A unique group of castaways that made international headlines completed another move this winter – this time into the Oregon Coast Aquarium’s exhibits.
Yellowtail jacks, Seriola lalandi, some over a foot long, and a banded knifejaw, Oplegnathus fasciatus, were trapped inside the hold of a derelict boat hull when it was spotted by fishers southwest of Newport in April 2015.
Yellowtail jacks are found across the Pacific, but knifejaws are only native to the western side of that ocean, hinting that the fish may have originated from the Tōhoku tsunami that inundated Japan in 2011. Genetic testing later confirmed that the yellowtail jacks also originated from the western population.
Jim Burke of the Aquarium and John Chapman, an aquatic invasive species specialist at the Hatfield Marine Science Center, sprang into action and headed out on the Aquarium’s vessel, the Gracie Lynn, to assess what the hull might introduce if it hit the beach.
“Unlike oil spills or chemical leaks that gradually decline over years, decades or millennia, introduced species increase from a tiny initial numbers to massive populations that never go away. Some of the introductions that arrived in the last few decades are clearly very bad by anyone’s standards. Moreover, introductions of marine species around the world seem to be increasing exponentially,” Chapman said.
Authorities arranged for the vessel, destined for a dump on dry land, to be towed into Yaquina Bay, and for the Aquarium care for the fish. According to Chapman, this approach was much less risky than letting the hull crash on a nearby shore where everything on board could get away.
The origins of the boat were uncertain. Chapman’s colleague, Gayle Hansen, an algal taxonomist at the Hatfield Marine Science Center, devised a method to discover the hull’s origins.
“My collaborator in Japan (Takeaki Hanyuda of Kobe University) completed a survey of the haplotypes of Ulva australis/pertusa species in Japan several years earlier. He was able to use this data plus his sequences from the Seal Rock Debris boat alga that we sent him to determine that the alga and boat were from the Iwate Prefecture of the Tōhoku coast of Japan where the tsunami took place,” Hansen said.
With the vessel on dry land and the threat of exotic species contained, the Aquarium’s staff focused on caring for the animals that had crossed the sea to their shore.
The 20 jacks and knifejaw inside the hull were underweight, and struggling with parasites.
The Aquarium’s life support system cleans and sterilizes all water before it leaves the facility, eliminating any risk of introducing exotic invasive animals or medications to the Oregon coast. This infrastructure ensured that the parasites only threatened the already infected fishes.
Six jacks succumbed to infections before treatment eliminated the gill flukes that were ailing them. By early summer the yellowtail jacks and knifejaw had a clean bill of health, but were not quite ready for exhibit.
“We wanted strong feeding behavior, good body tone and to acclimate them to the mid-50 to mid-60 degree Fahrenheit water they would encounter on exhibit,” said Evonne Mochon-Collura, Assistant Curator of Fishes and Invertebrates at the Aquarium who oversaw their care.
Honing in on a food the fish would eat presented another challenge. At sea, the fish subsisted on small invertebrates that grew on the hull and occasionally washed into the live wells where they were trapped. The meager diet and cold waters of the North Pacific where they lived for 3-4 years are likely to have stunted their development.
“They could not open their jaws wide relative to their size, so I had to prepare tiny, bite-sized food for them,” Mochon-Collura said.
She started with krill, shrimp and a nutrient-packed gelatin aquarists call gel food diced to the diminutive 3.5 cm, or 1.5 inch, size the jacks could easily eat.
The food delivery method also required customization. “At first, they were afraid of what we threw in because they saw the person throwing it. We learned to stay low and gently pour food into their pool, or hide the motion of throwing food in the tank as best as possible,” Mochon-Collura said.
Once Aquarium staff refined a protocol tailored to the fishes’ unusual life experience, the fish started to feed aggressively and were soon ready to transition to exhibit.
The yellowtail jacks can now be spotted in the Open Sea exhibit in Passages of the Deep, better known as the shark tunnel, where they appear to be thriving among a diverse population of pelagic fish species.
The banded knifejaw is settling into the California Kelp Forest exhibit in the Aquarium’s Coastal Waters gallery, where it was joined by a member of its own species that was famously pulled up in a crab pot near Port Orford in February 2015.
Chapman and Hansen’s studies are funded through PICES and the Japanese Ministry of the Environment.