,27 The Biology of the New Zealand Snapper By J. Grossland Fisheries Research Division Occasional Publication No. 23 The B¡ology of the New Zealand Snapper By J. Grossland Fisheries Research Division Occasional Publication No. 23 I 981 Published by the New Zealand Ministry of Agriculture and Fisheries Wellington r981 rssN 0r10-1765 Contents Page 5 5 5 5 7 Habitat 7 a Reproduction . Maturity Seasonal cycle 7 Spawning areas I Egg. I B Larvae 8 Age and growth B Mortality .,. ll Population structure and size ... r2 Food and feeding 12 Movements 13 Bibliography l5 Ë -.¿ *+ -F' 's .èlb+-.r ,T' .. ."lF f*,.-ì-. )l 'r:'*ifr ¡ é'.o åR.'* It.l r ,fr:#.. ,Í Ft , .-a - '*. ,' ] ar *r t. I I Lr B;l;'r' '-r a¿ì a t ) I å"ç¡1 -t ll r-.i' a .a -- tt ,:¡\ lr'Ðe ,* I lt r' m -: -lt-1. [f.. O. nirfrie photognph. The New Zealand snaPPer. separate by Japanese workers because of differences in lntroduction some of the skull bones. Whether all of these are really The abundance of snapper and its excellent distinct species depends much on the interpretation of qualities as a food fish make it the most important fish "species". Species do not suddenly become distinct species in New Zealand, both to commercial and because of geographical separation, nor do they do so amateur fishermen. Aspects of its life history have at a defined time; perhaps the four species mentioned been studied for many years and more is known about above are at present "half a species" apart. it than any other marine fish species. There are several books on New Zealand fishes in which it is included, but these do not contain much recent Additional literature: 2, 20, 26, 27, 30, 33. information and are often inaccurate or misleading. This account presents a summary of present knowledge about the biology oI snapper and is drawn lrom the literature shown in the bibliography on Page 15 and from unpublished data of the Fisheries Research Division. At the end of each section is a list oI numbers indicating literature relevant to that Description section. These numbers refer to entries in the bibliography, The snapper has a deep, oval-shaped body, with a large head and powerful jaws. The fin ray counts are: dorsal, 12 spines and l0 rays; anal, 3 spines and I Additional literature.' 15, 16, lB, 21. rays; and pectoral, 15 or 16 rays. The living snapper has beautiful coloration, which varies from delicate pink to dark red on its back and sides and fades to white on the belly. A series of brilliant turquoise sPots is scattered along the upper part of the body. The upper margin of the dorsal fin is edged in black. Young fish tend to be paler than adults, and in early juveniles there are five vertical bars. A large old Nomenclature snapper may show a blackening of the scales and occasionally have a hump on top of the head. This, The New Zealand snapper, Chrysophrys auratus the so-called "old man" snapper, may be of either sex (Forster), belongs to the sea bream family Sparidae. and is much less common in New Zealand than in Chrysoþhrys auratus is our only representative of this Australia. large family, which has about 100 species and is widely distributed over the Pacific, Indian, and Atlantic Oceans and the Mediterranean Sea. Additional literature.' 15, 16, 18, 21. Captain James Cook correctly recognised the New Zealand species when he named Bream Bay (near Whangarei) after the large numbers of bream caught by his crew. llowever, the species subsequently became known as "snapper" because of its resemblance to the true snappers (family Lutjanidae), which are not found in New Zealand. The name Distribution snapper has stuck and is the only one in common use today. The snapper is primarily a northern species (Fig. 1); its southern limits are determined by decreasing Chrysoþhrys auratus is very similar to the Australian the east snappers C. unicolor (South Australia and Western water temperatures. It is abundant along Island from North Cape to East Australia) and C. guttulatus (eastern states); so similar, coast of the North a fishery is centred on the Hauraki in fact, that illustrations of the Australian species have Cape, and major East Cape, been substituted for the New Zealand species in Gulf. Fewer snapper are found south of there significant population in Hawke several books. The similarity oî. C. auratus and. C. though is a common and only guttulatus has been shown recently during biochemical Bay. Further south they are not reach east coast the South Island. tests which gave identical results for both species. stragglers the of There is another species (the red sea bream C. major, Along the west coast of the North Island snaPPer from Japan) which in ourward appearance cannot be are also abundant and large numbers are found distinguished from C. auratus, but is considered to be outside harbours such as Kaipara and Manukau. 170" E r80' North Cope Hourqki Gulf Koiporo Hr Monukou Hr Eost Cope Tosmon 40' Howke Boy Greymouth Fig. l: Distribution of snapper. The width of the hatched area approximately indicates abundance (after Longhurst 1958). Their distribution extends further south than on the Reproduction east coast, and towards the south there is a gradual decrease in abundance. Sexually mature adults can be distinguished by the chin: the males are Quite large numbers of snapper are also found in colour differences under the north of the South Island. These are mainly in mottled dark grey and the females are white (Fig. 2). Tasman Bay, but there are some in the Marlborough This difference becomes more obvious with age. Sounds and along the northern part of the west coast, as far south as Greymouth. Additíonal literature.' 1, 19, 25,31. Stocks A biochemical study has shown that there are at least two genetically distinct stocks of snapper, One extends along the west coast, including the northern Fig. 2: Sexually mature áüults: male (above) and female part of the South Island, and the other, along the east (below). coast. The fish in Hawke Bay, though belonging geographically to the east coast stock, show more similarity to the west coast stock and may form a third stock. There is evidence for mixing of the east and Matur¡ty west stocks at Ninety Mile Beach, and for mixing of Investigations in the Hauraki Gulf showed that the the east stock and the possible Hawke Bay stock in the smallest sexually mature fish were 23 cm long' Most eastern Bay of Plenty and East Cape region, The were mature at 25 cm, and all were mature before genetic variation is thought to be influenced by water attaining a length of 30 cm. These lengths correspond temperatures. to fish that are 4 or 5 years old, which is the same age at which the Japanese species C. maior becomes mature. Addítíonal literature.' le, 2s. Seasonal cycle Snapper is a serial spawner and releases many batches of eggs over a period of several months. Most of the information on snapper reproduction comes from studies made in the Hauraki Gulf, where the annual breeding cycle can be divided into four Habitat periods. The first of these, the resting period, extends over late summer, autumn, and The snapper is a demersal fish occurring on the for about 7 months February August. The developing continental shelf down to a depth of about 200 m, but winter-from to preparatory to spawning occupies September. most abundant in depths of less than 70 m. It lives on period period of about 3t all kinds of bottom-sand, mud, rocks-and is found This is foilowed by a breeding in harbours and bays, along the oPen coast, and months from October to January, with peak spawning occurring during November. The final period, round off-shore islands. In large bays and on areas of usually clear bottom it is usually the dominant demersal during which the spent fish recover, is very short and lasts 2-3 weeks in late February. species, particularly in the northern Part of its range. January-early In foul ground areas it is less dominant and shares its Water temperature is the most imPortant factor habitat with a wider range of species. IJnderwater influencing the timing of the breeding period. Because observations of snapper are difficult because they are snapper spawns as the temPerature rises, spawning very wary and quickly move out of visual range. begins first in the north of its range, in the large shallow bays which are the areas that warm uP most quickly in spring. The observed range of sea surface Additional literature.' ls, 18. temperatures within which spawning takes place is l5o-23"c, but most occurs within the range l6'-21"c. TABLE l: Fecundity of snapper from the Hauraki Gulf The sea bottom temperatures are l5o-l7oc at peak Length Fecundity spawning. (.ttr) t974-75 1975-76 Superimposed 25 297 000 83 000 on the annual cycle is a rhythm of 30 616 000 393 000 serial spawning during the breeding season. From a 35 l 134 000 798 000 stock of developing eggs successive batches are +0 l 912 000 I 754 000 +5 3 02r 000 3 430 000 ripened and spawned. The interval between batches is 50 4 528 000 6 164 000 probably several days. Snapper is a daytime spawner. Spawning begins a few hours after dawn, reaches a breeding season. The number of eggs spawned in one peak about midday, and then decreases again towards batch ranged from 13 000 for a 25-cm fish to 104 000 dusk, As the season progresses, dawn is earlier, and for a 50-cm fish.