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Pertanika 8(2), 265 - 271 (1985)

Effects of Handling on Hatchability of Eggs of theLeatherback Turtle, Dermochelys coriacea (L.)

E.H. CHAN, H.D. SALLEH and H.C. LIEWFaculty of Fisheries and Marine Science,

Universiti Pertanian Malaysia,Mengabang Telipot, Kuala Terengganu, Terengganu, Malaysia.

Key words: Leatherback turtle; hatchery; infertility rate; handling; hatchability;

ABSTRAK

Kadar ketidaksuburan di antara kumpulan telur penyu belimbing (Dermochelys coriacea)yang telah dieramkan di Pusat Penetasan Penyu di Rantau A bang, Malaysia, dianggarkan sebanyak22%. Varians penetasan di antara kumpulan telur yang subur berjulat antara 35.7- 96. 7% (x =78%) bagi telur yang telah dikendalikan dengan penuh teliti. Untuk telur-telur ini kadar penetasantidak menunjukkan korelasi masa di antara peneluran dan menimbus semula. Telur-telur penyubelimbing hanya boleh menahan pengendalian secara kasar selama 5 jam selepas ovzposisi. Selepasdari tempoh ini cara penjagaan yang teliti untuk menahan darzpada penggulingan, pelanggaran,pusingan dan penyahorientasipaksi tegak dapat meninggikan kadar penetasan.

ABSTRACT

The infertility rate among clutches of leatherback sea turtle (Dermochelys coriacea) eggsincubated in the hatchery at Rantau A bang, Malaysia is estimated at 22%. Variance in hatchabilityamong fertile clutches ranges from 35.7- 96. 7% (x = 78%) for eggs handled with maximum care.For such eggs hatchability did not show a correlation with the time between ovzposition and reburial.Leatherback eggs can tolerate rough handling only up to 5 hours after ovzposition. Beyond thisthreshold, careful handling to prevent rolling, bumping, rotation and disorientation of the verticalaxis will enhance hatch rates.

INTRODUCTION

Hatchery operation is an important tool insea turtle conservation. Protected incubationunder natural conditions, coupled with releaseof hatchlings after emergence is considered byturtle conservationists as a safe and effectiveconservation technique (Ehrenfeld, 1981). InRantau Abang, Malaysia, natural hatching isnonexistent because of 100% commercial har-vesting of eggs of the leatherback turtle Dermo-chelys coriacea. A hatchery is critically im-portant. The one described by Siow (1982) wasset up by the Terengganu State Fisheries Depart-ment in 1961 and since then has released morethan 500,000 hatchlings into the sea.

One of the major problems in hatcherywork is the inconsistency of hatch rates. SiowandMoll (1981) reported that annual hatching ratesin the Rantau Abang Turtle Hatchery have fluc-tuated from 32% to 71 % between 1961 and1978, with an overall average of 51.6%. InPuerto Rico, in situ hatching success of naturalclutches of leatherback eggs averages 72%(Tucker & Hall, 1984). Low hatch success ofhatchery eggs has been attributed to movementinduced mortality (Bustard, 1972; Limpus et al.,1979; Parmenter, 1980)..Blanck and Sawyer(1981) suggested that the most critical period inthe handling of sea turtle eggs occurs from 2 days

to 2.5 weeks. In Chelonia mydas, transportationof eggs to the final destination within 3 hours

E.H. CHAN, H.D. SALLEH AND H.C. LIEW

after oviposition would enhance hatching rates.The most sensitive period was reported to occurfrom 1 - 7 days after oviposition (Parmenter,1980). Sensitivity to movement has not beenreported for leatherback turtle eggs. This paperdiscusses the effects of different handlingmethods and duration the eggs were held afteroviposition.

MATERIALS AND METHODS

The experiments were conducted in theRantau Abang Turtle Hatchery from 29 July1984 to 13 October 1984. All experimental eggswere collected from 29 July to 6 August 1984.Eggs from each nesting or clutch were collectedimmediately after oviposition and divided into 3lots prior to transportation to the Hatchery,about 1 km from the collection site. Number ofeggs per lot ranged from 20 - 36, depending onthe clutch size. These lots were designated AI,A2 and A3.

Al eggs were held in plastic pails filled withabout 4 cm of sand. There was very little rollingof eggs during transportation. When ready forreplanting, these eggs were removed singly fromthe pail and placed carefully in the sand-nests tomaintain their vertical orientation.

A2 and A3 eggs were transported in sugarsacks which is the normal practice in theHatchery. The vertical orientation of the A2eggs was carefully maintained when replanted insand-nests. A3 eggs, the control lot, were rolledonto the sand by inverting the sugar sack andthen placed in the sand-nests. These eggs werehandled quite roughly and their vertical axis wasnot maintained. This is the usual practice in theHatchery.

Clutches were held for varying times in theircontainers before replanting to determine thethreshold of sensitivity to rough handling. Thesetime treatments were:-

B1: replanted within I hour of oviposition

B2: replanted at 3 hours after oviposition

B3: replanted at 5 hours after oviposition

B4: replanted at 7 hours after oviposition

B5: replanted at 9 hours after oviposition

B6: replanted at 11 hours after oviposition

There was a total of 18 treatments (TableI). Eggs from a total of 18 nesting turtles wereused. The three lots from each clutch or turtlewere held for the same time before reburial.Each combination of handling and time wasreplicated three times.

In the Hatchery each lot was incubated inan individual open-air sand-nest at a depth ofabout 70 cm. The incubation period rangedfrom 54 to 62 days with most of the hatchlingsemerging between 56 to 58 days.

RESULTS

Infertile Eggs and Variation in HatchabilityA mong Clutches

Of the 18 clutches of eggs used for the expe-riments, four clutches were found to producezero hatch rates. Two of these clutches had beenreburied within one hour of oviposition while theother two had been reburied 11 hours after ovi-position (Table 1). When these unhatched eggswere excavated at the end of the experimentalperiod, i.e. after more than 70 days of incuba-tion, they were found to be in good conditionwith no signs of moulding on the external surfaceof the egg-shell. On opening, no embryonic stageswere detected. The eggs yolks were intact andsurrounded by thick albumin as in fresh eggs.These clutches with zero hatch rates were pro-bably infertile. If this is true, the infertility rate ofclutches in Rantau Abang can be estimated to be22%.

Different clutches of eggs produced diffe-rent hatch rates. By considering only Al lotswhere eggs were' handled with maximum careand the vertical orientation eggs was maintain-ed, variance in hatchability among lots rangedfrom 0 - 96.67% (Table 1). Hatchability did notshow a correlation with the time between layingand reburial for the Al lots. The average hatch-ing success for all Al eggs was 59%. If infertile

266 PERTANlKA VOL. 8 NO.2, 1985

TABLE 1Summary of data and results for treatments.

Al A2 A3 Dateof ::r::;l>

Time treatment Total no. Total no. % hatch Total no. Total no. % hatch Total no. Total no. % hatch Replicate nesting Zt:lplanted emerged rate planted emerged rate planted emerged rate r'

Z0

29 0 0 26 0 0 26 0 0 1 4.8.84 tTl"'1"'1

Bl 22 0 0 20 0 0 20 0 0 2 4.8.84 tTl(')...,34 31 91.18 35 31 88.57 36 29 80.56 3 6.8.84 '"

0Z

21 11 52.24 20 13 65.00 22 14 63.64 1 29.7.84 ::r::

'" ;l>rT1 B2 30 29 96.67 30 27 90.00 30 24 80.00 2 30.7.84 ...,;

E.H. CHAN, H.D. SALLEH AND H.C. LIEW

clutches were excluded, hatchability ranged from35.7 to 96.7% (x = 78.16%). Thus if infertileclutches can be identified before replanting,hatchery productivity may increase by about20 %. This is significant considering that eggsare purchased at $1.50 per piece for hatcherywork.

Handling and Time Effects

There was a very large variance amongclutches. The hatch rate data was neithernormally distributed, nor did it satisfy theassumption of homogeneity of variances. Para-metric statistical analysis was inappropriate.

TABLE 2Normalised and ranked values for handling and time treatments.

Normalised value, N = (x - x) for each treatment-time combination.S.D

Ranked values were assigned in ascending order based on the normalised data.

Handling Treatment

TimeTreatment

Normalisedvalue

Al

Rankedvalue

Normalisedvalue

A2

Rankedvalue

Normalisedvalue

A3

Rankedvalue

268

Bl

0.80 27.5 0.33 22.0 -1.12 4.0

-1.15 1.5 0.67 25.5 0.48 23.5

B2 0.93 32.0 0.13 17.0 -1.06 8.0

-1.10 7.0 0.85 31.0 0.25 18.0

-0.58 12.5 1.16 36.0 -0.58 12.5

B3 1.04 34.0 -0.10 15.0 -0.95 10.0

0.30 20.0 -1.12 4.0 0.82 29.0

0.08 16.0 0.96 33.0 -1.04 9.0

B4 0.83 30.0 0.28 19.0 -1.11 6.0

1.14 35.0 -0.39 14.0 -0.75 11.0

B5 0.80 27.5 0.32 21.0 -1.12 4.0

0.48 23.5 0.67 25.5 -1.15 1.5

B6

PERTANlKA VOL. 8 NO.2, 1985

HANDLING EFFECTS ON HATCHABILITY OF EGGS OF DERMOCHELYS CORIACEA

DISCUSSION

0.50 > P > 0.20; A2 = A3, 0.001 > p). Thisshows that the usual practice of rough handlingand rolling the eggs into the nest can causedecreased hatchability if eggs are replantedmore than 5 hours after oviposition.

Fig. 1. Relationship between normalised hatch ratesand time treatment for Ai (dots bounded byfull line); A2 (crosses bounded by brokenline) and A3 (open circles bounded by

dotted line) handling techniques, See text forexplanation of AI, A2 and A3,

,"",

~~~~-!._-----~ ....',. ,

..,",TIM( Tfl[~TM[NT

lAPSED AFTER OVIPOSITION)

",",

It is generally understood that not all turtleeggs deposited on the be