FULL-SCALE OPERATIONAL DEMONSTRATION OF FINE MESH SCREENS AT POWER PLANT INTAKES
V. Brueggemeyer, D. Cowdrick. and K. Durrell



### Tampa El

## ectri c Company

O. Box 111 

### Tampa, Florida 33601
S. Mahadevan and D. Bruzek Mote Marine Laboratory 1600 City Island Park Sa

## rasota, Flori

# da 33577

ABSTRACT Tampa Electric Company (TEC) operates four coal- fired generating units at the 

### Big Bend Station located on Tampa Bay in North Ruskin, Florida. All four units use once-

### through condenser cool i ng systems. Prior to the construction of Big Bend Unit 4, environmental agencies expressed 

## concern over entrainment of organi

# sms. Engi neering 

### and bi 01 ogi ca 1 

## studi es conducted in 1980 indicated that the application of fine mesh screens (FMS) at the station would reduce entrainment levels.As a result of this, the environmental agencies authorized the use of a oncethrough condenser cooling system in Unit 4 with the installation of FMS (0. 5 rom) 

### on both Uni ts 3 and 4. In conducting required post-operational (February 1985) studies to verify expectedscreening efficiencies, TEC identified that sampling methodologies. and the nature and extent of operational and maintenance procedures were critical in achieving good screening efficiencies. This paper summarizes TEC efforts in ascertaining adequate screening efficiencies.

INTRODUCTION In February 1985. Tampa Electric Company (TEC) placed in commercial operation 

### Unit 4 at the Big Bend Station. The site presently operates a total of four 

## coal-fired generating units in the 400 MW range and is located on the eastern shore of Tampa Bay in North Ruskin, Florida (Figures 1 and

# 2). All four units have once- through condenser cool ing systems. Each uni t draws 

## approximately 540 cfs of bay water from a single intake canal and releases it to the Bay via a single discharge canal. Both the Environmental Protection Agency (EPA). Region IV, and the Florida Depart

### ment of Environmental Regulation (FDER) expressed concern, prior to the construction of Unit 41 over losses of organisms due to entrainment into the existing 

### condenser coollng systems. Accordingly. early in 1979 TEC conducted a full-scaleprototype evaluation of a fine mesh screen (FMS) system as part of Unit 4' s 316



### Demonstration. The prototype studies were performed by Stone and Webster 

### Engineering Corporation (SWEC) and Mote Marine Laboratory (MML).Based on the positive results obtained from the prototype. the environmental agencies determined that Unit 4 could be constructed with a once- through condenser 

## cool ing system provided that a FMS system be incorporated into the intake structures 

### of both Units 3 and 4. 

## This novel system consists' of six continuously traveling 

## screens with 0. 5 mm screen mesh with specially designed organi sm troughs and spray 

## washes (Fi gures 3 and

## 4). Verification of expected screening efficiencies was required by the environmental 

# agencies. Results from the post-operational biological studies identified that not only was the sampling methodology not adequate. but also more crucially, there were operational differences between the prototype and the full-scale system. An intensive operational and maintenance (0 & M) auditing program was conducted. 

### Such a program enabled TEC to develop critical 0 & M procedures. All six screens are now in optimum operational conditions. With sampling methodology streamlined, TEC conducted additional biological studies during the 1987 spawning season in order to verify expected screening efficiencies. 

## Thi s paper focuses on the

## i ntens i ve 0 & M audi ti ng program performed as a mean to develop and implement critical 0 & M procedures; and furthermore, the subsequent verification of screening efficiencies.

FULL-SCALE PROTOTYPE SYSTEM 

# In 1979. two separate studies were conducted. One was a partial backfit of an existing traveling screen with 0. 5 mm FMS to determine whether Representative Important Species (RIS) as shown on Table 1 were capable of surviving impingement 

### on the screens under conditions of existing screen design. The other was a flume study in which RIS were impinged on a FMS panel over a range of impingement velocities and durations to determine the relationship between specific velocity/ 

### impingement duration conditions and survival rate. Both studies yielded positive results, with acceptable survival rates 

# (1). Based on this, a decision was made to proceed with a full-scale prototype investigation. A full-scale prototype, identical in every way to the proposed installation except 

## only 0. 6 m wide, was constructed and placed into service in March 1980 (Figures 

## 5 and 6). The prototype was located in the intake canal upstream of the existing Units 1 through 3 travel ing screens and pumps 

### (Figure 2). The screen was situated on a test platform connected to land by an existing bridge. 

### Figure 5 shows a more detailed plan of the screen operating deck. The prototype screen was of the dual- flow type and incorporated all of the features required 

### for fine mesh screening. 

## Seal s were incorporated between screen baskets and between the baskets and the side frames to minimize the passage of organisms through these 

### areas. The screening medium was a 0. 5 mm square mesh made of woven-monofilament polyester, and each of the 48 screen baskets were 0. 

## 6 m wide by 0. 6 m high.The screen was capable of operation at speeds of up to 14 cm/s and maximum impinge

### ment durations of 7 minutes. Flow through the screen was supplied by an in-

## line pump (bow thruster) located under the test platform and connected directly to the screen via a transition section (Figure 

# 6). Assorted pulleys allowed for flowadjustments which resulted in screen velocities of 8 to 46 cm/s. The test screen incorporated a shallow lifting bucket on ,

### each 0. 6 m wide screen 

## basket which retained approximately 2. 54 cm of water. 

## A low pressure (10 psi) spray header located on the ascendi 

# ng si de of the screen acted to remove organi 

### sms from the screen mesh surface and lifting buckets. A high pressure (55 psi) spray header was located on the descending side of the screen to remove any remaining 

# debris into a separate trough. A screenwash sump with a strainer was located 

### on the operating deck and took suction from the filtered water. 

## As each screen basket passed the spraywash. organisms on the mesh or in the lifting bucket were gently rinsed into a collection trough (Figure

# 6). Once in the trough. the organisms flowed by gravity into a collection tank where organisms were collected and transported to the 

## aboratory for anal ys is.The results of these studies concluded that the FMS technology was a viable alternative for removal of organisms from the circulating cooling water and that the 

### 5 rom mesh used was capable of effectively screening RIS ife stages under study 

# (1, 2). Furthermore, the studies also concluded that the installation of this technology on Big Bend Units 3 and 4 would result in entrainment losses less than 

### those experi enced wi th Uni ts 1 

## through 3 wi thout di 1 ut ion pumpi ng (1).In addition to the above studies, two other studies were conducted to gather information pertinent to the overall evaluation of FMS technology at Big Bend Station. 

### These studies indicated the following 

## (1).

The spraywash system was less effective than anticipated and a substantial 

### degree of carryover to the high-pressure wash occurred. A porti on of the organi sms encounteri ng the prototype screen were not effectively screened; length data from organisms which had not been screened suggested that ineffective sealing around the screen assembly could be partially responsible for this. On the basis of these results, TEC authorized SWEC to develop modifications. Two modifications were made and incorporated to the system for further evaluation 

### during the Spring of 

### 1981. One consisted of making the lifting buckets wider 

### and shallower. The other one consisted of installing new seals between individual screen baskets to prevent organism , 

### losses through these areas. 

## The rubber seals were capped with stainless steel tensioning bars to hold the rubber firmly against 

### each adjacent screen basket. In addition. the screen s frame-

## to-basket seal, which prevents losses between the stationary frame of the screen and the rotating baskets, were al so inspected and adjusted to achieve better sealing. Subsequent to these modifications, biological studies were conducted to determine 

# the effectiveness of these changes. The studies concluded that the improved design features successfully eliminated the previous inefficiencies in the low-

## pressure spraywash system; and that the replacement and adjustments of screen seals were 

### critical in obtaining high screening efficiencies () 80%) 

# (1). Results of this study are summarized in Table 2.Based on this, the environmental agencies determined that Unit 4 could be constructed with a once-through condenser cool ing system and that a FMS system be installed at the intake structures of both Units 3 and 4.

FINE MESH SCREEN SYSTEM Figures 3 and 4 show the arrangement of the screenwell equipment for Units 3 and 4. Six fine mesh (0. 5 mm) traveling screens. designed and fabricated by FMC Corpora-

### tion, filter all water entering the screenwell. Standard, coarse mesh, dual flow

traveling screens filter the water before it enters the four circulating water 

## pumps. The coarse mesh screens are required to protect the pumps from debris in the event that the emergency slide gates. in the sheet pile wall of the screenwell opens upon high differential pressure. Low pressure and high pressure screen wash pumps take suction from the circulating water pump discharge and provide wash water to the spray nozzle supply headers 

### in each of the six fine mesh screens. Spray wash water with entrained organisms 

### and debris is collected in a trough and routed to an organism return sump. 

### The sump incorporates a trash basket to faci 1 i

## tate removal of debri Three 50% capacity organism return pumps take suction from the sump and discharge 

### into one of two 18 inch fiberglass organism return lines. 

## The organism return system discharges into a natural embayment south of the circulating water discharge 

### canal (Figure 2). The organism return pumps are Wemco- Hidrostal centrifugal screw pumps operating at 375 RPM with clearances sufficient to pass a 5- inch spherical 

## object. Stop logs are provided to close the entrance to the screenwell when a fine mesh screen is removed for maintenance. A control system has been provided to vary the speed of the fine mesh screens 

### from 7 to 28 fpm to minimize differential pressure across the screens. 

## Screen speed is varied by a General Electric variable frequency, variable voltage, motor 

### speed control system. Differential level is measured across the intake structure with one of two bubbler type level probes.



### POST-OPERATIONAL BIOLOGICAL STUDIES In fulfillment of environmental permit requirements for the construction of Big Bend Unit 4, TEC conducted post-operational studies during the 1985 spawning season in the full-scale FMS system in order to verify the results obtained earlier by the prototype system.

FMS Survivabilit 

## Study This study was conducted in order to verify that RIS were capable of surviving impingement on the full-scale system once screened. Sampling for this study was conducted during March through September 1985, at 

### three locations pertaining to Unit 4: (1) the screenwash station in front of the screens after the organi sms were screened and washed to the screen return; (2) the organism return discharge (ORD) station at the discharge point of screened organisms in the northern embargement of Apollo Beach; and (3) the control station 

# at the intake canal in front of the intake screens. Station locations are shown 

## in Figure 2. Methods used during this study were essentially similar to those used during the FMS Prototype study. 

### Results from this study are summarized in Tables 3 and 4. The study concluded that survival rates obtained were comparable to those obtained by the Prototype study, and in some cases, they exceeded those of the Prototype study 

# (4). addition, there was no significant difference in survival rates between stations; however, minor differences can be attributed to natural mortal ity not associated to the FMS (1).

## .... ..,..... . "... .... .", ..... .., .

FMS Entrai nment StudThe FMS Entrainment study was conducted to evaluate and verify the screening efficiencies of the full-scale system. 

### Sampling was conducted at two stations simultaneously sampled. One station was located at the intake canal, and the other was located at an access manhole behind 

### the screens (Figure 3). Samples 

## were collected day and night using a 0. 505 mm 

### ichthyoplankton net. Four replicates were collected during each of the day and 

### night samplings. The intake samples were taken in oblique tows over the entire 

### water column. A volume of 100 cubic meters of water was filtered during each 

### intake replicate. The manholes samples were filtered through the net for a period 

## of twenty minutes over the entire water column. A flowmeter suspended inside the 

## mouth of the net determined the vol ume of water sampled.As indicated by Table 5, the results of this study showed that organisms, particularly eggs and larvae, were being entrained.

SOLVING THE PROBLEM As previously discussed, the testing of the FMS system during the 1985 spawning 

### season resulted in efficiencies much lower than expected. To address the problem, TEC establ ished a task force to identify potential problem areas and seek their 

# resolution prior to considering any design changes. Past 0 & M practices were 

# reviewed, as well as, test methodology. In addition, necessary maintenance was 

### performed to get the FMS in as designed conditions. These activities resulted 

### in significant findings affecting screening efficiencies. Each of these are dis

### cussed below.


## Maintenance During post-operational testing of the FMS system, it was noted that frequently one or more of the six screens were out of service due to mechanical problems 

### of the screen main chains. This caused higher flow rates through the screens,as well as, higher approach velocities, both of which had been identified as effecting screening efficiencies during previous studies (1, I). In an effort to address this, the screen chains underwent major repairs during the winter of 

### 1986. In order to determine the effectiveness of and optimum level of maintenance required for the screens, an auditing program was instituted by the task force and performed by MML. Weekly audits of the screens consisting of physical inspections of the 

# screens and the screen controls were performed. An audit form was developed and 

### used during the audit (Figure 7). The audits revealed the following problem items: 

## Tears and punctures of screens.
Tears of frame-

## to-frame seals. Inadequate installation of and tears of chain-

## to-frame seals. Clogging of spray nozzles and spray wash supply system. All of the above items were found to be associated with biofouling of the 

## system. In light of the above, TEC had new seals installed and adjusted. In addition, TEC implemented daily surveillance by operators, as well as, biweekly preventive maintenance plans by maintenance crews.

## ~-~---- d____--

Samp 1 i ng 

### Methodology In addition to the review of the 0 & M activities, TEC with the assistance of 

### MML reviewed the sampling locations and sample methodology. Divers inspected the marine environment within the screenwell and determined that sampling at this location would not be representative due to the establishment of fish populations within the screenwell. As a result of this finding, it was decided to add sample ports at the FMS assembly outlets (behind the screen themsel 

# ves). Sample ports were designed to be capable of sampl ing at three preselected flow elevations to account for a representative 

### flow through the screens. Engineering tests verified this and sample ports were 

### installed in all six screens 

## (~).

It was also determined that collection of inlet samples necessary for the calcula

## t i on of sc reeni

## ng effi ci enci es shoul d be done di rectly in front of the screens instead of using tows at the intake canal. Due to the significant increase in sampling costs related to these changes if sampling would take place at each of the six screens, TEC evaluated the viability 

## of sampl ing only one screen. Since the increased level of 0 & M practices assured that one screen would be mechanically representative of the others; it only remained necessary to assure that one screen would be hydraulically representative of the 

# others. In order to accomplish this effort, TEC contracted SWEC and Alder Research Laboratories to conduct the necessary flow and velocity measurements. Flow and velocity measurements were taken using an electromagnetic probe and meter. Velocities were taken along the centerline of the FMS discharge opening into the 

## screenwell at 0. 6 m intervals over 3. 

### 6 m of the opening. Horizontal velocity profiles were also determined by taking measurements at 0. 3 m of the centerline. Analysis of the data indicated that flow rates through all six screens were uniform 

# (~).

In addition, flow and velocities at the inlet and outlet of the 

## sampling points under consideration were determined to finalize the design of the new sample 

# ports. On the basis of this study, sample ports at both the inlet and outlet of two screens 

### were installed. One screen was used for actual testing and the other one as backup.

FMS Bi

### ofoul i ng Marine growth, particularly barnacles and oysters, was identified as the major source of screen mesh and seal failures, and of spray line and nozzle clogging. These organisms have a tendency to attach themselves to the larvae pan of the 

### FMS panels and puncture the screen mesh. Generally, these punctures are 

### small(pencil diameter or smaller); however, they are large enough to allow entrain

### ment of organisms. In an effort to promptly identify screen failures, TEC has implemented biweekly preventive maintenance inspections. Barnacle growth on the screen frames was also found to contribute to failure and poor performance of the frame-

## to-frame seals by causing them to deform and tear. Gaps between frames allow the passage of organisms into the screenwell. In response to this, TEC implemented both operator surveillance and maintenance inspections with a two-man crew capable of replacing these seals in a short time. Barnacles and oysters were found to lodge themselves in the piping system causing 

### spray pump performance to degrade rapidly. Although there is currently a duplex strainer in the suction to the high pressure pumps and one in the suction of the low pressure pumps, growth still occurs between the strainers and the pump suctions.0 & M procedures institued by TEC have found necessary to disassemble and clean the



### pumps as often as once a week. In an effort to minimize maintenance requirements, TEC intends to replace the duplex strainer in the suction of the high pressure pumps, where most of the clogging tends to occur, with individual strainers. Pump discharge lines were also found to be susceptible to biofouling resulting 

# in a decrease of pressure available to the screen spray nozzles. Loose shells tend to collect at elbows restricting pressure to the point that the lines must 

### be shut and cleared. This still remains a problem. Possible solutions beingconsidered are annual or biannual manual cleaning of the pumps during system outages, and modifications to the system to incorporate pipe line pigging capability. Loose shells in the spray nozzles were also identified as the cause of improper 

## removal of screened organisms. Operator surveillance implemented by TEC is geared 

### to evaluate spray patterns and intensity. Spray nozzle headers are flushed manually requiring the shutdown of a screen for a short period of time only. As discussed above, biofouling has been identified as a major source of maintenance 

### problems which greatly affects screening efficiencies. Control of it is very 

# difficult. Chlorination of spray water would defeat the intent of the FMS. 

### Toxin releasing paint applications have been practically banned by the environmental 

# agencies. Thus, TEC has opted to control it by mechanical means which are manpower 

### and cost intensive. One possible solution TEC is considering is the use of nontoxic, low surface energy paints on critical FMS components (e.g. screen frames and 

# troughs). Testing of these paints as to their viability in such a system is being eva 1uated by TEC.

FMS OPTIMIZATION STUDY As already described, the post-operational FMS Efficiency study and the 0 & M auditing program indicated that 0 & M procedures, as well as, sampling methodology were not adequate to determine accurate screening efficiencies. With screens in optimum operation condition and sampling methodology streamlined,TEC requested in March 1987 approval from both EPA and FDER to conduct a FMS Optimization study during the 1987 spawning season to verify screening efficiencies. 

### Sampling was conducted from both the intake canal (boat) and the fine mesh screen 

### platform (Figure 3). Six replicate pump samples were collected from behind screen 3A (designated as B- 3A), along with six replicate pump samples from in front of both sides of screen 3A (designated as 3A-West and 3A-

# East). Previous engineering flow studies determined that the flow of water was approximately equal across all six screens; therefore, screen 3A was designated to provide representative 

### information that can be applied to all six screens. In addition, three replicate pump samples were collected from behind each of the remaining five screens as back-up samples in the event sampl 

### ing appeared inadequate at screen 3A. 

### Pumps were run for 30 minutes and sampled three water levels (surface, middle, and bottom) 

### 10 minutes at each level. The flows from each pump were channeled into the intake screenwell located behind the screens, where the water from each screen location was pumped into a corresponding 0. 

### 505 mm ichthyoplankton net. A series of oblique tows (six replicates) was also collected in the intake canal by boat during each set of samples. Each sampling event consisted of two day samplings (morning and afternoon) and 

### one night sampling. Screening efficiencies were calculated by dividing the values from the B- 3A sample by the mean of the 3A-West and 3A-

## East samples. Thisprovides the percentage of organisms which were able to pass through screen 

# 3A. Multiplying this number by 100 then subtracting 100 provides screening efficiency. 

## Screeningefficiencies were calculated for each identified species, as well as for total species at various life stages (eggs, prolarvae, etc.
Resul ts presented here represent the ana 

### lys i s first three months (March - June) of the 1987 mean densities of eggs, larvae (prolarvae and lected over the four sampling dates indicated bers of organi sms observed. of samples collected for the 

### spawning season. Analysis ofpostlarvae), and invertebrates colan overall, strong increase in numTable 6 presents the summarized results for both the RIS and other species col

### lected in relatively high abundances. As results indicate, screening efficiencies 

### averaged va 1 ues in excess of the expected 80% previ ous 1 y concluded by the Prototype study; with eggs averaging 95%, larvae 85. 

### 5%, and invertebrates 100% 

## (1, ~).
SUMMARY AND CONCLUSIONSAs the data indicate, adequate sampling method and more importantly the implementation of adequate 0 & M procedures are critical to assuring good screening efficien- 

# cies. Because of environmental concerns, TEC has implemented 0 & M procedures primarily targeted to the manual control of biofouling, which is considered the 

### source of much of the FMS maintenance problems. Design modifications, as well as, the use- of non-toxic, low surface energy paints are being considered by TEC as ways of optimizing 0 & M procedures to reduce costs.The present level of 0 & M procedures has not required the addition of new oper

### ators or maintenance personnel. Costs associated with the repai r of screens and 

## seal s have been estimated to be in the range of $75, 000 - $150, 

### 000 per year. 

### The wide range is due to the uncertainty which still exists regarding the use of non- 

### lubricated chains. Even though the initial set developed problems during a short time frame, the present replacements may last 

## longer. In summary, the Big Bend Station FMS system is effectively screening RIS organisms and life stages.
REFERENCES Tampa Electric Company. " 316(a) and (b) Demonstration, Big Bend Station - Unit 4. " prepared by Stone and Webster Engineering Corporation, August 1980. Tampa Electric Company. " 316(a) and (b) Demonstration, Big Bend Station Unit, Fine Mesh Screen Study Report. " prepared by Stone and Webster Engineering Corporation, November 

### 1980. 

## Stone and Webster Engineering Corporation. "Supplemental Engineering Report Based on the 1980 Fine Mesh Screen Optimization Study, Big Bend Unit 4, Tampa Electric Company. " May 1981. Tampa Electric Company. " Fine Mesh Screen Survivability Study Big 

## Bend Unit 4. " prepared by 

## t4ote Marine Laboratory, December 1986. Stone and Webster Engineering Corporation. " Fine Mesh Screening Flow Measurements, Big Bend Station - Units 3 and 4. " February 1987. 

### Tampa Electric Company. "

## Fine Mesh Screen Optimization Study. " prepared by Mote Marine Laboratory, July 

### 1986.ST. PETE"SBURG

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### Figure 7. Fine Mesh Screen Operational Audit Form- -

Table 1 REPRESENTATIVE IMPORTANT SPECIES (RIS)

AT TAMPA ELECTRIC COMPANY 

### BIG BEND STATION (1)

Common Name Scientific Name Bay anchovy Black drum Silver perch Spotted seatrout Scaled sardine Tidewater siJverside Stone crab Pink shrimp Ar;Jeri can

### oyster B1 ue 

### crab Anchoa mi tchi 11 i Pogonias cromi s Bairdiella chrysoura 

### Cynoscion nebulosus Harengula jaguana 1'1enidia beryl1ina Men'i ppe mercena ri a Penaeus duora rum Crassostrea vi rgi ni ca Cal1inectes sapidus

Table 2
TEST RESULTS SPRAYWASH EFFICIENCY SAMPLING
1981 OPTIMIZATION STUDY 

# (l)

Tota 1 Number of Range of ~1ean Soeci es Name Life Stage Organ isms % Lass % Loss Anchaa mitch i 11 i Egg 5238 

### 3 - 1.5 Bairdiella chrysura Egg 1780 

### 0 - 14. Cynasci on nebulosus Egg 100. 0 - 100. 100. Cynosci an spp. Egg 114 

### 0 - Sciaenidae unid. Egg 1828 

### 1 - 30. Anchoa mi tchi 11 i 

### Pra1arvae 1007 

### 0 - 24. 1.7 Sciaenidae unid. 

### Prolarvae 0 - Anchoa mitchi 11 i 

### Pastl arvae 847 

### 0 - 22. 1. 7 Bairdiella chrysura 

### Postl arvae 

### 0 - 40. Cynosci on nebulosus 

### Postlarvae 0 - 100. 20. Pogonias cromis 

### Pastlarvae 0 - Sciaenidae unid. 

### Postlarvae 0 - Mem ppe mercena ri a Juvenil e 

### 0 - Shrimp unid. 

### Unidentified 498 

### 5 - 1.4 Brachyura unid. Un staged zoea 2854 

### 3 - Menippe mercenarJa 

### Ioeal 

### stage 171 

### 0 - 60. 1.8 Men i ppemercena ri a 

### Ioeal stage 2 

### 0 -Table 3

COMPARISON OF INITIAL SURVIVAL (%)

DURING THE PROTOTYPE AND FMS SURVIVABILITY STUDIES 

# (i)

Taxa Prototype Study FMS Survi vabiJ i ty Study

Screenwash Screenwash ORa Contra 1 Fish Eggs: Anchoa mi tchi 11 i Sci aeni dae Fi sh Larvae: Anchoa mi tchi 11 i 

### Sciaenidae 

### Invertebrates: Ca ri dea Xan th i dae Pi nnotheri dae 100

Table 4
COMPARISON OF FISH EGG HATCHABILITY AND LATENT 48 HOUR SURVIVAL (%)

DURING THE PROTOTYPE AND FMS SURVIVABILITY STUDIES 

# (i)

Hatchabilit Taxa Prototype Study H1S Survi vabiJ ity Study

Screenwash Screenwash ORD Fish Eggs: Anchoa mitchilli Sci aeni dae
Latent 48-Hour Survival Fish Larvae: Anchoa mitchi 11 i Sci aenidae Invertebra tes: 

### Caridea Xanthi dae 

### PinnotheridaeTable 5
TEST RESULTS 1985 FMS EFFICIENCY STUDY

t1ean Densi ty Mean Den s i ty Range Mean 

## li fe Stage Inta ke Manhole % Loss % Loss Fi sh Eggs 12184. 9545. 55- 100 78. Fi sh Larvae 177. 166. 100 94. 

### Invertebrates 203. 29. 100 14.

Table 6
SUMMARY DATA FOR RIS AND OTHER SPECIES FOUND IN RELATIVELY HIGH ABUNDANCES 

### COLLECTED FROM FOUR ANALYZED SAMPLING PERIODS 

## (~)

Mean Density Mean Density Sped es L He (fl00m (fl00m Range of 14ean Stage 

### Front Behind % Loss % Loss Sdaenidae spp. Egg 38595 1062 0- 44. Anchoa mitchilli Egg 12860 1071 0- 52. Anchoa mi tchi 11 i La rvae 239. 26. 0- 33. 11. Bairdiella chrysoura Larvae 

### Cynoscion nebulosus Larvae 1.1 1enippe mercenaria Zoea 24. 

### 1.2 Penaeus spp. Juven il e 1. 9 

### Blenniidae spp. Larvae 29. 0- 76. 17. 

### Gobiidae spp. Larvae 30. 5- 58. 25. 

### Gobiesox strumosus La rvae 1.1 100 11.2