Fish Populations in a Tidal Estuary in Marlborough Sounds, New Zealand, from 1971 to 2004.

Transcription

1 Fish Populations in a Tidal Estuary in Marlborough Sounds, New Zealand, from 1971 to J. Roger Bray and Gwendolyn J. Struik P. O. Box 494, Nelson 7040, New Zealand Fishbooknz@gmail.com J. Roger Bray and Gwendolyn J. Struik, 2006

2 Published in 2006 and obtainable from Copyright J. Roger Bray and Gwendolyn J. Struik 2006 P. O. Box 494, Nelson 7040, New Zealand All rights reserved. This book is copyright. With the exception of fair dealing for purposes of research or private study, or criticism or review, no part of this publication may be reproduced, stored or transmitted in any form or by any means, without prior permission in writing from the copyright holders. Copying for general distribution, for advertising or promotional purposes, for creating new collective works or for resale is prohibited. Special requests should be addressed to the copyright holders. ISBN Acknowledgements We thank Anne and Vic Marchant, Greg and June Harney, Claire and Ernie Twose; and Paul Creswell and Scott Williamson of Ministry of Fisheries; N.Z. Lottery Science Research, and the libraries of Canterbury University, Greta Point fisheries research and Nelson. About the Authors J. Roger Bray and Gwendolyn Struik have doctorates in plant and animal ecology from the University of Wisconsin. After teaching and research in the U.S.A and Canada, they moved to New Zealand in 1963 and have lived in Nelson and Duncan Bay where, since 1971, they have worked on forest regeneration, possum populations and estuarine fish. Dr. Bray has published over 70 papers in scientific journals and books in North America, Europe and Australasia on ecology and climatology, and has worked at the Universities of Minnesota and Toronto and at D.S.I.R. in New Zealand. Dr. Struik has scientific publications on forest ecology in North America, grasslands ecology and fisheries in New Zealand and has worked at Wheaton College, Nelson Polytech and D.S.I.R.

3 Fish populations in a tidal estuary in Marlborough Sounds, New Zealand from 1971 to J. R. Bray and G. J. Struik (2006). ABSTRACT From 1971 to 2004, we sampled the fish populations of Te Mako tidal estuary in Marlborough Sounds, New Zealand by setting a monofilament net, at low tide, in the same location for a total of 2832 tides. Fifteen hundred and eighteen fish of 23 species were caught and measured. Results showed percent tidal occurrence was 26, number per tide 0.54, mean weight per fish 783g, weight per tide 420g, mean length per fish 355 mm and length per tide 190 mm. The eleven major species, followed by family name and weight per tide, were divided into Early Dominants- Rig (Inshore shark) 73g and Yellow-eyed mullet (Mullet) 12g, Mid Dominants- Snapper (Seabream) 68g and Barracouta (Snake mackerel) 14g, Later Dominants- Kahawai (Kahawai) 119g, Warehou (Raft) 40g and Spotty (Wrass) 3g, and Invaders- Flounder (Right-eyed flounder) 29g, Grey mullet (Mullet) 14g, Blue mackerel (Tuna) 9g and Dab (Right-eyed flounder) 3g. Predominant species were the Early Dominants in the early and late 1970s, the Mid Dominants in the mid 1970s, followed by the Invaders in the early to mid 1980s and the Later Dominants thereafter. A schooling index was inversely related (Rs -0.98, p<.01) to percent of single individuals per tide. Of 55 species pairs, 18 had significant positive associations and none were significantly negative. Positive interspecific association was related to intraspecific association, to an environmental variable and to food preference, which indicated fisheating species had the highest percentage of significantly associated species pairs, while invertebrate and bottom feeders were less associated with other species. All species showed distinctive seasonal, temperature, rainfall and day/night distributions, and nearly every species peaked on a new or waning moon. A significant relationship was shown between spring precipitation and a consequent increase in fish weight and length followed in the next year by increases in weight, length and number per tide, and percent tidal occupancy, which may reflect a flushing of nutrients from land to sea during the crucial vernal warming period. The population variables for the sum of all species declined between and and, especially, from to when there were declines in weight per fish (71%), length per fish (48%), number per tide (70%), weight per tide (91%), length per tide from (85%) and occupied tides (46%). These massive declines may reflect the large increase in unregulated foreign fishing vessels in New Zealand from 1967 to 1977, subsequent increase in domestic fishing, deterioration of nearby benthic communities by trawling and dredging, and an increase in nutrient loss to farmed mussels.

4 Fish populations in a tidal estuary in Marlborough Sounds, New Zealand from 1971 to J. R. Bray and G. J. Struik (2006). SHORT ABSTRACT Fish netted in a tidal New Zealand estuary from 1971 to 2004 declined between and by 46% in percent occupied tides, 70% in number per tide, 71% in weight per fish, 91% in weight per tide, 48% in length per fish and 85% in length per tide. There was a shift from Early to Mid Dominant species followed by fluctuation between Later Dominants and, briefly, Invaders. Degree of interspecific association was significantly dependent on food preference, a seasonal variable and level of intraspecific association. Spring precipitation was positively related to increases in fish weight and length, followed in the next year by increases in number, weight and length per tide.

5 Table of Contents Chapter page Summary Introduction Site description and sampling methods Te Mako fish species and their New Zealand distribution Fish species data summary Species numbers, weights and lengths Species Importance Index Intraspecific and interspecific association Stomach content and fullness, food preference and interspecific association Species number, diversity and presence Diversity and global abundance-weight profiles Biyearly fish population variables Percent changes in the six biyearly population variables Biyearly running means for weight per tide and length per tide Early, Mid and Later Dominants and Invaders Environmental variables and fish populations Yearly fish population variables and precipitation Te Mako fish population trends References... 71

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7 Fish populations of a New Zealand estuary from 1971 to Bray & Struik (2006) 1 SUMMARY Chapter 1. Introduction. A monofilament net was set at monthly intervals on 493 occasions and 2832 tides from 1971 to 2004, at low tide, in the same location in Te Mako estuary, Duncan Bay, Marlborough Sounds, New Zealand (41 o 7 35 S, 173 o E). Chapter 2. Site description and sampling methods. Te Mako estuary has a catchment of warm temperate rain forest, sheep pasture and coastal shrubs, sedges and rushes. The estuary is tidal with patches of sand, silt and Eel grass. The set net was 27.4 m with stretched mesh size of 124 mm. Fish caught were weighed and measured. Chapter 3. Te Mako fish species and their New Zealand distribution. Of the twentythree species netted, there was a mean overlap with eleven New Zealand estuarine and coastal sites of 64%. For the eleven major species, the mean overlap was 75% with 91 to 100% overlap with the three closest sites. Chapter 4. Fish species summary. Eleven major species occurred in twelve or more years and twelve minor species occurred in three or less years. Seven original major species were first caught between 1971 to 1974, and four later arrivals first caught from 1977 to Number per tide x 1000 and mean weight per tide were Kahawai 130 and 119g, Warehou 110 and 40g, Yellow-eyed mullet 80 and 12g, Yellowbelly Flounder 68 and 29g, Snapper 53 and 68g, Blue mackerel 19 and 9g, Rig 19 and 73g, Barracouta 16 and 40g, Spotty 16 and 3g, Dab 9 and 3g, Grey mullet 7 and 14g. Chapter 5. Species weights, lengths and numbers. Mean weight per species was 1147g, mean length per species 418 mm, weight per tide 18g, length per tide 8 mm and number per tide Total number of individuals per tide was 0.54, of weight per tide 420g and of length per tide 190 mm. Chapter 6. Species Importance Index. A percent Importance Index based on an equal weighting of three relative frequency, two relative dominance and one relative abundance value showed Kahawai, with an Index of 22.7%, was double the amount for each of the next four highest species, Warehou, Yellow-eyed mullet, Flounder and Snapper. Chapter 7. Intraspecific and interspecific association. The percent of single individuals in an occupied tide varied from 31 for Rig to 96 for Barracouta and Spotty. Schooling indexes were a near mirror image of percent single individuals, varying from 1.0 for Barracouta and Spotty to 1.9 for Blue mackerel, 2.2 for Rig and 3.3 for Warehou. Number of species per tide varied from zero to four and an index of occupied tides for the eleven major species was significantly correlated with the number of their significantly associated species pairs. Of 55 species pairs, 18 had positive significant interspecific associations. When the 55 species pairs were divided into three levels of declining interspecific association, then in seven out of eight instances (X 2 4.5, p<.05) there was a decline in the rank correlations between the species pairs and four environmental variables, but only the seasonal variable was significantly related to the species pairs when they were considered separately.

8 2 Chapter 8. Stomach content and interspecific association. Kahawai and Barracouta eat mainly fish; Warehou, Snapper and Blue mackerel eat invertebrates and fish, Rig and Spotty eat mainly invertebrates, and Yellow-eyed mullet, Flounder, Dab and Grey mullet eat mainly invertebrates and benthic plants, detritus and sediments. The more a species depends on other fish for food, the higher its percentage of significant positive interspecific associations. Species which eat mainly invertebrates, or are bottom and detritus feeders, have the lowest percentage of significantly associated species pairs. These connections between food preference and interspecific association, and the correlations between intra and interspecific association and between an environmental variable and interspecific association illustrate the complexity of the relationships which underlie fish interspecific associations. Chapter 9. Species number, diversity and presence. When the influence of search effort on the number of species found was reduced by dividing species numbers by the square root of the number of tides, then the transfomed number of new species per year declined from an initial maximum in to and then increased to the present. This increase occurred during a time when the species population variables were declining which raises doubts of the usefulness of species diversity as an indicator of ecosystem stability or productivity. Chapter 10. Diversity and global abundance-weight profiles. If diversity is judged by degree of approach to a multitypic model in which each species has the same abundance or weight per tide then, by two different tests, abundance-weight profiles for Te Mako are more diverse than the mean of 52 global studies. Chapter 11. Biyearly fish population variables. The eleven major species were analysed for changes in six population variables during 17 biyearly periods from 1971 to 2004 and during two halves from and Between the first and second halves: Ten of the eleven species declined in percent of occupied tides with declines of 89, 80, 77 and 74% for Rig, Spotty, Snapper and Dab, and a mean decline of 53%. Ten species declined in number per tide with a mean decline of 54%. Rig, Blue mackerel, Spotty, Snapper and Dab each declined by over 70%. Eight species declined in mean weight per fish, with increases for Rig and Grey mullet that were not statistically significant. The largest declines were for Warehou 31%, Kahawai 30%, Barracouta 29%, Dab 25% and Yellow-eyed mullet 25%. All the eleven species declined in weight per tide by a mean of 64%. Major decreasers were Rig 94%, Spotty 83%, Snapper 82%, Dab 81% and Blue mackerel 79%. Eight species decreased in length per fish, with a mean decline of 5%. Species declines were less than for weight per fish, but the rank correlation between the two variables was significant (Rs 0.93, p<.01).

9 Fish populations of a New Zealand estuary from 1971 to Bray & Struik (2006) 3 All major species declined in length per tide by from 9% to 96% with a mean of 60%. Largest declines were by Rig 96%, Blue mackerel 87%, Spotty 84%, Snapper 81% and Dab 79%. Weight per tide and length per tide had a significant rank correlation (Rs 0.81, p<.01). Population variables calculated for the sum of all twenty-three netted species showed declines between and of 27% for percent of occupied tides,18% for number per tide, 52% for weight per fish, 30% for length per fish, 64% for weight per tide and 50% for length per tide. Chapter 12. Percent changes in the six biyearly population variables. Between the first and second halves there were 58 declines and 8 increases (X p<.001) in the 11 major fish species for the 6 population variables. Chapter 13. Biyearly running means for weight and length per tide. Non-weighted running means for both weight and length per tide showed six patterns: 1) steep declines for Rig and Yellow-eyed mullet, 2) sustained declines interrupted by lesser recoveries for Barracouta and Snapper, 3) persistent declines for Kahawai with two moderate recent recoveries, 4) declines to nil for Warehou and Spotty, then increase to secondary peaks and further decline, 5) increase from nil to peaks in mid 1980s for the major early invaders Blue mackerel, Dab, Flounder and Grey mullet followed by steep to gentle declines, 6) very slow increase for the eleven later invaders. Chapter 14. Early, Mid, and Later Dominants, and Invaders. Patterns of change in the number per tide and weight per tide were used to designate periods of dominance for four dynamic groups: 1) Early Dominants, Rig and Yellow-eyed mullet, , ; 2) Mid Dominants, Snapper and Barracouta, , , ; 3) Later Dominants, Kahawai, Warehou and Spotty, , ; 4) Invaders , The three groups of Dominants declined from to and partially recovered to accompanied by the appearance and rapid increase of Invaders from to Invaders then declined and the Later Dominants increased to the present with minor increases for the Early and Mid Dominants. Chapter 15. Environmental variables and fish populations. Every major species had a strong seasonal occurrence and every bimonthly period had at least one dominant species except March-April. Warehou peaked in July-August, Blue mackerel and Barracouta in September-October, Yellow-eyed mullet and Snapper in November- December, Rig, Spotty and Grey mullet in January-February and Kahawai and Flounder in May-June. Warehou and Barracouta declined from colder to warmer intervals, Kahawai, Blue mackerel, Flounder and Dab peaked in the second coldest interval, Snapper in the second warmest and Rig, Spotty, Yellow-eyed mullet and Grey mullet in the warmest. Yellow-eyed mullet, Rig, Spotty and Grey mullet peaked in the lowest rainfall period, Warehou and Dab in the intermediate period and Blue mackerel, Kahawai, Barracouta, Snapper and Flounder peaked strongly in the highest interval. Warehou, Blue mackerel, Yellow-eyed mullet, Spotty, Grey mullet and Dab peaked on a waning moon in the Last Quarter. Kahawai, Snapper and Rig peaked on the New Moon, Flounder on a waxing moon in the First Quarter and Barracouta on the Full Moon.

10 4 Warehou, Blue mackerel, Barracouta, Yellow-eyed mullet and Snapper appeared from 79% to 90% on night tides, the other species occurred 63% to 68% on night tides. Chapter 16. Yearly fish population variables and precipitation. The population variables were not related to Te Mako yearly precipitation, but there were highly significant relationships between spring precipitation and weight and length per fish and between summer precipitation and both weight and length per tide and the other three variables. There were discrete sequences from spring precipitation to the population variables. The basis for these sequences may be increased spring and summer rainfall, especially during the crucial vernal warming period, which resulted in increased flushing of nutrients from the land to ocean with a consequent increase in plankton at the bottom of the food chain, an increase in weight and length per fish and a subsequent increase in weight and length per tide and the other population variables. Chapter 17. Te Mako fish population trends. The six population variables for all species declined 40% from to and declined 69% from to which had losses of 46% for occupied tides, 48% length per tide, 70% number per tide, 71% weight per fish, 85% length per tide and 91% weight per tide. Dominant species shifted from Early to Mid to Later Dominants and, briefly, Invaders, but all major species have persisted. The decline in the six fish population variables at Te Mako may be the result of: 1) a large increase in unregulated foreign fishing vessels in New Zealand which removed a catch of from 20,000 t in 1968 to a peak 500,000 t in 1977, 2) rapid increase in domestic commercial and recreational fishing and the use of new technology, 3) destruction of nearby benthic communities by trawling and dredging, and, 4) increase in farmed mussels in Pelorus Sound which feed on the plankton base of the food chain. If the pressures which resulted in the fish declines in Te Mako estuary are reduced, then recovery scenarios can be predicted based on short term recovery dynamics observed over the past 34 years. Following a 45% decline, populations may recover to 60% for Dab, Flounder and Grey mullet in 2 to 3 years, for Kahawai, Yellow-eyed mullet, Barracouta, Snapper and Spotty in 5 to >31 years and for Blue mackerel, Warehou and Rig in >19 to >32 years. Mean recovery to 100% was 7 years for the fast species, and >27 years for the medium to slow recovery species. The three fast recovery species plus Spotty were the four least commercially valuable fish. Fast recovery species have a mean age to maturity of 2.9 years and a life span of 8.2 years compared with 3.6 and 23 years for the medium recovery species and 4.7 and 17 years for the slow recovery species.

11 Fish populations of a New Zealand estuary from 1971 to Bray & Struik (2006) 5 1. Introduction For 34 years, from 1971 to 2004, we set a monofilament net on 493 occasions and 2832 tides in the same location in Te Mako estuary, Duncan Bay, Tennyson Inlet, Marlborough Sounds, South Island, New Zealand ( S, E Figure 1). An initial publication (Struik & Bray, 1979) summarised results after the first eight years during which time the number of fish per tide and the mean weight per fish declined significantly for the five species with an adequate sample size for statistical analysis. Since 1994, we have been granted Ministry of Fisheries research permits and supplied them with annual information, for their data bank, on number and size of fish collected, species, number of tides fished, and dates of fishing. 2. Site description and sampling methods 2.1 ESTUARY LOCATION AND SIZE Te Mako tidal estuary is adjacent to the small settlement of Duncan Bay and is a part of a complex 600 km coastline of steep sided drowned valleys jutting north eastward into Cook Strait. The estuary is approximately seven ha in size with a maximum intertidal zone nearly 800 m long and 300 m wide at its widest diameter. The vertical tidal range at the net at high tide varies from 1 to 2.8 m.

12 CATCHMENT DESCRIPTION. The estuary s catchment is warm temperate angiosperm-podocarp rain forest. Some of the lower portion of this forest was selectively logged for podocarp species and all the lower flats were converted to sheep pasture in the late 19 th century. The immediate vicinity of the estuary is rain forest to the east and west, sheep, and occasionally cattle, pasture to the south and open water to the north. The settlement of Duncan Bay has 74 houses, twelve of which are occupied for at least half of the year, the others are occupied during weekends and holidays. All houses are on quarter acre sections, back from the waters edge, with some sections designated or informal forest reserves. On many sections, and on the road margins, the dominant vegetation is regenerating forest. Nearly all the catchment, except for the settlement and the margin of pasture owned by a local farmer, is publicly owned native forest reserve, administered by the N.Z. Department of Conservation. The catchment is drained by a permanent stream which rises to flood levels during high intensity rain storms. 2.3 ESTUARY HABITAT, PLANTS AND ANIMALS The estuary substrate is a matrix of alluvial gravels and small stones with a covering of silt, and occasionally sand, along the stream channels. Seagrass (Zostera), averaging 74 mm in length, grows on the silty edges of feeder streams. There have been very occasional green algal blooms, but the only sustained period, when about 10% of the estuary was covered with sea lettuce (Enteromorpha G. McRaild 1981, p.c.) was in September 1980 to January The intertidal part of the estuary margin is covered with salt meadow rushes (Leptocarpus and Juncus) and low ground plants (Samolus and Sellieria). The surrounding margin above the tidal zone contains Manuka (Leptospermum), Coprosma, and Plagianthus shrubs, mixed with sedges (Mariscus) and pasture plants. These coastal communities are described in Morton & Miller (1968) and Moore & Adams (1963). Shellfish present include Cockle (Chione stutchberyi ), Pipi (Paphies australe) and the non-native Pacific oyster (Crassostrea gigas) which arrived around 1986 and covered about half of the rocky substrate. The native Blue mussel (Mytilus edulis), and Green mussel (Perna canaliculus), seeded in by a local marine farmer in the 1980s, are both in very low numbers now, perhaps due to recreational harvesting or to oyster competition. The oyster population, with its white shells, is very evident still, but appears less robust than a decade ago. The Mud flat crab (Helice crassa) is common and found in the gut of fish such as Snapper and Flounder. Resident estuarine fish, all of which are too small to be caught in our net, include rock fish (Acanthoclinus quadridactylus) and triplefins (Tripterygion spp). In season, there are Galaxias spp in the stream, and these are found in the gut of fish such as Kahawai.

13 Fish populations of a New Zealand estuary from 1971 to Bray & Struik (2006) 7 Birds seen in the estuary while we were clearing the net, in order of decreasing numbers, were hybrid ducks, Spur-winged plover, White-faced heron, Variable oystercatcher (black phase), Paradise shelduck, Black-backed gull, Pied shag, Kingfisher, Welcome swallow, Black swan, White-fronted tern, Australasian gannet, Black-fronted tern, Black shag, Caspian tern, Australasian harrier and Weka (names from Heather & Robertson, 1997). Three aquatic mammals, Dusky dolphin, Orca and New Zealand fur seal have appeared in Duncan Bay, the Dusky dolphin nearly every year, one Orca mother and calf, for one day, and two male seals, one very large, for a residence of about four months. When the seals were present, eaten remains of fish in our net increased and there were large holes in the net on three occasions. These large holes were almost certainly the result of the seals, since no such holes had occurred in the net before they came and none have appeared since they left. Terrestrial mammals in the estuary are humans, dogs, rats, sheep and cattle with the pasture margin extensively grazed by sheep PHYSICAL ENVIRONMENT Rainfall is the major weather factor causing changes in the estuary. The mean annual rainfall in the past twenty years ( ) is 2460 mm with a range from 1620 mm (1985) to 3600 mm (1998). Three high intensity events resulting in stone, sand and silt deposition as well as change in stream courses happened in November 1994 (863 mm) and twice in October 1998 (191 and 536 mm). As far as we could determine, there was no noticeable long-term effect on bird or fish life in the estuary after these events. Air temperatures vary from 5 C to +35 C, but rarely reach these extremes. Ground frosts occur between 26 March and 2 October, with a mean of 37 per year (Bray, 1991). Frosts occur less frequently in the estuary than on the surrounding low open slopes. 2.5 SAMPLING METHODS A monofilament 27.4 m set net, stretched mesh size 124 mm, 16 units high was placed in the same position in the estuary at about one third the distance from the lowest low tide. The water depth at the net at high tide varied from approximately 1 m to 2.8 m. The net was cleared at all low tides, except when the low tide occurred in the middle of the night. Fish caught on these "double tides" could often be assigned to a single tide by their condition, and double tides which included only one fish could also be used in summary calculations. There were only two of our quantitative calculations, night and day tides and percent occupied tides, for which the remaining double tides could not be used. All fish caught were weighed and measured. In the early years, , weights were in pounds and ounces with an accuracy of 150 grams and smaller fish weighed together for an average measurement. After 1978, weights were to 10g accuracy and fork length measured to 1mm accuracy. Some lengths prior to 1978 were estimated from weight/length graphs of fish caught From , sampling was done throughout the year but on an irregular basis dictated by factors unrelated to the study. Since 1990, at least 8 tides per month were sampled (except January and February 1994). In the 34 years of the study 2832 tides and 1518 fish were sampled.

14 Te Mako fish species and their New Zealand distribution 3.1. FISH SPECIES IN TE MAKO ESTUARY Twenty-three fish species were netted and six species stranded in Te Mako estuary from Our species symbols, together with common, scientific and family names as in Ayling & Cox (1984), are shown in Table 1, with the order of species based on the number of individuals sampled. There were four cartilaginous species netted, Rig, Eagle ray, Elephant fish and Carpet shark, and nineteen bony species, Kahawai, Warehou, Yellow-eyed mullet, Flounder, Snapper, Blue mackerel, Barracouta, Spotty, Dab, Grey mullet, Jack mackerel, Blue cod, Trevally, Red mullet, Gurnard, Red cod, Red snapper, Skipjack tuna and Spotted stargazer. The six stranded species, in chronological order of arrival, were Leatherjacket, Estuarine stargazer, Porcupine fish, Ihi (garfish), Short-tailed stingray and Sunfish TE MAKO SPECIES IN OTHER NEW ZEALAND ESTUARIES AND NEAR COASTAL WATERS. Presence of the 23 netted Te Mako species is shown for five New Zealand estuaries (E) and six coastal and offshore waters (W) in Table 2. Te Mako estuary is approximately 600 km from the farthest south site, Otago, and 570 km from the farthest north site of Leigh. The sites are listed from south to north with each site followed by its reference(s): Otago (W), Graham (1956); central Canterbury (W), Beentjes et al,. (2001); Christchurch, Avon-Heathcote (E), Webb (1972, 1973), Owen (1992); Nelson, Waimea (E), Davidson & Moffat (1990), Struik (1975); Nelson (W), Grange et al. (2003); Te Mako (E), this study; Porirua (E), Jones & Hadfield (1985), Leach & Davidson (1976); Southern North Island, New Plymouth, Palliser Bay, Whakatane (W), Hickford et al. (1997); Napier, Ahuriri (E), Kilner & Akroyd (1978); Auckland, Manukau (E), Morrison et al. (2002); Hauraki Gulf (W), Kendrick & Francis (2002); and Leigh (W), Thompson (1981). No species was present in all of the eleven non- Te Mako sites of Table 2, but Kahawai, Yellow-eyed mullet, Barracouta, Dab, Gurnard, Red cod and Spotted stargazer were present in ten sites and Flounder, Spotty and Trevally were present in nine sites, so that nearly half the Te Mako species could be regarded as widely distributed. Snapper, Blue mackerel and Rig, three other major Te Mako species, occurred in eight of the sites, while Warehou was present in six of the eleven other sites. Grey mullet was in four of the sites around Nelson and northwards, but not further south in Canterbury or Otago. Three species, Red snapper, Skipjack tuna and Sunfish, which occur in the far north of New Zealand appeared only once, in each case in mid summer, and all since The percentages by which the 23 Te Mako species appeared in the eleven estuarine and coastal sites in Table 2 from south to north were 70, 70, 48, 70, 78, 78, 74, 57, 26, 78 and 61 with a mean percentage of 65 %. Overlap for only the eleven major Te Mako species with the eleven estuaries and coastal waters was substantially higher, with percentage values of 82, 82, 64, 91, 91, 100, 64, 82, 36, 87 and 54 with a mean of 75 %. There was an expected close percentage affinity of 91, 91 and 100% for the three nearest geographic

15 Fish populations of a New Zealand estuary from 1971 to Bray & Struik (2006) 9 Table 1. Fish species symbols, common, scientific and family names of the 23 netted and 6 stranded species in Te Mako estuary , listed in order of abundance. Eleven major species, from Kahawai to Grey mullet (in bold type), and 12 minor species, from Jack mackerel to Spotted stargazer, were netted. The remaining 6 species (in italics) were stranded. Nomenclature Ayling & Cox Symbol Common name Scientific name Family name K Kahawai Arripis trutta Arripidae W Warehou Seriolella brama Centrolophidae Y Yellow-eyed mullet Aldrichetta forsteri Mugillidae F Flounder, Yellow-belly Rhombosolea leporina Pleuronectidae S Snapper Chrysophrys aureus Sparidae Bm Blue mackerel Scomber australasicus Scombridae R Rig Mustelus lenticulatus Triakidae B Barracouta Thyrsites atun Gemphylidae Sp Spotty Pseudolabrus celidotus Labridae D Dab, Sand flounder Rhombosolea plebeia Pleuronectidae G Grey mullet Mugil cephalus Mugillidae J Jack mackerel Trachurus declivus Carangidae C Blue cod Parapersis colias Mugiloididae T Trevally Caranx georgianus Carangidae Rm Red mullet Upeneichthys lineatus Mullidae E Elephant fish Callorhynchus milii Callorhinchidae Gu Gurnard Chelidonichthys kumu Triglidae Rc Red cod Pseudophycis bachus Moridae Er Eagle ray Myliobatis tenuicaudatus Myliobatididae Rs Red snapper Centroberyx affinis Berycidae St Skipjack tuna Katsuwonus pelamis Scombridae Cs Carpet shark Cephaloseyllium isabella Scyliorhinidae Ss Spotted stargazer Genyagnus novaezelandiae Uranoscopidae L Leatherjacket Parika scaber Balistidae Es Estuarine stargazer Leptoscopus macropygus Leptoscopidae P Porcupine fish Allomycterus jaculiferus Diodontidae I Ihi, Garfish Hyporhamphus ihi Hemiramphidae Su Short-tailed stingray Dasyatis brevicaudatus Dasyatidae Su Sunfish Mola mola Molidae

16 10 Table 2. Distribution data for the 23 Te Mako species. Location of Te Mako species in other New Zealand estuaries (E) and in coastal waters (W): in Otago (O), Canterbury (C), Nelson (N), Te Mako (T), Porirua (P), southern North Island (S), Ahuriri, Napier (A), Manakau (M), Hauraki Gulf (H) and Leigh (L), listed from south to north. Eleven major species are in bold type. Spp Habitat ( W or E) and Location (O, C, N, T, P, S, A, M, H, L) Sym W O W C E C E N W N E T E P W S E A E M W H W L K x x x x x x x x x x x W x x x x x x Y x x x x x x x x x x x F x x x x x x x x x x S x x x x x x x x x Bm x x x x x x x x x R x x x x x x x x x B x x x x x x x x x x x Sp x x x x x x x x x x D x x x x x x x x x x x G x x x x x J x x x x x x x C x x x x x x x x T x x x x x x x x x x Rm x x x x x E x x x x x x Gu x x x x x x x x x x x Rc x x x x x x x x x x x Er x x x x x x x Rs x x St x Cs x x x x x x Ss x x x x x x x x x x x Data sources: WO-Graham 1956; WC-Beentjes et al. 2002; EC-Webb 1972, 1973, Owen 1992; EN-Davidson & Moffat 1990, Struik 1975; WN-Grange et al. 2003; ETthis study; EP-Jones & Hadfield 1985; Leach & Davidson 1976; WS-Hickford et al. 1997; EA-Kilner & Akroyd 1978; EM-Morrison et al. 2002; WH-Kendrick & Francis 2002; WL-Thompson 1981.

17 Fish populations of a New Zealand estuary from 1971 to Bray & Struik (2006) 11 sites to Te Mako: Nelson s Waimea estuary and Nelson coastal waters on the South Island and Porirua estuary on the North Island. From the south to north, the percentage overlap was 62% southern South Island, 69% northern South Island, 70% southern North Island, 55% northern North Island. For the eleven major Te Mako species the mean percent overlap from south to north was 76, 91, 82 and 58. These patterns show little difference in the mean overlaps south or north of Te Mako for the 23 species present, but a closer affinity for the sites immediately south of Te Mako for the eleven major species. The Te Mako estuarine species were not closely similar with New Zealand estuaries at a great distance as shown by percent overlap values of 48 for the Avon-Heathcote estuary, Christchurch, South Island and 26 for the Manukau estuary in Auckland northern North Island. The two closest estuaries to Te Mako, Nelson s Waimea and Porirua both had percent overlap values of 78, nearly twice the mean percentage for the three most distant sites. The six major Te Mako species that are shallow bottom feeders, Yellow-eyed mullet, Flounder, Dab, Grey mullet, Spotty and Rig occur in 89% of the estuaries and 67% of the coastal waters in Table 2, while the five species that are mainly pelagic, Kahawai, Warehou, Snapper, Blue mackerel and Barracouta occur in 67% of the estuaries and 87% of the coastal waters.

18 Fish species data summary 4.1. YEAR SPECIES FIRST APPEARED Six original species, Kahawai, Warehou, Yellow-eyed mullet, Snapper, Rig and Barracouta were caught in 1971 and together with Spotty, which was first caught in 1974, comprised 30 percent of the twenty-three species (Table 3, column 2). Five early invader species Flounder, Blue mackerel, Dab, Gurnard and Grey mullet were first caught between 1977 and 1981 and eleven later invaders were caught in two batches, Blue cod, Elephant fish, Trevally and Jack mackerel in and Red mullet, Red cod, Eagle ray, Skipjack tuna, Red snapper, Carpet shark and Spotted stargazer from Six species stranded in the estuary were Leatherjacket in 1972, Estuarine stargazer in 1974, Porcupine fish in 1974, Ihi in 1995, Short-tailed stingray in 1996 and Sunfish in TOTAL YEARS SPECIES CAUGHT The twenty-three species caught at Te Mako separate into two distinct groups: eleven major species which appeared in twelve or more of a possible thirty-four years and twelve minor species which were present in three or less years. The major species were present in from 33 to 97 percent of the 34 years while the minor species varied from 3 to 9 percent (Table 3, column 3). Of the eleven major species Kahawai, Yellow-eyed mullet and Snapper were netted in 30 to 33 years, Flounder and Barracouta in 25 years, Blue mackerel in 20 years, and Rig, Spotty, Warehou, Dab and Grey mullet in 12 to 15 years. Of the twelve minor species, seven were netted in 2 or 3 years, and five in only one year. 4.3 NUMBER OF SEASONS SPECIES CAUGHT The total number of times in which a species occurred in the summer (January, February, March), autumn (April, May, June), winter (July, August, September) and spring (October, November, December) is shown in Table 3, column 4. There were a total of 136 seasons for the period Yellow-eyed mullet occurred in 87 seasons, Kahawai in 82, Flounder in 70 and Snapper in 65 seasons, which were between 64 % and 48 % of the total possible seasons. Barracouta, Spotty, Warehou and Blue mackerel were in 26 to 18 percent of the total possible seasons, Rig, Dab and Grey mullet were around 12 % and the remaining twelve species occurred in less than 3% of the total seasons NUMBER OF TIDES SPECIES CAUGHT The number of tides on which each species was netted varied from 1 to 228 (Table 3, column 5). Of the 2832 tides for which the net was set, at least one fish was caught on 724 tides, a total of 26 % occupied tides. The five most common species, Kahawai, Warehou, Yellow-eyed mullet, Flounder and Snapper occurred in 228 to 93 tides for a total of 779 tides which was 79 % of the total number of tidal occurrences of 986 by all

19 Fish populations of a New Zealand estuary from 1971 to Bray & Struik (2006) 13 Table 3. Summary data for 23 netted Te Mako species plus 6 stranded species, Species symbol, first year caught or stranded, number of years caught, number of seasons caught, number of tides caught, number of fish caught (Abundance), total fish weight (kg) and total length of fish (cm). Species listed in order of abundance. Eleven major species are in bold type, the six stranded species are in italics. Species Symbol 1 st year caught Number of years Number seasons Number of tides* Number of fish Weight (kg) Length (cm) K W Y F S Bm R B Sp D G J C T <1 60 Rm E Gu Rc Er Rs St Cs Ss <1 18 L Es P I Sh Su *Double tides counted as a single tide when more than one fish of a species caught. There were 88 such tides.

20 14 species. The other six major species from Barracouta to Grey mullet were present in from 17 to 45 tides, a total of 180 occurrences, 18% of the total. The remaining twelve minor species had 27 tidal occurrences, less than 3% of the total. The number of tidal occurrences for the Te Mako species is closely related to the number of fish caught as shown by a rank correlation between the number of tidal occurrences and the number of individuals (Rs +0.87, p<.01) for the eleven most common species. The first five major species do not have a significant correlation between number of tidal occurrences and individuals (Rs p>.05) because of the low number of tidal occurrences of Warehou which has a ratio of 93 tides to 304 individuals (31 %) compared with 228 tides and 367 individuals for Kahawai (62 %) NUMBER OF FISH CAUGHT Fish abundance for the 23 netted species (Table 3, column 6) ranged from 367 to 1, with a well spread distribution between 24.1% and 0.1 % of the total. The five most common species, Kahawai with 367, Warehou with 304, Yellow-eyed mullet with 227, Flounder with 193 and Snapper with 151 made up 1242 or 82 % of the total catch while the six intermediate species from Blue mackerel with 55 to Grey mullet with 20 made up 16% of the total catch. The twelve minor species with 7 or less individuals made up the remaining 2 %. The well spread abundance values of Te Mako fish numbers contrasts with many estuaries and on-shore fisheries summarised in Chapter WEIGHT OF FISH CAUGHT The total weight of the 23 fish species ranged from less than 1 kg to 338 kg (Table 3, column 7) with a total catch of 1188 kg. Five species exceeded a total weight of 100 kg, Kahawai 338, Rig 208, Snapper 192, Barracouta 114 and Warehou 113 kg. Flounder, Grey mullet, Yellow-eyed mullet and Blue mackerel were between 81 and 25 kg, and all the other species were 11 kg or less, with eleven species 3 kg or less. 4.7 LENGTH OF FISH CAUGHT Total length of fish caught varied from 18 cm for Spotted stargazer to cm for Kahawai with six species, Kahawai, Warehou, Flounder, Snapper, Rig and Yellow-eyed mullet over 5000 cm. In spite of large differences in species shapes, the total length of the eleven major species (Table 3, column 8) was correlated with their total weight (Rs +0.79, p<.01). Yellow-eyed mullet had the highest length (cm) over weight (kg) ratio of 152 and Grey mullet, Rig, Snapper and Barracouta had the lowest ratios from 26 to 32. Kahawai, Warehou and Flounder, which had the three highest total lengths had intermediate length over weight ratios of from 41 to 79. The lowest ratio for the minor species was 15 for the broadly shaped Eagle ray.

21 Fish populations of a New Zealand estuary from 1971 to Bray & Struik (2006) Species numbers, weights and lengths 5.1 MAXIMUM, MINIMUM AND MEAN WEIGHTS AND LENGTHS Maximum weight per fish (Table 4) varied from 200g for Trevally to 7755g for Eagle ray. Mean weights were from 113g for Trevally to 5690g for Eagle ray and minimum weights were from 25g for Yellow-eyed mullet to 3625g for Eagle ray. Minimum lengths varied from 110 to 730 mm, maximum from 230 to 1150 mm and means from 180 to 1028 mm. A comparison of Te Mako species maximum lengths with maxima quoted in the literature shows nine of our species exceeded 75% of the quoted maxima including Rig, Kahawai, Flounder, Blue mackerel, Spotty, Dab, Grey mullet, Red mullet and Eagle ray. Only two very low abundance species, Blue cod and Trevally, were less than 50% of their maximum quoted lengths. 5.2 NUMBER, WEIGHT AND LENGTH PER TIDE The three major productivity variables, fish number per tide, weight per tide and length per tide are shown in the last three columns of Table 4. Number per tide x for the major species varied from 4 to 1296, with Kahawai and Warehou more than 1000, seven species from 159 to 802, two species from 71 to 92 and the remainder less than 25. There was a less even distribution for weight per tide due to greater differences in weight per fish. Eight species had more than 10 g per tide and 10 species were less than 1 g per tide. Eighty-one percent of the total weight per tide was concentrated in five species, Kahawai, Rig, Snapper, Warehou and Barracouta. Length per tide was dominated by six species which had over 18mm per tide, Kahawai, Warehou, Yellow-eyed mullet, Flounder, Snapper and Rig. Length per tide data were closely related to weight per tide (Rs +0.94, p<.01). Mean species weight per fish was 1147g, weight per tide 18.2g, length per fish 418 mm, length per tide 8.3 mm and number per tide For the ecosystem as a whole, the weight per fish was 783g, weight per tide 420g, length per fish 355 mm, length per tide 190 mm and number per tide 0.54.

22 16 Table 4. Maximum, mean and minimum weight and length per fish, number per tide times 10000, weight per tide in grams and length per tide in mm, for 2832 tides, Literature maximum lengths from Ayling & Cox 1984, Graham 1956 and Paul Eleven major species are in bold type Weight per fish grams Length per fish mm. Number per tide Weight per Length per Spp Max. Mean Min. Max. lit. Max. Mean Min. x tide grams tide mm. K W Y F S > Bm R B Sp D G J C T Rm E Gu Rc Er Rs St Cs Ss Means

23 Fish populations of a New Zealand estuary from 1971 to Bray & Struik (2006) Species Importance Index. 6.1 RELATIVE FREQUENCY Quantitative data on fish frequency, abundance and dominance were converted to a relative basis to allow direct comparisons between species and to facilitate the construction of a single index of the relative importance of the different species (Table 5). Three relative frequency values for years caught, for seasons caught and for tides caught are summarised in Table 5, columns 2 to 4, and the means are shown in column 5 as a single relative frequency value. The distribution of relative frequency values in columns 2, 3 and 4 of Table 5 shows Kahawai, Yellow-eyed mullet, Flounder and Snapper had the highest values in each of the three frequency distributions. Relative number of years caught (column 2) was strongly dominated by Snapper, Yellow-eyed mullet and Kahawai with values of 11.7 % to 12.9 %. The other major species varied from 4.7 % to 9.8 % and the minor species from 0.4 % to 1.2 %. The 23 values for percent years caught had a well spread distribution with no large breaks or dominance by a single species, possible evidence of a stable and mature fish population. The relative number of seasons caught had the same five major species as did the number of years caught, but with slightly higher relative values. Relative number of seasons caught had a highly significant rank correlation with relative number of years caught (Rs +0.97, p<.01) and with the number of tides caught (Rs +0.99, p<.01). The relative number of tides on which the five major species were caught had a slightly closer rank correlation with number of seasons caught (Rs +0.99, p<.01) than with the number of years caught (Rs +0.96, p<.01). 6.2 RELATIVE ABUNDANCE Relative abundance values in Table 5, column 6, again demonstrate the importance of the five most numerous species which have a total relative abundance of 82 percent. The five most abundant species include four species, Kahawai, Yellow-eyed mullet, Flounder and Snapper, which are in common with the five highest mean relative frequency species in column 5. Three of the most abundant species, Kahawai, Snapper and Warehou are in common with the highest relative dominance species in column RELATIVE DOMINANCE The two relative dominance data sets (Table 5, columns 7, 8) of weight per tide and length per tide have a significant positive rank correlation with each other (Rs +0.73, p<.05), but vary in their relationships with the various frequency and abundance distributions. Weight per tide is significantly correlated with weight per fish (Rs +0.73, p<.05), but not with abundance (Rs +0.50, p>.05) while length per tide and abundance have a highly significant correlation (Rs +0.95, p<.01), but length per tide is not correlated with length per fish (Rs +0.19, p>.05).

24 18 Table 5. Relative data for the 23 netted species: 1) three frequency values: Years caught (YC), Seasons caught (SC) and tides caught (TC); 2) Percent frequency (%F) which is the mean of YC plus SC plus TC; 3) Percent abundance (%A), which is the relative number of individuals per species; 4) Two dominance values, Weight per tide (W/T) and Length per tide (L/T); 5) Percent dominance (%Dom) which is the mean of W/T plus L/T. The Importance Index (I. I.) in column 10 is the sum of %F, %A and %Dom (columns 5, 6,and 9) divided by three. Eleven major species are in bold type. Species % % % % % % % % I. I. YC SC TC F A W/T L/T Dom K W Y F S Bm R B Sp D G J C T t Rm E Gu Rc Er Rs St Cs Ss t t t 0.1

25 Fish populations of a New Zealand estuary from 1971 to Bray & Struik (2006) 19 The three summary indexes in Table 5 (columns 5, 6 and 9) relative frequency, relative abundance and relative dominance have significant rank correlations with each other. There is a very high correlation (Rs +0.97, p<.01) between relative frequency and relative abundance. Relative frequency is also significantly correlated with relative dominance (Rs +0.88, p<.01) and relative abundance has a significant, but lower correlation with relative dominance (Rs +0.56, p<.05). 6.4 IMPORTANCE INDEX An Importance Index (Table 5, last column) for each of the 23 Te Mako species was constructed by calculating the mean of the sum of relative frequency in column 5, relative abundance in column 6 and relative dominance in column 9. The distribution of Importance Index values shows that Kahawai, with an Importance Index of 22.7, is nearly double the index for the next four highest species, Warehou, Yellow-eyed mullet, Snapper and Flounder, which varied from an index of 12.9 to The remaining six major species varied in Importance Index from 7.0 to 2.1, with a mean of 4.1. The twelve minor species numbered between seven and one fish with Importance Indexes from 0.6 to 0.1. The two highest minor species had indexes of 0.6 and 0.4 as a result of their relative frequency (Jack mackerel) and their relative dominance (Eagle ray) values. The distribution of the Importance Index values in Table 5 is skewed by Kahawai, which exceeds each of the next four species indexes by nearly double. Comparison of the distribution of the Importance Index values in the last column of Table 5, in descending order, with the distribution of relative abundance and weight profiles for the 122 global studies in Table 15.1, indicates the Te Mako Importance values are closer to a theoretic multitypic model than to a less diverse monotypic model.