Relative abundance and size composition of red sea urchin, Strongylocentrotus franciscanus, populations along the Mendocino and Sonoma County coasts, 1989
Underwater surveys were conducted in the spring and summer of 1989, as part of a three year survey, to determine density and size composition of populations of the red sea urchin, Strongylocentrotus franciscanus, along the Mendocino and Sonoma County coasts at three different depth zones. The study was composed of two parts: i) a broad scale survey, consisting of 22 systematically chosen sites from Fort Ross to Mendocino and ii) a fine scale survey, consisting of seven sites in the vicinity of Fort Bragg. The fine scale sites were selected to represent different habitat types and levels of commercial exploitation. The sites included the Point Cabrillo Marine Reserve (PCMR) as a nonharvested control and the Caspar Closure Area, established in1989 in an effort to assess the effects of closure upon recovery of previously harvested areas.The mean density for all broad scale sites was 1.1 red urchins/m2 (SD 2.4). The 15-ft. depth zone yielded only 0.5/m2. No site in the broad scale survey had greater than 4.1 red urchins/m2. Spring fine scale harvested sites yielded 1.5 red urchins/m2 (SD 2.8) while the PCMR had 7.8/m2 (SD 7.3). Summer fine scale harvested sites increased to 1.7 and the PCMR declined to 5.4/m2. Abundance was variable; however, highest densities were generallyfound at the 35-ft. and 50-ft. depth zones.Bimodality in red urchin size frequency distributions, indicative of canopy grouping (smaller urchins beneath the spines or tests of larger urchins), was apparent at PCMR, but not at harvested fine scale or broad scale sites. Broad scale sites had a similar percentage of juveniles as harvested fine scale summer and spring sites, at 7.3, 8.3 and 12.9%, respectively. Harvested sites continued to show a low level of recruitment during this second year of study. (Document has 114 pages) (114pp.)
| Main Authors: | , , , |
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| Format: | monograph biblioteca |
| Language: | English |
| Published: |
California Department of Fish and Game, Marine Resources Division
1991
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| Subjects: | Management, Fisheries, Biology, Red sea urchin, Strongylocentrotus franciscanus, California, |
| Online Access: | http://hdl.handle.net/1834/18226 |
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| Summary: | Underwater surveys were conducted in the spring and summer of 1989, as part of a three year survey, to determine density and size composition of populations of the red sea urchin, Strongylocentrotus franciscanus, along the Mendocino and Sonoma County coasts at three different depth zones. The study was composed of two parts: i) a broad scale survey, consisting of 22 systematically chosen sites from Fort Ross to Mendocino and ii) a fine scale survey, consisting of seven sites in the vicinity of Fort Bragg. The fine scale sites were selected to represent different habitat types and levels of commercial exploitation. The sites included the Point Cabrillo Marine Reserve (PCMR) as a nonharvested control and the Caspar Closure Area, established in1989 in an effort to assess the effects of closure upon recovery of previously harvested areas.The mean density for all broad scale sites was 1.1 red urchins/m2 (SD 2.4). The 15-ft. depth zone yielded only 0.5/m2. No site in the broad scale survey had greater than 4.1 red urchins/m2. Spring fine scale harvested sites yielded 1.5 red urchins/m2 (SD 2.8) while the PCMR had 7.8/m2 (SD 7.3). Summer fine scale harvested sites increased to 1.7 and the PCMR declined to 5.4/m2. Abundance was variable; however, highest densities were generallyfound at the 35-ft. and 50-ft. depth zones.Bimodality in red urchin size frequency distributions, indicative of canopy grouping (smaller urchins beneath the spines or tests of larger urchins), was apparent at PCMR, but not at harvested fine scale or broad scale sites. Broad scale sites had a similar percentage of juveniles as harvested fine scale summer and spring sites, at 7.3, 8.3 and 12.9%, respectively. Harvested sites continued to show a low level of recruitment during this second year of study. (Document has 114 pages) (114pp.) |
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