Herman, S.S. (1963). Studies on the life history and vertical migration of the opossum shrimp, Neomysis americana Smith. Ph.D. Dissertation, University of Rhode Island, Kingston, Rhode Island, USA. 95 pp.

158817

Herman, S.S.

1963

95 pp.

Publication

https://digitalcommons.uri.edu/oa_diss/2425

NeMys doc_id: 1217

Available for editors  

The vertical migration and certain aspects of the life history of the opossum shrimp, Neomysis americana. were studied over a period of one year, from February, 1960 to February, 1961. Samples were collected at least once each month near the entrances to the West Passage of Narragansett Bay. The normal procedure involved simultaneous tows from sunset to sunrise (usually every hour) with four half-meter number two plankton nets and a modified scallop dredge with a net attached, towing at the surface, 18 feet, 38 feet, 50 feet and bottom (60 feet). N. americana was the only mysid which could be captured the year round with a breeding cycle which was continuous throughout the year, and with major spawning periods occurring from May to June and October. Immature males and females dominated the population for most of the year with mature forms prevailing in May and June, and young in July and August. Peak abundance of mysids occurred from August through February. This mysid is rarely taken in a plankton net during the day, its normal habitat being on the bottom or immediately above it. N. americana undergoes a regular diurnal vertical migration which shows a regularly occurring midnight sinking and a dawn rise, dependent upon the time of the year and the number of hours the animals have spent in the dark. Light was found to be the most important single factor responsible for vertical migration, although other factors such as temperature, current activity and wind also had an effect. During their ascent, the mysids were located in areas of the water column where light intensities varied from 5 x IO”1 to 1 x IO-3 foot candles; by the time morning surface light intensity values had reached 5 x 10”1 foot candles, the animals had descended to lower levels. No differences were detected in vertical distribution of male and female mysids, but mature animals migrated only during the spawning season. Immature and young mysids migrated for most of the year, although there were indications that inhibition of this group may occur during the major spawning periods. An increase in migrational tendencies was noted from August through January with the peak occurring in January. Laboratory experiments were conducted on the spectral sensitivity of this animal. Under conditions of equal light intensity, they showed a preference for light of the wave length around 515 mu. Laboratory experiments also revealed that it was unlikely that a biological time clock was operating which controlled vertical migration.

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