EURASIAN WATERMILFOIL AS A FISHERY MANAGEMENT TOOL

Eurasian watermilfoil (Myriophyllum spicatum L.) poses new challenges to fishery managers as it continues to spread and multiply in North Am erican waters. Some of its effects can be detrimental to fisheries. Wh en dense, the plant obstructs swimming space of pelagic fishes, shelte rs too many juvenile fishes, and disrupts foraging movements of pisciv ores. In replacing native plants that harbor a diverse array of invert ebrates, watermilfoil creates food shortages for fishes. By blocking s unlight penetration and water movements, it depletes dissolved oxygen inshore that can cause fish kills when shoots decay in autumn. Therefo re, lakes with healthy native plants should be left undisturbed and gu arded against infestations of Eurasian watermilfoil. But the same plan t in other lakes can improve fish production, especially in waters too turbid to support native plant growth. By increasing the surface area for invertebrate colonization, Eurasian watermilfoil expands the food base for benthivores and protects emerging year classes from piscivor es. Through seasonal growth and senescence, it creates a dynamic litto ral zone where openings in plant beds appear and disappear, cruising l anes for piscivores come and go, and edge effect for crappies expands and shrinks.