Friday, March 2nd
Today was a wonderfully lemon-y day on the water for the RJD team and our friends from Miami Dade College. Captain Curt took us out in the beautiful R/V Endsley to a site in Everglades National Park called the middle grounds. We have often had great luck at this site before, catching blacktips, bull sharks and lemon sharks, but today we were in for a special treat: four female lemon sharks, the smallest of which was 242 centimeters—or just under eight feet! The largest was 8.3 feet, and estimated by the RJD team to tip the scales at around 350 lbs.
Though we might joke that lemon sharks take their names from their zesty flavor (not true) or sour disposition (not true), the real reason is probably that they are yellowish in color. The intensity of their color varies based on the habitat they are in—lighter and brighter in sand, darker and browner in mud or seagrass. Because of the muddy bottom in the area where we were fishing, none of our lemon sharks were very brightly colored. Luckily, there is another easy way to identify them: although most sharks have both a dorsal and a second dorsal fin along their back, in lemon sharks the second dorsal is nearly as large as the first.
Although lemon sharks can be found at this site on occasion at other times, we believe the sharks we saw today were here for a very special purpose: to give birth. The final, largest lemon caught today appeared to be heavily pregnant, and the shallow mangrove habitat found in Everglades National Park is the perfect place for baby lemon sharks (also called “neonate” lemon sharks) to begin their lives, as the shallow depth and protection offered by the mangroves can help them avoid becoming a snack for other predators.
Lemon sharks are viviparous, which means that they are attached inside the womb, drawing sustenance from their mother through a placenta and umbilical cord for 10-12 months before birth (similar to the way we mammals reproduce). Not all sharks reproduce in this way, but it is a very special and amazing adaptation rarely seen in fish. It means that when they are born, little lemon sharks are larger and stronger than other sorts of juvenile fish that hatch from eggs—but it also means that the mother lemon shark has invested much more in each individual pup (she carries between 4 and 17) than a fish that lays hundreds or thousands of eggs. The small number of pups they are able to carry is one of the reasons that it is so difficult for sharks to recover from overfishing.
Although the theme of the day was definitely “lemon,” they weren’t the only amazing animals we saw. We were also lucky enough to catch a 171 cm (5.6 foot) Blacktip Shark, who posed for a quick photo before heading back into the water. We even spotted a rarely seen bird—the beautiful Roseate Spoonbill (a relative of the Ibis, UMiami’s mascot) flying in the distance.
We caught some great sharks today, but there were even more that we didn’t catch—almost all of the bait we set out disappeared, although many of the sharks who snacked on it managed to avoid being hooked. Still, at the end of the day none of the team from RJD or our friends from Miami Dade College had anything to feel disappointed about: this was a truly amazing day of sharks!
-Catherine MacDonald, RJD Intern