704 



Larval abundance, distribution, and spawning habits 



of spotted seatrout iCynoscion nebulosus) 



in Florida Bay, Everglades National Park, Florida 



Allyn B. Powell 



Center for Coastal Fisheries and Habitat Research 



National Ocean Service 



National Oceanic and Atmospheric Administration 



101 Pivers Island Road 



Beaufort, North Carolina 28516 



E-mail address; allyn. powelliaJnoaa.gov 



The spotted seatrout (Cynoscion nebu- 

 losus ) is one of the most sought after 

 recreational fish in Florida Bay. and it 

 spends its entire life history within the 

 bay (Rutherford et al. ,1989b). The biol- 

 ogy of adult spotted seatrout in Florida 

 Bay is well known (Rutherford et al., 

 1982, 1989b) as is the distribution and 

 abundance of juveniles within the bay. 

 The habitats and diets of juveniles are 

 well documented (Hettler, 1989; Ches- 

 ter and Thayer, 1990; Thayer et al., 

 1999; Florida Department of Environ- 

 mental ProtectionM. Nevertheless, the 

 spatial and temporal spawning habits 

 of spotted seatrout and the distribu- 

 tion of larvae have only been partially 

 described (Powell et al., 1989: Ruther- 

 ford et al., 1989a i. 



An excellent description of the eco- 

 logical history of Florida Bay is given 

 by Fourqurean and Robblee (1999). 

 Briefly, Florida Bay is subtropical and 

 is generally oligotrophic. The bay is a 

 network of shallow basins, mud banks, 

 and mangrove islands (keys). Tides are 

 influenced by the Gulf of Mexico and 

 Atlantic Ocean, but mud banks, which 

 are connected to basins by channels, 

 restrict circulation in the bay and at- 

 tenuate tidal energy very quickly. As a 

 result there is essentially no lunar tide 

 over most of the central and northeast- 

 ern portion of the bay. 



This impediment to circulation could 

 have a negative effect on the recruit- 

 ment of early-stage planktonic larvae 

 into these portions of the bay. Within the 

 next few decades, plans to restore the 

 Everglades include increasing freshwa- 

 ter flows to Florida Bay. Prerestoration 

 information on larval distribution and 



spawning patterns of spotted seatrout 

 is a high priority because increased 

 freshwater flows can have potential 

 positive and negative impacts. At low 

 salinities, the planktonic eggs of spot- 

 ted seatrout could sink to the bottom 

 and would not be viable (Holt and Holt, 

 2002; Alshuth and Gilmore^). On the 

 other hand, increased freshwater flows 

 can alleviate hypersaline conditions 

 that could result in an expansion of 

 the distribution of the early life stages 

 of spotted seatrout (Thayer et al., 1999; 

 Florida Department of Environmental 

 Protection'). The objective of the pres- 

 ent study is to document the distribu- 

 tion and abundance of spotted seatrout 

 larvae to determine their early life his- 

 tory habitats and spawning habits in 

 Florida Bay. 



Methods and materials 



To describe the distribution and 

 abundance of spotted seatrout larvae 

 in Florida Bay, I devised a series of 

 ichthyoplankton surveys between 

 1994 and 1999. The initial survey was 

 conducted during nine nonconsecutive 

 months between September 1994 and 

 August \i)9r^. A total of 14 fixed sta- 

 tions wore selected in basins of Florida 

 Bay (Fig. 1). In accordance with rec- 

 ommendations by the South Florida 

 Ecosystem Restoration Prediction and 

 Modeling (SFERPMi, Program Man- 

 agement Committee (PMC), Florida 

 Bay was divided into six zones for ease 

 of reporting results (Table 1, Fig. 1). 

 These zones are based on the benthic 

 moUuscan and benthic plant commu- 



nities (Fourqurean and Robblee, 1999). 

 Paired bongo nets, 60 cm wide, were 

 fitted with 0.333-mm mesh and fished 

 from the port side of a 5.4-m boat. Nets 

 were towed during daylight, approxi- 

 mately 1 m below the surface for 5 

 minutes and volume estimates were 

 obtained from flowmeter readings. 



In 1996, sampling was conducted 

 monthly from April through Septem- 

 ber at stations where recently hatched 

 spotted seatrout occurred during 

 1994-95 (stations 5, 6, 9-13). In 1996, 1 

 used a paired 60-cm bow-mounted push 

 nets with 0.333-mm mesh similar to 

 that described by Hettler and Chester 

 ( 1990). Nets were fished approximately 

 1 m below the surface for 3 minutes. 

 The volume of water sampled with the 

 push net was slightly greater than that 

 sampled with the bongo nets (60 m'^ vs. 

 50 m-'). To test the efficiency of the two 

 gears, both were fished simultaneously 

 at 23 stations during 1996. A Kruskal- 

 Wallis nonparametric test was used to 

 evaluate differences (Sokal and Rohlf 

 1981 ). No significant differences in den- 

 sities offish larvae were found between 

 gear types (P=0.50). 



During and after September 1997 

 sampling for spotted seatrout was 

 limited to four stations in four zones 

 (Table 1; stations 6. 15, 16, 17) where 

 paired bow-mounted push nets were 

 employed. Sampling occurred during 

 July and September 1997; March, May, 

 June, July, and September 1998; and 

 May, July, and November 1999. 



' Florida Department of Environmental 

 Protection. 1995. Fisheries-indepen- 

 dent monitoring program, annual report. 

 Florida Department of Environmental 

 Protection, Florida Marine Research In- 

 stitute, 100 8'h Avenue SE. St. Petersburg, 

 FL 33701. 



^ Alshuth, S., and R. G. Gilmore Jr 1994. 

 Salinity and temperature tolerance limits 

 for lai'vai spotted seatrout. Cynoscion neb- 

 (//<).s».s- C. (Pisces: Sciaenidac). Int. Coun. 

 Explor Sea, Coun. Meet. Pap., ICES-CM- 

 1994/L: 17. 19 p. 



Manuscript accepted for publication 

 19 February 2003 by Scientific Editor 



Manuscript received 4 April 2003 at NMFS 

 Scientific Publications Office. 



Fish Bull. 101:704-711 (2003). 



