In the late 1920s, 22 mule deer were brought to Catalina Island for hunting; by 1947, there were 2,500

Mule deer were introduced to California’s Santa Catalina Island and grew into a long-running ecological problem. Twenty-two animals were brought to the island between 1928 and 1932, and by 1947, the population was estimated at about 2,500. The deer were originally introduced as game animals. They were native to mainland Southern California but had not historically lived on the Channel Islands, and with no established population of large predators on Catalina, the introduced herd expanded rapidly. A later scientific study found that the deer were also affecting rare plants that evolved without large mammalian herbivores. The story eventually became a conservation problem involving hunting, fenced research plots and efforts to protect Catalina’s native vegetation.22 deer became thousands within two decadesA 2016 study published in Ecology and Evolution reports that 22 mule deer were introduced to Santa Catalina Island between 1928 and 1932. The animals came from mainland California, and by 1949, the population was estimated at roughly 2,000 deer. The paper also notes that more recent estimates had ranged from about 1,000 to 2,500 animals.The population had already become a concern by the 1940s, since historical accounts cited in a recent Catalina Island Conservancy assessment say the deer had no natural predators capable of controlling their numbers. A 1947 estimate put the herd at about 2,500. Reports from that period described deer entering gardens and landscaped areas in Avalon. The issue was browsing was putting pressure on vegetation across an island where many plants had developed without deer.The problem was especially serious for rare island plantsCatalina’s native vegetation had evolved under conditions that did not include large populations of browsing deer, and that difference became important as the herd spread across the island. The 2016 study focused on one species in particular: Crocanthemum greenei, more commonly known as island rush-rose. The plant is endemic to the Channel Islands and occurs on Catalina. Researchers wanted to determine whether browsing by introduced mule deer was affecting the plant's ability to grow and reproduce.Researchers used protected plots instead of simply comparing areas with different numbers of deer. Some island rush-rose plants grew inside fenced exclosures, where deer could not browse them, while others remained exposed. The researchers found that plants that were protected from deer browsing were larger and had greater seed-production success than plants exposed to deer. In the study, heavily browsed plants could fail to produce seeds, while non-browsed plants inside the exclosures produced seeds. That result gave researchers a direct way to connect deer browsing with a specific reproductive problem in an island-endemic plant, while it also showed why population control mattered beyond the number of deer seen across the island.Hunting became the first major attempt to control the herdOfficials and island managers were considering ways to reduce the population by the late 1940s. One proposal involved capturing the deer and moving them to the mainland, but that effort did not remove the herd: only 150 deer were trapped, and 110 survived capture and transportation, according to historical records summarized by the Catalina Island Conservancy. A hunting season began in 1949, with 477 deer taken that season, and the state had hoped the hunt would remove substantially more animals.The approach continued for decades, but it did not eliminate the population. Deer numbers fluctuated with rainfall, food availability and hunting pressure, and they remained established across Catalina while other introduced large mammals were eventually removed or greatly reduced. A 2022 population study by Paul Stapp, Emily Hamblen, Calvin Duncan and Julie King found that mule deer still persisted on Catalina and that population density varied substantially between years. The researchers estimated island-wide densities between 6.3 and 16.9 deer per square kilometer during the years examined.Catalina is now considering removal rather than population controlConservation managers were dealing with a different question by 2021: was maintaining a smaller deer herd enough to protect Catalina’s native ecosystem? The Catalina Island Conservancy has used fencing, hunting and other management measures, but deer have continued to browse native vegetation. The Conservancy says the animals are the last remaining invasive mammalian herbivore on Catalina after other introduced ungulates were removed or substantially reduced. In January 2026, the California Department of Fish and Wildlife granted a Restoration Management Permit for a broader Catalina Island restoration project. State documents say mule deer browsing has reduced native vegetation and affected rare plants endemic to the island. The agency also describes shifts in some habitats toward nonnative annual grasslands and other vegetation less preferred by deer.The California Department of Fish and Wildlife's 2026 project concurrence states that mule deer were historically absent from the Channel Islands and that their browsing has contributed to declines in native plant populations on Catalina. The current restoration plan calls for professional removal of the invasive deer rather than relying only on recreational hunting. The issue remains contested, with opponents arguing that alternatives such as sterilization or expanded hunting should receive greater consideration. Catalina's management problem is therefore no longer about establishing a game population, since it is about how to protect an island plant community that evolved without the animals now browsing through it.Catch the latest World News and Live updates. Download the TOI app.