Kieran and I examined a dead Bat Ray (Myliobatis californicus) on the south shore of Lake Merritt last week. Bat Rays are a type of stingray that live in shallow coastal waters, bays and estuaries. We’ve heard from the park rangers that several pairs of Bat Rays live in Lake Merritt, which is technically not a lake, but rather a mixed salt and fresh water estuary. It’s too bad that our first sight of such a magnificent creature had to be a decomposing corpse. But seeing a dead Bat Ray’s better than no Bat Ray at all!
Unlike the other people walking along the lake shore, we didn’t just stand and stare and take a few smartphone photographs. Kieran and I got on our plastic dishwashing gloves and got down in the shallow water to flip the creature over and study it carefully. Though the tail had been partly amputated, we were able to find the stump of the stinger at its base.
The ray’s mouth was filled with curious, flat teeth, used for crushing shellfish and crabs, which make up most of its diet. We extracted one of the teeth and brought it home — it was held in by no fewer than eighteen “roots” like the tines of a comb. This ray measured about a meter across the wingtips.
The Lake Merritt Institute, to whom we sent our photos, told us the ray had probably died during the previous week’s heavy rainstorms. Falling rain causes Lake Merritt to stratify into layers of saline and fresh water, and there’s not enough oxygen in the lowest layers for the rays to survive. This problem is exacerbated by the closing of the flood gates that link the lake to San Francisco Bay, which happens sometimes during big storms.
We’re hoping to see a live Bat Ray someday. But for now, this was a unique opportunity to get to know more about these interesting creatures.