Every year, tens of thousands of giant spider crabs gather in Port Philip Bay near Melbourne to molt, shedding their old skin to grow. This process leaves them weak and vulnerable, making them easy prey for stingrays, which use a special organ to detect the crabs' electrical currents. The rays then suck the crabs into their mouths, often eating thousands in a single feeding frenzy. Despite their vulnerability, the crabs have no choice but to return to the bay each year to molt.
The spider crab population has been declining due to various threats, including overfishing by humans, who are not supposed to hunt them. Other predators, such as seagulls, seals, and dolphins, also feed on the crabs. The situation has become worse since a documentary by David Attenborough exposed the crabs' migration, leading to widespread hunting and poaching.
Conservation efforts are underway, including a petition to stop hunting spider crabs during their migration and to treat them with care.
Here are the key facts from the text:
1. In 1970, the bay by Philip was protected by sharks, allowing spider crabs to gather there once a year.
2. Over 50 years, more than 71% of the sharks in the bay have disappeared.
3. Tens of thousands of giant spider crabs gather in the bay near Melbourne every year.
4. The spider crabs gather in the bay to shed their old skin and grow new exoskeletons.
5. The new exoskeleton takes several days to harden, leaving the crabs weak and vulnerable.
6. Stingrays prey on the weak and vulnerable crabs during this time.
7. Stingrays use a special organ called the ampulla of Lorenzi to detect electrical currents from other animals.
8. This organ helps the stingrays detect the crabs without needing to see them.
9. Manta rays are the largest rays and can grow up to 7 meters in diameter.
10. Manta rays are known for their intelligence and have been observed using tools.
11. Some researchers claim that manta rays can recognize their own reflection.
12. Electric rays have special electrical organs that generate 50 to 220 volts.
13. The poisonous spike on a stingray's tail can be fatal to humans if it punctures the heart.
14. Steve Irwin, a naturalist, was killed by a stingray's spike in 2006.
15. Stingrays are not typically aggressive towards humans unless they feel threatened.
16. The number of stingray attacks is increasing, possibly due to an increase in their population.
17. Sharks have historically kept stingray populations in check, but their numbers have declined.
18. Spider crabs are preyed upon by various animals, including seagulls, seals, dolphins, and other crabs.
19. Humans are also a major threat to spider crab populations, with many people hunting them despite a limit of 30 crabs per person per day.
20. Spider crabs are not edible for humans, making the hunting pointless.
21. The migration of spider crabs was a secret until it was featured in a documentary by David Attenborough.
22. The documentary led to widespread knowledge of the migration, and the crabs began to disappear.
23. A petition has been started to urge people to stop hunting spider crabs during their migration.