Europeans first introduced common carp to North America in 1877 (mostly because European-Americans had devasted native fish stocks due to overharvesting and habitat destruction), and during the intervening century and a half they have become invasive across the continent. Conservationists spend millions annually in attempts to control their populations, and knowing when populations are at their lowest and where they’re most concentrated is critical. As for most species, carp populations are lowest in the winter, but finding these concentrations of carp when they’re the most concentrated in the winter can be tricky business.
As far back as 1977, researchers have been capturing, tagging, and using radio telemetry to follow carp movements during the fall and winter (source). In fact, this may be the first case of researchers using this technique to track down conspecifics. A carp collared in the late summer can lead researchers to these large mobile schools of carp in a lake ecosystem. These scout animals (a new term that is slowly replacing the antiquated “Judas goat” terminology) are essential conservation tools for locating reclusive or itinerant herd animals. In the 1977 study, the researchers gave the winter coordinates of the carp schools to fishermen who then harvested just over 100,000 pounds of carp (source). The table below shows the percent of carp populations that were culled by using scout carp to locate larger schools.
In stockyards, trained goats would lead goats to the slaughterhouse, much like Judas betrayed Jesus and lead the Romans to him. Similarly, in conservation, so-called Judas “goats,” animals captured and affixed with a transponder so researchers can follow the animal’s movements, have been used to locate populations of invasive species (like nutria in the Chesapeke Bay or pythons on the everglades). Noting the anti-Semitic undertones of the term (Judas was Jewish and Jews, by extension, have been associated with his deviousness and blamed for Jesus’s death), researchers working on a the python project co-authored a paper on finding a more neutral term (it is a truly excellent read: link). The researchers had been tipped off to the connection after an article on their work attracted the attention of a local rabbi who pointed out the anti-Semitic nature of the association between Judas and deception (see the American Jewish Committee’s glossary of anti-Semitic terms, themes, and memes link). The researchers also changed the name of their project.