California Halibut

California Halibut

Adapted from an Article by Naturalist Rosemary Flynn that appeared in the March 2007 edition of Tracks

The California halibut (Paralichthys californicus) is an important commercial fish that uses Upper Newport Bay as its spawning ground. Halibut and other fish such as turbot and sole are called flatfish because their bodies are flat and they have both eyes on the upper side, a unique adaptation to life on the seafloor. Halibut are not born flat, however. Rather, at a few months of age, the young go through a fascinating sequence of changes, taking on the adult form in a process believed to reflect the evolutionary development of the species.

A halibut begins life as a tiny egg about the size of a grain of sugar, just one of the several hundred thousands that can be produced by a female in a single spawning. Upon hatching, each larva remains temporarily nourished by the remnant yolk sack. Halibut begin feeding for themselves within a few days, when their jaws become functional and the yolk sac is depleted. At this time they still have eyes on opposite sides of their head like most fish. As they approach metamorphosis, however, one eye —usually the left, sometimes the right— begins to migrate over the top of the head to the same side of the head as the other, and the larva transitions to swimming on its side. When fully migrated, the eyes are able to move independently, so the fish can see in all directions as they lie at the bottom. As part of these changes, the halibut also takes on two-tone coloring, which serves as effective camouflage from prey and predators alike. Although the upper side can vary from a light brown to a more colorful speckled pattern, the lower side is always lighter in color. This coloration disguises a halibut from above (blending with the ocean floor), as well as from below (blending into the light from the sky). In general, halibut prefer a sandy bottom, although they can be found in areas with hard, muddy or gravel bottoms. Their numerous and sharp teeth, along with a large mouth and a high arch in the middle of their topside, make them easily identifiable from other flatfish that reside along the California coast.

California halibut are predators. Specifically they are ambush feeders that blend in with the bottom and wait for an unsuspecting sardine, anchovy, or other prey to get within striking difference. While they spend most of their time at the bottom, they do move up in the water column to feed. When in chase, California halibut have even been known to jump clear of the water to secure a meal. As a predator, the halibut is near the top of the marine food chain, serving as prey only to larger organisms such as seals, sharks, and, of course, people. A mature California halibut can range anywhere between 6–30 pounds, with some females (which are generally larger than males) as large as 60 pounds.

The rate at which California halibut larvae grow, and their survival success, depends a great deal on adequate habitat for spawning. Shallow coastal wetlands, particularly estuaries such as Upper Newport Bay, offer the warmer water temperatures and abundant food supply conducive to the spawning and development of halibut. Unfortunately, most of these coastal wetlands were lost to development in the 1900’s. Concurrently (between 1919 and 1970), commercial catch tonnage of California halibut declined from over 4.5 to less than 0.3 million pounds/year. While several factors (including overfishing) contributed to this decline, the loss and/or disruption of habitat is believed to be of most significance. Fortunately, in more recent years, California halibut catch tonnage has stabilized at over 1.0 million pounds per year, still less than 25% of 1919 levels, but significantly above the low of 1970.