Did you know that there are sharks able to learn to push a button to get food? Captured lemon sharks in Mote Marine Laboratory in Sarasota, Florida did that.

Lemonshark (2)” by Albert kokOwn work. Licensed under CC BY-SA 3.0 via Wikimedia Commons

Lemon sharks live in shallow subtropical waters in large groups. They are nocturnal and use electroreceptors to find fish, but also benefit from pack hunting. They live usually up to 20 years and grow up to 10 feet in length.

It seems that they travel long distances to mate, but return again to their own nursing sites to breed. Female lemon sharks reach sexual maturity around 16 years of age and can give birth to 7 to 10 pubs every two years.

Lemon sharks could be studied pretty well both in the wild, for instance in bays at Bimini Islands in the western Bahamas, and in the laboratory. That brought forth surprising results, like the button-pushing mentioned above. Or it was found out that, despite having to work 9% harder to breathe than by swimming, healthy adult Lemon Sharks use to lie quietly on the bottom for extended periods of time, propped up on their pectoral fins. Being no bottom-dwellers, they have to actively pump water over their gills. It can be hypothesized that this behavior is due to social reasons.

Humans hunt lemon sharks and regard their meat as a delicacy, ignoring that lemon sharks, as top predators, accumulate large amounts of toxins like DDT, PCB and methyl mercury in their bodies and their meat.  The latter is known to cross both the blood–brain barrier and across the placenta, resulting in allowable daily portions of shark meat (I have this number only for Spiny dogfish-meat, who is not even a top predator) of 10 g – for an adult of 70 kg. Pregnant women or children should refrain from eating shark meat altogether.

Preferring the same shallow subtropical waters as lemon sharks, humans tend to destroy their habitat and nursing sites. The studied population at Bimini Islands may disappear altogether – for a golf resort.

Sources: hereand here