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Sago Pondweed (Potamogeton pectinatus L.):
A Literature Review

Economics


Beneficial

Waterfowl and Aquatic Bird Food

Jepson (1905) was perhaps the first to write in detail about the importance of sago as food for waterfowl. Many studies or observations since confirm the use of sago by both sexes of juvenile and adult waterfowl of many species in various parts of the world. McAtee (1917) termed sago "the best all round duck food in North America," and Martin et al. (1951) ranked the plant's food value to waterfowl as "the outstanding species in this outstanding genus."

All parts of sago are eaten by waterfowl (Appendix D). Pochards or diving ducks (Aythyini) and swans (Cygnini), and some species of geese (Anserini), are able to exploit foods in bottom sediments, and probably feed mostly on turions, whereas dabbling ducks (Anatini) and whistling or tree ducks (Dendrocygnini) likely consume mostly drupelets. Rhizome fragments or nearly whole plants often appear on the surface after being discarded by waterfowl that feed on turions. Much of this material is readily eaten by dabbling ducks and coots (Fulica spp.).

Sago consumption benefits waterfowl in other ways. Sago drupelets serve as a grinding media in waterfowl gizzards (Wetmore 1921), and the addition of green sago plants to the diet of penned mallards can reduce the toxic effects of lead pellets (Jordan and Bellrose 1951).

Evermann (1902), Jones (1940), Willi (1970), Borowiec (1975), Hurther (1979), Verhoeven (1980b), and several authors listed in Appendix D noted that coots have used sago extensively. Huge (90 km2) Lake Ichkeul in Tunisia has contained up to 20 km2 of sago beds that have wintered up to 200,000 birds, including 70,000 coots (Skinner and Smart 1984). Dense sago beds can support coot nests (Harrison 1962). Sperry (1940) found that sago was consumed by the long-billed dowitcher (Limnodromus scolopaceus).

It has been recommended that the public be made aware of the importance of sago to wildlife in cases where the plant is otherwise considered a nuisance (Weisser and Howard-Williams 1982).

Water Quality

Lush stands of sago can take up sufficient P from water to suppress phytoplankton blooms, usually considered objectionable (Vermaak et al. 1981). Oxygen release by sago benefits filter-feeding organisms that may be important maintainers of water quality, especially in wetlands where sediments are largely anaerobic (Stewart and Davies 1986).

The importance of pollution-tolerant plants, such as sago, as biofilters of domestic sewage was extensively reviewed by Pieczynska and Ozimek (1976) They concluded that such plants are of no special significance, except in slightly polluted environments where plants must be regularly harvested before decomposition in order to reduce excess nutrients in the water. Harvest of sago along with other macrophytes has also proven ineffective or even detrimental in attempts to control phytoplankton through nutrient reductions in the water column (Neel et al. 1973).

Whitton et al. (1981) recommended that sago (as the only angiosperm) and four and five species each of algae and bryophytes be used for monitoring heavy metal pollution in rivers.

Property Protection

Putschog (1973) credited protection of shores and dams to the wave-dampening action of sago.


Detrimental

Sago is considered a noxious weed in waters used for recreational purposes such as swimming and pleasure boating (Harrison 1962; Hiltibran 1964; Vermaak et al.1981). Besides physically obstructing such activities, sago can also serve as a substrate for nuisance algae at such sites (unpublished material, cited by Stewart and Davies 1986). Dunst and Nichols (1979) listed sago as one of the eight most common nuisance plants in Wisconsin lakes. The plant is considered a nuisance at religious bathing areas in India (Dutta and Gupta 1976) and provides suitable habitat for the intermediate host of the bilharzia disease parasite in Egyptian irrigation canals (Khattab and El-Charably 1986).

Sago is a notorious reducer of flows in irrigation ditches and waterways (Frank et al.1963; Yeo 1965; Newroth 1974; Devlin et al. 1972; Mehta and Sharma 1976; Robson 1976; Moreria and Ferreira 1986). Sago can also aggravate flooding and cause unacceptably low nighttime O2 minima in streams used to transport sewage effluent (Madsen et al. 1988). Dense carpets of sago and other submersed macrophytes are also said to limit movements of predator fishes, trap fish fry, and inhibit fishing (Titcomb 1923; Engel 1984). Masses of floating sago can also clog water intake bays at power plants (Peltier and Welch 1969).


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