Scuba diver Lloyd Bond thought the first time he saw a spotfin butterfly fish under a Nova Scotia wharf it would be a one-off.

"It's like, oh wow, I saw a butterfly fish and a seahorse in the same year," the Halifax resident said. "Then the following year I [saw] the same thing, and it was twice as many."

Bond, who has been scuba diving around Nova Scotia for 23 years, says in the last three years he's seen increasing numbers of not only butterfly fish and seahorses, but cornet fish, trigger fish, puffer fish and many other species rarely seen in Canadian waters.

The fish are often vibrantly coloured or have fluorescent markings, and some have ranges that include the Caribbean and Gulf of Mexico to Brazil.

Bond spotted this spotfin butterfly fish off the southern coast of Nova Scotia in the waters near Peggys Cove. (Submitted by Lloyd Bond)

"They're usually about the size of a quarter, a loonie, something like that. They're quite small," Bond said.

Bond doesn't just look at the fish; he photographs them during dives several times a week. He's had dozens of sightings in a single year at different locations around Halifax, including at Paddys Head wharf and Prospect wharf near Peggys Cove.

Bond lives in Halifax and has been diving off of Nova Scotia for 23 years. (Shaina Luck/CBC)

Canadian scientists agree ocean temperatures have increased over the last century due to climate change caused by humans. In its April 2019 report Canada's Changing Climate, Environment and Climate Change Canada said the Earth's oceans are projected to continue to warm over the coming century due to greenhouse gas emissions.

Measurements taken by Fisheries and Oceans Canada have shown ocean temperatures rising sharply starting in 2010, with some areas such as Georges Basin — a deep-water hole in the Gulf of Maine — having the warmest temperature on record for that region last July.

Bond photographed this scrawled filefish off the Paddys Head wharf in St. Margarets Bay, N.S., in 2016. (Submitted by Lloyd Bond)

So far in 2019, DFO measurements do not show abnormally high water temperatures in the area, but research scientists such as Dave Hebert of Fisheries and Oceans Canada are continuing to analyze how the warm waters of the Gulf Stream interact with the Arctic waters of the Labrador Current.

Hebert says pulses of warm, subtropical waters are pushing cold Arctic waters back.

"Those two waters mix together off of Nova Scotia. It's really [dependent on] how much warm water versus how much cold water," he said. "Think of how you mix hot and cold water in your bathtub.

"It's not like it just turned really warm — it's like a pulse comes on, and it sort of builds up over time."

Bond photographed this seahorse near Paddys Head wharf in 2018.

Hebert says the fish are being carried north on those warm water pulses.

"They're just being transported with the water. It's not like they're coming up here because it's warm; they're coming with the warm water," he said.

Dave Hebert, a research scientist with the Department of Fisheries and Oceans, says the tropical fish are coming north with the warm water. (CBC)

Marine ecologist Boris Worm, a professor at Dalhousie University in Halifax, says while the presence of the fish themselves isn't likely to disrupt ecosystems, there's the possibility that invasive predatory species and warm water diseases won't be far behind.

Cornet fish like the one seen here are unusual in Nova Scotian waters and more commonly seen in the southern United States, the Gulf of Mexico and the Caribbean Sea. (Submitted by Lloyd Bond)

"What has a larger impact is the warming water itself, which changes the composition of the phytoplankton and ... it really reorganizes the food web," he explained.

Warmer waters may also eventually bring in fresh diseases to Nova Scotia waters.

"It's a general rule of thumb that a warmer world is a sicker world," he said. "More micro-organisms can survive in warmer waters for longer periods of time."

He cites the collapse of the lobster fishery off southern Rhode Island that occurred after a shell disease "that probably came in with warmer waters."

For now, though, it's unlikely the tropical fish stand a chance at competing with the hardier local species.

"It definitely seems unnatural," Bond said. "You're really happy to see them but it's kind of bittersweet because you know they're going to die off the first cold snap. As soon as the water gets cold, usually a couple of days later everything's gone."

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