Little Lost Tropical Fish Become Gulf Orphans on Cape Cod

Every summer, hundreds of tropical fish species ride the Gulf Stream from the Caribbean Sea to the Atlantic Ocean, and jumps off outside Cape Cod. A few weeks ago a rare Gulf Stream orphan, a Blue Angelfish, only two months old, sought refuge thousands of miles from home. It is the northernmost Angelfish recorded to date. We know our waters are warming, but what do new species' presence mean for us and our coastal ecosystems?

What is a Gulf Stream orphan?

25 October, 2024 – CAPE COD, MA – It was the first of three tropical fish over only a couple of early October weeks that oyster farmers Tim Silva and Danielle Orcutt would spot and try to rescue. A baby Blue Angelfish, only two centimeters long and a few months old, had surfed the Gulf Stream for thousands of miles from its home in the Caribbean Sea to the couple's oyster grant in Pleasant Bay, Orleans. Through the animal rescue center Wild Care of Cape Cod in Eastham the juvenile, which is the northernmost Blue Angelfish recorded, still northbound found its way to New England Aquarium where it will live out its life. A short while later the oyster farmers spotted another Blue Angelfish, same size, and a Spotfin Butterflyfish. This Angelfish did not survive but the Spotfin is thriving at the Cape Cod Museum of Natural History in Brewster. "It's eating like a champ," says Tyan Bassett, Animal Care Coordinator at the museum.

How will tropical fish impact our coasts?

These three tropicals, or Gulf Stream orphans, are among hundreds of its colorful kin wandering to the coast of New England every year. The phenomenon has been observed for over 120 years, but thanks to citizen science, Michael O'Neill, founder of the Gulf Stream Orphan Project, can monitor trends and changes in the tropicals' appearance likely responding to warming waters. He encourages people to report any unusual sightings to the portal iNaturalist where he collects the information for the GSOProject. "We think a lot about whether or not these fish could be indicators for ways in which our local ecosystems may be changing over time," says O'Neill. But climate change is not necessarily a cause for their presence, rather the Gulf Stream's natural process sweeping the fish north every year. "But that's part of the reason why I was motivated to try and gather more information about this," says O'Neill. " Because I think it's worth keeping an eye on as we move through time, because I think it's relatively safe to say that warmer water temperatures are going to benefit these fish so that their impact on native ecosystems here may become larger." O'Neill believes it is worth keeping tabs on the tropical species to eventually be able to see what it may mean for native species and the dynamics of our coastal ecosystems., 

Why Are Tropical Fish on Cape Cod?

Salt Pond in Eastham functions as what Owen Nichols, Director of Marine Fisheries Research Program at the Center For Coastal Studies, calls a live laboratory. Though the center is not specifically targeting tropicals, Nichols have noticed an increase in their presence. He explains how they manage to find their way to the Northeast. "This phenomenon is really interesting because we think that it's driven in part not just by the Gulf Stream itself, but by meanders and eddies and variability in the Gulf Stream. And the Gulf Stream will spit off these parcels
of warmer water that can make their way in closer to shore across the continental shelf," says Nichols. "When that happens, those parcels of warm water bring with them warmer water species from down south. So one of the next steps in this whole process is to really understand the mechanisms. It's fascinating to be able to see these species out here. It creates more questions than answers." One of the questions the phenomenon raises is how much climate change plays a role, but the scientists do not have evidence of that. "It's certainly an indicator to me of oceanographic variability in the sense that the Gulf Stream might be behaving differently from year to year," says Nichols.

What damage can invasive fish do?

The Gulf Stream orphans do not survive for long in Cape Cod's cold waters to be categorized as an invasive species, but as the temperatures are rising, others are starting to thrive. The Marine Fisheries Research Program, a partner to the GSOProject, has observed changes in certain migrating species' behavior. Black seabass and blue crabs are starting to "set up shop" here according to Nichols, with consequences for our ecosystems. "If you like to eat [black seabass,], that's a good sign, but they also eat a lot of baby lobsters. And so if you're a lobster fisherman, you may not be real happy to see black sea bass here," says Nichols. Blue crabs normally leave during the winter months, but now females lay eggs that go on to become full adults living out there entire lives here. "That tells us that we're starting to see more of a stable reproductive population here," says Nichols. "We want to know are these populations of fish kind of staying here? Are they stable?"

Could our ecosystems degrade?

"It's hard to say if the ecosystem is going to degrade. Certainly, I wouldn't say because the [tropical] fish are here, but I think sometimes the more of these fish that we see, it's a sign of an offshore situation that is changing," says Nichols. "And whether that's for the better or not, it's hard to say." The evidence of climate change on Cape Cod worries not least the fisheries, who are the first to be hit by warmer oceans. "We may not be concerned about the tropical species alone, but if those are moving, probably other species are moving too. And that can be a real negative thing. If you're a fisherman and you can only stay in one place, relatively speaking
and harvest a certain species of fish, then that species of fish also moves north," says Nichols.  "So I would argue that it's probably more an indicator of bigger picture changes. But as far as [tropicals] being here today, it's probably not an immediate negative impact to the water behind me, but it's a sign of other things that are happening offshore."