strait. Each year, we sample about 100 locations throughout Northumberland Strait. The CCGS M. Perley, a Canadian Coast Guard research vessel, slowly tows a ‘trawl’, or large net. The trawl is weighted down so that it rolls along the bottom on large rubber wheels. As the trawl approaches, lobster, crab and fish swim up and are captured in the advancing net.

The catch is then hoisted aboard the vessel, where the science team swiftly sorts all the fish and invertebrates by species, doing its best to dodge the many lobster claws! We weigh everything and measure each fish, lobster and crab. We determine the sex of each lobster and crab and record whether or not the females have eggs.

This year, we captured lobster, rock crab and lady crab and many species of fish, including rainbow smelt, herring, sand lance, gaspereau (i.e. alewife), winter flounder, cunner, cod and winter skate. The catch also included jellyfish, sponges, sea anemones, molluscs, and seaweed! The survey helps us understand the diversity, distribution and density of benthic species in Northumberland Strait. For lobster, we can use the data on abundance, the size distribution and the sex-ratio (the ratio of males to females) to assess the population status in the area and monitor it for changes

The trawl survey is also used to collect samples for other research projects. In 2018, we collected a few lobster to examine their stomach contents and study their diet. We gathered sponges for scientists looking at their distribution in the Maritimes (for more information on sponges: Cold-water corals and sponge reefs). Data on winter skate help us better understand the distribution of this rare species (for more information on skates: Skate research).

The Northumberland Strait multi-species survey is a long-term monitoring project that provides valuable information on the state of this ecosystem and how it is changing over time. Do we find the same species in Northumberland Strait as we did in 2000? Do lobster distributions shift as their density increases or decreases? Are lobster bigger or smaller than they were in the past? Scientists are working to answer these questions with data from the Northumberland Strait multi-species survey.