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A. Mariculture

icon Mariculture, defined as the farming of marine species, is expanding in California and throughout the world as wild populations decline, harvest closures increase, and demand for seafood increases. Total acreage of mariculture sites has doubled in California since 1979 (CA State Lands Commission 1994; Figure 8). California growers are targeting the growing worldwide demand for mussels, particularly in Europe, where native beds have been contaminated (ibid). Abalone, and to a lesser extent, oysters and mussels, are the most important mariculture crops in California and in MBNMS (B. Hulbrook pers. comm). Most of the shoreline of the MBNMS outside Elkhorn Slough is inhospitable to oyster and mussel mariculture, which requires shallow areas with gentle flushing.

The commercial shellfish industry in Elkhorn Slough began in 1923 with eastern oysters, an introduced species. The industry thrived until increasing coliform levels originating from various sewage discharges and dairy wastes resulted in total closure of Elkhorn Slough oyster beds by 1967. Beds were later reopened, but operations were again hampered in 1985 when the Monterey County Health Department issued an advisory against eating shellfish from Elkhorn Slough. Despite available lease sites, current interest is low. Only one oyster mariculture lease site is active in Elkhorn Slough; this is the only oyster mariculture commercial operation in MBNMS (B. Hulbrook pers. comm.).

Four abalone mariculture operations are currently active between Monterey and Pillar Point. Abalone meat and shells are valuable, and interest in mariculture is growing as the wild harvest continues to decline (B. Hulbrook pers. comm.).

The potential impact of mariculture on MBNMS resources has not been investigated, but effects such as severe alteration of the benthos, alteration of nutrient flow, and introduction of disease have been documented elsewhere (Norse 1993). Because so few mariculture operations currently exist in the MBNMS, negative impacts to the Sanctuary are likely negligible, with the possible exception of highly localized impacts within the sites.

B. Kelp

(and see Kelp Forest and Rocky Subtidal section)

Commercial harvest of giant kelp in California began in 1911. Volume and area of kelp harvest is currently regulated by the Fish and Game Commission (J. Spratt pers. comm.). Kelp is harvested for algin, which is used as a binder, emulsifier, and molding material in a broad range of products, and as a food source in abalone aquaculture operations (Resources Agency 1995, CA State Lands Commission 1994).

About 100,000 tons of giant kelp are harvested per year in California, primarily by one San Diego-based company (Forster and Schiel 1985, Tarpley 1992, CA State Lands Commission 1994). Six other lessees take kelp for algin and for abalone feed, and another operator leases a bed for research purposes (CA State Lands Commission 1994). Kelp is now taken mainly within the five mile-long area between Point Sur and Pfeiffer Point (NOAA 1992), and outside the MBNMS at Imperial Beach near the U.S./Mexico border (Leet et al. 1992). The vast majority, about 97%, of the California harvest is from the southern California sites, i.e. outside the MBNMS (NOAA 1992).

The kelp harvest increased from 10,000 tons in the early 1930's to a high of 170,000 tons in the late 1970's. An El Niño event in the early 1980's decimated kelp beds, and harvest levels remain significantly lower than those of the late 1970's, mainly because the kelp beds off of Santa Barbara have not recovered (CA State Lands Commission 1994, Leet et al. 1992). The kelp harvest was valued at $4 million in 1991 and $3 million in 1992 (Resources Agency 1995), though in the mid-1980's, kelp harvesting supported an industry worth more than $40 million annually (Tarpley 1992). The State of California receives a royalty on these profits (CA State Lands Commission 1994). Pre-1980's revenue values are not readily available.

No significant negative impacts on the kelp forest community have been attributed to kelp harvesting.

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Section III. Commercial Fisheries
Reviewed: September 08, 2023
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