Tropical fish appearing more frequently in Nova Scotian waters, scientists say

Scientists are seeing tropical fish in Nova Scotia with more frequency, and their arrival is prompting concerns about what their presence could mean for local species down the road.

Last fall, DFO scientists doing research near Taylor Head Provincial Park off Nova Scotia’s Eastern Shore came across a long, skinny fish with a large snout. It turned out to be a cornetfish, which usually resides in the warm waters of the Caribbean.

Other tropical fish found during the expeditions included the spotfin butterflyfish.

“It’s not necessarily that they’re completely new, but we’re probably getting them in higher frequency,” said DFO scientist Ryan Stanley.

Boris Worm, a professor of marine biology at Dalhousie University in Halifax, said many of the small, juvenile fish like the ones found by DFO come here because of warmer waters moving north or after storms.

“If it’s warm enough here, they’ll survive,” said Worm. “They may even grow and do their thing, but unfortunately, most of them will die in the winter because it is still too cold for them. But that could change in the future.”

However, he said other tropical species could be coming here willingly, looking for food and following warm currents.

Worm said the movement of tropical and subtropical species to Atlantic water could also provide a food source for local species.

Worm said he learned last summer from a fisherman about a fish called menhaden being caught off Nova Scotia. The small, forage fish is an important food for things like whales, seabirds and seals.

“This could be an opportunity for the ecosystem to even aid with the recovery of some of these larger predators that have been suffering in the past,” said Worm.

The cornetfish is not considered an invasive species because it has not established itself here and caused damage to native ecosystems, said Worm.

But cornetfish is related to and closely resembles the bluespotted cornetfish, a known invasive species from the Indo-Pacific.

“They’re really good at finding their ways into dense seagrass meadows and eating a lot of the small fish species,” said Worm.

Stanley said tropical fish species could also end up transporting parasites here.

All of these different scenarios mean it’s important to monitor what’s happening in the ocean.

“We can track when these things are coming in, potentially the influences of these warm-water fish species and we’re telling a story of change through time,” said Stanley.

eDNA helping track tropical species

One of the ways scientists can track what’s happening is through something called environmental DNA, which tests for trace amounts of genetic material shed by passing fish. This helps reveal what’s in the water.

Stanley said testing in 2019 revealed the presence of spotfin butterflyfish and triggerfish, but they were never observed by scientists.

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