Every year, tens of thousands of giant spider crabs gather in Port Phillip Bay, near Melbourne, to molt and shed their old skin. During this time, they are vulnerable to predators, particularly stingrays, which use their special organ called the ampullae of Lorenzini to detect the crabs' electric currents. The stingrays feed on the crabs, and sometimes only a few hundred crabs survive the molting process. Other predators, such as seagulls, seals, dolphins, and even other spider crabs, also prey on the vulnerable crabs. Humans are also a major threat, as they catch the crabs despite a limit of 30 crabs per person per day. The crabs are actually inedible for humans, and their removal affects the food source of other animals. The spider crab migration was once a secret known only to locals and scuba divers, but after being featured in a documentary, their numbers began to decline. A petition has been formed to urge people to stop catching spider crabs during migration and to treat them with care.
Here are the key facts from the text:
1. In 1970, Port Phillip Bay was under the protection of sharks.
2. Over 50 years, more than 71% of sharks have disappeared from Port Phillip Bay.
3. Giant spider crabs gather in Port Phillip Bay near Melbourne every year to molt.
4. The crabs shed their old skin to grow, but the new exoskeleton takes several days to harden.
5. After molting, the crabs are weak and vulnerable to predators.
6. Stingrays prey on the molting crabs, sucking them into their mouths like spaghetti.
7. Stingrays use a special organ called the ampullae of Lorenzini to detect tiny electric currents from other animals.
8. The ampullae of Lorenzini are like extra nostrils that help detect changes in the electric field.
9. Manta rays are the largest stingrays, growing up to 23 feet in diameter.
10. Manta rays are known for their intelligence and can recognize their reflection.
11. Some stingrays have learned to use tools to extract food from under rocks.
12. Stingrays have a venomous barb on their tail that can be deadly to humans.
13. Steve Irwin, a famous naturalist, was killed by a stingray's venomous barb.
14. Stingrays are not typically aggressive towards humans unless they feel threatened.
15. The number of stingray attacks is growing due to an increase in their population.
16. Sharks have historically suppressed the stingray population by hunting them.
17. With the decline of sharks, the stingray population has increased.
18. Spider crabs are preyed upon by various animals, including stingrays, seagulls, seals, dolphins, and other spider crabs.
19. Amur starfish are an invasive species that has been introduced to Port Phillip Bay and prey on spider crabs.
20. Humans are the primary threat to spider crabs, with a limit of 30 crabs per human per day, but this rule is often not followed.
21. Spider crabs are inedible for humans, and their destruction affects the food source of other animals.
22. The migration of spider crabs was once a secret known only to Melbourne and avid scuba divers.
23. The documentary "Blue Planet 2" by David Attenborough exposed the crab migration to the world, leading to increased exploitation.
24. A petition has been formed to stop catching spider crabs during migration and to treat them with care.