Group Title: Fishes of a Florida oxbow and its parent river.
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Creator: BEECHER, H. A
Subject: Fishes
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Biological Sciences


Department of Biology, University of West Florida, Pensacola, Florida 32504 (1);
Bream Fishermen Association, 1333 N. Spring St., Pensacola, Florida 32501 (2)

ABSTRACT: An electrofishing and seining survey of a 70-80 yr old oxbow lake and an adjacent
section of the Escambia Ricer in northwest Florida yielded 29 species of fishes in the lake and 58
species in the adjacent river. Electrofishing results indicated different abundances of individuals of
species common to both areas. A decrease in number of species corresponds to a decrease in habitat
diversity in the oxbow lake.
OxBow LAKES are common along coastal floodplain rivers where they are
often the only natural lakes. However, little literature is devoted to the ichthyo-
fauna of oxbow lakes. Ward (1972) discussed the invertebrate fauna of an incipi-
ent oxbow lake on the lower Escambia River in northwest Florida, and reviewed
the literature on oxbow lakes. Lambou (1959, 1961) discussed fish populations
of oxbow lakes along the lower Mississippi River in Louisiana. Shipp and Hemp-
hill (1974) studied fish populations in 3-yr old artificially created oxbow lakes in
the Alabama River system. An oxbow lake is derived from its associated river
when the parent river changes course; therefore, we can assume that the lake's
fish fauna must be derived from that of the parent river. We examined the fish
fauna of an oxbow lake isolated from the Escambia River. Fishes of this river sys-
tem have been extensively studied by Bailey, Winn, and Smith (1954). Their sta-
tion no. 14 corresponds to our river study area.
DESCRIPTION OF THE STUDY AREA-Our river study area, near the Alabama-
Florida border, extends downstream about 5 km from the bridge on State Road
4 between Jay and Century, Florida, at 30057'54"N, 8714'03"W. The lake is
approximately 1 km south of the bridge and about 400 m east of the river (Fig. 1).
During high water the lake and the river are sometimes connected through a
hardwood swamp in which beavers were active. A narrow channel between the
lake and river has been dug, and is maintained, by local fishermen. This channel
is navigable only at high water, but is completely blocked by a beaver dam at
low water.
The river study area is 1070 m long. During low water the river is 70 to 80 m
wide, and our low water area covered 7.8 hectares. At high water the river
spreads out into the surrounding swamp, particularly on the east shore, and the
surface area is greatly increased. Inundation of sandbars alone adds 3.6 hectares
to the river study area, which includes the channel between the lake and the river
west of the beaver dam (Fig. 1). The study area is 84 km upstream from the mouth
of the Escambia River, at an elevation of 8.67 m above mean sea level. The Es-

'The costs of publication of this article were defrayed in part by the payment of charges from funds made
available in support of the research which is the subject of this article. In accordance with 18 U. S. C, 1734,
this article must therefore be hereby marked "advertisement" solely to indicate this fact.

[Vol. 40



cambia River in the study area is an Order 6 or Order 7 stream (U.S. Army Corps
of Engineers, Mobile Office, pers. comm.; Kuehne, 1970).
State Road 4 1- I

500 m


20 km

rt I



Fig. 1. (upper) Location map of the study area. Inset at left shows vicinity of study area in more
Fig. 2. (lower) Number of fish species per collection in paired river (circles) and oxbow lake
(triangles) collections.


a ]1

The outer sides (cut-banks) of the bends in the river are steep sand-clay banks
often overhung by fallen trees. The river reaches its maximum depth near the
outsides of bends, being more than 2 m at low water to over 6 m at the highest
water levels. The inner sides (slip banks) of the bends are broad sand beaches
extending gradually into the channel. Gravel (1-2 cm diam) occurs at some bends
where small riffles extend part way across the river. The downstream ends of
these sandbars often partly enclose a backwater with no current and a bottom of
soft clay-mud.
A map published in the mid-nineteenth century (LaTourette, 1835) shows
the oxbow lake as a part of the river, forming the eastern channel, while the pres-
ent channel formed the western channel, with an island between. The lake is
locally known as Look-and-Tremble Lake, because it once formed a sharp bend
in the river where a strong current was a hazard to log booms. The peak of log-
ging activity for northwest Florida, with a center at Pensacola, was the last
decade or two of the nineteenth century. Therefore, the lake may have been part
of the river as recently as 70-80 yr ago. Today there is no perceptible current in
the lake, even when it is connected to the river during high water.
The oxbow lake, being an old bend in the river, is similar in form to other
bends of the river. The inside of the bend is shallow and covered with a thick
layer of decomposing leaf litter. Cypress trees (Taxodium distichum) and other
swamp vegetation have encroached upon what had been the old sandbar. The
outside of the bend remains a steep bank where the lake reaches its maximum
depth of 3 m at low water to over 6 m at high water. At low water the oxbow
lake has an area of 3.4 hectares. High water increased the area greatly by inun-
dating some of the surrounding swamp. In both the lake and the river the turbid-
ity remains quite high, with visibility rarely reaching 1 m.
The river study area has greater diversity in terms of current velocity and
bottom type than the oxbow lake. Both areas have similar morphometry and
numerous submerged logs. Aquatic vegetation, other than a seasonal growth of
filamentous green algae in the river, is absent from both the river and the lake.
Current velocity in the river grades from nil to moderate (regular current read-
ings were not taken, but a single reading in an area of strong current was 1.1
m/sec). Bottom types in the river included gravel, mixed sand and gravel, loose
sand, hard-packed sand, sand covered with a thin layer of clay and silt, clay, and
clay covered with leaf litter.
METHODS-Collections were made at irregular intervals from November 1971
to December 1972. We made river collections at least once a mo, but low water
levels prevented sampling in the oxbow lake during April, June, July, and August.
Low water continued into early December. Sampling was begun in December
1971 in the oxbow lake and in January 1972 in the river. A preliminary survey
was made throughout the entire river study area during November and Decem-
ber 1971.
Each sampling run took up to 2 hr. The time spent in each run was recorded
to the nearest 5 min. We made 36 runs in 68 hr of electrofishing in the river from

[Vol. 40



January to December, 1972. In the oxbow lake we made 11 runs in 22 hr from
December 1971 to December 1972.
We collected fish with a 220V 60Hz AC electric shocker (3-8 amps, ouce 1-1.5
amps immediately after heavy rains) mounted on the front of an outboard motor
boat. Two netters used long-handled dip-nets to place stunned fish in a holding
tank in the middle of the boat.
At the termination of a run, each fish was identified, weighed, measured
(standard length, SL), tagged with a dart-type tag (if 10 cm SL or more), and re-
leased. Unidentified fish (with the exception of Micropterus spp) were preserved
in 10% formalin and labeled with appropriate station data for later examination.
Additional collections were made by seining. Seine lengths ranged from 4.6 m
to 30.5 m, with a 1 cm stretch mesh, but the longer size was not practical. Few
seine collections were made in the oxbow lake because of many submerged snags.
Fish collected in seine hauls were preserved in 10% formalin and labeled.
We measured the water level at the State Road 4 bridge from highest water
in March 1972 through December 1972 (Fig. 5).
RESULTS AND DISCUSSION-The species of fish collected in the river and the
lake are listed in Table 1. We collected 58 species in the river and 29 species in
the oxbow lake. Thirty-one species collected in the river were not taken in the
lake, and 3 species from the lake were not taken in the river. Twenty-six species
were common to both areas.
The number of fish species per collection for paired river and oxbow lake
collections is shown in Fig. 2. Ten of 11 oxbow lake collections are paired with
the nearest (in time) 10 of 36 river collections. In 8 of the 10 pairs we collected
more species in the river than in the lake. In only one of the 10 pairs were there
fewer species in the river than in the lake. There are significantly (P <0.05) more
species in the river than in the oxbow lake.
As a result of the formation of the lake, the most noticeable change has been
the decrease in the number of species. The change in number of species has oc-
curred in two groups of species, the current dwelling and the euryhaline forms.
The darters (Percidae) were represented by 9 species in the river study area,
but were not collected in the oxbow lake. Although the lake appeared to be suit-
able habitat for the swamp darter (Etheostoma fusiforme), none were obtained in
a collection made after the study. As a group, the darters are typical of flowing
Such euryhaline species as southern flounder (Paralichthys lethostigma), hog-
choker (Trinectes maculatus), Alabama shad (Alosa alabamae), and Atlantic
needlefish (Strongylura marina) were also absent from the oxbow lake. A single
specimen of the skipjack herring (Alosa chrysochloris) was collected in a gill-net
in the river after the termination of the study. However, the euryhaline group
was not totally excluded, as shown by the presence of threadfin shad (Dorosoma
petenense), gizzard shad (D. cepedianum), American eel (Anguilla rostrata), and
a single striped mullet (Mugil cephalus) in the oxbow lake.
Three species, the taillight shiner (Notropis maculatus), brown bullhead
(Ictalurus nebulosus), and Everglades pygmy sunfish (Elassoma evergladei), were

No. 2, 1977]


TABLE 1. Occurrence of fish species in oxbow lake and river study area. Numbers indicate
total number of specimens and number collected by shocking (in parentheses). The catch rate in
number of fish captured per hour of electrofishing is shown.

Species Oxbow Lake River
Number Fish/Hr Number Fish/Hr

Acipenser oxyrhynchus -- 1(1)'
Lepisosteus oculatus 10(10) 0.45 5(5) 0.07
L. osseus 5(5) 0.23 47(47) 0.69
L. spatula 1(1)' 0.01
Amia calva 40(40) 1.82 29(29) 0.43
Anguilla rostrata 5(5) 0.23 10(10) 0.15
Alosa alabamae 9(8) 0.12
A. chrysochloris 1(0)2
Dorosoma cepedianum 77(77) 3.50 83(79) 1.16
D. petenense 16(16) 0.73 45(37) 0.54
Esox niger 26(26) 1.18 14(14) 0.21
Ericymba buccata 132(30) 0.44
Hybognathus hayi 22(22) 1.00 16(9) 0.13
Hybopsis aestialis 31(1) 0.01
H. amblops 91(66) 0.97
Notemigonus crysoleucas 4(1) 0.01
Notropis chalybaeus 4(2) 0.03
N. emiliae 24(23) 1.04 11(8) 0.12
Notropis longirostris 476(87) 1.27
N. maculatus 9(8) 0.36
N. texanus 2(2) 0.09 707(319) 4.60
N. venustus 5(5) 0.23 1271(363) 5.34
Carpiodes cyprinus 52(26) 0.38
C. velifer 2(2) 0.09 169(122) 1.79
Erimyzon tenuis 7(7) 0.32 5(5) 0.07
Minytrema melanops 33(33) 1.50 34(34) 0.50
Moxostoma carinatum 3(3) 0.04
M. poecilurum 35(35) 1.59 244(244) 3.59
Ictalurus natalis 3(3) 0.04
L nebulosus 1(1) 0.05
L punctatus -16(13) 0.19
Noturus leptacanthus -8(8) 0.12
Aphredoderus sayanus 1(1)
Stronlylura marina 4(3) 0.04
Fundulus notti 1(1) 0.01
F. olivaceus 2(2) 0.09 17 + (6) 0.09
Gambusia affinis 1(0) + + (0)
Labidesthes sicculus 106(60) 2.73 26(11) 0.16
Ambloplites rupestris 7(7) 0.10
Centrarchus macropterus -3(3) 0.04
Elassoma evergladei 1(0) -
Lepomis gulosus 25(25) 1.14 26(26) 0.38
L. macrochirus 850(846) 38.61 303+(303) 4.45
L. megalotis 29(29) 1.32 269 + (269) 3.95
L. microlophus 144(144) 6.55 87(87) 1.28
L. punctatus 2(2) 0.09 1(1) 0.01
Micropterus punctulatus
75(75)' 3.41 95(89)' 1.31
M. salmoides
Pomoxis nigromaculatus 26(26) 1.18 26(26) 0.38
Ammocrypta asprella 1(1) 0.01


TABLE 1. (continued)

Species Oxbow Lake River
Number Fish/Hr Number Fish/Hr

A. bifascia -27(6) 0.09
Etheostoma davisoni 7(0)
E. swaini 4(0)
E. histrio 1(1) 0.01
E. (Ulocentra) sp. 4(2) 0.03
Percina caprodes 37(36) 0.53
P. nigrofasciata 16(16) 0.24
P. uranidea 31(2) 0.03
Mugil cephalus 1(1) 0.05 136(136) 2.00
Paralichthys lethostigma -- 9(9) 0.13
Trinectes maculatus 45(35) 0.51

'Single specimens of Atlantic sturgeon (Acipenser oxyrhynchus) and alligator gar (Lepisosteus spatula) were
shocked, but they were too big to net. The sturgeon was shocked during a non-timed shocking run within the
study period but not part of the study.
'A single specimen of Alosa chrysochloris was gill-netted after the study in July 1975.
A single specimen of the pirate perch (Aphredoderus sayanus) was collected during the preliminary survey
in November 1971.
'A single specimen of mosquitofish (Gambusia affinis) was seined in the oxbow lake after the study in June
1975. Gambusia was usually uncommon in the river, but during winter high water we collected large numbers
in flooded areas.
'See text.

collected in the lake but not in the river. Only single specimens of I. nebulosus
and E. evergladei were collected in shallow water in the lake. Notropis maculatus
was common. Notropis maculatus is probably a resident in backwater lakes and
ponds of the Escambia River swamp (Bailey et al., 1954). This fish could disperse
without entering the river because the swamp lakes and ponds are sometimes
interconnected during periods of high water.
The single specimen of I. nebulosus was not necessarily representative of the
abundance of this species. All our catfish collections may have under-represented
these species because of our use of AC rather than DC, which is selective for cat-
fish (Edwards and Higgins, 1973). Immediately after one river collection in which
we collected no catfish, trotline fishermen took a number of channel catfish (I.
punctatus) in the same area.
Elassoma evergladei was collected only after the study during an attempt to
collect swamp darters. Pygmy sunfishes, because of their small size and habitat
preference, are probably inadequately sampled by shocking. They appear to be
uncommon in the oxbow lake. None were collected in the river.
The decrease in species in the lake was accompanied by changes in the rela-
tive abundances of the remaining species. Those fish normally found in quiet
areas of the river increased in abundance in the lake, while other river species de-
creased. Among the species which were more abundant in the lake, as indicated
by electrofishing yield (Table 1), were bowfin (Amia calva), gizzard shad (Doros-
oma cepedianum), chain pickerel (Esox niger), pugnose minnow (Notropis emil-
iae), spotted sucker (Minytrema melanops), brook silverside (Labidesthes siccu-
lus), warmouth (Lepomis gulosus), bluegill (L. macrochirus), redear sunfish (L.

No. 2, 1977]






IL i L B

A S 0 N D


1 1I1S

D0 F M A M J J A S 0 N D
Fig. 3. (upper) Monthly electrofishing yields of bluegill (Lepomis macrochirus) and longer sun-
fish (L. megalotis) in the river study area.
Fig. 4. (lower) Monthly electrofishing yields of bluegill (Lepomis macrochirus) and longer sun-
fish (L. megalotis) in the oxbow lake.
microlophus), bass (Micropterus spp), and black crappie (Pomoxis nigromacula-
tus). Those species which were more abundant in the river included longnose gar
(Lepisosteus osseus), weed shiner (Notropis texanus), blacktail shiner (N. venus-
tus), blacktail redhorse (Moxostoma poecilurum), highfin carpsucker (Carpiodes
velifer), longer sunfish (Lepomis megalotis), and striped mullet (Mugil cephalus).

[Vol. 40


The changes in relative numbers of centrarchids were of particular interest.
The bluegill was the most numerous species in both areas, but it was more
abundant in the oxbow lake. In the river, longer sunfish were nearly as abundant
as bluegills, and in some months longer sunfish exceeded bluegills in abundance
(Fig. 3). In the lake, longer sunfish were relatively scarce (Fig. 4), and in some
months they were totally absent from our collections. Both species showed a de-
crease in mean length and weight from the river to the lake. The mean weight
of bluegill dropped from 48 g to 32 g (33.3% reduction), while that of longears
dropped from 17 g to 4 g (76% reduction). The mean length of bluegills decreased
from 9.6 cm in the river to 8.5 cm in the lake, while that of longears dropped from
7.2 cm to 5.1 cm. During most of the spawning season there was no dispersal
route between the two areas. The changes in length and weight are probably
not a result of emigration. Longear sunfish did not appear to be competing suc-
cessfully with bluegills in the lake, although both species appeared to be about
equally successful (in terms of numbers) in the river. Presence or absence of a
current was probably not a factor by itself; longer sunfish were abundant in
quiet areas of the river as well as in areas of strong current.

140 0

30 2 C



i 0

N 0 J F M A M J J A S 0 N D
Fig. 5.: Monthly total electrofishing yields based on fish per hr in the river study area (solid bars)
and in the oxbow lake (cross-hatched bars).

The river gave a more constant yield of fish per hr of electrofishing than did
the oxbow lake (Fig. 5). During winter high water, the yields of the two areas
were similar, but during fall low water the fish in the oxbow lake were concen-
trated without an exit. The river yield did not show this dependence upon the
water level as clearly. Yields at low water in the oxbow lake suggested a very
high biomass. Unfortunately, although we tagged 517 fish in the lake and 907 in

No. 2, 1977]

the river, our returns of tagged fish (10 in the lake and 32 in the river) were too
low to allow a precise estimate of the population (but see Beecher et al., 1976).
Our tag returns did not indicate any movement between the river and the lake.
Elimination of current through the lake has resulted in decreased habitat di-
versity and a corresponding decrease in fish diversity. This process may be con-
tinuing with a further decrease in fish species probable in the future.
ACKNOWLEDGMENTS-This study was supported, in part, by a grant from
Humble Oil and Refining Company to Thomas S. Hopkins. We could not have
carried out this study without the dedicated help of the Bream Fishermen As-
sociation. Dr. Ralph W. Yerger (Florida State University) provided valuable as-
sistance with identification of fishes and reviewed the manuscript. Brooke
Beecher, John R. Stowe, and Karen Brockman aided in follow-up studies. Dr.
Robert L. Shipp (University of South Alabama), Thomas C. Lewis, and Gordon
Cherr (Florida State University) provided constructive criticism of the manu-


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Florida, with ecologic and taxonomic notes. Proc. Acad. Nat. Sci. Philadelphia 106:109-164.
BEECHER, H. A., W. C. HIxsoN, AND T. S. HOPKINS. 1976. Studies of Moxostoma poecilurum (Pisces:
Catostomidae) in two west Florida rivers. A.S.B. Bull. 23(2):42. (Abstract)
EDwARDS, J. L., AND J. D. HIGGINS. 1973. The effects of electric currents on fish. Final Technical
Report, Projects B-397, B-400, and E-200-301, Engineering Experiment Station, Georgia Inst.
Tech., Atlanta. 75 p.
KUEHNE, R. A. 1970. Applications of the Horton stream classification to evaluate faunal studies.
Pp. 367-370. In Bioresources of Shallow Water Environments. Amer. Water Resources Assoc.
Proc. Ser. 8 (Hydrobiology). Urbana, Illinois.
LAMBOV, V. W. 1959. Fish populations of backwater lakes in Louisiana. Trans. Amer. Fish. Soc.
1961. Fish populations of Mississippi River oxbow lakes in Louisiana. Proc. Louisiana
Acad. Sci. 23:52-64.
LATOURETTE, J. 1835. An accurate map of the state of Alabama and West Florida. Surveyor's Office,
Florence, Alabama, October 14, 1835.
SHIPP, R. L., AND A. F. HEMPHILL. 1974. Effects of canalization on fish populations of the lower
Alabama River. A.S.B. Bull. 21(2):83. (Abstract)
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dae (Insecta: Diptera). M.S. Thesis. Univ. West Florida. Pensacola. 79 p.

Florida Sci. 40(2):140-148. 1977.

[Vol. 40


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