Alewife (alosa pseudoharengus) and Blueblack Herring (alosa aestivalis)
When ready to spawn, adults usually return to the same
water in which they were born, although some straying does occur. No one
knows exactly how they do this. Many scientists believe this homing instinct
is due to a special sensitivity to magnetic signals, polarized light and
unique characteristics of the natal stream.
The onset of spawning is related to water temperature
and length of day. Spawning season for alewife generally runs from March
through April. Blueback spawn from mid-April through late May.
Blueback herring prefer to spawn in swift water, while alewife favor slow
streams. Upon reaching the spawning ground, males circle a lone female.
As this mass of fish swirls around, the females releases her eggs and
the males release their sperm. After spawning, the adults swim back downstream
and return to the ocean.
The eggs hatch in three to seven days. Swift flowing
streams carry the larvae downstream. In Chesapeake Bay rivers, juveniles
range throughout tidal and freshwater areas during the spring but move
upstream during summer with the encroachment of saltier water. During
fall, the water the young move downstream, beginning their first seaward
migration. Juvenile river herring remain at sea until reaching sexual
maturity in 3 to 6 years.
Herring are food for estuarine and coastal predators,
including striped bass. Historically, the ample supply of river herring
supported a large fishery. Colonists stored salted herring in for winter
food and used the oily backbones of blueback herring as lamp wicks.
Herring are still harvested. They can be eaten fresh,
pickled or smoked. Herring are also harvested for their roe (eggs). The
majority of commercially harvested herring, however, usually ends up as
crab and eel bait, fish meal, or pet food.
Commercial landings of herring in the Bay peaked in 1908
at nearly 66 million pounds. By the early 1970s herring stocks dropped
dramatically and commercial harvests plummeted. From 1965-1985, harvests
of herring in Maryland and Virginia declined by at least 80%.
A variety of factors has contributed to this decline.
Between 1967 and 1977, foreign offshore fishing caught huge quantities
of herring as the fish tried to migrate.
Recent depletion of river herring has been attributed
to overfishing, pollution, and loss of spawning habitat. Spawning river
herring must run a gauntlet of fishermen equipped with nets and rods.
Pollution such as sediment runoff or acid rain can kill sensitive larval
fish. In addition, dams, road culverts, stream gauging stations, and debris
impede herring migration. These blockages have eliminated nearly 1,000
miles of potential spawning habitat in Chesapeake Bay tributaries.
The decline of river herring has had significant economic
and ecological impacts. Thriving herring runs offer sport and commercial
fishing opportunities. In addition, they are a valuable food for fish,
mammals, amphibians, and birds. Largemouth bass, white and yellow perch,
and other fish feed on juvenile herring. Adult herring are consumed by
a variety of birds.
Of all anadromous fish in the Chesapeake, herring have dropped most dramatically.
Only a few rivers support healthy populations.To restore herring and other
anadromous fish, historic migration paths and spawning grounds must be
improved and in some cases re-established.
Where possible, barriers such as dams, culverts, and
debris are removed. Construction of artificial passageways, like fish
ladders and lifts, help fish get over or around larger dams. Since 1989,
almost 200 miles of spawning habitat has been restored and more rivers
are slated for opening. Additional restoration efforts include restocking
depleted streams with herring transferred from other river systems.
The water quality of spawning and nursery habitat must
also improve. Citizens can help. Maintaining streamside forests or vegetative
buffers, and reducing the amount of nutrients applied to farms and yards,
are two simple ways to protect the water quality of spawning grounds.
Ultimately, habitat must be restored and protected to ensure abundant
spawning runs of river herring in the Chesapeake Bay watershed.