The Big Skate!
by Stephanie Hansen
There is a fish in the bay that looks quite unusual. This fish is flat like a ray, but does not have a stinger. It is related to sharks and rays because it has five gill slits and cartilage for a skeleton instead of calcium bones. This is a skate, and not just any skate, the biggest of them all! The Big Skate usually grows to almost 6 feet (from wing tip to wing tip), weighing about 200 pounds! But the biggest Big Skate recorded was 7.9 feet long! The Big Skate is found in Pacific waters, that’s why we have found it in the San Francisco Bay. They can range in color from reddish brown, olive-brown to gray with small white spots or scattered dark blotches. If you look closely at a Big Skate, you may see false eye spots on its’ back. This is to act as decoys and confuse predators, like the broadnose sevengill shark. On the underside, you can see its’ gill slits and its’ Ampullae of Lorenzini, small jelly filled pores used to detect weak electric fields given off by their prey. The Ampullae of Lorenzini (pronounced amp-you-lay of lauren-zee-knee) also helps cartilaginous fish to find prey buried in the sand like worms, molluscs, crustaceans, and small benthic fish.
Skates are oviparous, meaning they lay eggs like birds, however their eggs are encased in a soft membrane called an egg capsule, or “mermaid’s purse”. Most skates have one embryo in each egg; Big Skates have been known to have up to seven embryos in one case! Big Skate egg cases are the largest of any skate, measuring between 9 and 12 inches long. Females deposit their eggs in pairs on sandy and muddy bottoms. This is perhaps why they like the San Francisco Bay, they too love our mud. After nine months, the young emerge measuring 7-9 inches. Juveniles have smooth skin, while the adults have small prickles on its dorsal surface and the underside of its snout. Females take 12-13 years to mature, while males only take 7-8 years. Off California’s cost Big Skates can live for 15 years, but in the British Columbia they have been found to live up to 26 years!