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The Ichthyofauna Associated with Zostera Capensis Setchell Ill the Swartkops Estuary, South Africa

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The Ichthyofauna Associated with Zostera Capensis Setchell Ill the Swartkops Estuary, South Africa The ichthyofauna associated with Zostera capensis Setchell ill the Swartkops estuary, South Africa Lynnath E. Beckley Department of Zoology, University of Port Elizabeth The ichthyofauna associated with Zostera beds in the lower Studies on the ichthyofauna of the Swartkops estuary near reaches of the Swartkops estuary was examined by means of Port Elizabeth (33°S8'SI2S037'E) have recently been under­ haul seine netting over 15 months. Thirty-nine fish species were caught In the Zostera beds and the small shoaling taken to follow up the pioneer surveys by Gilchrist (1918). species, Hepsetis. "'reviceps and Gilchrlstella aestuarius, con­ Work by Winter (1979), Marais & Baird (1980a, b) and stituted 55% of the t\..~'31 catch In terms of numbers. Juveniles Melville-Smith & Baird (1980) has provided information on of six mullet species occurred in the Zostera and recruitment the species composition, seasonal abundance and size fre­ took place throughout the year. Sparlds such as Rhabdosargus holubi and Dlplodus sargus showed marked spring and sum­ quency distribution of the adult, juvenile and larval fish oc­ mer recruitment. The recruitment patterns of Juveniles to the curring in the main channel of the estuary. Zostera beds is correlated with documented breeding cycles of Two relatively large creeks, Modderspruit and Tippers adults, particularly those breeding in the shallow inshore Creek, are located in the lower reaches of the 16-km long marine environment. The Swartkops Zostera beds were found to form an integral and important part of the nursery function Swartkops estuary (Figure 1). The creeks support about 9 ha of the estuary. (B. Talbot, pers. comm.) of the seagrass Zostera capensis. S. Afr. J. Zool. 1983, 18: 15 - 24 The importance of seagrasses such as Zostera, Posidonia ) 0 and Thalassia as nursery areas for juvenile fish is well 1 0 Die visgemeenskap in die Zostera-beddens van die Swartkops­ documented (Adams 1976; Weinstein & Heck 1979; Young 2 riviermonding is deur middel van treknetvangste oor 15 maande d 1981) and is emphasized by Kikuchi (1980) in his review of e bestudeer. Nege-en-dertig spesles Is gevang en 55% van die t a aantal vis wat gevang is, het ult die twee spesles Hepsetia faunal relationships in temperate seagrass beds. d ( breviceps en Gilchristel/a aestuarlus bestaan. Klein- The present study was aimed at determining the r tjies van ses Mugllidae-spesies het in die Zostera voorgekom e significance of Zostera beds in the Swartkops estuary as h en rekrutering het gedurende die hele jaar plaasgevlnd. s i nursery areas for juvenile fish and thereby supplementing l Sparidae soos Rhabdosargus holubl en Diplodus sargus het b the results of earlier workers who did not effectively sam­ u rekrutering gedurende lente en somer vertoon. Die rekruter­ P ingspatroon van klein vissies tot die Zostera-beddens Is gekor­ ple the vegetated creeks of the lower reaches. The study e releer met gedokumenteerde teelsiklusse van volwassenes, in h t forms part of a comparative programme on juvenile marine besonder, die spesies wat in die vlak kuswaters voortplant. Ole y fish in estuaries and the nearshore coastal region. Concur­ b stu die het bewys dat die Swartkops Zostera-beddens 'n in­ d tegrale en belangrike deel van die kweekfunksie van die rent with the present study were investigations of the in­ e t getyrlvler uitmaak. vertebrates associated with beds in the Swartkops n Zostera a S.-Afr. Tydskr. Dierlc. 1983, 18: 15 - 24 r estuary (Nusch 1981; Emmerson, Watling & Watling 1982) g e and the Kromme estuary (Hanekom 1982). c n e c i l Methods r e Fish were collected monthly from January 1980 through d n March 1981 by means of a small haul-seine net (10,5 m x u y 2,5 m) with a stretched mesh size of 2 mrn. At low tide a a haul covering about 60 m2 was made through the w Zostera e t at each of two stations in Tippers Creek and at one station a G in Modderspruit (Figure 1). A further haul was made in an t e area with no subtidal Zostera along the bank of the main n i b channel of the estuary between the two creeks. Surface-water a S temperature and salinity were measured in the creeks on each y b sampling occasion. d L)'llDllth E. BecIdey Catches were kept frozen until sorted, identified and e c Department of Zoology, University of Port Elizabeth, u counted, and total lengths of specimens measured in mm. d P.O. Box 1600, Port Elizabeth 6000, Republic of South Africa o As the small shoaling species Hepsetia breviceps (Cuvier) r p Received 24 May 1982; accepted 20 September 1982 and Gi/christella aestuarius (Gilchrist) were the subject of e R 16 S.-Afr. Tydskr. Dierk. 1983, 18(1) a 1 K081 Bay 2 St. Lucia 3 W. Klalmond 4 Kromma 5 KnY8na 6 K lain (Harmanu8) 7 Mllnarton b Tippers Creek SWARTKOPS ESTUARY . f1pre) 1 (a) Map of Southern Africa showing the geographical position of the Swartkops estuary and other areas mentioned in the text. (b) The middle 0 and1 lower reaches of the Swartkops estuary showing the sampling stations in the creeks (1-3) and channel (4). 0 2 d e 26 at separate study by Talbot (1982) only a subsample of 100 a specimensd of these two species was measured from each sta­ ( • • tionr each month. Juvenile mullet were identified from den­ 0 0 e 24 h .. tition characteristics (van der Elst & Wallace 1976) but as 0\ s \ i itl often proved difficult to identify mullet of less than 30 mm \ b (.) \ withu confidence all mullet of this size class were grouped . • P W 22 ~--\ /0 • \ I e a: 0 together. ::::I \ / h \ / t I- 0« \ / I y a: \ / Resultsb W \ 20 I CL \ d \ I Modderspruite and Tippers Creek in the lower reaches of the :::i: I t W \ 0 Swartkopsn estuary experience sernidiurnal tides with a mean I- \ /. a \ I r 18 \ • I springg range of 1,6 m (Beckley & McLachlan 1979) and a \ 0 /0 e \ • timec lag of about 1 h after predicted times for Algoa Bay. \ ,...-0, ./ n \/ '", Salinitye varies from 30 - 35°/00 except after heavy rains. As c 16 i l the creeks are shallow « 2 m depth) water temperature is r variablee and often differs considerably from that of the main d channeln of the estuary and the adjacent sea (Figure 2). u J F M A M J J A SON D y Haul seining proved to be an effective sampling techni­ a MONTHS quew for juvenile fish as during the IS-month study period, e 62t 020 fish were caught at the three Zostera stations and a Fillure 2 Water temperatures measured in Modderspruit ( .) and Tippers G 4371 at the channel station. Mean catch per haul was I 328 Creek (0) during the study period compared with mean monthly water t (SEe ± 296) fish for the Zostera stations and only 291 (SE temperature for the lower reaches of the estuary (. ____ after Marais & n i Baird 1980b) and Algoa Bay (__ after Beckley & Mclachlan 1979). ±b 43) fish at the channel station. Total combined catch per a monthS for the three Zostera stations varied greatly, rang­ y ingb from 481 to 11 437 fish depending largely on the catch ofd the small shoaling species H. breviceps (Figure 3). the Zostera, giving a total of 43 species caught during the e c u Thirty-nine species were recorded from the creek stations study period. The number of species captured in the Zostera d ando 30 species from the channel station (Table 1). Four each month varied between 12 and 28 with more species be­ r speciesp recorded in the channel area were not captured in ing caught in the summer months (Figure 3). e R S. Afr. J. Zool. 1983, 18(1) 17 12000~------------------------------------------------~30 rn J: w <.) I­ <3 < 8000 20~ <.) rn ...J < o I- a: o 4000 10 w I- ID ::E ::J Z JFMAMJJASONDJ FM MONTHS Figure 3 Total monthly catch by seine netting at the three Swartkops creek Zostera stations (. ---.) and total number of species captured in the Zostera each month (0----0). Table 1 List of fish species captured by haul seine netting during 1980/81 in the lower reaches of the Swart­ kops estuary. Lengths given in mm, Z indicates occurrence in Zostera beds and C indicates occurrence at the channel station. Species Length range J F M A M J J A SON D J F M Ambassis natalensis Gilchrist & Thompson 17 Z 22 C Amblyrhynchotes honckenii (Bloch) 21- 32 Z Z Z 23- 77 C C C Arothron hispidus (Lacepede) 34- 54 Z Z Arothron immaculatus (Bloch-Schneider) 15 - 25 Z Caffrogobius multifasciatus (Smith) 12-102 Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z 13- 61 C C C C C C C C C C C C C C . ) Clinus superciliosus (Linnaeus) 26- 81 Z Z Z Z 0 1 38- 98 C C C 0 2 Diplodus cervinus (Valenciennes) 9- 80 Z Z Z Z Z Z Z Z d e 9- 41 C C C C t a Diplodus sargus Linnaeus 10-134 Z Z Z Z Z Z Z Z Z Z Z Z Z Z d ( C C C C C C C C r 10- 93 e h Engraulis capensis Gilchrist 36 C s i l Epinephelus guaza (Linnaeus) 57 Z b u Etrumeus teres (Dekay) 31- 36 C P Gilchristella aestuarius (Gilchrist) 17- 50 Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z e h t 27- 52 C C C C C C C C y Hepsetia breviceps (Cuvier) 12- 68 Z Z Z Z Z Z Z Z Z Z Z Z Z b Z Z d 12- 75 C C C C C C C C C C C e t Jleteromycteris capensis Kaup 7- 44 Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z n a r 8- 56 C C C C C C C C C C C C C C C g Lichia amia (Linnaeus) 46- 98 Z Z e c n Lithognathus mormyrus (Linnaeus) 68 C e c Liza dumerili (Steindachner) 13-221 Z Z Z Z Z Z Z Z Z Z Z Z Z i l r 11-237 C C C C C C C e d Liza richardsoni (Smith) 11-160 Z Z Z Z Z Z Z Z Z Z Z Z n u 28-180 C C C y Lizo tricuspidens (Smith) 17 -116 Z Z Z Z Z Z Z Z Z Z Z Z a w 29-126 C C C C C C C e t Lophodiodon calori (Bianconi) Z a 11 G Lutjanus lulvif7amma (Forsskiil) 17- 21 Z Z t e Monodactylus falciformes (Lacepede) 7- 28 Z Z Z Z n i b 11- 17 C a S Mugil cephalus Linnaeus 7-153 Z Z Z Z Z Z Z Z Z Z Z Z y 8-172 C C C C C C C C C b d Myxus capensis (Valenciennes) 24- 29 Z Z e c Omobranchus woodi (Gilchrist & Thompson) 19- 20 Z Z u d 18- 19 C C o r p Pelates quadrilineatus (Bloch) 22 Z e R 18 S.-Afr.
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