While on our trip in southern Florida, we came across sharks on more than one occasion. There was however one species that we came across more often than any other, and it was the species that our group had the opportunity to have a hands-on experience with. In both our tagging lines and scuba trip, our group had observed and handled the nurse shark.
Photo credit to Dr. Z
Nurse sharks are a species that tends to live and hunt on the bottom of the ocean. Their coloring that usually ranges from a yellowish tan to dark brown reflects this as it helps camouflage the shark along the sea bottom. While the shark we caught on the tagging trip was smaller, these fish typically average around 7.5 to 8 ft long and over 200lbs. Some distinguishing morphological traits of the nurse shark are the barbels on either side of its mouth, small eyes and lack of a obvious lower lobe of the dorsal fin. These sharks are nocturnal and hunt at night, preferring to spend their daytime hidden in a crevasse or a cave. These sharks have also been observed behaving in group behavior, with as many as 40 individuals lying either close together or even sometimes on top of each other. When they are out hunting their diet consists of other bottom dwelling organisms such as crustaceans, mollusks, and rays. Nurse sharks are found all along Atlantic coastlines, meaning you can find them by us on the New Jersey coastlines as well.
Photo credit to Dr. Z
Nurse sharks are oviviparous meaning that their embryonic development occurs in an egg case while still in its mother's ovaries. Their reproduction occurs once every other year and the gestation period typically takes 5 to 6 months. A litter of around 25 young are born in late spring and early summer at around 11 inches in length. The mating 'ritual' is something that has been well documented in the Florida Keys. The male approaches the female lying near the bottom of the sea floor and bites its pectoral fins while attempting to push the female on its side in order to gain better access to the female's cloaca. Unfortunately, many males will try to mate with a single female, leading to females having many bite scars at the end of a season. this leads females to try to avoid males by swimming in very shallow water. The IUCN redlist lists Atlantic Nurse Shark populations as vulnerable with a decreasing trend, and the Pacific Nurse Shark as endangered with a decreasing trend.
Hi Chris! I am very intrigued by your post. When I read that nurse sharks are nocturnal and hunt at night, I found myself wondering why shark tagging typically occurs in broad daylight. I would be interested to read a study that goes over what time of day is most successful for shark tagging. The part you mentioned about females trying to avoid males mating with them reminds me of a National Geographic documentary I watched on the plane ride home from Florida. It is called "Maui Shark Mystery" and it is about how there are more tiger shark attacks in Maui than in other locations. In the end, their research was not finished, but it was leading towards results that showed it was females trying to get away from males mating with them, which provoked them and pushed them towards the Maui beaches.
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