NOTE Powell: Laa/al abundance, distribution, and spawning habits of Cynoscion nebulosus 



709 



juvenile spotted seatrout prefer H. wrightii over Syringo- 

 dium fiUforme. In Florida Bay juveniles are collected at 

 highest densities in western Florida Bay basins near the 

 Gulf of Mexico in habitats with deeper and more organic 

 sediments and with greater density and biomass of S. fili- 

 forme. In areas where spotted seatrout juveniles are rare 

 or absent, which generally reflects the distribution of their 

 larvae, organic matter and sediment depth are minimal, 

 water depth is generally deeper, and seagrass standing 

 crop, short shoot densities, and diversity are lower (Thayer 

 and Chester, 1989; Chester and Thayer 1990), 



Spotted seatrout larvae were collected consistently at 

 relatively high densities in Whipray Basin (station 6; 

 central zone) and length-frequency distributions indicate 

 spawning most probably occurs in this area. The major- 

 ity of larvae collected in this area were 2.0-2.4 mm SL (5 

 to 6 d old), and it is possible that larvae could have been 

 transported into this area from western Florida Bay. Nev- 

 ertheless, Whipray Basin is a nursery area for juvenile 

 spotted seatrout (Florida Department of Environmental 

 Protection^. However, Whipray Basin has a relatively 

 sparse standing crop of the seagrass Thalassia testudinum 

 (12 g/m'-) compared to Palm Key (station 16; western 

 zone) which has a higher standing crop of T. testudinum 

 (28 g/m-) and Halodule wrightii (14 g/m^), and has been 

 demonstrated to be an important nursery area for spotted 

 seatrout juveniles (Florida Department of Environmental 

 Protection'). 



Spotted seatrout eggs have been collected in other 

 waters ranging from 15 to 50 psu (Holt and Holt, 2002). 

 Presumably, larval spotted seatrout eggs sink to the bot- 

 tom at salinities <15 psu and are not viable (Alshuth and 

 Gilmore^). Therefore, it is surprising that recently hatched 

 (<5-d old) larval spotted seatrout were collected, although 

 infrequently, at Little Madeira Bay (station 15; northern 

 transition zone) and only at 12 psu. Whether these low sa- 

 linities, which occurred in July and September 1997, were 

 a result of drastic changes in salinities caused by weather 

 events that occurred after hatching is unknown. Still, it is 

 highly unlikely that a significant number of viable eggs can 

 be produced at those low salinities. 



The qualitative description of spotted seatrout spawn- 

 ing habits provides necessary baseline data in relation 

 to restoration activities, specifically freshwater inflow. 

 Restoration activities could have both a negative and posi- 

 tive effect because salinity can have significant effects on 

 spotted seatrout reproduction and early life history stage 

 processes ( Holt and Holt, 2002 ). For example, low salinities 

 (as discussed above) could be detrimental to egg viability; 

 whereas, alleviating hypersaline areas could expand the 

 spawning area, particularly in the central zone where hy- 

 persalinity conditions are persistent (Orlando et al., 1997; 

 Thayer et al., 1999). At high and low salinities, growth and 

 development rates of larval spotted seatrout have been 

 reported to be reduced because these processes are con- 

 strained by undeveloped osmoregulatory functions (Holt 

 and Banks, 1989). On the other hand, there is evidence that 

 spotted seatrout populations have adapted to reproduce in 

 extreme-salinity environments where spawning salinities 

 influence egg buoyancy and the salinity tolerance of early 



Sta 4 



^^ 



"1 — r- 



* Oi <• C7» * O) O 



— — c^ f>4 r^ t^ ^ 

 I I I I I I ^ 



o tn o <n o m 



— •- r«) fM »n rS 



I 



Sla. 5 



HrTT- 



30 

 20 

 10 



I 

 * o> ■• o>  a> o 



— — c«j ri -n ^ V 

 I ) I I I I M 



O lA O )0 o «o 



— •-^ c« <N K) rS 



Sta. 6 



30 - 

 20 - 

 10 - 

 - 



Sla 8 



I I I I I TT 



.«■ (71 V at t 31 o 

 '- — f^ r^ m r-i V 



30 - 

 20 - 



Sla 9 



^ oi ■» fft ■» w 9 



-- — r>* rj m »o « 



I I I I I I ^ 



O U^ O U^ o in 



— — IM (N lO •^ 



Sla 1 1 



10  

 - 



-n^ 



* Ot •♦ o> * Ol o 



— ^ rx M K> to * 



t I I I I I /< 



O <n o in o ui 



Sla 12 



30 • 

 20 



■frf 



« 0» » CTt * Ot O 

 — -^ rg CM »0 f^ * 



I I ( /I 



d' Sta 13 



1(1(11 



o 1/1 o in o in 



— — ri f^i *o o 



30 

 20 - 

 10 - 



Sta 11 



Length class (mm) 



Figure 4 



Length-frequency distributions of spotted seatrout by 

 station from 1994-95 collections depicting the spatial 

 spawning habitat. Larvae <2.0 mm were used as criteria to 

 indicate spawning sites. Diagonal lines indicate spawning 

 area. See Table 1 for station locations. 



