in the southeast, and north to 40°N latitude (they have historically been seen no farther north than the lower New York Harbor). They were not seen in many of the Great Lakes until the late 1800s and early 1900s, although they are suspected to be native to Lake Erie, reaching it after the last ice age. Gizzard shad typically live in lakes and reservoirs, although they can live in rivers and streams, and brackish waters. They reside in the limnetic zone, and can comprise up to 80% of fish biomass in certain lake systems. They prefer shallow lakes with muddy bottoms and relatively high turbidity. This may be due in part to their breeding preferences, but it probably arises from the fact that they have lower survival rates in clear waters and waters with high vegetative cover. Diet and feeding habits Gizzard shad are planktivorous in early life, feeding mainly on phytoplankton and zooplankton as larvae. Consumptive demand of young of year fish (including larvae) can be intense enough to cause collapses in the zooplankton community, which has far-reaching effects through the ecosystem of which they are a part. In midwestern USA reservoirs, where gizzard shad are often the most abundant fish (by biomass), they usually switch to diets dominated by sediment detritus during the first year of life, whereas in some natural lakes they may rely heavily on zooplankton throughout their lives. As zooplankton are a nutritionally superior food than detritus, if large zooplankton (e.g., Daphnia) are available, gizzard shad probably prefer to feed on this resource. However, in many reservoirs, large zooplankton are scarce so gizzard shad rely on detritus. Gizzard shad growth rates may be lower when they feed only on detritus (compared to zooplankton), and in reservoirs they may consume more zooplankton (and less detritus) when density of conspecifics is low and the abundance of large-bodied zooplankton is high. In such cases, Daphnia and other crustaceans make up a large portion of some gizzard shad diets. Gizzard shad feed mainly during the day, with minimal activity at night. They have been observed at night in Lake Mead, Arizona congregating in schools in very shallow water two to three feet deep during the fall. Reproduction The start of the spawning period is typically between mid-May and early June, and is triggered by rising water temperatures. The number of eggs per individual varies between populations, but typically it