It was 1984 when biologist Peter Ward discovered a new species of nautilus in the deep, cold waters of the Pacific Ocean. It was named Allonautilus scrobiculatus. Now, 31 years later with no other sightings, Ward has once again seen it.
The nautiluses are molluscs that are members of the cephalopod family, which is shared by the octopus, squid and cuttlefish. They are often considered living fossils because evidence of them in the fossil record dates back about 500 million years.
Nautiluses actually make up the nautilidae family. There are two genuses in the nautilidae family, which are nautilus and allonautilus. Allonautilus scrobiculatus is part of the allonautilus genus so calling it a nautilus can be slightly misleading but it is generally referred to as so anyway. The allonautilus genus it is a part of is very small with only two known members. There are distinct differences between the two genuses including differences in gill morphology and the male reproductive system.
Allonautilus scrobiculatus is characterized by a slimy, hairy layer covering its distinctive shell. It was found by using the ‘bait on a stick’ method. Small pieces of meat were suspended on stick and submerged to depths between 500 and 1300 feet deep, just above the sea floor. Activity around the stick was filmed for several hours and two different species of nautiluses were seen and one was Allonautilus scrobiculatus. Ward and his team were quite surprised to see it again after three decades without a sighting.
Also seen was a sunfish and all three seemed to be competing for the food on the end of the stick. A few individuals of various nautilus species were also captured and stored in cold water similar to the temperature of the water they normally inhabit. Small samples of tissue, shell and mucous were obtained and they were released.
Using the data they collected, the team examined the populations across the Pacific Ocean. The team found out that most of the populations were isolated from each other because they can only inhabit a small range of ocean temperatures.
“They swim just above the bottom of wherever they are. Just like submarines, they have ‘fail depths’ where they’ll die if they go too deep, and surface waters are so warm that they usually can’t go up there. Water about 2,600 feet deep is going to isolate them.” Said Ward.
This makes it difficult for nautiluses to reproduce and may lead to ‘founder populations’ where a new population is made from just a few individuals leading to lower genetic diversity.
Being a nautilus is becoming increasingly difficult. As ocean temperatures slowly rise due to global warming, the range in which they can survive is becoming smaller. Over fishing is also a problem. Nautilus numbers have been decreasing for some time because of their desirable shells.
In September, the US Fish and Wildlife Service will vote on whether to list them as a protected species. Doing so would limit harvesting of them and hopefully allow them to recover.