BENZIE; ASPECTS OF SPAWNtNG BEHAVIOUR OF WHITEBAIT 31

SOME ECOLOGICAL ASPECTS OF THE SPAWNING

BEHAVIOUR AND EARLY DEVELOPMENT OF THE

COMMON WHITEBAIT.

GALAX/AS MACULATUS ATTENUATUS (JENYNS)

VIVIENNE BENZIE'

Department of Zoology, University of Canterbury, Christchurch

INTRODUCTION

It may seem unorthodox to begin a paper thatpurports to describe the ecology of the early stagesof the fish, Galaxias maculatus attenuatus (Jenyns),(taxonomy revised by Stokell, 1966), with a lengthydescription of its breeding habits, but this is neces-sary; the adults select their breeding sites and soset the conditions for the development of theyoung.The spawning habits of G. m. aftenuatus are not

commonly known, yet they were the subject ofaccounts by Captain Hayes (1930, 1931, 1932) andhave also been mentioned by Burnet (1965). Scott(1938) studied the biology of the Tasmanian sub-species of G. maculatus and Pollard (1966)described the breeding habits of a land-lockedpopulation in Victoria, Australia. At present wecannot be sure if Pollard's population correspondswith either the New Zealand or Tasmanian sub-species as described by Stokell (1966).Briefly, the life cycle of G. m. aftenuatus is as

follows: Great shoals of ripe adult fish gather inthe freshwater streams in which they have becomesexually mature during summer. They begin amigration downstream so that they reach areas oftidal influence and eventually spawn communallyin estuaries at the peak of spring tides betweenearly January and early May. The present studywas undertaken to examine the timing of this pro-cess and to attempt to find the factors that couldtrigger off the migration. I have also tried to linkthe above behaviour with certain features ofembryology and development. The paper falls intothree sections: a description of the study area andspawning behaviour. an account of the character.istics of the spawning area, and a discussion ofthe factors affecting the development of the eggs.

STUDY AREA AND METHODS FOR OBSERVATION

OF SPAWNtNG HABITS

This study was carried out in only one area,Saltwater Creek, which runs into the Ashley Riverestuary north of Christchurch, in Canterbury. The

particular stream runs into Saltwater Creek besidethe Main North Road bridge, and a diagram ofthe area is given in Figure l. All areas submergedat normal spring tides are within the dotted con-tour, the present spawning area is marked indiagonal lines and the past, additional, extensivespawning area (which was destroyed when a newbridge was built) is shown in broken hatching.

FIGURE I. SaltWater Creek spawning area.KEY1. Scale - 3 metres.2. Present spawning areas.3. Past spawning areas.4. Areas apparently suitable for spawning.5. Tree.6. Estuarine area of bank.7. Fence.

The areas within the contour are all alike in thatthey are lower than those outside and have a gentleupward slope (0 to 10 degrees) until the inneredge of the contour is reached, when the rise isusually about 30 to 60 degrees. A pasture grassand clover mixture covers the ground almost downto the bank of the river. Saltwater influence isclearly indicated by the associated vegetation which

Ii< Mrs C. J. Burrows.

PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL. i5, 1968

is usually'a small sedge (Scirpus sp.) and by thefauna which is entirely composed of saline-tole~a'\tspecies. A salt-intolerant fauna (earthworms,spiders, collembola and nematodes) was always

found in the pasture, even among the eggs.During 1959-62, shoals of fish moving down to

spawn were caught in a seine net spanning a nar-

row part of the stream, These catches were madeas the tide dropped. The sex ratio was calculatedfor spawning shoals in different months for com-parison with the ratio on the feeding groundsinland. .

Naturally spawned eggs were collected by cut-ting out grassy slabs (turfs) and enclosing thesein plastic bags. Artificially spawned eggs were usedto obtain the earliest developmental stages.

FIGURE 2. Saltwater Creek. Predicted tides und

actual spawning dates, 1959.

Results

The predicted tides, the times of full and newmoon and the days on which spawning occurred.in successive years of study, are indicated inFigures 2, 3, 4, 5 and 6. Observed and predictedtidal levels were not always the same but therewere only two occasions when there was a grossdiscrepancy. These were at times of abnormallyhigh tides. Fish aggregated in the spawning areatwo or three days before spawning.

FtGURE 3. Saltwater Creek. Predicted tides andactual spawning dates, 1960. '

In 1959 only two spawnings were observed, .oachin a separate month, but other spawnings wouldhave occurred in that year. At that time work wasconcentrated on the embryology of the fish ratherthan on its spawning habits. The years 1959, 1961,

1962 and 1967 all show features in common. Thespring;,: tides )vere associated with either the newmoon or the full moon in each season and spawn-ing began from one to three days after the appro-priate moon phase. Eggs were laid on morning and

evening tides for up to three days alter spawning

began.

FIGURE 4. Saltwater Creek. Predictedactual spawning dates, 196/.

In 1960 (Fig. 3) an especially interesting pheno-menon occurred: the spring tides shifted from thenew moon to the full moon during the spawningseason. Only in this year was any irregularity ofspawning seen. The January and February spawn-ings were apparently normal but the fish spawned

, again just twenty-five days later on rising tides andagain ten days later at the new moon. This spawn-ing shared with the January and February spawn-iogs at the new moon the somewhat unusualcharacter of occurring on the day of the new moon.Similarly, the final spawning at the full moon inApril fell on the specific day. The data from thisyear will be examined in greater detail below andcompared with the data for 1962.

FIGURE 5. Saltwater Creek. Predicted tide.' andactual spawning dates, 1962.

In general, peak spawning appeared to occur asthe tide began to fall. The whole school moved intothe pasture grass and the fish spawned in such adepth of water that while their bellies touched thesubstrate their backs just broke the surface. Theextent of spawning could be assessed because theeggs from individual females were clustered in arestricted area. If spawning was Jight these masseswere easily recognisable; if it was heavy the dis-tinction broke down and there was a heavy cover

32

BENZIE: ASPECTS OF SPAWNING BEHAVIOUR OF WHITEBAIT

of adhering eggs. The eggs, which are just over

1mm. in diameler, adhere to the lower paris ofthe vegetation, especially in the rather fibrous grassroots found above ground level. As spawningoccurs on successive tides which may be of dif-ferent heights, the end result may be a deephorizontal band of eggs, up to three or four feetwide, on the spawning ground. There is no .evidencefor any male-female pairing in this spawning,rather it is a communal phenomenon. All the fishmove in to the area together and as the sex ratioin spawning shoals varies from month to monthit is very unlikely that a pair bond is formed. Eachfemale sheds all her eggs in a short series ofabdominal contractions associated with a laterallash of the tail. The males shed their milt and inthe disturbance it is spread so that the whole areaof water over the shoal looks milky.

FtGURE 6. Saltwater Creek. Predicted tides andactual spawning dates, 1967.

In addition, I kept a watch on the controlledoutlet from Horseshoe Lake, which empties intoKerr's Reach of the Avon River, Christchurch.Several large schools of ripe G. m. attenuatus werenetted there but they were caught only on daysimmediately preceding the spawnings at SaltwaterCreek. Presumably they were about to spawn inthe lower reaches of the Avan River.

While this study was in progress Burnet (1965)had begun observations on the downstream migra-tions of adult G. m. aftenuatus by observingcatches at a trap built to span a small tributary ofthe Waimakariri River, the main river south of theAshley River. Burnet placed juvenile G. m. aftenu-atus above the trap early in the summers of 1959-60 and 1962-63. In 1958 the fish which 0nteredthe trap were those which had entered that waterunimpeded during the summer preceding the build-ing of the trap. Figure 7 shows Burnet's catchesfor 1958, plotted against the predicted tide for thesame period. These fish would probably havespawned on the next spring tides if they hadbehaved in the same way as the fish observed inthe later seasons. "

FIGURE 7. Adult G. m. attenuatus caught in SouthBranch Trap, 1958 (after Burnet).

The combined data from all sources are shownin Figure 8 which represents in detail the 1960breeding season. Burnet's data are given as blackhistograms. The migrations of mature fish at Kerr'sReach clearly followed the same temporal patternas elsewhere but differed in the relative numbers.

FIGURE 8. Combined data for 1960 breeding season.N.B. Subjective data in diugonullines (own observations)

or dotted.KEY1. 5. Very extensive spawning.2. No spawning.3. Some spawning.4. Quite extensive spawning.6. A few egg masses.

33

TIDALHEIGHT

'"FEET

HOKITIKA

SALTWATER

CREEK

FISHMOVINGDOWN

"TRAP

FISNMOVING DOWN

"KERR.SREACH

PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL. 15, 1968

The absence of fish at any particular time at thissite may merely be because they were not noticed.but Burnet's data show conclusively that the migra-tion of mature fish can be correlated with the tides(or moon).Although the assessment of intensity of spawn-

ing is subjective it provides some scale of referenceand the dates are exact. Data from spawnings atthe mouth of the Hokitika River (A. Cutbush,pers. comm.) are included.A comparable figure for 1962 is given in

Figure 9. The peak migrations of mature fish atBurnet's trap once again preceded the observedspawnings at Saltwater Creek, although the pictureis much clearer because the tides were not thencomplicated, as they were in 1960.

FtGURE9. Combined data for 1962 breeding season.N.B. Subjective data in diagonal lilies.

KEV1. No spawning.2. Quite extensive spawning on three tides.3. Very extensive spawning on three tides.4. Quite extensive spawning on five tides.5. A few batches spawned on one tide.

Discussion

The data presented in Figures 2-9 inclusive showthat sexually mature G. m. aftenuatus migratedownstream at the phase of the moon appropriateto the nearest spring tide.Burnet (1965) analysed his trap results and

found that although they were clearly cyclic, andtherefore independent of climatic factors such asrainfall, their cyclic nature could be expressed interms of lunar, lunar plus tidal or tidal effects indifferent years. The additional data supplied tothe present study from Burnet's invaluable recordsat the fish-trap (Figs. 8, 9) show that the fishmigrated in large numbers just before the days onwhich spawning was observed at Saltwater Creek.

The only inference which may be drawn from thisis that the phase of the moon immediately associ-ated with the spawning tides cannot be correlateddirectly with these migrations since they actuallyprecede the moon-phase. The assumption had pre-viously been that the simplest stimulus the fresh-water fish living up to twelve and more milesinland could respond to is either moonlight or itsabsence. That this is too naive an explanation isclear because overcast weather has apparently hadno effect on the overall pattern. It is tempting tosuggest that the phase of the moon (full or new)immediately preceding the "spawning" phase (newor full) acts as a trigger to set off the downstreammigration but, in the absence of any further ,ovi-dence, it would be folly to be satisfied by thishypothesis. An examination of Captain Hayes'data presented in Figures 10 and 11, shows that

FIGURE10. Manawatu River. Predicted tides and'pawning dates, 1930.

spawning appeared to occur after and on ~itherthe full or the new moon in each year but thereappears to be no correlation with the tides in 1930and only a partial correlation in 1931. These resultsare presented as an indication that conditions forspawning may be very different in other areas.Other factors such as barometric pressure (Deelder1954) may also affect fish migrations; Burnet(1965) mentions these in the analysis of hisresults.

FIGURE 11. Manawatu River. Predicted tides and'paw/Zi/Zg dates, 1931.

Without a detailed study of all climatic factorsno further conclusions may be made, but it maybe possible to test for the initiation, by the appro-priate lunar phase. of downstream migration.,

34

TABLE 1. A verages of meteorological data forChristchurch, 1959-62.

Temperature in 0c. Jan. Feb. Mar. Apr. MayMean daily grass minim1;m 17.3 16.8 14.2 12.0 9.0Mean daily maximum 22.5 21.6 t8.9 17.4 13.6Mean daily minimum 12.1 11.3 10.t 8.2 4.9Mean daily grass minimum 10.6 9.6 7.9 5.0 2.4Mean days of ground frost - - 1.0 4.2 11.0

BENZtE: ASPECTS Or SPAWNtNG BEHAVIOUR OF WHITEBAtT 35

FACTORS INVOLVED IN THE CHOICE OF

SPAWNING SITE

A careful examination of the spawning area onmany occasions made it clear that spawning hadoccurred only in certain places (marked in Fig. I)but that it is restricted to far fewer of these places

than expected is, in itself. interesting.

Several theories may be put forward to explainthese apparent anomalies but almost all can berefuted. The first set of hypotheses are concernedonly with the characteristics of the spawningground:l. The areas are too deeply sabmerged at the

appropriate time: This is not true as they havethe same slope as the areas which are used and areimmersed to the same ,~xtent.2. There is not enough water at spring tides to

cover the area: This is not true of the area indi-cated.3. There is salt water influence at the spawning

level: This is not true.4. The vegetation is not suitable: The vegeta-

tion in all areas indicated is the same grass-clovermixture as in the areas which are reached byfreshwater only. The same small Scirpus sp. vege-tation occurs in the areas contaminated by salt-water.5. The areas are not accessible to the fish: All

such areas were equally accessible.6. The areQ!:,'ma:r be too far upstream: This

could be true of the areas upstream of the foot-bridge but the study was downstream from thisbridge and the spawning ground used regularly isone of the most upstream "bays" of the river bank.

Other hypotheses which take into account thebehaviour of the fish may also be put forward:l. There may be some chemical factor involved.

or some other such feature not detected bv ahuman observer: This is obviously possible and jtcould be that the precise balance between thesaltwater welling in from the estuary below andthe overlying freshwater flowing down the streamdetermines the spawning place. If so, it is ditlicultto reconcile the two different places in whichspawning occurs or has occurred. Le., ::tbove andbelow the road bridge. This hypothesis will haveto remain open, in the absence of any conclusive

evidence for or against.

2. It is possible "that the communal spawninghabit requires a concentration of fish in one area:As evidence for this there is the fact that the fishcollect in the area before spawning begins, whichsuggests that final maturation may be facilitatedby schooling. Further supporting evidence is sup-

plied by the 1967 spawning results. Very differentnumbers of eggs were laid on successive spawnings.

even between successive tides, yet each month alleggs were laid in the same area. Other "vidence [orthe importance of schooling behaviour is deducedfrom the fact that with these relatively light spawn-ings it was possible to see that eggs were coneen-

tratod in the areas easiest of access even thoUQh~

the tides were different in the different months sothat these areas varied. More .~vidence in :favourcomes from the observations made during theabnormally high tides of 1960. Then, eggs werelaid in a large hollow in the pasture itself, highabove the usual spawning areas which would havebeen submerged.During the years of this study all the ,'ggs col.

lected were taken from the pasture grass-clovervegetation. Assiduous searches of sedge beds fur-ther downstream, in which the dominant plantswere the tall Leptocarpus simplex and Scirpusamericanus, never uncovered any eggs. This isparticularly surprising as they have been collectedthere in past years (Mrs. F. R. Allison, pers.comm.) and Hayes (1930, 1931, 1932) mentionssedges and rushes as spawning areas.,

THE ECOLOGY OF THE EGGS

During the spawning season the range of theambient temperature from January to May variesconsiderably and daily fluctuations are also verygreat, especially in late April to May when thenights are cold. The nearest meteorological stationmeasuring similar climatic conditions is at Christ.church. The results for the appropriate years(1959-62) have been averaged in Table I (NZ.Meteorological Service, 1962-64).

These data were compared with the summaryof observations at Christchurch from 1905-60(NZ. Meteorological Service, 1966). The latter

,

have lower values but all the monthly trends arethe same. The significant features in Table I arethat the mean daily grass minimum, which wouldcorrespond with the temperature at which G. rn.aftenuatus eggs would be developing, is lower thanthe minimum air temperatures each month; andin May, which marks the end of the spawning

36 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL. 15, ]968

season, frosts have become prevalent (they areequally prevalent in the 1905~60 summary ofmeans).It is all the more surprising that laying occurs in

areas which are apparently high and dry for overtwo weeks out of four, when the relative stabilityof the temperature of water over such a periodis considered. Maximuffiwminimum thermometerreadings taken in these areas showed that a singlebatch of eggs may be exposed to a range between5°C. to 18°C. in one day; yet no abnormalities indevelopment were seen and egg mortality was verylow. Not only eggs collected in the field but alsothose fertilised artificially were used for studies ofthe influence of temperature and water on develop-

ment.During these studies I found that even although

eggs will develop in fresh water, salt water, onmoist cottonwooI or on damp turf, the success ofartificially fertilised eggs was far below that ofnaturally-spawned eggs. This was true even of eggsspontaneously shed and fertilised by captured fish,when such eggs were gently pipetted into the con-tainer or on to the substrate. Stripping and fertilisa-tion were easy but these eggs proved very suscepti-

ble to the attack of Saprolegnia, as did those eggsexuded spontaneously into a collecting bucket.A search for an explanation for this suscepti-

bility to infection led to the idea that the adhesivelayer which attaches the eggs to the grass and thesoil actually protects them against infections. Thisidea was supported by the fact that when eggswere removed from these masses with a fine paint-brush and stored separately in water they suc-cumped to Saprolegnia quickly and their adhesivelayer could be seen to be incomplete. Undisturbedeggs on turfs immersed in water came to no harm.I( must be important for eggs to be attached assoon as they are laid, so that this layer is undis-turbed; but an antibiotic effect from the soil cannotbe ruled out, at least as an additional factor. Innatural conditions the few eggs which die do so inthe first few days of development, so that theirdeaths may be attributed to a failure in develop-ment rather than to an attack from outside.The various requirements of the eggs during

development may be summarised as protection,supply of water and facilities for gaseous exchange.Protection is provided by the vegetation which isabout 6-8 in. high. Water is provided by the tidalcover twice daily for the first few days; it is thenconserved by the vegetation. The spawning groundand all similar areas are well sheltered from directsun by overhanging willow trees and by the closecover of low vegetation. The eggs are laid in the

lower levels of this vegetation, from soil level toabout an inch above it. The microclimate in suchan environment is very stable, with less (~xtremetemperatures than the air above and a very highrelative humidity and water vapour pressure(Geiger 1965). When the grass was undisturbedsuch an area was very close to an aquatic mediumand the eggs developed normally, according to thetemperature. Their turgidity was maintained unlessthe grass was cropped short by cattle, when desicca-tion occurred unless soil' moisture was high. Itwas only during the very'hottest periods that .oggswere killed in this way.

Gaseous exchange probably occurs by diffusionacross the moist, chodon. Towards the end ofembryonic development more complex wastesaccumulate inside the eggs so that eggs ready tohatch often appear yellow.

It had previously been found that in hot sum-mers the eggs were ready to hatch 14-16 daysafter laying (temp. max. 18°C., min. 1l0C.); andthat if eggs were kept cool in the laboratory therate of development was slowed. In 1967 constanttemperature cabinets were available at 4.4°C. and1 rc. Sample turfs in plastic bags were kept atthese temperatures and checked daily by the

Stage,. Stage

"

FIGURE 12. Stages in the embryonic development ofG. m. attenuatus.

Stage,.

Stage.

BENZtE: ASPECTS OF SPAWNING BEHAVIOUR OF WHtTEBAtT

removal of a number of eggs. As far as could bedetermined each turf carried eggs from a single

famale.Several stages of development are given in

Figure 12. (The details of embryonic developmentare to be the subject of another paper.) Thesestages are also indicated on the growth graphs inFigure 13 and show the relative effects of the twotemperatures. All eggs developed at the same rateat a constant temperature, but whereas embryoswere ready to hatch after 10 days at Ire., it took31 days at 4.4°e. The four stages of developmentof Figure 12 are marked on Figure 13. As theanatomy changes. very little during the last daysand the amount of yolk present varies a little withthe temperature of development, readiness to hatchis recognised by the softening of the chorion.

oTEMPERATURE c.

FIGURE 13. Rate of development of G. m. attenua-tus at di/Jerent temperatures, with field data added.Number.\' in body of graph are development stages,

.

as shown in Fig. 12.

The fact that this remarkable temperaturelability is actually called upon in development isshown in Figure 13, by the interrupted lines show-ing the field data for 1967. Whereas the Februaryand March eggs were ready to hatch after sixteenand seventeen days respectively, the April eggs

developed during cold weather and took twenty-nine days to hatch. Figure 6 indicates that whereas

the fiebrual'Y and March eggs would have had tosurvive for about thirteen days before hatching,the April eggs had already been immersed for atleast seven days before the first were ready tohatch and they hatched over three days. In everyother year of the study the periods of developmentin the different months were comparable with theresults for 1967.Hatching involves two processes:(i) The softening of the chorion by Stage 22.(ii) Immersion of the egg in cold water. The

embryo performs rapid coiling move-ments which rupture the chorion and sothe young fish ."capes.

Embryos may hatch spontaneously at Stage 22,but may take up to three more days (April eggs,1967).How did the experimental embryos really fare at

these diverse but constant temperatures, and howdo these findings correlate with observed fielddata? First, the experimentally-reared eggs experi-enced more difficulty in hatching than those rearedat less extreme temperatures. In fact, 4°C. and17cC. represent near-critical limits for normal

development at constant temperature. Yet in thefield, with wide daily fluctuations, eggs developnormally. Although below the grass cover theeggs remain moist they may occasionally becomequite dry. When the egg loses its turgidity, so thatthe chorion collapses upon the embryo, it is stillviable if it regains moisture in a day or two. Thisloss and gain occurs occasionally before, and oftenafter, the softening of the chorion; but if loss ofwater has occurred immediately before the eggsare immersed by a tide (or artificially). they hatchon the subsequent tide (or over half an hour later).Turgid eggs hatch in up to ten minutes after. .

lInmerSlOll.

Tides high enough for hatching may not occursoon after the spring tide on which the eggs werelaid. In 1962 one entire spawning had to wait sixweeks before immersion. These young had littleyolk left and did not survive when hatched in thelaboratory. In 1960 the flood tide which immersedpart of the paddock resulted in the total loss of theeggs which had been laid over the entire floodedarea, as none were ever submerged again.Normally, the rising tides cover the spawning

ground about three to three and a half weeks afterthe eggs are laid. The young hatch and swim uptowards the light and swim together as if schooling.These responses are' easHy demonstrated experi-mentally, but at this stage in the life-history the

37

38 PROCEEDINGS OF THE NEW ZEALAND ECOLOGtCAL SOCIETY, VO!.. 15. 1968

"schooling" response is only a reaction to a cur.

rent. (Almost all larvae face into an artificiallyinduced current.) They are then swept downimmediately as the tide falls. The river waterbanked up by the spring tide rushes out to sea, sothat the flow through the estuary is a maximum atthis time. (Captain Hayes netted newly-hatchedyoung at the mouth of a river as the tide fell.) Theseyoung vanish out to sea and reappear as animportant component of our commercial whitebaitcatch about six months later.

CONCLUSIONS

It is clear that, in the area studied, adult G. m.attenuatus migrate downstream at such a time thatthey spawn on the spring tides during mid- to latesummer. This spawning usually occurs just afterthe new or full moon, whichever is associatedwith these tides at any particular time.When combined data for the years 1960 (Fig. 8)

and 1962 (Fig. 9) are compared it is clear thatmigration downstream precedes the phase of themoon with which spawning is apparently associ-ated. The year 1962 is especially interestingbecause fish spawned at the tidal changeover.Burnet's data suggest that although a large quan-tity of fish migrated at the appropriate time jnMarch, very few moved before the additionalspawning a fortnight later. At Saltwater Creek anextensive spawning occurred when the ground wasfirst covered, but after the new moon (the appro-priate phase in January and February) there wasa very extensive spawning despite the fact that thetides were falling. This is the only clear evidenceadduced during the seasons of the study of bothlunar and tidal effects operating in the determina-tion of spawning time. Apart from this, the tidallevel seemed to be the dominant factor, althoughhow it is perceived inland is not known.The fact that there was this discrepancy in 1960

lends support to the idea that the aggregation offish in the spawning area facilitates completionof their maturation and suggests that they sub-sequentJy spawn in an area chosen as suitable oncethe tides are high enough for the banks to besufficiently submerged by freshwater.The basic differences in the data for 1930 and

1931 (Figs. 10 and II) cannot be explained interms of this section of the present study.The spawning season for G. m. attenuatw;

studied in Canterbury ranged between January andMay, peak spawnings occurred usually in February~hd March. The only information available on thespawning habits of the Tasmanian form is the

suggestion by Scott (1937, p. 127) that "sexuallymature fish normally emigrate from creeks andheadwaters of rivers, descending to brackish orsaltwater to spawn about April, and are absentuntil about June or July".

The observations of Pollard (1967 and pers.comm.) are of great interest, since he studied alandlocked form of G. macula/us in Lake Mode-wane, Victoria. The lake is slightly saline andadult fish migrate up intermittently in-flowingcreeks to spawn in late winter and spring. Spawn.ing occurs when creeks are swollen after heavyrain so that eggs are laid in flat flooded vegetationby the water's edge. These eggs are stranded as thewater subsides, develop out of the water, andhatch on the first flood after development is com-plete (about two weeks after spawning). Hatchingmay be delayed up to at least a month afterspawning. This description shows that the popula-tion studied by Pollard had the same overallbehaviour sequence in its spawning pattern as thespecies I have studied, except that the fish spawnedin the later winter and spring (interpreted as Julyto September or October in the absence of anyother indication). There is no report of spawningoccurring in the New Zealand population of G. m.attenuatus other than in mid- to late summer. Thepublication of the description of two new speciesof Galaxias from New Zealand, each very similarto G. m. al/enua/us (Jenyns) and each collectedfrom small land-locked coastal dune lakes inNorth Auckland (McDowall 1967) is of interest,as in fact these species seem very like Pollard'spopulation of G. macula/us. However, details oftheir life histories would clarify their position.McDowall (1966) questions the identity of the fishstudied by Pollard. Details given by Pollard (pers.comm.) suggest that the fish he studied is morelike G. macula/us than any other species.

These investigations emphasise the necessity foran overall study of the life histories of the Gal-axiids. The spawning habits of the annuallymigrating populations of G. m. attenuatus in theCanterbury area have been very regular; but thedivergence of the data from those of Hayes forthe seasons of 1930 and 1931 for the ManawatuRiver, and the entirely different seasonal emphasisfound by Pollard, suggest that generalisation maybe dangerous. The ecological conditions for thedevelopment of the eggs are in all instances similar,in that the eggs are laid in vegetation which isleft apparently out of water for part of the lifecycle, so that the same effect has been achievedin different ways. This suggests that the spawning

BENZtE: ASPECTS OF SPAWNtNG BEHAVIOUR OF WHtTEBAtT 39

cycle is primarily concerned with access to suitableareas for embryonic development to occur. Sub-sequent growth to the whitebait stage takes aboutsix months in all instances.The breeding cycle of Pollard's fish, with its

reliance on flooding on several occasions so thatthe grassy spawning areas are covered, may seemmore hazardous than that of the fish spawning atSaltwater Creek. The relative danger is increasedby fluctuations in the height of spring tides frommonth to month in the latter area. Occasionallythis has resulted in the stranding of large numbersof eggs. In addition, the peak of the SaltwaterCreek spawning is in the February-March earlyApril period when temperatures are high and aproportion of eggs is lost through desiccation ifthey are not immersed within the month. At veryhigh temperatures the yolk reserves are severelydepleted so that the hatching young may often beless fit than those of Pollard's fish, which developand hatch in cooler months.Almost all breeding G. m. attenuatus in the

Canterbury study area are in their first year(Burnet 1965); that is, are up to six months olderthan whitebait. Therefore it is remarkable that inevery year of the Saltwater Creek study the samesmall spawning area was used provided the tideswere normal. There is no evidence to suggest thatthe fish had visited that spawning area before (thepresence of unripe fish in the school would haveprovided such evidence). Any homing hypothesis,involving the return of the young to the area inwhich the eggs were laid. their migration upstreamtoo, feed and mature and their migration down

again at spawning time, must take into account oneimportant factor: The eggs hatch and are sweptout of the spawning area to sea within a few hoursof hatching, so that the idea that a firm associationwith the area is formed should be regarded verysceptically until it is demonstrated that such ashort time will suffice. The homing of salmonoccurs after up to two years on the nursery siteand has been shown to be effected in the last stagesby olfactory cues (Hasler 1960).We are left with a spawning cycle in which the

adult fish, living inland, migrate to estuaries sothat their arrival just precedes the peak of thespring tides. The eggs are ]aid at and after thepeak. Each fish sheds all its products at onespawning. The eggs develop in grass and the larvaehatch when next immersed by the tides.

ACKNOWLEIXJMENTS

It gives me much pleasure to acknowledge herethe generosity of Mr. Max Burnet in the heJp he

gave me in beginning this study arid the supportafforded to me by his fish-trap records.In addition I thank Professor G. A. Knox, of

the Zoology Department of the University of Can-terbury, and all my colleagues who have helpedwith collection, transport, photography and criti-cism of this text, especially Dr H. B. Wisely who,in my absence oversca6, accepted the task of cor"recting the proofs and seeing them through thepress.

SUMMARY

A spawning locality for Ga/axias maClllat/ls attelllwt/ls(Jenyns) is described. Details are given of spawningmovements and dates for 1959-62 and 1967. The complexrelationship which must exist for a freshwater fish (albeitwith a marine larval phase) to move downstream onlyat such times that it will reach estuarine areas at springtides is examined.

Spawning habits and the conditions under which theeggs develop and the rate of development :1t differenttemperatures are described. An attempt is made to co-ordinate three studies of the spawning behaviour of thisspecies.

REFERENCES

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