QUARTERLY JOURNAL OF THE FLORIDA ACADEMY OF SCIENCES Walter K. Taylor, Editor Henhy O. Whittier, Editor
Volume 45_Summer, 1982_Number 3
SEASONAL ABUNDANCE OF FISHES IN THREE NORTHWEST FLORIDA RIVERS
Hal A. Beecheb (1) and W. Carroll Hixson (2)
Abstract: The seasonal al'miiiam r.\ j \U fiih ~vivik in elecirofishnin collections uere compared in the Esramhu,, Choctuwhatchcc. and Apnlurhieola rivers of northwest Florida. Relative abundances, as indicated by catch per unit effort of electtvfishing, were examined in the Ekm-
j distinct in the larger Apalachicola. These seasonal iiiryhaltne fishes and the catostomids contributed the greatest amounts to the fish biomass in the Escambia River. The abundance oJCar-
fecflpfcjre study of Moxnstoma poecilurum, a dominant resident in the Escambia River, indicated
1095 504 in a I km lament nf the i cauihia If iter. Li-punii-. rrucriK'liiriis and L. megalotis were 2 of the most abundant j'i.s/u'-< u, the Vscambia River.
The fish communities of temperate rivers change throughout the year as temperature^;, flow, and day-kimUi afiect reproductive behavior, including mipalLMiift ;Schvwissm:mn. 1971), and as changing water levels induce other movements. Reproduction produces pulses of young fishes of different species at different seasons. However, long-term residence of some fishes imparts stability to stream communities. Most individuals of most species are
Residents in a small area of a stream (Ceiling, 1950, 195,1; Funk, 1955).
In the first part of this study we attempted to gain information on the Structure and seasonal changes of the fish community of the Escambia River in the vicinity of the Florida-Alabama border. A complete list of fishes col-
jtated at the Escambia River in 1971-72 is given by Beccher et al. (1977). The second part of the study, which w as carried out in conjunction with a study of Carpiodes cyprinus and C. veliirr (see ileeeher, 1979), compared
Fig. 1. Locations of study sites.
Escambia River seasonal patterns to patterns in 2 other northwest Florida drainages, the Choctawhatchee and Apalachicola rivers. A comparison of seasonal patterns in 2 different years at the Escambia River site was also made.
Few other studies have dealt with the community structure of large fishes in warm-water streams (e.g., Funk and Campbell, 1953; Gerking, 1950; Hansen, 1973). Tagatz (1968) indicated seasonal abundance of euryhaline fishes of the St. Johns River. Hellier (1967) collected and observed fishes of the clear, spring-fed Santa Fe River in the Suwannee drainage.
Description of Study AreaThe locations of the 4 primary stations are shown in Fig. 1, and drainage parameters are shown for 3 of these stations in Table 1. The fourth station (AB) is 40 km downstream from station AC, and the Apalachicola River receives no tributaries larger than intermittent third order streams in that distance.
The Apalachicola River, the largest of the 3 streams studied, is a seventh order stream, the Choctawhatchee River is a sixth order stream, and the Escambia River is a fifth order stream (determined from U.S. Geological Survey 1:250,000 topographic maps) according to the Horton stream classification (Kuehne, 1970). The Choctawhatchee and Escambia rivers, which
Table 1. Drainage parameters of stations on the Escambia, Choctawhatchee, and Apalachicola rivers.1
Station EJ CCA AC AB
Drainage Escambia Choctawhatchee Apalachicola Apalachicola
Location 30 57'N 87 14'W 30 46'N 85 49'W 30 42'N 84 51'W 30 42'N 85 00 'N
Elevation (m) 8.6 11.9 12.4 -
Distance from mouth (km) 84 106 164 124
Drainage area (km2) 9,880 9,050 44,300 -
Mean discharge (m3/sec) Oct 1971-Sept 1976 244 189 776
Minimum discharge (m3/sec) Oct 1971-May 1977 17 25 265
River height fluctuation (m) Oct 1971-May 1977 6.5 5.5 8.2
Stream Order 5 6 7 7
'Courtesy of U.S. Geological Survey, Tallahassee sub-district office.
have similar drainage areas and flows (Table 1), are part of a common faunal block (Bailey et al., 1954; Smith-Vaniz, 1968).
On the Escambia River, station EJ corresponds to station 14 of Bailey et al. (1954). The first part of the study concentrated on a 1 km segment of the river at this station (see Beecher et al., 1977), while in the later study collections at this station ranged over 18 km of the river.
At stations EJ, CCA, and AB, as well as at supplementary station CP, sandbars extended along the shore at the insides of bends (slip banks). The greatest depths at these stations were at the outsides of bends (cut banks) where steep banks were often overhung by fallen trees. The substrates were predominantly sand or clay-sand, while occasional patches of gravel occurred only at EJ. At high water the rivers inundated adjacent swamps.
At low water the maximum depths were 2-3 m at stations EJ and CCA. A navigation channel of 4-5 m is maintained in the Apalachicola River. Maximum depths which we encountered were 7-8 m at EJ and CCA, although higher flows occurred during the study. In the Apalachicola River depth at high flow was 5-6 m greater than at low flow, producing a maximum depth of about 10 m. Exceptionally deep holes at any of the stations could have exceeded these maximum depths.
The upstream boundary of station AC was Jim Woodruff Dam at Chattahoochee, Florida, and we covered approximately 5 km downstream. The substrates at station AC included sand, mixed sand and gravel, clay, and limestone.
MethodsFish were collected with a boat-mounted 230V 60Hz shocker that put out 1.5-8 amps, and with 2 gill nets. The most frequently used gill net was a 30.5 m nylon monofilament net with mesh size ranging from 3.5-9.0 cm stretch mesh, and the other was a 61 m cotton net with mesh size ranging from 7.6-12.7 cm stretch mesh.
During the first part of the study we shocked a 1 km segment of the Escambia River at station EJ at least once each month from January through early December 1972. The total electrofishing effort on this segment was
68.1 h, excluding several supplementary collections outside the 1 km segment. Two netters, using long-handled dip nets with a 1 cm stretch mesh in the bag of the net, attempted to net all fish. Fish were placed in a circulating holding tank, and at the end of each electrofishing run each fish was identified to species, weighed to the nearest g, measured (cm SL), tagged (if larger k than 10 cm SL and appearing healthy) with a Floy tag, and released. During early July we shocked the 1 km segment 13 times in 17 da, accounting for
28.2 h, in an attempt to increase tag returns.
Seasonal variation in depth affected the efficiency of our electrofishing. ; Electrode cables were 3.5 m long, but they reached this depth only when the j boat was stationary with reference to the water. The electric field may have extended another 1-2 m below the cables. The electrofishing apparatus used in the first part of the study on the Escambia River was somewhat more efficient, especially during high flow, because of maneuverability. The effect of seasonal variation in electrofishing depth and efficiency upon our results is discussed under Seasonal Dominance in the Escambia River and Community Structure in the Escambia River, following Species Accounts.
In the second part of the study, gill nets were set for 197 h at EJ, 24 h at CCA, 16 h at CP, and 17 h at AC. Electrofishing effort was 26 h at EJ, 40 h | at CCA, 25 h at AB, and 11 h at AC. The primary objective of the study was [ collection of carpsuckers (Carpiodes cyprinus and C. velijer). Other species were sight identified, but specimens were neither captured nor counted. The small effort at station AC was related to the ease of collecting C. cyprinus at 1 this station: a monthly sample of 10 specimens was often collected in less j than an hour.
Funk and Campbell (1953) discussed the selectivity of different collecting methods for large fishes, and Hansen (1973) noted that electrofishing was especially effective on carpsuckers and carp, but relatively ineffective on catfish. ;
SPECIES ACCOUNTS Acipenseridaesturgeons
Acipenser oxyrhynchus Mitchill. Atlantic sturgeon.
One sturgeon was shocked in early October 1972 in the Escambia River, but its size (ca. 2 m) precluded capture (Beecher et al., 1977). No sturgeoR were observed during subsequent electrofishing or gill netting in any of the 3 streams. The occurrence of the Atlantic sturgeon in the Apalachicola River was discussed by Swift et al. (1977).
Lepisosteus oculatus (Winchell). Spotted gar.
This gar was uncommon in mainstream collections in all 3 rivers, with no evidence of seasonality in this study (Fig. 2, Table 2) nor in electrofishing studies by Florida Game and Freshwater Fish Commission personnel (Cox et al., 1975).
Fig. 2. Numbers of spotted and longnose gar (bottom) and threadfin, gizzard, and Alabama shad (top) caught per hour of electrofishing each month during 1972 at station EJ on the Escambia River.
Lepisosteus osseus (Linnaeus). Longnose gar.
The longnose gar was dominant in all 3 rivers during winter, spring, and early summer, when water level and turbidity were high (Table 2). It was the largest common fish, but other fishes were more numerous. In the Escambia it was absent for the remainder of the year during low water (Figs. 2, 9). In the Choctawhatchee the longnose gar was observed regularly from March to September 1976 and from February to April 1977. It was abundant in April and common in September. None were observed on 31 October or 9 December, but a single longnose gar was shocked on 7 November. November was the only month in which the longnose gar was not observed at station AB on the Apalachicola, but at the altered environment of station AC it was observed in every month (Table 2).
The longnose gar outnumbered the spotted gar 47:5 in the Escambia River during 1972, and in March and June it constituted more than 40% of the electrofishing catch by weight. Catch rates were probably conservative estimates of the abundance of gars because many escaped from the electric field and from the holding tank. We observed many gars rolling at the sur-
Table 2a. Seasonal occurrence of fish species in gill net (G) and electrofishing (E) operations in the Escambia River at station EJ, 1975-77. + indicates that a species was observed in a collection; numerals indicate number of specimens collected.
Date Collection Method Species 8-9Mar75 G 30May-lJun G 4-6Jul G 17Apr76 G,E 23May E lOJul E 7Aug E 90ct E 13Nov E 10Dec76 E 8Jan77 E 5Feb G,E 20Mar E 9Apr E
Lepisosteus oculatus 4 - - _ _ _
L. osseus 9 14 6 + + + + _ + + + +
Amia calva - - + + + + + + +
Alosa alabamae - _ + _
A. chrysochloris - 1 _ _ _
Dorosoma cepedianum - + - + + _ _ +
D. petenense 3 - - _ _ _ + +
Esox niger 1 1 + + + _ + +
Notropis venustus 5 1 + + + _ _ + +
Carpiodes cyprinus 4 - 1 4 _ 1 1 1
C. velifer 4 7 5 7 4 4 1 9 5 2 2 4
Erimyzon tenuis - - - _ +
Minytrema melanops 4 1 - - _ _
Moxostoma poecilurum 2 2 1 - + - + + + + + +
M. carinatum - - + _ +
Ictalurus nebulosus - - _ +
I. punctatus 1 - - _ _
Strongylura marina - - + _ _ _
Lepomis gulosus 1 - _ _ +
L. macrochirus - + - + + + + + + +
L. megalotis - 1 + + + + _ _ +
L. microlophus 2 i - + _ _ _
L. punctatus 1 - _ _ _
Micropterus punctulatusi 1 2 + + _ _ +
M. salmoides1 1 + + _ _ +
Pomoxis nigromaculatus 1 - _ _ _ + +
Mugil cephalus - + + + + - +
'Species not differentiated in electrofishing collections.
Table 2b. Seasonal occurrence of fish species in gill net (G) and electrofishing (E) operations in the Choctawhatchee River at station CCA, 1976-1977.
Date 22Mar76 2Apr 18Apr 29Apr UMay 20May ljun 29Jun 13Jul 17 Aug 21Sep 310ct 17Nov 9Dec 12Feb77 12Mar 2Apr
Collection Method E E E,G E E E E E E E E E E E E,G E E
Lepisosteus oculatus - - - - + - - - -
L. osseus + + + + + + + + + + + + + + +
Amia calva - - + - - + + + + + + -
Anguilla rostrata - - - + + + + - - -
Alosa chrysochloris - - - - + - - - -
Dorosoma cepedianum + + - - + + - + - -
D. petenense - + - - - - - - +
Esox niger + - - + - - - - +
Notropis venustus - + - - + - - - - -
Carpiodes cyprinus 1 2 2 2 2 1 1 2 1 1 - 5 2 -
C. velijer - 6 10 4 3 12 8 7 14 10 18 22 19 14 -
Minytrema melanops - - - - - - - + +
Moxostoma poecilurum + + + + + + + + + + + + +
Ictalurus nebulosus - - - - - - - + +
Strongylura marina + - - - + - - - -
Lepomis macrochirus - - + + + + + + + -
L. megalotis - + + + + + + + - - -
L. microlophus - - - - - + - + -
Micropterus spp. - + - + + - + + + - +
Pomoxis nigromaculatus - - + + - - - - -
Mugil cephalus - - - + + - - - -
Table 2c. Seasonal occurrence of fish species in electrofishing operations in the Apalachicola River at station AR, 1976-1977.
Date Species 2Apr76 20Apr 29Apr 20May 29Jun 22Jul lOAug 23Sep 130ct 26Nov 12Dec 12Jan77 13Feb
Lepisosteus oculatus - - + _ _ +
L. osseus + + + + + + + + + + + +
Amia calva - - + + + + +
Anguilla rostrata + - + + _ + +
Alosa alabamae + _
Dorosoma cepedianum + + + + + + + + + + +
D. petenense + + + _ + + +
Cyprinus carpio + + - + + + +
Notropis venustus - - +
Carpiodes cyprinus 3 1 2 _ 2 3 3 3
Minytrema melanops + - + + +
Moxostoma sp. - + - + + + + + +
Ictalurus nebulosus - - _ +
I. punctatus + - + + + +
Strongylura marina - _ _ +
Morone chrysops - - _ + +
M. saxatilis - _ _ +
Lepomis auritus - _ _ +
L. macrochirus + + + + + + +
L. microlophus - - _ + +
Micropterus spp. + - + + + +
Mugil cephalus - + + + + + +
Paralichthys lethostigma - - - - + - +
Table 2d. Seasonal occurrence of fish species in gill net (G) and electrofishing (E) operations in the Apalachicola River (station AC) below Jim Woodruff Dam near Chattahoochee, Florida, 1975-1977.
Date Collection Method Species 28Jan75 G,E 12-13Feb E 26Mar G 6May E 20Apr76 E UMay E ljun E 13Jul 17Aug E E 21 Sep E 310ct E 17Nov E 9Dec E HJan77 E 13Feb E 18M E
Lepisosteus oculatus - 3 - - _ _ _ _
L. osseus + 7 + + + + + + + + + + + + +
Amia calva 1 + + + _ + _ _ _ _
Anguilla rostrata + - _ _ _ _
Alosa chrysochloris 1 - - - _ _ _ _ _
Dorosoma cepedianum 5 + 2 - + + - + + + + +
D. petenense + - + + - _ +
Esox niger 2 + - - - - _ _ _
Cyprinus carpio 1 - - + - + + + + + +
Notropis venustus + - - - _ _ _ + _
Carpiodes cyprinus 6 9 1 10 10 15 9 9 10 11 11 12 2 9 10
Erimyzon sucetta 1 - - - - _ _ _
Minytrema melanops 5 - - + _ _ _ + _
Moxostoma sp. 2 + - _ _ _ + +
Strongylura marina + 2 - + + _ _ +
Morone chrysops 1 + - - _ _ _ _ +
M. saxatilis + - _ _ _ _ +
Lepomis gulosus - - _ _ _ _ _ + _
L. macrochirus + - - + + + + _ +
L. microlophus 1 + - - + _ + _ _
Micropterus spp. + - + + + _ + + _
Pomoxis nigromaculatus 4 + - - _ _ _ _ _
Mugil cephalus - - - + + - _ _ _
face, gulping air, during months of collection, but saw none during low water in the fall when they were absent from our catch.
A melanistic individual was seen but not captured at station AC on 20 April 1976.
Amia calva Linnaeus. Bowfin.
The bowfin, a year-round resident in all 3 rivers, was abundant from late fall through winter and spring in the Escambia River (Fig. 9, Table 2). The pattern was evident in 1976-77 as well as in 1972 (2 winters: '71-72 and '72-73) in the Escambia River, but no seasonal pattern was apparent in the Choctawhatchee or the Apalachicola River.
Anguilla rostrata (Lesueur). American eel.
The American eel was most frequently observed during summer and fall months in the 3 rivers, although individuals were observed in other months (Fig. 9, Table 2). On 17 August 1976 we encountered a dense concentration of eels and highfin carpsuckers in an area of reduced current with a mud bottom at the mouth of a cypress slough in the Choctawhatchee River.
Alosa alabamae Jordan and Evermann. Alabama shad.
Alabama shad juveniles were collected in moderate numbers in the Escambia River in July, October, and November (Fig. 2). We did not collect Alabama shad in electrofishing operations in the Choctawhatchee River, and our only record of this species in the Apalachicola River was in April at station AB (Table 2). However, the abundance of clupeids in the Apalachicola River probably masked the abundance of this species, as we did not attempt to capture the many clupeids we shocked. Laurence and Yerger (1967) reported that adult Alabama shad occurred from late February through late April in the Apalachicola River, and that young-of-the-year moved gradually downstream during the remainder of the year.
Bailey et al. (1954) collected no Alabama shad from the Escambia River and suggested that it was rare. Our few specimens confirm its presence in the Escambia.
Alosa chrysochloris (Rafinesque). Skipjack herring.
We observed the skipjack herring only once in each of the 3 rivers (Table 2). However, the abundance of other clupeids may have masked the presence of this species at other times as we did not attempt to capture the many clupeids we shocked. Wolfe (1969) reported that the skipjack herring
was abundant below Jim Woodruff Dam (station AC) during its spawning run from late December or early January through early April.
Dorosoma cepedianum (Lesueur). Gizzard shad.
In the Escambia River the gizzard shad showed a well-defined seasonal distribution. It occurred in small schools, usually consisting of fewer than 10 individuals, from January through August 1972 with a peak catch rate in April (Fig. 2). During 1976-77 Escambia River electrofishing operations the gizzard shad was observed in April, when it was common, and August, and a single individual was shocked in November (Table 2a).
No seasonal pattern was evident for gizzard shad in the Choctawhatchee River. The gizzard shad was abundant in the Apalachicola River except in January, when it was not observed because of flooding. At station AC we observed gizzard shad most frequently from December through March (Table 2). No seasonal pattern was evident at station AB.
Dorosoma petenense (Giinther). Threadfin shad.
This shad was less numerous than its larger congener in the Escambia, but the 2 species co-occurred during March, April, and July (Fig. 2). In the Choctawhatchee threadfin shad were observed only in April (Table 2). Wigfall (1973) reported that the threadfin shad was abundant near the mouth of the Choctawhatchee during the week of 2-6 April 1973, when it occurred in 29 longnose gar stomachs out of 97 containing food and 196 examined.
In the Apalachicola the threadfin shad was abundant during winter months and was present throughout the year (Table 2; Cox et al., 1975).
Esocidaepikes and pickerels
Esox niger Lesueur. Chain pickerel.
The chain pickerel was uncommon, and no seasonal pattern was evident (Fig. 9, Table 2).
Cyprinus carpio Linnaeus. Carp.
The carp was introduced into the Apalachicola River drainage where it was observed irregularly throughout the year (Table 2), but it is absent from the Choctawhatchee and Escambia rivers. Because of its large size, it probably constitutes a significant fraction of the fish biomass in the Apalachicola.
Notropis venustus (Girard). Blacktail shiner.
This species, along with the weed shiner (N. texanus) and the longnose shiner (N. longirostris), was a dominant minnow in the Escambia and Choctawhatchee rivers throughout the year. In the Escambia River, the blacktail shiner was the most numerous fish and the weed shiner was the second most
numerous fish during the first part of the study (Beecher et al., 1977). In the Apalachicola the blacktail shiner is a dominant minnow along with the bluestripe shiner (N. callitaenia). The blacktail shiner is one of the few native cyprinids large enough to be caught in a gill net. The small size of the larger specimens and the difficulty of effectively sampling any of the native minnows with a shocker render it difficult to assess the significance of their contribution to the biomass (Table 2). Small fish are less susceptible to electricity than larger fish because of a smaller voltage difference across a shorter distance (Edwards and Higgins, 1973), and they also recover faster than larger fish. Many small cyprinids passed through the mesh of our dip nets. Similar comments apply to darters (family Percidae), which were much less abundant than cyprinids (Beecher et al., 1977).
Carpiodes cyprinus (Lesueur). Quillback.
In the Escambia and Choctawhatchee rivers the catch rate for quillback declined during low water in the late fall when the catch rate peaked for other resident fishes, including the quillback's smaller and more numerous congener, the highfin carpsucker. The quillback catch rate in the Apalachicola did not decline at the same time (Fig. 3). However, during the period of rapidly decreasing water temperature in November-December 1976 there was some evidence for a short-range mass downstream movement of quillback at station AC. On 31 October (water temperature = 16 C), quillback were scattered through a 500 m section of the river below Jim Woodruff Dam, but none appeared from 500 to 1000 m below the dam, a situation typical of many previous collections throughout the summer. In contrast, on 17 November (water temperature = 13 C), the quillback was abundant from 500 to 1000 m downstream from the dam. On 9 December (water temperature = 10 C), we were unable to locate any quillback in the 1000 m below the dam, but they were abundant from 1200 to 2000 m below the dam.
Quillback catch rates at station AB on the Apalachicola, at the Choctawhatchee, and in 2 yr (1972 and 1976-77) at the Escambia were all of the same order of magnitude (Fig. 3). However, a chi-square test, using number of quillback caught, indicated that the catch at station AB (equivalent to 0.97 quillback/hr of electrofishing) was significantly higher than at station CCA on the Choctawhatchee (0.55 quillback/hr) or at the Escambia (0.31 quillback/hr) ( x2 = 37.37, df = 20, P < .01).
Jim Woodruff Dam had a concentrating effect on quillback as well as on other fish species in the Apalachicola. Quillback abundance (catch per hour of electrofishing) at station AC immediately downstream from the dam was many times that at any other station (Table 3), and often equalled or exceeded the highest catch rates of the elsewhere more abundant highfin carp-sucker. Quillback abundance decreased sharply within 4 km downstream from the dam.
a 5 "
AB April 1976 April 1977 1.5 2.Q JS 13 '*
CCA April 1976 April 1977
lp',I L I i'
EJ April 1976 April 1977 2.3
m 2-4 3.0 3.9
II 7.9 O.Q ^
El November 1971-December 1972
Fig. 3. Numbers of highfin carpsucker (black) and quillback (striped) captured per hour of clectrofishing at stations on the Apalachicola, Choctawhatchee, and Escambia rivers (top to bottom). Figures above each month indicate numbers of hours of electrofishing effort.
Carpiodes velifer (Rafinesque). Highfin carpsucker.
The greatest catch rates for the highfin carpsucker occurred in October and November during low water in the Escambia and Choctawhatchee rivers, but we collected none in early December of 1972 or 1976 in the Escambia, despite continued low water and a high catch rate of other catostomids at that season (Figs. 3, 9).
Catch rates for the highfin carpsucker were similar in the 2 yr of electro-fishing on the Escambia. The total catch rates at the Escambia and Choctawhatchee were compared using a chi-square test of numbers of fish caught each month. The total catch rate at the Escambia (equivalent to 1.7 highfin carpsucker/hr) was significantly less than at CCA on the Choctawhatchee (3.9 highfin carpsucker/hr) ( x2 = 177.7, df = 26, P <.01).
Sex ratios of the highfin carpsucker changed with season. At CCA and EJ, females outnumbered males during much of the year, but from October-November to March-April sex ratios approached 1:1 (Fig. 4). However, at station CE, a downstream site on the Choctawhatchee, males outnumbered females (7:2). The small sample size at CE did not permit rejection of a 1:1 sex ratio, but the number of males was significantly higher ( x2 = 13.9, df = 1, P < .01) than would be expected if the sex ratios at CE and CCA were the same. The highfin carpsucker does not occur in the Apalachicola River.
table 3. Monthly catch rates for Carpiodes cyprinus at station ac compared to maximum catch rates for each species of Carpiodes at other stations. The number of hours of electrofishing effort is in parentheses.
Month Station AC Other Stations
C. cyprinuslhr C. cyprinuslhr C. veliferlhi
Apr 76 6.71 (1.5) 2.0 (1.5) AB 5.7 (1.7) CCA
May 76 7.01 (1.4) 1.5 (1.3) AB 2.2 (1.8) CCA
Jun 76 45.0 (1.3) 0.4 (3.6) CCA 4.6 (1.8) CCA
Jul 76 9.0 (1.0) 1.3 (3.0) EJ 4.7 (1.5) CCA
Aug 76 22.5 (0.4) 0.7 (1.7) CCA 5.2 (1.7) CCA
Sep 76 25.0 (0.4) 0.3 (2.9) CCA 4.6 (1.3) CE
Oct 76 16.5 (0.7) 2.0 (1.4) AB 16.4 (1.1) CCA
Nov 76 44.0 (0.2) 1.2 (2.6) AB 15.7 (1.4) CCA
Dec 76 8.6 (1.4) 1.5 (2.0) AB 9.5 (2.0) CCA
Jan 77 0.0 (1.7) 0.0 (1.8, 1.5, 3.7) 1.4 (3.7) EJ
AB, CCA, EJ
Feb 77 8.2 (1.1) 2.1 (1.9) CCA 5.2 (1.9) CCA
Mar 77 10.0 (1.0) 2.4 (2.5) AB 0.7 (3.0) EJ
'In April and May at station AC electrofishing was continued after 10 fish were captured, and, although many additional C. cyprinus were seen, no effort was made to capture them.
Fig. 4. Carpsucker sex ratios by season. Numbers of females (above horizontal lines) and males (below horizontal lines) of highfin carpsucker (black) and quillback (striped) in each collection at stations on the Apalachicola, Choctawhatchee, and Escambia rivers (top to bottom). Only adult fish were included in this figure. Letters at bottom indicate months.
Erimyzon sucetta (Lacepede). Lake chubsucker.
One specimen was gill-netted in the Apalachicola River at AC (Table 2d).
Erimyzon tenuis (Agassiz). Sharpfin chubsucker.
Five sharpfin chubsuckers were collected in the Escambia River during the summer of 1972 (Fig. 6) and one in December 1976 (Table 2a). None were observed in the Choctawhatchee. This fish is absent from the Apalachicola drainage (Yerger, 1977).
Minytrema melanops (Rafinesque). Spotted sucker.
This sucker was a year-round resident in all 3 rivers (Table 2), and the maximum catch rates occurred during low water in October and November in the Escambia (Fig. 6).
Among 4 specimens captured in gill nets in the Escambia on 8-9 March 1975 were a male with prominent breeding tubercles and a large gravid female. Swift et al. (1977) reported an aggregation of 14 spotted suckers in breeding condition below Jim Woodruff Dam (AC) in late March, and McSwain and Gennings (1972) described spawning activities of spotted suckers between March and May in Georgia tributaries of the Apalachicola drainage.
Moxostoma carinatum (Cope). River redhorse.
In the Escambia we collected single specimens of the river redhorse in February, July, and November 1972, and shocked but did not capture 2 others in August and December 1976. Yerger and Suttkus (1962) reported 8 specimens in a rotenone collection from the Escambia and suggested that this species might be expected from the Choctawhatchee. However, we did not observe the river redhorse in the Choctawhatchee, and Jenkins (1970) considered it unlikely to occur there. It does not occur in the Apalachicola (Jenkins, 1970; Yerger, 1977).
Moxostoma poecilurum (Jordan). Blacktail redhorse.
This redhorse was a common year-round resident in the Escambia and Choctawhatchee rivers (Table 2, Fig. 5). The 1972 catch rate was lowest at high water in March and greatest at low water in November (Fig. 5). A similar pattern was evident in the Choctawhatchee. This species does not occur in the Apalachicola (Jenkins, 1970; Yerger, 1977).
The blacktail redhorse was a dominant fish in the Escambia. During 6 months of 1972 (May, August-December), this was the dominant fish by weight in our electrofishing catch. Over the entire 1972 survey it constituted 16.5% of the weight of all fish shocked, and was second in weight only to the striped mullet (Mugil cephalus), a transient species. Only 2 sunfishes (Lepomis macrochirus and L. megalotis) and 2 minnows (Notropis venustus and N. texanus) exceeded it in numbers in our electrofishing catch.
Using the Schnabel mark-and-recapture method (Robson and Regier, 1971), we attempted to estimate the populations of all fish species in a 1 km long x 75 m wide segment of the Escambia, but only for the blacktail
Fig. 5. Numbers of blacktail redhorse caught per hour of electrofishing each month during 1972 at station EJ on the Escambia River.
111 mi I
YELLOW BULLHEAD III CHANNEL CATFISH
SPECKLED MADTOM BROWN BULLHEAD
Fic. 6. Numbers of sharpfin chubsucker and spotted sucker (bottom), catfishes (middle), and flier, shadow bass, and warmouth (top) caught per hour of electrofishing each month during 1972 at station EJ on the Escambia River.
redhorse was the return sufficient to justify a population estimate. Our final estimate (based on 19 recaptures of 180 tagged individuals) for the blacktail redhorse population in the 1 km segment of the river was 1095 fish larger than 10 cm SL (Table 4). The seasonal distribution suggests that this species was resident in our study area (Table 4). The recapture of a fish which was tagged 26 December 1971 was not used in estimating the population because data from that tagging date were lost.
The highest incidence of injury and death among shocker-caught redhorse occurred in April-June, and appeared to be associated with spawning stress. Injuries were restricted to the ventral surfaces and fins in these months. A 28 cm SL, 405 g male captured on 9 April had a tuberculate anal fin and was shedding milt. A local sucker fishery exists in March and April in tributaries, coinciding with the months in which the blacktail redhorse constituted less than 10% of the number of fish caught.
Moxostoma species. Grayfin redhorse.
The grayfin redhorse is endemic to the Apalachicola drainage (Jenkins, 1970), where it occurred throughout the year at both stations (Table 2; Cox et al., 1975; Yerger and Suttkus, 1962). It was common in September and October at AB, especially along steep edges of sandbars in moderate current (ca. 0.3 m/sec). Fish collected in late March at AC were spawning (Yerger and Suttkus, 1962).
Ictalurus natalis (Lesueur). Yellow bullhead.
Three specimens were captured during the 1972 Escambia River electrofishing survey (Fig. 6), but none were observed during subsequent collections in any of the 3 rivers.
Ictalurus nebulosus (Lesueur). Brown bullhead.
The brown bullhead was uncommon in electrofishing samples in all 3 rivers (Table 2, Fig. 6).
Ictalurus punctatus (Rafinesque). Channel catfish.
The channel catfish was the dominant catfish by weight and number in the Escambia in 1972 (Fig. 6), although it was probably under-represented in our catch because an AC shocker is less effective than a DC shocker for catfish (Hansen, 1973; Beecher et al., 1977). We collected no channel catfish in the Escambia or Choctawhatchee rivers in 1976-77. Yerger (1977) indicated that this species was plentiful in the Apalachicola in 1976, and, assuming our equipment was only minimally effective at catching them, our records concur (Table 2c). The ineffectiveness of the AC shocker on catfish was probably responsible for our failure to capture other catfishes (/. brun-neus, I. serracanthus, I. catus) which occur in the Apalachicola River (Yerger, 1977) or /. catus from the other 2 drainages where it may occur (Smith-Vaniz, 1968).
Table 4. Results of mark-and-recapture study of blacktail redhorse (Moxostoma poecilurum) in a 1 km segment of the Escambia River near Jay, Florida, during 1972. Ns is the Schnabel estimate of the population size and SE(NS) is the standard error of the estimate.
Date Catch Tagged Fish in Population Recaptures Dates of Previous Captures Ns SE(NS)
08 Jan 41 0 0 - -
23 Jan 1 4 0 - -
21 Feb 4 5 0 - -
25 Feb 8 9 1 8 Jan 72 72
04 Mar 1 13 0 85 85
05 Mar 1 14 0 99 99
07 Apr 2 15 1 8 Jan 65 46
08 Apr 5 16 0 105 74
09 Apr 9 20 0 195 138
22 Apr 8 24 0 291 206
05 May 9 25 0 403 285
06 May 10 31 1 5 May 373 216
07 May 11 40 22 5 May; 5 May; 26 Dec2 311 139
02 Jun 2 49 0 331 148
03 Jun 5 50 0 381 170
17 Jun 3 55 0 414 185
30 Jun 8 56 0 503 225
01 Jul 11 63 1 8 Jan, 7 Apr 535 220
02 Jul 5 73 1 1 Jul 511 196
03 Jul 3 77 0 544 207
04 Jul 4 80 1 30 Jun 516 183
05 Jul 2 82 0 536 190
06 Jul 3 84 0 568 202
08 Jul 1 87 0 579 206
10 Jul 3 88 1 6 May 6 May, 10 Jul3; 30 Jun 544 181
13 Jul 11 90 23 535 161
14 Jul 7 98 0 597 180
15 Jul 5 105 1 14 Jul 591 171
16 Jul 8 109 2 5 May; 7 May 569 153
26 Aug 6 115 0 618 165
09 Sep 13 121 3 16 Jul; 3 Jun; 6 May 602 146
28 Oct 19 130 0 747 182
12 Nov 37 149 2 28 Oct; 7 Apr 959 221
03 Dec 14 180 0 1095 252
TOTALS 2391 180 192
'Fish captured on first date, 8 January, are not included in total catch because no usable tags occurred in the population at that time.
*A fish tagged on 26 December 1971 was recaptured, but could not be considered in population estimation because data from tagging date were lost.
JOn 13 July a tagged fish died at the time of its second recapture.
A brown water snake (Natrix taxispilota), captured 13 July 1972 at EJ, had swallowed a juvenile channel catfish.
Noturm leptacanthus Jordan. Speckled madtom.
In the summer and fall of 1972 we collected 8 speckled madtoms in the Escambia River (Fig. 6). This was the second most numerous catfish, but its contribution to the biomass was negligible. It was absent from subsequent gill net and electrofishing catches in the 3 rivers.
Strongylura marina (Walbaum). Atlantic needlefish.
The Atlantic needlefish occurred in the Escambia in June and July, and in the Choctawhatchee in April and July, but it occurred throughout the year in the Apalachicola (Table 2). Swift et al. (1977) suggested that this fish reproduces in fresh water.
Morone chrysops (Rafinesque). White bass.
The white bass, introduced into the Apalachicola drainage (Yerger, 1977), was collected irregularly throughout the year at AB and AC (Table 2). During late winter and early spring these fish, as well as artificial hybrids with striped bass, were abundant at AB and were approaching spawning condition (Steve Babcock, pers. comm.)
Morone saxatilis (Walbaum). Striped bass.
Although this fish has been reported from the Escambia and Choctawhatchee rivers, it is common only in the Apalachicola (Barkuloo, 1967). Yerger (1977) indicated that the native population in the Apalachicola River has been augmented by stocking.
At AB 2 specimens were collected in November, and at AC specimens were observed in February (Table 2). Barkuloo (1967) reported that the sport fishery for striped bass in the Apalachicola has 2 peaks, the spawning run from March-May, and mid-September to December.
Ambloplites ariommus Viosca. Shadow bass.
Seven specimens were collected from the Escambia in 1972, 6 between July and November (Fig. 6). None was seen in subsequent collections in the 3 rivers.
Centrarchus macropterus (Lacepede). Flier.
Three fliers were collected from the Escambia in 1972 (Fig. 6), and a single flier was gill-netted from the Choctawhatchee at CP, 7 km S of the Florida-Alabama border, on 25-26 March 1975. None was taken from the Apalachicola River.
Lepomis auritus (Linnaeus). Redbreast sunfish.
The redbreast sunfish was observed in October at AB on the Apalachicola River (Table 2c).
Lepomis gulosus (Cuvier). War mouth.
The warmouth was taken irregularly throughout the year in the Escambia (Fig. 6), and was observed in February at AC on the Apalachicola (Table 2).
Lepomis macrochirus (Rafinesque). Bluegill.
The bluegill occurred throughout the year in all 3 rivers (Fig. 7, Table 2). It was the most abundant fish other than minnows in our electrofishing catch from the Escambia River in 1972 (Beecher et al., 1977). After the black basses (Micropterus spp.), the bluegill was the next most important cen-trarchid by weight and constituted 3.2% of the weight of shocker-caught fish. The catch rate peaked in April followed by a second peak in November (Fig. 7).
Lepomis megalotis (Rafinesque). Longear sunfish.
The longear sunfish occurred throughout the year in the Escambia and Choctawhatchee (Fig. 7, Table 2), but it is absent from the Apalachicola (Yerger, 1977). Peak catch rates for the longear sunfish coincided with those of the bluegill, and in May, June, August, September, and November 1972 it exceeded the bluegill in numbers in the Escambia (Fig 7; Beecher et al., 1977). It was the next most numerous fish after the bluegill in the 1972 Escambia River electrofishing catch, but because of its smaller size it constituted only 1 % of the weight of shocker-caught fish. During 1972, when all fish were captured and carefully identified, we did not find any specimens of the similar-looking L. marginatum. Numerous seine collections at EJ, CCA, and CP during 1971-76 did not yield any specimens of L. marginatus (Beecher, unpublished data), leading us to believe that all specimens of the longear sunfish were correctly identified in the second part of this study.
Lepomis microlophus (Gunther). Redear sunfish.
The redear sunfish or shellcracker occurred throughout the year in all 3 rivers (Fig. 7, Table 2). Because of its large size (mean weight = 140 g, mean length = 13.5 cm SL), the redear ranked next after the bluegill in contribution to the weight of shocker-caught centrarchids.
Lepomis punctatus (Valenciennes). Spotted sunfish.
Only 3 spotted sunfish or stumpknockers were collected in the Escambia (Fig. 7, Table 2a), and none was seen at any of the 3 rivers during 1976-77 electrofishing operations.
Micropterus punctulatus (Rafinesque). Spotted bass.
During the 1972 Escambia River survey we were uncertain of the identification of many bass, most of which were tagged and released, and therefore unavailable for confirmations of identifications. We tentatively identified 23 specimens as spotted bass and 89 as largemouth bass (M. salmoides), and confirmed the presence of both species. In 1976-77 electrofishing operations at all 3 rivers bass were observed but seldom collected, and identifications were often doubtful. All bass will be discussed together under largemouth bass.
Micropterus salmoides (Lacepede). Largemouth bass.
As noted under the spotted bass, identifications of bass in this study were doubtful and all bass were discussed together. Bass occurred throughout the
J F M A M J JASONI
Fig. 7. Numbers of bluegill, longear sunfish, redear sunfish, and spotted sunfish caught hour of electrofishing each month during 1972 at station EJ on the Escambia River.
Fig. 8. Numbers of bass (black) and black crappie (striped) caught per hour of electrofishing each month during 1972 at station EJ on the Escambia River.
year at all stations (Fig. 8, Table 2). They dominated the 1972 Escambia River centrarchid catch by weight and constituted 5.1% of the electrofishing catch weight. In the Apalachicola, the undescribed shoal bass (Micropterus sp.) occurs along with the 2 previously listed species (Yerger, 1977) although none was identified in our catch.
Pomoxis nigromaculatus (Lesueur). Black crappie.
The black crappie occurred throughout the year in all 3 rivers (Fig. 8, Table 2; Cox et al., 1975). In 1976-77 electrofishing operations it was common in the Escambia only in January. In November, anglers caught a number of crappies in the Choctawhatchee, although we shocked crappies only in June and July in that river. In the Apalachicola we collected crappies only in January and February. The black crappie is a popular sport fish during the colder months when it is active preparatory to spawning (Swift et al., 1977). The white crappie (P. annularis) has been introduced in the Choctawhatchee River (Smith-Vaniz, 1968), and specimens could have been misidentified as black crappie.
Mugil cephalus Linnaeus. Striped mullet.
The striped mullet was absent from all stations during late fall and early winter (Fig. 9, Table 2), coinciding with its offshore spawning season (Arnold and Thompson, 1958). At tidewater stations in the Escambia, it was more abundant in late October and early November than in Late March and early April (Bailey et al.3 1954). The large number of individuals in the fall presumably corresponded to the exodus through the river mouth on the spawning migration. At CCA, which is 22 km farther from the mouth of the Choctawhatchee than is EJ from the mouth of the Escambia, the mullet was present only in July and August, compared to January through early October at EJ. Similarly, in the Apalachicola, mullet occurred from March through October at AB, but at AC, 40 km farther upstream, it was observed only in June and July (Table 2). Hellier (1967) and Tagatz (1968) indicated similar seasonal occurrences of the mullet in the Santa Fe and St. Johns rivers, respectively.
The striped mullet was the dominant fish by weight (29.8%) in the 1972 electrofishing catch. However, the dominance of mullet was exaggerated by increased collecting effort in July when mullet were most abundant. Escambia River mullet had a mean weight of 665.9 g and a mean length of 31.9 cm SL. Individuals and small schools (2-10) inhabited shallow sand bars and areas of reduced current.
Paralichthys lethostigma Jordan and Gilbert. Southern flounder.
The southern flounder occurred throughout the year in the Escambia
Fig. 9. Monthly catch rate by weight of families of fishes during 1972 in the Escambia River at station EJ.
and Apalachicola rivers (Fig. 9, Table 2; Cox et al., 1975), but was not observed in the Choctawhatchee. Nine specimens from the Escambia had a mean length of 34.6 cm SL and a mean weight of 1021 g.
Seasonal dominance in the escambia riverFishes of the Escambia River can be classified as (1) resident fishes occurring throughout the year, or (2) transient euryhaline fishes.
The bowfin, chain pickerel, cyprinids, catostomids, ictalurids, and cen-trarchids are residents at EJ. Catch rates of many of these fishes were greatest during low water from July or August through early December (Fig. 9). Reduced flow at this season concentrated the fish and rendered all depths vulnerable to electrofishing, while during periods of high water fish may be scattered over a broad area and beneath the depth reached by electrodes.
High water, from late December or January through July or August, was characterized by the dominance of several transient euryhaline species, particularly the longnose gar and the striped mullet (Fig. 9). In some months these 2 species constituted over 50% by weight of the electrofishing catch. These fishes were absent from the Escambia at low water, when fish were most catchable, and therefore this seasonal occurrence is real, not an artifact of collecting. Mullet presumably left the river in a spawning migration, but the movement of the longnose gar is less easily explained. The simultaneous
absence of 2 dominant transients during low water, when water volume might otherwise become limiting, leaves that water volume to the resident freshwater fishes. This seasonal movement ensures that the community supports roughly the maximum sustainable fish biomass at any given season or flow.
The co-occurrence during high water of the longnose gar and the threadfin and gizzard shads is interesting in view of the demonstration by Wigfall (1973) and Summerfelt (1968, cited by Jester and Jenkins, 1972) that the longnose gar feeds heavily on threadfin and gizzard shad. The longnose gar may follow a major food source, the schools of clupeids, on their seasonal movements.
Community Structure in the Escambia RiverFall collections probably gave the most accurate samples. In October and November water levels in these streams reach the lowest levels of the year, between 10% and 30% of the mean discharge (Table 1). Resident fishes were concentrated in smaller areas and volumes, thus increasing the densities of these species. Consequently, our catch was greater during low water (Fig. 9; Beecher et al., 1977), and the larger sample size increased our chance of a representative sample. During these low-water periods the deepest areas at EJ were only 2 m deep and could be reached by the cable electrodes of our shocker. Bias against deep-dwelling fishes was minimized during low water, as shown by the increased catch of catfishes and eels (Fig. 9).
Catostomids were the dominant fishes by weight during the fall in 1971 and 1972. In August through early December 1972, catostomids constituted 60-70% of the weight of the electrofishing catch. They appeared to dominate in the fall of 1976, although data were not quantified for that year. Catostomids feed on small benthic invertebrates, diatoms, and organic detritus (Forbes and Richardson, 1909; Harlan and Speaker, 1956; Scott and Crossman, 1973; Beecher, 1979); thus they feed at a low tropic level, but are not first-order consumers.
Two other families, Clupeidae and Mugilidae, include fishes which feed at a low trophic level. Mugil cephalus and Dorosoma spp. are primary consumers, but are only seasonal members of the fish community of the upper Escambia River. Another clupeid, Alosa alabamae, feeds at a higher trophic level, but it is rare. Mullet reached maximum abundance when long days and warm weather coincided with high water in June and early July, probably resulting in high primary production in the river and adjacent swamp.
Centrarchids were the second most important family by weight in fall collections in the upper Escambia River. A few large bass (Micropterus spp.) constituted most of the centrarchid biomass, while abundant sunfishes (Lepomis spp.), including many young-of-the-year, contributed much less. The sunfishes feed on small invertebrates and on some small fishes, at a trophic level whose lower end overlaps that of catostomids. The larger bass are near the top of the food chain, feeding on aquatic vertebrates and larger crustaceans (Scott and Crossman, 1973).
Bowfins, eels, and pickerel occupy trophic levels similar to those of cen-trarchids (Scott and Crossman, 1973). Together these 3 fishes contributed approximately the same amount to the fish biomass as did the centrarchids.
The community organization in the upper Escambia River demonstrates the contentions of Elton (1946) and Larkin (1956) that "breadth rather than height in the pyramid of a food chain" characterizes freshwater community organization. The highest (pickerel, bowfin, and bass) and lowest catostomids) trophic levels among resident fishes are only a step and a half removed from each other. The dominant catostomids probably contribute little to the next level in the food chain. Most catostomids quickly attain a size equal to or greater than most of the piscivorous fishes, and only young catostomids are subject to extensive predation.
The seasonal influx of euryhaline fishes does not alter the community structure drastically. The gars feed at the same level as bass, pickerel and bowfin. Mullet and shad are primary consumers and detritivores, seasonally occupying the lowest trophic levels in the fish community, increasing by half a level the height of the pyramid of the food chain.
Stream OrderStream order (Kuehne, 1970) was related to variations in 2 attributes of fish populations examined in this study: seasonality of longnose gar and quillback abundance. The Escambia and Choctawhatchee rivers are fifth and sixth order streams, respectively, but very similar in flow and drainage area. The Apalachicola River is a seventh order stream, and is considerably larger than the other 2 streams (Table 1).
The longnose gar occurred every month except November in the Apalachicola, while in the Escambia and Choctawhatchee it was absent during a longer period in the fall. The longest absence of longnose gar occurred in the Escambia, the lowest order stream of the 3 studied.
Quillback catch rate was highest in the Apalachicola River and lowest in
the Escambia. The catch rate for the closely-related highfin carpsucker also
followed stream order in the 2 streams where it occurred: it was higher in the
Choctawhatchee than in the Escambia.
AcknowledgmentsThe members of the Bream Fishermen Association, especially Charles Lowery, aided greatly with the Escambia River collections in 1971-72. Publication charges were paid by the Bream Fishermen Association. Tom Lewis (Florida State University) and Brooke Beecher assisted with most of the field work in 1975-77 and commented on the manuscript. Karen Brockman (University of West Florida), John Stowe, Graham Lewis, Clay Small, David Eastman, Gordon Cherr, Chuck Duggins (Florida State University), and Mike Patterson assisted with field work in 1975-77. We thank Dr. Ralph W. Yerger (Florida State University) for his support and for critically reviewing parts of the manuscript. Dr. Camm Swift (Los Angeles County Museum) offered helpful suggestions on the manuscript. The initial part of the study was funded jointly by a grant from Humble Oil Co. (Exxon) to Dr. Thomas S. Hopkins (University of West Florida) and by the Bream Fishermen Association.
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HYDROLOGYPLANT COMMUNITY RELATIONSHIPS IN THE OKEFENOKEE SWAMP
Michael J. Duever
Ecosystem Research Unit, National Audubon Society, Box 1877, Route 6, Naples, Florida 33999
Abstract: We monitored 7 shallow wells along a transect crossing all of the major habitats in the Okefenokee Swamp and measured water levels, hydroperiods, and water table gradients. Although differences in ground surface elevations between habitats are minor within the swamp, hydroperiods varied from 246-346 da during 1977-78. Extrapolation from nearby staff gauge records indicates that marsh, shrub, and cypress communities were dry for periods of a month or more during 27 of the 36 yr of record, but waterlily communities were without surface water for a month or more only during 16 yr. Water table gradients suggest that ground water flows into the swamp from the surrounding uplands except during droughts, when the flow is reversed.
Because the composition of plant communities is largely a function of past and present environmental conditions, the relationships between specific site conditions and the occurrence of certain species or plant communities has been studied extensively. In wetland communities, a number of factors including hydrological and chemical conditions, soil types, fire history, and successional patterns (time) have been examined. Information derived from such studies is enabling land managers to develop programs to mitigate or reverse human impacts on wetlands.
Wetlands by definition exist because they are periodically inundated. Thus, hydrological factors relevant to inundation are obviously of prime importance in determining their location and composition. Recent studies have correlated the distribution of particular plant species or communities with specific frequencies of flooding or periods of inundation. (Franz and Bazzaz, 1977; Pesnell and Brown, 1977; Duever et al., 1975).