Growth model of the reared sea urchin Paracentrotus ... - SciViews

General introduction
intense fishing and, consequently, a rapid decline of the standing stock
(Allain 1971, 1972a; Le Gall 1990; Campbell & Harbo, 1991). In addition,
removing most adults from a site probably has a negative impact on the
survival of the remaining juveniles. The later could be more susceptible to
predation because they are no longer protected by the "spine canopy of
adults" (Tegner & Dayton, 1977).
An example of such a decline in landings is the Japanese fisheries
which produced 23 to 28,000 tons of whole live sea urchins per year from
1967 to 1982 (Hagen, 1996a). Landings dropped to 14,000 since 1991,
despite the establishment of hatcheries (to seed in the field) and of
artificial feeding of sea urchins in harvested areas (Saito, 1992). Chile and
the U.S.A. also produce less than before, and only Canada and Korea are
still increasing harvests (Fernandez, 1996) because the sea urchin fisheries
are more recent there. Average worldwide landings are still stable but are
obviously not sustainable in a near future. Aquaculture is a necessary
alternative in all countries with sea urchin fisheries.
b. Aquaculture potentials
Japan was the first country to address the issue of overexploitation, and
initiated stock enhancement programs very early (Saito, 1992; Hagen,
1996a). These techniques include habitat enhancement (artificial reefs),
artificial feeding, translocation and building of hatcheries that produce
several millions of seed a year that are transplanted to the field. For
instance, a single hatchery in Hokkaido produces 11 million juveniles per
year (Hagen, 1996a). Hatcheries may be a solution to ensure recruitment
where harvesting eliminates adults before they spawn, but good natural
habitats are required, like large tidal pools, to give enough protection to
juveniles released in the field (Saito, 1992, Hagen, 1996a).
Another way to enhance production is through gonad enhancement.
With an adequate artificial diet, it is possible to increase gonad size (de
Jong-Westman, 1995a; Spirlet, 1999; Spirlet et al, 2000), particularly with
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