Scientists who spent the summer studying monk seals in the Northwestern Hawaiian Islands rescued nine of the animals caught in fishnets and other marine debris. 

The National Oceanic and Atmospheric Administration’s monk seal research program leader Charles Littnan said Tuesday one seal was a female pup entangled in a 800-pound mess of buoys, fishing nets and clothes baskets off Kure Atoll. 

The rescues are among the work researchers do to protect the species, which is the most critically endangered marine mammal in U.S. waters.

There are only about 1,100 Hawaiian monk seals left in the world and the population is declining about 4 percent per year. Scientists say the species could disappear in 50 to 100 years if the trend isn’t reversed.