Art. XLIII.—Observations on New Zealand Fishes, &c., made at the Portobello Marine Fish-hatchery.
[Read before the Otago Institute, 13th November, 1906.]
Plates XVII, XVIII, XIX, XX.
Although the culture of trout, carp, perch, and many other species of fresh-water fishes has been, in vogue for centuries, it is only within very recent years that serious attention has been paid to the culture of marine food fishes. To such a fine art has the former pursuit been reduced that there exist at the present time, in England and elsewhere, fish-farms, some of which are privately owned, while some are formed into limited-liability companies. These farms are run, so to speak, on the same lines as a poultry-farm—the eyed eggs, fry, yearlings, &c., being purchased by farmers and others desirous of stocking any ponds, lakes, or streams on their property with fish.
In 1864 Professor G. O. Sars, the distinguished Norwegian naturalist, was commissioned to make an investigation of the cod-fisheries around the Lofoden Isles. During this work he discovered in his tow-net collections large quantities of minute transparent globules, which were afterwards identified as the floating eggs of the cod. The following year he succeeded in artificially fertilising and hatching these eggs. In 1868 Professor Malm found that the eggs of the flounder were buoyant, though he does not say they were actually floating on the surface. In 1882, in an account published in the United States by Professor Alexander Agassiz, he states that the eggs of many of the American fishes, including flat fishes, were of the buoyant type. In 1884 Professor McIntosh and Dr. Cunningham were engaged in the study of floating spawn in Scottish waters, when the eggs of the cod, haddock, gurnard, whiting, turbot, plaice, and many other fishes were added to the list of pelagic or floating eggs. Even so recently as 1885, during the sitting of the Royal Commission on beam trawling in Scotland, it was most confidently asserted by many “expert” witnesses that the beam trawl caused the destruction of millions of fish-eggs upon the seafloor.
Of late years a great deal more attention has been given to this subject in Europe, but the most notable success-has been achieved by the United States Fish Commission, which was established in 1871. As showing the extent to which fish-culture
has been carried on by the Commission, it may be stated that the total output of fry for 1904 was 1,267,343,025, including both indigenous and introduced fresh- and salt-water fishes.
Many of the declining fishing industries, such as the salmon, lobster, and shad, have been revived, and new industries created by means of artificial propagation.
Such is a brief outline of the history of the work in other countries, from which it will be seen that it is only a little over forty years since the floating nature of the majority of the eggs of marine fishes was first discovered.
An account of the marine fish-hatchery and biological station “established in 1904 at Portobello is published in the New Zealand Institute Transactions, vol. xxxviii. In this paper Mr. G. M. Thomson has given a history of the movement to establish a station, together with a statement of its objects and details of construction, and a report of the work undertaken during 1904. The following notes practically constitute a continuation of Mr. Thomson's paper.
The Gurnard (Trigla kumu).
Although fairly abundant around various parts of the coast, this fish is seldom caught by the local trawlers, and then generally only singly or in pairs.
On the 5th March about two thousand eggs were taken from a female on board the s.s. “Napier,” off Otago Heads. We were fortunate in securing a male fish in the next haul, and the eggs were impregnated and brought to the station. The egg (Plate XVII, figs, a, b, c, d, e, f, g) is the largest marine fish-egg secured up to the present time, and is 1·7 mm. in diameter. It is of the buoyant or pelagic type, spherical and transparent, with (chiefly) a single large oil-globule, but in some cases three or four, which soon appear to merge into one. This oil-globule is at first of a bright-orange colour, and gives the eggs a bright and conspicuous appearance when floating in a mass on the surface of the water. The colour gradually fades, and by the time the embryo is ready for hatching the colour has entirely disappeared. The eggs hatch on the seventh, day, at an average temperature of 9° C.
The gurnard is probably a summer spawner, as the eggs were collected when the water had reached its highest temperature. The larva (Plate XVIII, figs, b c, d, e) is about 4 mm. in length; the pigmentation is black and yellow, and the yolk-sac large and interspersed with the same black-and-yellow markings. By the second day the yolk-sac has appreciably diminished in size, and the larvÆ become more active. The
pectoral fins appeal to be chiefly used as a means of locomotion, assisted by a sharp wriggling motion of the body. Little change takes place until about the sixth day, by which time the eyes and mouth are open, the yolk-sac absorbed, and the little fish may be seen actively pursuing the minute organisms on which they feed. A few were reared until the twelfth day in a small aquarium jar, by which time they had begun to assume many of the characteristics of the adult fish. The pectoral fins are very prominent, and the three lower rays, although showing prominently, are still connected with the upper portion of the fin. It is interesting to note that the gradual disappearance of the colour in the oil-globule has been observed in Great Britain in the eggs of Trigla gurnardus and T. cuculus.
The Brill (Caulopsetta scapha).
This fine fish appears to be only an occasional visitor; it is seldom taken on the trawling-grounds off Otago Heads, and only in small quantities. It is a very handsome fish, and is greatly esteemed as a table delicacy. Nothing is at present known of its habits and movements, but it is a fish deserving every possible attention. Single ripe females have occasionally been taken, but, in the absence of males, the eggs were not fertilised. But on the 8th August of this year a small number were fertilised, as an experiment, with the milt of the sole (Peltorhamphus novœ-zealandiœ). These were taken to the station, and all were found to be fertilised. Development proceeded favourably until the 11th, when these, along with many other eggs in the boxes, were killed during a frosty night, and the interesting experiment of hybridizing these fish could not be followed up, but may be attempted on a future occasion.
On the 17th August a few thousand of the eggs were successfully fertilised by Mr. Baird, engineer of the trawler “Express,” and were sent to the station. The egg (Plate XIX, fig. c) is the largest of any of the local Pleuronectidœ, being 1·7 mm. in diameter. It is of the usual spherical form, transparent, and buoyant, and contains a large number of oil-globules evenly dispersed over the entire egg. It hatches at a mean temperature
of 5·5° C. in five days.
The newly hatched larva (Plate XIX, fig. e) is at first very inactive, generally floating helplessly on the surface of the water. The oil-globules remain in the yolk-sac after hatching, and the yellow pigmentation is very conspicuous. Owing to pressure of other work these larvÆ were only kept for a few days, and no further drawings were made. The larvÆ are easily identified by their large size, their colour, and by the peculiar extension over the head of the rudimentary dorsal fin.
Owing to the uncertainty as to the identity of the two species of flounders which were taken in the harbour, it was considered inadvisable in last year's report to publish an account of the eggs and larvÆ until the species had been definitely ascertained. This has now been done by Professor Benham, and we are able to give a few particulars of each species.
Rhombosolea plebeius, commonly known as the sand-flounder: This species was taken in large numbers by the steam trawlers and seine fishermen in June last, in Blueskin Bay. They were, almost without exception, very large fish, and the females greatly predominated. As many as twenty dozen were taken in a night's fishing with one seine net, from Purakanui Beach. It was decided to attempt to convey some of these fine fish to the spawning-ponds, in hopes that better results would be obtained from them than from the smaller fish taken in the bay the previous year. The fish taken in the trawl were all too much bruised for this purpose, and an arrangement was made with Messrs. King, of Purakanui, to retain the largest females in a coff until the following day, when they were towed off to the trawler “Express” and placed in tubs into which a constant stream of water was pumped, until arrival at Port Chalmers, where they were again transferred to the coff, towed to the station, and placed in the ponds. As seining is always carried on at night and on an open surf beach, these fish were subjected to a considerable amount of rough handling, on one occasion remaining in the coff overnight in Port Chalmers, through bad weather. This resulted in their being in very indifferent condition when they were placed in the ponds. Five dozen large females were obtained in this manner; the males and a few other females were afterwards caught in the harbour. From facts which have since been ascertained, it is very evident that these ocean-caught flounders should have spawned about the middle of August, as by the end of that month all the flat fishes that were examined on board the trawlers were spent, but nearly ripe females were still being taken within the harbour as late as the 30th September (both R. plebeius and R. tapirina). This fact would almost lead one to conclude that the flounders frequenting the harbour remain within or almost within the colder waters of the bay, and that the ripening of the ova is thus retarded. It is a noteworthy coincidence that the first eggs were collected from the pond on the 9th October, the exact date on which the first collection was made in 1905.
During the spawning season of 1905 the total collection of flounder-ova was 650,000, from which 562,000, or 87 per cent, of larvÆ, were hatched. Up to date of writing (30th November)
250,000 ova have been collected this year, and, 217,000, or 86.8 per cent. of larvÆ, hatched.
Some two dozen of the stock fish in the pond have succumbed at various times, and there is every reason to believe that the cause of death may be attributed to their removal to shallower and colder water, and that the long retardation, and non-extrusion of the eggs has caused these fish to sicken and die. Many of the females still retain their eggs, and it is expected that large numbers will be collected before long. The results from fish confined in the ponds up to the present-have been very poor, a very heavy handicap being the small range of tides in these waters, and the consequent shallow ponds with extremes of temperature. The beat results were obtained from the (evidently) late-spawning harbour flounders, and it will probably be found expedient to secure a stock of small immature fish and allow them to become acclimatised to the extremes of temperature experienced in the ponds. There are at present a few such fish, from 4 in. to 5 in. long, which are probably about three years old.
On the 8th August 283,000 ripe eggs were taken from a single flounder (R. plebeius) on board the trawler, and all were successfully fertilised. The egg (Plate XVIII, figs. f and g) is buoyant, and is very minute, being only 0.65 mm. in diameter, with from eight to thirteen small oil-globules. The larvÆ (figs, c and d) hatch in five days at an average temperature of 9° C. The newly hatched larvÆ are fairly active, and are almost transparent, with bright-yellow and black pigment markings. They are perfectly symmetrical, but are at first unable to see or feed, though they appear quite conscious of the presence of a dipping-tube or other instrument when placed near them. They are provided with a comparatively large yolk-sac containing the albumen on which they subsist until able to forage for themselves. The oil-globules remain in the yolk-sac after hatching. By the fifth day (Plate XIX, fig. b) the yolk-sac is almost absorbed, the eyes and mouth are open, and the larvÆ are able to seek out their own particular sustenance.
R. tapirina: The ova of this species is considerably larger than that of R. plebeia, being 0.8 mm. in diameter, and it contains a single large oil-globule of a light-orange colour. The larvÆ hatch in five days, as with the other species, but they are much larger and more active. No drawings were made of either eggs or larvÆ, as no fish were kept in the ponds this year.
The Sole (Peltorhamphus novœ-zealandiœ).
From the irregular nature of the observations made on this fish, which is commonly known, as the English sole, it is not
possible to give much information as to its annual movements. Vast numbers were taken by the trawlers in the shallower waters (5 to 6 fathoms) of Blueskin Bay during the months of June and July. Their presence there was generally stated by the local fishermen to be for spawning purposes. This belief was no doubt strengthened by the very large roes contained by the females. None of them were, however, found to be ripe, and no sole-eggs were taken in the tow-nets in the water of the bar. An examination of the contents of the stomachs disclosed in every instance large numbers of cumaceans (Diastylis novœ-zealandiœ), and it is very probable that the fish were attracted to this locality by the presence of myriads of these Crustacea, upon which they were feeding voraciously. Large masses of seaweed were dredged up at each haul, and were found to be full of these Crustacea. By the end of July the soles appear to have migrated into deeper water, and considerable hauls of them were being made by the trawlers in 13 to 18 fathoms of water to the north-east of Otago Heads. Almost all the females were found to be ripe early in August, and on the 8th the first ova were collected on board the trawler “Express.” Two collections were made, on the 8th and 10th August, when 1,422,000 eggs were successfully fertilised, and placed in the hatching-boxes. For some reason, which is attributed to the low temperature (2° C.) of the water in the boxes, all of these eggs died on the third night. After considerable experimenting with available material, it was found possible to maintain a steady temperature of 5° C., corresponding to the temperature of the water on the spawning-grounds. This was effected by placing four large Miller lamps under the supply-pipe, with a hot-air chamber of zinc above the pipe. By raising the lights a little in the evening and lowering them early in the morning a very even temperature of 5° C. could be maintained. Collections of the ova were again made between the 15th and 22nd August, a total of 3,175,000 being collected and fertilised, from which 2,747,000, or 86 per cent., of larvÆ were hatched. These were liberated in the harbour on the first of the ebb tide, from two to seven days after hatching
The egg (Plate XIX, fig. d) is 0.5 mm. in diameter. It is spherical and buoyant, and contains from two to six small oil-globules. The larvÆ hatch out in five days, at a temperature of 5° C. As is the case with all the Pleuronectidœ, the larvÆ are perfectly symmetrical, and do not bear the slightest resemblance to the unsymmetrical contorted-looking adult. The spawning season appears to be very brief, as by 22nd August almost all the females were spent, although a small quantity of ova could still be expressed from a few of the smaller fish until
the end of the month. The newly hatched larvÆ are the smallest and most helpless of any that have yet been handled; they are quite transparent and colourless, and lay for a long time motionless on the surface of the water. A drawing was made of a larva on the third day after hatching (Plate XIX, fig. f).
The Crayfish (Palinurus edwardsii).
The crayfish is very valuable to us, inasmuch as it is the only large edible crustacean at present inhabiting our coastal waters. It is generally supposed to be of sedentary habits, and to live for a great part of its life within a very restricted area. Large hauls of them are occasionally taken in the trawl some distance from shore, and on a sandy bottom. The fishermen say they are then on the move, and it would appear that at certain periods a great migratory movement takes place from one part of the coast to another. I do not know at what part of the year this occurs, or if at regular intervals every year, but no doubt more light will be thrown on the subject before long.
Two large berried females were brought alive to the station on the 27th April by Mr. J. Noble, of the ketch “Carrie.” These two have been continually under observation—for some time in a glass tank and some time in the tidal pond—for a period of eight months, and the eggs were found to be “eye-ing” at the end of November, and by the 7th December they were commencing to hatch out.
On the 8th November sixteen other berried females were brought to the station by Mr. Noble. All the attached eggs were eyed. The adults were placed in a 5 ft. by 5 ft. glass tank, where they soon made themselves at home, and fed well. During the daytime they generally huddled together in a heap in a corner of the tank, but moved about freely at dusk. They could often be seen “sitting up,” as it were, on their tail, and rapidly moving their swimmerets and attached eggs to and fro, as if in the act of swimming, using their last pair of legs, which in the females are chelate, to clean off any particles of sediment that had adhered to them.
The eggs of two were combed off into a McDonald hatching-jar on the 8th, and these commenced to hatch on the 18th November. The first embryos were seen in the large tank on the 24th November, and from that date until the 10th December vast numbers swarmed in the tank, swimming freely neat the surface, and generally congregating where the light was strongest. It is estimated that seven million embryos were hatched, most of which were retained in the hatching-boxes from three to nine
days, and then were liberated in the harbour on the first of the ebb tide. A technical account of these embryos is appended to this note by Mr. G. M. Thomson.
All the adults had finished spawning by the 10th December, but they will be retained, if possible, in one of the tidal ponds, in order to ascertain if moulting will take place, and whether spawning is annual or biennial. As showing the fecundity of the crayfish, 394,100 eggs were gathered from a specimen measuring only 9 in. The egg is 0.8 mm. in diameter, and is attached to the swimmerets by means of fine filaments during the period of incubation, which probably extends for about nine months of the year. Considerable numbers are still retained in a large glass tank, and it is hoped that a few may be reared through the various brephalops and megalops stages.
Note on the Development of Palinrus edwardsii, by George M. Thomson, F.L.S.
The embryo, on emerging from the egg, has the characteristic Phyllosoma appearance (Plate XX, fig. a). The length of the body, from the middle of the front margin to the extremity of the pleon, is 2 mm. The carapace is fully 1 mm. in length, and is nearly circular in form, with large well-developed eyes on stout pedicels. At the centre of the front margin, between the bases of the eye-stalks, there is a well-defined ocellus. The antennae are 1-jointed, and are nearly as long as the carapace. The antennules are considerably longer, and bear a number of plumose setÆ, by the lashing and waving of which the minute animal progresses through the water. At this stage the other limbs are more or less curled around and folded under the body, and appear to be functionless, there being no trace of the plumose filaments on the pereiopoda, by which later they swim.
How long this first stage lasts was not clearly made out. Probably it is only a few hours, for no moult was detected by Mr. Anderton, yet after a time the plumose filaments of the antennules had quite disappeared, while those of the three posterior pereiopoda were seen to be developed. In this second stage (Plate XX, fig. b) the length of the body from between the eyes to the end of the pleon is 2.5 mm., and the spread of the limbs is rather more than 6 mm. The carapace tapers more to the front than in the preceding stage, and the eye-stalks are relatively longer and more prominent. The divisions of the pereion were not clearly made out behind the broad base of the carapace, but it bears 5 pairs of pereiopoda. The antennae are 1-branehed and apparently 1-jointed; they are slightly longer than the eye-peduncles, and bear a single setÆ on their outer margin, and two fir three at their extremity. The antennules
are slightly longer than the first pair and are 2-branched; each branch ends in 3 spinose setae, of which the middle one is the longest. The only mouth organs detected were a pair of mandibles, working between the rounded upper and lower lips. The divisions of the pereion were not clearly made out behind the broad base of the carapace, but it bears five pairs of pereiopoda, each of them 6- (? 7-) jointed. The first pair are very short —little more than one-third as long as the carapace; and at the base of each, and in front of it, is a small rudimentary 2-jointed appendage (? branchia). The second pair are 1-branched and slender, and reach considerably beyond the front of the carapace. The third and fourth pairs are longer and stouter, and are 2-branched. The second branch springs from the end of the third joint, and is multi-articulate, bearing long plumose setÆ towards its extremity. It is by the vigorous lashing of this plumose appendage of the third and fourth pereiopoda that the animal now swims. The fifth pair are long, slender, and 1-branched. In all the pereiopoda there is a tendency to red coloration towards the extremity of the joints, especially of the propodos. The pleon is short, tapering, and ends in a bifurcate apex.
Among the larvÆ of a few days old there appears to be a third stage in which the carapace is broadly pear-shaped and the eye-stalks are longer and more slender. In this form the lobes of the liver were very clearly made out, and the movements of the simple heart were very easily seen. The colourless blood, marked by its corpuscular particles, is seen to pass into a wide open sinus at the posterior extremity of the vessel, and to be driven forward by the pulsation, to escape again at two apertures close to the anterior end of the tube, near the front of the carapace.
We are not yet able to establish the identity of this species with the free-swimming form known as “whale-feed” (Grimothea gregaria). The first Grimothea were noticed in the harbour early in November, but on the 8th and 14th I received a number of specimens of Munida sub-rugosa from Mr. S. Bradley, which had been picked up by his seine net. Two of these were females with the eggs attached to the swimmerets, but unfortunately both specimens were dead. The eggs (unmeasured) are very minute and of a greenish hue, and it is difficult to conceive that the large form at present so abundant in the bay is the product of this season's spawning. Several of the fishermen are at present on the look-out for the berried adults, and it may be possible this season yet to hatch out these eggs and to finally
settle the question. During the season that the “whale-feed” are found in the ocean and the bay, the stomachs of almost all fish, excluding flat fish, have then been found to contain large numbers of them, and it is certain that they constitute one of the most important fish-foods, and no doubt play a considerable part in the migrations of many fishes.
Introduction of Lobsters.
The desirability of introducing this valuable crustacean into these seas, a description of the pond for their reception, and other notes on the subject, are to be found in vol. xxx of the “Transactions of the New Zealand Institute.”
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Thirteen “berried” females and twelve males were procured by Dr. E. H. Allen, Director of the Marine Biological Station at Plymouth, and were forwarded to London by rail, for shipment by the Shaw, Savill, and Albion Company's steamship “Karamea.” The claws of each lobster were tied, and each fish wrapped in scrim; they were then placed in two fish-baskets and sent on by rail at 10 p.m. on the 8th May, 1906. They arrived safely on board the “Karamea” at noon of the next day, fourteen hours out of water, when they were at once placed in the tanks prepared for their reception. As it was not deemed advisable to use the foul and brackish water of the Thames, the tanks were filled with water from a ballast-tank which had been filled previous to entering the river. In this water they remained two days, during which the water was only renewed twice, and it was not until the third day that a regular flow was maintained by means of a pipe leading from the salt-water circulatory system. The temperature of the water in the English Channel was 51° Fahr., gradually rising until the maximum of 84° was reached on the 22nd May. A constant supply of water was maintained by means of a 3/1 in. rubber hose at first, but was replaced on the 17th by a 2 ½ in. hose, as the lobsters were looking very seedy, and the engineer considered that a larger flow was necessary. The supply-pipe was formed into a treble coil enclosed in a forty-gallon cask, which was filled with ice, renewed daily; but owing to the large volume of water and the rapidity with which it passed through the chamber, this apparatus proved altogether inadequate for the purpose of reducing the temperature of the water sufficiently, and only effected a reduction of 2° Fahr.
From the first the lobsters appear to have been very sluggish in their movements. This was no doubt due to their lengthy stay out of water, and their two days' confinement in stagnant ballast-tank water. Their vitality appears to have been so much impaired by this that they were unable to withstand the high temperatures which were soon encountered.
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The above table gives the dates on which the deaths took place and the temperature of the water on that date. It will be seen from this that the mortality was greatly increased with the increase of the temperature, and the greatest mortality occurred during the hottest period of the voyage. By the 26th May all but two were dead; but; as the water from this date gradually became cooler, these two survived, and arrived in Port Chalmers on the 29th June, when they were at once taken over to the station and placed in a large glass tank. Both are females, and had, unfortunately, shed their eggs only a few days previous to their arrival. A small number were still attached to the swimmerets of one, but on examination under the microscope were found to be dead, but with a well-developed embryo. Since their arrival, six months ago, these two lobsters have been kept in a glass tank measuring 5 ft. by 2 ft. 6 in. by 2 ft. deep. A steady supply of water is maintained, and their surroundings made as natural as possible by means of gravel, weeds, and rock shelters. Each lobster sticks religiously to its own shelter, to which it always returns after a forage for food. Whenever the tank is cleaned out, each one, on being replaced, goes at once into its own den head first, but immediately turns round so as to face the entrance, leaving only the large chelÆ projecting. They are fed somewhat irregularly on fish, but appear to be very small eaters; if a piece of fish is thrust into their hiding-place when they are not hungry they at once seize it and carry it out, dropping it some distance away.
In order to ascertain the possibilities of lobsters and crayfish living peaceably together, one of each, both accustomed to confinement, were placed in an observation-tank. But there can be no question as to the lobster being “boss,” as it chased the crayfish about the tank, snapping at it with its powerful claws, the crayfish having to ascend to the surface to get out of its way, so that they had to be at once separated.
It is interesting to note that the lobsters have not moulted since their arrival.
It is due to Mr. Purves, the chief engineer of the s.s. “Karamea,” to state that, although the shipment was intrusted to his care, the fitting of the tanks and the cooling-apparatus was not superintended by him. But he is quite sanguine that a number will be brought out on the next voyage of the “Karamea,” when a more effective cooling-apparatus will be fitted. The “Karamea” will probably arrive in the colony about February or March, and, if so, the eggs should not be so far advanced, and will not be so liable to hatch during the voyage. Therefore the arrival of a larger consignment with the attached eggs in a healthy condition may be confidently expected at an early date.
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Temperatures of Ocean and Bay.
We are fortunate this year in being able to give an almost continuous series of records showing the comparative temperatures of the surface waters of the ocean and of the bay as recorded at 9 a.m. daily. The ocean-temperatures are mostly taken at a distance of from five to nine miles to the eastward of the entrance to Otago Harbour, and consequently in the current running towards the north. From a glance at the tables it will be seen that the highest recorded ocean-temperature is 10.2°C.,
which is not reached until March, three months after midsummer. The minimum is reached soon after midwinter, early in and during the month of August, when 5° C. is recorded. The range between the maximum and minimum is therefore only 5.2° C. The daily variation even of the surface waters is very slight. It will also be noticed that, so far as has been learned, the flat fishes all spawn during the period in which the water is the coldest.
The maximum temperature of the bay is reached in the middle of January, when 13.2° C. was recorded, and the minimum, 1° C., on the 17th July, the range between maximum and minimum being 12.2° C., being 7° C. or 12.6° Fahr. in excess of the range of the ocean waters. The range of the waters in the spawning-ponds is slightly in excess of this, but was not recorded this year during the warmest months, as the ponds were empty and remained open. This table is most valuable to us, as it enables us to compare the temperatures of the local waters with those of Great Britain, from which the lobsters, crabs, or any fishes may be brought for the purposes of acclimatisation. I cannot at present find a complete annual record taken at any of the stations in Great Britain, but from a report of trawling investigations off the east coast of Scotland in the twenty-second annual report of the Scottish Fishery Board, the minimum temperature recorded during 1903 was 5° C., and this was only recorded on one day. The usual midwinter temperature appears to be about 7° C., and the maximum 13.2° C. Although in considerably higher latitudes, the high temperature is no doubt attributable to the effects of the Gulf Stream. Many species of deep-sea fishes appear very susceptible to any change in temperature, but from our brief experience here it would appear as if even a slight reduction is fatal to the incubation of the eggs. I think, from the slight difference in the temperatures of the British and local waters, we may conclude that any European fishes, once introduced, would not be injuriously affected by the slight change in the ocean waters, but that the only difficulty would be in keeping the adult fish in our ponds without some means of raising the temperature through the winter months, during which the temperature has at times fallen below 0° C.
Almost all the knowledge that has been gained up to the present time, such as the collection of eggs, ocean tow-nettings, temperatures, examination of stomach-contents, &c., has only been made possible by the kindness and cordial co-operation of Mr. F. G. Sullivan, of Dunedin. Fish that have been required for the purposes of the station have been freely given, and
accommodation, meals, use of pumps, &c., provided free of any cost whatever. I would like to take this opportunity of thanking Mr. Sullivan, and the captains, engineers, and crews of the trawlers “Express” and “Napier,” for their kind assistance at all times, and especially Mr. Baird, the engineer of the “Express,” for the collection of many thousands of ova when it has been impossible for me to leave the station.
With the present limited means and facilities it is not for one moment pretended that any practical results may be expected from the infinitely small numbers of larvÆ that are being from time to time liberated, the total for the two years being under five millions. The station must for some time to come remain a purely experimental one, involving only a small expenditure, the chief benefits to be derived from which are the accumulation of facts, which are now steadily being recorded, without a knowledge of which it is impossible to frame any beneficial legislation. This knowledge, if followed up carefully for a number of years, will form a substantial base for future and more extensive operations.
It is often remarked that it is not the small fish that, as at present, should be protected, but the large mature ones, at spawning-time: that is to say, there should be a close season, as is the case with the trout and salmon. This method of conserving the marine fishes, though quite practicable with a purely sporting fish like the trout, is obviously impossible with a staple article of diet, and would mean a suspension of all fishing during two or three months of the year. The injurious effects of overfishing have long ago been experienced in the older and more thickly populated countries, and these have in many instances been benefited by wise legislation, and latterly by artificial propagation. Notwithstanding this, it is still sometimes asserted that it is impossible for man by overfishing to upset the “balance of nature,” and that even if an area were completely denuded of all life, nature, in her bounteous generosity, would at once assert her rights and establish her former balance of species. In support of this, it is pointed out that more fish are taken annually around the British coast than was the case a hundred years ago. But it must be remembered that whereas all the fishing was then done by lines and sailing-trawlers, within easy reach of the coast, there are now engaged hundreds of large well-equipped steam-trawlers, engaged in trawling at a distance of hundreds of miles from the coast, and as far north as Iceland.
It is generally admitted that to maintain the balance of a species it is only necessary for two from the hundreds of thousands, and in many cases millions, of eggs produced by a single
fish to arrive at maturity. Whether this theory be accepted in its entirety or not, it is very evident, from the floating nature of the eggs of most marine fishes, and (locally) the close proximity of the spawning-area to the coast, that enormous numbers of these eggs must be washed on shore and lost, or otherwise destroyed. External fertilisation and consequent non-impregnation will probably account for the loss of a large percentage, and when we consider the vast hosts of enemies of the ova and fry swimming at or near the surface of the water, we cannot but conclude that it is during this helpless pelagic existence that the great bulk of the destruction is brought about. It is to compensate for this tremendous loss that nature has bestowed upon most marine fishes such wonderful provision for the maintenance of their kind. The vast heaps of “whale-feed” (Grimothea) cast up on the beaches at certain seasons of the year provide a visible and easily appreciated example of the enormous destruction that takes place in the early swimming stage of this important fish-food.
The waters around the New Zealand coast at the present time abound with a varied and valuable assortment of edible fishes. The fishing industry is as yet in its infancy, and it cannot be said that overfishing is being done, except in certain very limited areas, where, at any rate from local report, a marked decrease in the number and size of such fish as the flounder and blue-cod have been noted. It is chiefly amongst such purely littoral and estuarian fishes that a diminution of the supply may be expected as the result of human operations. Trawling on the east coast is at present confined to within about eight or nine miles from the land, and to about 24 fathoms of water. The absence of offshore banks and relatively quick shelving slopes around this part of the coast will probably tend towards keeping many species within a few miles of the land. The results of deep-sea trawlings will be awaited with interest, as it is intended to exploit the deeper waters and trawl to a depth of 100 fathoms. In the United States of America, large numbers of trained men, termed spawn-takers, are employed during the spawning season of the cod and other marine fishes. These men accompany the long-line fishermen at this season, and collect and fertilise the eggs of all the ripe fish that are caught. These eggs are forwarded (often by rail) to the nearest hatchery, where they are hatched, retained in the boxes as long as possible, and then liberated where it is considered that they are most likely to thrive.
The present method of liberating these tiny larvÆ before the yolk-sac has been absorbed is not at all satisfactory, and there can be no question that a great improvement would be
brought about if it were possible to rear and protect the fry for a longer period. But until our knowledge of their food and of the conditions suitable to their early stages is widened we must remain content with the present methods. Only on few occasions have the larvÆ of any of the flat fishes been reared until the adult bottom stage was reached, and then only in very small quantities, and with very constant attention. Experiments in planting the larval plaice in enclosed lagoons are now being conducted by the directors of the biological station at Port Erin, Isle of Man, and although no definite results have as yet been achieved, there appears to be every prospect of ultimate success.
Nothing has as yet been learned of the migrations, spawning habits and areas, &c., of most of the “round” fishes, such as the groper, ling, cod, moki, &c., but from our brief experience with the flat fishes it appears to be a matter of little difficulty to collect and hatch millions of the eggs (otherwise almost certainly lost) of many of these fishes. Even at the present time, when only two trawlers are engaged, it would be quite possible, by placing a spawn-taker on board of each trawler, to collect these during spawning-time in numbers far beyond the capacity of the present equipment of the station.
It was hoped that more use would have been made of the station as a base for original research work, but it is to be regretted that again during the past years so little scientific aid has been enlisted to assist in the elucidation of the many problems with which we are faced, and which are only possible to the trained biologist.
Explanation Of Plates XVII-XX.
Fig. a. Eggs of gurnard (Trigla kumu), twenty hours after fertilisation, at 9° C.
Fig. b. Eggs of gurnard (Trigla kumu), forty-three hours after fertilisation, at 9° C.
Fig. c. Eggs of gurnard (Trigla kumu), fifty-two hours after fertilisation, at 8.6° C.
Fig. d. Eggs of gurnard (Trigla kumu), sixty-eight hours after fertilisation, at 8.4° C.
Fig. e. Eggs of gurnard (Trigla kumu), ninety-one hours after fertilisation, at 8.4° C.
Fig. f. Eggs of gurnard (Trigla kumu), 115 hours after fertilisation at 9° C.
Fig. g. Eggs of gurnard (Trigla kumu), 139 hours after fertilisation, at 9.6° C.
Fig. a. Eggs of gurnard (Trigla kumu), 163 hours (just hatching), 9.8° C.
Fig. b. Newly hatched larva.
Fig. c. Larva, forty-eight hours after hatching.
Fig. d. Larva, four days after hatching.
Fig. e. Larva, six days after hatching.
Fig. f. Egg (unfertilised) of flounder (Rhombosolea plebeius).
Fig. g. Same, twenty-four hours after fertilisation.
Fig. a. Newly hatched larva of flounder.
Fig. b. Same, fifth day after hatching.
Fig. c. Egg of brill (Caulopsetta scapha), just before hatching.
Fig. d. Egg of sole (Peltorhampus novœ zealandiœ), four hours after fertilisation; segmentation commencing.
Fig. e. Newly hatched brill.
Fig. f. Larval sol three days after hatching.