Changes in Abundance of Two Percids, Perca

Changes in Abundance of Two Percids, P e m flupiatilk and Gymnocephalus ceruus, a ong a Productivity Gradient: Re to Feeding Strategies and Competitive Abi Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by 108.163.184.194 on 05/28/13 For personal use only.

Eva Bergman Department of Ecology! Lbirnnology, P.0. Box 65, S-22 1 00 Lund, Sweden

Bergman, E. 1991. Changes in abundance of two percids, Perca NuviatiBis and GymnscephaBus cernuus, along a productivity gradient: relations to feeding strategies and competitive abilities. Can. 1. Fish. Aquat. Sci. 48: 5 3 6 5 4 5 . Relative abundances of perch (Perca fBuviatibis) and ruffe (Cymnocephalus cesnuus) were studied in eight lakes ranked along a gradient sf increasing productivity. The diets of perch and ruffe in relation to food resources were quantified over a 5-mo period in one lake of moderate and one lake sf high productivity. 'The abundance of perch decreawd and that of ruffe increased along the productivity gradient. Large perch ate fish over the whole season in the more productive lake, but rarely ate fish in May and June in the less productive lake. All size classes of ruffe fed mainly on macrobenthos in both lakes. The diversity of macrobenthos was higher in the lake sf Isw productivity, as was the diet breadth sf ruf-fe. The abundance patterns of perch and ruffe are likely related to the simultaneous effect sf increasing prey abundance and decreasing light penetration with increasing productivity. Furthermore, the abundance of perch is likely affected by increasing interspecific competition and that of ruffe by decreasing predation pressure as productivity increases. b'absndance relative de la perche dfEurasie (Perca djuviatdlis) et de la gr6mille (Gymwscepha8us cernuus) a 6t6 6tudi6e dans huit lacs classes par ordre croissant de productivit6. Le regime alimentaire be ces esp&ces a et6 mesur6 en fsnction des ressources alimentaires, sur 5 mopdans un lac peu productif et dans un lac tres productif. Plus le gradient de prsductivite etait klev6, rnoins la perche etait abondante et plus la gr6rnille l'etait. La perche saison dans le lac le plus productif, mais s'en nsurrissait de grande taille se nourrissait de poisson tout au long de %a rarement en mai et en juin dans le lac le rnoins productif. Dans les deux lacs, la gremille de toutes les classes de taille se nsurrissait principalement de macrobenthos. be macrobenthos du lac le rnoins productif 6tait plus diversifie que I'autre, ce qui se reflktait dans le regime alimentaire de la gremille. Il existe probablement des rapports entre les rkgirnes d'abondance de la perche et de la gremille et l'effet simultantfi de I'abondance crsissante des prsies et de la rnoindre pentfitrationde la lurniere i3 mesure que s'accrsft la productivite. En outre, I'absndance de la perehe doit probablement &re influenc$e par la concurrence interspeeifique accrue et celle de la gremille, par la diminution de la pression de prMation i3 mesure que la productivite augrnente,

Received May IS, 1 990 Accepted October 16, 1990 ($A574)

enerdly, when European lakes are ranked from low to high productivity, a pattern of species succession in the fish community is observed. The typical pattern is as follows. At low productivity salmsnids are abundant, at higher productivity percids first increase and then decrease in abundance, and at high productivity cyprinids are very abundant (Leach et al. 197'7;Martmann and Nijlmann 1977; Leopold et al. 1986). Two common Eurasian percids , perch (Percafluvfatd&fs) and mffe (Gymno~ephaluscernuus), follow this general pattern, but the decrease for mffe occurs at higher productivities than for perck (Leach et a!. 19'97). The decrease in perch abundance in lakes of high productivity has been related to competition with roach (Rutklus ru#i&us)for zooplankton (Persson 1983, 1986; Persson and Greenberg 1990). In addition, Bergman (19%) found evidence that perch were affected by the presence of mffe and suggested that perch and mffe might compete for benthic macroinvertebrates . Also in a field experiment, mffe affected the growth of perch (E. Bergman and L. Greenberg, unpubl .) . Perch and mffe have different feeding strategies, as mffe rely on both visual and nonvisual sensory organs, while perch is a 536

visual hunter. The foraging ability of mffe is less influenced by light than that of perch (Bergman 1988). These results correspond well with the different abundances of perch and mffe in lakes of different productivities (i.e. turbidity) (see also Bergman 1990). Thus, increased competition between perch and roach and possibly mffe in combination with lower light levels in lakes of high productivity are two factors that could explain the different responses of perch md mffe to increased lake productivity. Besides eompetitisn, predation is a factor that c m influence population regulation. However, it is only recently that shifts in the impsflance of competition and predation as structuring factors on different trophic levels along m envbonmental gradient (productivity) have been discussed (e.g . Oksanen et al. 1981 ; Persson et al. 1988). In the model presented by Persson et al. (19881, predation is viewed as a more important regulating factor for the fish co unities in lakes sf moderate productivity whereas competition is more important im lakes of high productivity. Differences between young perch and mffe in susceptibility to predation could therefore be a third factor influencing the abundances of the two species. Can. J. Fish. P$qu&tt.Sci., k/8C. 48, 8991

TABLE1. Chlorophyll a, transparency, area, a d maximum depth for eight Swedish lakes in July or August. The m a vdue from M e s Smth md North Osby includes both basins, and the data from Lake S6vde are from late September. Data were obtained from Hamin ( 1993) (Lakes South md North Bolmen), Hamin et al. (1974) (Lake Ivij), e l i n and Ripl(1978) (Lake Hinna), ColHvin a d Persson (1975) (Lakes South and North Osby), GeHin (1991) a d H d n (1984) (Lake Vomb), and unpublished data (Lake S6vde).

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Chla (pg/L)

Secchi depth

Ma. Area

depth (b') (m)

Lake South Bolmen L&e Iv6sj6n Lake North Bdmen Lake HinnasjCin Lake South Osbysj8n Lake North Osbysj6n Lake Vomb L&e S6vdesj6n

The purpose of this study was to examine the differences in distribution of perch m d mffe. The study included a comparison of eight lakes of different productivity. Two of these lakes, one of moderate productivity and one of high productivity, were studied in more detail to discern seasonal patterns in diet and habitat use of perch and mffe. The distribution patterns of the two species within mad between lakes were related to the species' competitive abilities under different light and temperature conditions and to interactions with cyprinid species.

Materials and Methods Lake Description Sampling was conducted at eight locations of v q i n g productivity in six South Swedish lakes. The localities (hereafter lakes) were ranked by productivity (chlorophyll a) in July-September (Table 1). The two lakes that were studied in more detail were Lakes South Bolmen and Vomb. Lake South Bolmen is a medium productive Bake with submersed vegetation and some reed vegetation. The bottom consists of sand and mineral matter at water depths up to approximately 5 m and orgnic matter in deeper areas. Lake South Bolmen is rather deep (maximum depth 37 m, mean depth 8 m) and is usually themally stratified during at least part of the summer. Lake Vomb is a highly productive lake (Table I), almost lacking submersed vegetation but with some reeds. Regulation of the water level limits the area of emergent vegetation. In the shallower parts of the Bake, i. e. to depths of -3-4m, the bottom consists of sand and at deeper depths consists of organic matter. Lake Vomb (maximum depth 16 m, mean depth 6 m) is exposed to winds and is seldom thermally stratified. Field Sampling Data on fish abundances were obtained from my investigations of Lake Siivde (1982), Lake South Bolmen (1985), and M e Vomb (1986) and from previous studies of Lake South Bolmen (Hmrin B973), Lake Ivo (Hamin et d. B974), Lake North BoBmen (Hamin 1973), M e Hinna (Gelin m d Rip1 1978), Lake South Osby (Collvin and Persson 1975), m d Lake No& Osby (Collvin and Persson 1975). Sampling was performed with 1*5-m-deepsurvey link gill nets of a length of 56 m. Eight mesh sizes (9, 14.5, 18, 25, 30, 33, 38, and Can. J. Fish. Agmt. Sci., Vol. 48, 6991

46 mm) each 7 m long were used. At each locality, gill nets were set on the bottom at several depths for 1-3 d during May, July, or August in different years. All fishing data x e presented as catch per unit effort (CPUE) which is catch per net for 24 h in either numbers or biomass. Five additional samplings in Lake South Bslmen (MayOctober 1985) and Lake Vomb (May-September 1986) included fish, zooplmkton, benthic invertebrates, dissolved oxygen concentration (WinUer method), light transmission, and temperature. To sample the fish, I used survey link gill nets of the same type as described above that were placed on the bottom at six depths (2,5, 18, 15,26), and 25 rn) in Lake South Bolmen and four depths (3, 6 , 9 , and B 2 m) in Lake Vomb. In Lake South Bolmen, each sampling lasted for three 24-h periods and in Lake Vsmb only for one 24-h period because of the higher total abundance of fish in Lake Vomb. Captured fish were identified, memured (total length), weighed, and counted. In addition, stomachs from perch and mffe were removed and deep-frozen for later diet analysis. Perch and mffe were divided into several size classes (approximately year classes) and, if possible, 10 stomachs from each size class at each depth were taken. Due to the low numbers of stomachs in each size class, size classes sometimes had to be combined into wider classes. Size classes of mffe differ between lakes due to the different size distributions in the two lakes. Zooplankton samples were taken at each fish sampling location with a 2-m-long plastic core placed as close as possible to the bottom. Ten- and 5-L samples were taken from Lake South Bolmen and Lake Vomb, respectively. Samples were sieved through a 45-pm filter and the zooplankton were preserved in 4% formaldehyde. The benthic invertebrates were sampled at every second depth that had been sampled for fish (5, 15, and 25 m) in Lake South Bslmen and at every depth that had been fished in Lake Vomb. Six samples were taken at each locality using an Ekman grab (area 225 cm2). The material was sieved through a 0.5 mm net and deep-frozen for later analysis. Laboratory Analyses The zooplankton and the benthic invertebrates were identified, counted, and measured (length). Length measurements of zooplankton were used to convert abundance to biomass using length-weight regressions given in Bottrell et al. (1975). For benthic macroinvertebmtes, length-weight regressions from a south Swedish pond (Persson and Greenberg 1996)) and from Smock (1980) were used. The diversity of the benthic macroinvertebrate community was expressed by using the ShannonWiener index (-E Pisln Pi where Pi is the proportion of organism i in the sample). Stomach contents of perch and mffe were identified, counted, and measured. Dry weights of items eaten were estimated using length-weight regressions as described above. Due to small sample sizes in some size classes, statistical analyses could not always be performed. Diet breadths for perch and mffe were calculated using Levins' (1968) niche breadth measure:

where Piis the proportion of food item d in the diet.

Results Chemical and Physical Data Lake South Bolmen was themdly stratified during June, July, and August but not in May and October. Surface

Lake South Bolmen Lake Vomb Temperature, ' C

6

10

d

m


G

Oxygen saturation, Q/o 0

0

6

&.

&

Q

,

Lake South Bslmen

0

s.a

aao

a)

b)

60 80 180 120 140 160

0

Lake South Bo%men 10

4

ao

8

3

12

w 5

a w $0

+ May

4

June

July

Bug

* Sept/Oct

ma. 1. Temperature and oxygen concentrations at different depths during May, June, July, August, m d SeptemberiOctoberin Lake South Bolmn and Lake Vesmb.

temperature v k e d htween 6 m d 18°C and bottom temperature between 6 and 12°C (Fig. 1). Lake Vomb was never themally stratified (May-October) and the surface temperature varied between 11 and 20°C. The largest difference between surface and bottom temperature was 1.5". Dissolved oxygen concentrations were high at dates in and during the summer there was a strong supersaturation due to high phytop'dton production' In Lake South Bolmen9 dissolved oxygen was high at all sampling dates except in the in (23%) and August (408) Fig' '1' Water varied 3'6 and 5'0 rn in Lake South and Os2 and rn in Lake Vomb (Tab'e 2)'

"'

Vomb9

'"

Fish Community The total CPUE was more than five times higher in Lake Vomb than in Lake South Bolmen (Fig. 2a). In Lake South Bolmen the fish fauna was dominated by percids (28% perch

lZander

El Perch

E3 Roach

Ill Other cygrinids IOther

Ruffe

FIG.2. Composition of the fish community in Lake South Bolmen (1985) and Lake Vomb (1986). Cdculations are based on CPUE. Circles shows relative composition and the bus show means for the whole season ( = 5 mo). (a) Based on numbers of fish: (b) based on weight

26% mffe, m d 6% zmder (Stizostedion luciqerca)), which together made up 60% of the total number of captured fish. Cyprinids, such as roach, formed only about 25% of the totd captured. In Lake Vomb, 55% of the total number of fish were cyprhids (48% roach and 0.3% bream (Abramis brama)).Ruffe were the most common percid constituted 33% of the total number of captured fish. The proportion of perch and zander was 7 and 5 1 , respectively. Approximately the same pattern was present when biomass was substituted for numbers. The main difference was that m f e , which constituted a large number of the gstd abundance, only constituted a small part of the totd biomass. In contrast, b r e m composed a smdl mrnbea of the total abundance but a large part of the total biomass

TABLE2. Seechi depth, depth at 10% of surface light level, and temperature in M e South Bolmen (1985) and Lake Vomb (1986). Secchi depth (m> Bolmen May June July August September October

5.0

4.2 3.6 3.6 4.0

Vomb 0.8-1 .V 0.34.5" 8.24.4" 0.4 0.7 -

10%light (m>

Temperature

("@I

Bolmew

Vomb

Bolmen

Vsmb

2.4 2.4 2.5 2.2

2.1 1.1 0.9 1.5 1.3

6.1 13.8 17.5 16.1

11.8

2.6

-

12.6

-

-

15.5

19.8 17.2 13.2

-

"Estimated from light transmission curves. Can. 1 Fish. Aquut. Sci., Blob. 48, 1991


(Fig. 2b). The category 660ther' includes burbt (Lota h a ) , vendace (Coregonus albula), whitefishes (Coregonus lavaretus md C. oqrhynchess), md a few worthem pike (fiox lucius). This group formed 24% of the total biomass and 15% of the total abundance in Lake South Bolmen. The numerical abundance (CBUE) of perch fist increased and then decreased when the lakes were ranked from low to high productivity. The biomass abundance (CPW) of perch decreased continuously over the productivity gradient (? = 0.48, P < 0.05). The different patterns obtained for perch from numbers and biomass were a result of a decrease in mean size of perch dong the productivity gradient (see also Persson 1983). In contrast, the CBUE (numbers and biomass) of mffe increased with increasing productivity (3 = 0.74, P < 0.01 for mrnbers and 3 = 0.83, P < 0.01 for biomass) (Fig. 3). The low abundmce of mffe in Lakes Hinna, North Bsby, and South Bsby might be related to the shallowness sf these lakes. The length distribution of both perch and mffe differed between Lake South Bolmen md Lake Vomb (Fig. 4). Ruffe were bigger in Lake Vomb than in Lake South Bolmen whereas the opposite was the case for perch (chi-square P < 0.00%for both perch and mffe) . Vertical Distribution of Perch md Wuffe

Oligotrophic conditions - Eutrophic conditions --) Perch

Ruffe

PIG.3. (a) Abundance and (b) biomass of perch and ruffe in eight South Swedish lakes ranked along a gradient of increasing chlorophyll a values. CPUE is based on numbers or grams of fish. The data ape obtained from one fishing occasion during the summer season. Perch

Perch were more abundant in shallower than in deeper water in both Lake South Bolmen and in July and October in Lake Vomb (Fig. 5). Ruffe were rather evenly distributed between all depths in both lakes, although fewer mffe were caught at 9 rn thm at other depths in Lake Vornb. In Lake South Bolmen there was no seasonal difference in the vertical distribution of perch (chi-square P = 0.241, but there was a higher abundance of mffe at shallower depths in May csmpaed with July and October (chi-square P < 0.03) (Fig. 5). Catches, however, were higher in May than in July md October; if relative abundance is considered, this difference is not clear. In Lake Vsmb, Ruffe

FIG.4. Length distribution s f perch md mffe in Lake South Bolmen and Lake Vomb. Note the different scales on the y-axis. Can. J. Fish. Aquab. Sci., Vol. 48, 4991

539

Lake South Bolmen.


Numbers

Lake Vsmb

Relative abundance

Numbers

Relative abundance

Ruff e

e May

o July

8ct

FIG.5 . Vertical distributions of perch awd mffe in Lake South BoImen and Lake Vomb during May, July, m d October. The distributions are presented both as numbers and relative abundance.

perch were more restricted to the shallowest depth in July than in May and September (chi-square P < 0.001). Ruffe were less abundant at the deepest depth in July agld October in Lake Vomb (chi-square P < 0.001) (Fig. 5); looking at the relative abundmce, this is the case for July only. To compare differences between years, complimentary malyses were mn for Lake South Bolmen on data from July and October 1970, 1971, 1972, md 1985. The thermocline was most developed in July 1970, dmost absent in 1971, md intermediate in 1972 and 1985. There was a difference between the vertical distribution of perch in July agld October in 1970, but not in the other yeas (chi-square P < 0.001 in 1970, P = 0.134.68 in 1971, 1972, md 1985). For mffe there was generally not a difference between the vertical distribution in July and October (chi-square P = 0.05 1 in 1970, P = 0.872 in 1971, P = 8.38 in 1872, and P = 0.080 in 1985). There was a la-ge between-yea- variation in both perch and mffe abundance (chi-square P < 0.001 for both July and October). Prey Resources Total biomass of copepods was about five times higher in Lake Vomb than in Lake South Bolmen on all sampling dates (Fig. 6). In May and June, the biomass of cladocerans was 548

higher in Lake Bolmen thm in Lake Vomb. The opposite was true in August m d September-October when the biomass in Lake Vomb was about 10 times that in Lake South Bolmen (Fig. 6). There was no depth effect on biomass of cladocerans or copepods in the two Bakes (ANOVA F,,, = 0.62-1.96, P = 0.124.61). In Lake South Bolmen there was a minimum in cladoceran biomass in July (repeated measures ANOVA F,,4 = 11.95, P < 0.00 11, but not in copepod biomass (repeated measures ANOVA F , , = 2.09, P = 0.12). In Lake Vsmb there was an increase in cladocerm biomass over time (repeated measures APJBVA F , , = 28.12, P