SEASONAL ABUNDANCE AND DISTRIBUTION OF ...

SEASONAL ABUNDANCE AND DISTRIBUTION OF MYSIS AND POSTLARVAL WHITE AND BROWN SHRIMP IN KEITH LAKE ESTUARINE SYSTEM

A Thesis Presented to The Faculty of the College of Graduate Studies Lamar University

In Partial Fulfillment of the Requirements of the Degree Master of Science by Richard Lee Pollock December 2006

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SEASONAL ABUNDANCE AND DISTRIBUTION OF MYSIS AND POSTLARVAL WHITE AND BROWN SHRIMP IN KEITH LAKE ESTUARINE SYSTEM

RICHARD LEE POLLOCK

Approved:

Andrew C. Kasner Supervising Professor

Richard C. Harrel Committee Member

gjuJL fPaul F. Nicoletto Committee Member

Michael E. Warren Chair, Department o f Biology

Brenda S. Nichols Dean, College o f I

Sciences

Bradley Graduate Studies


© 2006 by Richard Lee Pollock No part of this work can be reproduced without permission except as indicated by the “Fair Use” clause of the copyright law. Passages, images, or ideas taken from this work must be properly credited in any written or published material.


Abstract Seasonal Abundance and Distribution of Mysis and Postlarval White and Brown Shrimp in Keith Lake Estuarine System By Richard Lee Pollock The objective of this study is to determine what species of planktonic shrimp mysis and postlarvae were recruited into Keith Lake, a part of the Sabine Lake estuary, and their seasonal patterns of abundance and distributions within Keith Lake in relation to weather and water chemistry. White and brown shrimp postlarvae were collected in Keith Lake, but they were not abundant. Total number of white shrimp postlarvae collected for the entire study was 42. Total number of white shrimp postlarvae in May and June 2005 were 18 and 13 respectively, which was 73.8% of all white shrimp postlarvae collected. The total number of brown shrimp postlarvae collected for the entire study was 45. The total number of brown shrimp postlarvae in March 2006 was 37, which was 82% of all brown shrimp postlarvae collected. White shrimp mysis were present during summer and were more abundant than white and brown shrimp postlarvae. The total number of white shrimp mysis from June-September 2005 was 424. White shrimp postlarvae were more abundant at north shoreline sample stations, with 57.1% of all white shrimp postlarvae collected at two sites. White shrimp mysis were widespread in Keith Lake but most abundant in the middle of Keith Lake with 43% collected at three stations. Brown shrimp postlarvae were also most abundant in the middle of Keith Lake, with 58% collected at 3 stations. Water temperature, salinity, and dissolved oxygen concentrations were all within the tolerance ranges of the two species of shrimp and appeared to have a limited effect on abundance and distribution of white and brown shrimp postlarvae and white shrimp mysis.


TABLE OF CONTENTS Page List of Tables................................................................................................................................iv List of Figures................................................................................................................................v Introduction.....................................................................................................................................1 Study Area......................................................................................................................................6 Methods..........................................................................................................................................9 Results........................................................................................................................................... 12 White Shrimp Postlarvae............................................................................................................12 White Shrimp M ysis...................................................................................................................20 Brown Shrimp Postlarvae.......................................................................................................... 24 Discussion.................................................................................................................................... 30 References.................................................................................................................................... 36

iii


LIST OF TABLES Page 1. Correlation Between Water Chemistry and Abundance of White Shrimp Postlarvae in Keith Lake, May 2005-April 2006................................................................................. 21 2. Correlation Between Water Chemistry and Abundance of White Shrimp Mysis in Keith Lake, May 2005-April 2006................................................................................. 25 3. Correlation Between Water Chemistry and Abundance of Brown Shrimp Postlarvae in Keith Lake, May 2005-April 2006...............................................................29

IV


LIST OF FIGURES Page 1. Sabine-Neches Estuary........................................................................................................... 7 2. Sample Stations 1-11 in Keith Lake....................................................................................10 3. Mean Water Temperature Measured from 11 Sample Stations in Keith Lake, May 2005-April 2006........................................................................................................... 13 4. Mean Dissolved Oxygen Concentration for 11 Sample Sites in Keith Lake, May 2005-April 2006..................................................................................................................... 14 5. Mean Salinity for 11 Sample Sites in Keith Lake,May 2005-April 2006.....................15 6. Mean Wind Velocity at Keith Lake, May 2005-April 2006 (NOAA Station SRST2-Sabine)...................................................................................................................... 16 7. Current Velocity of Incoming and Outgoing Tides at Keith Lake Cut, May 2005-April 2006..................................................................................................................... 17 8. Abundance of White Shrimp Postlarvae in Keith Lake, May 2005-April 2006.............18 9. Distribution of White Shrimp Postlarvae Among Sample Sites in Keith Lake, May 2005-April 2006........................................................................................................... 19 10. Abundance of White Shrimp Mysis in Keith Lake, May 2005-April 2006............. 22 11. Distribution of White Shrimp Mysis in Keith Lake, May 2005-April 2006............. 23 12. Abundance of Brown Shrimp Postlarvae in Keith Lake, May 2005-April 2006......26 13. Distribution of Brown Shrimp Postlarvae Among Sample Sites in Keith Lake, May 2005-April 2006......................................................................................................... 27

v


Pollock

1

Introduction White shrimp (Litopenaeus setiferus), brown shrimp (Farfantepenaeus aztecus), and pink shrimp {Farfantepenaeus duorarum) are three species of commercially important shrimp that breed offshore in the Gulf of Mexico and are recruited into Texas estuaries by tidal currents. Spawning occurs offshore when water temperature increases in the spring and declines in the fall (U.S. Fish and Wildlife Service 1983). These shrimp have five nauplial, three protozoeal, three mysis, and two postlarval stages of development (Cook and Murphy 1971). Early planktonic stages develop offshore with salinity of at least 27 parts per thousand (ppt) and remain planktonic through the end of the second postlarval stage. Shrimp plankton move toward shore and enter bays and estuaries with incoming tides during the first and second postlarval stages (U.S. Fish and Wildlife Service 1983). Predation rates in the open Gulf of Mexico would be devastating to juvenile shrimp populations without the environmental protection that estuaries and bays provide (muddy substrates and marsh vegetation), and growth would be limited without the abundance of rich organic sources of nutrients in the estuaries. Shrimp juveniles use estuarine substrates during summer and fall until they reach sizes of 120 to 160 mm long (U.S. Fish and Wildlife Service 1983). As juvenile shrimp grow, they move from shallow marshes to deeper creeks, rivers, and bays. Deeper water serves as staging areas for shrimp before they move offshore to breed (U.S. Fish and Wildlife Service 1983). Shrimp emigration from estuaries appears to be governed by size of the shrimp and environmental conditions within the estuarine system (U.S. Fish and Wildlife Service 1983).


Pollock

2

In Texas, white shrimp postlarvae enter inshore nursery areas from mid-April to midNovember. Peak abundance is in May-July, with a second peak in September-October (U.S. Fish and Wildlife Service 1983). Little is known about the density of white shrimp postlarvae in Texas. However, during a study of Galveston Bay, postlarvae of white shrimp were first collected at the bay entrance in May (Baxter and Renfro 1967). By June, advanced postlarvae of white shrimp became abundant in Galveston Bay and were present throughout the summer (Gunter 1960; Baxter and Renfro 1967; Benefield 1982). In the northern Gulf of Mexico, offshore spawning of brown shrimp may occur year round, but peak activity is believed to occur from April-June with a second smaller peak during September-November (Rogers, Shaw, Herke, and Blanchet 1993). Renfro (1959) and Gunter (1960) found only brown shrimp postlarvae in upper Galveston Bay during April and May. Brown shrimp postlarvae were collected from February to midDecember at the entrance of Galveston Bay and peaked from mid-March to mid-April (Baxter and Renfro 1967). Aldrich, Wood, and Baxter (1968) reported that brown shrimp come into the Galveston Bay entrance from March-April when water temperatures are about 25-32° C. Brown shrimp were the only planktonic penaid species occurring during December-April m Galveston Bay (Baxter and Renfro 1967). In the Calcasieu River estuary, abundance of brown postlarvae peaked in March (Rogers et al. 1993). However, they only collected brown shrimp postlarvae from February-May 1982 in the Calcasieu River marsh area. Pink shrimp are also an important part of the shrimp fishery in the Gulf of Mexico, supporting a major commercial market in the Florida Bay area (Ehrhardt and Legault 1999). Pink shrimp have been found in Galveston Bay, but they are rare (Baxter and


Pollock

3

Renfro 1967; Benefield 1982). Of about 47,000 juvenile shrimp examined from Galveston bait landings from 1960 to 1963, only 0.04 % were pink shrimp (Baxter and Renfro 1967). Pink shrimp are commonly caught off Galveston Island (27 to 37 meters), but most are reported as brown shrimp because of difficulty in distinguishing between the two species (Baxter and Renfro 1967). Water temperature is probably the most important factor affecting the abundance, distribution, and behavior of shrimp plankton (Rogers et al. 1993). In pink shrimp, reproductive maturation and appearance of larval stages coincide with rising water temperatures (Cripe 1994). In the laboratory, pink shrimp started spawning at water temperatures between 20°C and 28°C (Cripe 1994). In the fall, when temperature falls below 20°C, spawning slows or stops. Rogers et al. (1993) reported that most offshore brown postlarvae were collected in water with temperatures from 11°C to 15°C, whereas most marsh (Calcasieu River estuary) brown postlarvae were taken from 13°C to 18°C. White shrimp become abundant in estuaries by June each year when the water temperatures are consistently warm at 25°C to 32°C. Aldrich, Wood, and Baxter (1968) collected shrimp plankton near the beach at Galveston during July-August with water temperature at 29°C to 32°C, during which time it was possible for them to find postlarvae of brown and white shrimp together in transit from offshore spawning grounds to estuarine nursery areas. In laboratory experiments, Aldrich, Wood, and Baxter (1968) found vertical migration of brown and white shrimp occurred in response to changes in water temperature. When water temperature was lowered from 17°C to 15°C, both species settled to the bottom of the tank. When the temperature was lowered from 17°C to 12°C, only brown postlarvae


Pollock

4

burrowed into the substrate. However, no definite evidence of burrowing brown postlarvae has been observed in the field (Aldrich, Wood, and Baxter 1968). White postlarvae did not burrow into the substrate. Salinity is another important factor affecting the abundance, distribution, and behavior of postlarval shrimp. White shrimp are well adapted to environments with low salinity and can tolerate low levels of dissolved oxygen (Rosas, Martinez, Gaxiola, Brito, Sanchez, and Soto 1999). Postlarvae of brown shrimp decrease swimming activity during times of low salinity, saving valuable energy (Matthews, Schroeder, and Steams 1991). Rogers et al. (1993) hypothesized that brown postlarvae migrate down in the water column when they encounter very low salinity levels or cooler waters. Brown postlarvae may migrate down or cease activity and sink to the bottom as a result of negative buoyancy (Rogers et al. 1993). When temperature and salinity increase, brown postlarvae migrate up in the water column where the incoming currents more readily transport them into estuaries and bays (Rogers et al. 1993). Laboratory experiments indicated that, when temperature and diet are controlled, postlarval shrimp of all three species could survive and grow over a wide range of salinities (Zein-Eldin 1963a). Therefore, salinity may not play a direct role in survival and growth of postlarval shrimp plankton in the estuarine environment (Zein-Eldin 1963b), and food requirements may be a more important factor than salinity (Zein-Eldin 1963b). Rainfall and river outfall are major factors influencing salinity in an estuary. White shrimp harvest declines with extreme freshwater river runoff in Texas (Matthews, Schroeder, and Steams 1991). The interaction of salinity with temperature may have more pronounced effects than either factor alone on plankton counts (Matthews,


Pollock Schroeder, and Steams 1991). When temperature and salinity are low at the same time, this combination seems to reduce shrimp and shrimp plankton populations (Matthews, Schroeder, and Steams 1991). During times of heavy rain and freezing temperatures, plankton counts usually are close to zero in the estuary because of mortality and lack of egg production and maturation (Chen and Chen 2002). Dissolved oxygen is critical for postlarval shrimp survival. Experiments have shown that shrimp are sensitive to and actively avoid low concentrations of dissolved oxygen (Rosas et al. 1999). White shrimp avoided water containing less than 1.5 parts per million (ppm) dissolved oxygen, while brown shrimp avoided water having dissolved oxygen concentrations less than 2.0 ppm (Renaud 1986; Wannamaker and Rice 2000). Hypoxia remains a common occurrence in estuarine waters as human activity in coastal areas expands, and it likely affects the distribution of postlarval shrimp in estuaries (Wannamaker and Rice 2000). Ocean currents and wind direction also have significant effects on plankton shrimp movements. Recruitment of planktonic shrimp postlarvae into Calcasieu Lake occurred frequently during times of strongest atmospheric cold fronts that passed through southwestern Louisiana (Rogers et al. 1993). The cold fronts create extremely low tides as north winds blow water out of the estuary and marshes into the Gulf. When the wind changes directions to the east or south, incoming tides are extreme. These extreme tides, which occur approximately every three to eight days from October-April, transport shrimp plankton into southern bays and estuaries (Rogers et al. 1993). No one environmental condition influences planktonic shrimp postlarvae abundance and distribution within estuaries. Rather, a combination of factors probably influences


5

Pollock

6

abundance and distribution. Water temperature and salinity are probably the most important environmental conditions that influence distribution and abundance of planktonic shrimp postlarvae in the Gulf of Mexico and associated estuaries. Because of seasonal influences on these physical and chemical factors, shrimp abundance in coastal estuaries shows a marked seasonal cycle that varies with each individual estuary. Such cycles of abundance have been studied in other bay systems such as Calcasieu Lake (Rogers et al. 1993) and Galveston Bay (Aldrich, Wood, and Baxter 1968). However, no information is available on seasonal abundance and distribution of white and brown shrimp in the Sabine-Neches Estuary. The objective of this study is to determine what species of planktonic shrimp mysis and postlarvae are recruited into Keith Lake (a part of the Sabine-Neches Estuary) and seasonal patterns of abundance and distribution within Keith Lake relative to weather and water chemistry. The study attempts to answer the following questions: (1) which of the three species of shrimp occur in Keith Lake and how abundant are they; (2) is there a significant relationship between the abundance and distribution of planktonic shrimp mysis and postlarvae and dissolved oxygen, salinity, and water temperature; and (3) do wind and current direction influence abundance and distribution of planktonic shrimp mysis and postlarvae? Study Area This study was conducted in the Keith Lake system, located immediately west of Sabine Lake on the Texas-Louisiana border (Figure 1). The Neches and Sabine Rivers flow into the north portion of Sabine Lake and into the Sabine-Neches ship channel. Both Keith Lake and Sabine Lake are tidally influenced by currents in and out of Sabine


Pollock

Sabine River

Neches River Sabine-Neches

Keith lake

Sabine Pass

Gnlf el Mexico Figure 1. Sabine-Neches Estuary.


7

Pollock

8

Pass, Sabine-Neches ship channel, and the Gulf Intracoastal Waterway. Keith Lake is connected to the Sabine-Neches ship channel and the Gulf of Mexico by way of Keith Lake Cut. Keith Lake is a much smaller and shallower body of water than Sabine Lake, but, because of similar tidal influences, plankton present should be representative of the estuary. Keith Lake is shallow, with the mean low tide water levels between one half and two meters, and it is surrounded by emergent stands of marsh plants dominated by Spartina and Phragmites. The surrounding marsh is drained by several small bayous that empty into Keith Lake. Keith Lake is the first in a chain of marsh lakes reaching greater than 13 km into the marsh.


Pollock

9

Methods I collected plankton samples every other week from 11 sites in Keith Lake for a oneyear period from May 2005-April 2006 using a bongo-type plankton tow net (mouth diameter 30 cm, length 150 cm, mesh size 253 microns). The volume of water filtered during a plankton tow during this study was 7.07 cubic meters. The sample sites were (1) Keith Lake Cut, (2) three sites along the north shoreline of Keith Lake (one of these at mouth of a bayou), (3) four sites along the south shoreline of Keith Lake (one of these at mouth of a bayou), and (4) three sites in the center of Keith Lake (Figure 2). Two replicate 100 meter tows were made at each site on each collection day. I towed the plankton net one meter to the side of the boat to minimize net avoidance during sampling. I alternated sampling between incoming and outgoing tides, so that each month at least one sample was taken on an incoming tide and one on an outgoing tide. All sampling was done during daylight hours. Sampling stations were extremely shallow, thus only surface tows were made as not to disturb the substrate. I brought the samples to the laboratory, counted, and identified on the day of collection. I preserved the samples in ethanol in the laboratory until counting and identification was completed. I counted plankton using a Petri dish and stereoscopic dissecting scope, and I calculated densities as numbers per cubic meter. I identified postlarvae and mysis to species (white or brown shrimp) using illustrated keys (Pearson 1939; Ringo and Zamora 1968; Cook and Murphy 1971). It is possible that pink shrimp occurred in samples because pink shrimp and brown shrimp postlarvae are morphologically identical at the postlarval stage (Ringo and Zamora 1968). Without DNA analysis, it is not possible to distinguish between pink and brown postlarvae.


Pollock 10

Kilometers

Figure 2. Sample Stations 1-11 in Keith Lake.


Pollock 11 However, pink shrimp are extremely rare in this study area (0.04%), so misidentification of brown shrimp postlarvae should be rare (Baxter and Renfro 1967). I measured the total length of postlarvae from the tip of the rostrum to the tip of the telson. I measured water temperature, dissolved oxygen, and salinity at each sample site using an YSI 85 multi-parameter probe. I calibrated the multiprobe in the laboratory following manufacturer’s procedure. I used a current meter (flow meter) in Keith Lake Cut to determine tidal speed, and I recorded direction as incoming or outgoing. I obtained data on wind direction and velocity from National Oceanic and Atmospheric Administration (NOAA) station SRST2-Sabine. I performed all statistical calculations using StatView for Windows (SAS Institute Inc., Copyright 1992-1998, Version 5.0.1.) or SigmaStat for Windows (Systat Software, Inc., Copyright 2004, Version 3.10). I presented means in the text with their standard errors. I computed a complete descriptive statistical analysis on densities and species size to determine differences in the two postlarval species and their distributions in the estuary. I used Pearson’s correlation to determine relationships between the abundance of white and brown shrimp postlarvae and water temperature and salinity in Keith Lake. I also used Pearson’s correlation to determine relationships between the abundance of white and brown shrimp postlarvae in Keith Lake and water current velocity at Keith Lake Cut. I used Mann-Whitney Rank Sum Test to determine difference between abundance of white and brown shrimp postlarvae during incoming and outgoing tides when postlarvae were present. I considered statistical tests significant if P C

-1— M

i J

1----- “i—

i— A

)

N

D

M

Months Figure 6. Mean Wind Velocity at Keith Lake, May 2005-April 2006 (NOAA station SRST2-Sabine).


Water velocity (cm/s)

Pollock 17

incom ing O - outgoing

Months Figure 7. Current Velocity of Incoming and Outgoing Tides at Keith Lake Cut, May 2005-April 2006.


Pollock 18

Number of white shrimp postlarvae

20 1 18

-

16

-

14

-

12

-

10

-

8

-

6

-

4

-

2

-

0

—r M

—T"

s

O

N

~r~

~r

D

J

M

Months

Figure 8. Abundance of White Shrimp Postlarvae in Keith Lake, May 2005-April 2006.


Pollock 19

Number of white shrimp postlarvae

16 1 14

-

12-

10

-

8

-

6

-

4-

2

0

-----

-----

----

-

--------------

—

i

1

--------- 1--------------------------------------------- ^

2

3

4

5

6

7

8

----------------------- 1—

9

10

11

Sample stations Figure 9, Distribution of White Shrimp Postlarvae among Sample Sites in Keith Lake, May 2005-April 2006.


Pollock 20 3 (9 and 15 respectively). I collected 57.0% of all white shrimp postlarvae at these two stations. White shrimp postlarvae were rare during the sampling period at the rest of the sampling stations. The south shoreline, stations (5, 6, 7, and 11), the area farthest away from incoming tidal currents, had 24% of all white shrimp postlarvae collected. The middle of the lake stations (8, 9, and 10) had the remaining 18.9%. No white shrimp postlarvae were collected in Keith Lake Cut. Water chemistry had little influence on distribution and abundance of white shrimp postlarvae. There were no significant relationships between the abundance of white shrimp postlarvae and water temperature nor salinity in Keith Lake (Table 1). When white shrimp postlarvae were present in Keith Lake, there was not a statistically significant difference between abundance of white shrimp postlarvae during incoming and outgoing tides (7=582.5, P=0.57). There was no significant relationship between the abundance of white shrimp postlarvae in Keith Lake and differences in water current velocity (r=0.02, P=0.91). White Shrimp Mysis Surprisingly, white shrimp mysis, which typically occur offshore near Gulf passes, were collected from June-September in Keith Lake. The total number of white shrimp mysis from June-September was 424 (Figure 10). June was the peak month for white shrimp mysis, with 166 mysis collected and mean density 0.53 ± 0.46/m3 SD. Mean water temperature for June was 30.3°C. The June-September mean density of white shrimp mysis was 0.34 ± 0.45/m3 SD. White shrimp mysis were widespread in Keith Lake (Figure 11) but most abundant in the middle of Keith Lake (stations 8, 9, and 10) with 43% collected at these three stations. White shrimp mysis were least abundant on


Pollock 21 Table 1. Correlation Between Water Chemistry and Abundance of White Shrimp Postlarvae in Keith Lake, May 2005-April 2006

Parameter

Water temperature Salinity

r

P

N

0.130

0.545

24

-0.143

0.506

24


Pollock 22

180 -|

Number of white shrimp mysis

160140-

120

-

100

-

806040-

20 0

-

“I

M

O

N

D

~r

-r-

J

F

M

iA

Months Figure 10. Abundance of White Shrimp Mysis in Keith Lake, May 2005-April 2006.


Pollock 23

701

Number of white shrimp mysis

60-

50

-

40

-

30

-

;:|

_________

20-

10

0

—

;

-

i —

H —

1

2

^

3

—

4

5

6

7

8

9

10

i

11

Sample stations

Figure 11. Distribution of White Shrimp Mysis in Keith Lake, May 2005-April 2006.


Pollock 24 the south shoreline, farthest away from Keith Lake Cut (stations 5, 6, 7, and 11), with only 19% of all white shrimp mysis collected at these four sample stations. The north sample stations (2, 3, and 4) had 30.4% of all white shrimp mysis collected. Keith Lake Cut (station 1) had 7.8% of all white shrimp mysis collected. There was no relationship between the abundance of white shrimp mysis and salinity (Table 2). However, there was a positive relationship between white shrimp mysis abundance and water temperature in Keith Lake (Table 2). When white shrimp mysis were present in Keith Lake, there was no significant difference found in the abundance of white shrimp mysis between incoming and outgoing tide (T=2110, P=0.206). There was no significant relationship between the abundance of white shrimp mysis and water current velocity (r^-0.18, P=0.40). Brown Shrimp Postlarvae The total number of brown shrimp postlarvae collected for the entire study was 45. The total number of brown shrimp postlarvae in March 2006 was 37, which was 82% of all brown shrimp postlarvae collected (Figure 12). The mean water temperature in March was 17.6°C. Brown shrimp postlarvae for the rest of the sampling period were rare, and no small second peak was collected in Fall 2005 as expected. The mean total length of all brown shrimp postlarvae was 14.3 ± 1.39 mm, with a range of 10-17 mm. Brown shrimp postlarvae were distributed unevenly in Keith Lake (Figure 13), with 58% collected in the middle of Keith Lake at stations 8, 9, and 10. The north shoreline (stations 2, 3, and 4) had 29% of all brown shrimp postlarvae collected. Brown shrimp postlarvae were rare on the south shoreline (Stations 5, 6, 7, and 11), with only 13% collected in this area. No brown shrimp postlarvae were collected in Keith Lake Cut.


Pollock 25 Table 2. Correlation Between Water Chemistry and Abundance of White Shrimp Mysis in Keith Lake, May 2005-April 2006

Parameter

Water temperature Salinity

r

P

N

0.544

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