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The Peculiar Mola Mola


When you think of a fish, the Mola mola is probably not what you’d picture. This strange fish has a somewhat circular body that is flattened from side-to-side with no caudal (tail) fin and rudder-like top and bottom fins, which the fish flaps to swim. Mola molas are found in temperate (cool) and tropical waters worldwide and are commonly seen on Hornblower Whale Watching trips off San Diego. It is also called the ocean sunfish due to its habit of lying on its side at the water’s surface. This bizarre behavior may help a mola mola warm up after a deep dive or be done to invite seabirds to peck parasites off its skin. The mola mola also often basks near kelp paddies or in kelp beds to allow small fishes to pick off parasites.

The mola mola is the world’s heaviest bony fish, reaching a maximum weight of 5,000 pounds (2,250 kg)! It remarkably attains this great weight on a diet tons of jellyfish, but also occasionally eats small fishes, squid and other gelatinous creatures such as salps. Although mola mola are not endangered, they often eat floating plastic bags—mistaking them for jellyfish prey—which can choke or suffocate these fish. You can help mola molas by making sure your trash (including plastic bags) is always properly disposed of so that it can’t reach the sea. Even better, bring and use reusable bags whenever you are grocery shopping. By taking these simple steps, you can help keep the oceans healthy for mola molas and other ocean wildlife.

Invasion of the Jellyfish!

white-spotted jelly White-spotted Jellyfish have been recently spotted in San Diego Bay

While we may occasionally get visitors from Australia on Hornblower Whale Watch Cruises, recently another Australian visitor has been spotted floating and pulsing in San Diego Bay by the boats. These visitors are white-spotted jellyfish (Phylorrhiza punctata), which are native to Australia, and introduced many areas including Hawaii, the Caribbean, and the Gulf of Mexico. White-spotted jellyfish were first noticed in San Diego waters in the 1980s and were probably accidentally brought to our coast in the ballast tank or attached to the bottom of a ship. In September of 2015 and again this year, the warmer waters from El Niño may be linked to population explosions and increased sightings of this species.
Jellyfish are cnidarians —a group of aquatic, stinging animals that includes sea anemones, corals, box jellies, hydroids, and siphonophores (Portuguese man-o-wars and other colonial, gelatinous drifters.) Most jellyfish transform from a tiny planktonic larval stage to an attached anemone-like stage to a free-swimming life stage called a medusa. The medusa (or adult stage) is what we typically think of as a jellyfish and is the life stage of the white-spotted jellies in the bay.
Like most other jellies, white-spotted jellyfish have stinging cells in their tentacles that they use to capture zooplankton (tiny, drifting animals) and for defense against possible predators. Although these jellies sting, they are considered mildly venomous and not harmful to humans. However, they can harm habitats. Unintentionally introduced species like the white-spotted jellyfish are termed an “alien” or “invasive” species. The problem with invasive species is that they can out-compete native species that eat the same kinds of prey, especially during population explosions. While no harmful impact has been seen in San Diego, in the Gulf of Mexico, large swarms of these alien visitors have threatened some populations of native fishes and shrimp.

Dolphin stampede!

dolphin stampedeWhile the large baleen whales are often the highlight of whale watching cruises, their smaller cousins, dolphins, often steal the show. On most whale watching cruises, we encounter groups of 50 or more common dolphins. These playful and energetic dolphins often ride the bow and wake of the boat. Occasionally, we see a stampede of common dolphins porpoising at high speed in the same direction. Porpoising is a much more efficient and faster way for  dolphins to travel since the animals experience much less drag (resistance) in air than water. Why do dolphins stampede? They may be traveling towards a large ball of schooling fishes to feed. Often, the cause is a mystery. Whatever the cause, a dolphin stampede is always a thrilling experience!