Weighing the Risks
Monday, March 5, 2018

Aquaculture now accounts for more than 50 per cent of the world’s fish used for food.

With the population expected to reach nine billion by 2050, aquaculture is expected to play an even larger role in ensuring food security in the future.
But what are some of the issues created by an increasing reliance on farmed fish?

Some of Memorial’s experts are working hard to figure these issues out. The Department of Ocean Sciences has been working to identify the impacts of escaped hatchery fish and provide information to industry regulators, so they can better manage those risks.

Three components

The overall project, led by the department’s Dr. Ian Fleming, is broadly divided into three main components.

The first is being undertaken by Dr. Mark Abrahams, Memorial’s associate vice-president of research, pro tempore, and professor of ocean sciences and biology, and Mike Piersiak, a PhD candidate in ocean sciences.

The research team is investigating the probability of escaped hatchery fish surviving and getting to a spawning site.

“We want to know what sea cage aquaculture does to the marine environment, particularly the risk environment, because you’ve now made a small section of the ocean very predictable,” said Dr. Abrahams.

“We’ve seen from previous research that sea cages tend to concentrate a lot of marine life in the vicinity of the aquaculture sites. So, how many of these animals are going to be predators on salmon as they move through?”

Their current work has shown that these are, in fact, high-risk environments. They are now trying to determine how the wild and farm fish deal with them.
“Farm fish, when they escape, tend to stay in the general vicinity of the aquaculture site, because food has always come from that particular location,” Dr. Abrahams said.

“However, lots of predators are also there, so while they are waiting to be fed, they are food for others. We’re trying to quantify their survival rates, but also, what that is doing to the wild salmon population.”

Mr. Piersiak collects data using telemetry, or fish tagging, to track fish as they move through different aquaculture sites in the marine environment.

He also monitors fish using a mobile hydroacoustic platform that uses sound beams to paint a picture of what’s going on below the surface.

“You can get very fine scale pictures of fish schools and it allows us to better characterize the environment these fish are moving into and extrapolate out how well they’ll do in an environment that’s heavily influenced and altered by human activity,” he said.

“It’s a unique tool traditionally used for stock assessments. No one has really used it to answer questions like these.”

Early results have indicated that, in general, wild fish are not attracted to the sea cages and move straight through the area.

The hope, then, is that the risk environment created by the sea cages, in combination with the behaviour of the escaped and wild fish, may minimize the number of escaped fish that make it to a spawning site.

Documenting interbreeding

The second component of the research, led by Dr. Ian Bradbury, a Department of Fisheries and Oceans research scientist and adjunct professor in the Department of Ocean Sciences, together with post-doctoral fellow Dr. Brendan Wringe, develops genetic/genomic tools to identify and then document the successful breeding of escaped salmon in wild populations and determine the relative survival of hybrid offspring in nature.

“In other words, how common is hybridization and how quickly might natural selection drive the farmed genes out of the population?” said Dr. Fleming.

“A large escapement in 2013 on the South Coast of Newfoundland resulted in something close to 20,000 nearly mature fish escaping and entering rivers in the area. In sampling 18 of those rivers the following year, 17 had offspring that were either pure farmed offspring or were hybrids with wild fish. One year later, there was a decrease in those numbers, which may be a good sign suggesting they were being selected out through time, though the demographic consequences remain uncertain.”

This information is being used to develop models of how these populations may respond to escape events that will directly inform future management and mitigation efforts.

Consequences of hybridization

The final piece, undertaken by Dr. Fleming and Shahinur Islam, an ocean sciences PhD candidate, explores the consequences of interbreeding on trait expression and competitive interactions.

Mr. Islam has compared development and behavioural differences of farmed and wild fish, and their hybrid offspring, concentrating on wild populations from Garnish and Placentia Bay, and two farmed fish populations — one from the Saint John River and one of European origin.

“One proposal government has been presented with would introduce European farm fish into Placentia Bay,” said Dr. Fleming. “Those would be sterile fish, but sterility might not be 100 per cent and we wanted to know the consequences of hybridization between these fish.”

His team has made a series of farmed-wild fish crosses in the lab and are investigating their differences. So far, they’ve noted farmed groups have similar behaviour, likely a consequence of long-term domestication. They tend to be more aggressive, bolder and less risk-averse in their activity. Hybrid fish behaviour is somewhere in the middle.

“Aggressive interaction in the wild can lead to the displacement of wild fish from their native environment, and differences in risk-taking behaviour and boldness could expose fish to greater predation,” said Dr. Fleming. “So, interbreeding could lead to a depression in the wild population.”

Future projects

They are also working with Dr. Matt Rise, another professor in the department, to investigate gene expression in the early fry stage to see if there are differences in farmed and wild fish and their hybrids. In collaboration with assistant professor Dr. Javier Santander, this team is also about to begin investigating whether the fish differ in their susceptibility to disease.

The knowledge from the data being collected can help industry regulators with planning and design of sites, including where cages should be placed and in what density, and how to minimize impacts if, and when, escapes do happen.

“The industry has been very forward-looking and have been our willing partners on this research,” said Dr. Abrahams.

“It shows they are in it for the long term. They want it to be a sustainable practice and recognize this is a legitimate risk associated with the practice and are working with us to find solutions.”