In the past, we used to see lots of Bat Rays, Myliobatis californica, in Lake Merritt, which is a mixed salt- and freshwater estuary connected to San Francisco Bay. Kieran and I even once extracted a flat, plate-like tooth, used for crushing shellfish, from a dead ray on the lake’s shore.
But we hadn’t seen Bat Rays in the lake for at least a year, after a die off during a low oxygen crisis in the lake. Although concerned people have, over the years, set up aerating fountains to help control oxygen levels in Lake Merritt (the fountains are also aesthetically pleasing, and are illuminated at night), the fountains don’t run all the time, so oxygen levels vary, sometimes plunging to very low levels that kill creatures living at the bottom, like rays.
It seemed for a while as though we’d lost all our Bat Rays. But today we saw five small ones on the north side of the lake, near the Kid Kingdom playground. Kieran, being the science teacher he is, promptly dragged a group of kids and parents over from the playground to show them the rays and tell all about them.