The spotted pearlfish is no more than five-and-a-half centimeters long, but feasts on plankton and hunts at night.
"It would surprise me if I don't find a pearlfish again," said Jørgen Berge, a marine biologist who made the discovery last week.
Researchers were participating in an expedition aboard the Helmer Hanssen and were trawling of about one hundred meters depth en route to Kongsfjorden when the small fish came up with the catch.
The spotted pearlfish is equipped with its own light that allows it to adapt to life in the depths and darkness, but the catch joins a long series of discoveries made in the sea around Svalbard during the polar night.
Marine research and coffee cups: Jørgen Berge, Geir Johnsen and Martin Ludviksen, NTNU, aboard Helmer Hanssen. FOTO: Øyvind Ødegård
Deepwater in the shallows
"Surprised? Yes, in a way because we have not seen one before.," said Berge, upon returning from his fifth cruise aboard the research vessel. "But on the other hand it is not surprising that we find such fish."
Instead, it is the setting that intrigues the biologist: the polar night and a fish commonly found in very deep waters coming up to hunt for prey with self-produced light.
"This is a fish with light-producing organs, since the dark time is in a way a kind of deep-sea environment in shallow waters," he said.
Along with his colleague Geir Johnsen, Berge called it a very exciting and interesting observation that a deepwater fish found its way to the surface under cover of darkness. In a separate article published this week in Svalbardposten, they detail their observations from the expedition.
"The Mueller's pearlside I
actually caught in a coffee cup"
Caught in a coffee cup
Another deepwater fish caught during the same cruise was a Mueller's pearlside. This species has been observed several times previously, but Berge said he sees a pattern.
"Absolutely," he said. "One of the things we've seen is that deepwater organisms that we otherwise find in the depths tend to come up. The Mueller's pearlside I actually caught in a coffee cup on the surface."
This Mueller's pearlsid was caught in a coffee cup. FOTO: Geir Johnsen
The fish was alight and lively and – as with the spotted pearlfish – measured, weighed and thoroughly documented as only scientists can.
The Mueller's pearlside is a member of the pearlfish family. It can be descend up to 1,500 meters in depth, but usually rises up into higher layers of water at night.
The spotted pearlfish are up to five-and-a-half centimeters long, and are equipped with shiny shells and light-producing organs on their heads and the abdomens. The fish primarily live 200 to 500 meters deep, but have been observed at depths of 2,400 meters.
The entire polar sea
The expedition at sea during the polar night in Svalbard has led the researchers from The University Centre in Svalbard, University in Tromsø, and the Norwegian University of Science and Technology to observe an environment and an ecosystem in a totally different mode than they expected. Another lesson from the research in Kongsfjorden is life throughout the entire polar sea changes its behavior when the light disappears, going to a 25-hour daily rhythm cycle because the moon is the only light source.
Now the scientists have further proof that deepwater species migrate up toward the water surface during the polar night in the furthest north seas on the globe. The researchers aren't ruling out finding more deep-sea species in shallow waters in the polar night.
"The polar night has many similarities with the deep sea, there is a dark habitat where we see species that we usually never see the shallows," Berge said. "I would not say that we expect that, but it would not surprise me if we do it."