Introduction

It has for many years been common knowledge to Auckland fishermen that, in the summer months, snapper aggregate and spawn in the Hauraki Gulf, particularly on the grounds between Kawau and Tiritiri Islands. The late Captain C. Daniel, of the Marine Department, during the course of his duties as District Inspector of Fisheries, made a study of the occurrence of spawning snapper and of snapper eggs in the plankton. Unfortunately this information has not been published and, since the death of Captain Daniel, many of his records have been lost. However, it is known that snapper eggs were artificially fertilised and were identified in the plankton in the summer of 1925–26. In the following year Mr. M. W. Young, then biologist, Marine Department, took charge of snapper investigations which were continued for some years (Hefford, 1928–33). Figure 1 summarises some of the data collected by Young and Daniel. Floating snapper eggs were recorded within the larger stippled area to the west in November 1931 to January 1932, December 1933 to January 1934, and in December 1934, while in the smaller area off the coast of Coromandel Peninsula they were recorded in December 1926 to February 1927, November 1931, and December to January, 1932.

The greater part of the Hauraki Gulf is to-day closed to trawlers and Danish seiners, but there is a considerable fleet of line-fishing boats operating in the Gulf waters. In the summer these boats are often concentrated in or about the larger of the two areas indicated in Figure 1. Lines are commonly set, not on the bottom as at other times of the year, but at a depth of about 10 fathoms, the average depth

of the water being a little over 20 fathoms. Usually the fish caught at this depth are in a ripe or spawning condition and are of the class known as “school fish” or “schoolers”. They have an iridescent silvery lustre, usually with a decided reddish tinge which contrasts with the less conspicuous grey-blue coloration often found in other snapper. Many fishermen believe that the school snapper is a distinct race of fish which enters the Gulf from outside waters for spawning purposes only. It is also claimed that, owing to their pelagic feeding habits, the school fish have sharper, less worn teeth than the bottom-feeding snapper usually resident in the Gulf. Unfortunately neither coloration nor tooth form are sufficiently definite characters for this theory to be readily tested Marking experiments have so far been unsuccessful, while condition factor and morphometric data have not revealed any significant racial differences. It would seem unlikely that any genetic differentiation exists, since ripe fish of both classes are often found together, and on at least one occasion eggs from a female school fish were successfully fertilised from a “non-school” male.

During the summer the outer waters of the Gulf are invaded by great numbers of the “chain jelly”, Thallia democratica (Fuller 1953) which often forms the principal food of the schooling fish. It would not appear that any appreciable nourishment is obtained therefrom, since, although the entire alimentary tract is often tightly packed with Thallia, those discharged from the anus are usually entire and show little signs of any digestive action.

The act of spawning has been observed by various people. Naturally only instances where this takes place near the surface would be seen The fish, whether male or female, is usually lethargic and drifts near the surface with the minimum of movement, rolling over on its side to discharge clouds of eggs or milt into the water.

Fig 1—Reported occurence of snapper eggs in Hauraki Gulf, 1926–32.

In a previous paper (Cassie, 1956) the developmental stages of the snapper have been described. From this information it has been possible to identify snapper eggs and larvae when they appear in the plankton In the surveys made by the author in the summers of 1950–51 and 1951–52 only one sample was obtained containing appreciable numbers of larvae, so the present discussion will be limited to the distribution of eggs.

The majority of the field work was conducted from the fisheries research vessel “Ikatere”, but in the later part of December, 1951, to February, 1952, owing to a mechanical defect in “Ikatere”, operations were transferred to the patrol vessel “Ocean Star”.