Distribution of Fish Larvae Relative to Time and Tide in a Gulf of Mexico Barrier Island Pass

Two, 37-h series of near-surface and near-bottom meter plankton net collections were taken at Dog Keys Pass, in the central region of Mississippi Sound, in January (102 samples) and May (84 samples), 1981. The collections yielded a total of 41,651 specimens of larval and juvenile fishes. Brevoortia patronus (gulf menhaden) and Leiostomus xanthurus (spot) were the dominant taxa taken in January, accounting for 59 and 18% of the total number of larvae collected. Larval and juvenile Engraulidae (anchovies) dominated the May samples, making up 83% of the specimens collected. Patterns in abundance and vertical distribution of larvae in Dog Keys Pass relative to time of day and tidal stage did not conform to the generalized model for larval transport into and maintenance within stratified estuaries found along the east coast of the United States. Mississippi Sound is a well-mixed estuary where tidal periodicity is diurnal, and where, in at least one pass, duration of ebb and flood tides can differ by a factor of two. This physical regime is unlike that found in some United States east coast estuaries where estuarine transport and retention appear to be based on the diel migrations of larvae into and out of vertically stratified tidal currents. No consistent diel and/or tidal periodicity in abundance and distribution of larvae of either winter or spring spawning species was observed in Dog Keys Pass which might facilitate movement into and retention within Mississippi Sound. Transport of fish larvae into Mississippi Sound through Dog Keys Pass was favored regardless of depth in the water column or time of day since landward flow lasted 1.5 to 2 times longer than seaward flow. Accumulation of larvae in shallow Gulf estuaries such as Mississippi Sound may also be more dependent on long term larval immigration from multiple cohorts produced during protracted spawning seasons than on the Atlantic coast.