![Thumbnail: [Volume 84, 1956-57 page 317]](/journals/rsnz/images/rsnz_84/thumbnails/rsnz_84_02_0364_0317_ac_02.gif)
Distribution of Eggs
Since the egg stage of the snapper lasts approximately 45 hours (at 18° C.) it is clear that any one concentration of eggs will not exist for more than two consecutive days unless it continues to be renewed by the parent fish. In practice it was never possible to trace the same group of eggs for more than a day. This may be because the fish normally spawn at some depth (probably 10 fathoms or more) and the time taken for eggs to reach the surface reduces their term of availability to little more than a day. The early blastoderm stages representing the first 14 hours of life were rarely identified in plankton samples, and in most cases where eggs were kept alive the majority in any sample could be hatched out in less than 24 hours.
In effect it was found that each day's samples bore little or no relation to those of the previous or the following day An area which on one day had a clearly delimited and dense patch of snapper eggs might be entirely barren on the next. The records of the 1925–32 investigations may perhaps be misleading in that, although they indicate where eggs were found, they seldom indicate where eggs were absent. Possibly, once the two likely areas shown in Fig. 1 had been located, the investigators tended to return to those places rather than to others where they had previously been unsuccessful It is seen from Figs. 4–9 that eggs may be found in very nearly all parts of the area investigated. There is perhaps some tendency for spawning to be concentrated in the western region, but evidence here is not altogether conclusive since time and resources did not permit such an intensive survey of the eastern and particularly the north-eastern section of the Gulf. In nearly all areas which were studied at all intensively, snapper eggs were detected at some stage of the investigation, the only exceptions being the enclosed water south of Rangitoto and Waiheke Islands which are not included in the figures. There is no one zone which seems to be particularly favoured as a spawning region.
Although it has in most cases been possible to draw contours of egg density for any one day, little would be gained by showing these in detail, both because of the variation in pattern from day to day and because it was not possible to sample the entire Gulf each day. In order to give an overall picture of the distribution it
![Thumbnail: [Volume 84, 1956-57 page 318]](/journals/rsnz/images/rsnz_84/thumbnails/rsnz_84_02_0365_0318_ac_02.gif)
Fig. 4.—Density of snapper eggs, Hauraki Gulf, November, 1950.
Fig. 5—Density of snapper eggs, Hauraki Gulf, December, 1950.
![Thumbnail: [Volume 84, 1956-57 page 319]](/journals/rsnz/images/rsnz_84/thumbnails/rsnz_84_02_0366_0319_ac_02.gif)
Fig 6.—Density of snapper eggs, Hauraki Gulf, November, 1951.
Fig. 7.—Density of snapper eggs, Hauraki Gulf, December, 1951.
![Thumbnail: [Volume 84, 1956-57 page 320]](/journals/rsnz/images/rsnz_84/thumbnails/rsnz_84_02_0367_0320_ac_02.gif)
Fig. 8.—Density of snapper eggs, Hauraki Gulf, January, 1952.
Fig. 9.—Density of snapper eggs, Hauraki Gulf, February 1–15, 1952
![Thumbnail: [Volume 84, 1956-57 page 321]](/journals/rsnz/images/rsnz_84/thumbnails/rsnz_84_02_0368_0321_ac_02.gif)
seemed desirable to divide numerical estimates into a relatively small number of categories which when plotted would give a visual impression of the average density throughout each month. Since the frequency distribution of sample counts is highly skewed with a very large number of zero or near-zero counts and a small number of very high counts it was found that a logarithmic interval was most suitable to give approximately an equal number of samples in each category. The four different sizes of sample, each with an upper class limit ten times the previous one, are indicated by lines of varying thickness along the track of the ship in Figs. 4–9.
The information in these Figures is further summarised in Figure 10, which gives the proportion of samples of each density for the entire area of each month. The figure in the white sector represents in each case the total number of samples taken. Since the pattern of sampling varied somewhat from month to month these diagrams are only approximately representative, so that only gross changes should be taken into account. Note also that only one count of over 1000 was recorded in each of the last three months, so that the varying size of the black sector probably signifies little more than a difference in the number of samples.
Fig. 10.—Summary of snapper egg density, Hauraki Gulf, 1950–51 and 1951–52.
The spawning patterns for the two years are by no means identical. In 1950–51 the density of eggs had already reached its maximum in November, and declines steeply through December and January. Unfortunately it is not known whether the November spawning commenced suddenly or was built up slowly in the previous month. In 1951–52 the November density is relatively low, the maximum being in December, with a much slower decline through January and February. It would appear then that the peak of the spawning was reached at least one month later in the 1951–52 summer, but the evidence is scarcely adequate to show which season produced the greater number of eggs. While no one month in the second season equalled November, 1950, it is possible that the more protracted spawning compensated for the lack of intensity at any one time.