Nicholls State University
Master of Science in
Marine and Environmental Biology
Masters Thesis Proposal
“Seasonal fish assemblages of Bayou Lafourche
above and below the Thibodaux weir”
Submitted by Heather Pace Dyer
and approved by Committee Members
_______________________________ Date_______________
Allyse Ferrara, Assistant Professor, Committee Chair
_______________________________ Date_______________
Quenton Fontenot, Assistant Professor, Committee Member
_______________________________ Date_______________
David Schultz, Associate Professor, Committee Member
Project Summary
This research was initiated to assess seasonal differences in the fish community above
and below the Thibodaux weir in Bayou Lafourche. This study is in response to the
proposal of the Mississippi River Water Reintroduction into Bayou Lafourche (MRWR)
project. The MRWR project plans to increase the water flow from the present rate of
200 cubic feet/second (cfs) to approximately 1,000 cfs, dredge parts of Bayou
Lafourche, and to remove the Thibodaux weir. This increased discharge and removal of
the weir would transport valuable sediment to nourish and sustain wetlands and marsh
and help to control saltwater intrusion in Bayou Lafourche (MRWR 2005). These
hydrological modifications could also influence the ichthyofauna community structure as
well as the behavior of some fish species currently inhabiting Bayou Lafourche. The
results of this study will allow us to predict changes in the fish community that may
occur with the implementation of the MRWR project and removal of the Thibodaux weir.
Fish will be collected from several locations in Bayou Lafourche between 09
February 2006, and 31 August 2007. Total length, weight sex, and gonad weight will be
collected for each fish. These data will be used to describe seasonal differences in the
current fish community of Bayou Lafourche.
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Introduction
Bayou Lafourche and the Barataria-Terrebonne National Estuarine System
Bayou Lafourche runs through the heart of the Barataria-Terrebonne National
Estuarine System (BTES), located in southeastern Louisiana. The bayou serves as the
border between the Barataria and Terrebonne estuaries (Fig. 1) flowing 172 km from
the Mississippi River to the Gulf of Mexico (McKensie et al. 1995, Emmer et al. 2003).
The BTES was defined and protected by the Barataria –Terrebonne National Estuary
Program and the Environmental Protection Agency (EPA) in September 1990 and
encompasses approximately 16,835 km2 (McKensie et al. 1995). The inclusion of the
BTES into the National Estuary Program helps prevent activities from occurring within
the complex that threaten the system’s water supply, harms fish, shellfish or wildlife
populations within the estuarine complex or negatively impacts recreational
opportunities for the residents of the estuary (BTNEP 1995).
Bayou Lafourche was a distributary of the Mississippi River until 1904, when it
was cutoff by a human-made levee. Prior to its damming, Bayou Lafourche was used
for fishing, recreation and travel by local residents. Steamboats and other vessels
carried passengers and commerce along the length of the bayou between
Donaldsonville and the Gulf of Mexico (Emmer et al. 2003). In approximately 1830, a
canal was built by the Lafourche and Terrebonne Navigation Company, connecting
Bayou Lafourche to Bayou Terrebonne in Thibodaux. The company built this canal in
order to facilitate passage of sugarcane freight between Terrebonne Parish and New
Orleans markets via Donaldsonville. The city of Thibodaux became a busy trade and
transportation hub for agricultural commerce within the region (Lafourche Heritage
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Society 1988). Due to the profitable agriculture output of the area, leaders began to
recognize the need to protect bayou-side communities from seasonal flooding.
Although levees were already in place adjacent to Bayou Lafourche, discussion of
damming the head of the bayou at the Mississippi River began in the 1840s.
During the planning and building of the Bayou Lafourche dam, i.e. a levee at the
Mississippi River junction, the potential consequences of removing Mississippi River
water and sediments from the system were unknown. Community leaders were seeking
a solution to the problematic spring floods that often destroyed homes and businesses
(Emmer et al. 2003). Bayou Lafourche was cutoff from the Mississippi River in 1904,
and the hydrologic system of Bayou Lafourche and the surrounding wetlands was
severely altered. The Mississippi River levee built in Donaldsonville essentially made
Bayou Lafourche a long, slender reservoir (MRWR 2005). The hydrology of Bayou
Lafourche became principally driven by local precipitation. Several severe
consequences of this lack of flow became clear in the following decades. In the late
1930s and early 1940s Bayou Lafourche was described as stagnant and suffering from
encroaching aquatic vegetation such as water hyacinths, Eichhornia crassipes (Emmer
et al. 2003). The lack of freshwater flow down Bayou Lafourche also allowed periodic
saltwater intrusion as far up as the central reaches of Bayou Lafourche in St. Charles,
LA. In 1930, a 17-mile pipeline was built to bring water from the Mississippi River to
Thibodaux in order to have a potable drinking water supply (Emmer et al. 2003). The
Bayou Lafourche Freshwater District (BLFD) addressed these problems by planning to
build a pump and siphon station at the junction of the Mississippi River and Bayou
Lafourche in Donaldsonville. In 1955, a pump station was installed that could pump
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freshwater from the Mississippi River into Bayou Lafourche at a rate of 340 cfs. In
1969, a weir was installed in Thibodaux to help regulate upstream water levels by
retaining water behind a concrete wall, creating a reservoir of freshwater in Bayou
Lafourche above the weir. This controlled water retention system ensures an adequate
drinking water supply for Lafourche Parish (MRWR 2005).
Although measures have been taken to increase the flow in Bayou Lafourche the
waterway still suffers from reduced movement of water and sediments, diminished
channel capacity, choking aquatic vegetation populations and occasional saltwater
intrusion (A. Chaisson, BLFD, personal communication). Additionally, flows of
Mississippi River distributaries that historically delivered sediments, freshwater and
nutrients to the coastal wetlands, thus replenishing the marshes and facilitating land
building have been cut off from the River (Reed et al. 1995). Due to hydrologic
modifications, Bayou Lafourche no longer transports significant amounts of Mississippi
River sediments or nutrients to the surrounding wetlands. Instead, most of the
sediments are carried through the pump station at Donaldsonville and, due to low flow
velocity, accumulate in the channel of Bayou Lafourche (MRWR 2005).
Effects of Anthropogenic Structures on Fish Communities
Construction of water retention structures can seriously alter habitat, fish
populations and aquatic communities (Schlosser and Ebel 1989, Jurajda 1995). The
fragmentation of Bayou Lafourche by anthropogenic structures such as the levee in
Donaldsonville, the Thibodaux weir, and the Gulf Intracoastal Waterway created a
disconnected aquatic community. Many inland fishes move substantial distances within
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waterways for reproductive and foraging purposes (McKeown 1984, Northcote 1984,
Harris and Mallen-Cooper 1994). Other studies have found that structures such as
weirs and dams create obstacles to fish movement and as a result can affect the
population structure (Harris and Mallen-Cooper 1994, Lucas and Frear 1997). In Bayou
Lafourche, the Thibodaux weir may create an impediment for migratory fishes by
limiting movement up or down the bayou.
A frequent problem in analyzing effects of human modifications of river systems
is the absence of baseline data prior to the alteration (Bain et al. 2000). Ideally, a
comparison could be made between states of an ecosystem before and after a
modification. Unfortunately, Bayou Lafourche has been the focus of few published
ecological studies and there is little published information on the water body (Schultz
1996, Rodrigue 2005). A water quality characterization was completed examining
summertime water quality characteristics such as pH, temperature, salinity, specific
conductance and depth (Rodrigue 2005). Another study (Schultz 1996) seined 90
stations between Donaldsonville and Port Fourchon. Each site was sampled on one
occasion and over 25,000 fish were collected composed of 110 species from 40
families.
Mississippi River Water Reintroduction into Bayou Lafourche (MRWR)
The MRWR was originally proposed in 1996, as a plan to transport nourishing
sediments, freshwater and nutrients to diminishing wetlands. This transport system
may affect up to 121,000 acres of wetlands in the lower Barataria and Terrebonne
estuaries (Fig. 2). The MRWR project will increase the water flow from the present rate
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of 200 cfs to approximately 1,000 cfs, dredge parts of Bayou Lafourche, and remove the
Thibodaux weir. Increased discharge and removal of the weir would transport valuable
sediment to nourish coastal wetlands and help to control saltwater intrusion in Bayou
Lafourche (MRWR 2005). The major components of the project include:

Construction of a new pump station in Donaldsonville to increase flow
capacity from ~200 cfs to ~1,000 cfs.

Dredging upstream portions of Bayou Lafourche to ensure that increased
water flow will not raise surface levels and impinge on private property
rights.

Removal of the Thibodaux weir and possible replacement with inflatable
weirs or another system to ensure control of drinking water supply as
needed.
Proposed changes to the hydrology of Bayou Lafourche will have significant effects on
the ichthyofauna community. This research was initiated in response to the MRWR
project and will serve as a baseline study of the fish community prior to further
hydrologic modifications.
Significance of Research
Since there is little previous data with which to make a comparative analysis this
study will serve as a baseline study on the current fish community of Bayou Lafourche.
The aim of this research is to estimate the abundance, distribution and species diversity
of the adult fish community. This study will also examine the possible effects of the
Thibodaux weir on the migratory species of Bayou Lafourche. A common method of
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circumnavigating the absence of data prior to modification is to compare a section of the
water body with a similar, yet unaltered water body (Englund and Malmqvist 1996,
Pilcher et al. 2004). In this case, there are no data regarding migratory fish runs up
Bayou Lafourche. However, in nearby Bayou Chevreuil, gizzard shad Dorosoma
cepedianum, a migratory species, has been documented traveling to the upper reaches
of the bayou to spawn (Fontenot 2006). Since the upstream migration of gizzard shad
in Bayou Lafourche is impeded by the Thibodaux weir this study will compare total
distance (river miles) traveled between Bayou Lafourche populations and Bayou
Chevreuil populations of gizzard shad.
This completed study will serve as a baseline for future work assessing the
impacts of hydrologic alteration of Bayou Lafourche. It will provide data regarding the
current fish community and suggest potential impacts of the MRWR project on the fish
community.
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Figure 1. Bayou Lafourche extends 172.2 kilometers from the Mississippi River to the Gulf
of Mexico creating the border between the Barataria Estuary and the Terrebonne Estuary
(BTNEP 1995, Emmer et al. 2003).
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Figure 2. Physical environments transected by Bayou Lafourche (BTNEP 1995,
Emmer et al. 2003). Fresh marsh, intermediate marsh, brackish marsh and salt
marsh may benefit from the introduction of sediments and nutrients to the system via
Bayou Lafourche.
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Purpose
The purpose of this study is to assess the seasonal abundance, distribution and
diversity of adult fishes in the current Bayou Lafourche.
Goals and Objectives:
The goal of this study is to provide quantitative data on the seasonal abundance,
diversity and distribution of adult fishes inhabiting Bayou Lafourche above and below
the Thibodaux weir. This research will provide the necessary data to predict potential
effects that the removal of the Thibodaux weir may have on the distribution and/or
behavior of the fish community. This study will serve as a baseline assessment of the
current ichthyofauna community of Bayou Lafourche. Specific objectives of this study
are as follows:
1) Assess the seasonal distribution of species above and below the Thibodaux
weir.
2) Estimate seasonal species abundance and diversity of adult fishes inhabiting
Bayou Lafourche.
3) Predict possible effects of removal of the Thibodaux weir on fish distribution
and migration.
4) Provide a baseline assessment of the current fish community for use in
predicting possible impacts of future hydrological modifications.
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Methods
Adult fish will be collected twice monthly using monofilament gill nets at two
locations; one above the Thibodaux weir and one below the weir. The above weir
Thibodaux site is located at the Jean Lafitte Acadian Cultural Center, 314 St. Mary
Street, Thibodaux (29° 47.825’ N, 90° 49.525’ W). The below weir Thibodaux site is
located across Hwy 1 from Nicholls State University main entrance (29° 47.767’ N, 90°
48.039’ W; Figure 1). Five gill nets of various bar mesh sizes:

(2) 38mm bar mesh, 23m long x 1.8m deep

(2) 25.4mm - 38mm experimental bar mesh, 23m long (11.5/mesh size) x
1.8m deep

(1) 95mm bar mesh, 23m long x 1.8m deep
Different sized nets are set in a random pattern each sampling trip. The nets are set
roughly 1m from the bank and stretched towards the middle of the bayou at
approximately a 45° angle to the bank of the bayou. Nets are set using two concrete
weights attached to the lead line and two floats attached to the float line. Nets are set at
approximately 0900 – 1000 hours and are left to soak for approximately 4 hours. Nets
are picked up between 1300 – 1400 hours. Fish are removed from each net, identified
by net and site, and taken back to the laboratory. Fish are processed by measuring
length (mm), weight (g), and gonad weight (g). Sex of each individual is also
determined.
Dissolved oxygen (DO; mg/L), water temperature (°C), salinity (ppt), and specific
conductance (µS) are measured at each site using a handheld YSI meter (Yellow
Springs Instruments, Yellow Springs, Ohio). Secchi disc depth (cm) is also measured at
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each site during each sampling trip. Donaldsonville Pump Station water flow
information will be obtained from the Bayou Lafourche Freshwater District (BLFD) for
each sample date. Aquatic vegetation mowing activities for the duration of this study
will also be obtained from BLFD.
Catch per unit effort (CPUE) for each site will be determined by the total number
of fish caught per net hour. The CPUE will be calculated as the mean of five nets at
each site. If needed, CPUE will be calculated for each mesh size by site. Diversity will
be calculated using the Shannon-Weiner Diversity Index (H’=∑pilog2pi ). Evenness
Index (E=H’/log2S) and total abundance will be calculated for each site (Krebs 2001).
Preliminary Findings
We have collected 393 individuals consisting of 24 species (Table 1) from 11
families during 18 sampling trips. A total of 380 fishes have been collected from sites
located immediately above or below the Thibodaux weir. Two hundred one fish have
been collected above the Thibodaux weir and 179 collected below the Thibodaux weir.
Another 13 individuals were collected at a site located near the headwaters of Bayou
Lafourche in Donaldsonville. We collected three species that had not previously been
reported in Bayou Lafourche (Schultz 1996). Erimyzon oblongus (creek chubsucker)
was collected at the above weir site. Five Ictiobus bubalus (smallmouth buffalo) have
been collected both above and below the weir. One Alosa alabamae (Alabama shad)
with large lacerations on its body, suggesting that it passed through the pump station
turbines and over the Thibodaux weir, was collected at the downstream site.
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The composition of species by family was markedly different between the above
weir and below weir Thibodaux sites (Fig. 3). Above the weir, 69% of the fish collected
were Centrarchids as opposed to only 10% from below the weir. Additionally, 45% of
the fish collected below the weir were clupeids while above the weir only 4.5% of the
catch consisted of clupeids. Those data may prove important when assessing the affect
of the Thibodaux weir on migratory behavior of some fish species.
Preliminary data were used to calculate the Shannon-Weiner Diversity Index by
season for the Thibodaux sites (Table 2). The above weir site had the highest diversity
in the summer (2.13) and the below weir site was most diverse in the fall (2.14).
Evenness for the two sites was also calculated based on data collected through
December 2006 (Table 3). Interestingly, winter was the most even (0.97) at the above
weir site and the least even (0.57) at the below weir site. Fall was the most even for the
downstream site (0.93).
The collection of gizzard shad above and below the Thibodaux weir was
examined as an indicator of possible effects on migratory species. Above the weir we
collected 9 gizzard shad over the ten months of sampling compared to 74 caught below
the weir (Fig. 4). This may indicate that the Thibodaux weir is creating an obstacle to
annual upstream spawning migration of gizzard shad in Bayou Lafourche.
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Table 1. Total number of individuals of each species captured from Bayou Lafourche
between 9 February 2006, and 05 December 2006.
SPECIES
Above Weir
Below Weir
Donaldsonville
Micropterus salmoides
82
11
2
Mugil cephalus
19
37
2
Lepomis microlophus
15
1
0
Lepomis macrochirus
14
0
0
Lepomis gulosus
13
5
0
Ictalurus punctatus
12
14
5
Lepisosteus oculatus
12
13
2
Dorosoma cepedianum
9
74
1
Lepomis megalotis
6
0
0
Pomoxis nigromaculatus
5
0
0
Lepomis miniatus
4
0
0
Ictiobus bubalus
3
2
0
Lepisosteus osseus
2
0
0
Morone mississipiensis
2
6
1
Aplodinotus grunniens
1
2
0
Erimyzon oblongus
1
0
0
Morone chrysops
1
0
0
Alosa alabamae
0
1
0
Alosa chrysochloris
0
4
0
Amia calva
0
1
0
Cyprinius carpio
0
2
0
Dorosoma petenense
0
2
0
Elops saurus
0
3
0
Lepomis cyanellus
0
1
0
201
179
13
TOTALS
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100
Above weir
90
Below weir
80
% Catch
70
60
50
40
30
20
10
ei
d
er
st
pi
so
al
ur
Ic
t
O
th
ae
e
ae
ilid
M
ug
lu
p
C
id
a
Le
C
en
t
ra
rc
h
id
ei
da
e
ae
0
Figure 3. Percentage of catch by family of species caught above and below the
Thibodaux weir between 09 February 2006, and 05 December 2006.
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Table 2. Shannon-Weiner Diversity Index values calculated for sites above and below the
Thibodaux weir.
Season
Above Weir
Below Weir
Spring
1.836
1.771
Summer
2.129
1.793
Fall
1.638
2.139
Winter
1.889
1.115
Table 3. Evenness Index values calculated for sites above and below the Thibodaux weir.
Season
Above Weir
Below Weir
Spring
0.8357
0.806
Summer
0.9245
0.862
Fall
0.6593
0.929
Winter
0.9708
0.573
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12
Mean # Collected
10
8
6
4
2
0
Above weir
Below weir
Figure 4. Mean abundance (+S.D.) of gizzard shad D. cepedianum collected above and
below the Thibodaux weir between 09 February 2006, and 05 December 2006.
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