Growth And Survival Of Bay Anchovy (anchoa Mitchilli) Larvae In North Biscayne Bay, Florida

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Degree Name

Doctor of Philosophy (Ph.D.)


Abundance, age-structure, growth, mortality, feeding, and production of bay anchovy larvae in north Biscayne Bay, Florida were estimated by five, eight to twelve-day field experiments. Relationships between fish larvae and other zooplankton were investigated. Bay anchovy eggs (18.4 m('-3)) and larvae (3.1 m('-3)) comprised 87% of all fish eggs and 76% of all fish larvae collected. Crab zoeae (394 m('-3)), predominately Porcellanidae, the ctenophore Mnemiopsis mccradyi (7.5 ml m('-3)), copepods (245 m('-3)) and natant shrimps (59 m('-3)) were the most abundant zooplankters in the 333-um mesh bongo net collections. Dinoflagellates (210,000 m('-3)), predominately Ceratium spp., copepods (167,000 m('-3)), tintinnids (27,000 m('-3)), and larvaceans (24,000 m('-3)) were the most abundant zooplankters in 20-um mesh pump sampler collections.Primary otolith growth increments of laboratory-reared bay anchovy larvae, which were used to age larvae, determine growth rates, and estimate cohort mortality rates, were formed daily beginning on the second day after hatching. A correction for shrinkage, based on the standard length: otolith diameter relationship for lab-reared bay anchovy larvae, was used to correct lengths of net-collected larvae which shrank 22 to 30%. Shrinkage increased as a function of higher temperatures and longer tows, and was most severe for the smallest larvae. Growth rates of bay anchovy larvae ranged from 0.43 to 0.56 mm d('-1). Daily mortality rates ranged from 26 to 36%.Bay anchovy larvae in north Biscayne Bay probably did not significantly reduce the numbers of their copepod prey < 100 um in width, but they may have reduced the numbers of the larger less abundant copepodites and adult copepods. Based on larval size-dependent feeding rates predicted from laboratory studies and based on the abundance of copepods < 100 um in width, estimated from 20-um-mesh pump samples, bay anchovy larvae consumed less than 1% of this size-class of copepods. Larvae were estimated to have consumed a higher proportion (5 to 10% day('-1)) of the less abundant copepodites and adults 100 to 200-um in width. Prey consumption (ug C d('-1)) by cohorts of bay anchovy declined throughout each field experiment because few larvae survived, while prey consumption by the mean population of bay anchovy larvae (all cohorts) usually increased for older, larger larval age and size-classes. Estimated mean daily production of anchovy larvae was 194 ug C m('-3) d('-1). . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI


Biology, Zoology

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