American shad

DepthOften mid-column to lower during river migration, shifting with flow, temperature, turbidity, and daylight.

Moving waterMigratory adults travel through sustained river flow and pause in velocity transitions, current breaks, and staging water as conditions change.

LightSpawning activity is often strongest from dusk into darkness, but migration and angling encounters occur throughout the day depending on flow and turbidity.

Seasonal activityAdults enter rivers in spring; Massachusetts notes fish remain in fresh water until July. Juveniles rear in fresh water through the summer and emigrate in autumn as river temperature falls — Leggett and Whitney give a juvenile downstream migration trigger below 15.5°C.

Temperature-driven behaviourLeggett and Whitney found Atlantic coastal migration tracking the 13-18 C isotherms as those isotherms move north and south seasonally. Across the rivers they examined, peak upstream movement was recorded at 18.0 C in one large western river (90% of runs between 15.5 and 19.5 C over 32 years) and averaged 19.5 C in a large northeastern river, with maximum movements near 14-15 C in lower-river and estuary-transition settings. Reported spawning optimum is 16-20 C; NC Wildlife Resources Commission gives spawning at 11-15 C and the Northwest Power and Conservation Council 15.5-18.3 C. The catalog band of 50-65 F (about 10-18 C) brackets the lower and middle of that range. Massachusetts describes shad as fluvial specialists in fresh water that tolerate warm water. River names are omitted here deliberately: migration timing is described, the waters it happens in are not.

Depth movementNorthwest Power and Conservation Council: eggs are most numerous near the bottom but occur at any depth during the spawning season; larvae occupy main channel, shoreline, slough and backwater habitat. Adult oceanic diel vertical migration follows prey.

Open waterOutside the spawning run, adults are pelagic and schooling. ASMFC describes primary offshore feeding grounds and three offshore wintering areas; the directed ocean fishery has been closed since 2005.

Spawning (conservation context)Anadromous spring spawner. ASMFC: males enter rivers first, followed by females, and spawning typically occurs at night or under overcast conditions. NC Wildlife Resources Commission gives spawning at 11–15°C with eggs hatching in 8–12 days. Reproductive strategy follows a latitudinal gradient: populations south of Cape Hatteras are semelparous, with females releasing up to 700,000 eggs and dying after spawning, while northern populations are iteroparous, producing around 300,000 eggs and surviving to spawn in several years. Spawning, the upstream migration itself, and any structure that constricts that migration are conservation context and are excluded from target guidance.

Adults filter larger zooplankton, chiefly copepods and mysids, through crowded gill rakers, and also take fish eggs and small fish (NC Wildlife Resources Commission, Northwest Power and Conservation Council). Massachusetts gives a wide variety of zooplankton, shrimp and small fishes at sea. The critical qualifier for this species: NC Wildlife Resources Commission states adults typically do not feed during the spawning run, and Massachusetts states they eat little in fresh water and only occasionally take small prey. Dietary capacity here is largely a marine-phase capacity and is not evidence of a current in-river forage event.

Feeding style

Mixed

Feeding zone

Pelagic

Diet capacity is not proof that a hatch or prey event is occurring. Observed current forage still comes from a user observation or Hatch Match. This matters more than usual for American shad, whose in-river adults are sourced as largely non-feeding.