Diagnostic characters:
Body compressed, fairly deep, head rather large; abdominal scutes 30 to 35, forming distinct keel; double line of modified predorsal scales; copious body mucus. Upper jaw with distinct median notch, no teeth. Gill rakers very fine and numerous. Dorsal fin at about midpoint of body; anal fin fairly short, its origin located slightly posterior to vertical through posterior dorsal-fin base; 6 branched pelvic-fin rays; posterior margin of pelvic fin rounded, length of inner rays equal or nearly equal to outer rays; pelvic-fin base at vertical through anterior portion of dorsal fin. Scales in lateral series 40 to 58 (usually about 45 to 52), those on dorsum above anal-fin base and at base of caudal finmuch smaller and irregularly placed; exposed part narrow, their posterior edges pectinate with sharp points. Colour: dorsum dark green-blue, sides brassy green; large dark spot on side posterior to gill cover, usually followed by variable number of smaller dark spots lying in one or more (up to 6) approximate horizontal lines; fins yellow to brassy, sometimes with dusky spots.
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Habitat, biology, and fisheries
Marine, pelagic, usually in shallow waters, both adults and juveniles forming very large and compact schools at the surface; school sizes vary greatly from year to year; schools comprised of similar-sized individuals. Inshore in summer; adults migrate into deeper water in winter in the northern part of range, but less offshore migration occurs in the south. North/south migrations (spring and summer versus autumn) occur, as also short-term migrations in and out of bays and inlets depending on tides, season, and weather. Tolerates wide range of salinities, from almost fresh to full-strength sea water. Spawning season apparently limited by high temperatures (20.5°C maximum monthly mean); spring spawners (April, May) in Cape Cod and Long Island waters, autumn spawners (October, November) from Long Island to North Carolina (plus some spawning June to August), probably winter spawners off Florida (December to March). Determinate, multiple spawners; spawn over broad geographic and temporal ranges. Minimum size at maturity about 180 mm. Estimated fecundity 48,000 eggs (180 mm fork length) to over 500,000 eggs (360 mm fork length). Eggs buoyant, spherical, transparent, 1.3 to 1.9 mm; egg size positively correlated with female size. Recruitment success depends heavily on transport to nearshore areas bywater currents. Nursery areas are in estuaries. Feeds by filtering phyto- and zooplankton (diatoms, copepods, euphausiids); as individuals increase in size trend in feeding regime changes from predominately herbivorous to more omnivorous diet. The most important of Atlantic coast menhadens to fisheries; majority of fishing landings occur outside the area. Reported catch within the area for 1995 was 27 314 t (USA only). Great fluctuations occur in abundance, however. Caught commercially with purse seines, although some are taken in long haul seines and in pound nets, and minor quantities with ordinary seines, drag nets and gill nets. Marketed fresh, salted, canned and smoked in limited amounts, the flesh not being generally esteemed (very oily and bony); chiefly used as a source of fish oil, also as fish meal and fertilizer and used as bait in some crustacean fisheries.
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