Dive Dry with Dr. Bill

113: Grass Rockfish

On several occasions while diving off Casino Point I've encountered a fish that initially I couldn't identify, but assumed it was one of the rockfishes. I sent a few images to friends at Dr. Milton Love's UCSB fish lab and received a positive identification. It was a grass rockfish. I have encountered what appears to be the same individual at least four times in the last four years, all within the same general area in the park. If this is the only member of this species within the park, I feel a bit sorry for it. After all, who will it have to mate with? Then again, who will it have to ask it to weed the nest or defend it against much larger and more aggressive predators? Perhaps the solitary life isn't so bad after all.

Rockfish are members of a large fish family that includes the scorpionfish, boccacio, "rock cod," treefish, kelp rockfish and others. There are at least 49 different species (some sources report 70) in California waters, making this family the largest one in fresh or salt water here. The grass rockfish's specific name (rastrelliger) means "I bear a small rake." No, this isn't a reference to the tool its mate demands it use to weed the nest. Instead it is descriptive of the fish's small gill rakers. This species is green in color with black or brown mottling, and has heavy head spines for protection.

The grass rockfish is found from Oregon to central Baja California. It is most common in shallow coastal waters from the tidepools to a depth of 20 feet, but occasionally as deep as 150 feet. Habitat preferences include high relief rocky areas with plenty of seaweed, consistent with the locations in the Casino breakwater I see this one in. It usually is a PITA (pain in the ***) to dive and search for them due to the shallow depths they frequent, especially during periods of swell and surge.

Individuals may reach lengths of 22" and live as long as 13 years. According to Dr. Love, an expert on the rockfishes, their biology and natural history are not well known. It is believed they spawn during winter. Females ranging from 10" to 18" in length may produce from 80,000 to nearly 800,000 eggs. This tenfold increase in reproductive potential is an important reason that upper size limits should be considered for most fish species. Our current focus on taking the largest individuals means we eliminate the ones with the greatest potential to reproduce the species.

These fish tend to be sexually mature at an early age, half of them by four years (very precocious!). Actually, I was teasing about tending and defending nests. It made for good copy despite the scientific inaccuracy. The fertilized eggs and early larval stages actually drift with the plankton, perhaps as much as 300 miles off the California coast. When the young settle, they often frequent tidepools until they grow too large.

Grass rockfish have a diet I could survive on easily. Crabs, shrimp, fish and octopi are their preferences. I'll bet their cholesterol levels are better than mine though, since I'm also a sucker for pan dulce and other sweets. In turn, rockfishes are a popular food fish with an intense commercial and sport fishery. In the early fishery, they were sold dead as filets. However, a rapidly escalating number have been sold live to restaurants and live fish markets. Even the early residents appreciated their taste based on remains in Native American kitchen middens. Concerns have been raised about the population sizes of many of these species, and the California Department of Fish and Game (CDF&G) has had to close the fishery on several occasions to ensure its survival. Some species may already have declined below the population levels necessary for recovery.

Some reports say this species is one of the most common shallow water fishes in our state. Then why do I see only this one individual in the dive park? There are a number of mainland fish species that have not successfully colonized the offshore islands like Catalina. However, most of these fish lack a planktonic egg and larval stage that would allow them to disperse here easily. This is not true of the grass rockfish which has such a dispersal stage. Another mystery to add to my list. Perhaps I'll write a multi-million dollar grant to study this dilemma. Of course writing it is easy... getting it funded is another thing!

© 2004 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Slight color variations in grass rockfish in algae and on kelp;
grass rockfish resting (as they often do) with head on rock for a pillow.

This document maintained by Dr. Bill Bushing.
Material © 2004 Star Thrower Educational Multimedia