These deep-sea fish, ‘the ocean’s canaries in the coal mine,’ are feeling the

Shane Gross is a marine conservation photographer and co-founder of the Canadian Conservation Photographers Collective (CCPC).

As I carefully moved from rock to rock along the beach, the stench of death was putrid in the air.

It was 45 degrees, a new record for this part of Vancouver Island, and the heat of the day coincided with an extreme low tide. With every couple of steps, I found another dead crab, sea star or fish. In between, hundreds of barnacles were starting to rot. I took pictures, but none did the scene justice. “So,” I thought to myself, defeatedly. “This is climate change.”

A billion animals died of heat exposure that week in June 2021, according to Christopher Harley, a professor at the University of British Columbia.

Among the dead fish were plainfin midshipman, a curious little fish I’d planned to photograph that day, long before I knew a record heat dome was coming. I brought a special probe lens that would allow me to see into their dark nests, which they build under rocks in the intertidal zone, where ocean meets land.

As humans stress the ocean with climate change, acidification, overfishing, plastic and other pollutants, the amount of prey available to midshipman will likely decrease and lead to a population decline, according to Dr. Sigal Balshine, a professor and director of the Aquatic Behavioural Ecology Laboratory at McMaster University. For scientists, studying the midshipman is a unique opportunity to discover the secrets of the deep sea.

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What’s interesting about plainfin midshipman? Where should I begin? This is a venomous, deep-sea species that can emit their own light, and swims all the way up to the shore each spring to spawn. Males dig out the sediment under flat rocks, preparing their nests and then sing to attract females.

Yes, the fish sing. To us the singing sounds more like a low hum which has, historically, irritated and confused people living on houseboats – but to a female midshipman a good song is irresistible. She will choose her mate based largely on his singing prowess and lay her eggs in the nest he built. Once her eggs are laid, the singer (a.k.a. guarder) male has a chance to fertilize the eggs.

But there is a twist. A second type of male may beat him to the punch. He is called a sneaker male and he will hang out at the edge of the nest looking like a female, (smaller and more slender than singer males). When the opportunity arises, a sneaker male will sneak in to fertilize the eggs before the guarder male does.

The guarder male will then take care of and defend the eggs for months until they are ready to swim off on their own. Guarder males may not realize many of the babies are not his own.

To us, finding out a fish sings is just another fun fact, but for the midshipman it’s survival. Our ocean is becoming a noisier place from marine vessels, sonar, deep-sea mining and resource extraction.

According to Mackenzie Woods, an MSc student at the University of Victoria, noise pollution potentially increases stress on midshipman, reducing their ability to care for their young, which can last for more than four months.

When it’s not breeding season, the fish can be found at great depths, deeper than 200-400 meters (650 – 1,300 feet) feeding on crabs, squid and krill.

“Midshipman can teach us so much about the deep sea without the expense and risk of physically going down there. They are the ocean’s canaries in the coal mine,” explained Dr. Balshine.

That’s because on a biochemical dietary level the fish bring some of the deep sea with them to the intertidal zone. What they bring up in their tissue gets passed on to the seals, sharks and even terrestrial animals such as eagles and herons who then feed the fish to their chicks.

Bald eagles in some areas depend heavily on the fish, as nesting time for the birds coincides with midshipman spawning time. How much contamination is transferred between species is an area currently studied by Dr. Balshine and her team.

When Dr. Balshine was asked about the 2021 heat dome she was cautious: “My guess is…