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Determination of age ofkahawai Arripis trutta(Bloch & Schneider)D. Eggleston aa Fisheries Research Division , Ministry ofAgriculture and Fisheries , Wellington, NewZealandPublished online: 30 Mar 2010.

To cite this article: D. Eggleston (1975) Determination of age of kahawaiArripis trutta (Bloch & Schneider), New Zealand Journal of Marine andFreshwater Research, 9:3, 293-298, DOI: 10.1080/00288330.1975.9515568

To link to this article: http://dx.doi.org/10.1080/00288330.1975.9515568

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1975] 293

DETERMINATION OF AGE OF KAHAWAI ARRIPISTRUTTA (BLOCK & SCHNEIDER)

D. EGGLESTON

Fisheries Research Division, Ministry of Agriculture and Fisheries,Wellington, New Zealand

(Received 17 January 1975)

ABSTRACT

Scales are unsuitable for age determination in Arripis trutta older than 5y(approximately equivalent to 40 cm L.C.F.). Otoliths can be used for fish of allages. The maximum age recorded is 22 y.

INTRODUCTION

The kahawai Arripis trutta is an important commercial fish ("Aus-tralian salmon") in Australia and is of considerable potential import-ance in New Zealand. Studies have started recently on the fisheriesbiology of this species in New Zealand waters. As a first step it wasnecessary to develop a reliable means of age-determination; this paperdescribes the investigations carried out and the conclusions reached.

There has been considerable work on Arripis trutta in Australia(Fairbridge 1951; Malcolm 1959, 1960, 1966; Nicholls 1973). Australianworkers have relied solely on scales as a means of age-determination(W. B. Malcolm, N.S.W. Department of Fisheries; C. A. Stanley,CSIRO, Cronulla; and R. C. J. Lehanton, W. Australian Department ofFisheries and Fauna, pers. comms) and the maximum age recorded h7 y for the eastern subspecies, A. trutta trutta Whitley, and 9 y for thewestern subspecies; A. trutta esper Whitley (Malcolm 1966). Scalesof New Zealand kahawai have been found to have up to six clearannuli, and in some cases a further four were counted, but the edge ofthe scale proved difficult to interpret in fish longer than about 45 cmfork length. As fish up to 60 cm in length were caught, otoliths wereexamined as a possible means to determine the age of larger fish.

MATERIAL AND METHODS

From May 1972 to April 1974, scales and otoliths were collected fromkahawai caught from the research vessels James Cook and Ikatere, andthe technology vessel W. J. Scott. The fish were taken by trawling ortrolling and were caught at many localities around New Zealand. Thesnout to caudal fork length of the fish was recorded to the nearest wholecentimetre below.

N.Z. Journal of Marine and Freshwater Research 9 (3): 293—8

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294 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [SEPT.

. 4 '- . '

, fy • "

. > '

1 '••', ?-:

' • * : • * 7 ' : :

• . ' • 1 f - *

FIG. 1—Scale of kahawai Arripis trulla; annul! 1-6 indicated by whitebars.

Scales were taken from below the lateral line in the mid-region ofthe body. Both scales and otoliths were stored dry for later examination.

Scales were examined with a scale projector. They are weakly ctenoidwith numerous fine circuli and a series of annuli (Fig. 1); terms usedare as in Lagler (1947). The annuli are formed in the anterior field by2-3 thin or fragmented circuli, at the antero-lateral corners, and in thelateral field by fragmented circuli and at the postero-lateral corners bycurvature and abutment of circuli. In some scales the annuli can be seento continue in the posterior field. Some scales had fragmented or thincirculi in the anterior field which were not accompanied by fragmenta-tion in the lateral field or the typical pattern at the postero-lateralcorners. These were regarded as false annuli and were disregarded.Replacement scales were frequent on larger fish: such scales werediscarded. Three or four scales from each fish were examined and thenumber of annuli recorded. Counts from the same fish were usuallyconsistent.

The otoliths are relatively thick and dense (Fig. 2). When examinedin 70% alcohol a series of opaque and hyaline zones could be seen but

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1975] EGGLESTON—AGE OF KAHAWAI 295

•\y.ji[.

FIG. 2—Otolith of kahawai Arripis Irutta; a-whole unbimil ololilh; b partof otolith a (as indicated) after light burning.

because of the density of the otolith they could be counted reliablyonly in young fish. However, alternating light and dark brown zonescould easily be seen if the otolith was split across the nucleus and thebroken surface ground smooth, then lightly burnt with an alcohol flamebefore being placed in 70% alcohol and examined by low power stereo-microscopy. The dark zones correlated with the hyaline zones in theunburnt otolith. Further examination showed that if the whole otolithwas carefully heated to a light biscuit colour the zones were clearlyvisible on one face of the otolith (see Fig. 2b) without splitting andgrinding. Comparisons of counts of zones on whole otoliths and groundsections showed exact correlation in the number of zones and all furthersamples were examined by counting the dark (hyaline) zones on heatedwhole otoliths. Otolith readability was excellent, and no otoliths werediscarded as unreadable.

RESULTS AND DISCUSSION

In order to determine whether hyaline otolith zones or scale annuliwere deposited annually, scales and otoliths collected during all monthsof the year were examined. The fish were considered in 3 size groups:

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50-

401

c 30-

20^

10-

Otolith zones

Scale annuii

5 10 15Otolith zones and scale annuti

20

FIG. 3—Length range of kahawai Arripis trutla grouped bynumber of otolith hyaline zones and by number of scaleannuii.

TABLE 1—State of otolith and scale edge of kahawai Arripis trutta in each month (10 fish ineach size group examined each month; data collected between May 1972 and April 1974and pooled)

Fish Size M

Number of Fish with Hyaline Otolith MarginLess than 40 cm 0 0 3 940-50 cm 0 0 0 8More than 50 cm 2 1 3 8

Number of Fish with Ring at Edge of ScaleLess than 40 cm 0 0 0 040-50 cm 0 0 0 0

M

71010

00

J

101010

00

J

101010

00

A

101010

06

s

1098

55

O

98•5

55

N

833

107

D

000

35

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shorter than 40 cm, 40-49 cm, and longer than 50 cm. Kahawai firstspawn at 35-40 cm. Ten fish in each size group were examined eachmonth. The data recorded were number of hyaline zones on otolith andstate of otolith edge; number of scale annuli, width of scale margin,and (subjectively) whether the scale was growing or being resorbed.The results relating to scale and otolith margins are shown in Table 1.

Otolith zones are annual in all size groups; in general, hyaline materialis laid down from March to November and opaque material for therest of the year. By comparison the scale annulus of fish smaller than40 cm is laid down in September-December, and for 40-50 cm fish inAugust-December. In larger fish the scale cycle is less clear, and noperiod of annulus formation could be distinguished although subjectiverecordings of the state of the scale edge indicated a cycle of growth andresorption, with growth from December to May. Thus scales cannot beused to determine the age of large kahawai.

Completion of the otolith hyaline zones in November coincides fairlyclosely with completion of the scale annuli in December. Since kahawaispawn from January to March both these events occur about ninemonths after the middle of spawning. Accordingly, these events takeplace at ages of approximately 9 months, 21 months, 33 months, and soon.

The 120 aged fish were grouped by number of both otolith zones andscale annuli. The length range of each group is shown in Fig. 3, whichis only indicative of the general growth pattern, as it includes fish from allmonths and a wide range of areas. A discrepancy between scale andotolith readings begins at age 5 and it is apparent that otoliths must beused to determine the age of fish older than 5 or longer than about40 cm. Otolith aging shows that kahawai can attain ages of 22 y.

The fact that New Zealand kahawai stocks contain fish more than20 y old, and not the maximum age of 7 y as anticipated from Australian:publications, is of considerable importance to pelagic fisheries develop-ment and management strategy in New Zealand. Slow growing, long-lived species are more susceptible to overfishing than rapidly growing,short-lived species. However, the likely impact of fishing on kahawaistocks cannot be assessed until more information is available on stocksize: such data are being collected.

LITERATURE CITED

FAIRBRIDGE, W. S. 1951: Some populations of the Australian salmon, Arripistrutta. Indo-Pacific Fisheries Council Proceedings, 2nd Meeting, Sec-tion II: 80-4.

LAGLER, K. F. 1947: Lepidological Studies. 1. Scale characteristics of the familiesof Great Lakes fishes. Transactions of the American MicroscopicalSociety 66 (2) : 149-71.

MALCOLM, W. B. 1959: The populations of Australian "salmon", Arripis trutta,(Bloch and Schneider) in Australian waters. Australian Journal ofMarine and Freshwater Research 10: 22-9.

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1960: Area of distribution and movement of the western subspecies ofthe Australian "salmon", Arripis trutta esper Whitley. AustralianJournal of Marine and Freshwater Research II: 282-325.

1966: "Synopsis of FAO Species and Stocks Thesaurus of data onArripis trutta (Bloch and Schneider). Pp. 1-17 in "Commonwealth-States Fisheries Conference, Southern Pelagic Committee, TechnicalSession, Cronulla 1966". Vol. 3, SPP(T) 66/4A (Mimeogr.) (CSIRO,Australia: Cronulla, NSW).

NICHOLLS, A. G. 1973: Growth in the Australian "salmon" Arripis trutta (Blochand Schneider). Australian Journal of Marine and Freshwater Re-search 24: 159-76.

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