This paper not' to be cited without prior rererence to the authors•I,,

International Council ror C.H. 198 7/K:5Jthe Exploration or the Sea Shellrish Committee

•

EXPLOITATION OF LIHPETS (PATELLA SPP.) IN TIIE AZORE

WITH A PHELIHINARY ANALYSIS OF THE STOCKS

by

Helen R. Ma~tinsl, Ricardo S. Santos l and Stephen J. Hawkins 2

lDepartment o:f Oceanography and Fisheries, University or theAzores, P-9900 1I0rta, Azores, Portugal

')

....Department of Marine Biology, University or Liverpool,Port Erin, Isle or Man, U.K. (rormerly Department o:f E~viron­

mental Biology, University or Manchester, U.K.)

SUNMARY

Limpets are consumed locally in the Azores or exported to Azoreancommunities in U.S.A. T}le stocks have been declining rapidly duringrecent years. In S. !'Ü{J.lel limpets occupied the Gth place (monetary value)'in the :fisheries statistics compiled ror 1985 by the'Azorean :fisheriesauction service.Tlleir systematics are not resolved. We use local names ror working re­rerences which are "Iapo. bravo." (cr. Patella aspera) and "Iapo. manso."(cr. P. caerulea?) :for the two common exploited species."Lapa-brava" was round to reach maturity between 111-45 mm shell length.It had highest gonad development in January, lowest in May-June. Wesugges t tim t "Iapo. bravo." is 0. partial protandrous hermaphrodi te. Sexrati6s llave been seriously distorted by exploitation as remales arelarger than males. "Lapa manso." reaches maturity at lG-20 mm length. Itdoes not appear to change sex. Stocks can withstand lleavy exploitationin the intertidal due to hißh recundity. The stock of "Iapo. bravo."seems secure in S. Niguel. We recommend, however, prohibition :for limpetcollectinß by diving in the Central Group (both species). We also re­commend minimum sizes, 40 and 20 mm respectively :for tlle two species.

ReSUMe

Les patelIes sont consommees locallement OU alors exportees pour lescommunautees acoreennes aux etats Units. Les stocks on decline rapide­ment dans ces derniere annees. Ce mollusque occupait en 1985 le Gernelieu en valeur de 10. peche totale a l'11e de S. Mißuel. 'Leur systematiqueest mal connue. Dans la pratique nous utilizons les designations local­les de "Iapo. brava" (cr. Patella aspera) et "lapa manso." (cr. Patellacaerulea?) pour les deux especes qui sont exploitees. "Lapa bravo." atteint10. maturite sexuel quand 10. coquille est ~ peut-pres 41-45 mm. Les ßO­nades presentent le developement maximum en Janvier e le minimum auxmois de Nai-Juin. Nous croyons que "lapa brava" est une espece herma­:frodite protandrique. Le bouleversement dans les "sex-ratios" est peut­-etre le resultat de l'exploitation puisque les remelles ont plus ßrandetaille q~e les mAles. "Lapa manso." at teint 10. maturite sexuel a 10.taille de 16-20 mm. Cette espece ne semble pas chanßer de sexe. A causede son eleve fecondite le stock peut supporter une exploitation intensedans 10. zone intertidal. Le stock de "Iapo. bravo." se maintien en equili­bre dans l'11e de S. Niguel. Cependant, pour Ies lIes du Groupe Centralnous recommend6ns 10. pro}libition de l'exploitation en plongee (pour lesdeux especes). Nous recomrnendons aussi 10. taille minimum de 40 mm et20 mm respectivement pour les deux espoces "Iapa brava" et "Iapa mansa".

2

INTRODUCTION

Azoreans have exploited their littoral communities since the

.first colonization in the 15th century. Key ecological species,

including algal tur.f species, space-occupying barnacles, predatory

gastropods and decapods, and the grazing limpets considered here,

are all heavily exploited. Almost nothing is known about the Azorean

littoral and the basic knowledge to help manage ir~shore resources is

unavailable. Until around 15 years ago the exploitation was mainly ln

the intertida~ ~one. llowever, a.fter the introduetion o.f snorkeling

equipment during the 1970's, the subtidal also became a target .for

severe exploitation o.f crustaceans and molluscs.

Lirnpets in particular are highly regarded as sea.food in the

Azorcs. Thcy are sold alivc on the loeal market or export cd to the

Azorean communities in Ncw England. There is also considerable sub- •

sistcncc gathering o.f limpcts. In economic value, the Patella .fishery

was thc 6th most important taxa in 1985 in the island o.f S. MilJuel.

In 1983, a.fter a rapid decline o.f Patella stocks in the. Central

Group o.f islands, our Department was asked by the Sccretariat o.f Agri­

culture and Fisherics o.f thc Regional Govcrnmcnt, to recommend measur­

es to be taken to prevent .further depletion o.f limpets. The decline

appeared to be duc to a continuous over-exploitation couplcd with a

catastrophic mass-kill. The latter was veri.fied by surveys on the

southern coasts o.f Pico and S. Jorge during the summer o.f 1983. The

same ycar a ban on limpet colleeting by diving was proclaimed .for the

Central Group. From 1985 on, more extensive work has been carried out

on .four o.f the nine islands in the archipelago. These are S. Niguel •

in the Eastern Group, Faial and Pico in the Central Group and Corvo in

the Western Group o.f islands.(See .figure 1).

Two species are exploited. A larger species that has an orange

co10urcd .foot and occurs mostly in the subtidal zone and a smaller

one, with a erey .foot whieh is .found mostly in the intertidal. These

havc been ca11ed Patella aspera Lamarck, 1819 (syn. o:f P. aspera

Rödine, 1798, whieh is valid) and Patella caoruleu Linne, 1758 respec­

tively by several authors (e.g. Nobre 1930, Horton 1967). Whether

the Azorean species correspond to these continental European ones is,

however, questionable. There.fore, we have chosen .for the time being

to use as working rei'erences, the apt local names, "lapa brava" ror

the 1areer spceies and "lapa mansa" .for the smaller one. They are

derinitely two good species. Preliminary work by one oi' us (S.J.H.)

indiea tes tImt" lapa brava" has elose a.ffinties wi th P. aspera. The

I I I.CORVO

AZORES ISlANDSI

• FLORES

WesternGROUP

~ GRACIOSA

I 1rRCEtRA

~ .1rAtAL

.. p,r6·· ..~ .." .............................~

Central

GROUP

.' .......... AlfecledS. MIGUEL

N;;;;;;;;;;:;:< ZONES ---1983

•Easlern

GROUP

.-Sla.MARIA

i

Fig.l. Map of the Azores with indication of areas affectedby the mass-kill of limpets in 1983.•

39

31

31

31 30 29 21 21 2& 2S

1

•

position of "lapa mansa" is less clear, but may correspond to P.candei

D'Orbigny, 1840 as referred to by Chri tiaens (197 4 ).

In this paper, particular attention has been given to "lapa brava",

the most valuable and also the most vulnerable species. We present some

statistics on the extent and value of exploitation of Azorean limpets.

Preliminary findings on size at sexual maturity, changes of sex ratio

with siz , and reproductive seasons are given for both species. We

have compared the size structure of natural populations with catches

obtained in various ways for both species. For "lapa brava", the size

structur in 1986 compared with samplesfrom before the mass-kill of

198J ar given. "Lapa brava" stocks have also been assessed in the

Central Group and in the island of S. Miguel. Preliminary management

recommendations have been formulated on the information available so

far.

MATERIAL AND METHODS

The data concerning quantities harvested and their economic

valu were furnished by th Azorean fisheries auction service (LOTA-

c;OR) •

The limpets examined were obtained by intertidal shore collecting

as weIl as subtidal, by snorkel-diving. Some commercial sampIes were

also bought from str et traders and bars. The spec~mens were worked

up fresh, or deep frozen for later study. Monthly commercial samples

taken from August 1985 to July 1986 were suppl~ed by Mr. Manuel Ferre:ira,

4

at Mosteiros, S. Migue1. These were rixed and preserved in 4% rorma1fie­

hyde to await examination.

Tho 10ngth or tho sho1ls wero moasurod along the median axis to

the noarost mm using vernier calipers. The sex of' all specimens was

doterminod and tho maturity stages or tho gonads were estimated using

a modif'ication of' Orton's gonad scale f'or Patella (Orton ~ al.1956).

Brooding cycles were estimated by calculating percentages of' ani~

mals with gonads in stagos I--N-I+ (almost empty, neuter, starting

to develop) and those in stages IV+-V-IV- (almost f'ull, f'ully ripe,

spawning started) f'or oach sampIe. Immature animals were excluded.

Tho monthly sampIes were washed out in f'roslwater, blotted and

tho visceral mass as weIl as the gonads were woighed wet and arter

llaving boen dried. (approx.J days at 600 e) , to an accuracy of' 0.0001 g.

Tho gonadosomatic index (GSI), (gonad weight (w) expressod as •

porcentago of' tho total weight (w):GSI w= W x 100

was calculated rrom the monthly sampIes.

Timod 1/2 llour dives by an ex-prorossional limpot risherman wore

developod as a moan of' assossing stock density and population structure.

Recrui ts « 5mm) and juveniles (>5mm< JOmm) were counted using=randomly positioned quadrats of' 25x25 cm in the "lithothamnia"/eorallina

region of' the low intertidal which seems to be the nursery ground of'

both species.

RESULTS

Exploitation •It is not possible to make an accurate estimate or the total

quantity of' limpots tllat are harvestod each year as people gather them

ror thoir own use, or f'or selling privately to restaurants and bars

without going through tho orricial auctions. The quantities or Patella

sold at the of'f'icial auction services f'rom 1975 to 1986 are shown in

rigure 2. These numbers should be regardod as minimum values. As seen

rrom the histogram, organised markets ror limpots are only properly

developed in S. Niguel. The maximum catch was in 1984 when 94 tons

wore auctionod in S. Niguol and only J tons in tho rest or the islands.

The relative importance in monetary value compared to both inshore

and orrshoro rishorios during the years 1975 to 1986 is shown in

f'igure J. In 1985 limpets occupied the 6th place (preceeded by species

of' f'inrish and squid) in S. Niguel, and the 9th place f'or the archi­

pelago as a whole.

1115 1118 1911 11

.1000~g

100

10

IQ

10

50

40

30

20

10

S.MIGUEL

_ TIHI olh.r IStANDS

f ig.2. Limpet harvesl in Azores, 1975 10 1986.

-'---2 _

-'----'---

• SÄO MIGUEl* ALL ISLANDS

L-­

l-­

L-

zl..-­Q •... ----(j) 10~--

-"---

10 11 n 15 ..fig.5. Relalive posilion of lJmpets (economJc valuel

in the overall calch of Marine species soldthrough lhe fjsh auction in the Azores 1975-1986.

-'

~'I

II

I

II

II,,...

II.

II,

I,I

-'-'

~I;?c

"c;:....

%

--OL_......--fl0'-='~'::..:'--'2I""O.::::~:=3;.O----!AO-----::5I"O---760::----=7r:-O---:8J:.O:---'J90~-

...zUJoa:UJa.

LENGTH OF SHELL mm

fig.4. Cu.ulative percent of slze classes of'lapa brava'froM Pico island.

6

>­zwua:wQ.

~50>­«.J:J::!:JU

/

~ /,/

l,/':T

"//

10 20 30 40 50 60LENGTH Of SHELL m In

70 80 90

Fiy.6. Cumulalive percent size c)asses of'Japa brava~

from S. Miguel and CorvQ ls1ands.

rig.5. CumuJalive percent of size classcs of tapa bravafrom Manhenha, Pico, 1966 co~pared ta previou5years.

•

•75706560

5550

---_ ...

r@#,~MOSTEIROS

,/ Fi8h auellon

30 35 40 45 50 55LENGTH OF SHELL

f,,,,I

II

/I

I

25

I

25 30 35 40 45

LENGm OF SHELL mm

,,I

t __(§):=b::.....,/,-'__ FAIAL,CAPELINHOS

Comercial ••mpltl

20

20

1_""'::::"'+---'--- FAIAL·CAPELINHOSTotal S8mpling

15

15

I

;wl

10

10

®RtB~IH~~l ~~~~E~INTERTIOAl

o

10 %

o

t­ZwUa:wa.w>.=<IJ

]:?]u

>­zwua:wQ.

W

~>-:'i:J::!:>u

rig.7. CUllllll<:llive percenl cf size classes of ·Japa mans<l(rom S. Miguel and raial isJands.

7

TABU: 1

Minimum and maximum maturity stages of gonads and gonadosomatic

indexes (GSI) (mean) from monthly samples of "lapa brava". Mos te i­

ros (S. Miguel). August 1985 to July 1986.

l--N-[+ "Illlost empty, neuter or gonad Just started dl'''tdoping;

lY+-Y-lY- gOllad lIearly ripe, ful1 or Just started sp"wnillg;

n = l1uml.H~r in each sample.

Month - +I -N-I%

+ -IV -V-IV

"eSI n

•

August 12.5 45.8 10.54 24

Septellluer 12.5 48.8 12.01 80

Octouür 1).8 27.5 10.)1 80

Novelllhur 7.1 42.9 13.31 42

Uecemuer 10.7 53.6 1).)1 28

January 10.8 6).1 :W.05 65

February 0 41.7 1).61 )6

March )0.0 50.0 1).78 40

April 2).2 42.9 12.18 56

May 85.0 1.4 1.4) 72

June 95.6 1.1 0.65 96

July 56.3 6.) ).)1 80

Reproduction

"Lapa brava"

Minimum and maximum maturity stages 01' gonads in the monthly

commercial sampIes from Mosteiros, S. Miguel are shown in Table I to­

gether with the mean gonadosomatic index for each month calculated

from softbody dry weights. Both methods show maximum maturity in Janua­

ry and minimum ftom MöIy toJuly when there apparently is a resting period.

Ripe gonads, however, can be found all the year round. No distinct spa~ ,

ing season could be determined. The population seem to be reproductively

active from August to April, with continual spawning during this pe­

riod. The dip in October may represent a small synchronised release.

Similarly, the rapid decrease in proportion 01' ripe individuals bet-

ween April and May suggest a final synchronous release before entering

a resting period. These data should be viewed as essentially prelimi­

nary. The anima1s came from severa1 different loca1ities on the north-

west coast 01' S. Miguel which may mask any localized synchrony in

spawning, expected in an externa11y ferti1izing anima1.

"Lapa brava" was 1'ound to reach sexual maturity at a shell length

between 41-45 mm (see Appendix).

8

Minimu~ und maximum muturity or some or tlle 1/2 hour sampIes is

shown in Table 2. They all show relatively high numbers or specimens

in low maturity stages and rew with maximum maturity which was to be

expected at least ror July sampIes.

"Lapa mansa"

No trend could be round rrom preliminary data on the reproductive

state or "lapa mansa". This species seems to be spawning all the year

around without any synchronized restinß period. "Lapa mansa" was round

to reach maturity between 16 and 20 mm in lenßtll (see Appendix).

Population structure or stocks and catches

"Lapa mansa"

Size distribution of' "~apa munsa" is shown in f'igure 7. The ~argest

limpets (c) are round at the rish auction at Mosteiros, S. Miguel, next

comes u commercia~ sump~e f'rom Cape~inhos, Faia~ (b). Line (a) shows

the size distribution or the whole population at Capelinhos, collected

lfIf!IfiIIMALESEiTIFEMALES

NELJTER DR IMMATURE

•(.~T,t. 6I>.~<;A

• "".yjogd'.547. c;>·a27.N-2Jt°1"

[-41...""

n H"r'vl ~14oq lt

0-44r. 9-e1'l.N·~5·1.

--- ---=:...:..:..:..:.=====--::...:..:::.........:....-=--==-_...:...-=-=._===~j:'ll -.~~ <>~ li ilIL;;J[f i)'l..~ (c~)1r UürrÜ'U[}2)~

~o:, . tJU@JC1::DL~

OCTOBER 1986

------

•riq.O. Asse'isment Of "1<1pa brava" bv 1/7. haur dives in 'j. MiQuel,

Octobcr 1986. The area of lhe circles is prODort ional t.olhc weiQhl of lhe sampies. n;number, N=nculer, TW:lotal,L=mcan Jenglh.

';\ ~:.:j ~<.: !>li \rl.lc.l?JÜl.l'tl-~ LUl1i; UnlhJ'UIJ2.l@~

1~t'\11. ", ,ILJULY, 1986

I' _-j Males

_Females

[-.=J Neuler Or ImmalUre

,} (\l

1'... · I'Jt:' ;j

eS ."1:, I - c.fl1.N -,V' ..

I :".11'11>1

I),~o

'W'a5'llt,cr'16·/.(t· 2 "N·BZ",4L:4G m""

", e4r", • .I401tci'.:~~1~ 9-'1·/.N '>\'>:'.i..~"Il~

"."}71W·~'lBiI

d'·1'l.~·1.'f·~g,%N. 7b,~tr.I.. 4'2."", ...

fig.9. Assessment of lapa brava by 1/2 hour dlves in raiat,July 1986. Tne area of the circles ls proportion;)!ta the weight of the samples

10TABLE 2

Results lrom assessment 01 lapa brava by 1/2 hour dives in S. ~ligueJ.. Faial

and Pico. n = number in sampIe, W= mean ,,'eight 01 specimens, :\ = neuter,

TL mean length, s = standard deviation.

\.'eight~öO ~9q

fi~s TLts TL~~ Nax. 1--:\-1+ IV+-V-n'-

n \.' ~,XX

g OÖ \j!!i! XX length ~.~ $<

S. ~Iigue1

( 7- Ci Octoter l"S6) :

Porto Formoso 1507 109 1).8 51. )8 40.)7 8.26 44.84:5.)6 48.57:8.89 21. ))%11.)) 70 8.2 42.9

Ponta Gar~a )90 50 7.8 54 .00 22.00 24.00 42.26:5. 6 1 47.09:6.)9 35.00: 5.60 59 28.2 /. I

P. da Ba1e ia 1400 186 7.6 44.86 21.62 )5·51 )8.96:4.57 42. )5:5.)5 31.87: 7.85 5)

Rabo de Peixe 1181 126 8.) 55.56 25. 40 19.05 46.47:5·95 49.91:6.68 1).71:10.85 65

P. da Ribeirinha 464 56 8.) )5.71 44.64 19.64 40.25: 0 • 12 42.16:9.59 30.91: 8.66 i4

Faial

(15... )0 Ju1y 1986):

.;,-

"

Feteira 700 72 9·7 )6.62 0.00 6).38 46.92:7. 44 37.93: 8.63 58 75.5 4.1

Feteira 770 94 8.2 17.02 8.51 74. 4 7 47.)1:8.48 51.6):9.82 37.67: 6.48 61 76.~ 2.8

Varadouro 340 24 14.2 J).)J 8.)) 58.)) 54.75:4 .97 61.50:0·5 46.00: 9.11 62 6'1.6 8.7

Capelinhos 152 0 70 21.7 28.99 27.54 43.48 54.)0:6.09 56.89:6 • 16 45.116: 7.)6 72 54 • 4 10·5

P. <::0 ~~rt-e 259 50 5. 2 16.00 2.00 82.00 41.)8:5.70 57 38.34: 5.08 57 92·5 2.5

,,_. Ribeirinha 254 )1 8.2 2).)) 16.67 60.00 50.57: 4 • 8 1 54 .60:5. 28 42.50: ).95 60 74 . .!., 3.2

P. do A1moxarile 400 28 14.) 25.00 14.28 60.71 46.4):4.66 54 .25: 4 .02 44.44:: 6.)5 60 71.4 0

SC:j J fio QJf\ , , I" ') 19. 4 1< ).8'/ ;6.62 43.2;:4.61< 4t<.6;;!;i.O) 40.42:t 4.1Q y; q::!.o 0

Pico

( 18-20 .lu1y 1086) :

S. !'Ia teus 664 56 11.9 25.00 7.14 67.86 52 • 2 :9.)8 59.75!;.4 42.27= 9.18 7J b;.) 6.1

S. Joao 522 60 8.7 )0.00 18.)) 51.67 47.56:7.90 52.82::';.59 40.58: 7. 2 7 65 63.9 2.8

Lajes 584 52 11. 2 38.00 16.00 46.00 52.00:7.)6 56.25:6.48 42.22: 7.20 68 50.0 2·9

~Ianhenha 512 50 10.2 22.00 10.00 68.00 52 .55:10.49 56.60:6.)1 43.32: 8.14 70 :;.8 11.1

P. do ",orte 9'10 126 7·9 23.58 2.44 73.98 47.56:5.85 55.00:2.16 42.43: 6.19 60 81. 5 3.1

S. Roque 9 44 160 5·9 6.2'1 6.29 87. 4 2 44.89:5.00 44.44:5.64 38.35: 5·35 56 ',; .6 0

Cachorro 250 58 4.3 10.17 1.69 88.14 43.50:2.99 4) )6.94 : 5.74 50 ,,'" 0'-. ,

Calhau 745 82 9·1 2J.17 2J.17 53.66 46.03:6.56 52.16:5. 11 43.14: 7.54 60 75·5 5·7

•

77

~D©(Q)IID~§~@~ @'lf OO[J1fi)[l2)@~§

JULY·7986

•

"' ..59lW·250 lt.d"10,% 9-2.1­1'1-86"/.I>39",,,,

n.ge.,,,,.'74~~

c!'.2.31. 'j? 231.N- • "/.

" 6'l'lIlTl

~Males

_Females[=::J Neuter or immature

fig.10. Assessment of laps brava by 1/2 hauT d.ives in Pico,July 1986. fhe area of the clrcJes is proportionalta lhe weighl of the sampies. (c:;~p leopnr1 Fin.f:\'.

-L--__

s..,'"GITE'.JJULY 7986

fig.l1. OP.nsity of recruits of "laps brave" inthe lower intertidal zone at varlauslocalities on S. Miguel Island. Thearea of the circles 1s proportional tathe number limpets pr. m'

J~====--

I-­I''1''

<::smrn

I ,o.5mm :§" 30rrtn

37

"

with more

12

from random quadrats. Exploitation c1ear1y concentrates on the larger

sizes, all of which are sexua11y mature.

Assessment of stock size

Assessment of density by timed 30 minutes dives was carried out

during tIlü month of October 1986 around the coasts of S. Miguel and

during July 1986 in Faial and Pico. Figures 8, 9 and 10 show maps of

the respective islands with the localities that were assessed. The

results in numbers are shown in Tab1e 2. The best stock of "lapa brava"

is undoubtedly on the north eoast of S. Miguel. Also Capelinhos, Faial

has a healthy population.

The sex ratios of "lapa brava" from the assessed localities (Figs.

8,9 and 10 and Table 2) show an overall lower percentage of females.

The results from July 1986 are of limited value, as this time of the.

year many individuals are in the neuter resting stage. Only at one 10­

eality on the north eoast of S. Miguel was there more females than

males. On Pico, two localities had an equal number of the two sexes.

In one snmple from Feteira, Faia~ no females were encountered. The dis­

erepaneyl~re~~%.A diserepaney of more than 30% was also found at

two loealities in S. Miguel. It ean also be seen from Table 2 that the

mean length of females is greater tIlan that of the males in 19/21

cases.

Recruitment

"Lapa brava"

The densities of new recruits and juveniles (~30 mm) in the lo'eintertidal at various localities on S. Higuel are shown in figure 11.

The northwestern coast had the highest number of animals-2than 1000 111 in one of the loealities counted.

Recruitment counts were also tried in Faial and Pico. Here,

however, the recruitment or "lapa brava" in the intertidal was almost

zero.

"Lapa mansa"

The rücruitment of "1apa mansa" seems to be adequate everywhere,

although no counts have been made, juveniles are plentiful on most

shores in the Azores.

•

DISCUSSION

"Lapa brava"

Reproduction

The ereater mean size or remales (Table 2) and the greater propor­

tion or remales in tlle larger size classes (see Appendix) suggest that

"lapa brava" is a partial protandrous hermaphrodite. Orton ~ ale (1956)

suggested the same ror Patella vulgata rrom Britain, as did Thompson

(1979) ror P. aspera in SW Ireland and Guerra and Gaudencio (1986)

ror populations or P. aspera on the coast or Portugal.

A spawnine peak in winter (December-January) and a resting period

in summer (June-July) were found by Guerra and Gaudencio (1986) ror

populations or P. aspora in tho south or Portugal. This corresponds to

what we round for "lapa brava" in tho Azores althoueh the spawning pe­

riod ror the latter is extended and the resting period is from Nay­

-July. On the north and center or the Portuguese coast they reported the

spawnine peak to.be a rew months earlier (October-December). The sea­

-surrace temperatures in,the Azores and the Alearve correspond approxi­

mately, which could be one or the ractors responsible ror the simila­

rity in breeding cycle.

"Lapa brava" in the Azores matures at a much larger size than

P. aspera rrom continontal Europe and the British Isles, to which it

has the closest taxonomic arrinities. While "lapa brava" attains ma­

turity at a shell leneth or 41-45 mm, the corresponding sizes ror

P. aspera in SW Ircland is lJ-20 mm (Thompson 1979) and ror thc Por­

tuguese coast l8-2J mm (Niriam T. Guerra, personnal communication).

Size and stocksI

Also, thc Azorean "lapa brava" is overall larger in size in rela~

tion to P. aspera as can be seen rrom the mean lengths in Table 2 com­

pared with thc loneth rrcquency given by Thompson (1979) and by Guerra

and Gaudencio (1986)~ In unexploitcdpopulations on Corvo Island the

limpcts attain a lcngth or 90 mm. The maximum shell length ror P.

aspera was eiven as 57 mm in SW Ireland (Thompson 1979) and as 49 mm

in Portueal (Guerra and Gaudencio 1986).

Comparison or population structures or different types or catches

shows that the proressional divers or Nosteiros, S. Miguel,

take steps to rogulato catches to maximizo and sustain yiolds.

Amateur and casual collectors take limpets of all sizes and may prevent

that a large numbor oi' "lapa brava" attain sexual maturitY. On the

o~her hand, the mean individual shell length in the pro1'essional

exploited populations 01' S. Miguel is lower than the amateur exploit­

ed ones on the other islands. At the present level 01' exploitation,

the 1'uture 01' the valuable Mosteiros "lapa brava" 1'ishery appears

secure. However, 1'luctuations 01' the stock may occur occasionally.

During the last winter 1986/87, 1'or instance, prolonged storms with

heavy seas played havoc with the boulders 01' the rocky coasts and

did severe damage to the limpet stocks particularly on the NW coast

01' S. ~liguel, the Mosteir05 limpet .1'isheries area.

The stocks 01' 'lapa brava" in the Central Group 01' islands are

low, but seems to be recovering 1'rom the heavy exploitation and the

mass-kill 01' 1983. The extent and the cause 01' the latter remain a

mystery. It was virtually over be1'ore an investigation could be start-

ed. Hower, it seemed to occur primarily on the southern coasts. •

Possible culprits include red tides (see work by Southgate ~ ale

1984, in Ireland) or unusual warm temperature or desease. Pollution

is unlikely to have been the cause as other animals were not a1'1'ected.

On the islands investigated, the best stocks 01' limpets are

generally 1'ound on the northern coasts. These are less populated,

have rougher seas and are thus less accessible.

Recruitment and algal interaction

Wave action have been 1'ound to stimulat'e spawning (Orton ~ ale

1956; Thompson 1979) and may thus enhance recruitment on the northern

coasts. Here, we probably also 1'ind greater availability 01' nursery

grounds due to storm removal 01' algal tur1's. The latter, which re­

produce vegetatively, establish itsel1' in areas where uncontrolled

human exploitation 01' limpets has taken place. These algal tur1's do

not relinquish the rock sur1'ace once this has been covered. Thus, the

limpets are deprived 01' a "lithothamnia" covered nursery ground

which can be easily grazed. In NW Europe, however, where we 1'ind

di1'1'erent species 01' algae which reproduce sexually, the balance bet­

ween limpets and algae is erected in 5-15 years a1'ter experimental

removal or killing orr or limpets by pollution (Hawkins ~ ale

1984).

It would be expected that removal 01' the larger animals in a

partial protandrous hermaphrodite will distort the sex ratio. The

larger remales would be rarer and tlle egg production reduced and thus

•

lead to recruitment failure (see Table 2). At Feteira, Faial, one popu­

lation had no identifiable females in July 1986.

The dispersal of larvae is also an important factor for success of

recruitment. It:is notk~own ir'the 'la~vae have a pelagic stage. If that

is the case, the smaller, more isolated islands would have a greater

loss of larvae offshore.

The tllree factors mentioned, lack of nursery grounds, distorted

sex ratios and an eventual loss of pelagic larvae could explain the

lack of recruits in the Central Group. The latter factor would be of

great importance in Flores and Corvo as weIl if the populations of ~im­

pets on tllese small islands become more exploited in the future. S.

Miguel is larger, which may enhance recruitmont.

"Lapa mansa"

In contrast with "lapa brava", "lapa mansa" does not seem to

change sex. At present it appears that tlle intertidal stock can with­

stand hoavy exploitation duo to fast growth, early sexual maturity and

consequently high fecundity. However, the mean sizo of individuals

llave been decreasing in re cent years in exploited populations.

Conclusion

Thus, in conclusion, we can say that it seems unlikely that "lapa

mansa" should sufler "recruitmont overfishing". "Growth overfishing",

howevor, will rosult in smallor limpets.

"Lapa brava" is susceptible to "recruitmont overfishing" due to

distortion of the sex ratios by removal of tho larger females and to

heavy exploitation which destroys the well-grazed "lithothamnia"

dominated habitat needed for continual recruitment.

Hore detailed work on reproductive seasonality is under way and

growth studies have just commenced. Furtller work is urgently noeded

on :fertilization, gamotes and larval biology which are unknown areas

in limpet biology. Interaction between algal turfs and grazing limpets

and tllO provision of nursery grounds also needs further investigation.

RECOMHENDATIONS

It must be stressed that these recommendations are of preliminary

nature and that further work is essential before derinitive measures

can be firmly suggestod.

16

1. Prohibition 01' 1impet collecting (both species) by diving should

continue in the Centra1 Group.

2. In the archipe1ago as a who1e, a minimum size 01' 40 mm 1'or "1apa

brava" and 20 mm 1'or "lapa mansa" should be proclaimed. A maximum

size could perhaps also be introduced (e.g. 70 mm) to protect 1'e­

male reproduction in "lapa brava".

3. It is essential to set up an unexploited area (all species) with

very tough regulations to prevent poaching. Research in this re­

serve will tllen a110w good, sensible management recommendations.

Calhau on Pico is chosen as a suitable site for reserve.

4. In the future, harvesting 01' limpets by diving should be subject

to a license with compu1sory sale through the auction service,

similar to that 01' Hosteiros, S. Miguel. It is very important to •

introduce this system to Flores and Corvo to prevent the at present

little exploited population being reduced to the low level 01' the

Central Group.

ACKNOWLEDGEHENTS

We are greatly indebted to the Secretariat 01' Agriculture and

Fisheries 01' the Regional Governrnent 01' the Azores for financing the

research. We also acknowledge the kind cooperation 01' Azores Fisheries

auction service (LOTAgOR). Our thanks are due to Mrs. Carmelina Lea1

who did laboratory work, calculations and typing and to Mr. Norberto

Serpa 1'or collecting material, especially during the 1/2 hour dives.

In S. Higuel we acknowledge great help 1'rom Mr. Joäo Brum 01' the

Department 01' Biology 01' the University 01' the Azores, and Hr. Manue'

Ferreira and Mr. Henrique Miguel, both 1'rom Hosteiros. Mr. Jos~ Carlos

da Silva made the graphs.

REFERENCES

Christiaens, J. 1974. R~vision du genre Patella (Mollusca, Gastropoda).

Bulletin du Hus~um National d'Histo±~e Naturelle 3~ s~rie,

no. 182, Sept.-Oct. 1973, Zoologie 121:'1305-1392.

Guerra, M. T. and Gaudencio, M.J. 1986. Aspects of the eco10gy of

Patella spp. on tlle Portuguese coast. Hydrobiologia 142:

57-69.

•

Hawkins, S.J., Southward, A.J. and Barrett, R.L. 1984. Population

structure of Patella vulgata during succession on rocky shores

inSouth-West England. Acta Oceanologica, Special no.: 103-107.

Morton, B.S. 1967. Malacological Report. In: Chelsea College Azores

Expedition. July-October 1965. Final Report, pp. 86.

Nobre, A. 1930. Materiais para 0 estudo da Fauna dos A~ores.

Porto 1930, pp. 108.

Orton, J. H., Southward, A.J. and Dodd, J.M. 1956. Studies on the

bio10gy of 1impets II. The breeding of Patella vulgata L. in

Brituin. Journal of the Marine Biological Association of the

United Kingdom, 35: 149-176.

Southgate, T., Wilson K., Cross, T.F. and Myers A.A. 1984. Recoloni­

zation of a rocky shore in S.W. Ireland following a toxic bloom

of tlle dinoflagellate, Gyrodinium aureolum. Journal of the Marine

Association of the United Kingdom, 64: 485-493.

Thompson, G.B. 1979. Distribution and population dynamics of the

limpet Patella aspera (Lamarck) in Bantry Bay. Journal of

Experimental Marine Biology and Ecology, 40: 115-135.