ResourcesIdentification of Important Habitats in Coastal New HampshireChapter 16. River HerringAlewives (Alosa pseudoharengus) and blueback herring (Alosa
aestivalis) are commonly termed "river herring". These are anadromous
clupeid fishes, ranging from the mid Atlantic to Nova Scotia. River herring
still are harvested recreationally and commercially during their spawning
runs, but are far less abundant than historically. Both species also are
important prey of larger fishes, birds, and marine mammals. They are treated
together because of similarities in appearance and overlap of biological
habits. Accordingly, the following model should be generally applicable
to both species within the Gulf of Maine. SPAWNING HABITAT Alewives and blueback herring spawn in tributaries of the Great Bay estuary
between April and July (Nelson 1981). Alewives spawn above the head of
tide in freshwater ponds, lakes, and slow-flowing rivers and streams (Bigelow
and Schroeder 1953, Scott and Scott 1988). Blueback herring spawn over
hard substrates in fast-flowing water of rivers and streams and over organic
material in slower-flowing rivers and streams (Pardue 1983). Alewives
spawn in tributary waters at water temperatures between 9 to 27 degrees
celsius (Bigelow and Schroeder 1953, Cianci 1969, Edsall 1970, Kissil
1974). Blueback herring spawn in tributary waters at water temperatures
between 14 and 26 degrees celsius (Bigelow and Schroeder 1953, Loesch
and Lund 1977, Pardue 1983). We found no reports of either species spawning
in brackish water. Substrate type does not appear to be critical during
spawning (Bigelow and Schroeder 1953, Edsall 1964, Mansueti and Hardy
1967). After spawning, adults return to the sea (Bigelow and Schroeder
1953). Because of the paucity of information on spawning habitat requirements
of these two alosids, we mapped spawning habitat of river herring as those
sections of rivers where spawning is known to occur (D. Grout, NHF&G).
These areas were scored as 10 (0 - 10 scale) since they in fact meet all
environmental requirements (Figure of Spawning Habitat).
LARVAL HABITAT Water-hardened eggs are pelagic and drift downstream (Loesch and Lund
1977). Incubation time for eggs is related to water temperature (Edsall
1970). The larval stage lasts from yolk-sac absorption (2 - 5 days) at
a mean total length (TL) of 5.1 mm, until transformation to the juvenile
stage at 20 mm TL (Mansueti 1962, Cianci 1969). Larvae were collected
in salinities of < 12 ppt in Chesapeake Bay (Dovel 1971). Therefore,
in rivers where spawning occurs, we mapped habitat for larvae as those
reaches which have salinities < 12 ppt. These areas were given a score
of 7.5 (0 - 10 scale) based upon apparent suitability of conditions, but
where presence of larvae has not been documented (Figure
of Larval/Early Juvenile Habitat). JUVENILE HABITAT Juvenile river herring occur in tidal freshwater and estuarine areas
in spring and early summer, moving upstream as more saline waters encroach
(Warinner et al. 1969, Pardue 1983). Salinity < 5 ppt is considered
optimal for early juvenile river herring (Pardue 1983). Juvenile river
herring migrate from freshwater-estuarine nursery areas to coastal waters
between late summer and fall, as water temperatures decline (Warinner
et al. 1969, Burbridge 1974, Loesch 1987, Gray 1991). Because of the paucity of information on later juvenile habitat requirements
of these two alosids, we mapped only their early juvenile habitat. This
included locations where juveniles have been collected (New Hampshire
Fish and Game Department) and which have salinities < 5 ppt. Adjacent
waters having salinities < 5 ppt were scored as 7.5 (0 - 10 scale)
based upon the apparent suitability of conditions, but where presence
of juveniles has not been documented. Larval, early juvenile, and spawning habitat were combined using the
maximum score of either, to produce a coverage of overall habitat for
these stages of river herring (Figure of Habitat
for Combined Life Stages). Additional data and analysis will be needed
to identify whether later juvenile stages use more saline habitats within
the estuary, or migrate quickly out to sea. |
