Meeting Abstract

24.2  Monday, Jan. 4  Downstream Hatching Migrations of the River Shrimp Macrobrachium ohione in the Lower Mississippi River System OLIVIER, T.J.*; BAUER, R.T.; University of Louisiana-Lafayette; University of Louisiana-Lafayette tjo1457@ull.edu

Macrobrachium ohione is the most widely distributed species of Macrobrachium in the United States. Historically found within the Mississippi River System as far north as the Missouri and lower Ohio Rivers, M. ohione is now only abundant within the lower Mississippi River and its major distributary, the Atchafalaya River. M. ohione has an amphidromous life history, in which larval development occurs in brackish and marine waters. Females of amphidromous shrimps may hatch out larvae in fresh water, which will then passively drift downstream to the sea. Alternatively, gravid females may deliver their larvae to coastal bays via a downstream migration. Recent studies report a reduction in M. ohione survival after 3-5 days of drifting in fresh water prior to reaching saline waters. In both the Atchafalaya and lower Mississippi Rivers, we hypothesize that embryo-bearing females migrate downstream to deliver (hatch out) larvae to estuaries. A female “hatching” migration will ensure that the larvae reach the required salinity in time for the critical molt to the second (first feeding) stage. To test the predicted downstream movement, we conducted an 18-month investigation on location, reproductive condition, and seasonality of reproductive-sized females. Shrimps were collected by trapping at upstream (Butte La Rose, La; St. Francisville, La) and downstream (Atchafalaya Delta WMA; Pass A Loutre WMA) locations within the Atchafalaya and Mississippi Rivers, respectively. We found higher proportions of reproductive-size females and females with embryos near hatching at the downstream locations during M. ohione’s reproductive season. Support from NOAA LA Sea Grant R/SA-04 is acknowledged.