Report SFRC-87/01 b 

Abundance and Distribution of 

Ichthyoplankton ikl ~lorida Bay 

and Adjacent Waters 

. . 

Everglades National 

F.I.U. URBAN & REG. DOCS. LIBRARY, - 

'~ark, South Florida Research Center, P.O. Box 279, Homestead, Florida 33030 
TABLE OF CONTENTS 

LIST CF TABLES .......................................................... i 

LIST OF FIGURES ......................................................... ii 

ABSTWCT ................................................................ 1 

INTROWCTION ...................... ...................................... 2 

ETHODS ................................................................. 2 

Ichthyoplankton Sampling ........... .. ................................ 2 

Processing of Samples ................................................ 7 

Larval Identification ..... .. ........................................ 7 

Statistical Analysis ................................................. 11 

RESULTS AND DISCUSSION. .................................................. 11 

General ............................................................... 11 

Spotted Seatrobt ........... ......................................... 13 

Geaq.Assessment ................................................... 13 

Disfribution and Abndance ........................................ 27 

Abundance and Distribution of Total Ichthyoplankton ........ ... ....... 23 

CONCLUSIONS ............................................................ 34 

ACKNOWLEDGMENTS .......m.....m... ................................ 35 

LITERATURE CITED ............... .\.%...................................... 36 

APPENDIX A .......................................................... 38 
LIST OF TABLES 

. 

Table Page 

1 . Locations, depth and date of ichthyoplankton collection ............ 4 

2 . Summary of samples analyzed for total ichthyoplankton .............. 8 

3 . Distinguishing characteristics among snappers ...................... 10 

4 . Sumnary of snapper data ..................................... 12 

5 . Summary of larval spotted seatrwt ................................. 14 1 

6 . Total fish larvae abundance ........................................ 25 

7 . Dominant ichthyoplankton from neuston tows ......................... 31 
-a 

LIST OF FIGURES 

Figure 

1. Location of sampling stations...................................... 3 

2. Bongo net assembly ................................................. 6 

3. Frequency distribution of larval spotted seatrout stages.. ........ .l6 

4. Frequency of spotted seatrout per sample. ......................... -18 

5. Size and stage frequency of spotted seatrout....... ................. 19 , ,, 

6. Spotted seatrout' relative abundance -- spring ...................... 20 , 

< 

7. Spotted seatrout relative abundance -- summer......................21 *.J8. spottd seatrdut relative abundance -- fall.. ..................... .22 

9. Mean seasonal sallinities and ranges.. ............................ .24 

10. Abundance of ichthyoplank~o'h -- Spring.. .......................... .27 

11. Abundance of ichthyoplankton -- Summer.............................28 

12. Abundance of ichthyoplankton -- Fall.. ............................. .h 

13. Frequency of atherinids by tow type ........ :...........kC1..........33 , 

Appendix 1 

A. Design and operation of a tiongo net,deployment system for 

small craft. .............. :......................*. ........... *:.**38 
w 

ABSTRACT 

An ichthyoplankton survey was carried on in Florida Bay and adjacent waters 

that focused on the abundance and distribution of larvae of four target 

species--red drum (Sciaenops ocellata) , snook (Centro omus undecimalis ) , 

gray snapper (Lut janus 9ri~eumotted seatrout -+!T C noscion nebulosus). 

Twenty sampling stations were established--eight to document larval entry 

into Florida Bay and adjacent estuarine waters, and 12 within Florida Bay 

and adjacent estuarine waters--to provide insight into larval fish 

distribution and movement. 

Spotted seatrout was the only target species whose larvae were regularly 

collected. No snook, one red drum and 16 potential gray.snapper were 

collected. Based on the distribution of early stage larvae, spotted 

seatrout spawned in,,fitermediate to high salinity waters within western 

Florida Bay and adjacent estuarine waters, but did not appear to spawn in 

brackish waters. We never collected spotted seatrout in the Keys area. 

Temporally, spotted seatrout have a protracted spawning season with 

spawning minimal during late fall and winter and most intense from May to 

September. 

Based on the absence of early Ia~val stages, gray snapper, snook and red 

drum apparently spawn outside of the Park. All larvae identified as 

snapper larvae were found in the ocean but young juveniles were found both 

in Florida Bay and the ocean. It appears that gray snapper spawn near 

offshore reefs in the Atlantic Ocean and at least some enter the Park as 

juveniles. The lack of larval snook and red drum in our samples does no2 

indicate they are absent from the area. Adults spawn outside the Park, 

thus the larval supply may be susceptible to considerable mortality prior 

to migrating into the Park. They are less vulnerable to the gear because 

they are relatively well developed, and they may not be available to 

standard ichthyoplankton gear due to preference for the poorly sampled 

microhabitats (e.g., crevices, the bottm and channel edges). 

Step-oblique tows with standard ichthyoplankton gear was appropriate for 

sampling early stage trout larvae to determine the spatial and temporal 

distribution of spawning. The development of different gear may be 

required to study the late larval and early juvenile stage. 

Although our research focused on the four target species we were able to 

gain an insight into the distribution and abundance of non-gamefish within 

Florida Bay and adjacent 'waters. One of the most striking pattei'ns was the 

dominance by and ubiquitous distribution of gobiid larvae. 
INTRODUCTION 

This research focuses on red drum (Sciaenops ocellatus), snook (Centropomis 

undecimalis), gray snapper (Lut janus ariseus), and spotted seatrout 

(Cynoscion nebulosus), and its objective is to determine the larval 

distribution of these species in the Park. Such information may be useful 

in determining spawning sites and points of entry into the Park. 

Previous studies in the Park and adjacent areas have provided preliminary 

information on the spawning seasons and general life histories of adults 

(Croker 1960; Starck 1964; Fore and Schmidt 1973; Thue et al. 1982; 

Rutherford et al. 1982, 1983). There is less known about the early life 

history stages of these species although some information is available on 

sampling techniques and distribution in the Park and surrounding area 

(Jannke 1971; Starck 1970; Houde and Chitty 1976; Gilmore et al. 1983; 

Collins and Finucane 19843. 

II The general questions that we attempted to answer were: 

1) How are larvae distributed in the Park? 

2) What changes occur with season? 

3) Where does spawning occur? 

4) Where do larvae enter the Park? 

METHODS 

II Ichthyoplankton Sampling 

Ten larval fish collecting trips were made between March 1984 and September 

1985. Twenty stations were selected in and around the Park (Fig. 1). The 

areas sampled include eight locations to document spawning or larval entry 

and twelve inside locations to document inter-regional larval distribution 

within Florida Bay and adjacent waters. Some stations were sampled only 

during the day, because of night-time navigational difficulties; some only 

during the night, because of time constraints; and some both day and night 

(Table 1). In addition, we included-data on the four target species from a 

collecting trip in September 1985 designed to evaluate other 

ichthyoplankton gear. 

Ichthyoplankton was taken with a 61-cm bongo sampler fitted with 333 vm 

mesh nets that was fished from the side of 6.7-y-long boat. Towing from 

the side kept the nets from fishing in the boat s wake. A mast-boom 

assembly and an electric winch were used to lower and raise the sampler 

(Fig. 2 and Appendix A). At each station, three oblique tows and one 

surface (neuston) tow were made. We took replicate step-oblique tows to 

insure against loss or breakage and so material could be archived for 

future studies (e.g., feeding) that were not within the objectives of this 

study. The oblique tows consisted of lowering the net to within 1 m of the 

bottom while underway at towing speed, fishing at that depth for 1.5 min, 

raising the sampler to within 1 m of the surface and fishing until 3 min 

elapsed. Towing speed was approximately 1 m/sec and was maintained by 

running the outboard engine at 1000 rpm. A flow meter mounted in the net 

mouth gave readings for calculating water volumes filtered. Neuston tows, 

also made at 1 m/sec, were made with the net mouth approximately one-half 
EVERGLADES 

NATIONAL 

PARK 

Figure 1. Location of i chthyoplankton sampling stations. 
 able 1. Locations, depth, and date of coll6ctions of ichthyoplankton stations in 

Everglades National Park. D designates day sample only; N designates night 

sample only; DN designates day and night sample; dash (-) indicates no sample 

taken. I 

I 

Date of Collection I 

Depth \ 

Station Locat ion (m) Mar May 3un Jul Aug Sep Nov Nov/Dec Apr Jun Sep i 

84 84 84 84 84 84 84 84 85 85 85 I, 

1 

11 LowerMatecumbeKey 2.7 D DN ON DN N N N N N N DN I 

Channel 5 

12 PetersonKeyBank 2.4 D DN DN DN N N N N N N - 

Bowlegs Cut 

13 OldOanBank--Park 2.4 O ON DN ON N N N N N N - 

Service Boundary 

Marker 

14 Alligator Reef 8.2 D MJ DN DN N - N N N N - 

15 Ponce De Leon Bay 3.0 D D D 0 D D D D D D D 

16 Shark River LI LL 3.0 D D D D D D D D D D - 

Marker 6 

17 Shark River 2.1 D D D D 0 0 D D D D - 

Marker " 8" 

18 Cormorant Pass 1.5 0 0 D D D D D D D D - 

Marker "4" 

19 East Cape Sable 2.7 D ON DN DN ON ON DN DN D DN ON 

20 Middle Ground 2.7 0 D DN DN ON DN DN DN D DN - 

21 Flamingo Channel 1.8 D DN ON DN DN DN DN DN DN DNMarker " 10" 

22 Tarpon Bay 1.5 - D D D D D 0 D D D - 

23 Man-of-war Channel 3.0 - D D D D D D D D D - 

24 Oxfoot Bank--near 3.0 - D D D D D 0 D 0 D - 

Marker " 11 " 

25 Oxfoot Bank-- 3.0 - D D D D D D 0 D D D 

Between Markers '88888 and 88 10" 
Table 1 Contd. '4' 

Date of Collection 

Depth 

Station Location (m> Mar May Jun Jul Aug Sep Nov Mv/Dec Apr Jun Sep 

84 84 84 84 84 84 84 84 85 85 85 

26 Blue Bank-- 1.8 - D D D D D D D D D - 

West Edge 

27 Snake Creek 3.6 - D D D D DN N N N N D 

28 Cotton Key 1,. 8 - D D D D N' N N N N - 

,,' , 

29 Cotton Key Basin 2.1 - - D D D N N N N N - 

Marker " 78" 

3- r 

30 Whale Harbor "2.1% - - - - - - N N N N - 

Channel - Entrance 

Marker 8) 88 1 

J 
1 

i @ 25 KG DEPRESSOR I 

Figure 2. Bongo net deployment, mast, boom and winch assembly. Safety chain 

is detached before net is deployed. Preventor bar is unpinned at 

lower end and safety chain is attached before net is raised out of 

water and brought aboard. Winch shown was later replaced with a 

sel f-tail ing automatic windlass. Mast assemljly was mounted 

4 meters from the bow on the boat's starboard side. 
submerged. Tows were made in a right-hand circle about 30 m in diameter 

to prevent entanglement of the nets or towline in the propeller. 

it 

Material from the outboard net was washed into the cod end with seawater 

from a hose, mangrove leaves, seagrasses, macroalgae and large ctenophores 

were removed. Material was collected on a 200 um screen and preserved in 

glass 1-liter jars in a 10% buffered seawater-Formalin solution. 

Temperature and salinity of the'surface and bottom waters was measured 

using a YSI temperature/salinity recorder. The two readings at each 

station were averaged. 

Collections were made independent of current direction and tide stage. 

Night collections, conducted to provide insight into both the net avoidance 

problem and the possibility of die1 changes in the water column in response 

to ambient light,'wete made regardless of moon phase. Night collections 

were made with deck lights out to reduce larval attraction or avoidance. 

2- f A A7 

Processing of Samples 

Samples were processed in three stages. First, all fish larvae were 

removed from the sample; secon'd, target species were removed, measured and 

staged; third, non-target species were identified to the lowest taxon 

possible (generally to the family level). For this study, we identified 

target species from at least one neuston and one step-oblique tow sample 

for each station, for both day and night periods on all sample dates. This 

resulted in the processing of 467 samples. We identified pon-target 

species from at least one sample per station for seven cruises during the 

following months- -- March 1984, May 1984, June 1984, July 1984, August 

1984, September 1984, and November 1984. Additional samples, although not 

a complete series from late Ndvember 1984 and April 1985 were also 

examined. This resulted in the proce~~sing of 231 samples (Table 2). 

Larval Identification J 

Larval identification was accomplished by reference to published - 

descriptions (Fable et al. 1978; Richards and Saksena 1980; Holt et al. 

1981; Lau and Shafland 1982) of laboratory-reared specimens and by studying 

preserved specimens from reference collections. Although gray snapper have 

been described (Richards and Saksena 1980). and they can be se~arated from 

vermillion snapper (Rhomboplites aurorubens) larvae- (Laroche 1977), other 

snappers that co-occur with the gray snapper in this area have not. - - 

_ Therefore, the separation of snapper larvae to species is not possible. It 

is not until the juvenile stage when fins, vomarine tooth patches, gill 

rakers, scales and coloration develops that identification to species is 

possible for snapper. We have considered all snapper larvae that do not 

have the full complement of meristics to be "~utjanus s." ("snappers" ). 

Those snappers that have the full meristic complement could be divided into 

three groups --gray snapper, lane snapper (C. synagris) , and yellowtail 

snapper (0. chrysurus) (~able 3). Gray snapper, lane snapper and 

yellowtail snapper were the only species collected in a concurrent juvenile 

survey within Florida Bay (Thayer et al. 1987), but most snapper we 

collected were from Alligator Reef (Station 14) that is outside of Florida 

Bay, Here a greater diversity of snapper species co-occur (Starck 1970). 
, Table 2. Summary of s8mples taken for analysis of total ichthyoplankton. D 

indicates day step olbique tow; N, night step oblique tow; DS, day 

neuston tow; NS, night neuston tow. When more than one sample was 

taken the number appears in parentheses following the tow type. 

' Date of Collection 

Mar May Jun Jul Aug Sep Nov Nov/Dec Apr 

Station 84 84 84 84 84 84 84 84 85 
Table 2 (Contd) 'id 

Date of Collection 

Mar May Jun Jul Aug Sep Nov Nov/Dec Apr 

Station 84 84 84 84 84 84 84 84 85 

L1 

Total 

Samples 19 33 28 28 22 44 23 22 12 
-. . * 

I 

Table 3. Groups of sfiapper \sharing the same meristic counts and 

, distinguishing characters among groups with characteristics 

from Randall (1983). . 

Group Species Characteristics 

snapper gray snapper 14 dorsal rays 

6-11 lower gill rakers 

mutton snapper 

schoolmaster 

cubera snapper 

dog snapper 1 

lane snapper lane snapper 

mahogany snapper 

12 dorsal rays and 

8-13 lower limb gill 

rakers 

yellowtail snapper yellowtail snapper 21-22 lower limb 

gill rakers 
We used developmental stage as an indication of larval age. Preflexion, 

flexion and postflexion stages occurred before, during and after the upward 

flexion of the notochord tip, respectively. For gray snapper, flexion 

occurs at about 4.2 mm SLY postflexion at- about 6.2 rnm SL and the juvenile 

stage at about 12.0 mm' SL (Richards and Saksena 1980). For spotted 

seatrout (based on our material), flexion occurs at about 2.4 mrn SL and 

post flexion at about 4.1 mm St. We did not observe the size when the 

juvenile stage began, but, based on Powles and Stender (1978), the juvenile 

stage sllouicj begiq by at least 8 mm SL. 

Statistical Analysis of Sampling Techniques 

In order to evaluate sampling methods, we compared differences in the 

frequency of larval trout development stages between day and night tows and 

differences in,,nurnbers of trout larvae between step-oblique and neuston 

t3ws. Twelve'dag and twelve night stations from stations 19, 20 and 21 

(Fig. 1) were used for comparisons between day and night tows. We only 

us@ ,those samples where trout were captured in at least one of the 

day-night ~amples.~~To compare differences between step-oblique and neuston 

tows, we used 32 concurrent day samples and 12 concurrent night samples. 

We assumed that sample densities followed a negative binomial distribution 

and, therefore, data 'were transformed (Ln x +1) for comparing means. Means 

f rorn a contagious, distrib'tJt ion were compared as out lined by Elliot (1977) 

and, when variances were unequal, Sokal and Rohlf (1981). 

RESULTS AND DISCUSSION 

General $. 

With the exception of spo'tted seatrout, the other target species were 

conspicuously absent from'our collections. No snook, one red drum and 16 

potential gray snappers were colle+cted. The one red drum larvae was 

collected i~ late Novernbek near Flamingo (Station 21). The mcjority of 

snapper larvae were collected from Alligator Reef (Station 14) -- the only 

station where preflexion snapper larvae were taken (Table 4). The presence 

of postflexion lwvae/juveniles at near-inlet stations (12 and 13) 

indicated that snappers enter the Park as advanced larvae. The absence of 

preflexion snapper larvae in our study and the reported rare occurrence of 

ripe adult snappers within the Park (Rutherford et al. 1983), supports the 

suggestions of Croker (1960), Starck (1964) and Rutherford et al. (1983) 

that gray snapper spawn outside the Park in offshore watefs. The spawning 

habitat for gray snapper, that immigrate into the Park is apparently 

offshore reefs such as Alligator Reef where spawning has been reported 

(Starck 1970),\ The presence of large juvenile gray snapper in northwestern 

Florida Bay (Starck 1970; Thayer et al. 1987), but the absence of larvae 

and small juveniles that we and Starck (1970) found there suggested that 

gray snapper in northwestern Florida Bay may be recruited from adults 

spawning over reef areas south and east af northwestern Florida Bay. The 

evidence, however, is not substantial and does not preclude spawning in the 

Gulf of Mexico. 

Red drum larvae previously have been collected in large numbers at the 

entrance to Little Shark River (Jannke 1971). These larvae were collected 

with a 1-meter net fished, at night, during the fall season as red drum 
Table 4. Summary of snapper data. N indicates neuston tow; SO indicates 

step-oblique tow. 

Tow Mmber &an STAGE FREQUENCY Gray 

Date Station ~ibe Type Caught SL mn Pre- mion Pastflexion snappers 

flexion Juvenile (N) 

Jun 14 0855 

1984 0930 

2110 

Jul 12 0300 

1984 

0154 

SeP 11 2205 N 1 12.5 0 0 1 1 

1985 

TOTAL 26 6 0 20 16 
larvae entered into Everglades estuarine waters. These were relatively 

well developed nektonic larvae (4.0 to 8.5 rnrn SL), and, on the basis of a 

laboratory study of red drum development (Holt et al. 1981), we estimated 

Jannke's larvae to be from late flexion to postflexion stages. They had, 

therefore, been spawned outside of Florida Bay. Jannke's relatively large 

collection of red drum from this location (which is only 3 km from our 

Station 15), compared to our collections, could be due to his sampling 

scheme that consisted of intensive and nighttime sampling. Our sampling 

scheme was extensive and we did not sample during the night at our Statian 

15 that was in close proximity to Jannke's station. Furthermore, we did 

not sample during October, a time when red drum larvae were most abundant 

in ~aunkee's collections. Peters and McMichael (1987), using a l-m 

diameter conical net for surface and bottom tows, collected numerous red 

drum larvae in Tampa Bay, Florida both during the day and night. They did 

not, however, collect red drum in daytme surface tows. Their larvae were 

smaller than those captured by Jannke (1971) and they commented that red 

drum may spawn'fwrther offshore from the Everglades than those in Tampa 

Bay. I 

Sndok larvae,have rarely been collected. Gilmore et al. (1983) collected 

two relatively large larvae ,(postflexion stage) at an ocean inlet station 

in east-central Florida. These observations led them to believe that snook 

spawning did not occur in lagoons or inlets, but shallow nearshore oceanic 

waters. i A 

We believe that the absence or rarity of larval snook, red drum and gray 

snapper can be attributed to a complex of factors that influence larval 

availability and vulnerability. There is good evidence that these species 

spawn outside the Park (e.g., Starck 1970; Rutherford et 81. 1982, 1983; 

Collins and Finucane 1984; this study). Immigrants into ttie Park have 

undergone significant natural mortality and growth. They are, therefore, 

relatively uncommon to rare in abundance, and have become better able to 

avoid standard ichthyopiankton gear. In addition, they may not be 

available to the gear due. to habitat preferences (bottom, oyster bars, 

crevices, and channel edges) upon"their immigration to the sampling area. 

Such differential availability and/or vulnerability during ontogeny has 

been demonstrated in our study for spotted seatrout. 

Future studies that deal 6"th estuarine-dependent fishes that ?pawn out side 

of estuaries and are relatively uncommon will be most valuable if 

innovative sampling gear for late stage larva are designed. This gear may 

include a bow-mounted surface net, a high-speed, two-boat , larval-fish 

trawl, and a bottom sled. Furthermore, because of net avoidance, nighttime 

sampling should be employed, regardless of gear type. 

Spotted Seatrout 

Gear Assessment 

Our trout larvae collections were dominat5d by preflexion stage larvae 

(Table 5, Fig. 3). We believe that the frequency distribution of larval 

stages reflected the differential vulnerability of larvae to our gear (net 

avoidance by larger larvae), dispersal of larvae from a spawning 

aggregation (older larvae would be more dispersed), and natural mortality. 
'B > 

Table 5. Sumnary of larval spotted seatrout data. N following the station number 

indicates neuston tow; all other tows are step oblique. 

' NumSer Stage (Frequency ) 

Temperature Salinity of Mean Pre- Post - 

Date Station Time *C ' o/oo Trout SL rrm s flexi~n Flexion Flexion 

Mar 

1984 

May 

1984 

Jun 

1984 

Jul 

1984 

hug 

1984 

Day 

Day 

DJY 

Cay 

Day 

Day 

Night 

Day 

Day 

Day 

Night 

Day 

Night 

Night 

Day 

Day 

Night 

Day 

Night 

Night 

Day 

Night 

Night 

Day 

Day 

Day 

Day 

Day. 

F:ight 

Night 

Day 

Da Y 

Night 

Day 

Night 

Night 
Table 5 Contd. w 

Number, Stage (Frequency) 

Temperature -Salinity o f Mean Post - 

Date Station Time *C o/oo - Trout SL m s Preflexion Flexion Flexion 

SeP 19 Day 28.0 29.9 1 , 2.9 - 0 1 0 

1984 20 Day 28.0 29.9 7 1.9 0.4332 6 1 0 

20 Day 28.0 29.9 5 1.9 0.3227 5 0 0 

20N Day 28.0 29.9 1 1.8 - 1 0 0 

APr 15 Day 23.0 35.0 

1985 18 Day 22 .p 32.0 

18N Day 22'. 0 32.0 

19 Day ' 21.5 37.5 

20 Day 21.5 40.0 

25 " Day 21.5 r,: 39.0 

26 Day 22.0 40.0 

Jun 16 

1985 18 

18N 

19 

19N 

19 

19N 

20 

20 

21 

21N 

21 

21N 

24 

Day 

Day 

Day 

Day 

Day 

Night 

Night 

Day 

Night 

Day 

Day 

Night 

Night 

Day 

Sept 15 Day 28.0 33,. 0 

1985' 19 Day 28.0 38.0 

19 Night 28.0 37.0 

25 Day 27.5 37.0 

' .. Total 718 610 - 81 7 
.._.' -. 

1 a 

ALLIQATOR REEF 

o STAQt 

MATECIABE 

KEY 

.Trout Captured 

0 No Trout Captured ik $- 

e 

STAQE 

Larval Stage Legend 

(example) 

Figure 3. The frequency di s tri butt on of 1 arval spotted seatrout developmental stages. 

All the larvae captured by the bongo sampler (N = 719) are included. 
Because of high variability in abundance of trout larva6 and the limited 

sampling possible at any one given time, we chose to use the data primarily 

in a qualitative way. The number of trout Larvae per sample resembles a 

negative binomial distribution (Fig. 4) that imposes certain restraints and 

limitations on the use of our abundance data. We feel our sampling scheme 

was not adequately designed to make quantitative or statistical areal 

comparisons. 

A greater density of trout larvae were taken by day step-oblique tows than 

night step-oblique tows (22.9 vs. 8.5 per tow), but differences of means 

from transformed data were not significant (0.30 < P > 0.20). We concluded 

that tows taken during daylight adequately sampled recently-spawned 

planktonic larvae. There appeared, however, to be a slightly greater 

proportion of larger larvae taken at night (Fig. 5). Although there was a 

slightly greater proportion of flexion larvae captured at night, very few 

postflexion larvae were collected (Fig. 5). This suggested to us that 

these older nektonic larvae were not accessible to the gear and to study 

this li-fe history stage would require the development of different sampling 

gear. ' f 

More trout larvae were captured in step-oblique tows than neuston tows both 

during the day (14.3 vs. 0.5 'per tow) and night (8.6 vs. 2.4 per tow). 

Neuston tows fileer approximdtWy. one-half the volume of water of 

step-oblique tows and they would be expected to catch half as many larvae 

if they were distributed uniformly. The relatively low catch in the day 

neuston-tows may indicate active avoidance of the surface by seatrout 

larvae during daylight hours, as there was a greater proporti~n of seatrout 

larvae in the neuston at night than day. We concluded from our gear 

assessment analysis that step-oblique tows are preferable to neuston tows, 

especially durirrg daylight, and that they can provide information valuable 

in describing spawning areas both spatially and temporally. Step-oblique 

tows at night provided very limited additional information beyond day-tows 

in describing the life history of postflexion larvae. 

Distribution and Abundance 

A, 

Seatrout larvae were captured throughout the year except cruises in 

November and December (Table 5, Figs. 6-8). They never were the dominant 

species (Figs. 6-8). We collected the majority of trout during late 

spring and throughout the summer. Our seasonal collections along with 

those of Jannke (1971) demonstrate that spawning is minimal during late 

fall and throughout the winter months, peaks during mid-to-late spring 

continues during the summer at moderate levels, then declines with the 

onset of winter. 

The spatial distribution of trout larvae (Table 5, Figs. 3, 6-8) and 

juveniles (Thayer et al. 1987) suggested that spawning and the early life 

history of spotted seatrout occurs mainly in the western section of the 

Park, but studies by Park personnel indicates that there is some spawning 

activity in northeastern Florida Bay, an area not sampled by us. To 

determine the specific areas where spawning occurred, we used the 

occurrence of preflexion larvae to indicate recent spawning (Fig. 3). 

Based on a laboratory study (Fable et al. 1978), preflexion larvae are no 

older than approximately 7-days. Spawning appeared to be most intense in 
NUMBER OF TROUT PER SAMPLE 

Figure 4. The frequency of spotted seatrout per sample. 
7 E r6 

WU 

E E 

Er6 

E3 l-u 

$2 

u 
SPRING 

MARCH 1984 

APRIL 1985 

7 Trout Larvae1 100d 

61284 -Total ~arvae1100m' 

Day Sample 

Night Sample 

LEGEND 

Figure 6. The relative abundance of spotted seatrout and total fish larvae 

during spring. Dash indicates no sample taken. 
JUNE 1984 

SUMMER 

JUNE 1985 

JULY 1984 

AUG 1984 

Figure 7. The relati& abundance of spotted seatrout and total fish larvae 

during summer. Dash indicates no sample taken. 
FALL 

SEPT 1984 

SEPT 1985 

NOV 1984 

NOV-DEC 1984 

Figure 8. The relative abundance of spotted seatrout and total fish larvae 

during fall. Dash indicates no sample taken. 
the Cormorant Pass area (Station 18) and in the northwestern portion of 

Florida Bay (Stations 19,20, and 21). Moderate spawning appeared to occur 

in the southwestern part of Florida Bay (Stations 24,25, and 26) and in 

Ponce de Leon Bay (Station 15) in the northwest area of our study. On the 

western side, we never caught trout in Man of War Channel (Station 23) nor 

Tarpon Bay (Stations 22) and preflexion trout were never captured in the 

upper Shark River (Stations 16 and 17). Studies by Park personnel also 

indicate that spotted seatrout spawn mainly in western Florida Bay. 

To determine if we could discern any relationship between station salinity 

and presence of preflexion trout larvae, we began by plotting seasonal 

salinities against stations (Fig. 9). There are, in general, three groups 

of stations with different salinity characteristics. Most of the stations 

we sampled were in relatively high salinity waters. Two, Cormorant Pass 

(Station 18) and once de Leon Bay (Station 15), had intermediate 

salinities while three in the upper Shark River (Stations 16 and 17) and in 

Tarpon Bay (Station 22) had low and highly variable salinities. Based on 

the abundance of preflexion trout larvae it appears that spawning occurs in 

moderate and high salinities, but no spawning occurred at low and variable 

salinities. Therefore, based on past studies (Collins and Finucane 1984), 

this study and ongoing studies (National Park Service, unpublished data), 

spotted seatrout do not appear ,to spawn in brackish waters of the western 

estuaries of the Evergiades National Park. 

Abundance and Distribution of Total Ichthyoplankton 

Although not a primary objective of this study, we have analyzed 230 

samples (Table 2) to gain an insight into the general ichthyoplankton 

abundance, distribution and diversity. Because our collections were 

usually dominated by early stage larvae i., preflexion larvae) we can 

gain some understanding as to the spawning time and areas of major 

taxonomic groups. This should provide guidance for more in-depth studies. $& 

Peaks in larval fish abundance' appeared to occur during early spring (March 

1984, April 1985) ; moderate abundances during the summer ; and relatively 

low abundances during the late fall (~ovember/&cember 1984) (Table 6). We 

are unable to explain the relatively low, abundances .in May, but it appeared 

that the early spring peak was an outcome of intensive gobiid spawriing in . 

the Shark River area (Stations 15-18) (Fig. 10 and see discussion below on 

specific taxa). For example, during March 1984, one sample taken at the 

upper Shark River (Station 17) yielded approximately 14,000 .gohiid larve 

per 100 m3. 

Larval abundances were consistently high in the Lower Matecumbe Key area 

(Stations 10-12), Alligator Reef (Station 14), Cormorant Pass (Station 18) 

and the area near Flamingo Channel (Station 21) (Table 6). The habitats in . 

these areas differ (Thayer et al. 1987) as do the dominant ichthyoplankton 

groups (Figs. 10-12). For example, gobiid larvae almost solely dominate at 

Cormorant Pass (Station 18). At Flamingo Channel [Station 21) gobiid 

larvae dominate, but there is a slightly more diverse group of dominant 

ichthyoplankton. At Alligator Reef (Station 141 high abundances were 

accompanied by a high diversity of taxonomic groups (Figs. 10-12). 

Relatively low abundances of ichthyoplankton were collected at Tarpon Bay 

(Station 221, Blue Bank (Station 26) and Snake Creek (Station 27) -- three 

diverse areas. A greater diversity of ichthyoplankton was collected at 
40 - 

o o @ fpanfQnQQQ 

Spring 

Mar 84 

20 Apr 85 

May 84 

22 17 16 18 30 15 28 27 29 19 20 21 25 12 26 14 13 24 23 11 

Summer 

Jun 84, 85 

Jul 84 

Aug 84 

- Fall 

Sep 84, 85 

Oct 84 

Nov 84 

STATION 

Figure 9. Mean seasonal sal in1 ties and ranges at ichthyopl ankton stations. 

Stations are arranged by increasing sal inity. Darkened circles 

denote those stations *ere preflexion 1 arvae were collected. 
Table 6. Total fish larvae abundance (number per 100 m3) in each cruise. 

When replicate and day-night tows were taken, data were averaged 

(geometric mean). 

STATIaJ 

DATE 11 12 13 14, 15 16 17 18 19 20 21 

Mar 

84 1095 826 1067 157 194 1212 5368 1824 569 1089 3558 

, 

Jun 

84 444 289 433 1061 217 328 82 2782 103 124 452 *> , 

Jul 

84 146 239 275 77 398 108 38 1337 155 246 823 

Nov 

84 98 118 204 48 40 10 29 103 163. 222 103 

Jun J. 

85 463 83 227 225 32 50 44 3862631- 398 2612 

Geometric -. 

Mean 223 178 234 176 103 68. 80 357 148 ' 110 295 

Geometric Mean 

(excluding 

Mar 84) 

187 150 197 179 96 49 50 298 127 85 224 
Table 6 (Contd) 

SnXrIQrJ 

Geometric 

DATE 22 23 24 25 26 27 28 29 M mean 

Mar 

84 - 

May 

84 0 

Jun 

84 11 

Jul 

84 30 

Aug 

84 29 

sep 

84 15 

Nov 

84 0 

Nov/Dec 

84 0 

APr 

85 231 

Jun 

85 9 

Geometric 

Mean 12 
COW .,aJ P cnc 

a E ac, u 3- + s P't 

L EO 0s- 
Jun. 1984 

Jul. 1984 

Aug. 1984 

Figure 11. The dominant ichthyoplankton of Florida Bay and adjacent waters 

during the summer. See Figure ID for explanation. 
FALL '- 

scot 1984 

Oct 1984 

Nov. 1984 

TARPON BAY 

BlennlMae-7 

OPhM~idsbo 

-27 Cumoidae-6 aobl#u -27 OoMe.ocid.b4 

EnqdMss-11 L.brid.H 

r&yz ESfLe-s 

8.n.n16e-e Enq-e-3 

$fennildam-2 -el 

CIMdas-2 R.gnuc.rotldr1 Cynogloasldae-2 ' , ,. ch.ot~M..-l 

Sclaenidao-2 Q0nomtwtld.o-1 

UMsntHied-2 , CirnnJ.tId80-1 -1 

MTECUUE Trn.odOntid.cl 

KW Umlo8mpm~l 

Figure 12. The dominant i chthyoplankton of Florida Bay and adjacent waters 

during the fall. See Figure 10 for explanation. 
Blue Bank and Snake Creek than at Tarpon Bay. The latter was dominated by 

gobiids. -, , \ 

'8 1 

, One of the most striking patterns we have been able to discern from our 

study is the dominance and ubiquitous distribution of gobiid larvae (Figs. 

10-12). Gobiid larvae ranked first in abundance of 13-, 16-, and 18-out of 

20 stations during the spring, summer and fall, respectively (Fig. 10-12). 

They dominated our collections in diverse habitats. For example, during 

the summer they were first in abundance at low salinity stations at Shark 

River (16, 17 and 22), at many northwestern Florida Bay stations (20, 21, 

23 and 26), ' at most Florida Bay stations adjacent to the Keys (11-13, 28, 

29), at Alligator Reef (14) and Whale Harbor Channel (30). At every 

cruise, they ranked first in abundance at eight stations, two in eastern 

Florida Bay (Stations 13 and 30), two in western Florida Bay (Stations 21 

and 23), and four in Shark River and adjacent waters (Statons 16, 17, 18 

and 22). Although we do not have the gobies separated to species, Thayer 

et al. (1987) and Roessler (1970) suggested that there are numerous 

species occurring within the Park and adjacent waters (e.g.! Alligator 

Reef). The separation of these gobies into species is difficult as the 

larval stages have not been described for many of the species. 

It appeared that certain larval fish types are more available to neuston 

tows than step-oblique tows. The Atherini formes (Atherinidae, Belonidae 

and Exocoetidae) were more dominant in neuston tows (Table 7) than 

step-oblique tows (Figs. 10-12). Seasonally, atheriniform larvae were 

rarely a dominant component of the ichthoplankton collected by step-oblique 

tows and they were only relatively abundant at stations adjacent to the 

Keys (Figs. 10-12). When we compared concurrent tows (i. e. ,step-oblique 

tow followed by a neuston tow) the difference in occurrence of atheriniform 

larvae between neuston and step-oblique tows was dramatic (Fig. 13). Heavy 

melanistic and xanthic pigmentation in atheriniform larvae provides 

protection from ultraviolet radiation and allows this group to exploit a 

seemingly food rich environment [Moser 1981). These differences in catches 

demonstrate that neuston tows are valuable when atheriniform life histories 

are of interest. 

We were not able to determine if water clarity affected larval 

vulnerability. With the exception of one station (Snake Creek -- Station 

271, all stations in east Florida Bay have clear water. On the western 

side of Florida Bay and adjacent waters, all stations except Blue Bank 

(Station 26) and Man of War Channel (Station 23) had turbid waters either 

from the suspension of calcium carbonate mud, detritus or high tannic acid 

loads. We observed slightly lower abundances at Blue Bank and Man of War 

Channel (Stations 26 and 23, respectively), stations of high water clarity 

that were only sampled during daytime, than at two adjacent stations 

(Stations 24 and 25) where water clarity was poor but were also only 

sampled during daytime (Table 6). 

The dominant ichthyoplankton we found was similar to that reported in a 

previous ichtyhyoplankton survey along the west coast estuaries of the 

Everglades (Collins and Finucane 1984) and adjacent areas (Biscayne Bay, 

Houde and Lovdal 1984). In Biscayne Bay, a relatively shallow subtropical 

lagoon, the most abundant family was Clupeidae, followed by Engraulidae, 

then by Callionymidae and Gobiidae. In our collections clupeoids were not 

as dominant as in Biscayne Bay, but Callionymidae larvae were among the 

dominant ichthyoplankton in eastern Florida Bay stations (12, 13, and 29) 

during certain seasons (Figs. 10-12). Like Houde and Lovdal (1984), 
Table 7. Dominant ichthyoplankton collected by neuston tows. 

" 

Total* Rank 

Date Station Time Larvae First (%) Second (46) Third (%) , 

Mar 84 15 Day 23 Gobiidae (78) Sparidae (9) Sciaenidae (4) 

Unknown (9) 

16 Day 76 Gobiidae (80) Atherinidae (8) Gobiesocidae (7) 

18 Day 300 Gobiidae (76) Atherinidae (15) Engraulidae (4) 

19 Day , 189 Clupeiformes (63) Gobiidae (12) Unidentified (12) , Atherinidae (12) 

2 1 Day 37 Clupeiformes (49) Atherinidae (24) Unidentified (14) 

May 134 13 Night 53 Gobiidae (55) Exocoet idae (13) Atherinidae (9) 

Belonidae (13) 

14 Night ., 387 Olbpeidae (76) Unknown (15) 

15 Day 60 Atherinidae (57) Gerreidae (25) 

18 Day 34 Atherinidae (50) Blenniidae (44) 

19 Night 38 Exocoetidae(26) Gobiidae(18) 

24 Day 58 Atherinidae (47) Clinidae (24) > L 

26 Day 1 ' Exocoetidae (100) - 

Gobiidae (7) 

Engraulidae (8) 

Gobiidae (3) 

Syngnathidae (3) 

Unknown (16) 

Gerreidae (13) 

Unknown (9) 

28 Day 29 Abherinidae (79) Clupeidae (21) - 

Sep 84 11 Night 9 Ciinidae (56) Atherinidae (11) - 

Gerreidae (11) 

Balistidae (11) 

Unknown (11). .-- 

12 Night 81 ~allion~mida~(36) Gobiidae (16) ~lupeidae (7) 

Clinidae (36) 

13 Night 121 Gobiidae (49) Clinidae (39) Clupeidae (5) 

15 Day 9 Blenniidae (33) , Gobiidae (22) Atherinidae (11) 

~ngraulidae (22) Carangidae (11) 
Table 7 (Contd) _, y 

, '1 

\ L 

Total . Rank 

Date Station Time Larvae First (%) Second [%) Third (%) 

-- 

Sep 84 (Contd) 

17 . Day 2 Atherinidae (2) - - 

18 DaY 25 Gobiidae (48) Blenniidae (40) Clinidae (8) 

19 Day 24 Clupeidae (75) Gobiidae (20) Clinidae (4) 

20 Day 30 Clinidae (33) Clupeidae (2) Athekinidae (17) 

Engraulidae (20) 

21 Day 18 Atherinidae (72) Gobiidae (22) Engraulidae (6) 

22 Day 2 Atherinidae (100) - - 

23 Day 6 Clinidae (50) Atherinidae (33) Gobiidae (17) 

24 Day 14 Gobiidae (29) Blenniidae (21) Atherinidae (7) 

Clinidae (29) Gerreidae ( 7) 

Syngnathidae (7) 

i 25 Day 6 Atherinidae (33) Callionymidae (17) Clupeidae (17) 

Gobiidae (17) - 

Microdesmidae (17) 

26 Day 1 Gobiidae (100) - - 

27 Day 11 G~biidae (55) Clinidae (27) Gerreidae (38) 

Night 16 Gobiidae ($1) Atherinidae (12) Unknown (6) 

28 Night 23 Gerreidae (39) Clinidae (30) Cynoglossidae (13) 

29 . Night 28 Gobiidee (43) Callionymidae (25)~linidae (21) 

MV/ 84 19 Night 8 Gobiidae (50) Balistidae (25) Blenniidae (12) 

Dee Wgilidae (12) 

\ 

Collins and Finucane *(I9841 reportedithat clupeids and engraulids dominated 

their,collections, but clupeids were rarely caught at estuarine stations. 

'A paucity of ichthyoplankton, both in terms of abundance and diversity, was 

collected in the estuarine zone compared to the coastal marine zone. They 

concluded that low and variable salinity was one of the several 

environmental factors that limited the abundance of larvae in the estuarine 

zone. At our estuarine stations (Stations 15, 16, 17, 18 and 22), 

diversity was also low (Figs. 10-12) but, with the exception of Tarpon Bay, 

abundances were not unusually low. Tarpon Bay had variable and lowest 

salinities (Fig. 9) and the overall abundance was the lowest we observed 

(Table 6). 

CONCLUSIONS 

1. Spotted seatrout spawn in intermediate to high salinities of 

western Florida Bay and adjacent waters, but did not appear to 

spawn in bracki~h~habitats in this area. 

2. Spotted seatrout larvae were never collected in the Keys. The 

central and eastern region of Florida Bay and adjacent waters should 

be sampled to provide additional insight into trout spawning in 

Park waters. 

3. Spotted seatrout have a protracted spawning season. Spawning appears 

minimal during late fall and winter, peaks in mid-to-late spring, 

continues during the summer at moderate levels, then declines with the 

onset of declining temperatures and photoperiods. 

4. Gray snapper, snook and red drum spawn outside of Park waters. 

5. Gray snapper larvae can not be positively identified in 

ichthyoplankton samples because of possible confusion with related 

species that have not been adequately described. 

6. Based on the location, size and timing of snapper larvae it appears 

that they spawn offshore in summer and at least some migrate into 

Florida Bay as juveniles. 

7. The lack of larval snook and red drum in our samples does not 

indicate they are absent from the area. Adults spawn outside the 

Park, thus the larval supply is susceptible to considerable 

mortality prior to migrating into the Park. They are less 

vulnerable to the gear because they are relatively well developed, 

and they may not be available to standard ichthyoplankton gear due 

to preference for the bottom, crevices or channel edges. Our lack 

of intensive nighttime sampling, especially during October, may also 

have accounted for our lack of red drum. 

8. Step-oblique tows are appropriate for sampling preflexion larvae. 

Unfortunately, the life stage which is more likely to provide 

critical life history information in the Park is the unstudied 

post f lexion/early juvenile period. Studying that life stage would 

probably be the most cost efficient way to increase our knowledge 
of the life history of these species, but it may require development 

of different gear. 

9. Goby larvae dominated most larval collections especially in 

northwestern Florida Bay and the Shark River area. 

ACKNOWLEDGMENTS 

We thank the staff at Everglades National Park for their cooperation, 

background information and hospitality, and Joanne Schultz, Gulf Coast 

Labortory, for verifying the identification of many of our trout larvae. 

The U.S .-Polish Plankton Sorting and Identification Center ably assisted in 

the sorting of plankton. We are grateful to the following WS, Southeast 

Fishery Center staff for their laboratory and field assistance: Don Field, 

Mike LaCroix , Kenyon Lindeman , Patti McElhaney , Keith Rittmaster , Jose 

Rivera, Vicky Thayer and Stan Warlen. 
LITERATURE CITED . / 

Collins, L, A. , and 3. H. Finucane. 1984. Ichthyoplankton survey of the 

estuarine and inshore waters of the Florida Everglades, May 1971 to 

February 1972. NOAA Tech. Rep. NMFS 6, 75 p. 

Croker, R.A. 1960. A contribution to the life historv of the arav 

(mangrove) snapper, Lut janus griseus (~innaeus ) . M.S. thesis .- Univ . of Miami, Coral Gables, FL. 

Elliot, J.M. 1977. Some methods for the statistical analysis of samples of 

benthic invertebrates (2nd edition). Freshwater Biol. Assoc, Sci. Publ. 

No. 25, 160 p. / 

Fable, W.A., Jr., T.D. 'williams, and C.R. Arnold. 1978. Description of 

reared eggs and young larvae of the spotted seatrout, Cynoscion 

nebulosus.~ Fish. Bull.,,U.S. 76: 65-71. 

Fore, P.L., and T.W. Schmidt. 1973. Biology of juvenile and adult snook, 

Centropomus undecimalis , in the Ten Thousand Islands, Florida, Chap. 16. 

- In Ecosystem analyses of the Big,Cypress Swamp and Estuaries. U.S. 

Environmental Protection Agency, Surveillance and Analyses Div., 

Athens, GA., 188 p. 

Gilmore, R.G., C.J. Donahue, and D.W. Cooke. 1983. Observations on the . 

distribution and biology of east-central Florida populations of the 

common snook, Centropomus undecimalis (Bloch) . Florida Sci . ' 46: 313-336. 

Holt, J., A.B. ~ohnson, C.R. Arnold, W.A. Fable, Jr., and T.D. ~illiams. 

1981. Description of eggs and larvae of laboratory reared red drum, 

Sciaenops ocellata . Copeia 1981 (4) r 751-756. 

Houde, E.D., and N. Chitty. 1976. Seasonal abundance and distribution of 

zooplankton, fish eggs and fish larva in the eastern Gulf of Mexico, 

1972-74. U.S. Dept. Commer., NOAA Tech. Rep. NMFS SSRF-701, 18 p. 

Houde, E.D., and J.A. Lovdal. 1984. ~easonaiit~ of occurrence, Poods and 

food preferences of ichtyhyoplankton in Biscayne Bay, Florida. 

Estuarine, Coast., Shelf Sci. 18: 403-419. 

.- 

Jannke, T. 1971. Abundance .df young sbiaenid fishes in ~ver~ladbs .~ational 

Park, Florida in relation to season and other variables. Univ. Miami 

Sea Grant Tech. Bull. 11: 

Laroche, W.A. 1977. Description of larval and early juvenile vermillion 

snapper, Rhomboplites aurorubens . Fish. Bull, U.S. 75:547-554. 

~au , S. R. , and P.L . Shaf land. 1982. Larval development of snook , Centropomus undecimalis (Pisces : ~entropomidae).. Copeia 1982(3) : 

618-627. 

Moser, H.G. 1981. Morphological and functional aspects of marine fish 

larvae, p. 88-131. In (R. Lasker, ed.) Marine fish larvae. 

Washington Sea ~rantFrogram. 
peters. K.M.. and R.H. &Michael, Jr. 1987. Early life history of the red 

dm, ~ciaeno~s ocellatus I~isces r ~ciaenidae ),in Tampa ~ay, Florida. 

Estuaries 10892-107. 

Powles, H., and V.W. Stender. 1978. Taxonomic data on the early life 

history stages of ~ciaedidae of the South Atlantic Bight of the United 

States. South Carolina Mar. Res. Ctr . , Tech. Rep. 31, 64 p. 

Randall, J.E. 1983. Caribbean reef fishes. T.F.H. Publ., N. J. 

Richards, W. J., and V-P. Saksena. 1980. Description of larvae and early 

juveniles of laboratory-reared gray snapper, Lutjanus griseus 

(Linnaeus ) (Pisces, Lut janidae ) . Bull. Mar. Sci . 30 t 515-521. 

Roessler, M.A. 1970. Checklist of fishes in Buttonwood Canal, Everglades 

National, Park, Florida, and observations on the seasonal occurrence and 

life histories of selected species. Bulk. Mar. Sci. 20: 860-893. 

Rutherford, E., E. Thue, and D. Wlker . 1982. Population characteristics, 

food habits and spawning activity of spotted seatrout, C noscion 

nebulosus, 

Research Center Report 

in Everglades 

T-668, 48 

National 

p. 

Park, Florida. South + Flor da 

. 1983. Population structure, food habits, and spawning 

activity of gray snapper, Lut anus griseus, in Everglades National 

Park. South Florida Research --+ Cen er Report SFRC-83/02, 41 p, 

Sokal, R.R., and F. J. Rohlf. 1981. Biometry (2nd edition). W.H. Freeman 

Co., San Francioks, 859 p. 

Starck, W.A., 11. 1964. A contribution to the biology of gray snapper, 

(Linnaeus), in the vicinity of lower Matecumbe Key, 

issertation. Univ. of Miami, Coral Gables, FL. 

Starck, W.A., 11.. 1970. Biology of the gray snapper, Lut 'anus qriseus 

(Linnaeus), in the Florida Keys, p. 11-150. In W.A* I1 and R.E. 

Schroeder . Investigatf ons on the gray snappec ~ut janus griseus . Stud. frop. Oceanogs, Idnkv. Mami 10, 

~ha~er, G.W., W.F. Hettber, Jr., A.J. Chester, D.R. Colby, and P.J. 

McElhaney . 1987. Distribution and abundance of fish communities 

among selected estuarine and marine habitats in Everglades National 

Park. South Florida Research Center Report SEW-87/02, 166 p. 

The, E.G., E.S. Rutherford, D.G. Buker. 1982. Age, growth and mortality 

of the 6 S~POO~, (Bloch), in the 

Everglad t ional rida Research Center 

Report T-483. 
APPENDIX A 

Design and Operation of a Bongo Net 

Deployment System for Small Craft 
ABSTRACT 

Bongo nets towed at low speeds have proven to be successful in 

ichthyoplankton surveys, This gear, however, is usually towed from 

hydrographic winches mounted on large research vessels. To allow bongo net 

tows to be made in shallow water, a low cost all-metal mast and boom 

arrangement was designed tfoc deployment of such gear from an open, outboard 

motor boat. The entire device is portable, detachable and can be used in 

waters as shallow as 1.5 m. 

INTRODUCTION t 

In January 1984<'the Beauf ort Labor ator y , Southeast Fisheries Center, 

National Mardne Fisheries Service, began a survey of the distribution and 

abundance of larval fish entering and utilizing the waters of the Everglades 

Natidrral Park,, Florida. The waters to be surveyed were mostly shallow (1-3 

m), confined, or otherwise unaccessible to craft large enough to mount and 

deploy a standard 60-cm bongo net. 

The nature of the environmknt, the need for ichthyoplankton tows at various 

levels of the water column, and-the need to cover many stations each day 

during the sampling period, required devising a method of deploying bongo 

nets from a fast, highly maneuverable, shallow draft craft. Further, the 

nets needed to be towed from the side of the vessel to avoid sampling in the 

propeller wake. 

A number of small-boat mounted sampling systems have bee'h .described (Dove1 

1964, Sevedberg 1967, NetsCh et al. 19711, but none address the problem of 

towing 60-cm bongo nets, which have become a standard larval fish sampling 

gear (Posgay et al. 1968; Houde et al. 1979). 

Here we describe the system we developed for safe and successful'deployment 

of 60 cm bongo nets from a small craft. 

.d 

DESCRIPTION, AS~MBLY AND OPERATION 

The deployment device (Fig. 1) operates much like a cargo-handling mast and 

boom assembly. The device was-fabricated from galvanizedfsteel pipe by a 

local machine shop at a cost of $400. All of the ancillary hardware-stays, 

lines, etc., were available in local hardware or boating supply stores. 

There are four basic parts to the device (Fig. 2): an upright mast, with an 

attached "POW-R-winch" Model 412C winch; a mast mounting base; a horizontal 

boom with swivel block, forestay, safety chains, and a 'snap back" preventer 

spar; and a short bar welded to the boom to provide leverage when swinging 

the gear in or outboard. The winch is poweled by four 12 Volt m~rine 

batteries wired in parallel. An alternator attached to the boat s outboad 

motor recharges the batteries as the boat runs from station to station. 

C)- 26 KG DEPRESSOR 

- *. . L L 

-' 

Figure 2. Bongo net deployment, mast,. boom and wtnch assembly. Safety chafn is 

detached before net is deployed. Preventor bar is unpinned at lower 

end and safety chain is attached before net is raised out of water 

and brought aboard. Winch shown was 1 ater replaced with a self-tqi ling 

automatic windlass. Mast assembly was mounted 4 meters from the bow on 

the boat's starboard side. 
" 

To assemble the device, we first fit the upright mast into the base. This 

base (Fig. 3) is permanently mounted to the hull, 3.6 m forward of the 

transom by four lag bolts and a "sandwich" type Bracket, which is fitted 

over the starboard gunwale and through-bolted for maximum rigidity. 

Positioning the device in the forward half of the boat allows the use of the 

greater deck space there and provides for better weight distributionin our 

craft. 

Assembly continues by attaching the boom at its pivot point on the mast by 

using a slightly undersized bolt which allows free up and down motion of the 

boom. Finally, the preventer spar, support chain, and forestay are 

attached. This operation completes the assembly of the deployment device. 

Before getting underway, the bongo nets are attached to the device. This is 

done with 11-mn dacronydouble braided tow line, shackles and swivels. The 

tow line is threaded through the swivel block on the boom and a sheave atop 

the mast. After this, a small safety chain is connected to the bongo net 

frame. Since ,it is impractical to travel with the gear dangling outboard, 

the entire assembly can be swung inboard by use of the attached bar. It can 

then be secured while moving between stations. 

When on station, the boat is slowekl to towing speed 0.5 - 1.0 m/sec and the 

gear is lifted with the winch. It is then swung outboard and lowered to the 

water. We then pin the usnapback" preventer spar into position, release the 

safety chain, and lower the nets to the desired sampling depth. Once in the 

water, the gear is fished in a right-hand circle 50-100 m in diameter. This 

prevents entanglement of the nets or towline in the propeller. While 

towing, the forestay prevents the boom from bending +aft as a result of drag. 

Additionally, the mast is pinned to its mounting base to likewise prevent 

its turning due to the forces involved. 

To retrieve the gear, the deployment process is reversed., The nets are 

brought to the surface by means ofdthe winch. The boat is then stopped,, the 

safety chain re-attached, and the snap-backw preventer detached. The nets 

are then hauled onboard, again using the winch, for wash down and sample 

removal. 

3, 

For safe operation, the design must include the small safety chain between 

the boom and the bongo net frame and the "snap-back" preventer. It was 

found that while raising or lowering the nets without the safety chain, the 

boom tended to nriden the towline when the angle between the mast and boom 

was less than 45.. This caused the bongo net frame to drop dangerously 

several feet as the boom rose to the vertical position. The safety chain, 

attached at all times when the nets are not in the water, prevents this. 

Additionally, we found that, while fishing, the boom tended to "snapback" to 

vertical due to vector forces being applied. A heavier boom might have 

prevented this effect but, in order to save weight, the "snap-backw 

preventer was incorporated into the design. T 
Figure 3. Mast mounting base is permanently bolted to starboard sf& of hull. 

Mast is shown inserted and pinned in ffshins msition. 
DISCUSSION 

The gear is being successfully used in estuarine areas of both Florida and 

North Carolina. Experience Ras shown that a complete 3-minute oblique tow, 

from launch to recovery, in 2 m of water can be accomplished in less than 6 

minutes. Minimum working depth is 1.5 m and maximum depth is restricted 

only by length of line onboard and battery power available to retrieve the 

nets from depth. The gear can easily and safely be deployed by a crew of 

three - two handling the gear and bne handling the boat. 

Since small craft can enter waters not accessible by most vessels which 

currently mount bongo net and can exceed 45 km/hr while traveling between 

stations, a much wider area is now available for sampling with bongo nets. 

,,' , ACKNOWLEDGMENTS < 

This work ,was funded by the U.S. Department of Interior, National Park 

Service aiSd the National Marine Fisheries, Service, NOAA, under an 

interagency agreement. Use of trade names does not imply endorsement by the 

National Marine Fisheries Service, NOAA. We also thank the members of the 

staff of the U.S. Naval Academy Hydromechanics Lab who provided valuable 

advice during the design, of this gear. 
\ 

' \ ., > ' f REFERENCES , 

Dovel, W.L. 1964. An approach to sampling estuarine macroplankton. 

Chesapeake Sci. 5: 77-90. 

Hwde, E.D., Leak, J.C., Dowd, C.E., Berkeley, S.A., and Richards, W.J. 

1979. Ichthyoplankton tibundance and diversity in the eastern 

Gulf of Mexico., Final Report to Bureau of Land Management, 

Contract No. AA550-(37-28. 

Netsch, N.F., A. Houser, and L.E. Vogele. 1971. Sampling gear for larval 

reservoir fishes . Prog . Fish-Cult . 33(3) : 175-179. 

Posgay, J.A., R.R. Marak, and R.C. Hennemuth. 1968. Development and 

tests of new zooplankton samples. Int . Comm. Northwest Atl. Fish. 

Res. Doc. 85. 

Swedberg, D. 1963. A trawling device for small boats. Prog. Fish-Cult. 

29 (4) : 241-242.