LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Bay anchovies typically grow to around 10 cm length (Robbins et al. 1986).
Able et al. (2001) report Anchoa mitchilli populations are composed
of multiple year-classes in Delaware Bay marsh creeks, suggesting a
lifespan of more than one year.
Bay anchovies are often seasonal numerical dominants in areas in which they
occur. Castillo-Rivera et al. (1994) report A. mitchilli accounted
for 55% of all fish caught in an ichthyofaunal study of Pueblo Viejo Lagoon,
Veracruz, Mexico. Peak abundance in this study occurred during September
and October with a general increase in abundance during the wet season.
Szedlmayer and Able (1996) note that bay anchovies accounted for more than
half of all fish caught in their study of a southern New Jersey estuary
Rilling and Houde (1999) state that A. mitchilli is the most
abundant fish in Chesapeake Bay.
Anchoa mitchilli is a a pelagic, serial spawner (Luo and Musick 1991,
Zastrow et al. 1991). Szedlmayer and Able (1996) report that the species
spawns both within estuaries and offshore over the continental shelf.
Fives et al. (1986) suggest that individuals become sexually mature once
they exceed 40 mm SL.
Field surveys by Rilling and Houde (1999) revealed that bay anchovy
spawning in Chesapeake Bay occurred from May through September and peaked
during July in the seaward third of the bay. The authors estimate that
baywide daily egg production increased from 4.25 x 1012 in June
to 8.43 X 1012 in July. Olney (1983) reports that 99% of fish
egg catches and 67-88% of larval catches during this period are bay
anchovies. During peak spawning, pelagic egg densities range from
10-1,000/m3 and larval densities reach 1-100/m3
(Olney 1983, Dalton 1987).
In the southern portion of its geographic distribution, spawning appears to
occur year-round (Houde and Lovdal 1984).
Larval duration in bay anchovies from the Newport River Estuary, NC, is
around 45 days, at which time individuals of approximately 22.5 mm complete
metamorphosis. Rapid larval growth rates likely allow animals spawned early
in the season (May to early June) to mature and spawn by late summer or
early fall of the same year (Fives et al. 1986).
Jordan et al. (2000) reports that Anchoa mitchilli larval growth
rates are spatially and temporally variable, averaging 0.39-0.88 mm/day
over two seasons of field investigation in the mid Hudson River Estuary.
The authors postulate that small-scale zooplankton patchiness, not salinity
or temperature differences, governed growth rate variation.
Bay anchovies are primarily zooplanktivorous DeLancey (1989) listed
brachyuran crustacean megalopae (larvae), copepods, and mysids as the most
important prey items recovered from the guts of A. mitchilli
collected from a South Carolina beach surf zone.
Bay anchovies are a major component in the diets of several species of
piscivorous fish, including commercially important species such as weakfish
(Cynoscion regalis), and striped bass (Morone saxatilis)
(Baird and Ulanowicz 1989). Chain Pickerel (Esox niger) have also
been reported as predators of bay anchovies (Meyers and Muncy 1962).
Safina and Burger (1989) indicate bay anchovies are one of two prey fish
species most preyed upon by predatory fish and terns near Fire Island
Inlet, NY. Bluefish (Pomatomus saltatrix) were identified as a
major consumer of bay anchovies by these authors, and appear capable of
altering anchovy population numbers through predation. McGinnis and Emslie
(2001) report North Carolina royal Terns (Sterna maxima) and sandwich terns
(S. sandvicensis) both prey on bay anchovies.
A strong association between bay anchovies and the Atlantic brief squid
(Lolliguncula brevis) in a study by Ogburn-Matthews and Allen (1993)
is likely reflective of a strong predator-prey relationship between these
species. Gelatinous predators such as sea nettles (Chrysaora
quinquecirrha) end ctenophores (e.g., Mnemiopsis leidyi) are
known to consume bay anchovy eggs (Breitburg et al. 1997, Rilling and
Anchoa mitchilli is primarily a pelagic (water colum) species, a
habitat preference that is consistent with the zooplanktivorous dietary
habits of the species. Individuals are encountered over seagrass beds and
unvegetated benthic areas (Orth and Heck 1980). Castellanos and Rozas
(2001) collected more individuals over bare substrata than over vegetated
areas. Bay anchovies occur in protected waters and tide pools as well as
in beach surf zones (Crabtree and Dean 1982, DeLancey 1989).
Castillo-Rivera et al. (1994) captured significantly more bay anchovies in
nighttime collections and suggested the nocturnal activity pattern might be
a predator avoidance strategy.
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