REPORT N9 29 › static › FullTextFiles › 055205.pdf · u.re1s eM *TTOf'N'T snutTnNVd) ulrs801...

REPORT N9 29

Published by lhe Oireclor oi Fisheries and Witdtite. perth.unde. lhe au lhor i l y o l lhe Hon. Min is te r to f F isher ies 6nd Wi td l i te

The Predation ofPot-Caught Western RockLobster (Panulirus Longipes

cygnus) by Octopus

BY

L. M. JOLL

1977

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CONTENTS

SUMMARY

I NTRODUCT I ON

THE WESTERN ROCK LOBSTER FISHERY

PREDATORS OF POT-CAUGHT WESTERN ROCK LOBSTER

ESTIMATION OF THE LOSS OF WESTERN ROCK LOBSTERSTHROUGH PREDATION

METHODS

RESULTS

(i) Total predationCii) Predation by various species(iii) Size and sex of predated rock lobstersGv) Loss of commerciilly-sized rock lobsters[v) Financial loss to the fishery[vi) Estimate of the number of octopus caught

DISCUSSI ON

ASPECTS OF OCTOPUS PREDATION

A. THE ATTRACTTON OF OCTOPUS TO ROCKPOTS

I4ETIIODS

(i) Aquariunexperiments(ii ) Field experiments

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IOBSIER 28

RESULTS

(a) Bait locat ion tr ia ls(b) sensi t iv i ty t r ia ls(c) Pot l_ocation trial_s

DISCUSS TON

B. REPI'LSION OF OCTOPUSES FROM ROCK IOBSTER POTS

C. ENTRY IlilTO A}ID ESCAPE F'ROM ROCK I,OBSTER POTSBY @TOPUS

}IETIIODS

RESUTTS

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TABLES (contd.)

SIZE (CARAPACE I.,ENGTH) OF PREDATED ROCK LOBSTERSIN COMI4E RCIAL CATCH SAMPI,ES

SEXES OF PREDATE D ROCK LOBSTERS IN COMI{E RCIALCATCH SAMPLES

ESTIMATED NUMBER OF I,,EGAL-SI ZED ROCK LOBSTERSPREDATED

MEAN WXIGIITS (g) Of' PREDATED, LEGAL-SIZED ROCKLOBSTERS

ES TTI!4ATED WEIGHT LOSS (kS) THROUGH PREDATTON

ESTTMATED FINANC]AL LOSS THROUGII PREDATION

ESTII4ATED NUMBER AND WEIGHT OF OCTOPUS CAUGHT

LOCATION OF HfDDEN BAITS BY OCTOPUS

SENSITTVITY OF OCTOPUS AND ROCK LOBSTER TODILUTIONS OT ABALONE FOOT MUS CIJE HOMOGENATE

NUMBER OF POTS ENTEPiED BY OCTOPUSES IN POTLOCATI ON TR]ALS

EFFECT OF USTNG OCTOPUS AS A COMPONENT OF ROCKLOBSTER BAIT

AREAS OF ENTRY INTO ROCK ],OBSTER POTS BY OCTOPUSES

AREAS OF EXIT OF OCTOPUSES FROM ROCK IOBSTER POTS

SEXES OT' ROCK LOBSTERS PREDATED IN POT ENTRYTRtALS

CArcIIES OF NORIVIAL COMMERCIAL ROCK LOBSTER POTSAND POTS FITTED WITH OCTOPUS TRAPS

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COI4BINED RESULTS OF COMMERCIAIJ FISHING TRIAIJS ATDONGARA AND FREMANTLE US]NG NORMAL ROCK IOBSTERPOTS AND POTS FITTED WTTI1 OCTOPUS TRAPS

PERIOD OF RESIDENCY BY OCTOPUS IN ROCK ]-,OBSTERPOTS CONTAINING OCTOPUS TRAP S (AOUARII'M TRIAIS)

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In an attempt to quantify more exactly the loss of \,7estern rockl-obsgers due to octopus predation, a prograrnme of research fundedby the Fishing fndustry Research Trust Account, was conunenced inDecember 1973. Considerat ion was also to be given to possibleways of reducing the losses caused by predation of pot-caughtrock l-obsters by octopus. This repore d.escribes the outcome ofthe research.

II THE I^IESTERN ROCK LOBSTER FISHERY

The fishery for the western rock l_obster is the most important.single species fishery in Austral-ia with a value of appioxirnatelv$32 000 000 in L! i 'e 1975/76 season. I t is governed by- i complexset of regulat ions which have been reviewed by Bowen (1971_). Thefishery is located along the wesLern coast of the southern half ofWestern Australia [Figure 1) and takes place from November 15 toAugust 14, except at the Abrolhos Is. where f ishinq is onlv per-mitted from March 15 to August. 14.

Rock lobsters are caught in baited pots Ltraps) set amongst reefareas which are the habitat of rock lobsters. The pots are usual lyconstructed either of wood.en battens fixed to a rectanqul-ar wood.enframe or- lengths of cane or wire mesh on a steel , beehive-shapedframe (Figure 2). O1d cane pot.s are sometimes covered. with wiremesh eo reinforce lhem and prolong their useful l i fe. The usageof the three pot types var ies in di f ferent areas of the f ishery.In the L973/74 season Morgan and Barker (1975) recorded that thepercent.ages of the various pot types used by fishermen completingvoluntary 1og sheets were:

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Pots have a single entrance (neck), usual_ly on the upper surfaceof the pot, and are required by law to have an escape gap withminimum dimensions 54mm x 305mm, to a1low the escape oi !mal1rock lobsters. The minirnum J-ega1 size of rock lobi ters is 76mm,measured from the base of the rostral horns to the poster ioredge of the carapace. Undersized rock lobsters capiured in pocsmust be returned. to the sea.

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a) Two octopus predated rock lobsters.

fwo cutt, l -ef ish predated rock lobsters.

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'1:ode: sTr{? Jo uo14e:edard Jo aur-F + oq+ ?p eTqeTTeA€ 1ouara.|'r uosees 9 L/9 L6I er{+ .rol: sa.rn6Tl: +-rof Ja aL{ ' (c - EJ Z aTqeJur uAoqs are suosEas SL/VL6I pue 'VL/|L6I 'eL/2L61 eq4 ]oJ {coTq

z{.rana :o;: qfuou qcea .roJ S1J:TT 1od 3o r sclumu TE?o? aqfi 'uosEas auodue ur ,{raqsr;: aq+ }o lJofJe eq? fo %99 ̂Te+Eurrxordde .ro} 4unocces{coTq as aI-lJ, 'gTZe 'gTTt 'gToe 'tTot 'VI6Z - s{coTq oT x oT aATJoq+ uo.rl: papJocal a:ar'r saldures 'pe4epa.rd-qsTJ puP ' pelepa'rd-qs-F J-aTf?.nc ' pa4epa-rd.-sndo4co o4u1 papTATp aJ€ s.ra1sqoT )tcol palepa:d

aql suoseas o/'\f .ra+4pT aq+ ro.{ '9L/9L6I pue 'gL/VL6I 'VL/€L61, €L/ZL6I suosEas aq4 6ut.rnp 6urqs-53: Jo sr{+uotu ue4 ar{? Jof (p - e) Ta1qel u1 a6ue: qldap r{q uatoqs a.re 1q6nec sndo?co Jo .requnu aq4 pue

sra+sqoT >{cof, palepaf,d }o Jaqonu aq? 'peTdures s4od Jo sf,equnu aqJ

SlINS]U

'ue)ip4 e.raru treq1 qoTqA uT )tcoTq ^T x .rT ar-T401 pa+€coTTe e-raA saldures aq? 'sPeJE +ueral:frp ur +rolJa uf suor

-?errell. aq1 +raTJa.r o4 pa4qSrala aq pTnoc s+Tnsal aldures 3r{+ +eq+ oS'(T a.rn6TJ) slooTq pr.r6 apn116uoT ...,T x epn+r4eT oT u-F IraqsTf aq? fo

4JoJJo re+o1 er44 pap.rocaf, scr4H14e?s Jo nee:fig u€TTe.rlsnv aql Iqpellauroc pue uaur:aqi TJ TTe [q pa?eTduroo suf,n?ef, ,{1q4uour '{:oslnduro3

' a4ef qc?pc eq+ qa-IA tr1as:eau1 par.r€A paldures slod io f,€Jqurnueql 'paTdules sf,alsqoT lco.r Jo .raqumu oq+ Jo suJa4 uT sem 1a6:e1

ar{4 asneceg '.Ieqleallr peq .Io sa+El qc?ec }\oT Jo asneceq 'Io uoseesaql Jo seuT+ auos ?E peqsrJ ?ou a.ren saEupl qldap u1e1:ec asnecaq

j"q+t" 'pJrrllrn: sder"rle +ou sen ?46:e4 aru 'lrod ?cee 1€ q4uolu'

q"e.-toj ag"": qldep qcee uo.rJ sJalsqoT {co.r 00? }o 4e6:e1 eqlTA / lurd0t .re^o pu€ 'urd0E-02 'ur,{qZ-qT 'ur,{qT-0) se6ue: q4dap rnol:

*o'r j s ".i.ii c elaurei 01 parrre aurure:6o.rd Furldures eq; ' ( T a'rn6 rde:e6uoq /uarf,nf 'urTooueT 'eT 4ueuef,.{) s?.rod :no] o+ 'Teau 'ro uo'r}

6u-54e:ado sleoq paldures aurure:6o:d 6utldures qc+p3 TeTclaunuoc aqI

YI

IiI

TABI,E 1 Commercial catch samples I972/73 Lo l975/76.

TABIE la r v I z / t 5 u e a s o n .

BLOC( 29!i l0l4 ,015 lr15 3215

9 rp 2p ro. g lp 2p 30+ 9 rp 2p ro+ lp 2p ro- l0 20 3n+

t 5 1 3 1 0

120 rao 167 3r

2 0

l r

JUIl€

19

1 4

9T

It

zzz oz1 51I

3rr rez

.IIII

sB? sea 05r

IIZ

I

*or i7 or d{t o'z oi d0r 0z 0I

{t o? ol ri0t 0z 0I

tr niz or ri0t 0z 0I

a:020T0

sErSII{EIOIhT0thT6Z)10'ts

'uosees v L/t. L6I'qT sT sv,r

TABLE Ic. 1 2 1 1 / t a u e a s o n .

BLOCK 20!r 1014 1015 3115 3215

P lP 29 ro.0 2 0 1 0

? r P 2 P t u10 20 l0

1l 2p lo*20 30

0ro

I P 1 0 n20 l0

P ]p 2g to*0 2 0 1 0

DEC.

1 5 7 9

0 00 o

1 5 t 3 0 79 79 105

0 0 01 03 0 2

o 0

103 r0rI

0 ,

121

256 100

05 0

23t

3

I

I

I32

l s 0 II

t

, 1 6

LI

I.I

I1

lNna

tLI L9 S?a

art

II

I

I

rf30

6trII

-0' ;i ;t E'.& Ht ;f 6'-& 3t if u',0( 3t 3{.& ;i Ht E'slztEII'sI0tIrT0th16Z)00'18

'uoseas 9L/9L61'pT sr w'r

ELOCK

EFFoRT GoT LIFn) BY BL0CK AND |40NTH 1972171 SEAS0N,

JANUARY MARCH APRIL JULY Aueust I

26L2

26L3

2712

27 L3

27 14

2 8 1 3

2814

29L2

2913

29t4

3012

3013

3014

30I5

3112

3I13

3I14

3115

32 r3

3214

3 3r4

3315

34 t4

8 9 9 7

6 061

r4a 347

I 3 9 4

9 735

74L

260 326

702

1 6 4 1

720 220

3 0 4 4 1

3 1 0 2

976

L4 358

167 779

20 6L2

r 74 l

2 6 9 8 8 6

1 0 2 9 0

5L0 267

2 807

13 655

3 0 2 8 6 9

84 304

3 807

46 9r1

28 840

L6 247

L23 244

2 7 7 5

242 852

7 008

184 047

2 820

46 774

238 036

1 404

4 078

L63 221

5 r . 2 9 8

2 1 1 5

4 455

L 020

43 42r

I 260

3 8 4 0

225 969

2 456

2 479

202 La6

5 3 8 7 6

3 1 3 4

39 452

2 400

47 2L9

L 260

8 369

2 434

9 0 0

18 566

1 5 8 6

27 384 26 6L0 20 379

10 857 12 884 15 726

1 589 2 7A6

2 270 260 976 432 77L

99 064 93 209 A2 433

980 11 561 75 220

21 688 20 A95

11 337 rL 72r

2 300 642

305 327 !28 L66

87 462 67 592

t-I 674 2 733

23 7 t4 9 561

14 500 9 2A2

I 861 255

161 651 65 342

64 655 2L s20

4 634 L 544

840

60 621 60 446 20 73L

8 690 7 057 3 050

r52 529 L49 472

I 052 I 169

5 342

168 483 79 I1 ] -

42 69 t 9 744

2 679

240

29 079 7 235

196 719 88 557

l3s 669 135 t9s 43 249

4 561 724

69 088 55 185

5 5 6 0

L 260

1 1 9 0

60 072

I 5 0 0

3 600

50

1

I 2 3 2

136 2A 372

3 0 0

380 3 523

1 002 95 52

24 ?40 1 I 989 5 376

4 409 3 312 2 390

l 8

OL

980 Z

09t

0t0 I

098 Z

8e0 €z

€99 t

809 e€

toz I

sr5 t€

0tz

oLs z

t81 T

ogL 't

000 €

gTl 00r

1ZZ Z

8e8 9

zco 6L

069

zz0 t

s€9 z

Z8O LL0 tT 06

090 t

189 TLE

tgt t,

zEE t

999 I

T'O T8

g0€ s0€

6t0 I

r00 €09

LTL EI

'O' II

0s€ reaz zr06€ 9r

008 T

869 Z

t00 tI

cTc acT

996 8r

t8r €

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T€L SZI

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210 €

vr6z

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988 Sr

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60€ 0l

666 99r

ezL 0z

099 Z

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9€0 €

098 Z

69€ 88

€89 r

IT' 9TT

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660 99

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092 T

809 91

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999 I

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'ZI 8T

069 66

s€r

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196 te

tez 867

296 '

€t8 i8T

z'tg zz

009 z

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s68 8r

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096 T

682 t9

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618 't

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8€Z 96

tot z9z

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808 8€

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996 9

tLg Z

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9rl 96

8OI €

896

990 tr

0€€ 982

06t 9s

98e r

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te"E 6v

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586 T

ttz LLz

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998 Et

216 '

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SNnlAW'lt8dv Hl8vtlIUVnNVCA0N)30'19 $ngnvA'lnf

'N0sv]s hll/6r HlN0t^i It,lV )]0-lB 18 (Sllll tod) lu0lllsz fl8vr

TABI.E 2c EFFORT GOT LIFTS) BY BLOCK AI.ID I]ONTH 1974/75 SEASON,

BLOCK NOV DEC JANUARY JUNEMARCH A P R I L I'1AY JU LY AUGUST

2612

27 12

27 L3

27 14

2At2

2 8 1 3

2aL4

29].2

29L3

29r4

3 0 1 2

3013

3014

3 0 1 5

3 L t 2

3113

3114

32r2

3 213

3 2 I4

33 r4

3414

3 2 6 0 2 8 8 0

24 470

15 530

320 765

7 0 7 0 3

I 447

L72 9L9

L6 7 I4

3 787

t10 51?

50 L24

420

131 433

15 014

7 9 8 8 2 2

10 185 20

r 911

L3L 272

310

1 5 ] 2

249 26s

L 296

1 3 8 4 1 7

1 4 1 0

r 2 0 0

20 691

199 503

261 903

1 7 0 1

7 620

3I3 410

7 020

5 7 7 0 8

41-6 994

6r0

l L2

8 6 0 I 7

4 4 8 8

44 997

2t 559

6 8 8 5

L12 954

972

5 472

I 9 l 8 2 9

5 1 6 8 8

322 008

2 9 8 5

97 407

3 402

235 2L0

182 658

56 547

2 961

1 9 5 0

5 4 7 4 r

128 683

I 5 9 1

105 017

2 I 3 4

5 0 3 9

42 243

r 9 8 0

25 79 ! 28 839

15 084 18 303

2 4t0 2 320

268 826 457 t98

96 368 9L 294

5 112 13 708

233 602 I99 576

t 624 1 39s

4 385 2 L?A

228 534 200 629

6L 429 55 685

2 961 2 A20

I 950 3 180

5 5 1 7 5 3 8 s 2 0

343 243 287 065

I 4 8 0

23 033 L5 2A4

15 072 5 s49

1 5 5 1 1 0 6 8

I2 I 633 49 926

55 328 35 397

1 3 2 0

64 433

3 402

r 0 0 0

74 484

2 7 ' t 2

111 803

29 62 r

I 7 2 5

6 782

176 654

4 s 8 0 1

I 4 4 0

L 2 7 5

\2 296

153 940

3 8 7 8 9 27 AL2

7 9 2

14 399

8 5 4

85 I35

2L 872

81 865 4L 707

t6 81r 10 31"?

7 2 4 2 7 5 5 3 8 4

360 I 4 I0

2 736 2 296

2 0

'Jolepard r{cEe-dq palepa.rd. €.ren qcTqlr seldures eq? uT sJa?sqoT >{c o.r Jo a6eluac:adT T€.reAo €qf trq sre+sqoT )icor pe4epe:d 3:o :aqumu T€?o4 aq4 6uri{1dr-11nur trq pa?purrase sE}\ (t aTqeJl 9L/9L6I p-uE- SL/VL6I u1 uotlepa:dTE4o4 arl+ 04 sro?€paf,d snor:el sqa f o uoTlnq-Fr?uoc er{,I 's.raf sqo1

1co: qq6nec-aod 3o s:o4epa:d 1ed1cu1.rd eqa ate sasndo4co leqf Aoqs(p pue c 'T eTqpf,,) suosees 9L/9L6I pue 9L/VL6I aI{1 rol: sprocar aqf,,

sslSEais snoruvn I's Nor,lvqsdd (l-t)

000 ote

000 LLe

000 E0z

000 e9t

9 L/SL6I

SL/V L6I

v L/t 161t L/7L6T

s.ralsqoT ]Icou pa+€pe.rd 'oN '4sEuosPe s

'91/9L6I - tL,/ZL6I suoseas eq4ur sf,aasqoT lJo.r pa4Epa:d 3:o .requmu Te?o1 pa+eurrlsge grsv,l

'elPluT1sa T€1o4e u1p4qo o? ('llnuoc 'srad 'ue6:o6 'u'o - s+f TT fod uoITTTru 9'6

.,{1a1eurxo:dde1 uosees aq4 .roJ 1.rol:l:e Te1o4 palpu-F+sa eql .dq parld-5-1{nur .{1du-r1s sen seldures aI14 uT 4JTT ?od red s.relsqoT >t3o.r pe4ppa.rd

Jo .raqumu u€eu aq? / aTqeT-F€AE lou a-rel'\ se:n6r; uol:Ja qcrqA .ro]'uos€es 9L/?L6I aq4 .roJ '(t 3TqPill uotlepard T€+o? er{+ Jo a4euTlse

ue altb b1 paururn s areA sq4uolu/)tcoTq pue s{coTq palduresun pednoJ6^TTeuTpn?T4eT aql :toJ pu€ st{4uour/{coTq peldues er{4 .roJ ssletuTlse

ul.J !+spo!^q equ 'TaAaT TEuTpn4T4€T eues aq4 uo s{coTq 'Ietl?o aq?pue s>tcoTq asoq+ l:o sq?uouJ pelduresun aq4 uT lroJ:l:a aq1 o+ parTdd€

a4ef, ueeu aLI4 pue palood a:ervr 9T0e puE ?Tgt JoJ sefEur+sa eI{J,''TT8-ZTTE pue '1IZt-ZIZ| 'eT/tIte 'VM s)tcoTq o1 parldde sen

STT8 f,oJ ale.r aq+ a:Llqr tI/2162 pue 'VI\Z-ZIqZ 'VILZ-ZILZ '|I/ZI7Z

slcoTq J.o 4.rol:Ja oql o+ parTddE sPlr tT6Z f,oJ a1€.r aq4 'e'T 'pasn

sEA looTq paldures +sesoTc aq4 ;o a?eJ ueeu aq4 /peTdures ?ou of,aAqclqn 'I:aqs-FJ eq+ J:o s>tcoTq r{Trer{fnos pue ,{1.raq4.rou af,our aq+ f,o'{

' 11 a:n61.f) 9TT€ fo sq?uoul palduresun eq4 o? se TTaA s€ ?TT€ pue'tTT€ 'ZTT€ slcoTq o+ patTdde seA ETTC .roJ e+eJ TenuuE ueeu aql '6'e

'>tcoTq 4pq1 fo sq?uout pelduresun eqa uT ?f,oIle arl4 sE TToA s€ 'uoT1T

-sod leurpn1-!?eT aur€s eq1 l:o sltcoTq ur 4.roJ;a pep.rocal er{? o1 trTuopelldde a.roJa.raq+ spl"r '{JoTq e Jo sqluotu peldures eq1 uo.rf peleTncT€o

1J'tT +od red s:alsqoT {cor pelepe:d Jo e+ef, qc+ec po4eurr+se eqJe6e.ra.ne ruroTeq ,ro abe.rane .{11ensn e.rer"r s1coTq lal{4o eqf altqr'l a6e:eaeanoqe .d1trua+srsuoc 6uTeq ( tI6z) >lcoTq ?soulu.raq+Jou aI{4 ' 1f TT aod rad

s-ra4sqoT {ro.r pe1€pa:d g:o .r aqurnu aq?_ ur s{coTq peldues eq1 ueenf 3q( I0 ' 0 > aI) secuo.raJJTp ?uEcrl;rubTs a.re'& af,aq1 suoseas anuos uI

's{coTq palduresun aql uT sp TTaA sP peTdures 1ou e-Ta^r slcoTq Tpnsnaq4 r.lcrqA ur sr{?uour aq+ uT uol4epa:d aq1 fo eleuT+sa u€ uTe?qo

o1 .A:essecau s€Jq ?r r{:eqsr]: eq+ uT uollepe:d Te+o? aql aleur-F?sa o'l

'paldures e.rer\ s>[JoTq snoTJEA eq1 l-l3Tr{r'l ur sq+uou eI{4ur 6ur::ncco uotlepa.rd eq? fo o1€tur4sa ue peptao:d se?PurJse uoT1ep

-a:d uotlepa:d z{1q1uour aq? f o uns aqf,, 'q4uotu aeql uT {coTq 4€I{? .rol:

lroJJa 6u-!qsrl: Te+o? eqf r{q eldues aq+ uT lfTT +od :ad s:a4sqoT }tco.r

TAB LE 4 - Estimated number of rock lobsters predated byocr.opus, cutt l -ef ish and f ish in the Ig74/75 inoL 9 7 5 / 7 6 s e a s o n s .

Se a son OctopusPred ated

Cutt lef i shPredated

} ' I S N

Predated

r 9 7 4 / 7 5

1 A 1 q / 1 A

3 3 4 0 0 0

3 2 1 0 0 0

3 9 0 0 0

0 0 0

4 0 0 0

1 4 0 0 0

(iii) SIZE AND SEX OF' PREDATED ROCK LOBSTERS

Not al l predated rock lobsters in the sanples from the L974/75and. L975/76 seasons were of legal commercial- s ize (7, .76nn carapacelength LTable 5L. In the two seasons respect ively only 55.4% and60.0U of the measurable octopus-predated rock lobsters in thesamples were of legal s ize.

TABLE 5 - Size fcarapace length) of predated rock lobsters incommercial catch sampl-es.

) 7 6mm < 7 6mm Unmeasurable.

7A/ ' t s 75 /75 7 4 / 7 5 7 5 / 7 6 7 4 /75 7s /7 6

Predated

Cu t t l e f i shP redated

t t s nPredated

2 0 0 2 4 A

2 7

1 5 1 1 5 6

I 2

t_l_

z )

1

Many fishermen claim that octopuse.s always attack the largese rocklobster in a pot. To examine this, records were made dur. inq the1975 /76 season , when t i ne pe rm i t t ed , o f t he s i zes o f rock l obs te rsin a pot where octopus predation had occurred. Many pots containedonly one dead rock lobster, e i ther because the pot only containedone rock lobster when the octopus ent€ired or because other rocklobsters present in the pot had escaped from the pot following theentry of the octopus. In some pots two dead rock l-obsters werefound but no live animal-s, while other pots showed both live anddead rock lobsters. Pots in which both l ive and dead rock lobstersoccurred provided an opportunity to examine whether any seJ-ectionfor s ize occurred. (Fiqure 4). The data show no obvious select ionfor rock lobsters of any part icular s ize or rel-at ive size. Therewas no signi f icant d. i f ference between the mean carapace lenqth ofthe predaaed rock lobsters and that of al l the rock lobster i in thepots whe re predation occurred.

2 2

tz'?od euo ut :aq4a6oq s,ralsqoT {cof,

;o sqq6ual ecede:ec urof saurl ueqo.rq TEcr+.reA

JelsqoT >[cofepe:d 1 pue a^TT T

f,alsqoT {coJ aATT z

le?s qoT1co: pe4epe:d 7

.r31sqoT {cor aATT

.r3?sqoT {co.Ipa4epe:d sndo4co

i?tl

e!?i?AE r?,ldiit 'r,rl

Ar.,,A,l Y*XYda +*

x9r?il

a ,.i tlol?8to,'

*??i llli io8f ??6egBrtis?^rl I t r ' I i" ld* v t " i 6f r. rr , , I o l,

? I d'Y*" '" *; !i6 * dr 't

+II

IIIlIIIIIIII

*

I6 ?R*i

6TTll

di6

f+

o I

I

lTtl

slr ,1,

?rlT?I

9t.,, 1

lr'l 'lll

ll

,l x

*lI

Tlt'

I

I,I

,l

l1

6

o

o8r

'pa.r.rncco uollepe.rd sndo4co ef,aqn sq.odTETcrauuoc ur sJa4sqoT )tcoJ Jo sq16ue1 acede:e3 '7 e.rn6-p.t

'saldwog

Both male and female rock l-obsters were predated by the variouspredators [ fable 6). fn the L975/76 sample there were no signi f -icant di f ferences between the nunbers of each sex predated, assum-ing equal numbers of males and females availabl_e in the pot, whiJ-ein the 1974/75 sample, there were signi f icant ly more (p < 0.05)females than males predated by octopus. However the ratio ofmales to females in pots is not constant but var ies with depthand t ime of season (Morgan and Barker, 1974, 1975), so that i tis possible that the greater number of females predated in the1974/75 sample simply ref lects a higher proport ion of females inpots where octopus predat ion occurred..

TABLE 6 Sexes of predated rock lobsters in commercial catchsamp les .

MaIe Female Unsexable

7 4 / 7 s 7 5 / 7 6 7 4 / 7 5 7 5 / 7 6 7 4 / 7 5 7 5 / 7 6

Pred.ated

Cutt le f i shP reda ted

! a s nP redated

1 4 8 1 6 5

_13

187 t96

z 5

1 t

J f , 6 0

1 t v ) LOSS OF COMMERCfALLY-SIZED ROCK IJOBSTERS

As not all the rock lobsters predated by the various predatorswere 1ega1-sized, saleable indiv iduals, the immediate l_osses wereless than the total losses, as the undersized indiv i_dual-s wouldhave been thrown overboard anyway. The loss of legal-s ized rocklobsters ' ( Table 7) was est imated. by mult ip ly ing the total est i -mated l-oss from the various predator-s by the percentage of pre-dated legal-s ized ind. iv iduals in the samples. por LgjZ/ lZ And1973/74 seasons a mean percentage from the l9 j4/75 and, I9j5/76samples for al l predators was used..

TABLE 7 Est imated number of tegal-s ized rock 1obsters predated.

Season r97 2/7 3 r97 3/7 4 I 97 4 /75 r 97s /76

All predated

P reda ted

Cut tle fi s hP redated

-r, l-snP redate d

2 0 5 0 0 0 1 1 8 0 0 0 2 1 5 0 0 0

1 8 s 0 0 0

0 0 0

0 0 0

2 7

2 0 3 0 0 0

1 9 5 0 0 0

0 0 0

0 0 0

2 4

\c

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-Ees rnoJ eq1 u-t pred 6>t/ac-F:d e6e:ezre eq1 Iq pa11dt11nur aq uaq+

lsnu (6 aTqeo suoseas snoT.reA aq4 .roJ ssoT 1I{6TaA peleurT+se aqJ

6 ?vv

b ztg

6 zvs

b 9gv

6 gts

6 zgs

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9L/SL6I9L/VL6I

's.IalsqoT

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'(6 gg91 pasn sel\,\ saldures 9L/9L6I pue

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aq4 uT sf,alsqoT :1cor pa+epo.rd 3:o 4q61aA uearu eq+ aleulTfsa oJ

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uearu Ten?cp oql Jo a+eur1sa.repun 4q611s e eq TT-FA dno:6 azrs qcea- ^ ..^ 4..^-rv q+uqel sseu -y-I tuoJJ pauTu.ra?op enTel 4q61an eql' 'q16ue1 ueaulaq1 6u1sn / dno.r6 azrs qcea .rol: pa?eTnoTEc enTeA 1q61ar't upau € pue

paurur.re4ap s el,r 6utdnol6 azrs qcea .lo; q46ue1 ueau eq,l 'sdno.r6

ezrs unug T oAuT s:e+sqoT {coJ pelepa.rd pezrs-1e6e1 'eTqp.rnseeur aqf6urdnor6 z(q saldrues 9L/SL6I pue 9L/VL61 ori? -roJ peuTuralep a.rel'\

1g alqe,r) s.ra?sqoT >{co.r palepa.rd 'pez1s-1e6e1 3:o slq6t arl upeu eqtr,

(.qndun ,ue6row .u.9) (b) VVt,ZT Tt8Z00'0 = M

eTnuro] aq+ 6uTsn qlbueT^^*,f- --^

-n+ *JrJ paleuqr?sa aq ueg s.ro4sqoT >1co-r Jo 1q61aal eq,r'sTseq 1q6ren e uo s-! pred ec1.rd oq4 se '4q6TaA Jo slu.ua+ ur ssoT eq1

AOU>[ 04 r(:eSSecau sr +T sulJe? TercueuTJ ur ssoT ar{? aleurlsa oJl

ATISHSI,{ AHf O.I SSOT TVIDNVNIJ (^)

r 972 /73 t 9 7 3 / 7 4 I97 4/75 t975/7 6

A1tPred.a tors

OctopusPredate d

cutt ,_LetashPredate d

! asnPredated

L 1 2 0 0 0 6 4 0 0 0 I22 000

1 0 4 0 0 0

I 7 0 0 0

0 0 0

l_10 000

1 0 5 0 0 0

0 0 0

0 0 0

TABLE 9 Estimated weight ]-oss (Kg) through predation.

TABIE 10 Estimated financial- loss through predation.

(vi ) ESTfMATE OF THE NIJMBER OF OCTOPUS CAUGHT

Using the same methods as rrere used to estimate total predation,the total number of octopus caught was estimated from the sampleda ta (TabLe 11 ) .

TABLE lI - Estimated number and weight of octopus caught.

Season N o . o fOctopus

we r_gnt o tOctopus (Kg) *

I972 /7 3

L973/74

797 4/7 5

L975/76

2 6 3 0 0 0

1 6 7 0 0 0

191_ 000

1 4 7 0 0 0

2 4 7 0 0 0

1 6 0 0 0 0

I 8 0 0 0 0r -38 000

L 9 7 2 / 7 3 I e1 3 /7 4 L97 4/7s 7 e 7 5 / 7 6

All_

OctopusPredated

Cutt lef ishPredated

.E l- snPredated

$ 2 6 9 0 0 0 $ 1 7 3 0 0 0 $ 3 3 0 0 0 0

$ 2 8 1 0 0 0

$ 4 6 0 0 0

$ 3 0 0 0

$ 4 0 5 0 0 0

$ 3 9 2 0 0 0

$ 7 0 0 0

0 0 0$ 7

behe aded 2 6

l- LC

'saTceds

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selt autuel6o-rd but:olruoul Ja4sqoT )tco.r aq? Jo ruTP ct;rcads aql sV

NOISSN]SIO

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uaaAlaq d.rea r(eur s?od uT 1q6nec sasndcr4co TpnpTlTpur ;o 1q61an aq;

ASPECTS OF OCTOPUS PREDAT](.JN

An integral part of the research programme was the considerat ionof possible ways of reducing ei ther the degree of octopus predat-ion or the cost of octopus predat ion to the f ishery. With thisobject ive in mind a number of aspects of octopus pred.at ion wereexamined in both the f ie ld and the laboratory.

A , THE ATTRACTION OF OCTOPUSES TO ROCK LOBSTER TRAPS

The cephafopod eye is a highly developed. sensory organ and appearsto be the ma jo r senso ry o rgan used by squ id , cu t t l e f i sh , andoctopus in locat ing and successful ly at tacking prey at c lose range(We l l s , L966) . The ana tomy o f t he eye and cond i t . i ons o f v i s i b i l i t yunderwater suggest that the eye is not used for distance vis ion(We l - I s , 1966) and i s un l i ke l y t o be used to l oca te p rey a t a d i s t -ance. The eye is also useless i f +-he prey is obscured by thete r ra in . Kayes (1974) showed tha t 0 . t u l ga rLs i s bas i ca l l y anocturnal species, making long hunt ing tr ips at night, whi ledur ing the day indiv iduals general ly remain in, or wi thin c losep rox im i t y t o , t he i r 1a i r . Ya rna l l ( 1969) found 0 . eAanea Eo becrepuscular, feeding i -n the morning and evening whi le remaining' i n i t s h o l e d r r r i n . r f h e m i d d l e o f t h e d a w a n d n i c h f - T , i l - f l a i sknown of ehe dai ly hunt ing pattern of 0. tetr icus bat octopuseshave been found in rock lobsCer pots set amongst reef dur ing theday and checked sho r t l y a f te rwards (D . Wr igh t , pe rs . comm. ) . I nA . uu lga r i s , a t l eas t , t he l i gh t l eve l s p reva i l i ng du r ing thehunt ing per iod are l ikely to l imit the usefulness of the eye asa prey-d.etector.

Ya rna l l ( 1969) found EhaE 0c topus eAanea in a na tu ra l s i t . ua t i onei ther waited in their l -a ir for prey to pass by or undertookshort hunt ing tr ips from their la i rs and made apparent ly specul-at ive at tacks on l ikely places where crabs may be found. Li t t leattent ion has been given to distance chemorecept ion as a senseused in l oca t i ng l i ve o r dead p rey , a l t hough We l l s (1963) no tedthat sardine blood in the water exci ted" 0. auLgari ,s in aquaria tomove around their tanks. Wel ls (pers. comm.) considered that0. ouLgaris are scavengers as wel l as pred.ators.

Octopuses, l ike other coleoid cephalopods, have a smal l group ofn a l t e l n a : + - d b e t w e e n t h e h i n d b o r r l e r o f f h e c v c a n d g f i gu J s s r r v

edge o f t he man t le (Watk inson , 1909) , t he so -ca l l - ed "o l f ac to ryorgan". Laboratory test ing of the "ol- factory organ" in var i .ouscephalopods has, however, produced inconclusive resul ts. Pol imant i( l -91-3) showed that Sepia, c lamped by means of the cutt lebone,

made violent escape movements when a var iety of substances [acet icacid, c love oi1, bergamoC oi l and. others) were released into thewater near the "ol factory organ" but he did not repeat theseexperiments with the organ denervated or removed. Giersberg (J-926) ,We l l s (1953) , and Messenger 11957) showed tha t ex t i r pa t i on o f t he"ol factory organ" produced no vis ible changes in the response ofoctopuses to f ish ju ices. Woodhams and Messenger (1974) examined.the ul t rastructure of the "ol factory organ" and conclud.ed thatthe anatomicaf evidence indicated that the organ had a chemosensoryfunct ion. However the neural connect ions of the organ led them tosurmise that i t may possibly be involved in the detect ion of sexualpheromones. 2B

--T-

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(e95T ,sTTaM) uT.:r ralcns eq1 uTsTTeJ an r+Tsuesouaqc aql ^q- palcalep ser\ +T a.reqn sute aq4 o1 aclni

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1Eq1 +Taf (196T) ra6uassahl . su.re aq? oluo acrnf auTp.rps 6ui+1adfa.ro sndo4co papuTTq e Jo sure eq? uo.rJ rucz ?noqp aurp.zes e 6urploq r^ ^^--^-*^ ^---- ^q pc+TorTa ?eq1 o+ .r€TTrurs seat esuodse: eqtr . etl4T.rn o4 ue6eqsuJp eq+ pue osuodse.T aruos paAoqs sasndolco spuoces Te.raAas .re4JV ' asuodsa.r a?prpeuruT ou pecnpo:d ,, ue6:o ,{:ro1cel1o,, aqi +e pa+aaara

saclnI aurp.res sesndo4co pepuTTq uT +€r{? paa.f,asqo 119511 :a6,lassary

Tr

tr

Iox

slod:eqsqolslua+uoc 1ne

'l 66=N)

{Jo.r ur 1q6nec sesndolco;o

METHOD S

(i) Aquarium Experiments

Octopuses (200 - I 000q) were col lected from terracotta octopustraps set in depths of 5 to 8m in the vic ini ty of the W.A. MarineLaborator ies. They were transported to the laboratory in wet cal icobaqs and isolated' each in a covered asbestos cement aquarj-u.mmeasuring 63 x 50cm x 48cm high, wi th a f low of c lean seawater (2l i t res/min) at anbient temperi ture (L7-22oc). Each octopus wasprovided with a terracotta pot as a refuge.

Octopuses were fed a diet of mussels (Myt iLus eduLi.s) and abalone(Hal i .ot is z,oei) , each animal- being fed enough food to approximatelymaintain i ts \" /e ight at capture. (An average food intake of I to22 of the octopus body weight per day is suff ic ient to maintainbody we igh t ( Jo I l , 1977 ) . oc topuses were fed th ree t imes pe r weekand kept for a period of approximatel-y two weeks to allow them toadjust to the aquarium si tuaCion before use in t r ia l -s.

(a ) Ba i t Loca t i on T r ia l s

The bai t locacion tr ia ls were conducted in a rectangular asbestoscemen t t ank (F igu re 6 ) 150 x 50cm x 38cm h igh w i th a wa te r dep th o f29cm (total volume 25I l i t res). The tank was div ided for approx-imately 752 of i ts length into three equal width (20cm) channelsand at the head of each channel a sub-surface jet provided a f lowof c lean seawater at 2 l i t res/min. Three overf low pipes were pro-vided at the undivided end of the tank and these were mounted intoa plast ic roofed refuge area so that water was drawn from under, aswel l as above, the refuge. The undivided area of the tank could beseparated from the div ided area by sl id ing down a perforated part i t ion.

Each channel contained a pair of of fset sheets of PVC, to act as sightbaff les. These were set approximately 40cm from the in let jet , whi leat the far end of the channel, 20cm back from the end of the div ider,another. PVc baff le (C in Fj-gure 6) wi th a 10cm diameter hole in themiddl-e served to control the f low patterns in the tank, Prel iminarydye tests with flouroscein showed that there was no leakage from onechannel to the next and no backf low or eddies carrying water f romone channel into any of the others. Apart f rom a smal- l opening atthe undivided end to al1ow a l-ow level of illumination, the aquariumwas screened wj- th black plast ic sheet ing to prevent octopuses fromseeing the observer. Observat ions were made through smalf peepholesin the sight -scree ni ng.

Octopuses were fasted for 3 days pr ior to a tr ia l to ensure that theywere hungry. They were introduced into the test aquarium approxj-mat-ely four hours before a tr ia l and were al lowed access to al l partsof the tank dur ing thj-s per iod to fami l iar ise themselves with i tsarrangement. At the end of the fami l iar isat ion per j-od octopuseswere usual ly located in the refuge in the undivided area of the tank,but i f not they were moved into this area. The perforated part i t icrnwas then lowered to separate the octopus from the divided section ofthe tank. Bai t mater ial , e i ther f reshly opened mussel- , the visceralmass and shel- l of an abalone (H. v 'oei) af ter removal of the foot orcrushed crab (Leptogrzdpsus uar i ,egatus), was placed in one of thechannels immediately below the in let jet and behind the sight baff le.

II

3 0

tt

'slaTlno .re+pM '0' ea:e e6n3: eg ' ,4

- TTe^r 6urpr^-Fc ' S--J -^^-r^- T- r

uu !+ l+r su Ps+sr\Jjreq. Lr'aTfJ€q

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(qcPa urur/T Z) slat laTuI 'V

AarA ap-JS

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AaTA UeTd

A period of approximately 20 minutes was al lowed to elapse to al lowthe ' i r r ices from the bai- t mater ial to f low down the channel andestabl- ish a reasonable concentrat ion gradient, as dye tr ia l -s hadindicated that 20 nr inutes was suff ic ient t ime to establ ish a sat is-factory concentrat ion gradient.

After the 20 minute per iod the perforated part i t ion was raised andthe octopus al lowed free access to the div ided port ion of the tank.The octopus was al-lowed a further 20 minutes in which to locate thebait . An octopus was scored as having successful ly located the bai tif it moved into the channel- where the bait was located and tookthe bait within the 20 minute period. Movement into another channel(past baff le c) pr ior to movement into the correct channel and takingthe baie was scored as a fai lure as this may have only represented.rand.om searching. Movement into the incorrect channel, movement intothe correct channel but failure to take the bait, or no movement ata l - I we re a l so sco red as fa i l u res ( i . e . an ima ls e i t he r f a i l i ng tolocate the bai t successful ly or apparent ly fai l ing to detect the"odour" at al l ) . Each octopus was given three tr ia ls in theexperimental aquarj-um, the bai t being placed nonsequent ial ly oncein each of the three channels.

( h l S A n s i f i \ r i 1 - v T r i a f s

A stock solut ion of I0g (wet wej -ght) o f abalone (8. yoei ) foo| -muscle homogenized j -n 10ml of f i l tered seawater , made up f reshlyeach day, was used to examine the sensi t iv i ty of octopuses todissolved chemical "odours" . Di lu ted test so lut ions were made upfrom I ml of the stock solut j -on by progress ive 10x d i lu t ions.

Hungry octopuses were t ransferred to the test aquar ium (Figure 7)in the i r re fuges and le f t for a min imum of I hr to acc l imat ize.The refuge was p laced approx imate ly 30 cm away f rom, and fac ing,+ h a i n ] 6 + ; ^ + r . , h i ^ h w a s f e d f r o m a c o n s t e h + h a a A c r r n n l r r ' t

m l o fthe test solut ion was rapidly in jected into the out let f rom theconstant head apparatus and the responses of octopuses observedthrough a one-way window. Posi t ive responses to the test so]ut ion(novenent out of the refuge towards the jet) were rewarded withsmal1 pieces of abalone f l -esh. Seawater blanks were in jected pr iorto each test solut ion. For comparison, tests were also made of thesensi t iv i ty of a rock lobster.

The di lut ion of the test sampl-e af ter in ject ion into the testaquarium was measured by in ject ing I ml of f louroscein dye solut ionand sampl ing from the dye cfoud at the entrance to the octopusre fuge . Op t i ca l - dens i t i es o f t he samp les were measured a t 493nanometres. The dye took approximately 3 sec. to reach the refuge,the maximum concentrat ion being 4 x 10-2 of the appl ied concentrat ion.

( i i ) F i e l d F l x n c r i m e n t s:_::i:___:jir:L

Pot Locat ion Tr ials

To exam.ine the importance of bait in attract.ing octopuses to pot-caught rock lobsters a f ie ld t r ia l - was conducted in an area westof Garden Is. T\ , /enty-four wire research pots (without escape gaps)were div ided into four categories and set and pul led dai ly over af n r r r - da r r ne r i nd tT rhA f r t r t r r - a fe r ro r i eq wF fe 3

3 2

ee?uauoAcru paAoqs qcTqA sT€llrTue auru Jeqlo aql l:o '1T€q Qq1 >{Oo1

pue Tauueqc ?cel.roc eq? o?uT tr14cel1p palou sasndolco eaTJ-r(?uen?'puodser pTp 1eq1 esoql l:O '(ZT eTqe,I) pel"ro1Te sa1nuTu 0Z atn

uTqlTA {ue? aq4 Jo Pe.re papT^Tpun eql Jo 4no 6u1nou ?ou ueq:} J:o oT4.[1uo '.r a1ea,r eq4 uT rsf,nopoo ]:o ecuesef,d eq4 o4 esuodser lueuaAou e

peioqs i11e:eua6 sasndo4co 'un: ereA qcTqn sTPTr4 x1s-.[1.r1q1 aq? uI

sTeT.r,L uoTlEcoT lTeg

'uoT1ce.xl?e Jo s?e.reg:o tr1r11q1ssd eqa acnper o4 1:ede ?eef Ot 1s€oT 1€

s.relsqoT {cor .nol: puE ?Teq

.[1uo s:elsqoT {coJ .rno3

ITuo (peeq qsTt pue {coq eT?1ec) aTeq

tredure

'wr 0€

(e)

S;LTOSEU

6u1u1e1uoc saod eq? uo.rJ: sJelsqoT {coJ }o ed€psepup I.ro6a1ec ,,^d1uo 1Teq,, eq? u1 slod o?uT sre4sqoT

eq1 4uale:d o? f,arro pe:r 1aa .[11e11:ed a.ram slod TTP 01

JO UoT?.cereluTlOS eXeJtl S?Od

' sfe1sqoT {co.raqa luerre:d o1

}lcof, l:o Lr?uasecuP.rlue eqtr

(p)

(c)

(q)

(e)

'e6ryagsndolJo

'snptoddy

pDaH luDJsuoS

's?sa? tr4-5^111sueS :o3: luaue6uerre Te?ualT.redxg 'l e.rn6T'{

responses, six moved into an incorrect channel before moving intothe corr:ect channel and taking the bait while three moved into thecorrect lane initially but did not take the bait, either remainingstationary for the remaj-nder of the 20 minute period or moving offto another channe l-.

If the movement response was not rel-ated to any positive chemo-reception by octopuses then initial penetration of any one of thethree channels would be expected to be equally distributed. Theresul- ts show that s igni f icant. ly more (P < 0.001) of the in i t ia l -movenent responses were into the channel containing the baitindicating an ability to detect. the presence of the bait by dist-ance chemoreception, whil-e the high percentage of octopuses whichtook the bait indicated an abilitv to locate its source with

TABIE l-2 - Location of hidd.en baits bv octopus.

OCTOPUS

CHANNEL COMAINING BAIT

1 .'

Res ul-t Bait r tme Result Bai t r ame Re s ult Bait I rme

7 8

7 9

8 l

8 2

8 3

8 7

8 8

8 9

9 0q ?

9 4

9 5

f

+

0

+.r

+

x

-r

+

+

A

M

A

A

A

A

A

c

A

< I

o

< 1

f,

< 1

< 1

*

+

+

+

+

+

+

+

++

A

M

A

A

A

A

A

A

3

8

5

<l_

< I

8

++

0

+

+

X

M

A

A

A

A

c

I

*

< 1

< 1

L a r t . - + = successful ly l -ocated bai t , entered correct channel on1y.

fai led to locate bai t or entered incorrect channel f i rst .

fa i led to locate bai t ; d id not move into any of the

channe l-s .

Abalone

Musse I

Crab

are in minutes; *Times

perforated barrier before

= cl imbed or squeezed

it . was raised.

Lane f i rst but did not

3 4

under the

take bai t .= moved into correct

:L

uAoq s oJe sasndolco ,{q pere4ua d'ro6e1€cqcee ur s?od

'?T eTqet, uTfo raqumu aql

s1e1:,1, uoT1ecoT 1od(cl

IuPTq 01 asuodsar aAT?Tsoa

asuodsaf oN

a^T ?Tsoal

€ T grsv'r

.l-

'aleueEouroq-lnTTp o? re?sqoT >tco.r

eTcsft[ ?oo]i auoTEqe JO suoTpue sndolco 3:o ,{lT^TaTsues

'TTert se slueTq eq? o? sasuodsel aATlTsod

6ulatoqs ue6eq Je+sqot trior eq? suoTler?uecuoc 're>1eee\ +v '(uoT

-1ce[uT f,e1Je sr-0T x 71 -uo1?n1os,]?-"-1?-:t{1

Jo 1eq1 €1-0T suoTlPrl

-uaJuoc q?TA suoT+nr6! +sj+ o1 sasuodse'r a TlTsod paAoqs 'ralsqoT

{co.r eq,tr 'uoT?nrTos 1co4s aq1 }o ?eq? r r -0T x 7 '[1e1eur1xo'rdde sen

uoTlerluacuoc erq;1ca?ep ?sa{Pa!l eqi'Tx ool-{I:1:*i1rli3) uor-1ce[uT .ralJe uoTlnro" +"i+ eql Jo,uoTln]Tp-1.".11:":."Y1^,"::::li::;;;'-:(;i':;fii-;-ot tt sarnsai orqerx;^ pel\'roqs s6 'oN

?ngolcolqonoqlle-'uorento;-iioes eqi :o e-0J Y:11 l:1::1 :::ii:lT":l::i;;;;-Ji;Tdi3I--i""+'1ca1ep oa etiE'n areA paasel sesndo4co

-_ 0T 9L-NT

eT-'-z1-"'-- 0T t t-^- 0T u t-

-07 o-

g-t t

.07

^07

-07 Y-

-07 v-^07 L-

NTz--'

++++-+++++++++++)-J-i

++

zz<,'f

+++f

+.t

+

uoT?nlos 1se4J O UOT+P.T4U3cuOD .ralsqoT >{cou

Elelr,r, TiraTlTsues

TABLE 14 Nrunber of pots entered by octopuses in pot locationtr ia Is .

Pot category Empty Bait only Rock lobsterson Iy

Bait andlob ste rs

No entries

Entries include both pots capturing octopuses as well_ as pots whereoctopuses have escaped pr ior to l_ i f t ing the pot. In pots cont.ain-ing rock lobsters evidence of escaped octopus is usual ly providedi.n the form of a typical octopus-predated rock lobster, but unl_essthere was severe damage to the bait it is possible that the enrryand escape of an octopus from the ,'bait only" pots would go undel-ected. Ilowever the resul-ts serve to il_lustrate that bait is notthe oni-y factor involved in the location of pot-caught rock l-obstersby octopus.

D ISCUSS I ONrn responding to rrodours" in the water octopuses often extended thearms greatly and. were seen to move their suckers, somewhat in themanner of an octopus which has just received. a piece of fooil at theend of one arm and passes it from sucker to sucker towards the mouth.rn determining in which channel- to move first in the food locationtr ia ls ' octopuses often approached the lower baff le at the enEranceto t.he channel and extended one or several arms through the hole,apparently to sense the "flavour" of the water passinq out thatchannel. This behaviour was simi lar to the arm wri thing reportedby Messenger (1967) when a sardine was placed in c lose proximity to thearms of 0. uulgar ls or sardine ju ice pipetted onto the arms.

The results of the bait location trials showed that octopuses cansuccessfur ly f ind bai ts without v isual assistance whi le Lhe behav-iour observed in both the food rocation and the sensitivitv trialssuggests that the chemoreceptors involved are probably locited onthe suckers. rt may be argued that the concentration of attractantchemicals in the water in the food location trials was unrealistic-al-l-y high and that the suckers would not normallv be involved indetect i -ng concentrat ions of chemicals at t .he revers l ikery to comefrom rock lobster bai ts in the sea. However Wel ls L1963)l in exam-ining the erbility of 0 ' uulga,i.s Lo disti.nguish becween hydrochloricacid, quinine sulphate or sucrose and sea water by contac-t of thechemosensory suckers with absorbent material soaked in solut.ionsof various s trengths ' _ found octopuses to be sensitive to concentsrat-i o n s a s l o w a s 2 x I 0 " u ( Z : 3 x I 0

q g l l ) { H c l } , 2 x l o - a M ( 6 . 8 x 1 0 - 2

g , / l ) {Suc rose } , and 4 x 10 -e r r , r (3 .1 x - I0 -6g / I ) i qu in ine su lpha te } .At these levels the octopuses were stil1 responding very cbnsistentlyand werrs considered that there was no reason to reri-eve that thethreshold for the chemotactile sense of the octopuses had beenapproached. werrs €t aL (L955) showed octopuses could discr iminatewith their sgckers between Kcl solutions and seawater with concen-t ra t i ons o f Kc l as l ow as 10 -sM (7 .5 x ! \ - aq /L ) wh i l e some ind i v -idgals were able to detect concentrat ions ai low as IO-t0M (7.5 xL}-e g/ I) . The behaviour of 0, tetr icus in the sensi t iv i tv t r iatssuggests that the distance chemoreceptors of octopuses ar6 alsolocated on the suckers.

J O

LL

'slTPq d.reurp:o q4TA ueql : err'ro1 .[11uecr-1-gubrs peureuar ITT?s sfa4sqoT )tcol to sa?eJ qc+ec aq? anq '^Ta^r

-4cadse: lreq sndo?co lo sle{seq eeJql pue oA? 01 pasealcuT seA lTeq-^ a- -- -*- r- ^..^J L,r r\+ !+ur!(! -y+ ST€T.I1 pJTr{+ pu€ puoces aql uI '?Teq f o s]unoulE

a?enbepeur J;o lTnso.r aql uaaq aA€q êu slalsqoT {cof, Jo elE.r qclecAoT aq? pue pasn sen sndolco l:o ?a>lseq euo dluo Terl? ?slTl: aI{1 ur

'sndo?co 1tq uor?epard acnpe.r o+ sldura+1p tl+TA^-^---.ftt,^^ ^^ - -c Ly r +Esqvs -y +Ju pTnoA lTnsa-r e r{3ns 'sndo+co Jo siro?Ppa.rd eq1

-^ r--- +v r!+ -! ie+f,olu pasee.rJuT uP 01 pPaT O.rOJa;Ar{4 z{eUr sndolco

r{+tn s4od go 6u141ea 'uaurJeqsT} dq uo-5ldunsuoc cTlseuop .ro aTes

JoJ paTTTl ue?Jo aJE slod u1 lqbnec s:1.r€r{s 6uo6aqqo14 's1od olur

s T€urEue esaq+ lcEra?e leu sndolco q?Tx\ slod ltT+ttq ('sqo 'sJed

pue ifOf 'q6noroqe11lTi1c) sndo?co Jo ro1€pe:d e a:e s1:eqs 6uo6-"qqo^ i?-

-'snao+co qjpr'd1iro pe?Teq slod en13-tr?xTs orl4 uT 1r{6nec

ereA ('ds snqo';o7oan7) s:4te:qs 6uo6aqqoat JnoJ Ter.r1 lslTJ aI{? uI

'pa+cadxeun eq ?ou pTnoA s?Teq sndolco eq1 'uo 6urpaeJ: pue/Iq uoTlcef,+4€ 1eq1 0s /saTceds u,|lto rTeq? lee 01 pa^fasqo ueeq al\Bq

.,- - *-- r-- u!! r4slrlE e!r+ uL pue pTTA aq+ uT sesndo+cg 'papueT a:arq s?od aq?uaqi"r lreq sndo4co aq1 uo 6u1pae1 a.r aA lTeq sndolco qlut slod aq1

u-t ?q6nec sasndolco or!r4 eq1 TerJ? p.rTl{? oq1 uI 's4Teq snoTf e1\ aq4dq sndo4co Jo aler qc4€o oq? uT acua.rel:JTp 1uecTf Tu6-ps ou peAoqs

(ET eTqe,D s?Tnsa.r aI{J 'tL6T IeW pue qcrew u-F palcnpuoc a.reA lreqaq4 uT sndo?co peep burpnlcur Jo lcafJe eq? aururexe 01 sTeTJl pTa-5J

'4Teq or{4 u1 sndolco peep 6urpn1cu1 dq slod.relsqoT IcoJ luojrJ sesndo4co 6ur.r.ra4ep 3:o d111rq1ssod aq1 pe1sa66ns

s-FqI 'sde.r4 uro-:J setceds 1€l-{4 Tada.r o+ 4Teq eq1 ur papnTcur a'r a1!tsarcads lsed re1nc11:ed g:o sueac€?snJc peep eleqrr saTJeqsTl; 'x'o uo.l}

salduexa raqlo T€raâs paqT.rcsap osTe eH 's?od pe4req ATTeu.rou ueq+s.refsqoT {cor ssaT z!14uectg:tu61s 4q6nec 4Teq o4 uoTlTppp uT s.relsqoT

{co.r p€ap 6urule4uoc slod .ralsqoT }tcol 4Pq1 parloqs (tL6T) }icocueH

srod ut-Ls8ot )30u l^Joul s3snd0r30 l0 N0 Islndlu's

3rr1 .ror alqrsuodsa: ;-:i fi3:3:'n1i:i i:rl::l;3";":";";:I1';l:E 'sasndo4co qc+ec osTe +TPq ou 4nq uraq4 u-t slalsqoT >[co-r ATuo r{1TA^^^ -^^r .^-^.{ -^-^^^++es s+oo .ae+sqol {coJ lel{1 pa^\ot{s sT€T.r? pTaTJ eq - sfocr rir+ltq()l

{coJ e1€coT sasndo1co I{crI{A ^q asuas € s€ auoTe uo-F?cEJTo o4 uarrt6aq +ou pTnoqs +q6rerq enpun 'saoue+srp a4eJepou luo.lJ ueql e+ecol

pue +ce?ap 04 oAT?T suas z{11uerc1J:Jns eq plnoa'r ura4sz{s ,{:o1ce3:1osndo?co eq+ 1€q? trTa>l-lT sreadde 1T 1nq uAou{un sT Pes eq? ur s+T€q

.ralsqoT {oof luo.r] 6ulleireure ,, s.rnopo,, 1ue4cE.T1+e l:o uoT+e.r?uacuoc aqf,'

'sra+sqoT {Jo.I fo 4€i{1 se eATlTSues S€fou qbnoq4Te '^+TT-!qedEc r{tolcel:To pedolaaep 11ar"r d1:re; E e4ecrpur

reô/'\oq op sTer.rl d11n111sues eq1 Jo s+Tnsair aqtr 's?ueuoduoc

T€nprlTpur fo ?eI{4 ueql Jo?eeJ6 ,llqeqo.rd sT aJn+xrul E to uoTlcerl?eaLIl ' (tt6T a-FIceI{) sna.puwz:6 snaDwoq .ra+sqoT aq+ q+T^{ sV 'lrlv\ou{un

e.re rnoTleqeq 6ut>1eas poo; 6ut1e1nuT?s .loJ alqrsuodse.: aTcsnur 4ooJauoTeqe ulorJ penr.rep aJn?xTlu xdlduroc er{4 uT sT€cTuaqc :e1nc11:ed eq,tr

.uroJ .r€Tour ur pessa:dxe a.ren sTecruel{c a.rnd 3:o suoT?nTTp eql a.r aqA(e96T) sTTaM lo osoq+ o1 elqeredu.Ioc d11ca.r1p lou er€ ,,s.rnopo" pooJpenTossTp Jo suorlnTTp 'sno-!.rel aI{+ o+ sasndolco 3:o r{4rarlrsues aq'1,

,ill

TABI.,E 15 Effect of using octopus as a component of rock lobsterba i t .

Bait

Trial l -+ T r ia l 2++ Trial 3+++

otJ

.p r'l-.1

ll1 t-.1

lra).lJ

J 4 ( 'o . Qo op < } f

o

{J

(ttJ

.u '.1-l

A | l

l.lc)

s oo . ad A

oo.tJ

a.lJ

{ J r H

A ' l

c){J

' l 4 Oo . a

o

.tJ

Hock &-B 1Sn

OctopusOnly

Hock ,. t . l sn &Octopus

a t J

b f ,

o t t

1 8 r[ 2 . 1 8 )

8 3( 1 . 2 8 )

2 4 91 3 . 6 6 )

1 9. 2 3 )

8. 12)

I 4.2 r )

( o

( o

( 0

7 5

7 5

3 3 1( . 4 . 4 1 )

1 9 1t 2 . s s )

( - )

I1 0 . 0 1 )

3( 0 . 0 4 )

( - )

1 9

I f ,

5 7c 3 . 0 0 )

10( 0 . 6 7 )

0( 0 . 0 )

2( 0 . 1 3 )

( - )

+ 1 bai t basket f rozen octopus++ 2 bai t baskets f rozen octopus

+++ 3 bai t baskets f resh octopusFigures in brackets are the catch/pot l i f t

Fresh octopus was used in the third t r ia l to examine the possibi l i tythat any repel lant act iv i ty of the dead octopuses used. in the f i rstand second. trial-s may have been degraded by freezing the octopus.Although the data is limited the results do not suggest that thereis any benef i t to be gained by using fresh rather than frozen occop-uses as ba i t .

The resul ts of the f ie ld t r ia ls using octopus as a component of thebait did not indicate any repellant activity to octopuses by deadoctopus. Considerat ion was also given to the potent ial repel lantact ion of other organisms, such as moray eels and starf ish. Morayeels have been reported as predators of octopus by a number ofau tho rs (e .9 . Lane 1957 , Voss 1971 , Be r ry 1971 , R i t ch ie 19721 wh i l econtact wi th starf ish tube feet or exposure to aqueous extracts ofstarf ish tube feet has been shown to el ic i t . escape responses in anumber of gastropod and bivalve mol l -uscs (Feder 1963, Feder andLasker 1964, Feder and Christensen 1966). However octopuses pre-sented with food (abalone foot muscle) in associat ion with aqueousex t rac ts o f s ta r f i sh (Cosc inas te r i as ca lamar ia (e tav ) ) o r sc rap ingsof epidermal s l ime from moray eeJ-s (Gynnothonax sp. i d id not s i row-any escape responses or inhibi t ion of feeding. Exposure of octop-uses to ink ejected by other octopuses did not el ic i t any behaviouralresponses indicat ive of "a1arm substances, ' of potent ia l value asrepe l l an ts .

The possi-bi l i ty of repuJ-sion of octopus from rock lobster pots bya substance which would act select ively for octopus and not s imult-aneously depress rock lobster catches seems remote. However thevisual acui ty of octopuses suggested that a v isual repel lant maybe a possibility. An e.xperinrent to examine the potenlial forvistral repell-ants was cond.ucCed in the laboratory using a modelof a moray eel , made from a piece of car inner tube, s ispended

3 8

o'

a:arrr s10d tuoJJ slTxa uaolJTJ .reAelltoH '6u1u.rour

6ur:np palitasqoun 4od eq4 11e1 dllensn sosndo?3opa+cnpuoc a.aoA sTeTf,l ^.r1ua ?od aqf,, '(9T aTqefi)

xlf,Tq? 6ursn fno parJ.rPc aJ.aA sTPT-r4 z{rlua 4od

lod ar{1 Jo STT€A aI{? fo cr.rqeJ aqf

i s.ralsqoT {cof,TTeors fo lueuredecse aq1 /vroTTE o1 pau6lsep

qod eq1 J:o cr.rqel: aqf u-! de6 ul79 x 90€ aql

(LT aTqe&) peA.resqor!1:ee :o qq61u aq1pue dep aq1 6uTf,np

sesndo+co +ua.re]Jrpd1au1u l:o Te?o1 v

s,rrnssu

ap-!s (T-tr)

- de6 adecsE

- }[coN

rTT\

fTli+od ar{4 Je4ue sre?sqoT

{coJ r{crqA trq 1od aq4 fo dcja eq+ ur 6utuado aq1

'sdno.r6 ea.rr41 l:o euo se papJocar pue pazr:o6a-+EC a.raA z{:1ue 3:o sEa-re aq.l 'palou sPA (1od eql aprsur dla4elduroco? aceauoc ?s-r-!f urorJ ) 1od e f,a?ua o? sndolco ue .roJ ue>tE? aurrl aq.l

'seT.res aqf uT p.rTql -ro puocas '1sJ-!J se seuTl J:o raqurnu Tenba uepeluese.rd seA ed^? 1od qcea 4eq+ os pe6ue.r:e a.raA sTerl+ eqJ' '(Z

a:n61g) I:eqs1g: aLIl uT pesn sadl? 1od 4ua.ra;Jrp aalql aq1 Jo l{cea uo

TeTf,? euo / sndolco qcea q+T!l pe?cnpuoc aJaA sTPrJ? A:+ua +od aa:q'I

'ulnT.renb€ aq+ fo eprs aq+ ?e ,,apTrl, e ur AopuTA IPA-auo Pqbno.rq4 peAJasqo ser"r sra+sqoT >tcoJ er{4 pue sndolco aq+ Jo Jno-!êr{aq

aqfi ' 16 a:n61U) ebn;a: sndolco eql uo]l ^06 ?asffo de6 adecse aq1q1rr"l a6ng:ar sndolco aq? uro.rJ ur1 z{laleurtXo:dde paceld sel"r lod eq,I,

'1ood aq1 o?ur pacnpollu-! s€tt s.ra?sqoT :1col pazrs-TebaT ea.rql lo oA?burutequoc 4od :a1sqo1 >lcof e umTJenbe a6:e1 aq1 o+ uorlezT+€luTTcce

s.rnor{ Te.reês .ra+Jv ' sTeTJ? tr:?ue f od .rot umr-renbe Jooplno ( 'urul

/se'rll]r ZT AoTJ .ra+eA 'deap uT /'ureTp ugJ e6.re1 e o1 e1:enbe TTEluseq+ uo.rJ sa6n;er .rreq? uT pal.rodsue:1 tr11enp1nrpur e-ran sesndo4co

pazTleurTTccv '(8 e:n61s) slod u1 srelsqoT >tco.r 3?epard +ou opsrq? u€rl4 ssal 6u1q61en sasndolco 1EI{+ pe1e3-Fpur suor4elrasqo pTaTJ

asneceq pelseTas sen 6 ggg Jo ezrs unurTurlu v '(spoq4aN) v A uoT+cesur peqr.rcsep se pourpluTeu pue pe.rnldec e.rol"r (6 009 <) sesndo4cg

SCOH'IflW

' ,,g: oo.rd-sndo1co,, s4od eI€ur 01 pa6ueqc eq pTnoc qcTqAu6rsap 1od 1o slcadse ?q6-!Tri6Tq 4q6Tur ?T 1eq? uT TnJesn pajrep-Fs

-uoc s€A s4od re4ua pu€ .raTJJeq srq? aleJAeuad o4 sesndolco ,{q pesnspoq4aur aq4 Jo e6pelnou>1 v 'srolEpe.rd 6uTqceotdde pue sjraf sqoT >[cor

peddeJl uaoAleq -raTJrpq lectsz{qd e saprno.rd 1od -ra4sqoT lco.r aI{J

sndoDo A8 SJ-Od Ulls€ol )lou Noul ldvls3 cNV 01NI AUINS'3

'sndo?co eq1 lede: 01 luarcTJJns JTas+TuT ?ou sEA acue.readde 1ens1a eq4 T epoul er{+ Jo urlol: aq? pazru6ooef,

^Tluer€ddE sndo?co aq4 aTTqM 'Tapour aql 01 uor4u3?1e a:our ou pled

puP Je+sqoT {co.r p pa.rnldec trl4uanbasqns sndo4co eqfi '>tcau aq1

qSno:q1 pe.ralue pue- 1od aq1 dn paôu 'ure s4T pe?ceJlae sndo?co

aq? uoT+euTlu€xe eTT+ce1 ?foqs P falJv 'Tepou aq? Jo uoTleuTuexa

a1j1"e1 'e

ue6aq pue 1od eq+ Jo saprs aI{? q6no'rq1 ru'r€ up paqc1af,1s

sndolco eq? 'urlu T lnoqe Ja+JV 'z{11ens1a Tepou ar{? auruExe

01 pe.readde pue '4od

aq4 -per{ceo.rdde

umTrenbe aq? uT peceld sndolco

uv 's.relsqoT )icor oA4 6ulute4uoc 1od .ra4sqoT {co'r Taa?s e apTsur

F igu re 8 . Gut content ofrespect to the

pot-caughts i ze o f t he

octopuses with

Eg

3 zooooo

o

.9,o

Rock Lobster

Gut Content

0ther

4 0

tv

sjod )alsqol 4JoJ

JoJ p!4s 6urPool

ap!H uotlD^Jasqo

'sesndolco.^c.,, * - -- f,u+ +uduo!u srf, s

r^ crDTaa

lrnrronl'rr

-uJ L-

I:trua 1od -r elsqoT {roJ.. .ThA?T

F

TAB I,E 16 Areas of entry into rock lobster pots by octopuses.

TABLE 17 Areas of exj- t of octopuses from rock lobster pots.

Pot Type

Area of Exit

Neck u::;n" side

ware

0

0

0

1

I A

DTSCUS S ION

The results shou/ clearly that in cane and batte.n pots, the mostconmon types of pots, the major area of entry is through_ the fabricof the sides of the pot, the escape gap and the neck being used lesscommonly. The dimensions of the spaces between the sticks of caneand the wooden slats varied between 20 and 40mm L3,24,, - 1L") andbetween 20 and 35 cm (8" - 14') long and did not ser iously f ramperthe passage of octopuses through tlre spaces -. octopuses simplyfl-attened their bodies and. passed through. The 55mm f2,.) hexagonalwire mesh cover ing the wire pot did, ' however, ser iously obstructthe passage of octopuses into pots. OId cane pots covered withwire mesh probably present a s imi lar di f f icul ty to octopuses.

Despite the small d.rmensions of the wire mesh some octopuses stillmanaged to squeeze through, but most octopuses entered wire pots viathe neck. Entry of octopuses through the neck of wire pots appearedto be largely fortui tous rather than by , , recognit ion, ' on the partof the octopus that this provided an alternative site of entry.With al l types of pot octopuses usual l_y made their f i rst contact onthe side of the pot and began reaching through the sides anal attack-ing rock lobsters. With cane and batten pots octopuses ofteneventual ly just "s l ipped through" the sides into t?re pot, but thedimensions of the mesh prevented this happening in wire pots. Withwire pots octopuses still attacked from outside initially. but whenthey were unable to grasp the rock lobsters properly tlrey usually

Pot Type

Area of Entry

Mean time to Enter (Mins)Neck ":: ;n" side

Cane

Batten

Wi re

2 L)_

J I

1 8 3

7 7

2 0

o

1 . 4 8

1 . 8 5

3 . 1 6

4 2

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On contacting a rock lobster pot octopuses usually attempted toattack the trapped rock lobsters ehrough spaces in the fabri.q .gthe pot before eventuall-y entering the pot. This external attackphase var ied in durat ion from about 10 secs. to l0 mins. With caneand batten pots the external attack phase was usually fairly shortand ended with the octopus entering the pot. Because of the greacerdifficulty in entering wire pot.s, tle external attack phase wasusually somewhat longer. During the period of external attack therock lobsters showed some "agitation" and usually moved to a pointin the pot as far away from the octopus as they could get. Some-times an octopus managed to capt.ure a rock l-obster from outside thepot but, in all cases, was wrable to secure an adequate grasp onthe rock lobster, which eventualJ-y escaped from its hotd.

When an octopus finally entered a pot, the rock lobsters showedconsiderable "agitation" and moved. quickly away When contacted byan octopus arm. Octopuses showed. no select ion of rock l_obstersby size (Figure 10) or sex (Table 17) and usual ly at tacked thenearest rock lobster. Rock lobseers sometimes towered theirantennae toward the octopus in an apparentty defensive gesture.Octopuses often grasped and pulled the antennae, at which pointthey i,rere usually autotomized by the rock lobster, Rock lobsrersattacked by octopuses also commonly autotomized legs to escapethe grasp of the oceopus.

TABI,E I8 Sexes of rock l -obsters predated in pot entry t r ia ls.

& I

Total No. presentedin pots 8 9 8 1

No. predated z a 3 3

In some cases rock lobsters which were the subject of an at tack byan octopus showed a swimming escape reaction. This swimminqreact ion, in which rock Lobsters swim backwards properled ly t t reirta i ls, is a normal react j_on by rock lobsters to octopuses in t t rew i l d (Be r ry 1971 and pe rs . obs . ) . Observa t i ons i n t i r e aquar iumindicated that rock lobsters can swim considerablv fastei thanoctopuses. Unhindered rock lobsters placed in the Iarge (5m diam. )outdoor aquarium with hungry octopuses began the swimmlng escapereaction when approached by the octopus. Octopuses usuaily b.g.r,swimrnin g in pursuit. but were easily outdistanced bv the ro-cklobster. In the f ie ld such a react ion is probably an ef fect iveescape measure but, wi thin the conf ines of a pot, rock lobstersare unable to escape farther than the length or d.iameter of thepot. In t .he circular cane and steel pots, rock lobsters sometimesswam in circles around the periheter of tlae pots. fn one insrance,a rock lobster began a swinming escape reaction upwards whilestanding beneath the neck of the pot and actually- swam out of thepot.

4 4

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Co.opoce Langlh.

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'sTeT.rf ,{:4ue 4Od Urn'r:enbB ut -sesndolco o1pe4uaie:a site+sqoT 1cd: 3,o sqlbueT ecede:e3 'g1 e;n6tg

After an octopus had entered a pot, rock lobsters sometimes attemptedto escape through the escape gap. Because (except in one instance)only legal-s ized rock lobsters were used. in the tr ia ls, the escapegap was usually too sma11 to allow them to pass, although one rocklobster (77mm carapace length) managed to pass through the escapegap. Octopuses sometimes attempted to pull captured rock lobstersout of the pot through the escape gap but they were usually toolarge to pass through. In one case an octopus pulled a 77mm cara-pace-length rock l-obster through the escape gap, but on other occas-ions octopuses were forced. to abandon this course of action andreturn inside che pot to feed.

once an octopus succeeded in secur ing a rock lobster, i t was heldfirmly by aII the arms, ef fectivel-y restraining movement. The webof the octopus was usually spread to its max i:num size to form an"umbre1la" over the rock lobster. Rock lobsters \ r /ere usual ly heldfrom the dorsal surface but were sometimes held sicle-on or on theventral surface. Death of the rock lobster occurred 20-30 min.af ter capture. In a separate ser ies of experiments, rock lobstersfed to octopuses and then pul led away again af ter 5-15min., showedno signs of mechanical in jury or puncture marks. The rock Iobsterswere sometimes completely rigid with "fear" or from the toxicaction of the sal-iva, but recovered within I0 min. . As \,!rith theprey of other speci .es of Octopzrs and Eledone (Sidder 1966), therock lobsters showed no puncture marks or other forms of mechanicalinjury. The lack of puncture marks suggests that the toxic salivawas secreted into the chamber formed by the web of the octopus andabsorbed by the rock lobster through the gills and other permeablesu r faces .

The nature of the venom in the sal iva of 0. tetv, icus was not examined,bu t i t i s p robab ly s im i l a r t o t ha t o f 0 . uu lga i r s CGh i re t t i 1960 ) ,since the time taken for the death of the prey is similar in0, uuLgari ,s and O. tetr icus. The venom was certainly not as viru-lent a! that of the smal l - b lue-r inged octopus uapaLochlaena macuLosa,where the death of crabs occurred. within 2 Lo 3 mins of attack(Tranter and August ine, 1973). Hrnnans bi t ten by 0. tetr i ,cus donot show any of the usual]-y fatal symptoms associated with bitesfrom E. macuLosa (Suther land and L.,ane 1969, McMichael 19711, al thoughs ome local discomfort and swel l ing may occur.

As with other octopods (Bidcler 1966, Mori . s} : . i r -a et aL 1974, Morishi ta1974 a, b, c) , the sal ivary secret ions of O. tetv ' icas have a digest-ive action on the tissues of the prey. this digestive action breaksalorrn the attachment of tissues to the exo-skel-et.on, allowing theprey to be easily dismembered and allowing the octopus to consumetissues from otherwise inaccessible areas of the body. 0. tety. ' tcususually severs the cephalothorax (head) from the abdomen (tail) andfeeds first on the organs and muscle tissue in the head. Octopusesusually only commence on the muscular tail region after consrnningthe conten€s of the head.

The attachment of the muscle t issue in the tai l is of ten completelysevered by the dj-gest ive act ion of the octopus' sal iva, so that,on hauling the pot to the surface, the muscle tissue may fall outof the severed tai l sect ion, giv ing the impression that the t issuesof the tail have also been eaten. However, data on octopus gut con-tents indicate that an octopus would not be capable of eating theamount of tissue in a leqal-sized rock l-obster. The maximurn weicrht

4 6

LV

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to standard cornmercial rock lobster pots, extendeal field trialswere conducted with comnercial operators.

The f ie ld t r ia l -s were based on pots set and. pu1led on a daiJ_y basj_s.Fishennen operating in deeper water or in the latter part. of theseason often have pot settings of 2-4 days, while incl-ement weathermay sometimes cause other fishermen to leave eheir pot.s se€ forseveral days. fn order to have a basis for predicting what mayoccur in pots set for periods longer than one day, aquarium trialsrre re und.ertaken to examine the resul-t of protracted occupation oftraps by octopuse s .

METHODS

(i ) Fiel-d Tr ials

Two approximately 3-week trials were conducted from commercialboats, one operat ing out of Fremant l-e using cane beehive pots,the other operat ing out of Dongara using batten pots. Terracottaoctopus traps were secured with t.l-e-wire s into hal-f the pots, theentrances of the traps being placed so that they faced upwardswhen the pot v/as hauled. Pot.s with octopus traps and ordinarypots were mixed together so that any line of pots contained approx-imate l-y equal numbers of each pot type. The pots were pulJ_ed ona da i l y bas i s .

Records were kept for each pot of t.he number of rock l-obsters andoctopus caught. The nunber of octopus-predated rock lobsters wasnoted as well as whether or not octopuses were occupying the trapsaL the t ime of capture. Pots not catching octopus but showingoctopus-predated rock lobsters or other signs of former octopusoccupat ion were noted. The number of 1j-ve, 1ega1-sized rockIobsters caught by the two pot types was recorded for the wholef ishing per iod at Dongara. At Fremant le the number of l ive, Iegal_-sized rock lobsters caught by the two pot types was only recordedafter the f i rst nine days of f ishing, ani l i t was necessary tomake a change to the normal hand.ling practice in order to recordthe se data.

( i i ) aquarium Trials

Trials were conducted in the large outd.oor aquarium Ccf . V c. Fig; 9)Hungry, aquarium-accl-imatized octopuses were placed in the largeaquarium with a terracotta pot as a refuge. A rock lobster potcontaining three legal-sized rock lobsters was introiluced into theaquarium, and the time of entry by the octopus into the pot noted.The pot was checked regularly and the time of exit and the fateof the trapped rock lobsters recorded..

RESULTS

Tab1e 18 La and b) shows the resul-ts from the two ports on a dailybasis, whi le Table 19 shows the combined resul ts. The resul ts ofthe aquarium tr ia ls are shown in Table 20.

For I-day settings, the catch rate of octopus in pots with octopustraps t0.187 octopus,/pot l i f t ) was signi f icant ly higher lp < 0.001)than in pots without octopus traps [0.059 octopus/pot J- i f t ) , whi lethere was no significant difference at the 5? leve1 in the catch

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rates of rock lobsters (2.958 rock lobsters/pot l i f t for standardpots as against 2.906 rock lobsters/pot l - i f t for pots with octopustraps . There was no signi f icant di f ference, at t ,he 5g tevel , inthe catch rates of J- ive, legal-s ized rock lobster by the t \ , ro pottypes (1.259 rock lobsters/pot l i f t for standard pots, as againstl - .205 rock lobsters, /pot f i f t for pots with octopus traps).

DISCUSS ION

Although the di f ference in catch rate of I j -ve, legal-s ized rocklobsters between pots with and without octopus traps was not stat-ist ical l -y s igni f icant, general observat ions suggest that the smal lreduct ion in catch rate record.eat (4.3?) cannot be ignored and mightwel-1 become stat ist ical- ly s igni f icant in a larger sample. eui tea fev/ pots with octopus traps which caught octopus in the traps,did not contain any predated rock lobsters, the octopuses presum-ably having entered the pot to feed on the bait. In pots whererock lobsters have been predated, the remains would probably actas such a strong repel lant to other rock lobsters (Eancock, I974)that the delerrent effect of octopuses retained i.n pots wherepredation has occurred is unlike1y to be of much consequence.Octopuses remaining in pots where no pred.ation has occurred prob-ably also act as repel lants to rock lobsters and. prevent such potsfrorn functioning as normal catching unj.ts. Catching and cullingsuch octopuses d.oes have the advantage that it prevents the octopusfrom re-entering a pot at some time in the future and perhaps pre-dat ing a rock lobster.

For one-day settings, the mean percentage retention of octopuseswhich entered pots wi. th octopus traps was 80.1?, compared with43 .92 for ord. inary pots. No f ie l -d d.ata were avai labl_e on the abi l_ i tyof the octopus traps to retain octopuses over the periods longerthan one-day sett ings, but the resul ts of the aquarium tr ia l-s(Table 20) indicated that octopuses would take up residence intraps in the rocklobster pots for prolonged per iods, despi te theavai labi l i ty of other refuges. Only one octopus did not take upresidence in the trap in t.he thirteen trials conducted. The meant j-me spent in the pot in trials in whj-ch octopuses took up resid-ence in the trap was 7.5 days, with a range from tiro to sixteendays. These observat ions indicate that octopus traps coutd beexpected to retai.n octopuses in the pots for longer than one day.A problem associated. with the prl-onged retention of octopuses rnpots is that two to three days after the i-nitial predation, octopusesusually regain their appet.ite sufficiently to attack and killanother rock lobster, i f one is avai lable in the pot. Where anoctopus stayed in a pot for. longer than four daysl two rock lobsterswere always predated and, in five cases where octopuses stayed. forperiods of longer than nine days, a1l three rock lobsters werepredated.

Of the 288 octopuses caught in pots with octopus eraps, 154 wereoccupying the octopus traps at the time of capture. This behaviourindicates that the traps do provide an acceptable refuge whichoctopuses wi l l occupy in a f ie ld s i tuat ion, instead of leaving thepot. Terracotta t raps, such as were used j -n the experiment, wouldnot be sui table for general use in commercial rock lobster pors, asthey are expensive, heavy, and prone to f racture. A l ight, cheapand durabl-e pl-astic trap would probabJ-y function as welt, in termsof providing a sui table refuge for octopuses. In the aquariumoctopuses have shown that they wiJ-I occupy refuges made of a variety

5 2

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Both the "odour" of the bai t and the presence of t rapped rock lobstersappear to be responsible for at t ract ing octopuses to iock- lobsterpots. The part icular chemicals in bai ts responsible for the at tract-ion of octopuses are not known, but i t would seem l ike1y that. octopusesrespond. to a spectrum of chemicals simj.lar to that which attractsrock lobsters. There woul-d appear to be l i t t1e prospect of develop-ing bai ts which are simultaneously at traceive to rock lobsters annon-attract ive to octopuses. As the presence of t rapped rock lob-sters is also at tract ive to octopuses, the use of bai ts which aremerely non-attractive to octopus would not prevent the attractionof octopuses to pots containing rock lobsters.

The observat ions of Hancock (1975) on the repulsion of crustaceanspecies by the dead of the same species raised the possibi l i ty ofact ive repulsion of octopuses by the incorporat ion of dead 0etopu6as a component of the bai t . Field t r ia ls with )ctopue bai ts, how-ever, showed. no repel lant act iv j ty to octopuses of 0ctopus bai i - .Indeed.. there were even indicat. ions that )ctopus bai t rnay be attract-ive to octopuses. ?ctopus bai t a lone was a poor bai t for rocklobster. Limited laboratory test ing of moray eel- and starf ishextracts, for which there was some basis for consider ing as pot-ent ia l repel lants, did not reveal any repel lant act iv i ty. A tr ia lwi th a model moray ee1 suggested that octopuses would not berepel led by visual- deterrants, such as models of their predators,unless the models were extremelv real ist ic in both visual and+ ^ . ' f i I 6 : a n 6 . . + a

Cctopuses proved capable of penetrating pots made of a varietl' ofmater ials. Wire-covered pots proved the most c l i f f icul t for octopuse-sto enter, but the wire cover ing only delayed their ul t imate entry,and did not prevent i t . With the necessi ty for pots to have anentry port for rock lobsters, and the legal requirement for potsto have an escape gap, i t is di f f icul t t , t conceive of any changesin pot design which coul-d make pots octopus-proof. Even i f thefabr ic of the pot was impenetrabl-e, octopuses would st i1 l event-ual ly gain entry to the pot through ei ther the neck or the escapegap .

Laboratory observat ions did not indicate that the escape gap wasof s igni f icance in al lowing the escape of octopuses whi le potswere st i l1 on the bottom, although observat ion of commercial potsshowed that octopuses sometime s escape through the escape gapwhen pots were hauled. In many of these cornmercial pots, theescape gaps were situated opposite the hauJ-ing rope, and on thelower edge of the pot, so that. oceopuses were pushed up againstthe escape gap and almost forced out of the pot by the thrust ofwater when the pots were hauled to the surface. Many fishermenwere under the misapprehension that it was a legal requirementfor the escape gap to be so posi t ioned. placing escape gaps inthe upper surfaces of pots, or nearer the attachment of the haulinqrope, would. probably reduce these last minute escapes.

The use of octopus traps in rock lobser pots s igni f icant ly reduced.the escape of octopuses from pots, by providing a refuge whichoctopuses occupj-ed instead of l -eavi .ng the pot. Use of oct ,opustraps d.oes not prevent. predat ion occurr ing, but has the benef i tthat octopuses caught may be sotd, thus part ia l l -y compensat ingfor the loss by predat ion. Cul l ing of an octopus prevents furtherpredat ion by that indiv idual . Eowever, the overal l ef fect of the

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Bowen, B. K. l -971. Management of the western rock lobster(Panu l i rus Long ipes cA gnus George ) . pyoc . I ndo -pac i fddF i s h . C o u n c . I _ 4 t r r l : f 3 9 - 1 5 3 .

Burd .on , T .w . 1973 . The V ic to r i an F i sh ing Indus t r y . F i shey , i esCon tyLbu t i on , V i c toz ,4a 392 76 pp .

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Fed ,e r , H .M. and Chr i s tensen , A .14 . 1966 . Aspec ts o f as te ro idbiology. 1n Physiology of Echinod.ermata. Ed. R.A.Booloot ian. Wi ley Interscience, . . l iew york.

Feder, H.M. and Lasker, R. 1964. P ar. t_ial pur i f icat ion of a sub-stance from starf ish tube feet which el_ic i ts escaperesponses in gastropod mo1luscs. Li fe Sciences 3. (9) z1 0 4 7 - 1 0 5 1 .

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carstang, W. 1900. The plague of octopus on the south coast, andi ts ef fect on the crab and lobster f isher ies. J. Mar.B i , o L , A s s o c . U . K . g z 2 6 0 - 2 7 3 .

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