Moses and Dugongs

The other day my SIL asked me a question about Exodus 35:7 :

4 Moses said to the whole Israelite community, "This is what the LORD has commanded: 5 From what you have, take an offering for the LORD. Everyone who is willing is to bring to the LORD an offering of gold, silver and bronze; 6 blue, purple and scarlet yarn and fine linen; goat hair; 7 ram skins dyed red and hides of sea cows [a] ; acacia wood; 8 olive oil for the light; spices for the anointing oil and for the fragrant incense; 9 and onyx stones and other gems to be mounted on
the ephod and breastpiece.

The question: sea cows?? What are sea cows and how did the Israelites get their hides? The "sea cows" that Exodus speaks of are actually called "dugongs". Wikipedia says: Dugongs (Dugong dugon) are the smallest members of the order Sirenia (which also includes the manatees and Steller's Sea Cow), with adults generally growing to less than 3 meters long. The dugongs are found in the Red Sea and the Persian Gulf.

Since Egypt is bordered on the east by the Red Sea, it makes sense that dugongs would have been hunted or traded for in Egypt, so the Israelites may have already had the dugong hides. However, it would have been possible for the Israelites to hunt for the dugongs as well. This Map shows their wilderness wanderings. Once Moses led the Israelites out of Egypt, they crossed the Red Sea (at the Bitter Lakes area which is actually north of the larger main part of the Red Sea) and then turned south-east to follow the Red Sea on the Sinai Peninsula all the way to Mt. Sinai at the tip of the peninsula where the Tabernacle was built.