Mustang is one of the most common breeds that has been released on Assateague. It's commonly stated that the Mustangs did not adapt to living on Assateague and died. However, many did survive and thrive on Assateague. They have had a significant impact on the breed that can still be seen today.

Multiple sources state that twenty Nevada Mustangs were purchased from the Bureau of Land Management in 1939 and set free on Assateague. Their survival rate is unknown.

Circuit Breaker in 1995

In 1977 a group of 38 BLM Mustangs were added to the herd to fill a void left when half of the herd had tested positive with Equine Infectious Anemia in 1975 and had to be euthanized. A 1978 article in Equus magazine stated that 32 mares and and 6 stallions were adopted from a BLM adoption center in Susanville, California. An article from the Virginia newspaper Radford News Journal reported that solid bays, blacks, and greys were chosen with the goal to bring the Chincoteague herd back to the original solid colors. The Assateague Ponies by Ronald Keiper states that most of these Mustangs didn't adapt to the new environment and died within the first year. The Los Angeles Times reporting from the 1979 Pony Penning wrote that there were 15 surviving Mustangs. One of the Mustangs that survived was the stallion Circuit Breaker, whose BLM brand reads that he was gathered in 1974.

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Pirate, aka Broken Jaw. Photo courtesy of Kathy O'Dette.

The famous stallion Pirate, aka Broken Jaw, was born to a bay Mustang mare that was one of the 32 Mustang mares introduced in 1977. She was in foal with him when brought to Assateague. Although he was full Mustang Broken Jaw was born on Assateague and lived there until his death in 1994. He had three known sons kept in the feral herd and two known daughters kept for the feral herd. He most famously sired the popular stallion Surfer Dude, confirmed via dated photos. Likely more of Broken Jaw's offspring were kept that are currently unrecorded.

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Another group of BLM Mustangs seems to have been introduced in 1981. A photo of an appaloosa Mustang mare and foal was contributed to The Colorful Chincoteague and the contributor said they were part of a group of new Mustangs. A September 1981 Sunday News article mentions the presence of appaloosas in the herd at that year's Pony Penning.

More Mustangs were introduced at some point in the 80's as there were two Mustang mares branded as having been gathered in 1982 in Montana. The mares survived in the feral herd into the 2000's and were the last Mustangs on Assateague. The last mare, Distant Traveler, died in 2004. The 1993 mare Mermaid was an Assateague born full Mustang. She was by Broken Jaw and out of 1982 gathered Mustang Unbridled's Passion. Mermaid is the dam of current feral stallion Effie's Papa Bear, aka Hoppy.

Unbridled's Passion, gathered in 1982

Distant Traveler, gathered in 1982

The Chincoteague Pony management plan from 2014 stated that "A wide variety of breeds such as Morgan, Welsh, Shetland, Arabian, and Mustangs were placed in the Chincoteague pony herd to increase genetic diversity and vigor among the present stock".

Read an examination of the BLM Mustangs on Chincoteague Pony History.

Unidentified Mustang mare, Screenshot from video by CLAP-E Productions

Unidentified Mustang in 1987, Photo courtesy of Kathy O'Dette.

Unidentified Mustang in 1993, Screenshot from Kratt's Creatures.