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How Much Do California Halibut Move Around?





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Posted by DFG News Release on February 17, 2011 at 15:04:08:

Question: I have a question about the halibut out at San Clemente Island. Is it a self-contained population due to the long distance between the island and mainland? If so, is it harder for this island population to mix and propagate with the mainland coastal halibut? I understand that all fertilized fish eggs, larvae and fry drift with the sea currents, but wouldn't it be easy to overfish this one homegrown species of fish at San Clemente Island? (Steve)

Answer: California halibut do move inshore-offshore and along the coast to spawn. They also follow feed and favorable ocean conditions. Unfortunately, there is no good answer to your question regarding the fish at San Clemente Island, mostly because no data is available.

According to Department of Fish and Game (DFG) Associate Marine Biologist Travis Tanaka, more than 26,800 coastal mainland halibut were tagged as part of a halibut study performed in Southern California from 1992 to 1997. The study seemed to indicate that migration was related to the size of the fish, but this was not statistically proven. Most of the fish in the study (64 percent) were recaptured in the same region as the original capture. However, halibut larger than 550 millimeters (21.9 inches) in length traveled on average 29.5 kilometers (18.3 miles). At the same time, smaller halibut less than 550 millimeters averaged from 4.6 to 5.6 kilometers (2.9-3.5 miles). The greatest distance of travel was accomplished by a 559 millimeter (22 inch) halibut, which traveled 319 kilometers (198.2 miles). The lesson here is that fish do move, and in the case of this particular study, the movement was mostly to the north. (The results of this study can be found in DFG's scientific journal, California Fish and Game, vol. 85, no. 2.)

To assess the population size of San Clemente Island fish, someone would have to tag many of them, then catch them again and see where they ended up. Extensive tagging studies require money and time -- two resources that are in pretty short supply.

You are correct regarding fertilized halibut eggs. Halibut are broadcast spawners, meaning that when conditions are right, the males and females release their sperm and eggs into the water, and a meeting of the two by random chance takes care of the rest. Currents created during El Niņo events improve recruitment (survivability of individuals) because the fertilized eggs will stay closer to the shore where they can settle out. While young halibut may spend their first few years around San Clemente Island, they won't necessarily stay there. The same applies to juvenile halibut along the mainland coast. They will move.

To determine whether the halibut were being overfished, we would need to know the historical stock size and current stock size and conduct a formal assessment of the population. We don't have that information right now. However, a fishery scientist contracted by the DFG is currently completing a first-ever statewide stock assessment of California halibut. These assessments do not look at micro populations, but rather at the big picture.

For more halibut information, please see the Marine Region's State Finfish Management Project's webpage at www.dfg.ca.gov/marine/sfmp/index.asp.



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