Production and energetics of Atlantic menhaden in Chesapeake Bay

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Laboratory experiments were conducted to examine the effects of temperature and prey type on maximum consumption, absorption efficiency and gastric evacuation rates of age 0 Atlantic menhaden Brevoortia tyrannus. Maximum consumption reached a peak or asymptote between 25 and 29°C. Temperature had no effect on absorption efficiency, but gastric evacuations rates increased with increasing temperatures. Artemia sp. nauplii were absorbed more efficiently than the diatom Ditylum brightwelli. Prey type had no effect on gastric evacuation rates at temperatures below 25°C but D. brightwelli was evacuated faster than Artemia sp. nauplii at 28°C. Field estimates of daily ration based on stomach content analyses for age 0 menhaden were 5.5% of dry body weight (3.6% wet weight) in June and 3.6% of dry body weight (3.0% wet weight) in August. Most prey in menhaden stomachs were dinoflagellates, diatoms and a mixture of amorphic phytoplankton and detritus. Less than 1% of total biomass in menhaden stomachs was copepods. A diurnal feeding periodicity was apparent with peaks in stomach contents occurring around dusk. A bioenergetics model was developed for age 0 menhaden in mid-Chesapeake Bay. The model incorporated temperature and weight-specific parameters for consumption and respiration and site-specific parameters for growth, diet, energy density of predator and prey and water temperatures. Model estimates of population consumption and production were sensitive to assumptions about annual mortality rates. Daily population consumption peaked in September which coincided with the second annual peak in primary productivity typical of mid-Chesapeake Bay. Daily production peaked from mid-August through September. Model results showed that in 1990 menhaden population consumption would have removed <5% of primary production in mid-Chesapeake Bay from June through October.