cns news & features
A long-term study by California Fish & Game marine biologists
could place new restrictions on urchin diving in California
waters. But so far the study is not complete and no new
restrictions are planned.
The study looks at how juvenile sea urchins settle on the bottom. "We do dive surveys," said Fish & Game marine biologist Pete Kalvass, "where we count and measure sea urchins at different locations on an annual basis along the coast, but we can only see them with the naked eye down to about a half an inch in diameter."
In order to find out what happens at younger stages, Fish & Game has set up collections stations along the coast where juvenile urchins are collected and counted each week. The juveniles are collected just after the larva stage where they metamorphose into small urchins that would then normally settle to the bottom.
They are collected on scrub brushes that are suspended near the bottom.
"After fertilization," said Kalvass, "there is a 6 to 8 week larval period, then they metamorphose. They change into what looks like a sea urchin that then settles to the bottom and starts growing." Before this they float in the currents like plankton.
At the point that they settle on the scrub brushes they are tiny--about .5 millimeters or .02 inches.
Fish & Game is looking for patterns that can tell them something about the early life of urchins, such as how seasons influence settlement and whether there are differences between settlement in southern and northern California.
So far they have found that there are seasonal differences. Said Kalvass, "Settlement is stronger in spring and summer." That corresponds to the spawning period of the urchins, when gametes are released, so such a pattern would be expected.
A more elusive goal of the study has been to determine the source of larvae. Said Kalvass, "If we saw a pattern where the first waves of settlement occurred in the most northerly stations, and then through the season it progressed towards the south--towards southern California--then you might expect that most of the larvae is coming from the north and then moving by currents south."
So far, however, such a pattern has not been verified.
If such a pattern did exist, it could be good news for urchin divers, because it would mean that the replenishing stock comes from outside an area that is being harvested, and that depleting a stock does not destroy it in the long run. On the other hand, if replenishing comes from the stock itself, reducing the inventory could be harmful.
One thing that has been observed is that large settlement occurred during the 1993-1994 El Nino condition. But whether parent urchins were from the area or outside is unknown.
Said Kalvass, "The rates of replacement in northern California haven't been that good." If it is found that the size of stock in an area influences the replacement rate, then Fish & Game policy could change.
The largest urchin diving industry is in southern California, but in the late 80s the north exceeded the south. In 1988 30.4 million pounds of urchins were harvested from the north; now that number is down to about 4 million pounds. With the decline in the population, it takes more work to find legal size urchins, and so some have dropped out of the business or are going elsewhere to dive. And some southern California divers who used to come up north for part of the season no longer do so.
Until the late 80s, there was virtually no regulation of the industry. Then in 1988 the number of permits was limited and a minimum size was established. There are currently 550 permits, and a minimum size requirements of 3.5 inches in the north and 3.25 inches in the south. In addition, certain days, weeks, and months are closed.
(9/25/95)