- -,:'-•..., \

This paper not to be ci ted without prior reference to the author

International Cauncil for CM 198J/G:18

the Exploration of the Sea Demersal Fish Committee

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PRELIMINARY STUDIES OF THE EXPLOITED STOCK OF KITEFIN SHARK

Scymnorhinus licha (BONNATERRE, 1788) IN THE AZORES.

by

Helder Marques da Silva

Universidade dos A90res

Departamento de Oceanografia e Pescas

9900 HORTA - AQORES - PORTUGAL

ABSTRACT

Information is given about the commercial fishery for

the Kitefin shark Scymnorhinus licha (Bonnaterre, 1788) in

the Azores. Efforts to determine age, and some observations

on the reproduction, embryology and food habits are discussed.

A length/weight relationship is established for each sex sepa

rately. Catch and effort data (1977 - 1982 period) are analy­

sed and Maximum Sustainable Yield (MSY) calculated for the fi

shery around the islands Faial and Pico.

RES~

On definit l'interet commercial du "lixa", Scymnorhinus

licha-(Bonnaterre, 1788), aux Azores. L'age ne fut pas encore

determine avec riguer, la -situation des recherehes sur ce

point est presente." On fournit quelques observations sur la

reproduction, l'embriologie et les habitudes alimentaires. La

relation taille/poids du corps est etabli pour chaque sexe.

Des analyses sur les donnes de prise et effort sont faites

pour le periode 1977 - 1982 et la Capture Maximale Sustenta~

ble (MSY) est determinee pour les lIes Faial et Pico.

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INTRODUCTION

The Kitefin shark is cosmopolitan in distribution, oc­

curing mainly in warmer seas. It is found regularly from the

Irish Atlantic slope to off Marocco, Madeira and Azores. It

is also present in the western Atlantic, South African waters,

and around New Zealand and Australia, Japan and Taiwan. It is

a benthic, sometimes mesopelagic, species, which lives in

depths ranging from 90 to about 1000 m, mainly on slope areas

between )00 and 700 m. In Azores, its mainly caught at 150­

-200 m, the deepermost record from 500 m (KREFFT & TORTONESE,

1973) •

Besides the Blackspot seabream (Pagellus bogaraveo),

the Kitefin shark represents the most important demersal spe­

eies in the Azores. In 1981 the recorded catch w-as 2.239 thou

sand tonnes, making 19 percent of the total fish catch in the

Azores. However, it is fished only around three of the islands:

Pico, Faial, and San Niguel. In Pico it is the most important

species in the fishery.

Traditionally, the fishery for Kitefin shark has been

an artisanal fishery from small boats using vertical handlines.

In later years this fishery has also been taken up by larger

'boats using nets.

The flesh of the Kitefin shark is dried and exported

to continental Portugal where it is much appreciated. Its li­

ver, which represents approximately 20 percent of the total

body weight, yields a thin.oil with a high content of squalen,

and is exported.

The biology of the Kitefin shark is poorly known, but

beeing a viviparous with a long period of gestation and rela~

tively few offspring, it will be sensitive to exploitation.

MATERIAL AND NETHODS

It has been possible to obtain 21 specimens for com­

plete biological samples, from Azorean research vessel R/V

"Geralda" , from the Portuguese research vessel R/V "r;oruega",

., \

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and from loeal fishermen. All speeimens were taken from Se­

ptember 1982 to July 1983, and the sites o~ eapture are given

in Figure 1. In addition, 274 speeimens has been measured and

weighed at the factory "Maria Gon9alves" in Pico.

For all" fish the sex was recorded, the total length

measured to the nearest em below, and the weight to nearest

50 g.

For eomplete biologieal sampIes the previous data were

reeorded, as weIl as length of elasper in males (TESHI}~ et

al, 1971), number of embryos, number of eggs, length of embrz

os and diameter of eggs ~or ~emales, and also the weight o~

gonads in both sexes and the weight of the liver. Par stomach

content studies the ~ull and empty stomach weight as weIl as

the liquid and solid content weight were measured. The solid

contents were than put in unbleached cloth bags and the bags

introduced in 10% formalin. For age determination vertebral

sections were prepared aceording to DAIBER (1960).

Basic information about catch and number of crew for

each vessel for the islands Pico and Faial for 1977 - 1982

has been obtained from the "Servigo Agoriano de Lotas" and

compiled by staff from the "Departamento de Oceanografia e

Peseas". Although such information exists also for the years

1972 - 1976, it is judged to be unreliable (SILVA, 1982).

From San Miguel information about the number o~ crew is not

available.

It is assumed that for the artisanal fishery with hand

lines the number of lines,.and hence the effort, is proporti~

nal to the number of crew. For the"modern" fishery with nets

the number,of nets used by each boat is not known. It seems,

however, that the number of nets is not closely dependent on

the number of crew, and a reliable measure for effort is

therefore only available for the artisanal fishery." For these

reasons it has been decided to use effort data only from the

artisanal fishery, with "man trip" as the unit of effort.

With the above data, the ~itting o~ a Graham curve (according

to RICKER, 1975) to the fishery around Pico and Paial has

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been attempted, using the data given in Table 3.

RESULTS AND DISCUSSION

1. Age determination

Daiber's technique for age determination (DAIBER, 1960)

in the Skate Raja eglanteria has been attempted for Scymnorhi

~ licha. This technique inc1udes dehydration with 10 per­

cent formalin and absolute alcoho1, than paraffin impregna­

tion and finally xylene clearing. After preparation according

to this author's method vertebrae were observed with different

amplifications but no rings could be distinguished. Also thin

cuts, from 0.3 mm to 1 mrn have been observed with a HITUTOYO

profile projector (transrnitted light) without any positive re

sults.

However,opaque rings alternating with gray trans lu­

cent rings became visible to the naked eye, using a good re­

flected light. These rings were not all equally distinct in

all vertebrae of the same vertebral column. Not only the dis­

tinctness of the ring varied, but also the number of visible

rings. In one female specimen of 140 cm and 16.15 Kg, 9 to 13

rings could be counted betweenthe 21st

and the 30th verte-th

brae. Posterior to the JO vertebra the number of visible

rings decreased progressvely and after the 57 thno rings were

distinguishable. Anterior to the 21st

vertebra, the number of

clearly visible rings also decreased, and rings could not be

distinguished in the four most anterior vertebrae.

Immersion of vertebrae and vertebral sections in mure -

xid before observation with different amplifications did not

giye results either.

2. Lengthjweight relationship

Lengthjweight relationship have been calculated separa

tely for males and females according to the formula:

bW = a.L

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where W is weight in Kg, L is length in cm, and a and bare

the parameters to be determined. Using logarithmic transform~

tions of lengths and weights for each individual and regres­

sion analysis, the following formulas were obtained:

Males (50 specimens, correlation coefficient 0.7 2 )

W = 5.13 x 10-5 x L2

• 52

Females (224 specimens, corre1ation coefficient 0.71)

-4 x L2 .)5W = 1.50 x 10

The curves for the re1ationships are shown in Figure 2 •

Hean weight for each centimeter has also been ca1cu1ated (Ta­

b1es 1 and 2).

Table 1. Hean weight in each centimeter group for

males.

L W n( cm) (Kg) (number of

specimens)

102 6.65 110) 0104 6.)0 1105 8.00 1106 0107 6.17 )108 5.48 2• 109 0110 9.15 1111 6.42 )112 7·1) 411) 7.88 9114 7.60 )115 7.35 4116 8.10 1117 8.61 5118 8.61 1119 8.64 4120 8.00 2121 8.60 2122 012) 9.50 1124 0125 10.55 1126 10.25 1

L W n'

114.18 7.76 50

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Tab1e 2. Mean weight in eaeh eentirneter group for

fema1es.

L W n(ern) (Kg) (numbers)

125 15·50 1126 0127 0128 1).00 1129 14.50 11)0 12.25 21)1 01)2 1).54 4I)) 14.90 11)4 14.61 6• 1)5 14.58 91)6 16.00 11)7 16.51 51)8 16.)4 51)9 16.24 11140 17.)5 I)141 17.00 17142 17.60 1414) 17.88 12144 18.74 8145 18.4) 18146 18.75 I)147 18.96 17148 19.88 11149 20.24 7150 20.28 16151 19.59 7152 20.15 615) 19.69 4• 154 20.20 4155 20.04 4156 21·75 )157 0158 20·50 1159 21.05 1160 0161 19.05 1

L W n

144.09 17.94 224

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I ...... , ••'

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.. ,'J ,',''':'_

If we eompare these equat~ons w~th those g~ven by RI­

PLEY (1946) for Galeorh~nus zyopterus and OLSEN (1954) for Ga

leorhinus australis whieh found a b cf 3.2 the more we eonfirm

~ts smallness. Any ~~y, eaeh speeies has its own b value, and

as these are speeies of the same genus it is logie that they

have a similar b whieh, on the other hand, is very different

from a mueh different speeies as Seymnorhinus lieha.

3. Reproduetion

It'is a v~viparous speeies of the non-plaeental type,

without uterine eompartments and eontinuous reproduet~on. Em­

bryos develops at the expenses of ~ts yolk sae and also by

absortion of its "mother's milk" whieh, aeeording to BUDKER

(1958) are female substaneies of ~ts plasma, that by the capil

lary circulation existent ~n the uterine villosities passes to

the uterine liquid and are absorbed by the embryo through its

gills.

On our samples, the b~ggest embryo weighted 600 gr and

·~ts, length was of 40 cm, the number of embryos present ~n the

uterus varying from 7 to 14, all ~n ~qual developmental stage.

,The smallest pregnant female measured 140 em.

... Gestation period has not been determined but,' accor-

ding to BUDKER (1958) it ,takes 'lOmonthes and ,the weight of

; .

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the embryos on its final deve10pement is of 188gr. LO ZANO(19 28) presents a figure of an embryo lengthing 370 mm (after

CIPRIA, 1936), which is also a lower va1ue than the biggest

one I have observed. The number of embryos per fema1e is of

10-16 according to RISSO & CANESTRINI (1) and 6-8 according

to LO BIANCO (1909) (after CIPRIA, 1936). Probably, the num­

ber of embryos in the uterus per fema1e is of 14-16 and lower

values are caused for abort before sampling.

An interesting observation results from the fact that

all the fishermen contacted say they have never fished a

small Kitefin shark. So, it seems that parturition takes pla­

ce in deep waters and just when adults they come to 1ess dee­

per waters, once that even when different gears are used in

the fisheries no small sharks are caught.

4. Stomach contents

Only 18 stomaehs were checked. Of these, 11 were em­

pty, and in the remaining 7 it waS possible to recognize Loli

~ forbesi and beaks of squids in 3 stomaehs and bait in one.

The scabbard-fish Lepidopus caudatus was found in 2 stomaehs

and the skeleton of an undentified teleost in one.

5. Catch and effort

Using the data given in Table ), catch per unit of ef

fort (CPUE) fbr the artisanal fishery with hand-lines in the

years 1977-1982 has been plotted against time (t) in Figure ).

The regression lirie has been calculated as

CPUE = 0.28 - 0.0) x t

with regression coefficient r = 0.99

The relationship between catch per unit of effort and

calculated total fishing effort (f) has been calculated as a

regression line:

CPUE = 0.22 - 2.0 x 10-5 x f

with a correlation coefficient r = 0.56

The co~relation coefficient is low, and in order to check on

Table J. Catell and effort data in the fishery for Seymnorhinus lieha around the

islands of Pieo and Faial in the years 1977-1982. The total effort (I')

i5 a theorieal value for the effort that would have been needed if the

total eateh was taken in the artisanal fishery, obtained by dividing

total eateh (C) with the eatch per unit of effort in tlle artisanal fi­

shery (CPUE).

Artisana1 f'ishery "Modern" fishery Total 1'ishery(Handlines) Nets

Year Cateh Effort CPUE Catch Cateh Et'fort (Caleulated)tonnes man trips tannes tonnes tonnes man trips

man trips

1977 188. lt 742 0.25 - 188.5 7 lt2

1978 168.7 734 0.2J 2 .l~ 171.1 74 lt

1979 215.6 1091 0.20 5.9 221,6 1121

1980 201t .1 1153 0.18 J19.5 523.6 2958

1981 107.4 791 o .llt l~ J6. 5 5 /t 3.9 lt007

1982 53.7 l~ 58 0.12 77·5 131.2 1119

"

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its va1idity aT-test was made of the nu11-hypothesis "the

corre1ation coefficient is zero", and it w~s found that the

nu11-hypothesis could be rejected with a probability of only

something over 70 percent.

If we exclude 1982, the re1atioship between catch per

unit of effort and calcu1ated fishing effort for the period

1977 - 1981 (Figure 4), is given by the regression 1ine:

CPUE = 0.25 - 2.7 x 10- 5 x f

with a correlation coefficient r = 0.93

For the fishery around Faial and Pico in the years

1977 - 1981 it is possible to fit a Graham curve, of the form

(RICKER, 1975):

2C = af - bf

where the catch (C) is the total catch for the area and fi­

shing effort (f) is the calculated total effort in "man trip",

in effect assuming that the total catch could be taken by the

artisanal fishery, or that an empirical formula had been

obtained that al10wed the transformation of fishing effort in

the "modern" fishery with nets to the units used in the arti­

sanal fishery.

The parameters a and b can be obtained from the re­

gression 1ine between CPUE and f (RICKER, 1975) with a = 0.25

and b = 2.7 x 10-5 • The resulting parabola

C = 0.25 x f - 2.7 x 10-5 x f2

is illustrated in Figure 5. The top of the parabola correspo~

ding to Haximum Sustainable Yie1d (HSY) is given by

2a

C = 4b = 579 tons

The corresponding va1ue of fishing effort (provided this catch

was taken in the artisana1 fishery) is

f =~b = 4630 man trip

In order to check on the validity of the obtained values for

MSY and corresponding effort, it has been attempted to calcu-

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late MSY and corresponding I when the data Ior one year at a

time are excluded, starting with the exclusion 01 1981

("Jack-kniIe method"). The Iollowing table 01 values is obtai

ned:

I MSY:Han trips tonnes

5061 633

4371 546

4362 567

4529 566

5128 615

Mean value 4690 585

Standard deviation 336 74

Using a Student's t-distribution on the above data it

is Iound that the 95 percent conIidence intervals Ior the mean

values 01 land MSY are, respectively:

4223 <. f < 5157

482 <MSY <688

The calculated values MSY = 579. tonnes and I = 4630 man trips

are weIl within these limits.

When explo~ation 01 a stock increases Irom a low le~el

to a higher level, CPUE must decrease as the biomass 01 the

stock decreases. This is demonstrated in the present stock

when catch increased Irom a low level in 1977 to a much higher

level in 1980-1981, and CPUE decreased accordingly.

According to oIIicial statistics the price Ior the Ki

teIin shark Iell Irom 18 Escudos per kilo in 1980 to 10 Esc/Kg

in 1981: The reduction in ellort in 1982 was thereIore proba­

bly due to a Iurther reduction in price. 1982 should also be

considered an "atypical" year in relation to the tleory behind

the Graham curve, because the biomass 01 the stock had not

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had time to adjust to t11e new level of' exploitation - the

stock was not in equilibrium. For thi5 reason 1982 has been

excluded f'rom the calculations. It should be noted that catch

durin~ the year 1981 was relatively close to MSY, and it

would be un,,-ise to increase the ca t ches beyond the level of'

that years.

REFERENCES

BUDKER, P., 1958. La viviparite chez les selaciens. In Traite

de Zoologie. Ed. Masson & Cie. XIII; 2: 1755-1790.

CIPRIA, D., 1936. Embrione di Scymnorhinus licha Bonnaterre.

Consiglio Nazionale delle Ricerche. R. Comitato Talas

sograf'ico Italiano. (227): 5pp:

DAIBER, F., 1960. A technique f'or age determination in the

skate Raja eglanteria. Copeia, 1960. (13): 258-60.

KREFPT, G. & E. TORTONESE, 1973. Squalidae. In Check list of'

the f'ishes of' the North-eastern Atlantic and of' the

Mediterranean. UNESCO (Unit. Nat. Ed. Sei. and Cult.

Org.). 1.: 46.

OLSEN, A., 1954. The biology, migration and growth rate of'

the school shark, Galeorhinus australis (Macleay)

(Careharhinidae) in South-eastern Australian waters.

Australian waters. Aust. J. Mar. Freshwat. Res., 2:353-410.

RICKER, W., 1975. Computation and interpretations of' biologi­

cal statistics of f'ish populations. Bull. Fish. Res.

Board Can. (191): 382pp.

RIPLEY, W., 1946. The soupf'in shark and the f'ishery. In The

biology of' the Soupf'in Galeorhinus zvopterus and Bio­

chemical Studies of' the liver. Fish. Bul1. Calif'.

(64): 7-37.

SILVA, H., 1982. MS. Parecer acerea das perspectivas futuras

da captura de gata-lixa. Departamento de Oceanogra­

f'ia e Pescas, Horta. 8pp.

STEVENSON, D., 1979. MS. Results of' stock assessement work in

the Azores 1977-1978. University of' Rhode Is1and. 35pp.

- 13 -

TESHIHA, K., H. YOSHINURA & K. MIZUE, 1971. Studies on the :

sharks-II. On the reproduction of' Japanese Dogf'ish Mus

te1us manazo B1eeker. Bu11. Fac. Fish. Nagasaki Univ.

(32): ln-50.

31' 30' 29' 28' 27" 26' 25',----1---------+---------+---------+---------+--------+-------_~:...--------.....40'

COAVO• ARQUIPELAGO DOS ACOPES

GRACIOSA,"a

M

'"';;...~~O~.

formig••"''"

58nl. MARIA•Fig.l.: Positions where sarnples havp beeil obfa-inpd, -indicatl'd by points.

39'

38'

37'

25

20

15

Cl~

.....ICj

W~

...J«.....0.....

W9 = 1.50 x 10-4 ~.35; n.224

wJ =5.13 x 10-5 ~52 n.50

5

120 140TOTAL LENGTH (cmsl

160

mit I P and 1'PII1<1 1(' Sr', nlllorh inus li eha.

Fig.J: Variation of CPUE 1'1'0111 1971 to 1~H3~2 1'01' the a1'­

tisunul fi:·;lw1'y h-ith hand-1inE:s around Faial and

8281

ICPUE=O.2B-O.03t I

IC PUE=O.25-2.7 x10~5f I

79 80

TIME (YEARSl

781977

Pico.

0.25

0.1

0.10

0.05

02

~~.rn-zC::

~O.l5w::Ja..Ü

0.2

0.05

~~o.2rnä:Zl-

8~O.l5w::Ja..Ü

•

2 3CALCULATED EFFORT/1000

Fig.4: Relationship oetheen CPUE and effort 1'01'

the urtisanal f'ishery during the years 1977­

-1982 in Faial and Pico.

, •6

5Ci)wzzg:I:

~C3 4

30

2 3I

4 5 6CALCULATED EFFORTÄOOO

7 8 9 10

rig.'j: (,t'ahalll {'\ll'\P fot' catch Hnd pfrort 1'ot' ScynlIlorhillus

liclla <l1'Olllld t11p j:-;Iallds 01' Pico alld FaLl!. (ateh is

total cateh ill thp ·(U't~U. Errort t'pfprs to thp units

\1St'<! in tIw art isana I risIH~ry. Cat eh for tllP ypars

19i1-l()01 is :-;ho"l1 as hPII. Thp pffort that \\ould ha-

v p b p p n 11 f:.' P d p d i l' t 11 P S P ca t c 11 (> s ha d be e n t a k e n i 11 t h p

arti::;UIHll 1'l.::;]wry i5 outaill(~d by dividiIlg" total cBtell

pp r 1111 i tor p I' f () r t i 11 t lJ par t isa Il n I f' j s hp r y f 0 r t h f:.'