| Life history |
Diet |
Mainly prey on non-decapod crustaceans |
Consume both pelagic and benthic prey, but more selective than alewife |
Adults cannibalize juveniles in nearshore areas on their migration back to sea |
| Adults also feed on copepods and krill |
| Larger individuals (> 20 cm) feed on mollusks, |
Juveniles primarily feed on zooplankton |
At sea, adults feed on copepods, mysids, and small fish |
| cnidarians, and bony fish |
Adults also consume zooplankton, as well as small fishes, fish eggs, and small crustaceans |
| Growth |
Evidence of 114 – 127 mm of growth in their first year in the Chesapeake Bay estuary |
Adults grow up to 197 – 322 mm in fork length |
Juveniles migrate to sea when they reach 38 – 114 mm |
| Females are larger than males; 289 mm and 277 mm, respectively |
Shad are larger than alewife and blueback and reach up to |
| Adults are sexually dimorphic; females spend longer at sea and reach a larger average length of 284.3 mm, whereas males average 271.6 mm |
760 mm |
| Growth rates plateau after spawning, and there is little growth between spawning events |
Females are larger than males |
| Northern populations are larger than southern contingents |
| Maturation at sea takes 3 – 6 years |
Energetic trade-off between frequent spawning and at-sea growth (multiple spawners are smaller) |
Maturation at sea takes 2 – 6 years; males typically mature in 2 years, females mature in 3 – 4 years |
| Lower latitude populations are shorter lived and quicker to mature |
| Average VBGF growth parameters: |
| VBGF growth parameters: |
Maturation at sea takes 4 – 5 years for females and 3 – 4 years for males |
L ∞ = 481 mm |
| L ∞ = 291.67 mm (males) – 310.48 mm (females) |
K = 0.44 |
| VBGF growth parameters: |
t 0 = 0.32 |
| K = 0.4 (females) – 0.441 (males) |
L ∞ = 231.33 mm (males) – 259.85 mm (females) |
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| t 0 = 0.103 (females) – 0.142 (males) |
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K = 0.469 (females) – 0.590 (males) |
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t 0 = 0.283 (females) – 0.338 (0.338) |
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| Spawning |
Adults exhibit spawning site fidelity and return to their natal stream or pond using olfactory cues |
Adults return to their natal river to spawn |
Adults exhibit spawning site fidelity and return to their natal river to spawn; low levels (3%) of straying have been observed |
| Exhibit iteroparity and will spawn up to four times |
| Higher-latitude populations demonstrate more frequent iteroparity |
Northern populations are iteroparous and can spawn up to five to seven times, whereas the southern populations are semelparous |
| Gravimetric fecundity positively correlates with age and decreases with increasing latitude |
| Interannual returns are higher among males |
| Precede blueblack in spawning migrations of shared rivers |
Spawning season lengthens with increasing latitude |
Semelparity is observed only in St. Johns River, Florida, and Ogeechee River, Georgia |
| Spawning can take place in brackish water |
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| Return to spawn later in the spring than alewife |
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| Mortality |
Lower-latitude populations live 3 – 4 years; northern counterparts live up to 9 – 10 years |
Maximum age of an individual observed in sampling studies were 8 and 12 years old |
Can live up to 13 years |
| Natural mortality rates differ based on latitude due to reproductive styles; northern populations live longer |
| Predation is a primary cause of mortality |
Females live longer than males |
| Energy movement and nutrient input in the marine environment are understudied but likely comparable to the contributions in fresh water |
Males are more abundant in younger age classes |
Predation by sharks, several fish species, and marine mammals significantly contribute to adult mortality |
| Predation by fish, sea birds, and marine mammals is a leading cause of mortality in the marine environment |
| Adults commonly die during spawning migrations |
| Key driver of predator movement (i.e., Atlantic cod |
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| and other gadids) |
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| Behavior |
Migration |
Range from Carolina to Newfoundland |
Marine range from Florida to Nova Scotia |
Migrate from Florida to Newfoundland |
| Juveniles join large schools of similar-sized individuals after they leave their spawning river |
Some migratory contingents remain resident in estuaries near spawning rivers; some undertake offshore migrations |
Intraspecific schools of juveniles and postspawning adults overwinter in deep waters offshore Florida, the Mid-Atlantic Bight, and along the Scotian Shelf |
| Schooling with menhaden or blueback is common |
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Move northward and inshore in the spring and offshore and southward in the fall |
Summer aggregations consist of a mixed stock of contingents from multiple rivers |
Overwintering aggregations are heterogenous mixtures of populations from many rivers |
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Found along the Mid-Atlantic coastline in the winter and spring |
Move southward in the fall to aggregate offshore in deeper waters in overwintering sites in Mid-Atlantic Bight and along Scotian Shelf |
Spawning migrations occur when water temperatures are between 8 and 26 C |
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Movement is regulated by zooplankton productivity and by abiotic factors, such as temperature, tidal currents, salinity, and depth |
Southern populations begin northward spawning migrations in January, and northern populations begin spawning migrations progressively later into the spring as latitude increases |
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Migration follows temperature contours in northern limit of range and zooplankton availability |
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Marine temperatures> 14 C are avoided |
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Water temperatures 5 – 10 C cue spawning migrations |
Move to mid-depth, coastal waters in the spring |
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Migration to spawning rivers when water temperatures range 14 – 22 C |
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Spawning begins late March in the south and progressively later into July further north |
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Spawning begins later than blueback herring, in late April |
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Foraging |
Use a mixture of inshore and offshore foraging areas |
School as single-species aggregations or with alewife to optimize feeding |
Juveniles join large intraspecific feeding schools along the coast |
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Demonstrate diel feeding patterns following zooplankton |
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Feeding schools are mixed stock of several populations |
Undertake diel vertical migrations following zooplankton throughout water column |
Primarily feed in the evening |
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Summer foraging grounds include surface waters in the inner Bay of Fundy, the inner Gulf of St. Lawrence, and off Newfoundland and Labrador |
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Have diel vertical migrations following zooplankton |
Demonstrate active foraging and filter-feeding |
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Feeding migrations from North Carolina to Nova Scotia have been recorded |
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Use both particulate (during day) and filter-feeding (during night) strategies |
Majority of foraging occurs in the marine environment |
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Some populations utilize inshore embayments for feeding in the summer |
Adults demonstrate passive filter feeding and active foraging |
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Zooplankton productivity and foraging partially regulate movement at sea |
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Forage in nearshore habitat until water is too warm (>14 C) |
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