Reproductive biology and population dynamics of a bowfin (Amia calva) population in
southeastern Louisiana
A Master of Science Thesis Proposal
Johnathan Davis
Department of Biological Sciences
Nicholls State University
15 December 2005
1
Summary
Bowfin Amia calva are a top-level predator in the swamps and bayous of
Louisiana. Because of the popularity of their meat and roe as food and their local
recreational appeal, bowfin are a valuable commodity within south Louisiana. An
understanding of their reproductive biology, most notably egg size, number, and time of
development, is not only important commercially for individuals who sell the roe, but
also for the refinement of population models for the management of the species. In this
study, age and growth data as well as the reproductive data will be quantified for a
population of bowfin from southeastern Louisiana. Fishes will be collected with gill nets
from the Bayou Chevreuil-Grand Bayou system near Chackbay, Louisiana, using gill nets
and from various locations across southeast Louisiana with the assistance of commercial
fisherman. Total length, weight, egg size and number, sex, and gonad weight will be
collected for each fish. This information will be used to improve existing population
models and to develop an individual-based harvest model for bowfin using data from
populations within southeast Louisiana. Estimating reproductive potential and describing
the population characteristics of bowfin can potentially insure protection of the stocks of
bowfin and aid in providing a sustainable and prosperous bowfin fishery for the users in
Louisiana.
Introduction
Bowfin belong to one of the oldest groups of fishes and are the last extant species
of Amiidae. The lineage has been traced back to the Mesozoic era (Patterson and
Longbottom 1989). Bowfin are important to Louisiana as a commercial species for both
their meat and their roe. The population dynamics of bowfin in southeastern Louisiana is
2
poorly understood, and information on current stocks is limited also. Found in the
swamps and backwaters throughout the region, bowfin may become stressed from
changes in their habitat. These swamps and backwaters are no longer subjected to yearly
flood pulses that contribute to the productivity of the system. Although the bowfin
adapts well to these hypoxic habitats, reductions in primary and secondary production
can affect populations of top-level predators such as bowfin. Nutrients that are available
on the floodplain are no greatly reduced in the system in the absence of a flood pulse,
reducing the amount of energy available to species. This energy is not transported up the
food chain to bowfin, and therefore, less energy is available for growth and reproduction.
Regarded as a non-game species in some areas of their range, bowfin are not
actively sought after by anglers nor are they a primary species of concern for fisheries
managers. Bowfin can be an excellent recreational species (Reighard 1903; McClane
1957). Bowfin have often been viewed as harmful and nuisance species to game fishes
and recreational anglers (Scarnecchia 1992). Therefore, most management has focused
on eliminating this fish, and, as a result, research on this fish species is limited.
Furthermore, the ecological role that this species plays is not yet fully understood and
could be a vital element in the structure and function of swamp ecosystems. Although
bowfin may consume some gamefish species, they also consume many non-game species
(Lagler and Hubbs 1940; Berry 1955; Cook 1959, Dugas et al. 1976). Other species once
considered as “trash” species such as alligator gar Atractosteus spatula may play
important an ecological role by maintaining balanced populations of various fish species
(Scarnecchia 1992; Scott 1968; Haase 1969; Becker 1983). Bowfin may play such a role.
3
Without proper management based on population models and knowledge of
reproduction, this species can become prone to over harvest. Bowfin are commercially
fished throughout this region, and in 2003, the commercial fisheries landings of bowfin in
Louisiana totaled more than 128, 157 dollars from 203,607 pounds harvested (Louisiana
Department of Wildlife and Fisheries 2005). The meat must be harvested from the fish
immediately or very soon after death due to the release of an enzyme that causes the
tissue to break down.
Assessment of bowfin populations is needed for the effective management of
bowfin in areas from which the species is harvested. Currently, research on other longlived commercially fished species in Louisiana is being conducted. These studies on
focused on the hatching and rearing of alligator gar and the genetic differences among gar
populations from different regions in order to support scientifically-based restocking of
alligator gar in native areas (Campbell, U.S. Fish and Wildlife Service, pers.
communication; Graves, pers. communication). Little information on the bowfin is
available (Davidson 1991). The study of bowfin is important for providing accurate
information so that future management strategies will be effective in allowing this species
to be protected, yet productive.
Purpose
The purpose of this project is to analyze fecundity, age, and growth of bowfin to
assess the population in southeast Louisiana in order to develop and to adjust population
models.
4
Goal
The goal of this study is to learn more about the age and growth and the
reproductive biology of bowfin for population management and modeling purposes
through the study of life history traits such as fecundity, egg size, age of maturation,
length of spawning season, and gonad development. This project will also define the
spawning period of bowfin and the age of maturation for a southeast Louisiana
population, as well as describe population structure using age, growth, length and weight
data. This information will be used to improve population models for bowfin using data
from populations within southeast Louisiana.
Objectives of Research
Specific objectives of the research are to:
1.)
Estimate total fecundity of female bowfin in a southeast Louisiana
population.
2.)
Determine the age of maturation for bowfin from a southeast Louisiana
population.
3.)
Define the spawning period of bowfin from a southeast Louisiana
population.
4.)
Characterize the population structure of a southeast Louisiana population
of bowfin using age, growth, and fecundity data.
5.)
Compare results to historical data.
5
Preliminary Data
A total of 51 individuals have been collected. With the addition of fish collected
in March 2005 for other research, 45 sets of otoliths and 68 gular plates have been
collected for determining age and growth. Data on weight, length, girth, sex, and gonad
weight are available for 51 individuals (Appendix). No data on egg number or egg
diameter is has been calculated to date. The Louisiana Department of Wildlife and
Fisheries published a report in which the spawning period for bowfin was late January to
early March (Davidson 1991). 29 ripe ovaries were sampled, and average fecundity per
ovary was 36, 179.
Methods
Bowfin will be collected on a monthly basis from September 2005 through
September 2006 from the swamps and bayous of the Grand Bayou-Bayou Chrevelle
complex. Twice a month researchers will collect fish using gill nets and also trot lines
when possible. Bowfin will also be collected from commercial fisherman in the local
swamps and bayous when possible. Bowfin will be weighed to the nearest tenth of a
kilogram and measured for total length and pre-pelvic girth to the nearest millimeter.
The heads and gonads will be collected and put on ice for processing in the lab. Otoliths
will be removed, washed and dried, and placed in labeled vials for aging. Whole otoliths
will be viewed under a dissecting microscope for age determination Multiple readers
will age otoliths and gular plates, and any discrepancies in age will be discussed until an
age is agreed upon (Nash and Irwin 2000). Photographs of each otolith and gular plate
6
will be taken for documentation and reference. The feasibility of using otoliths for age
determination will be assessed. Observation of otolith annuli formation from different
age classes throughout the year of sampling will provide a time of annulus formation
(Maceina and Betsill 1987). Gular plates will also be removed. They will be boiled on a
hot plate in order to remove skin and tissue and then washed, dried, and stored for aging.
Sex determinations will be made based on externally visible characteristics such
as the presence (male) or absence (female) of a tail spot and fin coloration. Sexual
identification will be confirmed by observation of the gonads. After sex determination is
made, gonads will be weighed to the nearest gram and gonad developmental state will be
determined (Burr and Ladonski, in press). Gonad descriptions will be made based on
color, texture, appearance, and any other noticeable trait. Following the procedures of
Ladonski and Burr (in press), a subsample of eggs will be taken, and individual egg
diameters will be measured to the nearest millimeter. Additionally, an estimate of the
total number of eggs will be made. Egg diameter will be determined using digital
calipers and imaging software (Ferrara 2001). Another subsample of eggs weighing 10%
of the total ovary weight will be removed from the ovary, and the total number of eggs in
the subsample will be counted (Ladonski and Burr, in press). The accuracy of this
method will be tested by making a count of all eggs from the ovaries of a few individuals
and comparing the actual egg count to the estimated egg count. Ovaries will be labeled
and stored in a 10% formulin solution for reference. Gonadosomatic index (GSI) will
also be determined for males and females to assist in determination of spawning period
(Wilson and Nieland 1994; Ferrara 2001). GSI will be calculated following the method
of Johnson and Noltie (1997) according to the following equation:
7
GSI= (gonad weight)/(total body weight) x 100
Significance of Research
A majority of bowfin research has focused on stomach contents (Ashley and
Rachels 1999, Dugas et al. 1976, Todd 1970) and air-breathing capabilities (Daxboeck et
al. 1981, Hendrick 1994), with some work studying biology and populations (Davidson
1991). However, recent work has begun assessing nitrite uptake of bowfin (Boudreaux
2005). Unfortunately, the reproductive biology of bowfin is poorly understood. A single
population of bowfin will be collected over a single year. Furthermore, determining the
times of the year in which egg diameter is greatest within females could provide
commercial anglers a guideline for the most profitable time to harvest bowfin eggs. This
could limit harvest of under developed individuals during early times of the year.
This study will collect data from populations within a defined area and will
provide additional reproduction data which can be used to create population models as
well as to develop a population specific harvest model. Management strategies such as
creel and harvest limits are based upon population models. Therefore, by improving
models and developing new population specific models, more appropriate and effective
management strategies will result.
A better understanding of spawning season duration will help to develop
measures of protection for bowfin during critical spawning times if necessary.
Additionally, determination of age of maturation from a population within one region
will allow managers to better evaluate regulations restricting harvest of immature
individuals in areas where protection of the population is necessary. Because of this
8
study’s significance in describing a self-sustaining population, many researchers will cite
this publication, and many agencies will look to this study in facilitating protection of
bowfin in native areas.
Potential for Additional Funding and Eminence
Results of this study will be presented at the annual meeting of the Louisiana state
chapter of the American Fisheries Society, with the potential to be presented at other
scientific meetings. This research will also be published as a master’s thesis and
submitted for publication to a peer-reviewed journal.
The potential exists for collaboration with agencies interested in the protection
and management of bowfin populations. This data can be used to justify management
actions taken by these agencies. It will also provide the opportunity to garner agency
funding in the future for in-depth studies of other bowfin populations and assessments of
other species. Completion of this research will demonstrate that the researchers are
capable of conducting investigations of this nature in the future. Finally, it will serve as
an opportunity to promote the research capabilities of Nicholls State University.
9
Bibliography/ Citations
Ashley, K.W. and R.T. Rachels. 1999. Food habits of bowfin in the Black and Lumber
Rivers, North Carolina. Proceedings of the Annual Conference of the
Southeastern Association of Fish and Wildlife Agencies 53: 50-60.
Becker, G. C. 1983. Fishes of Wisconsin. University of Wisconsin Press, Madison,
Wisconsin.
Berry, F.H. 1955. Food of the mudfish (Amia calva) in Lake Newman, Florida, in relation
to its management. Journal of the Florida Academy of Sciences. 18: 69-75.
Boudreaux, P.J. 2005. Acute ammonia toxicity and chloride inhibition of nitrite uptake
in non-teleost Actinopterygiian fishes. A Master’s Thesis. Nicholls State
University.
Chivers, C. J. 2005. Fishing for dinosaurs. Field and Stream. 1005: 58-61, 91-92.
Cook, F.A. 1959. Freshwater fishes in Mississippi. Mississippi Game and Fish
Commission. Jackson, Mississippi.
Davidson, R.B. 1991. Bowfin (Amia calva) population, biology, and gillnet selectivity
research report, 1990-1991. Louisiana Department of Wildlife and Fisheries.
Baton Rouge, Louisiana.
Daxboeck, C., D.K. Barnard, and D.J. Randall. 1981. Functional morphology of the gills
of the bowfin, Amia calva, with special reference to their significance during air
exposure. Respiration Physiology. 43: 349-364.
Dugas, C.N., M. Konikoff, and M.F. Trahan. 1976. Stomach contents of bowfin (Amia
calva) and spotted gar (Lepisosteus oculatus) taken in Henderson Lake,
Louisiana. Louisiana Academy of Sciences. 39: 28-34.
Ferrara, A. M. 2001. Life-history strategy of Lepisosteidae: Implications for the
conservation and management of alligator gar. Doctoral dissertation. Auburn
University, Alabama.
Ferrara, A. M. and E. Irwin. 2001. Standardized procedure for internal sex identification
in Lepisosteidae. North American Journal of Fisheries Management. 21:956961.
Goodyear, C. P. 1967. Feeding habits of three species of gars, Lepisosteus, along the
Mississippi Gulf Coast. Transactions of the American Fisheries Society. 96:438449.
10
Gowanloch, J. N. 1940. Control of garfish in Louisiana. Transactions of the North
American Wildlife Conference. 5:292-295.
Graves, K. 2005. Personal communication. United States Fish and Wildlife Service.
Tishomingo National Fish Hatchery.
Haase, B.L. 1969. An ecological life history of the longnose gar, Lepisosteus osseus
(Linnaeus), in Lake Mendota and in several other lakes of southern Wisconsin.
Ph. D. Dissertation, University of Wisconsin, Madison, Wisconsin.
Hedrick, M.S., S.L. Katz, and D.R. Jones. 1994. Periodic air-breathing behaviour in a
primitive fish revealed by spectral analysis. Journal of Experimental Biology.
197: 429-436.
Johnston, K. H. 1961. Removal of longnose gar from rivers and streams with the use of
dynamite. Proceedings of the Annual Conference of the Southeastern Association
of Game and Fish Commissions. 15:205-207.
Ladonski, J. B. and B. M. Burr. In press. Reproductive biology of shortnose gar
(Lepisosteus platostomus) in waters of the upper Midwest, with comments on the
role of gars in fisheries management. Journal of Freshwater Ecology.
Lagler, K.F., and F.V. Hubbs. 1940. Food of the long-nosed gar (Lepisosteus osseus)
and the bowfin (Amia calva) in southern Michigan. Copeia. 1940(4): 239-241.
Louisiana Department of Wildlife and Fisheries. 2005. The Economic benefits of
fisheries, wildlife, and boating resources in the state of Louisiana. Prepared by
Southwick Associates.
McCarley, H. and L. G. Hill. 1980. Reproduction of the alligator gar in Lake Texoma.
Southwestern Naturalist. 24(4):683-714.
McClane, A.J. 1957. The wise fisherman’s encyclopedia. William H. Wise and
Company, Inc. New York.
Mendoza, R., C. Aguilera, J. Montemayor, A. Revol, and J. Holt. 2002a. Studies on the
physiology of Atractosteus spatula larval development and its applications to
early weaning onto artificial diets. In: Cruz-Suarez, L.E., D. Rique-Marie, M.
Tapia-Salazar, M.G. Gaxiola-Cortes, and N. Simones (Eds.). Avances in
Nutricion Acuicola VI. Memorias del VI Simposium Internacional de Nutricion
Acuicola 3 al 6 de Septiembre del 2002. Cancun, Quintana Roo, Mexico.
Mendoza, R., Aquilera, G. Rodriguez, M. Gonzalez, and R. Castro. 2002b. Morphophysiological studies on alligator gar (Atractosteus spatula) larval development as
a basis for their culture and repopulation of their natural habitats. Reviews in Fish
Biology and Fisheries. 12:133-142.
11
Patterson, C., and A.E. Longbottom. 1989. An Eocene amiid fish from Mali, West
Africa. Copeia. 1989(4): 827-836.
Poly, W. J. 2001. Distribution of the alligator gar, Atractosteus spatula, in Illinois.
Transactions of the Illinois State Academy of Science. 94:185-190.
Rayner, D.H. 1941. The structure and evolution of the holostean fishes. Biological
Review of the Cambridge Philosophical Society.
Reighard, J. 1903. The natural history of Amia calva Linneaus. Henry Holt and
Company, New York.
Sakaris, P. C., A. M. Ferrara, K. J. Kleiner, and E. R. Irwin. 2003. Movements and
home ranges of alligator gar in the Mobile-Tensaw delta, Alabama. Proceedings
of the Annual Conference of the Association of Fish and Wildlife Agencies.
57:102-111.
Scarnecchia, D. L. 1992. A reappraisal of gars and bowfin in fisheries management.
Fisheries. 17:6-12.
Scott, T. M., Jr. 1968. Spotted gar predation on bluegill and selected forage species.
Proceedings of the Annual Conference of the Southeastern Association of Game
and Fish Commissioners. 21: 357-360.
Siedensticker, E. P. 1988. Food selection of Alligator Gar and Longnose gar in a Texas
reservoir. Proceedings of the 41st Annual Conference of the Southeastern Fish
and Wildlife Agencies. 42: 229-233.
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Fishes of the Western Atlantic; Part Three, soft-rayed fishes. Yale University
Memoir Sears Foundation for Marine Research I, New Haven, Connecticut.
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Wildlife Department, Technical Series Number 6.
12
Appendix
13
Table 1. Preliminary data for bowfin Amia calva collected from southeast Louisiana.
Fish
ID
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1036
1035
1034
1033
1032
1031
1030
1029
1028
1027
1026
1001
1002
1003
1004
1037
1039
1038
1040
1041
1042
1043
1047
1046
1045
1044
38
39
40
41
42
43
45
1048
Collection
Date
6-Dec-05
6-Dec-05
6-Dec-05
6-Dec-05
6-Dec-05
6-Dec-05
6-Dec-05
6-Dec-05
6-Dec-05
6-Dec-05
6-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
12-Dec-05
11-Nov-05
11-Nov-05
11-Nov-05
28-Oct-05
17-Oct-05
17-Oct-05
17-Oct-05
14-Oct-05
14-Oct-05
14-Oct-05
14-Oct-05
20-Sep-05
20-Sep-05
20-Sep-05
20-Sep-05
20-Sep-05
20-Sep-05
22-Sep-05
22-Sep-05
Location
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
Bayou Chevrevil
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
Total
Length
(mm)
527
592
562
579
698
597
601
523
600
600
591
423
514
388
522
391
382
372
527
597
489
448
418
400
551
387
379
431
432
362
598
626
632
657
577
660
366
600
580
521
580
595
575
513
556
Weight
(kg)
1.1
1.7
1.4
1.8
3.1
1.9
1.8
1.1
1.8
2.2
1.8
0.6
1.1
0.5
1.3
0.5
0.5
0.4
1.2
1.7
0.8
0.7
0.6
0.5
1.5
0.4
0.5
0.6
0.8
0.4
2.3
2.3
2.1
2.6
1.8
2.9
0.5
4.9
3.3
2.6
4.4
4.7
2.1
1.3
1.8
Girth
(mm)
216
254
226
270
321
272
269
219
275
295
274
178
224
162
735
166
160
157
238
262
201
193
180
175
258
164
174
186
206
Left Gonad
Wt (g)
4
45
4
33.4
100.9
62.2
32.7
3.9
45.6
87.2
47
5
9.4
7
7.5
3.4
3.2
3.7
8.2
52.6
6.1
18.1
7.4
3.9
54
2.1
4.2
4.7
4.5
4.6
31.2
27.7
28.2
11.8
5.2
22.5
0.1
12.2
1
4.6
1.2
11.1
16.8
0.6
1.9
Rt Gonad
Wt (g)
4.1
44.4
4.3
32.3
90.2
61.9
34.1
3.6
49.2
76.4
37.9
2.9
8.2
4.2
10.3
3.1
2.6
2.6
7.2
50
5.4
16.3
6.6
3.6
80
2.7
3.8
3.8
4
3.5
31
27.8
28
7.5
17
53
0.1
12.3
1
4.1
1.2
12.3
12.7
0.6
1.2
14
Sex
M
F
M
F
F
F
F
M
F
F
F
F
M
F
M
M
M
M
M
F
M
F
M
M
F
M
F
M
M
F
F
F
F
M
M
F
M
F
M
F
M
F
F
M
M
49
48
44
46
47
50
22-Sep-05
28-Sep-05
28-Sep-05
28-Sep-05
29-Sep-05
3-Oct-05
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
J. Ledet
621
646
618
474
398
458
2.1
11.6
10.6
15.3
1.8
1.5
0.5
11.9
11.8
16
2.1
1.5
0.3
15
F
F
F
M
M
M