Centropomus Undecimalis - Ingenta Connect

BULLETIN OF MARINE SCIENCE, 62(2): 509–529, 1998

REPRODUCTION AND EARLY LIFE HISTORY OF COMMON SNOOK, CENTROPOMUS UNDECIMALIS (BLOCH), IN FLORIDA Kevin M. Peters, Richard E. Matheson, Jr. and Ronald G. Taylor ABSTRACT This paper combines published literature and unpublished Florida Department of Environmental Protection (FDEP) data on snook reproduction and early life history. Published literature originally dealt with fisheries investigations (1950s) and freshwater culture (1970s) but has expanded to include marine stock enhancement, spawning, and larval and juvenile ecology. In addition, ongoing FDEP projects provide considerable information. Snook are protandric hermaphrodites that probably spawn near river mouths, passes (inlets), and points of land in central and southern Florida estuaries. Females are older and larger than males at 50% maturity (5 yrs and 500–522 mm SL versus about 2 yrs and 330–348 mm SL) and have group synchronous ovarian development. The spawning season is long (approx. April to December or January) and includes multiple spawnings. Most spawning occurs between May and September. Spring spawning occurs at water temperatures >22°C and salinities >27‰. Several researchers noted increased spawning activity around the times of spring and summer new or full moons. In pre-spawning behavior, females are escorted by a number of (usually) smaller males, but actual spawning has not been documented. In the laboratory, eggs averaged 0.70 mm diameter and hatched in 17–18 h at temperatures of 26–29°C and salinities of 28–38‰. Newly hatched larvae (1.4–1.5 mm notochord length) spend ~2.5 wks in nearshore waters before their arrival at shallow-water nursery sites. Eggs have been collected during field studies in only one secondary embayment of lower Tampa Bay, but preflexion larvae have been taken in lower Tampa Bay and just off the beach at Naples. Postflexion larvae have been reported from both coasts of Florida, but only 16 larvae are listed in published literature. Late-stage larvae recruit to vegetated shorelines of quiet, shallow-water creeks, canals, and lagoons in both low-salinity (riverine) and high-salinity (mangrove swamp and salt marsh) environments. Early juvenile-stage snook occupy a spatially restricted microhabitat along shores having limited water movement, moderate shoreline slopes, and vegetation extending over and/or into the water; as the juveniles grow, their habitat becomes less defined and restricted. Early juveniles (4400 juvenile snook 6– 15 mm SL.

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BULLETIN OF MARINE SCIENCE, VOL. 62, NO. 2, 1998

Figure 1. Tampa Bay study area showing locations of rivers and secondary bays. Studies of larvae were conducted mainly in the Little Manatee River and lower Tampa Bay. Studies of juveniles were conducted mainly in Mangrove Bay, the Alafia River, the Little Manatee River, and Terra Ceia Bay. The extent of tagging studies of adults are shown as crosshatched areas off the Interbay Peninsula and Port Manatee. Habitat restoration studies took place in a borrow pit adjacent to St. Petersburg’s Mangrove Bay Golf Course and in Snook Bayou. The borrow-pit study was intended to provide information about the current state of juvenile fish populations within the pit. Snook were a primary target species of the survey because adults occurred in the pit, spawning populations occurred nearby, and the basin exhibited numerous snook nursery-habitat characteristics. Three samples per month were taken

PETERS ET AL.: REPRODUCTION AND EARLY LIFE HISTORY OF COMMON SNOOK

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Figure 2. Southwest and southeast Florida coasts showing locations of principal passes. Studies of larvae were conducted in the vicinity of Gordon Pass and Naples. Tagging studies of adults were conducted along the coasts from Bonita Beach to Caxambas Pass on the southwest coast (a) and from Fort Pierce Inlet to Palm Beach Inlet on the southeast coast (b). with a fine-mesh seine for examination of snook size distribution and abundance. The Snook Bayou restoration work was intended to monitor artificial habitats (Fig. 3) and to reveal whether a combination of shade and underwater structure might provide suitable habitat for settling larvae within newly restored sites prior to the growth of natural vegetation. The site was selected for artificial habitat testing because of the presence of settling snook in previous years. Although weekly pullnet sampling of 10 habitats produced information on seasonal occurrence, snook were less abundant than they had been in previous years, and the results were inconclusive. Additional snook life-history information was obtained during two large-scale survey programs at FDEP. In the Little Manatee River, FDEP personnel surveyed the distribution of juvenile fishes

Look for nursery habitat of early juvenile stages

Program and purpose of study Stock Enhancement Document area and time of spawning Early Life History Document and characterize habitat of larvae

Jun, Jul, and Sep Jun–Oct Aug–Sep

1992

1992

1993

Jun–Dec

Jun–Oct

1991

1991–1996

May–Sep

1990

Jun–Dec

May–Oct

1986

1990–1991

Months

Year

1-m dia., 0.333-mm mesh plankton net

Method

Little Manatee River 0.5-m × 1.0-m or 1-m × 1-m mouth opening, 0.5-mm or 1-mm mesh plankton nets Little Manatee River 1-m × 1-m mouth opening, 1-mm mesh plankton nets Lower Tampa Bay 1-m × 1-m mouth opening, 1-mm mesh plankton nets Dollar Bay, 1-m × 2-m mouth Naples area opening, 1-mm mesh plankton nets Gordon Pass and 1-m × 1-m mouth nearshore Gulf, opening, 0.5-mm and Naples area 1.0-mm mesh plankton nets Lower to middle 1.2-m × 12.2-m, 1.6Tampa Bay, mm mesh seine; Breder southeast shore traps; 0.5-m × 1-m and 1-m × 1-m push nets; underwater video Snook Bayou, Underwater surveys Terra Ceia Bay while skin diving

Terra Ceia Bay

Sampling area

Larvae

4,400

1,000 larvae

Stages sampled

100

No. of samples

Table 1. Abbreviated methods of unpublished Florida Department of Environmental Protection studies that contributed information on snook ecology and reproduction.

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Adult Snook Monitoring Estimate annual abundance, age, growth, and reproduction

Fisheries-Independent Monitoring Program Monitor annual abundance of fishes in Florida estuaries

May–Jul

May–Jul Jun–Aug Jun–Jul

1994

1984–1996

1990–1997

Jan–Dec

1991–1996

1976–1987

Jan–Dec

1989–1996

Jan–Dec

Jun–Oct

Feb–Feb

1995–1996

1995–1996

Months

Year

Little Manatee River Survey Examine distribution 1988–1991 of fish along salinity gradient of river

Quantitative sampling of artificial habitats

Program and purpose of study Early Life History (cont.) Prerestoration Survey

Table 1. Continued

1.2-m × 12.2-m, 1.6mm mesh seine Tripod structures with 2.4-cm posts, shade cloth, underwater structure, and 1.5-m dia., 1.6-mm mesh pull nets

Method

Tampa Bay

Southeast coast

Southwest coast

Southwest coast

Charlotte Harbor

Tampa Bay

2.4-m × 84-m, 3.8cm/23-cm mesh trammel net Hook and line; electroshocking 2.4-m × 84-m, 3.8cm/23-cm mesh trammel net

3.7-m × 305-m, 3.8-cm mesh bag seine

1.8-m × 22.7-m, 3.2mm mesh bag seine; 6.1-m, 3.2-mm mesh otter trawl 1.8-m × 22.7-m, 3.2mm mesh bag seine; 6.1-m, 3.2-mm mesh otter trawl

Little Manatee River 1.8-m × 22.7-m, 3.2mm mesh bag seine; 6.1-m, 3.2-mm mesh otter trawl

Mangrove Bay Golf Course borrow pit Snook Bayou, Terra Ceia Bay

Sampling area

>100

>100

100

>1,000

>1,000

>100

>100

3,000

>3,000

>300

10,000

Juveniles–adults

Juveniles–adults

Juveniles–subadults

Early juveniles

Juveniles

Stages sampled


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Figure 3. Diagram of artificial habitat and pull net showing the relative sizes and positions of the tripod, shade cloth, net, and PVC prop roots used for sampling pelagic juvenile snook. When the shade cloth was closed, it covered most of the sampling unit. along the salinity gradient. Biweekly sampling consisted of two to three seine hauls and two to three trawl hauls at each of six stations. A state-wide fisheries-independent monitoring program of Florida estuaries began in 1989. Although this program currently monitors six areas around the state, we only used data from Tampa Bay (1989–present; Fig. 1) and Charlotte Harbor (1991– present; Fig. 4). In addition to random-stratified sampling throughout both estuaries, selected (fixed) stations were maintained at sites supporting juvenile snook. Sampling occurred during spring and fall at randomized sites and monthly at fixed sites. Adult snook tagging studies at FDEP, conducted primarily for monitoring of population abundance, occurred in three areas of Florida — off the southwest coast, the southeast coast, and the west central coast (Figs. 1, 2). Information was also gathered on seasonal movements and reproductive cycles. On the southwest coast between Bonita Beach and Caxambas Pass, fish were collected


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Figure 4. Charlotte Harbor area showing the major rivers and three FDEP fixed seine stations used as nursery habitat by juvenile snook: Upper Peace River (1), Key Point Creek Canal (2), and Bokeelia Pond (3). every weekday during the spring and early summer with a haul seine (1976–1987) or a trammel net (1994). Sampling on the southeast coast between Fort Pierce and Palm Beach Inlets was carried out daily with hook and line. Sampling in Tampa Bay off Port Manatee and the Interbay Peninsula occurred at 2-wk intervals in early June and early July. During most studies, salinity, temperature, pH, and dissolved oxygen (DO) were measured at the surface (tagging studies) or surface and bottom (other studies) of the water column. Additional information on climate, tides, and hydrology were derived from various governmental publications such as NOAA Local Climatological Data (U.S. Dept. Commerce, 1992a), NOAA Tide Tables (U.S. Dept. Commerce, 1992b), and Hillsborough County Environmental Protection Commission’s Surface Water Quality reports (Boler, 1995). Terminology of early life-history stages generally follows Kendall et al. (1984); approximate length ranges are given as notochord length (NL) or standard length (SL) and are based on Lau and

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Shafland (1982) and our observations. Larval stages are preflexion (≤3.4 mm NL), flexion (3.5–4.4 mm NL), postflexion (4.5–10.0 mm SL), and transformation (5.5–10.0 mm SL). The transformation stage occurs as postflexion larvae change from planktonic to schooling pelagic habits and undertake a migration to the nursery grounds. We use the term “pelagic juvenile” to denote the early juvenile stage that, having arrived in the nursery area, schools in the water column and continues feeding on plankton before taking up the more demersal habits of larger juveniles. The size range of pelagic juveniles varies considerably, beginning as low as 6 mm SL and ending between 15 and 40 mm SL.

RESULTS REPRODUCTIVE MATURITY.—Snook are multiple spawners (Marshall, 1958); females probably spawn throughout the summer and ovulate as frequently as every 2 wks (Chapman et al., 1982). Histological evidence indicates that the ovary may return to spawning condition in less than 2 wks and that snook are indeterminate spawners because ovaries contain three or more batches, or groups, of oocytes (Tucker and Campbell, 1988). Size at maturity is somewhat confounded by the discovery that snook are protandrous. Although all immature fish have developing testes, it is unclear whether all fish mature first as males before becoming females or whether females might arise directly from immature males. Of the fish examined that contained testes, 50% were mature at 330– 348 mm SL (1.9–2.3 yrs old), and all fish with testes were mature by 500–522 mm SL (about 5 yrs old; Marshall, 1958; R. G. Taylor and H. J. Grier, FDEP, unpubl. data). Of the fish examined that contained ovaries, 50% were mature at 434–560 mm SL (2.5–3.5 yrs old), and all fish with ovaries were mature by 630–718 mm SL (7–8 yrs old; R. G. Taylor and H. J. Grier, FDEP, unpubl. data). Taylor and Grier (unpubl. data) found that male snook on the Atlantic coast mature at a smaller size and a greater average age than those on the Gulf coast; female snook on the Atlantic coast were larger and older than those on the Gulf coast. These life history differences may be genetically based because, on the basis of protein electrophoresis and mitochondrial DNA, Tringali and Bert (1996) found Atlantic and Gulf of Mexico stocks to be distinct. SPAWNING SEASON.—Gonadal maturation and/or spawning begins when water temperatures reach 22–23°C (Tucker and Campbell, 1988) and the photoperiod exceeds 13 h (Taylor, unpubl. data). Spawning continues after the summer solstice while photoperiod is decreasing (Tucker and Campbell, 1988). In Florida, the snook spawning season extends from April to December (Marshall, 1958; Fore and Schmidt, 1973; Tucker and Campbell, 1988; McMichael et al., 1989). Gilmore et al. (1983) reported spawning year round in the Indian River Lagoon, but a lack of small recruits during April and May suggests a winter break in spawning. The periods suggested for maximum spawning activity are May to mid-July (Marshall, 1958; Volpe, 1959; Chapman et al., 1982; southwestern Florida), and July to September (McMichael et al., 1989, west-central Florida). Taylor (unpubl. data) found that maximum gonad maturation occurred about 1 mo earlier on the west coast of Florida than on the east coast. Some of the differences among studies can be attributed to differences in sampling times and methods. Studies defining spawning season on the basis of adult reproductive condition have been based primarily on samples taken early in the season, when spawning fish concentrate in large groups (Marshall, 1958; Volpe, 1959; Chapman et al., 1982;


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Taylor, unpubl. data), whereas studies of ichthyoplankton or juvenile abundance have included samples from the entire season, including periods late in the season when fish are more dispersed (Fore and Schmidt, 1973; Gilmore et al., 1983; McMichael et al., 1989; Peters, unpubl. data). SPAWNING TIMES.—Certain synchronizing cues are often necessary to stimulate final maturation of fishes prior to spawning (Munro, 1990). In snook, these cues are probably lunar or tidal effects. Chapman et al. (1982), for example, reported peak spawning activity during new and full moons. In addition, spawning aggregations, spawning activity, egg collections, and backcalculated spawning dates of juveniles generally coincide with periods of strong afternoon ebb tides (Chapman et al., 1982; our studies), which occur around the time of the new and full moons. Eggs released on evening ebb tides would thus be taken out into relatively stable open waters rather than into the unpredictable conditions of the inner estuary. Egg and larval distributions generally support this hypothesis. For example, eggs were present in Terra Ceia Bay during afternoon ebb tides and during subsequent flood tides and were most common between 18:00 and 06:00 (FDEP-SERF staff, unpubl. data). One of us (K.M.P.) found preflexion- to postflexion-stage larvae in lower Tampa Bay and along the beaches off Naples, but no small larvae were found within the Little Manatee River or Dollar Bay, supporting the belief that eggs or larvae are transported to or maintained in nearshore waters. Evidence contradictory to the afternoon-ebb-tide cue is the occurrence of at least some histologically determined ripe fish during each quarter-moon phase (Taylor, unpubl. data). The finding that ovaries contain several groups, or batches, of developing eggs that may mature at 2-wk intervals (Tucker and Campbell, 1988) adds another complicating factor. We found evidence for multiple spawning peaks using backcalculated spawning dates of wild larvae and juveniles. Although larvae evidently had been spawned or had greater survival from eggs spawned during lunar periods with late-afternoon ebb tides, there was evidence of two spawning peaks for some spawning events in both Dollar Bay and lower Tampa Bay data (Fig. 5). SPAWNING AREAS.—Exactly where snook spawn in the wild has never been reliably documented, but evidence is strong that they spawn in high salinity regions of estuaries at the mouths of passes, canals, and rivers or off sandy beaches (Marshall, 1958; Volpe, 1959; Chapman et al., 1982). This hypothesis is supported by findings that snook sperm require salt water for activation (Ager et al., 1976), that fertilized eggs require salinities of 28‰ or greater for buoyancy (Chapman et al., 1982), and that spring movements include a migration out of the upper rivers and backwaters to the river mouths and passes (Murdock, 1957; Marshall, 1958; Volpe, 1959; Chapman et al., 1982). Although no actual release of sperm or eggs was observed, Chapman et al. (1982) reported spawning aggregations containing running ripe individuals along beaches in or near passes. In large estuaries such as Tampa Bay, we have found aggregations of ripe adults around points of land and spoil islands and at the mouths of secondary bays. Edwards (1993) used ultrasonic transmitters to track 24 adult fish during the spawning season and found a pattern of daily and tidal movement between a pass and nearby embayment. Further support for this hypothesis comes from our ichthyoplankton surveys. Stockenhancement personnel from FDEP found eggs and newly hatched larvae in Terra Ceia Bay (lower Tampa Bay), and we found larvae 1.6–6.2 mm SL (mean = 3.4 mm SL, n = 114) in open bay waters outside Terra Ceia Bay and larvae 1.9–4.8 mm SL (mean = 3.8

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Figure 5. Estimated spawning dates of larval snook in lower Tampa Bay and Dollar Bay during 1992 ichthyoplankton sampling. Open boxes along x-axis indicate the ranges of sampling dates. Arrows indicate ranges of sample dates potentially affected by red tide, ctenophores, and porcelaincrab zoea and the date of Hurricane Andrew’s passage. Filled circles, new moon; open circles, full moon.

mm SL, n = 9) along the beaches off Naples (outside Gordon Pass). Only late-stage larvae large enough to settle out in shallow water have been collected within the Indian River Lagoon (Gilmore et al., 1983), Naples Bay (Tolley et al., 1987), and the Little Manatee River and Dollar Bay (K.M.P., unpubl. data). SPAWNING BEHAVIOR.—Although there are no confirmed reports of snook actually spawning, prespawning behavior has been observed in several instances. Near the suspected time of spawning, large fish (presumed to be ripe females on the basis of size and season) are often escorted by two to seven smaller fish (presumed to be males on the basis of their small size and the presence of free-flowing milt; P. Chapman, Florida Game and Fresh Water Fish Commission, pers. comm.). Male-female parades of this type have been observed in Tampa Bay (by R.G.T.), off Naples (by K.M.P.), and around the passes of Marco Island (Chapman et al., 1982; P. Chapman, pers. comm.). Females appear to lose equilibrium or float sideways at the surface, a behavior attributed to the buoyancy of hydrated ova (P. Chapman, pers. comm.; R.G.T., unpubl. data). Spawning almost certainly would have to occur nearby because females seem unable to swim without great effort.


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LARGE-SCALE ONTOGENETIC CHANGES IN HABITAT.—Snook in the egg and larval stages spend only a short time in the high-salinity open waters of larger bays or in the nearshore area before moving into nursery habitats. Eggs (~0.70 mm dia.) hatch in 17–18 h (Chapman et al., 1978; Lau and Shafland, 1982; Tucker, 1987). Larvae are 1.4–1.5 mm NL at hatching (Lau and Shafland, 1982). They spend approximately 2.5 wks in the nearshore environment before settling at 6–7 mm SL (Lau and Shafland, 1982; McMichael et al., 1989; K.M.P., unpubl. data). Eggs and larvae have been reared in the laboratory at temperatures of 26–29°C, salinities of 28–38‰, and pH of 7.8–8.2 (Chapman et al., 1978; Shafland and Koehl, 1979; Chapman et al., 1982). One of us (K.M.P.) found early larvae in the field at temperatures of 28.7–31.5°C, salinities of 25.6–35.5‰, pH of 7.7–8.3, and DO of 4.1–7.7 ppm. Transformation larvae (3.5–9.0 mm SL) are found in areas between the spawning and nursery habitats within a wider range of salinities (0.6–35.3‰; Gilmore et al., 1983; Tolley et al., 1987; K.M.P., unpubl. data). The smallest stages of juvenile snook (5 to >15 mm SL) are pelagic and found along mangrove shorelines (Peters, unpubl. data), in salt marshes (Harrington and Harrington, 1961), and in riverine backwaters (Gilmore et al., 1983; McMichael et al., 1989; K.M.P., unpubl. data). Shafland and Koehl (1979) were able to transfer hatchery-reared larvae to fresh water after 14–16 d growth. Data on habitat usage by small juvenile snook are limited somewhat by sampling methods. Specimens