Species Description: The bay anchovy, Anchoa mitchilli, is a common and often extremely abundant fish of coastal and inshore waters of the western Atlantic. It is gray with a short head, very short snout, and a narrow silvery stripe about as wide as the pupil of the eye, running along the sides of the body. The dorsal fin is set far back on the body, just above or slightly in front of the insertion point for the anal fin. Ray counts are: dorsal = 14-16; anal = 24-30; pectoral = 11-12 (Hoese and Moore 1977, Robbins et al. 1986).
Potentially Misidentified Species: Bay anchovies are similar in appearance to two other common Anchoa species that co-occur throughout much of Florida. The striped anchovy (Anchoa hepsetus) often grows to be somewhat larger (to 15 cm) than the bay anchovy, and both it and the Cuban anchovy (A. cubana) have a dorsal fin that begins well in front of the anal fin. Bay anchovies are the only U.S. anchovies in which the dorsal fin begins at a point right above or only very slightly in front of where the anal fin begins (Robbins et al. 1986).
Regional Occurrence: Bay anchovies occur from the Gulf of Maine and Cape Cod, MA, south to Yucatan, Mexico, and throughout the Gulf of Mexico (Hoese and Moore 1977, Fives et al. 1986, Robbins et al. 1986).
IRL Distribution: Bay anchovies occur throughout the IRL system.
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.
Abundance: 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 fish community.
Rilling and Houde (1999) state that A. mitchilli is the most abundant fish in Chesapeake Bay.
Reproduction: 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).
Embryology: 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.
Temperature: The species exhibits a tolerance for a broad range of temperatures, as evidenced by its distribution extending from Cape Cod south to Yucatan, Mexico.
Gunter (1947) indicates larger individuals (> 27 mm) are significantly more susceptible to lethal low temperatures.
Salinity: Bay anchovies display a tolerance to a fairly wide range of salinities. A coastal Texas field survey by Gelwick et al. (2001) reveals the species is typically found at salinities above 15 ppt in this environment. In contrast, Rozas and Hackney (1984) report that bay anchovies are a dominant member of the fish community of North Carolina low salinity intertidal creeks where salinity is often regularly 5 ppt or less. Felley (1987) reports that bay anchovies are found at salinities approaching freshwater in coastal Louisiana bayous. Individuals are occasionally parasitized by the glochidia larvae of the freshwater unionid mussel Glebula rotundata, suggesting individuals may spend time in low salinity waters (Parker et al. 1984).
Simmons (1957) reports that bay anchovies have been collected in hypersaline environments at salinities of up to 75-80 ppt.
Dissolved Oxygen: Bay anchovies are highly intolerant of low oxygen conditions, and they are usually among the first animals to asphyxiate when they are captured in seine and trawl nets.
Gelwick et al. (2001) encountered bay anchovies at dissolved oxygen levels ranging from 7-10 mg/L. Laboratory observations by Breitburg (1994) indicate larval bay anchovies actively avoided hypoxic (< 1 mg/L DO) areas which are lethal to individuals within 24 hours.
Trophic Mode: 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.
Predators: 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) and ctenophores (e.g., Mnemiopsis leidyi) are known to consume bay anchovy eggs (Breitburg et al. 1997, Rilling and Houde 1999).
Habitats: 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).
Activity Time: 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.
Special Status: None.
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