Draft:Tropical Strays

A stray Red Goatfish (Mullus auratus) caught in New Jersey, far outside its native range, by Zakqary Roy.

Tropical Strays, also known as "Gulf Stream Orphans" or simply "strays" colloquially, are marine creatures which have been displaced as juveniles, larvae, or even eggs by the Gulf Stream. These underdeveloped creatures, which can include fishes, shrimps, crabs, nudibranchs, and much more, then grow up on the shores of the Northeastern United States and Nova Scotia, where the summer temperatures allow them to survive. When late fall occurs in these areas and the ocean temperature drops, strays slowly becoming less and less active, until they inevitably die.

Displacement

Tropical strays can originate from a variety of locations in Central - North America, but the main binding factor is that the Gulf Stream must have a presence in the area. Many marine animals spawn, releasing clutches of eggs and sperm into open water, where they will drift until hatching or until finding a surface to cling to, depending on species. In this drifting time, eggs are particularly susceptible to currents, as they have no method of fighting the pull of even a light current. This is part of these fish's reproductive strategy, to spread out their young and give a higher chance that some find suitable nursery grounds and grow to adulthood.

However, sometimes these eggs will drift into a powerful current, such as the Gulf Stream, which will rapidly and uncontrollably send them shooting northwards into the Atlantic Ocean. Newly hatched animals, such as larval fishes, can be caught by these same currents due to their poor swimming capabilities. In some species, particularly those adapted to a sedentary life on reefs, juveniles can even be weak enough swimmers to be carried away by these currents.

The Gulf Stream

Once the eggs, larvae, or juveniles are swept up by the Gulf Stream, they are carried north, many likely ending up in arctic waters where they will be unable to adapt to the lack of food and temperatures and die. However, the Gulf Stream is known to form spinoffs, essentially vortexes which shoot out the side of the main current and carry on until they make landfall. These spinoffs are particularly common in the Central Atlantic, where they frequently head west, directly towards the Eastern Coast of the United States. These spinoffs carry with them the orphaned animals, sending them to inshore habitats along the Northeastern coastline.

Once these animals arrive in whatever life stage, if conditions are suitable, they may continue their life history and begin to grow up. Tropicals strays have been documented hunting, showing prey avoidance, and a variety of other activities that would typically be done in their native habitats. They will grow up throughout the summer months, being a part of the ecosystem. Some tropical strays can even be so abundant, such as Spotfin Butterflyfish on Long Island, that they may represent an important prey species for native predators, which have an easy time picking off these poor-swimming juveniles.

Finally, when temperatures drop in late fall and early winter, the metabolism of these tropical waters-adapted animals slows down, until it reaches a point where the animal's body cannot sustain itself, and they die. Many tropical strays die from predation due to being unable to swim properly in waters colder than they are adapted to handle, and those that don't will die of starvation or shutdown of internal organs.

Relevance to Humans

Collecting tropical strays for aquaria is a common hobby for environmentally minded individuals in the Northeast. Seeing as these strays will perish in the long term if left alone, many collectors consider it "doing a good thing" to collect them and raise them in aquaria themselves or donate them to a local aquarium. Also, since these fish are not native, they are not regulated species in any of the areas they end up drifting to, making their collection legal without a permit. Selling them, however, would likely require a permit for the local authorities.

Others enjoy catching and documenting these fish for the novelty of seeing new species, especially so far outside their native range. Some species of deep-sea reef fish have only ever been documented as strays, never having been caught in their native deepwater reefs in the Caribbean, instead being found as strays in Long Island in incredibly rare circumstances. These opportunities for scientific discovery, as well as the simple thrill of not knowing what one can find in a given location on a given night, lead many individuals to hunt tropical strays as a hobby. This practice is particularly beloved by lifelisters, who view these fish as a rare chance to catch a new species which would normally not be found anywhere near them.

Records

While an exact list isn't publicly available at this moment, an iNaturalist project documents 79 species of tropical stray fishes through citizen science, while still missing obvious records which were documented prior to the creation of iNaturalist, or simply were sampled by individuals who don't use the website. In reality, the actual list of documented stray fishes is likely in exceedance of 150 species. This number is continuously rising, as every year brings unique conditions, and subtle changes in spawning and current timing can send an entirely different group of animals to the Northeast. Some years certain strays are abundant, and other years those same species are completely absent.

Documentation of invertebrate tropical strays, such as crabs and shrimps, is much worse, due to less interest from collectors and naturalists, as well as their naturally lower catch and identification rate, being smaller on average. Currently, there are ~50 documented invertebrate tropical strays, though the number that have actually occurred is likely far higher.

The Definition of a "Stray"

"Stray" as a term and concept, are entirely colloquial. No scientific paper has as of yet given a proper definition to the term. However, the generally agreed upon definition meets a few requirements:

1. The organism must have been swept north to colder climates by the Gulf of Mexico
2. The organism must have been a juvenile at the oldest by the time it was swept away

In addition, there are requirements that most people would agree upon, but leave room for some exceptions anyways, showcasing the lack of a good definition:

1. The organism must not join its reproductive population, instead dying when water temperatures decline*
2. The individuals which are brought in by the current must represent a relatively small percentage of the overall species' population**

*Some strong swimmers, such as groupers and jacks, are speculated to be able to make the journey south and rejoin their reproductive population but are still generally considered strays despite this.

**Some species, such as Atlantic Crevalle Jacks or Scamp Groupers, which show up in high abundance AND can make the return journey south to breed, raise questions as to whether they are strays or simply a subset of the population which follows a unique life history.