Wild lobsters thrive near salmon farm

A long-term study conducted in a salmon aquaculture production site in a channel off Grand Manan Island, New Brunswick, Canada, indicated that fish farming had no negative impact on lobster abundance in the area.

“After eight years of counting [wild] lobsters in the survey areas, we saw no indications of a decrease in the lobster population, as lobster counts both within the lease and outside of the lease increased over time,” Tara Daggett told Aquaculture North America. Daggett is a Senior Marine Environmental Biologist at Sweeney International, a marine environmental management company based in New Brunswick.

“The salmon farm benthic monitoring indicated that the seafloor around the cage canopy maintained oxic conditions, which indicates that the farm was well-maintained with respect to organic inputs.”

         Daggett presented the study, Lobster (Homarus americanus) Abundance in Proximity to a Salmon Aquaculture Operation, at the Aquaculture Canada and Cold Harvest 2016 held in September in St John’s, Newfoundland.

“We compared the increase in lobster abundance observed during our study with lobster fisheries data. The catch per unit effort for the lobster fishing area, where the salmon farm is also located, increased during the same time period. This indicates that the lobster population in general increased,” she said. “Therefore, the increase in lobsters seen at the farm and the nearby area is likely a function of the overall increase in lobsters in the broader area.”

         From 2008 to 2015, according to the study abstract, diver transects and free-area spot-dives were used to measure the carapace length (CL) and determine the sex (including berried state) of each lobster encountered both inside and outside the lease boundaries.

Results indicate that greater than 50 percent of the lobsters fell within the 61-100 mm CL size range with no significant increase or decrease in the percent of females berried in or out of the lease area.

Using fisheries data, Daggett and her team compared the surveys to results in lobster fishing areas 38 and grid group 6, where catch per unit effort data indicated a 150- to153-percent increase in lobster biomass over the eight-year period.

A salmon farmer commissioned Sweeney to do the study of comparing lobster counts in the area of the lease before the site was constructed to lobster counts during and after production. The salmon farm benthic monitoring is a requirement of the New Brunswick government.

The requirement of five years of monitoring was extended by three more years when the salmon farmer requested a production increase.

The Department of Fisheries and Oceans (DFO) initiated the study design by choosing the locations for survey within the lease area and nearby the lease area.

“We compared the increase in lobster abundance observed during our study with lobster fisheries data. The catch per unit effort for the lobster fishing area where that salmon farm is located also increased during the same time period. This indicated that the lobster population in general increased,” she said. “Therefore, the increase in lobsters seen at the farm and the nearby area is likely a function of the overall increase in lobsters in the broader area.

Daggett said the most important finding of the study was that they saw no evidence of a negative impact of the farm on lobster numbers, which further indicates that salmon farms can coexist with the lobster population without negative impact.

While the study yielded positive findings, Daggett stressed that it was conducted on one farm only. “Further work on other farms in other areas would be required before any generalizations could be made with confidence,” she said.

— Ruby Gonzalez