The Science of Size Limits Regulations Are Protecting Abalone

March 26, 2007

Contact: Christina S. Johnson,, 858-822-5334

California Department of Fish & Game's current legal size limit for red abalones is optimal for protecting the most reproductively important adults, a new California Sea Grant study shows.

red abalone

Red abalone. Credit: Dave Rudie

According to "matrix modeling" of red abalone reproduction, abalones about 1 inch shorter than the legal size limit of 7 inches are the size class with the greatest influence on population growth. The current regulation, therefore, protects abalones that will most contribute to the next generation.

"In our matrix models of red abalone populations, the size class with the greatest influence on population growth was protected by the current size limit," said lead investigator Laura Rogers-Bennett of the California Department of Fish & Game, who received California Sea Grant funds to conduct the study. "These results suggest the current size limit regulation should stay where it is. It should not be shortened."

Rogers-Bennett and doctoral student Robert Leaf published their findings in the journal Ecological Applications. In that same paper, the authors suggested that, in light of the results, more should be done to educate novice red abalone divers on how to reduce incidental mortality of the critical sub-legal size class. They also suggested tightening enforcement of existing abalone laws prohibiting high grading, an illegal practice in which divers release small legal abalone for larger ones they find later.

Recreational abalone diving is now strictly regulated in California. Only one species is allowed to be fished, the red abalone, and only in Northern California, seasonally, without SCUBA and only in daytime. There is also a daily bag limit of three abalones, a yearly limit of 24, and as already mentioned, only abalones 7 inches or longer can be taken.

The main problem is that abalones are easily injured in the process of "popping" them from substrate, Rogers-Bennett said. Sub-legal abalones that must be released and reattached to substrate have high mortality rates.

This vulnerabilty stems from the fact that abalones have no blood-clotting mechanism. They are effectively hemophiliacs and are prone to lethal bleeding and/or deadly infections from seemingly minor injuries. Divers should learn to eye the legal size before popping one, as the best way to prevent harming reproductively important animals is to leave them alone in the first place. "They also should never high grade, toss back smaller abalone for larger ones they encounter," she said.

To increase public awareness about the issue, California Sea Grant is collaborating with the California Department of Fish & Game to publish an educational brochure for abalone divers, explaining basics of abalone biology, how it relates to current red abalone regulations and diver techniques for protecting important sub-legal adults.

In addition to performing analyses of red abalones, the scientists also performed similar calculations for white abalones, which are federally protected under the Endangered Species Act and subject to a recovery effort. In the matrix models of white abalones, it was the largest size class (between 5.5 inches and 6.9 inches) that was most important for population growth. This length range constitutes the largest size class for white abalone as white abalone are a smaller species than red abalone. The authors say that their findings suggest white abalone restoration efforts should focus on protecting adults not juveniles.