Fish populations of the Avon heathcote estuary

Transcription

1 New Zealand Journal of Marine and Freshwater Research ISSN: (Print) (Online) Journal homepage: Fish populations of the Avon heathcote estuary B. F. Webb To cite this article: B. F. Webb (1973) Fish populations of the Avon heathcote estuary, New Zealand Journal of Marine and Freshwater Research, 7:4, , DOI: / To link to this article: Published online: 29 Mar Submit your article to this journal Article views: 117 Citing articles: 7 View citing articles Full Terms & Conditions of access and use can be found at

2 1973] 307 FISH POPULATIONS OF THE AVON-HEATHCOTE ESTUARY 5. RECORDS OF LESS COMMON SPECIES* B. F. WEBB Zoology Department, University of Canterbury, Christchurch, New Zealand (Received for publication 13 September 1971; revision received 12 January 1973) ABSTRACT An account is given of nineteen fish species of slight or irregular occurrence in samples taken from the Avon-Heathcote Estuary, Christchurch, New Zealand between April 1965 and April The fish were red cod, Physiculus bacchus (Bloch & Schneider); clingfish, Trachelochismus pinnulatus (Forster); rockfish, Acanthoclinus quadridactylus (Bloch & Schneider); brown trout, Salmo trutta Linnaeus; sandfish, Leptoscopus angusticeps Hutton; spotted stargazer, Geniagnus monopterygius (Bloch & Schneider); red-finned bully, Gobiomorphus huttoni (Ogilby); giant bully, G. gobioides (Cuvier & Valenciennes); short-finned eel, Anguilla australis Richardson; whitebait, Galaxias maculatus attenuatus (Jenyns); moki Latridopsis ciliaris (Forster); red gurnard, Trigla kumu (Lesson & Garnot); long-finned eel, Anguilla dieffenbachi (Gray); smelt, Stokellia anisodon (Stockell); garfish, Reporhamphus ihi (Phillipps); barracouta, Thyrsites atun (Euphrasen); thornfish, Bovichtus variegatus (Richardson); seahorse, Hippocampus abdominalis (Lesson); and rigg, Mustelus antarcticus (Guenther). Details are given of sampling locality and date, length, weight, sex, gonad maturity, gut contents, and parasites. Where the data permit, breeding status is inferred and discussed. INTRODUCTION This paper completes a series of five presenting aspects of the biology and ecology of the fish population of the Avon-Heathcote Estuary, Christchurch, New Zealand from April 1965 to April Nineteen fish species are discussed, being those species which were scarce or of irregular occurrence in the samples. Sampling methods (see Webb 1972) were such that the relative numbers of each species obtained did not reflect relative population sizes in the study area. The samples of each species obtained were 27 red cod, Physiculus bacchus; 6 clingfish, Trachelochismus pinnulatus; 4 rockfish, Acanthoclinus quadridactylus; 14 brown trout, Salmo trutta; 4 sandfish, Leptoscopus angusticeps; 6 spotted stargazer, Genwgnus monopterygius; 2 red-finned bully, Gobiomorphus huttoni; 3 giant bully, G. gobioides; 86 short-finned eel, Anguilla australis; 199 whitebait, Galaxias maculatus attenuatus; 6 moki, Latridopsis ciliaris; 4 red gurnard, Trigla kumu; *Part 4. Parasites. N.Z. Journal of Marine and Freshwater Research 7 (4) : tpresent address: Fisheries Division, Department of Agriculture, G.P.O. Box 192B, Hobart, Tasmania. N.Z. Journal of Marine and Freshwater Research 7 (4) : 3071

3 308 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [DEC. TABLE 1Biological data for red cod, Physiculus bacchus, from the Avon-Heathcote Estuary, Date of Capture & (n) T.L.&(S.L.) (mm) (g) Sex & Gonad Maturity Age (y) 11 June (1) 15 June (2) 27 October (1) 10 November (1) 22 November (1) 24 November (14) 8 December (6) 18 April (1) 380(350) 500(455) 405(370) 272(248) 305(278) 320(300) 270(245) 282(269) 268(245) 262(242) 260(235) 290(268) 230(210) 265(245) 235(215) 258(238) 228(208) 255(230) 242(222) 260(238) 310(285) 250(238) 242(225) 240(218) 262(238) 318(290) 408(375) V < t V ii : > 2 2 II _2 I 1 > -III : 9 ii 2 II 9 in ; 1 1 > : r-3 and one each of long-finned eel, Anguilla dieffenbachi; smelt, Stokellia anisodon; garfish, Reporhamphus ihi; barraeouta, Thyrsites atun; thornfish, Bovichtus variegatus; seahorse, Hippocampus abdominalis; and rigg, Mustelus antarcticus. The localities and habitats from which each species was obtained are briefly described (Fig. 1). Lengths are given as T.L. (total length, tip of snout to tip of tail) and S.L. (standard length, tip of snout to tip of caudal peduncle). Estimates of age are given for red cod, clingfish, rockfish, and brown trout, based on length:age criteria proposed by other authors. s are recorded, and a length: weight regression analysis is given for short-finned eel (Fig. 2). Specimens were sexed whenever possible, and the gonad maturity determined on the criteria proposed by Bowers (1954), modified here as Appendix 1. Gut contents and internal parasites were also ascertained by dissection. The above data are presented for most species in tabular form. Due to very small samples and lack of points for discussion, red gurnard,

4 1973] WEBBFISH OF AVON-HEATHCOTE ESTUARY if 11 I S - ^ -^^Shag Rook// (T \ s \ / Avon River \ /, \l / n Dyers Rd Bridge / / / J 0 Scale ^ ^ AVON RIVER J //' CHANNEL /. / \ / ' y^- ~ ~~ -~ ~ ^ -~v i i ^ ^^ a. 1 i Urn / -. Charleston Linwood A / v ^ _ J ( Drainer I \ e Culvert / -I.-'I 1 / 1 y / I 1 / / \\ 1 \\ )\ Sj,' r' ^~ MONCKS BAY y~^j«f/ r^ J 1 k.,/^heathcote 7 / ~ RIVER CHANNEL \ \ N^\Heathcote Bridge 0/ \ j Heathcote River FIG. 1Localities in the Avon-Heathcote Estuary mentioned in the text. long-finned eel, smelt, garfish, barracouta, thornfish, seahorse, and rigg are omitted from the text descriptions, and presented in Table 10. RESULTS Red cod, Physiculus bacchus (Bloch & Schneider) This stenohaline species was confined to the deep waters of Moncks Bay (Fig. 1), amongst rocks and kelp (mainly Macrocystis pyrifera). Only 27 specimens were obtained, mostly from anglers; all but one were female. The ages quoted in Table 1 are derived from age:length parameters proposed by Parrott (1957): 6 months, mm; 1 y, mm; 2 y, mm; 4 y, 510 mm (lengths converted from inches, presumably T.L.). Most specimens were in their second year, though a few other individuals were obtained. Red cod apparently have a rapid growth rate, reaching about 280 mm and 210 g at 1.5 y, and about 450 mm for a four-fold weight increase at 3 y. Parrott (1957) gave the breeding season as July to November, a view supported by the evidence in Table 1. Females apparently reach sexual maturity during their fourth year. Although one female with ripe ovaries was caught in the estuary, the area is probably only used

5 310 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [DEC. for feeding; the capture of only juvenile specimens during spring and summer also suggests breeding outside the estuary. Gut content analysis showed red cod to be a predator. For the 17 specimens, rounded % occurrences of dietary constituents were fish {Aldrichetta forsteri, Tripterygion nigripenne, and Trachelochismus pinnulatus) 65%, and crabs (Hombronia depressa and Hemigrapsus crenulatus) 34%. Crabs were found only in the summer diet. Parasites found were cestodes (1 in 10 specimens), the nematode Capillaria physiculi (1-3 in 2), trematodes (1-10 in 8), the isopod Nerocila orbignyi (1 only), and the copepod Lernaeocera lotella (1 only). The specimen of Nerocila had consumed the entire left pectoral fin of its host. Clingfish, Trachelochismus pinnulatus (Forster) This species was not specifically searched for, being small in size and confined to deep water. However, six specimens were brought up in otter trawl hauls with shell fragments, weed, debris, etc. Four specimens were from Moncks Bay, and one each from the Avon and Heathcote river channels {see Fig. 1). TABLE 2Biological data for clingfish, Trachelochismus pinnulatus, from the Avon-Heathcote Estuary, 1965 Date of Capture & {n) e.. & (S.L.) (mm) (g) Sex & Gonad Maturity Age (y) 4 May (1) 29 June (1) 24 August (1) 24 August (1) 13 September (1) 10 November (1) 60(50) 50(45) 38(32) 42(35) 45(40) 40(35) 9 VI 9 VI or VII 9 V-VI Coakley (unpublished 1964) proposed the following length rage relationships: hatching, 5 mm; 1 y, 181 mm; 2y, mm; 3 y, mm. He also found a sex ratio of 2 cf : 1 9 at Scarborough, Banks Peninsula, a few miles from the present study area. The capture of only female specimens here is probably not significant in so small a sample. All six specimens were sexually mature adults; sexual maturity is reached at the end of the second year. The incidence of specimens with mature gonads suggests that the clingfish breeds in the estuary during the spring-summer months. Of the six specimens, four were without gut contents, two contained amphipod remains, and one also contained Ulva lactuca and detritus. No parasites were found.

6 1973] WEBBFISH OF AVON-HEATHCOTE ESTUARY Rockfish, Acanthoclinus quadridactylus (Bloch & Schneider) Rockfish were confined to the deep waters of the Moncks Bay shoreline (see Fig. 1), living among rocks, Mytilus beds, and algal fronds (Macrocystic pyrifera, Viva lactuca). Only four specimens were obtained, one of which (25 September) was found at low tide alive beneath rocks at mid-tide level. TABLE 3Biological data for rockfish. Acanthoclinus quadridactylus, from the Avon-Heathcote Estuary, 1965 Date of Capture T.L. & (S.L.) Sex & Gonacl Age & (n) (mm) (g) Maturity (y) 25 September (1) 68(58) 3 $ November (1) 120(105) 25 I 3 6 November (1) 200(175) 84 II-IV December (1) 85(70) 7 9 VI 1.5 The ages in Table 3 are derived from Jillett's (unpublished 1961) age: T.L. parameters: 1 y, 59 mm; 2y, 100 mm; 3 y, 123 mm; 4 y, 140 mm; 5y, 157 mm; 6y, 176 mm; 7 y, 183 mm; 8y 186 mm; 9.5 y, 193 mm. Gonad maturity indices suggest that sexual maturity is reached in 1 years, and that spawning occurs in the estuary during summer. Only one specimen was found to contain food, the crab Hemigrapsus sp. No parasites were found. Brown trout, Salmo trutta Linnaeus Fourteen specimens of this anadromous species were obtained in beach seine hauls from Moncks Bay and the Avon River channel (see Fig. 1). Parrott (1932) and Woods (1963) have suggested that brown trout commonly enter estuaries and the open sea, when accessible from breeding streams; Allen (1951) showed that limited movement occurred between the Horokiwi Stream and Pauatahanui Inlet. Ages quoted in Table 4 are based on age:length criteria proposed by Parrott (1932), who showed a sexual differential in growth rates: ly, 155 mm (J 1 )/120 mm (9); 2y, 215/232mm; 3 y, 305/330mm; 4 y, 400/410 mm; 5 y, 484/450 mm; 6 y, 510/485 mm. Allen (1951) and Stokell (1955) have placed the breeding season between June and August, and indeed three ovigerous females caught in late April in the Avon channel were probably moving upriver to spawn. One fourth-year female caught at this time had immature gonads, but was perhaps exceptional, as two of the three ovigerous females were only slightly larger, and hence of comparable age. The remaining ten

7 312 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [DEC. TABLE 4Biological data for brown trout, Salmo trutta, from the Avon-Heathcote Estuary, {- = not recorded; *egg counts for the three ovigerous females were respectively ( ) = 1905, ( ) = 5012, and ( ) = 2140} Date of Capture &(n) T.L.&(S.L.) (mm) (g) Sex & Gonad Maturity Age (y) 15 July (1) 27 My (1) 24 August (1) 7 October (2) 8 October (1) 11 October (2) 27 October (2) 20 April (2) 22 April (2) 400(365) 315(285) 265(238) 385(350) 330(310) 350(320) 685(645) 275(242) 288(258) 255(230) 448(385) 605(510) 485(410) 430(365) Si $I I 8 I 9 VI* 9 VI* 9 VI* 9I ^ ^t specimens were caught in the winter-spring period, and, apart from one mature but unripe male, were all sexually immature. Food groups found from gut content examination were fish (Aldrichetta forsteri, Rhombosolea plebeia, and R. leporina) and crustaceans (the isopods Metacirolana japonica and Zenabiana sp., and amphipods, thought to be Gammarus sp.). There was some variation in gut contents with sampling locality: (a) Moncks Bay, fish, isopods, few amphipods; (b) Avon channel (mid-estuary), fish, few amphipods; and (c) below Dyers Road bridge, amphipods, few fish. Parasites found were the nematodes Hedruris spinigera and Cucullanus antipodeus (1-6 in 4 specimens) and trematodes (1-4 in 3). The trematodes occupied only the duodenum and ileum, whereas the nematodes occurred in the stomach also. Sandfish, Leptoscopus angusticeps Hutton Four specimens were obtained in low tide beach seine hauls from Moncks Bay. Parrott (1960) gave an average length for adult sandfish of 305 mm (T.L.), but the sexually mature specimens obtained in this study were substantially smaller. A larger sample of both sexes would be necessary to establish significant variance from Parrott's results, however. Three specimens were without gut contents, the other contained two Aldrichetta forsteri of 80 mm T.L. No parasites were found.

8 1973] WEBBFISH OF AVON-HEATHCOTE ESTUARY TABLE 5Biological data for sandfish, Leptoscopus angusticeps, from the Avon- Heathcote Estuary, Date of Capture T.L. & (S.L.) Sex&Gonad & (n) (mm) (g) Maturity 29 June (1) 150(135) 15 7 December (1) 278(248) V-VI 9 December (1) 245(220) April (1) 255(225) 84 9 VI Spotted stargazer, Geniagnus monopterygius (Bloch & Schneider) The spotted stargazer was obtained from Moncks Bay and the lower Avon-Heathcote channel (5 adults), and from the Redcliffs shoreline (1 juvenile). Five specimens were taken by other trawl and one by dip net. TABLE 6Biological data for spotted stargazer, Geniagnus monopterygius, the Avon-Heathcote Estuary, from Date of Capture & (w) T.L. & (S.L.) (mm) (g) Sex & Gonad Maturity 26 April (1) 3 November (1) 15 November (1) 24 November (1) 15 February (1) 20 April (1) 250(215) 253(200) 265(228) 260(225) 208(175) 65 (53) S III I II Gonad maturity data for this species throw little light on its breeding habits and maturation. Three specimens had no gut contents, and the remainder contained fish or their remains. One had three Aldrichetta jorsteri averaging 110 mm T.L., and one had two Tripterygion nigripenne. No parasites were found. Red-finned bully, Gobiomorphus huttoni (Ogilby) Two specimens were caught, one from the Redcliffs shoreline amongst Ulva lactuca, the other below Dyers Road Bridge. Biological data were respectively 7 September, 55(48) mm, 2g, 9 VI; 25 September, 65(55)mm, 4g, d HI. Gonad maturity suggests breeding within the estuary (see Stokell 1955). Gut contents (amphipods) were found only in the latter specimen. A trematode parasite was found in the region of the duodenum-ileum of one specimen. Sig-4

9 314 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [DEC. b=2-956±0-101 (b coeff.=0-4346) a= r= y=2-956x Log I FIG. 2Regression analysis of logio length against logto weight for 86 shortfinned eel, Anguilla australis, from the Avon-Heathcote Estuary, Original mensuration in millimetres and grams; graphed points derived from mean data at 5 mm intervals. Giant bully, Gobiomorphus gobioides (Cuvier & Valenciennes) The three specimens obtained were from the shoreline near Dyers Road Bridge, in similar habitat to the common bully (Webb 1972). Biological data were: 5 November, 79(68) mm, 7g t f IV; 8 April (1966), 102(85) mm, 13 g d 1 II; same date, 98(80) mm, 11 g, 3 II. No conclusions about breeding are possible from these data, but Woods (1963) suggested that males are strongly territorial, building a nest and caring for the eggs, while females join the males only for spawning, and also that giant bully and red-finned bully tend to breed further upstream than the common bully {see Webb 1973). Amphipods were found in the intestines of all three specimens, and one also contained filamentous green algae. No parasites were found. Short-finned eel, Anguilla australis Richardson This species was obtained throughout the study area. Larger specimens (40) were taken mostly by otter trawl and beach seine; dip netting was introduced in August 1965 to obtain mostly smaller, sexually immature specimens (46) not retained by the mm mesh of the heavier gear (Table 7). Sampling produced specimens in the size range mm, from small elvers to sexually maturing adults. The adults were apparently of seasonal occurrence in the study area, the first specimen being taken in late September The status of juveniles is uncertain, due to the late commencement of effeotive sampling. Regression analysis (Fig. 2) reveals a slow weight increase for this species.

10 1973] WEBBFISH OF AVON-HEATHCOTE ESTUARY TABLE 7Biological data for short-finned eel, Anguilla australis, from the Avon-Heathcote Estuary, (- = not recorded) Date of Capture & (B) T.L.&(S.L.) (mm) (g) Sex & Gonad Maturity 25 August (1) 3 September (8)» 7 September (2) 12 September (2) 17 September (1) 25 September (1) 26 September (1) 11 October (1) 18 October (1) 27 October (1) 1 November (3) 3 November (1) 5 November (2) 6 November (1) 8 November (2) 16 November (1) 18 November (3) 24 November (2) 25 November (5) 29 November (2) 1 December (1) 6 December (1) 7 December (1) 17 December (14) 250(246) 108(107) 102(101) 115(114) 55(-) 55(-) 55(-) 140(139) 140(139) 170(169) 65 (-) 250(248) 658(650) 595(590) 575(570) 655(640) 625(620) 410(405) 645(635) 670(660) 65(-) 152(150) 550(545) 665(655) 620(610) 680(670) 648(638) 625(615) 558(548) 715(700) 648(638) 698(688) 595(585) 680(670) 605(598) 662(652) 312(305) 405(395) 710(695) 722(712) 700(690) 165(163) 155(152) 88(87) 68(67) 62(60) 60(59) 135(134) 238(235) _ _ _ _ 5 26 II -- & I 8 I 2 HI 2 III 2 IIT 2 III 2 III 2 III 2 III 2 III (Continued en page 316)

11 316 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [DEC. TABLE 7 (continued) Date of Capture & in) T.L.&(S.L.) (mm) (g) Sex & Gonad Maturity 17 December {cont.) 18 December (1) 10 January (1) 15 February (11) 17 February (3) 8 April (5) 19 April (1) 20 April (6) 138(136) 165(163) 225(223) 195(192) 195(192) 138(136) 90(89) 682(672) 705(690) 755(740) 700(690) 122(120) 258(256) 482(478) 115(114) 172(170) 110(109) 140(138) 82(81) 810(800) 740(730) 765(750) 515(505) 425(418) 392(390) 95(-) 662(650) 832(825) 660(650) 740(725) 630(615) 705(690) 715(700) ( ) ll II 9 1 S I ll Stokell (1955) states that juvenile short-finned eels migrate up rivers after coming in from the marine nursery areas. Woods (1963) supports this, and further suggests a period of rest in the estuaries before the move up-river. In the present study, juveniles were in the approximate ratio of two females to one male. Most of the adults caught were females, and were found to have maturing gonads, though the ovaries were only just beginning to develop in the September-early October specimens. Later specimens had enlarging ovaries containing discrete eggs and small dense granules. The age of these females was probably 8-15 years (fide Woods 1963). The eyes were not noticeably enlarged. Between the Heathcote channel and Moncks Bay there was a slight colour change from brown or brownishgreen to yellow-greenish brown dorsally, and from white to pale grey ventrally.

12 1973] WEBBFISH OF AVON-HEATHCOTE ESTUARY The predominance of females in the sexually maturing population supports Stokell's (1955) assertion that only the females move upriver as juveniles, the males remaining in coastal waters. Hence only the females are catadromous in their breeding behaviour. Most of the maturing females sampled apparently entered the estuary from the Heathcote River, running through its polluted lower reaches (Bruce unpublished 1953; Hogan & Wilkinson 1959); the first specimen from the Avon channel was caught in November. During September and early October, adults apparently entered the estuary from the Heathcote River only with the high tides, but subsequently at any time. Gut content examination revealed an adult diet of fish {Gobiomorphus huttoni), crabs (Hemigrapsus crenulatus, Hombronia depressa, Helice crassa, Petrolisthes elongatus), molluscs (Potamopyrgus sp., Paphies australe, Lepsiella scobina albomarginata), and ascidian remains. The juveniles contained young Helice crassa, amphipods, mysids, polychaete remains (Pisionidae?), and crustose and filamentous algae. Crabs were found in 91% of adults, and molluscs in only 8%. Fish and ascidian remains were found in one specimen each. For juveniles, the equivalent figures were crabs 33.2%, mysids 28.5%, polychaetes 28.5%, and algae 9.4%. Differences in diet are reflected in the juvenile habitats not used by adults. For example, mysids were found in specimens from the Linwood Avenue culvert - Charleston drain area, and algae in those from the shoreline near Dyers Road Bridge. Parasites were found only in adult specimens, and confined to the duodenum-ileum region, being 1-4 trematodes in two specimens, and 1-6 nematodes (Hedruris spinigera) also in two specimens. Whitebait, Galaxias maculatus attenuatus (Jenyns) Difficulty in sampling shoaling whitebait was caused by iheir habit of diving for deeper water when disturbed. However, a total sample of 199 specimens was obtained, the first shoals appearing along the Moncks Bay-Redcliffs shoreline in mid-august. TABLE 8Biological data for whitebait, Galaxias maculatus attenuatus, from the Avon-Heathcote Estuary (- = not recorded) Date of Capture &(«) T.L. & (S.L.) (mm) (g) Sex & Gonad Maturity Sampling Locality September 1965 (75) November 1965 (80) 5 November 1965 (1) December 1965 (25) February 1966 (7) April 1966 (7) 8 April 1966 (1) 8 April 1966 (1) 8 April 1966 (2) 40-70(35-60) 40-70(35-60) 85(78) 40-70(35-60) <2 <2 <2 <2 5 4 Juv. Juv. 311 Juv. Juv. Juv. 9V-VI V -IV Various Various Dyers Road Bridge Various Various Dyers Road Bridge Dyers Road Bridge Dyers Road Bridge Dyers Road Bridge

13 TABLE 10Biological data for eight fish species from the Avon-Heathcote Estuary, (- = = nil) Spscies Red gurnard, Trigla kumu (Lesson & Garnot) Long-finned eel, Anguilla dieffenbachi (Gray) Smelt, Stokellia anisodon (Stokell) Gar, Reporhamphus ihi (Phillips) Barracouta, Thyrsites atun (Euphrasen) Thornfish, Bovichtus variegatus (Richardson) Seahorse, Hippocampus abdominalis (Lesson) Rigg, Mustelus antarcticus Guenther Sampling Locality & (n) Moncks Bay (4) Dyers Road Bridge (1) Linwood Avenue culvert (1) Moncks Bay (1) Shag Rock (1) Moncks Bay (1) Moncks Bay (1) Moncks Bay (1) T.L. & (S.L.) (mm) 180(150) 180(150) 200(165) 195(160) 250(245) 67(5,8) 280(258) 882(782) 43(38) 165(-) 320(315) (g) Sex & Gonad Maturity S I-II S I $ 1 III (gonads 370 X 40 mm) SI (152juvs in poach) 3 I Gut Contents Shrimps (7) Shrimps (2) Hemigrapsus sp. (2) Galaxias sp. (3) Copepod remains - Algal remains Aldrichetta forsteri (2) Amphipods, Viva lactuca, Porphyra sp. Hemigrapsus sp. (6) Parasites i i i i Hedruris spinigera (nematodes) - Contracaecum (Thynnascaris) aduncum (nematode) Unidentified nematode 318 N.Z. Jo URNAL OF MARI z X > H M m SEARCH [DEC

14 1973] WEBBFISH OF AVON-HEATHCOTE ESTUARY Some measurements were not taken. Sex determination in juveniles was not possible due to the microscopic size of the gonads. The data obtained give little indication of the breeding habits of whitebait in the study area. However, shoals were observed in the vicinity of Dyers Road Bridge and Heathcote Bridge, suggesting that both the Avon and Heathcote rivers are used for breeding. The five adult specimens obtained all had amphipod remains in the gut. The digestive tract of juveniles was visible through the body wall as a ventral silvery line, and most had no food contents. A few specimens variously contained ostracods and mysids (Linwood Avenue culvert area), amphipods (Linwood Avenue culvert and Charleston drain), and polychaete remains (all areas). No parasites were found. Moki, Latridopsis ciliaris (Forster) Six specimens of moki were obtained from Moncks Bay, during the summer months of the study period. TABLE 9Biological data for moki, Latridopsis ciliaris, from the Avon-Heathcote Estuary, (- = not recorded) Date of Capture T.L. & (S.L.) Sex & Gonad & (re) (mm) (g) Maturity 22 November (2) 280(230) 238 -II 22 November (2) 288(232) 242 T 9 December (1) 272(225) 175 -III 17 February (1) 300(240) April (2) 322(260) - 19 April (2) 352(328) - -II Considering that moki are known to grow to 9 kg in weight, these specimens were probably maturing juveniles using the estuary for feeding. Examination of gut contents revealed crab remains (Hemigrapsus sp., Ovalipes sp.) in one specimen, amphipods in all six, mollusc remains (Paphies australe, Mytilus edulis aoteanus) in two, hydrozoan remains in one, and detritus. No parasites were found. Of the remaining eight fish species found in the study area, four specimens were obtained of red gurnard, and one each of long-finned eel, smelt, garfish, barracouta, thornfish, seahorse, and rigg. Biological data for these eight species is summarised in Table 10. Most species recorded in this study provided insufficient specimens, and hence data, for any broadly significant conclusions to be reached about their status in the Avon-Heathcote Estuary.

15 320 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [DEC. ACKNOWLEDGMENTS I wish to thank Professor G. Knox and Dr J. F. C. Morgans, Zoology Department, University of Canterbury, for advice during the thesis stage; Mr T. Dix for parasite identification in Salmo trutta; Dr P. Jansen for identification of Nerocila orbignyi; Mr M. Mitchell for the donation of fish specimens; Mr I. Mannering, Zoology Department, University of Canterbury, for help in mollusc identification; and my colleagues of the Marine Department, Christchurch, for practical assistance in the field. LITERATURE CITED ALLEN, K. R. 1951: The Horokiwi Stream. N.Z. Marine Department Bulletin 10: 231 pp. BOWERS, A. B. 1954: Breeding, and growth of whiting (Gadus merlangus L.) in Isle of Man waters. Journal of the Marine Biological Association of U.K. 33: BRUCE, A. unpublished 1953: Report on a biological and chemical investigation of the waters in the estuary of the Avon and Heathcote rivers. Christchurch Drainage Board report (mimeo), 58 pp. Copy held by author. COAKLEY, A. unpublished 1964: Life history and general biology of Trachelochismus pinnulatus (Forster) (Order Xenopterygii). M.Sc. thesis, University of Canterbury Library. 73 pp. HOOAN, D. J. and WILKINSON, C. 1959: A survey of pollution in the Avon and Heathcote rivers, Christchurch, New Zealand. N.Z. Journal of Science 2: JILLETT, J. B. unpublished 1961: Studies in the biology of Acanthoclinus quadridactylus. M.Sc. thesis, University of Auckland Library. 71 pp. PARROTT, A. W. 1932: Breeding in Salmo trutta. N.Z. Marine Department Fisheries Bulletin 4: : Sea Angler's Fishes of New Zealand. Hodder & Stoughton, London. 176 pp. 1960: The Queer and the Rare Fishes of New Zealand. Hodder & Stoughton, London. 192 pp. STOKELL, G. 1955: Freshwater Fishes of New Zealand. Simpson & Williams, Christchurch. 145 pp. WEBB, B. F. 1972: Fish populations of the Avon-Heathcote Estuary. 1. General ecology; distribution, and length frequency. N.Z. Journal of Marine and Freshwater Research 6 (4) : : Fish populations of the Avon-Heathcote Estuary 2. Breeding and gonad maturity. N.Z. Journal of Marine and Freshwater Research 7 (1 & 2): WOODS, C. S. 1963: Native and Introduced Freshwater Fishes. Nature of New Zealand series. A. H. & A. W. Reed, Wellington. 64 pp.

16 1973] WEBBFISH OF AVON-HEATHCOTE ESTUARY APPENDIX 1Gonad maturity index (modified from Bowers 1954) Male IImmature; testes small, no sperm II-Mature unripe; sperm extruded on cutting and squeezing III-Ripe; as for II, but testes enlarged and lobate IVRipe running; as for III, but milt extruded by pressure V Spent; testes crinkled and shrunken, little sperm left. Female Iimmature; ovaries very small, translucent, eggs microscopic IIMature unripe or virgin maturing; ovaries small to moderate, eggs microscopic, ovaries often translucent IIIMature ripening; ovaries of moderate size, eggs visible and opaque IVAlmost ripe; ovaries enlarged and distended, eggs clearly visible and opaque VRipe; ovaries enlarged and distended, tunica bursts easily, some eggs transparent VIRipe running; nearly all eggs transparent, eggs extruded by slight pressure VIISpent; ovaries flaccid and shrunken, with some residual eggs.