Distribution and Relative Abundance of Blue Crab Callinectes sapidus in the Upper Barataria Estuary

99 Pages·2007·4.32 MB·English

DISTRIBUTION AND RELATIVE ABUNDANCE OF
BLUE CRAB CALLINECTES SAPIDUS IN THE
UPPER BARATARIA ESTUARY, LOUISIANA

A Thesis

Submitted to the Graduate Faculty of
Nicholls State University
In partial fulfillment of the requirements for the degree of
Master of Science
in
Marine and Environmental Biology

by
MattiLynn D. Dantin
B.S., Nicholls State University, 2005

Spring 2007
CERTIFICATE

This is to certify that the thesis entitled “Distribution and Relative Abundance of
blue crab Callinectes sapidus in the Upper Barataria Estuary, Louisiana” submitted for
the award of Master of Science to Nicholls State University is a record of authentic,
original research conducted by Mrs. MattiLynn D. Dantin under our supervision and
guidance and that no part of this thesis has been submitted for the award of any other
degree, diploma, fellowship, or other similar titles.

APPROVED SIGNATURE DATE
Quenton Fontenot, Ph.D.
Assistant Professor of
Biological Sciences ______________________________ ____________
Committee Member

Allyse Ferrara, Ph.D.
Assistant Professor of
Biological Sciences ______________________________ ____________
Committee Member

Earl Melancon, Ph.D.
Professor of
Biological Sciences ______________________________ ____________
Committee Member
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ABSTRACT
Blue crabs Callinectes sapidus are marine organisms that seasonally migrate
within an estuary and contribute to energy transfer throughout the system. Because blue
crab is a commercially and recreationally important species within Louisiana estuaries, it
is important to understand factors that may affect blue crab distribution and abundance.
The Barataria Estuary is bordered by the Mississippi River to the east, Bayou Lafourche
to the west, and the Gulf of Mexico to the south. The upper-most reaches of the Barataria
Estuary are comprised of approximately 41% of forested freshwater wetlands including
the Lac Des Allemands/Bayou Chevreuil area. Blue crabs were sampled weekly between
11 July and 6 December 2006, with modified commercial crab traps at seven fixed sites
in Bayou Chevreuil. Traps were baited with fish carcasses or chicken pieces, and
remained deployed for approximately 24 hours. Surface and bottom water temperature
(°C), salinity (ppt), dissolved oxygen (DO; mg/L) and specific conductance (µs) were
measured at each site when traps were deployed. Blue crab catch per unit effort (CPUE)
was determined as the mean number of crabs collected per trap per day. Crabs were
enumerated and transported to the Bayousphere Research Laboratory to be sexed,
reproductive state determined, and measured for carapace width (mm), carapace length
(mm), cheliped-free body weight (g), and individual cheliped weight (g). Individual trap
CPUE ranged from 0-24 crabs/trap/day. Of the 649 blue crabs collected from Bayou
Chevreuil, there were 24 immature females, 34 mature females, and 591 males. Overall,
females were wider than males, but males were heavier than females of similar width (P
< 0.0001). Temperature, dissolved oxygen, salinity, and specific conductance were
positively correlated (P < 0.05) to blue crab abundance. Distribution and abundance were
ii
highest in July and August and lowest in November and December. Blue crabs are a
seasonally abundant species in Bayou Chevreuil.
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ACKNOWLEDGEMENTS
I would like to thank my committee members, Dr. Earl Melancon and Dr. Allyse
Ferrara for their continued support, kindness, and pool of knowledge. Special thanks is
regarded for my major professor, Dr. Quenton Fontenot. He has been my mentor and
friend throughout my graduate experience. The never ending guidance, wisdom, and
patience of my graduate committee has kept me motivated in the pursuit of this degree.
I would like to thank the Nicholls State University Department of Biological
Sciences and the Nicholls State University Bayousphere Research Laboratory for the use
of their vehicles, vessels, and equipment during this endeavor. I would also like to thank
Mr. Joey Toups for donating the crab traps that were used in this study.
Special thanks are held for my family and friends. None of this would have been
possible without the constant love and push by my parents to do better for myself. They
have always supported my decisions for further education and have made themselves
available for whatever tasks that entailed. I thank my siblings and their spouses. They
too were always willing to assist in this undertaking with physical labor and moral
support. I cannot continue without recognition of my graduate professors and fellow
graduate students. They are truly a wonderful group of peers whom every one of them
has helped with the completion of this project. I only wish I could thank everyone by
name. As for my office mates, Olivia Smith and Heather Dyer, I hold great appreciation.
I could always count on these two women, no matter the situation.
The greatest appreciation is held for my husband. He believed in me and my
success when I no longer did. His love and encouragement was my drive and confidence
to accomplish this goal.
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TABLE OF CONTENTS
Certificate…………………………………………………………………………………..i
Abstract……………………………………………………………………………………ii
Acknowledgements………………………………………………………………….……iv
Table of Contents…………………………………………………………………….……v
List of Figures…………………………………………………………………………….vi
List of Tables………………………………………………………………………….….ix
List of Scientific Names…………………………………………………………………...x
Introduction……………………………………………………………………….……….1
Methods………………………………………………………………………..…………14
Results……………………………………………………………………………………19
Discussion………………………………………………………………………………..47
Recommendations………………………………………………………………………..54
Literature Cited…………………………………………………………………………..55
Appendix I……………………………………………………………………………….60
Appendix II………………………………………………………………………………76
Appendix III……………………………………………………………………………...83
Biographical Sketch……………………………………………………………………...86
Curriculum Vitae………………………………………………………………………...87
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LIST OF FIGURES
Figure 1. Location of the Barataria Estuary (gray area) in southeastern Louisiana…...…2

Figure 2. Approximate salinity gradient within the Barataria Estuary based on
data obtained from Braud et al. (2006), LDWLF (2005), and Jaworski
(1972)……………………………………………………………………………...3

Figure 3. Geographic distribution of blue crab. Populations around Europe and
Japan have been introduced and are not native to those areas…………………….7

Figure 4. Sexually dimorphic characteristics of male and female blue crabs.
Illustrated above is the abdominal apron of the male (a), immature female
(b), and mature female (c) blue crab………………………………………………9

Figure 5. Approximate inland most regions occupied by blue crabs in the Barataria
Estuary for each stage of the blue crab life cycle………………………………..13

Figure 6. Bayou Chevreuil and Lac Des Allemands in the Barataria Estuary
(earth.google.com). Location of seven fixed study sites………………………..15

Figure 7. Modified commercial crab trap with closed escape rings…………………….16

Figure 8. Mean (±SD) water temperature in Bayou Chevreuil for all sites combined
for each sample date……………………………………………………………...21

Figure 9. Mean (±SD) water temperature for each site in Bayou Chevreuil for all
sample dates combined from 11 July 2006 to 6 December 2006………………..22

Figure 10. Mean (±SD) dissolved oxygen levels in Bayou Chevreuil for all sites
combined for each sample date. The dashed line represents DO levels at
2.0 mg/L………………………………………………………………………….23

Figure 11. Mean (±SD) overall dissolved oxygen for each site in Bayou Chevreuil
for all sample dates combined from 11 July 2006 to 6 December 2006.
Means with similar letters are not different……………………………………...24

Figure 12. Mean (±SD) salinity in Bayou Chevreuil for all sites combined for each
sample date……………………………………………………………………….25

Figure 13. Mean (±SD) specific conductance in Bayou Chevreuil for all sites
combined for each sample date…………………………………………………..26

Figure 14. Mean (±SD) specific conductance for each site in Bayou Chevreuil for
all sample dates combined from 11 July 2006 to 6 December 2006. Means
with a similar letters are not different……………………………………………27
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Figure 15. Size distribution based on carapace width of male and female blue
crabs collected in Bayou Chevreuil from 11 July 2006 to 6 December 2006…...29

Figure 16. Percentage of male, mature female, and immature female blue crabs
collected from Bayou Chevreuil on each sample date from 11 July 2006 to
6 December 2006………………………………………………………………...30

Figure 17. Mean (±SD) width (mm), length (mm), and body weight (g) for male
and female blue crabs collected in Bayou Chevreuil from 11 July 2006 to 6
December 2006. Means within each group that share a common letter are
not different………………………………………………………………………31

Figure 18. Carapace length (a.) and width (b.) as a predictor of cheliped –free
weight for male and female blue crabs in Bayou Chevreuil. There is no
difference between males and females based on length-weight relationship.
Males weighed more than females of similar width (P < 0.0001)……………….32

Figure 19. Carapace width as a predictor of left (a.) and right (b.) cheliped weights
for male female blue crabs in Bayou Chevreuil. Males had larger chelipeds
than females of similar width (P < 0.0001)……………………………………...33

Figure 20. Mean (±SD) condition (K) of male and female blue crabs in Bayou
Chevreuil from 11 July 2006 to 6 December 2006………………………………...34

Figure 21. Mean (±SD) condition (K) of male and female blue crabs for all sites
combined in Bayou Chevreuil for each sample date………………………………35

Figure 22. Mean (±SD) CPUE for each site in Bayou Chevreuil for all sample
dates combined from 11 July 2006 to 6 December 2006. Means with similar
letters are not different…………………………………………………………...36

Figure 23. Mean (±SD) CPUE of blue crabs in Bayou Chevreuil for all sites
combined and the mean (±SD) water temperature for all sites combined
for each sample date. Critical temperature (15 °C) is the water temperature
that blue crabs have been documented to migrate down estuary for the
winter months (Jaworski 1972)…………………………………………………..37

Figure 24. Water temperature (°C) and blue crab CPUE at sites 1 – 7 in Bayou
Chevreuil by sampling date……………………………………………………...39

Figure 25. Mean (±SD) CPUE of blue crabs in Bayou Chevreuil for all sites
combined and the mean (±SD) DO for all sites combined for each sample
date……………………………………………………………………………….40

Figure 26. Mean (±SD) CPUE of blue crabs in Bayou Chevreuil for all sample
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dates when DO > 2.0 mg/L was higher than mean CPUE of blue crabs in
Bayou Chevreuil for all sample dates when DO ≤ 2.0 mg/L (P < 0.0039)………41

Figure 27. Dissolved oxygen (mg/L) and blue crab CPUE at sites 1 - 7 in Bayou
Chevreuil by sampling date……………………………………………………...42

Figure 28. Mean (±SD) CPUE of blue crabs in Bayou Chevreuil for all sites
combined and the mean (±SD) salinity for all sites combined for each
sample date……………………………………………………………………….43

Figure 29. Mean (±SD) CPUE of blue crabs in Bayou Chevreuil for all sites
combined and the mean (±SD) specific conductance for all sites combined
for each sample date……………………………………………………………...44

Figure 30. Specific conductance (µS) and blue crab CPUE at sites 1 - 7 in Bayou
Chevreuil by sampling date……………………………………………………...45

Figure 31. Mean (±SD) condition (K) of all blue crabs collected in Bayou Chevreuil
and the mean (±SD) condition of all blue crabs collected in Fourchon/Grand
Isle for each sample date. Circles group saltwater samples with the closest
freshwater samples before and after each saltwater sample. Means with a
similar letter in each group are not different (P < 0.05)…………………………46

viii
LIST OF TABLES
Table 1. Total number of species collected in Bayou Chevreuil from
11 July 2006 to 6 December 2006, using modified commercial crab
traps…………………………………………………….………………………20

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