Go to National Library of New Zealand Te Puna Mātauranga o Aotearoa
Volume 51, 1919
This text is also available in PDF
(4 MB) Opens in new window
– 42 –

Art. VI. — A. Preliminary Investigation of the Age and Manner of Growth of Brown Trout in Canterbury, as shown by a Microscopic Examination of their Scales.

[Read before the Philosophical Institute of Canterbury, 4th September, 1918; received by Editor, 20th September, 1918; issued separately, 14th May, 1919.]

Plates I-VI.

The possibility of determining the age of fish by a microscopic examination of their scales was first demonstrated in 1899 by Hoffbauer (3), who made a special study of carp-scales.

The same principle was applied to salmon-scales by Johnston (4) in three papers published in the 23rd, 25th, and 26th Annual Reports of the Fishery Board for Scotland. Johnston further demonstrated that it was possible to trace the whole life-history of a salmon from its scales, and to say with tolerable certainty how long the fish had spent in fresh water as a “parr,” at what age it had become a “smolt” and migrated to the sea, whether it had re-entered fresh water to spawn, and, if so, the approximate dates of its re-entries and returns to the sea.

Working on the same lines, Dahl (1) made a most careful study of salmon and trout scales in Norway, and showed that, in addition, it was possible to calculate with considerable accuracy the length attained by the fish each year of its existence.

The fundamental fact on which these investigations are based is that carp, salmon, and trout—and, indeed, most if not all kinds of fish—each year

– 43 –

pass through a period of rapid growth followed by a period of comparative stagnation. This periodic growth has generally been attributed to changes of temperature and corresponding changes in the abundance of food-supply; and in regard to many species of fish it has been demonstrated that the maximum rate of growth roughly coincides with the maximum temperature of the water. There is evidence, however, to show that this periodic growth is well marked in the scales of some deep-sea fish, which can hardly be subject to any marked seasonal changes of temperature, and in the case of the squeteague (Cynoscion regalis) Taylor (6) has shown that the period of stagnation roughly coincides with the spawning season in midsummer. It seems probable, therefore, that the period of stagnation is determined more by a voluntary fast during the spawning season than by any actual shortage of food, and that individuals which have not arrived at sexual maturity subject themselves to this annual fast, though not to the same extent as the mature specimens. This voluntary-fast theory is further borne out by the observations of Masterman (5), who in a most careful critique of the previous work on salmon points out that a certain number of salmon captured at sea throughout the summer show no evidence of summer feeding. He concludes that some salmon start their spawning-fast many months before entering fresh water. This may cause the age of salmon to be underestimated in some cases, and certainly throws grave doubt on Johnston's claim that he can tell approximately the month of entering fresh water. In the case of trout there is no evidence of prolonged fasts, except during the spawning season, which occurs in midwinter, and it is of little importance whether the cause be lack of appetite or lack of food. There is some evidence to show that in Canterbury the maximum rate of growth, especially amongst the larger fish, occurs in spring rather than in summer. It is probably quite safe to assume, however, that the period of stagnation occurs in the winter.

Roughly speaking, a trout-scale (Plate I, fig. 1) consists of a transparent plate of more or less elliptical form, having its centre of growth approximately at one of the foci. Surrounding this and roughly concentric with the outer edge of the scale are a number of lines or “circuli.” The scale grows by the addition of these circuli round the periphery, which are added in greater numbers and more widely spaced during the periods of rapid growth. This alternate spacing and crowding produces light and dark zones, one light and one dark corresponding to a complete year's growth. The dark zones are called “annuli,” or “winter bands.”

In the case of spawning fish the stagnation is more complete, and the winter band is narrower and more clearly defined. In salmon (Salmo salar) the act of spawning leaves a clearly defined scar or “spawning-mark” on the scales, due to disintegration or reabsorption of the scale, especially along the lateral edges and the outer surface containing the circuli. A true spawning-mark is not very common in trout, but the character of the winter bands gives a fairly reliable indication of spawning. Plate I, fig. 1, shows one such winter band.

The exact cause of the spawning-mark in salmon is still in dispute. Johnston (4) attributed it to the vicissitudes of river life, whereby the fish shrank in girth, and says, “The compression of imbricated scales tends to increase the amount of overlap, and from this or dermic influences we find that their margins become ragged or frayed.” Masterman (5) has shown that this fraying or erosion in many cases starts long prior to the fish's entry into fresh water, and concludes that the phenomenon is one of

– 44 –

“erosion or absorption by the living tissue which is known to envelop the scale.” Two possible explanations are suggested: “The process may be an anticipatory reduction of the size of the scale to meet the approaching reduction in the girth of the body, or it may be connected directly with the formation and development of the ova.”

In Canterbury the spawning-mark is by no means so uncommon in trout as it appears to be in England and Norway. With male fish of considerable size (say, over 24 in.) it is rather the exception to find scales that do not show a definite spawning-mark—at any rate, in the Selwyn River (see Plate III, fig. 2). In females the act of spawning seems to leavea less decided scar, and most of the cases come within the region of uncertainty mentioned by Masterman, and introduce the personal element. In handling a large number of spawning fish this year, whilst collecting scales, I found that I could in almost every case detect the males by the texture of the skin. The males had a thick tough outer skin, and great difficulty was experienced in removing the scales, whilst no such covering was present in the females, and the scales were easily removed. Under the microscope the scales themselves were in many cases readily distinguished, those of the males being very much more eroded than those of the females. The ripe testes form a very much smaller proportion of the total weight of a male than the ripe ova of a female, so it is natural to suppose that the wastage of tissue in producing the former would be less than in producing the latter, and the shrinkage in milting is certainly less than in spawning, yet the scale-erosion is greater in males. All this seems to suggest that scale-erosion at spawning-time, in trout at any rate, is intimately connected with the production of the thick tough skin assumed by the males. Dahl has noticed that the erosion of scales in spawning salmon is more pronounced in the males, but apparently attaches no significance to his observation. In many cases it is a matter of opinion whether there is a spawning-mark corresponding to any particular winter on a trout-scale, but of the thirteen tagged fish from which I have scales every one shows, if not a distinct spawning-mark, at least a sharply defined winter band, such as the third winter band in Plate I, fig. 1, corresponding to the winter when the fish was stripped and tagged. I think it is probable that such winter bands are tolerably reliable evidence of spawning, but there is an almost perfect gradation from the broad ill-defined bands of the first two winters in Plate I, fig. 1, and many cases must always remain doubtful.

Dahl (1) assumed that the scales grew in the same proportion as the fish, and consequently that the distances from the centre of growth to the successive winter bands would be in the same ratio as the lengths attained by the fish in each successive winter. This assumption was almost in the nature of a corollary from what was previously known of the formation of winter bands, but experimental proof was desirable. Dahl and others have collected such a wealth of indirect evidence in favour of this hypothesis that there is little danger in accepting it as the basis of my investigations. Direct evidence, however, is difficult to obtain, and is meagre. As the whole of the present investigation depends on the truth of Dahl's hypothesis, it will be as well to add my small quota, more especially as Masterman and others have raised the objection that direct evidence is almost, if not entirely, lacking.

The North Canterbury Acclimatization Society annually strips a number of trout in the Selwyn River for piscicultural purposes, and takes the opportunity to tag two or three hundred fish each year with a small silver

– 45 –

label bearing a distinctive number; at the same time particulars of length, weight, and sex are recorded. Through the kindness of the society, and of anglers who have had the good fortune to recapture tagged fish, I have secured scales from thirteen of these fish when recaptured, and have calculated from these scales the length of each fish when tagged.

The following table shows the length when recaptured; the length (a) actual, measured at time of tagging, and (b) calculated from the scales; together with the difference in each case between the calculated and the measured lengths:—

Tagged Length.
Log No. Tag. No. Length when recaptured. (a) Measured. (b) Calculated. Difference.
Inches. Inches. Inches. Inch.
B 25 1101 21½ 19½ 20 ½
B 26 1074 21 20 19¾ ¼
B 27 1037 21 20 19½ ½
B 28 1088 22½ 20 20 0
B 136 1374 23 21½ 21½ 0
B 147 1401 28 27 27¼ ¼
B 159 1398 21 20 20 0
B 236 1095 21½ 19 19¼ ¼
B 246 1352 22½ 21 21 0
B 253 1346 22½ 21 21¼ ¼
B 277 1428 20½ 19 18¾ ¼
B 278 1380 22¼ 21¼ 21¾ ½
B 284 1304 21 19 19¼ ¼

In no case is the difference between the calculated and the measured length more than ½ in., and in only three cases is it so much, whilst in four cases the agreement is exact. Considering the difficulty of measuring two or three hundred live fish accurately, these results may be taken to fall well within the limits of experimental error in measuring. In practice the fish are generally measured to the nearest ½ in., and an error of ¼ in. at time of tagging and another ¼ in. when recaptured would be sufficient to account for the largest discrepancy of ½ in.

Two scales taken from one of these fish (tag No. 1374) at different times are shown (Plate II, figs. 1 and 2). The scale in Plate II, fig. 1, was taken on the 17th June, 1917, when the fish was tagged, and measured 21½ in. The scale in Plate II, fig. 2, was taken on the 28th October, 1917, when the fish was recaptured, and measured 23 in. The lengths each winter, calculated from a set of scales taken in June and a set of scales taken in October, are as follows:—

Winters 1 2 3 4 5 6 7
June scales (inches) 5 14½ 17¼ 19¼ 21½*
October scales (inches) 14¼ 17 19 21½ 23*

[Footnote] * Actual measured length.

– 46 –

Two fairly well-defined spawning-marks are shown in Plate II, fig. 2, and the space between the outer spawning-mark and the edge of the scale represents the growth of the fish between June and October. This growth (1½ in.) certainly appears large as against 2½ in. for the whole of the previous year. It seems, however, to be a pretty general rule that the most vigorous growth takes place in the spring, and very little after midsummer, except perhaps in quite young fish. It should also be noted that the posterior end of this scale is well developed. This is usually a characteristic of vigorous growth, and this portion of the scale is usually the first to be eroded when deterioration sets in.

It has been objected that scales are not permanent, but are shed and replaced by new scales. There may have been something in this objection until Dahl pointed out that scales with the so-called “expanded centre of growth” were in reality “replacement scales,” and supplied the connecting-link in a drawing of a scale which had been displaced in its socket but not actually lost. Plate I, fig. 2, shows a particularly fine example of such a “displacement scale,” and is of itself almost convincing proof that normally scales are retained throughout a trout's life, and grow with the fish by additions round the outer edge.

The Material.

The material examined consists of three samples comprising respectively 33, 140, and 65 fish taken from the Selwyn River on the occasion of the annual stripping by the Acclimatization Society in 1915, 1917, and 1918 respectively, and smaller samples from several other rivers and lakes. I shall deal with each separately.

Selwyn River.

Table I (A) gives the complete figures for thirty-three fish, all males, stripped in the Selwyn in June, 1915. The scales were collected by Dr. C. Morton Anderson, who kindly handed them over to me. It is interesting to note that these scales had been simply folded up in paper for nearly two years when I received them, and had not deteriorated during that time.

The second parcel of scales was taken by myself on the 17th June, 1917, and consists of scales from 140 fish, all being females except one, a particularly large male weighing 10 lb. The full figures are given in Table I (B).

The average growth-curves are shown in fig. 1. The curve for the 1915 fish is a broken line, and that for the 1917 fish a continuous line. On the same diagram are also shown the curves for 173 fish from Lake Mjosen, in Norway, plotted from figures given in Dahl's book. The broken line again is the curve for males, the continuous line for females. In each case the males continue vigorous growth for a longer period than the females, and eventually outstrip them. As the males were from fish taken in 1915 and the females from fish taken in 1917, I thought it desirable to test this apparent difference between the sexes further, and with that object collected scales from twenty-nine males and thirty-six females at the annual stripping this winter (1918). The full figures are given in Tables I (C) and I (D). The average growth-curves are shown in fig. 2. Again the males continue vigorous growth longer and attain a greater size than the females.

– 47 –
Picture icon

Fig. 1.

Picture icon

Fig. 2.

– 48 –

From the Acclimatization Society's records I have calculated the average length of the fish tagged each year since 1915. The figures in parentheses give the number of fish measured:—

1915—Males, 20.8 in. (100); females, 20.1 in. (98).

1916—Females, 19.3 in. (199).

1917—Females, 20.4 in. (140).

1918—Males, 22.6 in. (66); females, 21.5 in. (156).

In the years 1915 and 1918, when both sexes were tagged, the males averaged about 1 in. longer than the females. The average lengths of the samples from which I took scales are as follows:—

1915—Males, 21.3 in. (33).

1917—Females, 20.4 in. (140).

1918—Males, 22.5 in. (29); females, 21.7 in. (36).

These figures agree closely with the averages for the total fish measured, so the samples were in all probability fairly representative. The year 1918 was remarkable both for the number and large size of the spawning fish. The average ages [see Tables I (A) to I (F)] indicate that the males either have a shorter life, or cease to run up the river at an earlier age. This bears out the general belief that the spawning mortality is greater amongst the males.

Picture icon

Fig. 3.

A point to notice in these curves is that they are nearly straight lines for the first four years. This does not mean that each individual fish increases in length by approximately the same amount each year up to four years old. So far as my experience goes, growth of this character is almost unknown amongst trout in Canterbury, although such apparently is not the case in Norway. In Canterbury I have found that unless some outside influence is at work the rate of growth almost invariably starts to decrease quite appreciably in the third year, and this decrease is

Picture icon

Fig. 1.—Brown trout, ♀, 20 m., 4 years; Selwyn River, 17th June, 1917; B 48 [Table I (B)].
Fig. 2.—“Displacement” scale, from Rakaia River; taken from the same fish as fig. 2 of Plate IV.

Picture icon

Fig. 1.—Brown trout, ♀, 21½ in 6 years, Selwyn River, 17th June, 1917; B 105 [Table I (B)]. (First and second winter bands not well shown in photograph.)
Fig. 2.—Brown trout, ♀ 23 in., 6 years 4 months: Selwyn River, 28th October, 1917; B 136 [Table I (E)] (Taken from the same fish as fig. 1 of this plate. Note the new growth, corresponding to 1½ in. increase in length.)

Picture icon

Fig. 1.—Brown trout, ♀, 22½ in., 6 years; Selwyn River, 17th June, 1917; showing migration after second winter; B 107 [Table I (B)]
Fig. 2.—Brown trout, ♀ 22 in., 5½ years; Lake Ellesmere, 17th November, 1917; showing migration after fourth winter, and pronounced spawning-mark in fifth winter; B 151 [Table I (E)]

Picture icon

Fig. 1.—Brown trout, ♀, 26½ in., 8 years (nearly); Opihi River, 28th March, 1918; showing 4 years of poor growth in river followed by 4 years of vigorous growth subsequent to migration. Length at completion of each winter, 4¼ in., 7¼ in., 9 in., 10½ in, 16 in., 21½ in., 24¼ in., 26½ in
Fig. 2.—Brown trout, ♀, 25 in., 4½ years, Rakaia River, 12th January, 1918; second winter band divided; B 190 [Table III]. (From same fish as fig. 2 of Plate I.

– 49 –

more marked in the fourth year. A close examination of the figures in Tables I (A) to I (F) will show that in practically every case there is one year for each fish in which it has made more than normal growth; it may be the second, third, fourth, or fifth year, but in almost every case there is this break in the growth-curve. This sudden jump or break is generally attributed to migration to more favourable surroundings, and there is every reason to believe that this is the case with the Selwyn fish. Practically all the spawning in the Selwyn takes place in the shallow, shingly part. Except in the spawning season, fish of any considerable size are rare in this part of the river. The traps are set just about the junction of the shallow water and the deep, to catch the fish working up to the spawning-beds. Consequently every fish caught has come from the deep water. Probably every fish was hatched and spent its early youth in the shallow part of the river; therefore at some period it must have migrated to deep water. An examination of its scales will generally disclose when that migration took place The average curves, therefore, are really compounded of a number of different curves representing one-, two-, three-, four-, and possibly five-and six-year-old migrants. In fig. 3 are shown typical curves for a two-year-old and a four-year-old migrant. Plate III, figs. 1 and 2, show scales from these fish respectively, in which the period of better growth subsequent to migration is very distinctly shown. Whenever an average growth-curve closely approximates to a straight line for four or five years it is a fairly definite indication that the fish from that locality are migratory.

Table I (E) shows the figures for thirteen trout caught last summer with rod and line at the mouth of the Selwyn and other streams running into Lake Ellesmere. The average rate of growth is about the same as that of the 1915 males, or intermediate between those of the 1918 males and females.

In order to ascertain whether results in any way reliable could be obtained from smaller samples I calculated the average growth for the first, second, third, &c., twenty fish in Table I (B). Considering the very complex nature of the water, the agreement is quite satisfactory, and indicates that results of some value can be obtained from quite small samples.

Trout in the Selwyn, whatever the mode of growth, seem to have a more or less fixed limit of growth at about 23 in., which is rarely exceeded. Other waters also seem to show a maximum size-limit. It is curious, however, that this limit is occasionally considerably exceeded, and not necessarily by very old fish. These abnormally large fish, so far as I can ascertain, show no peculiarity of growth common to all, but their scales seem on the average unusually broad in proportion to their length, though I am at present unable to state this definitely. Whether the large size is determined by heredity or by unusually favourable environment I cannot say, though I am inclined to attribute it to the former. It is certainly a point worthy of further investigation. Particulars of five of these abnormally large fish are given in Table I (F).

Rivers.

From the angling point of view the rivers of Canterbury may be divided into two classes—snow rivers and rain rivers. The former contain large trout, for the most part, of sea-going habits; the latter comparatively small trout, which are not as a general rule migratory.

– 50 –

The material which I have examined up to the present consists of a quite inadequate number of fish from several rivers of each class.

In Table II particulars are given of thirty-five fish from the Cam, North Branch of the Waimakariri, Styx, Selwyn No. 2, Opihi, and Tengawai, all of which I class as rain rivers. There are individual differences, but the average rate of growth in all these is very similar. The average for the whole thirty-five fish is—

Winters 1 2 3 4 5 6
Inches 4.6 9.0 12.0 13.7 14.7 17.7

In Table III particulars are given of nineteen fish from the Ashley, Waimakariri, and Rakaia. The figures for the Ashley and the Rakaia agree very closely, but the figures for the Waimakariri are nearer to those for the rain rivers. The probable reason for this is that four out of the seven fish were taken from the Belfast branch of the river, which is frequently very low, and probably contains only a small percentage of sea-going fish. The average for the whole nineteen fish is—

Winters 1 2 3 4 5 6 7 8 9
Inches 4.7 9.7 14.3 17.1 19.7 21.1 19.5 21.5 22.7

The averages for seven-, eight-, and nine-year-old fish are the figures for one fish only, an old jack from the Rakaia, which showed no sign of ever having been in the sea. The growth-curves plotted from these figures are shown together in fig. 4 for comparison—the rain-river fish by a continuous line, the snow-river fish by a broken line.

The points to notice are that, although the rate of growth is approximately the same in each class for the first two years, the rain-river fish fall off

– 51 –

rapidly in the third, fourth, and fifth years, whilst in the snow-river fish a good growth is maintained. The growth-curve for the snow-river fish is a typical curve for a sample of which the individuals have migrated to more favourable surroundings at varying ages. Probably no individual fish has a growth-curve of this type, but the average curve is compounded of several different types representing the one-, two-, three-, and four-year-old migrants respectively. The sudden jump during the sixth year in the rain-river curve is the result of two fish only, and no importance attaches to it.

It may seem rather arbitrary to include the Opihi as a rain river and the Ashley as a snow river. Each of these rivers is more or less on the border-line. Sea-going fish frequent each, and each contains a large number of small fish which have not been to sea, though possibly they may go later. It so happens that all my examples from the Opihi, which were caught in November, 1917, near the junction with the Tengawai, belonged to this latter class, whilst all the Ashley fish were largish fish which had probably been to sea.

In view of the exceptionally poor growth of the Opihi and Tengawai fish, it would be most interesting to get scales from some of the large sea-run fish for which the Opihi is so famous, and to see whether these represent a later stage in the development of fish which as three- or four-year-olds had averaged only 10 in. to 12 in., or whether they belong to a different race. The matter is of some importance to the South Canterbury Acclimatization Society. If these poorly developed three- and four-year-olds are practically the “parr” stage of the larger sea-going trout the present condition of the Opihi is healthy; if not, then in my opinion it is carrying a stock far in excess of its food-supply.*

Plate IV, fig. 2, shows a scale from one of the Rakaia fish, and is an example of a very clearly marked scale, which is none the less difficult to read. The first winter band is clearly shown, and so is the second; but immediately outside the latter is another darkening; there is then a space indicating rapid summer growth, and the rest of the scale is normal. If this peculiarity existed in one scale only it might be attributed to some accident to or displacement of that particular scale. I have ten scales from this particular fish, and every one of them shows the same peculiarity. It has some meaning if one could only find it out. With some diffidence I offer the following explanation: The fish lived in the stream where hatched—probably the Rakaia—throughout the first year and the second summer and autumn; when the second winter band was nearly complete it migrated to the sea, and immediately responded to the stimulus of sea-water. The stimulus, however, was short-lived, and winter stagnation again set in, causing the third check. So the second and third checks are really one winter band divided by a short period of rapid growth in winter, due to the tonic effect of sea-water. I have met this same peculiarity in one or two other fish from the Rakaia.

Peculiarities such as this are not uncommon, and when they occur in one scale they invariably occur in every scale from the same fish, showing

[Footnote] * Since writing the above I have received scales from two of the large sea-run fish of the Opihi, 26 in. and 26½ in. in length. The former appears to have migrated as a yearling when about 6 in. long, the latter as a four-year-old (possibly three-year-old) when about 10½ in. long. The early growth of this latter corresponds closely with that of the small Opihi fish previously mentioned. A scale from this fish is shown in Plate IV, fig. 1.

– 52 –

that they are the result of some peculiarity in that fish's growth. Whilst very puzzling, these peculiarities are encouraging, for they open up possibilities for fresh discoveries in scale-reading.

The Back-country Lakes.

The material examined comprises ten fish from Marymere, fifteen from Lake Heron, three from Lake Coleridge, and two from Lake Alexandrina.

Marymere.—The average growth in this lake is as follows:—

Winters 1 2 3 4 5 6 7 8 9
Inches 5.4 12.6 17.2 19.7 21.5 22.7 23.4 24.2 24.4

The full figures are set out in Table IV (A), and the growth-curve is shown in fig. 5. The most striking feature of the curve is the large growth made during the second year, which exceeds even that of the first year; and not only is this the case in the average curve, but it is true of every

– 53 –

one of the ten fish examined, except one, in which the growth was equal for the first and second years. Such a state of affairs would generally be explained by saying the fish migrated at one year old to more favourable conditions. This cannot be the explanation in Marymere, as there are no streams running either into or out of the lake. It must be remembered, however, that the insects in our back-country districts are mostly large in size, and it seems probable that the true explanation is to be found in the fact that the main bulk of the food-supply is of a nature more suitable to fish after they have passed the yearling stage. Gilbert (2) has shown that quinnat and sockeye salmon which have migrated to the sea as fry a few months after hatching have very similar scales.

No brown trout have been liberated in Marymere since 1908, and so it is clear that they must breed in the lake itself, as three of the ten fish appear to have been hatched in 1914. It is curious that the next-youngest fish seems to have been hatched in 1911. In dealing with such small samples it is dangerous to generalize, but it certainly looks as if 1914 was an exceptionally favourable breeding season. Plate V, fig. 1, shows a scale from one of these fish hatched in 1914, and Plate V, fig. 2, a scale from one of the older fish. The latter illustrates clearly the difficulty in determining the age of old fish, owing to the way in which the winter bands are crowded together towards the edge of the scale. It is probable that the percentage of ova hatched in Marymere, except in very favourable seasons, is abnormally low, and that the stock of fish is maintained mainly by the greater average age attained. Whether this latter is due to natural causes or to the limited amount of angling I am unable to say, but it is a characteristic not only of Marymere but also of other back-country lakes. The average age is 6.4, calculated to last winter; and as these fish would probably all have survived until next spawning season their average age would then have been 7.4 years, or about 1½ years older than the Selwyn fish.

Lake Heron.—The average growth is as follows:—

Winters 1 2 3 4 5 6 7 8 9 10
Inches 4.4 9.0 14.4 18.2 20.4 21.5 22.6 23.0 23.7 23.7

The full figures are set out in Table IV (B), and the growth-curve is shown in fig. 6 as a continuous line, the Marymere curve being reproduced

as a broken line for comparison. Although the size of the older fish approximates fairly closely to that in Marymere, the average length of the younger

– 54 –

fish is distinctly lower, especially at two, three, and four years old. It is also noticeable that the curve is nearly a straight line for the first four years, and that even in the fifth year the falling-off is not very pronounced. In dealing with the Selwyn fish I pointed out that a curve of this character was to be associated with a sample of fish containing individuals which probably migrated to more favourable conditions at varying ages. An examination of the figures in Table IV (B) shows the characteristic increase of growth to have taken place in every case, and examples can be found of one-, two-, three-, and four-year-old migrants. Lake Heron differs from Marymere in that there are several small tributary streams flowing in and one fair-sized stream flowing out of it. In the spawning season these are packed with spawning trout. No doubt also a large number of trout spawn in the lake itself. I have selected five fish from the fifteen which appeared to have scales similar in character to the Marymere fish, and calculated the average rate of growth as follows:—

Winters 1 2 3 4 5 6 7
Inches 5.1 12.2 18.2 20.5 21.7 22.3 23.0

Fig. 7 shows the growth-curve for these, and the broken line shows the growth-curve for the Marymere fish. There is a difference of 1 in. at three years and 0.8 in. at four years old; elsewhere they agree to within 0.5 in.

In dealing with such small samples the agreement is most remarkable, and suggests the probability that these fish were bred in the lake itself or migrated as fry.

Picture icon

Fig. 1.—Brown trout, ♀ 21½ in., 4½ years; Marymere, 24th December, 1917; B 178 [Table IV].
Fig. 2.—Brown trout, ♀, 26 in., 9½ years; Marymere, 25th December, 1917; B 189 [Table IV]

Picture icon

Fig. 1.–Brown trout, ♀, 10½ lb., probably about 27½ in., 3 years 5 months; Lake Coleridge, 5th November, 1917; B 141 [Table IV].
Fig. 2.—Brown trout, ♀, 34½ in., 17 lb., 4 years' poor growth followed by 4 years' vigorous growth and (probably) another year of little or no growth; Lake Coleridge, 10th March, 1918; B 218 [Table IV]

– 55 –

The average age—6.93 last winter or 7.93 at next spawning—is again high—higher than Marymere.

Lake Alexandrina — This lake contains some very large fish, and the average size is certainly greater than in either of the last two lakes. Unfortunately, I have been able to obtain scales from only two fish; the figures for these are shown in Table IV (C).

Lake Coleridge.—This lake was first stocked with brown trout in 1868, and has for many years been noted for the exceptionally large size of its trout. I have been able to obtain scales from three fish only from this lake, but two of them are so remarkable that I have included a photograph of a scale from each fish. Plate VI, fig. 1, shows a scale from a fish of 10½ lb. captured about the 5th November, 1917. The length of the fish was not supplied to me, but would probably be about 27½ in., and I have made my calculations on this assumption. The fish seems to have been three years old in the winter of 1917, and shows a most remarkable growth since the last winter. The figures for each year are as follows:—

Winters 1 2 3
Inches 7 15 ¾ 23½

This scale apparently belongs to the Marymere type, and the fish was probably bred in the lake. It is considerably larger than any three-year-old I have ever heard of. The second fish was captured on the 10th March, 1918. A photograph of one of these scales is shown in Plate VI, fig. 2. The fish weighed 17 lb. and measured 34½ in. in length. The scales are, I think, the most beautifully marked and at the same time the most interesting in my collection. Surrounding the centre of growth are four winter bands close together, denoting four years of poor growth. These are followed by a year of growth which, so far as I know, is quite unique. There is another year of good growth, and then two years of moderate growth. The last winter band is right at the edge of the scale, and it is perhaps open to question whether this represents the winter of 1917 or the beginning of the 1918 winter. The difficulty of reading the scale is increased by the fact that every scale is more or less broken or worn at the edge. The fish was an egg-bound female, and in this abnormal state it is unlikely that she would grow much. On the whole, I think it more probable that the winter band right at the edge of the scale represents the winter 1917, and that there has been practically no growth since then (represented by one or two rings only), and that the fish was going back in condition when caught, as is evidenced by the frayed lateral edges of the scale. On this assumption the figures are as follows:—

Winters 1 2 3 4 5 6 7 8
Inches 4 8 10½ 24 30 32½ 34¼

The individual growth-curves for these two fish are shown in fig. 8. It is a fortunate coincidence that in three fish from this lake I should have

– 56 –

hit on two such striking and extreme examples of different types of growth. The probable weight of the 17 lb. fish each year would be about—

Winters 1 2 3 4 5 6 7 8
Weight 1 oz. 4 oz. 4 oz. 8 oz. 5½ lb. 11 lb. 14 lb. 16½ lb.

Conclusions.

1.

The scales of a trout give fairly reliable evidence of age and length attained by the fish each winter.

2.

Some scales are difficult to read, and errors may occur mainly in three ways: (a) The first one or two winter bands are often very indistinctly marked; (b) in very old fish the winter bands may be so crowded together towards the edge of the scale as to be indistinguishable—possibly in some cases the scale may cease growing altogether; (c) some scales, whilst clearly marked, are at present difficult to read: when this is the case all scales from the same fish present the same peculiarity.

3.

A true spawning-mark is not uncommon amongst the large males, and is probably formed by absorption of the scale, especially the outer surface, in formation of the tough skin assumed by the males at spawning-time. In other fish the character of the winter band gives in many cases a tolerably reliable indication of spawning.

4.

Under normal conditions trout increase but slowly in length after the third winter. Growth is most rapid in the first two years, and generally the first year shows the best growth of all.

5.

Very rarely does a trout growing in this manner attain a large size (say, over 2 lb.). Large trout almost invariably show a break in the growth-curve when a year of rapid growth succeeds slower growth. After the rapid

– 57 –

growth has set in the growth follows the normal curve again, getting less every year. This break or jump is probably caused by migration to more favourable surroundings.

6.

Trout which have been stunted by unfavourable conditions for four or even five years, and possibly longer, are still capable of rapid growth.

7.

Any particular water seems to have a fairly definite maximum size of fish. In waters where this is large, such as Lake Ellesmere and the back-country lakes, the maximum size will be reached no matter what the age of migration, and the age of migration seems to have little or no effect upon the size ultimately attained.

8.

Lake Ellesmere has a maximum size in the neighbourhood of 23 in., but some fish considerably exceed this. Whether this is due to an inherited tendency to rapid growth or to some specially favourable circumstances I cannot at present say. It is certainly a point worthy of investigation.

9.

In Canterbury trout grow much more rapidly in the early stages than in Norway, but the growth slows down earlier. The very large Mjosen trout are mostly very old, and still growing vigorously. The average age of migration is also much higher there than in Lake Ellesmere, for instance.

10.

Yearling trout average about 5 in. in Canterbury, as calculated from the scales. From Victoria Lake 112 yearling trout averaged 6 in., but the conditions there are certainly more favourable than the average. In Norway yearling trout average about 2 in. (Dahl).

11.

Lake Coleridge seems to favour the most rapid growth of all. The sea is slightly more favourable than Lakes Heron, Marymere, and Ellesmere, which are about the same.

12.

Except in very complicated waters, a fair idea of the average growth can be obtained by examining small parcels of ten to twenty fish, provided they are of fair age and fairly representative.

I take this opportunity of expressing my thanks to Dr. Chilton for much kindly instruction in microscopy, and to the North Canterbury Acclimatization Society and many anglers for assistance in collecting scales. The photographs are by Messrs. Leghorne and Colgan, of the Radia Studio, to whom I am much indebted for their infinite pains and trouble to secure the best possible results.

References TO Literature.

(1.) Knut Dahl, The Age and Growth of Salmon and Trout in Norway, as shown by their Scales (translated from the Norwegian by Ian Bailee), Salmon and Trout Association, London, 1910.

(2.) C. H. Gilbert, Age at Maturity of the Pacific Coast Salmon of the Genus Oncorhynchus, Bulletin U.S. Bureau of Fisheries, vol. 32 (Document No. 767), 1912.

(3.) C. Hoffbauer, Die Altersbestimmung des Karpfen an seiner Schuppe. Allgemeine Fischerei Zeitung, Jahrg. 23, pp. 341–43, 1898; Jahrg. 25, pp. 135-39, 150–56, 297, Munchen, 1900.

(4.) H. W. Johnston, The Scales of Tay Salmon as indicative of Age, Growth, and Spawning-habit, Fishery Board for Scotland, Ann. Rep., vol. 23, pt. 2, 1904; vol 25, pt. 2, 1906; vol. 26, pt. 2, 1907.

(5.) A. T. Masterman, Report on Investigations upon the Salmon, with Special Reference to Age-determination by Study of Scales, Board of Agriculture and Fisheries, Fishery Investigations, Series 1, Salmon and Fresh-water Fisheries, vol. 1, London, 1913.

(6.) H. F. Taylor, The Structure and Growth of the Scales of the Squeteague and the Pigfish as indicative of Life-history, Bulletin U.S. Bureau of Fisheries, vol. 34 (Document No. 823), 1914.

– 58 –
Table I (A)
.
Thirty-three Trout from Selwyn Stripping, June, 1915.
Log No. Sex Length each Winter.
1 2 3 4 5 6 7 8
In. In. In. In In. In. In. In.
A 11 M 3 ½ 6 ½ 11 18 20 22
A 12 M 5 10 14 22 23 ½
A 13 M 6 ¾ 13 ½ 17 ¾ 20 ¼ 22 22 ½
A 15 M 3 ¼ 5 ¾ 10 19 21 ¼ 23 ¼
A 16 M 3 ½ 7 11 ½ 15 ¾ 20 ½ 22 ½
A 17 M 3 6 ¼ 12 ½ 14 ¾ 20 ½ 21 ¾ 25
A 21 M 4 ½ 8 14 ½ 16 ½ 19
A 22 M 5 10 ½ 14 ¾ 18 ¾ 21 ¼ 22 ½
A 23 M 7 ¼ 12 17
A 24 M 3 ½ 6 ½ 12 ¾ 16 ½ 20 ½ 22
A 25 M 3 6 12 ¾ 18 ½ 21 ¾ 23
A 26 M 6 ¼ 9 ¾ 14 ¼ 17 ¾ 21
A 27 M 5 8 ½ 10 ¾ 15 19 ½ 20 ¼ 21 22 ½
A 30 M 6 ¼ 12 18 20 20 ¾ 22
A 31 M 6 14 ¼ 18 ¼ 20
A 32 M 6 10 ¾ 18 ½ 23 25
A 33 M 6 ½ 14 ½ 17 20 21 ¾ 23 ½
A 34 M 4 ½ 7 ½ 9 ½ 12 16
A 35 M 4 15 ¼ 18 19 20 ½ 21 ½ 22
A 36 M 6 14 18 ¼ 19 ½ 21 ¼ 22 ½
A 37 M 3 ½ 6 ½ 13 ½ 17 19 ¾ 22 23
A 38 M 3 ½ 6 ¼ 12 18 ½ 19 ½
A 39 M 3 ½ 9 ½ 18 ½
A 40 M 5 ¾ 10 18 ½ 23
A 41 M 5 ½ 12 ¾ 17 ½ 20 ¼ 23 ½ 25
A 42 M 3 ½ 7 12 ½ 15 ½ 17 ¾ 21
A 43 M 3 ¼ 7 ½ 10 ½ 15 ½ 17 ½
A 44 M 6 ¼ 12 18 ½ 21 ½ 23
A 45 M 4 ½ 10 ½ 13 18 ¼ 21 ¾
A 46 M 4 ¾ 11 ½ 18 ½
A 47 M 6 12 ½ 18 ½ 20 ½
A 48 M 3 ¼ 8 ¼ 12 ½ 16 ½ 19 19 ½ 20
A 49 M 4 ¾ 7 11 ½ 17 ½
Averages 4.7 9.7 14.7 18.3 20.7 22.2 22.2 22.5
Average age 5.4
Average length 21.3
Average length of 100 males marked in 1915 20.8
– 59 –
Table I (B).
140 Trout from Selwyn Stripping, 17th June, 1917.
Log No. Sex. Length each Winter.
1 2 3 4 5 6 7 8 9 10 11
In. In. In. In. In. In. In. In. In. In. In.
A 50 F 13 15 17¾ 20¼ 21 21½
A 51 F 4 12½ 18½ 20
A 52 F 13½ 16½ 18¾ 21¾
A 53 F 17 20½
A 54 F 13¾ 18½ 21
A 55 F 11½ 15½ 17¾ 19 20¼
A 56 F 12 18½ 20½ 21¾ 23
A 57 F 12 17¼ 20 21½ 23
A 58 F 4 13 14¾ 17 19 20½ 21½
A 59 F 7 11 13¾ 16¾ 18¼ 19½
A 60 F 12½ 18½
A 61 F 63/1; 10¼ 14 18½ 21
A 62 F 12¼ 14½ 17½ 19½ 20¾
A 63 F 13½ 16 17¾ 19
A 64 F 10 13½ 16 18 19½
A 65 F 11 14½ 16¾ 18 19 19¾ 20½
A 66 F 12 18
A 67 F 10 14½ 18 19¼ 20¼ 21
A 68 F 10½ 14¼ 16½ 18½ 20½
A 69 F 7 10½ 13¾ 17 18¾ 20½
A 70 F 7 14¾ 17½ 18½ 20½
A 71 F 9 12¼ 16 18¼ 20½
A 72 F 12½ 19
B 1 M 5 17 22½ 27
B 2 F 12½ 18½
B 3 F 12 14½ 16 17½ 18 18¾ 19½ 20½
B 4 F 5 8 10½ 14½ 16¼ 19¼ 20¼ 21
B 6 F 4 10½ 16¾ 20 23
B 7 F 16½ 18 19 20 20¾ 21½ 22
B 8 F 4 9 14½ 17 19¼ 20½ 22¼
B 9 F 7 13 16 18½
B 10 F 13¼ 17½
B 11 F 13½ 19
B 12 F 10¼ 14¼ 17¼ 19½
B 13 F 8 14 16 18½ 20
B 14 F 5 14 19½
B 15 F 3 7 12¾ 16½ 18½
B 16 F 6 10 17¼ 19 21
B 17 F 13¼ 18
B 18 F 15 17¼ 18½ 21
B 19 F 4 12 17½
B 20 F 11½ 15¾ 18¾ 20 21½
B 21 F 5 9 13 16½ 18¼ 20
B 23 F 7 13¾ 16¾ 18¾ 20 21¼ 22 22½
B 24 F 5 10¼ 18 19¼ 21
B 25 F 10¾ 15 18 20 21½
B 26 F 11¾ 15 17¾ 19¾ 21
B 27 F 12½ 15¼ 18 19½ 21
B 28 F 6 12 14¾ 18½ 20 22½
B 29 F 4 13½ 19
B 30 F 9 11½ 14 16½ 20½
B 31 F 12½ 14½ 17¼ 19
– 60 –
Table I (B)—continued
140 Trout from, Selwyn Stripping, 17th June, 1917—continued.
Log No. Sex. Length each Winter.
1 2 3 4 5 6 7 8 9 10 11
In. In In In. In In In. In. In. In. In.
B 32 F 7 11¼ 14¼ 17½ 20
B 33 F 10¾ 16 19¾ 21¼
B 34 F 12½ 18½
B 35 F 12¾ 16¼ 17¾ 18¾ 20 21
B 36 F 13¼ 19
B 37 F 12¼ 16¼ 18½
B 38 F 13¼ 18½
B 40 F 13½ 17½ 19½ 21½
B 41 F 7 11¾ 14¾ 18 19½
B 42 F 11 14½ 17 19½ 21
B 43 F 14¾ 16½ 20½ 21¼ 22 23
B 44 F 11 15¼ 17½ 20
B 45 F 11¼ 14¾ 17 18¼ 19½ 20½
B 46 F 7 14½ 17 18½ 20½
B 47 F 12½ 15½ 18 19¼ 21¼
B 48 F 11¼ 17 20
B 49 F 11¼ 15¼ 19 20½
B 50 F 12 16¾ 18¾ 19½ 21
B 51 F 4 13 18¼ 21
B 52 F 11 17 18¾ 20½
B 53 F 10¾ 15½ 17¾ 18½ 19 20
B 54 F 6 12¾ 16¾ 18½
B 55 F 11½ 15¾ 19½ 21½
B 56 F 5 13¼ 18½
B 57 F 11¼ 15 18 19½ 21
B 58 F 12 16½ 19½ 20½ 21 22½ 23
B 59 F 13¾ 16 18 19¼ 20½
B 60 F 5 12½ 17 19
B 61 F 12¼ 17 19¼ 20½
B 62 F 9 16¼ 19¼ 20 20½ 20¾ 21¼ 21½
B 63 F 10¾ 14¾ 20½
B 64 F 14½ 18¼ 20½
B 65 F 12¼ 18
B 66 F 11½ 15½ 19¼ 20¾ 22½
B 67 F 13¾ 16 17½ 19¼ 20½
B 68 F 11¾ 13¾ 16½ 18½ 19¼ 20½
B 69 F 9 13 17 20½
B 70 F 11½ 18
B 71 F 9 13½ 15½ 17¼ 19
B 72 F 13¼ 17¼ 19¾ 21¼ 23
B 73 F 14 19
B 74 F 9 12¾ 15¼ 17¼ 19
B 75 F 10¼ 18 19½ 21
B 76 F 12 18½
B 77 F 5 11 13 15¼ 17 19 20½
B 78 F 13¾ 18½
B 79 F 13¼ 16 18 20
B 80 F 10½ 14¾ 19¼ 21
B 81 F 12¼ 17 20½ 21½
B 82 F 13½ 16¼ 18½ 21
B 84 F 13¼ 16½ 18¼ 20¼
B 85 F 11 13¾ 19
B 86 F 11¾ 15¾ 18½ 19¼ 21
– 61 –
Table I (B)—continued.
140 Trout from Selwyn Stripping, 17th June, 1917—continued.
Log No. Sex. Length each Winter.
1 2 3 4 5 6 7 8 9 10 11
In. In. In. In. In. In. In. In. In. In. In.
B 87 F 10½ 14¼ 16½ 18¼ 19½
B 88 F 15¼ 17¾ 19¼ 21¼ 22¼ 23½
B 89 (a) F 9 11¾ 14½ 17 18½ 20
B 89(b) F 14½ 19¼ 21¾ 22¼ 23½
B 90 F 4 13¼ 17 17¾ 19½ 20 20½
B 91 F 7 10 14¼ 16 18 20½
B 92 F 6 13 16 18¼ 21½
B 93 F 4 11½ 13¾ 15½ 17¼ 18¾ 19½ 20
B 94 F 14¾ 17 19¼ 20 21¼ 22
B 95 F 4 12¾ 17½ 19½ 21 22½
B 96 F ¼ 6 13¾ 20
B 97 F 13 15½ 17¼ 18¼ 20 21¾
B 98 F 5 11¼ 13½ 15½ 18½ 20½ 22½
B 99 F 4 10 12¼ 14¾ 17¼ 18½ 19½
B 100 F 10¾ 13 16 18½ 19½ 21
B 101 F 4 8 11½ 14 15¾ 17¼ 18 19 21
B 102 F 8 12¼ 15¾ 18½
B 103 F 4 11¼ 13½ 15
B 104 F 14½ 19 21½
B 105 F 5 14¾ 17¼ 19¼ 21½
B 106 F 4 11 14 16¾ 18 19½
B 107 F 14¾ 18½ 20¼ 22½
B 108 F 4 11¼ 13¾ 16½ 18½ 20½
B 109 F 11 15 18¼ 19½ 21
B 110 14 19½
B 111 F 5 12¾ 18
B 112 F 4 12 15¾ 18
B 113 F 11 18
B 114 F 13¼ 19½
B 115 F 10¾ 18
B 116 F 8 11 14 17½ 20 20½ 22
B 117 F 12¾ 16 18
B 118 F 11½ 15¼ 17¾ 20¼ 22
B 119 F 5 6 11¼ 14 15¾ 18¾ 19½ 20¾ 22
B 120 F 4 8 15 17 18½ 20¼ 22½ 23¼ 24½
Averages 5.1 9.3 13.8 16.9 18.6 19.8 20.6 21.2 21.5 21.1 22.0
Averages for each Group of Twenty.
1st twenty 5.3 9.4 14.0 17.0 18.8 20.0 20.6 20.5 21.5
2nd twenty 5.2 10.3 15.3 18.2 19.6 20.3 20.5 20.7 21.2
3rd twenty 5.8 10.6 14.8 17.6 19.3 20.7 21.7 22.5
4th twenty 5.2 9.5 13.7 16.9 18.8 20.0 20.7 22.1 23.0
5th twenty 4.7 8.4 12.5 16.7 18.7 19.2 20.6 20.6 21.2 21.5
6th twenty 4.5 8.4 12.6 16.1 18.0 19.4 20.6 21.5 20.0
7th twenty 4.7 9.0 13.5 16.2 17.1 19.2 19.7 20.7 21.7 20.7 22.0
Average age 5.9
Average length 20.4
– 62 –

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Table I (C).
Twenty-nine Trout (Males) from Selwyn Stripping, 16th June, 1918.
Log. No. Length each Winter
1 2 3 4 5 6 7
In. In. In In. In. In. In.
B 235 6 13¾ 20
B 237 4 7 14½ 19½ 22½ 24½
B 239 6 13½ 18 20½ 22 22½
B 240 5 13 17 19¼ 21¾ 23
B 241 7 15
B 242 13 20¼ 21½
B 243 14¾ 17¾ 20 22¾ 24
B 244 7 14 20½ 22 23
B 247 13½ 21 23½
B 248 14¼ 20¼ 21½ 24
B 250 13½ 20½
B 251 6 14 19½ 21¼ 22½
B 252 15 22 26
B 254 13½ 18½ 21½ 23½
B 255 14¾ 20¼ 22
B 256 15½ 21½
B 257 8 17½ 24
B 259 7 13¼ 21 24
B 260 4 8 12½ 21 23
B 261 9 17
B 262 12½ 20 23¾ 24½
B 269 11¼ 15 21 23 25 26
B 270 13½ 21¼ 25
B 271 12¾ 21¼ 23¼ 26½
B 276 17 21¼ 23¼ 24
C 3 6 15½
C 5 16½ 19½
C 8 13½ 18¼ 20¾ 22
C 13 15¼ 20½ 23½ 25
Averages 5.5 10.9 16.8 20.9 22.5 23.5 24.2
Average age 4.8
Average length 22.5
Average length of sixty-six males marked in 1918 22.6
– 63 –

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Table I (D)
Thirty-six Trout (Females) from Selwyn Stripping, 16th June, 1918.
Length each Winter.
Log No. 1 2 3 4 5 6 7 8 9
In. In. In In. In. In. In. In. In.
B 236 4 14¾ 17¼ 19¼ 21 21½
B 238 8 13¾ 16½ 18½ 20 21¾ 23 24 25
B 246 13½ 18¼ 21 22½
B 249 7 12½ 18½ 19½ 20¾ 21½ 22¼ 24¾ 25½
B 253 10¼ 14½ 16¾ 19 21¼ 22½
B 263 13 15½ 17½ 20 21
B 264 14 16¾ 19¼ 21¼ 22½
B 265 14 15¾ 17¼ 19 20½ 21½
B 266 13¼ 18
B 267 10¼ 14¾ 21 24
B 268 4 11½ 16¼ 17¾ 19 20
B 272 4 15¼ 20½
B 273 10 13½ 18½ 20¼ 23 24 25¼ 26
B 274 14¼ 17¼ 19¼ 21½ 22¾
B 275 4 13½ 19½ 20½ 22 23
B 277 12½ 16½ 18¾ 20½
B 278 7 10 12¾ 15¾ 18½ 19¾ 21¾ 22½
B 279 11¾ 16 17½ 19 20¼ 21½
B 280 13 19
B 281 6 11½ 17¾ 20¼ 21 22¼ 23
B 282 14½ 19¼ 21
B 283 11½ 16 18½ 19½ 20½ 21
B 284 13½ 19¼ 21
B 285 15¼ 17¾ 19½ 21 22
B 286 14¾ 18¾ 20¼ 21½
B 287 7 12½ 15 17½ 20½ 22
B 288 13½ 18¾ 20
C 1 4 15 17 18½ 21 22½
C 2 7 11¾ 14¾ 17 18¾ 20½ 21½
C 4 12¾ 16 18¼ 20 21
C 6 14¼ 21 23
C 7 13¼ 16¾ 19 20½
C 9 4 13¼ 19½
C 10 13¾ 17½ 19
C 11 5 9 13½ 17¾ 20½
C 12 10½ 14¾ 18¼ 19½ 21 22
Averages 5.4 10.3 14.9 17.9 19.6 20.8 21.6 23.2 24.7

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Average age 6.2
Average length 21.7
Average length of 156 females marked in 1918 21.5
– 64 –

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Table I (E)
Thirteen Trout caught with Rod and Line, Lake Ellesmere, 1917—18.
Length each Winter
Date. Log No. Weight. Length. Sex. 1 2 3 4 5 6 7
lb. In. In In In In In. In. In
20/10/17 B132 11 28 M 10¼ 13¼ 18½ 22¾ 24½ 26¾
21/10/17 B 133 25 F ? 13¾ 16½ 19 21½ 24¾
27/10/17 B 136 23 F 14¼ 17 19 21½
17/11/17 B 147 28 M 10 16¼ 22½ 27¼
17/11/17 B 150 22 M 11½ 14¾ 16¾ 21¼
17/11/17 B 151 22 M 10¼ 13 15¼ 20
17/11/17 B 152 17¼ F 11¾ 15
9/12/17 B 159 21 F 5 13½ 15¾ 17¾ 20
8/1/18 B 185 25 16 19¾ 21½ 24¼
6/1/18 B 198 24 F 12¾ 22
9/3/18 B 213 7 24 F 9 14¾ 19½ 22¼
9/3/18 B 214 7 25¼ F 15¼ 18¾ 22¾
9/3/18 B 216 4 19¾ M 5 11¼ 16¾
Averages 5.1 9.7 14 6 17.9 20 8 22.2 25.7

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Table I (F)
Fvae Large Trout from Lake Ellesmere.
Length each Winter.
Date. Log No. Weight. Length Sex. 1 2 3 4 5 6 7 8 9
lb. In In In. In In In In In In In
28/12/16 A 1 13½ 28½ F 6 21½ 25½ 27½
—/6/15 A 18 11¼ 29 F 13 17 21½ 23½ 25¼ 26½ 27½
20/10/17 B 132 11 28 M 10¼ 13¼ 18½ 22¾ 24½ 26¾
17/11/17 B 147 28 M 10 16¼ 22½ 27¼
10/5/18 B 232 13½ 33 M 13 17 21¼ 27½ 31
Averages 5.8 10.2 16.2 20.9 25.3 26.5 26.0 26.5 27.5
– 65 –

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Table II.
Rain Rivers.
Length each Winter.
Date. Log No. Weight. Length. Sex 1 2 3 4 5 6
A. Cam.
Ib. In. In. In. In. In. In. In.
1/10/17 B 121 18 13¼ 14¾ 16½ 18
1/10/17 B 122 ½ 12 5 10¾
4/10/17 B 123 15¾ 12½ 14½
4/10/17 B 124 15¼ 12¼ 14
26/10/17 B 134–5 ¾ 14¾ 4 8 12 14¼
26/11/17 B 153 15¾ 4 10¾ 13½ 14½
23/12/17 B 160 16¼ F 13½ 15
B. North Branch, Waimakariri.
9/10/17 B 127
9/10/17 B 128 ¾ 14 8 11¼ 13½
9/10/17 B 129 ½ 11½ 11¼
8/12/17 B 161 14¾ F 4 12¼
8/12/17 B 163 14¾ M 11¼ 13¼
8/12/17 B 165 ¾ 12 10
8/12/17 B 169 15½ M 13¼
30/12/17 B 173 15 4 13¼
30/12/17 B 174 ½ 11¼ 10¼
8/4/18 B 231 18¼ M 12¾
C. Styx.
24/2/18 B 208 15 9 13¼ 14½
24/2/18 B 209 1 13 6 11¼ 12¼
24/2/18 B 210 ½ 10½
D. Selwyn No. 2.
7/10/17 B 125 2 18 M 10½ 13¾ 16 16¾ 17½
7/10/17 B 126 ¾ 13½ 10 12¾
13/10/17 B 130 12¾ 10½ 12¼
14/10/17 B 131 15½ F 5 13½ 14¾ 15½
28/10/17 B 137 1 14 12½ 13¾
28/10/17 B 138 15¼ M 4 13 14 15
28/10/17 B 139 8
28/10/17 B 140 ¾ 13¼ 12
E. Opihi and Tengawai.
9/11/17 B 162 10½
10/11/17 B 164 10
9/11/17 B 166 13½ 4 7 10¼ 11½ 12¾
10/11/17 B 167 10 6 9
9/11/17 B 170 11 10½
9/11/17 B 172 13½ 11½ 13
9/11/17 B 168 11 10¼
Averages 4.6 9.0 12.0 13.7 14.7 17.7

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Averages for each River.
A. Cam 5.0 10.0 13.0 14.4 15.5 18.0
B. North Branch, Waimakariri 4.8 9.0 12.5 13.5
C. Styx 3.6 7.2 11.5 12.9 12.2
D. Selwyn No. 2 4.7 9.0 12.7 14.1 15.7 17.5
E. Opihi and Tengawai 4.2 7.5 10.0 12.2 12.7
– 66 –

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Table III.
Snow Rivers.
Length each Winter
Date. Log No. Weight. Length. Sex. 1 2 3 4 5 6 7 8 9
A. Ashley.
lb. In. In. In In In. In In. In. In. In
23/1/18 B 195 24½ 11¾ 16½ 20¼ 22¾
23/1/18 B 197 20½ F 11 16¼
7/3/18 B 212 3 18½ M 6 10 14 16½
7/3/18 B 215 20½ 5 8 14¾ 17½ 20
B. Waimakariri.
3/12/17 B 154 17 M 4 12 13½ 14¾
3/12/17 B 155 12 6 10½
30/11/17 B 156 16 F 10¾ 14
23/1/18 B 194 21½ M 14½ 16½ 18¾ 20¾
28/1/18 B 196 18 M 11¼ 16
2/2/18 B 202 17¾ F 10 13¾ 17
B 217 20 10 14½ 18
C. Rakaia.
10/11/17 B 144 23½ M 11½ 13½ 15½ 19½ 21½ 22¾
12/1/18 B 190 25 F 13½ 18 22¾
11/1/18 B 192 5 24½ M 16½ 19¾ 23¼
20/1/18 B 193 1 14 F 10¾
B 199 21 F 5 11¾ 14¾ 16½ 18¾
3/2/18 B 200 7 28 F 11½ 18 24 25¾ 27½
B 203 21 F 10 15 18 19¾ 20½
10/2/18 B 204 3 19 M 4 8⅓ 16¼
Averages 4.7 9.7 14.3 17.1 19.7 21.1 19 5 21.5 22.7

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Averages for each River.
A. Ashley 5.3 10.2 15.4 18.1 21.4
B. Waimakariri 4.6 8.7 12.8 14.9 16.7 20.7
C. Rakaia 5.1 10.2 15.3 18.8 20.2 21.1 19.5 21.5 22.7
– 67 –

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Table IV.
Back-country Lakes.
Length each Winter.
Date. Log No. Weight. Length. Sex. 1 2 3 4 5 6 7 8 9 10
A. Marymere.
lb. In. In In In In In In. In. In. In. In.
23/12/17 B 175 23 M 10 15¼ 17½ 19½ 20¾ 21¾ 22¼
24/12/17 B 176 6 24 F 6 12 15¾ 17¾ 20¼ 21½ 22¼ 23 23½
24/12/17 B 178 21½ F 6 15¼ 19
23/12/17 B 179 26 M 6 12¼ 16 20 22¼ 23½ 24½ 25½
27/12/17 B 180 6 26 M 13¼ 18½ 21¾ 23¾ 24¼
27/12/17 B 181 7 27 F 12 16¾ 20½ 22¼ 24 25¼ 26¼
26/12/Z7 B 182 5 22 M 13 19¼
26/12/17 B 183 20½ F 12 18
24/12/17 B 188 24 F 6 12½ 15½ 20 21 22 23¼
25/12/17 B 189 7 26 F 13¾ 17¾ 20½ 21¾ 22¾ 23½ 24¼ 25¼
B. Lake Heron.
2/11/17 B 142 6 24½ 7 10½ 17 21 23¼ 24¼
2/11/17 B 143 5 21½ 11½ 17 19 20½ 21¼
1/11/17 B 145 8 26 M 9 18 21½ 22¾ 23½ 24½ 25¼ 25¾
8/11/17 B 146 6 24 4 11¾ 17¾ 20½ 21 22 22¾ 23¼ 23¾
24/11/17 B 158 8 26½ M 10½ 17½ 20¼ 23½ 24¾ 26
31/3/18 B 221 5 21¾ M 16 20¼
31/3/18 B 222 5 22¾ M 10½ 17½ 20 21¼ 22¼
31/3/18 B 223 22¾ M 12¾ 19½ 20¾ 21¾
31/3/18 B 224 6 23½ F 5 11 19 20½ 21¾ 22¾
31/3/18 B 225 24 M 5 12¼ 16 19¼ 20½ 22 23
31/3/18 B 226 4 22¾ F 15 18 19½ 20¾ 21¾ 22¼
31/3/18 B 227 6 22¾ F 14 18 21 22¼
31/3/18 B 228 5 21½ F 4 11½ 15¼ 18¼ 19¾ 20¾ 21¼
31/3/18 B 229 19¾ F 4 13½ 16¾ 18¼ 19
31/3/18 B 230 7 24¾ M 5 14½ 19¼ 22¼ 23¼
C. Lake Alexandrina.
10/2/18 B 205 23½ M 6 11½ 16½ 22¼
10/2/18 B 206 10 28¼ F 11 17 23½ 26 27¾
D. Lake Coleridge.
5/11/17 B 141* 10½ 27½ F 7 15¾ 23½
10/3/18 B 218 17 34½ F 4 8 10½ 24 30 32½ 34¼
3/6/18 B 234 20 33½ F 7 12¼ 19½ 26½ 29½ 31¾

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Averages.
A Lake Marymere 5·4 12·6 17·2 19·7 21·5 22·7 23·4 24·2 24·4
B Lake Heron 4·4 9·0 14·4 18·2 20·4 21·5 22·6 23·0 23·7 23·7
" “natives” 5·1 12·2 18·2 20·5 21·7 22·3 23·0
" “migrants” 4·1 7·4 12·4 17·0 19·7 21·2 22·5 23·0 23·7 23·7

Marymere—Average age, calculated as at last winter: 6·40 years.

Lake. Heron—Average age, calculated as at last winter: 67·93 years.

[Footnote] * The length of B 141 (Lake Coleridge) was estimated from the weight.