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Volume 53, 2002© CSIRO 2002

A journal for the publication of original contributionsin physical oceanography, marine chemistry,marine and estuarine biology and limnology

© CSIRO 2002 10.1071/MF00075 1323-1650/02/010049

Mar. Freshwater Res., 2002, 53, 49–57

Diet of Patagonian toothfish (Dissostichus eleginoides) around Macquarie Island, South Pacific Ocean

S. D. GoldsworthyAC, M. LewisA, R. WilliamsB, X. HeA, J. W. YoungA and J. van den HoffB

ACSIRO Marine Research, GPO Box 1538, Hobart, Tas. 7001, AustraliaBAustralian Antarctic Division, Channel Highway, Kingston, Tas. 7050, Australia

CPresent address: Sea Mammal Ecology Group, Zoology Department, La Trobe University, Vic. 3086, Australia. email: s.goldsworthy@zoo.latrobe.edu.au

Abstract. A total of 1423 stomach samples were taken from Patagonian toothfish, Dissostichus eleginoides,caught by bottom trawls at two fishing grounds near Macquarie I., over three fishing seasons. Fish were caught atdepths ranging from 500 to 1290 m, and ranged in size from 310 to 1490 mm total length. The 462 stomach samples(32%) that contained prey items indicated that toothfish preyed on a broad range of species including fish,cephalopods and crustaceans (58%, 32% and 10% biomass, respectively), suggesting that they are opportunisticpredators. The bathypelagic fish Bathylagus sp. was the most important fish prey (14% dietary biomass); however,nototheniid, macrourid, morid and myctophid fish were also taken. The squid Gonatus antarcticus was also animportant prey species (16% biomass), and many other cephalopod species were taken in low frequency. Prawn-like crustaceans (Nematocarcinidae, Mysididae, Sergestidae and Euphausiidae) were the most importantcrustaceans taken (9% of prey biomass). Significant inter-seasonal and inter-fishing-ground differences in dietwere found, but dietary composition was not related to fishing depth, fish size (with the exception of one fishingground in one season) or the time of day of capture. Comparison with other studies reveals biogeographicaldifferences in the diet of toothfish. Diet of Pat agoni an toothf ishS. D. G ol dswor thyet al .

MF00075

IntroductionThe Patagonian toothfish, Dissostichus eleginoides(hereafter toothfish), is widespread throughout the SouthernOcean, occurring mostly in waters near and to the north ofthe Antarctic Polar Front. In South America, its rangeextends northward from southern Patagonia to Peru andArgentina. In the Southern Ocean, its range includes theFalkland Is, South Georgia and other islands and seamountsin the Scotia Arc (Fischer and Hureau 1985; Gon andHeemstra 1990), in the southern Indian Ocean on theKerguelen Plateau, at Iles Crozet and the Prince Edward Isand in the southern Pacific Ocean at Macquarie I. (Duhamel1981; Duhamel and Pletikosic 1983; Gon and Heemstra1990; Williams and de la Mare 1995). The species isgenerally confined to waters north of –55ºS (Gon andHeemstra 1990). A congeneric species, Dissostichusmawsoni, occurs further south on the Antarctic continentalshelf.

Toothfish reach sexual maturity when they reach ~100 cmin length (Konforkin and Kozlov 1992), and spawn duringwinter on slopes at depths of >1000 m (Duhamel 1981;Konforkin and Kozlov 1992). Early life history is poorly

known; juveniles are thought to develop in schools ofeuphausiids and then prey increasingly on fishes as theygrow (Duhamel 1981). The species is generally foundbetween depths of 70 and 1500 m, although adult fish inChile are occasionally caught at depths down to 2500 m(Fischer and Hureau 1985; Mora et al. 1986).

Trawl fishing for toothfish in the Southern Ocean beganin the mid 1980s on the continental slope off South Georgiaand Shag Rocks, and at Iles Kerguelen (Kock 1992), andprogressively switched to longlining. Recently, trawlfisheries for toothfish have developed within AustralianCommonwealth waters around Heard I. and McDonald I.(March 1997) on the Kerguelen Palateau, and atMacquarie I. (November 1994). Two main fishing groundshave been discovered at Macquarie I.: one just west of theisland (southern ground) and one north of the island(northern ground) on the Macquarie Ridge. The distancebetween fishing grounds is ~60 km.

Ecologically sustainable development (ESD) of thetoothfish fishery around Macquarie I. requires anunderstanding of the ecological interactions betweentoothfish and other components of the ecosystem, especially

50 S. D. Goldsworthy et al.

trophic interactions between toothfish and other mainpredators. These have recently been investigated byGoldsworthy et al. (2001). Here, we present data on the dietof toothfish around Macquarie I., interannual andintraseasonal differences in the diets of toothfish from eachfishing ground, and the influence of fish size and of depthand time of capture on diet. We compare the diet of toothfishat Macquarie I. with those from other parts of the SouthernOcean.

Methods

Study area and sample collection

Macquarie I. (54°30′S,158°55′E), a subantarctic island in the south-west Pacific Ocean ~1500 km south-east of Tasmania, Australia, is animportant breeding locality for seabirds (2.7 million) and seals (89000)(Goldsworthy et al. 2001). The island is on the narrow MacquarieRidge, which in the vicinity of the island has a small shelf area ~180 kmlong and 20 km wide, with only 2500 km2 shallower than 1000 m.Trawling for toothfish is restricted to the central part of this ridge,usually between 500 and 700 m, although in one small part of thenorthern ground trawling can be conducted down to 1290 m.

Toothfish stomachs were obtained from fish caught near theisland during cruises by the trawler Austral Leader. Stomachs werecollected over three summer fishing seasons, between November1995 and January 1996, between November 1997 and March 1998,and between November 1998 and January 1999 (hereinafter referredto as Seasons 1, 2 and 3, respectively) (Table 1). Fishing in Season 1was concentrated to the west of the island (southern fishing ground),but during Seasons 2 and 3 fishing also occurred to the north of theisland (northern fishing ground) (Table 1). Management of thefishery restricts fishing to trawling and to a single vessel. Dischargeof factory waste and rubbish is also prohibited. Fishing observerscollected fish specimens and recorded the date, location and depth oftrawl. The total lengths of ~65% of the fish sampled were alsorecorded. Stomachs were stored frozen until they were examined inthe laboratory.

Data analysis

The state of digestion of stomach contents was assessed on a three-point scale: fresh, partially digested and digested. Stomach contentswere identified in the laboratory to the lowest possible taxonomiclevel by use of otolith and whole-specimen collections of fish andsquid obtained from the fishing grounds, voucher collections of squidbeaks supplied to the Australian Antarctic Division by MR Clarke,the otolith keys of Williams and McEldowney (1990), and thedescriptions of cephalopod mouthparts in Clarke (1986). Where the

degree of digestion permitted, prey items were weighed and counted.Individual prey items were weighed (wet mass) in order to determinethe contribution to total prey biomass of individual prey taxa.Differences in percentages of non-empty stomachs between fishinggrounds and fishing seasons were tested by two-way contingency Gtests.

In total, four indices were calculated for each prey category:frequency of occurrence (%F), frequency by number (%N), frequencyby wet mass (%M), and index of relative importance (IRI). IRI (Georgeand Hadley 1979) for each prey category (a) was calculated as follows:

where n is the total number of prey categories and IAI is the index ofabsolute importance (Cortés 1997) calculated as:

For the overall analysis of prey composition, prey items wereaggregated, usually to family level (Table 2). Difficulties in identifyingthe families of cirrate octopods resulted in these being grouped assimply ‘Cirrate octopods’. Nematocarcinidae, Euphausiidae, Mysidaeand Sergiestidae were grouped together as ‘Prawn-like crustaceans’.Prey groups that occurred in <1% of stomachs were grouped into otherfish (OFish), other cephalopod (OCeph) and other crustacean (OCrust)categories. For comparisons of the diets of toothfish among fishlengths, depths of capture and times of day, and between fishinggrounds and seasons, prey categories were reduced further to includeonly prey groups that contributed 3% or more to total prey biomass.Fish, cephalopod or crustacean groups that constituted <3% of preybiomass were combined into the OFish, OCeph or OCrust categories.The influence of time of capture on diet was examined by dividing a dayinto six 4 h periods (2200–0200; 0200–0600, 0600–1000, 1000–1400,1400–1800 and 1800–2200 hours). Because of the high latitude ofMacquarie I. and the summer fishing season, most of the dark period isencompassed by 2200–0200 hours.

Differences in the diets of toothfish among fish lengths, depths ofcapture and times of day, and between fishing grounds and seasons,were tested by Mantel’s test (Mantel 1967; Manly 1991); this is arandomized method and its test statistic is the correlation between twomatrices. The significance of the test statistic is determined bycomparing the test statistic with the distribution of the statisticsobtained from randomly re-allocating the order of the elements in oneof the matrices. For testing differences in the diets of toothfish amongfish lengths, the first matrix, A, was defined as the dissimilarity matrixof diet compositions between all pairs of individual fish. The second

Table 1. Number of toothfish sampled for diet analysis around Macquarie I. in the 1996/96, 1997/98 and 1998/99 fishing seasonsNumbers and percentage for each season and ground, the mean total length of fish and the depth at which they were caught are also listed

Season Ground No. stomach samples

No. with contents Mean total length, mm (s.d., n)

Mean depth, m (s.d., n)

1995/96 Southern 495 424 (86%) 1006.7 (214.5, 11A) 895 (83, 404; range 724 – 902)1997/98 Northern 372 124 (33%) 689.2 (114.3, 371) 1167 (92, 372; range 770 – 1290)

Southern 37 32 (86%) 628.3 (72.3, 37) 902 (39, 37; range 815 – 922)1998/99 Northern 350 166 (47%) 639.4 (121.1, 350) 1136 (131, 350; range 666 – 1260)

Southern 169 117 (69) 604.2 (176.4, 158) 822 (144, 169; range 500 – 990)

A Only 11 fish were measured.

,

[IAI]

[IAI]100[IRI]

1∑

=

=

n

aa

aa

.%F%M%N aaaa )([IAI] +=

Diet of Patagonian toothfish 51

matrix, B, was defined as the difference matrix of fish length betweenall pairs of individual fish. That is, for m individual fish,

where

Pih and Pih are proportions of diet item h for individual fish i and j, n is

where li and lj are the total lengths of fish i and j. For testing differencesin the diet among fishing grounds, depths or seasons, the first matrix,A, was the same as the previously defined matrix. The second matrix,B, had bkl values of 1 if k = l and values of 0 otherwise, where k and lrefer to fishing seasons or fishing grounds.

Because both matrices are symmetric, the correlation between all theoff-diagonal elements in two matrices is the same as the correlationbetween the m(m–1)/2 elements in the lower triangular diagonal parts.The test was conducted for groups where >30 individual fish with noempty stomachs were sampled (m >>= 30). The correlation between twomatrices was compared with the distribution of the correlationcalculated from randomly reallocating the elements of the B matrix 5000times. The null hypothesis that there was no difference in dietcompositions among fish lengths, fishing grounds or seasons wasrejected if the test statistic was smaller or greater than 5% of values in thedistribution. Statistical significance was accepted at the P = 0.05 level.

Results

Stomach fullness and mean prey mass

In total, 1423 toothfish stomachs were collected (495 during1995/96, 409 during 1997/98 and 519 during 1998/99)(Table 1). The percentage of stomachs collected in eachseason that contained prey items varied significantly (G-test,P <0.001) from 38% (Season 2) to 85% (Season 1). In thesecond and third seasons of fishing, a significantly greaterpercentage of stomachs contained prey items in the southernground than in the northern ground (G-test, P <0.001 forboth) (Table 1). The total mass of prey items in the stomachsof toothfish that contained prey remains ranged from 0.01 to1490.6 g. The average mass of prey items was 47.5 g (s.d. =91.1, n = 863). The absolute mass of stomach contents wasunrelated to the length of the fish (ANOVA). There was noevidence of regurgitation of stomach contents; toothfish lacka gas-filled swim bladder and stomachs do not evert whenfish are brought to the surface. Of the stomach contents,74% were classed as digested, 25% as partially digested andonly 1% as fresh.

Overall diet

Of the prey categories identified (Table 2), fish accountedfor the greatest proportion of prey biomass (58%), with thebathypelagic fish Bathylagus sp. being the most importantfish prey (Table 3). Of the cephalopod genera (32% preybiomass) taken by toothfish, the most important wasGonatus antarcticus. Prawn-like crustaceans were thedominant crustaceans taken (10% prey biomass) and wereone of the most numerous of all the prey items (Table 3).Stone crabs (Lithodes spp.) were also occasionally taken.

Fish diet relative to body length, depth of capture and time of day

Of 1423 toothfish sampled, 927 were also measured. Theirtotal length ranged from 310 to 1130 mm (mean 657,s.d. = 124), with only two specimens longer (1354 and 1490mm). There was no significant difference in the dietcomposition of toothfish of differing lengths caught withineach fishing ground and season (Mantel’s test: Season 2northern ground, n = 124; Season 2 southern ground, n = 32;Season 3 northern ground, n = 166), with the exception of thesouthern ground in Season 3 (n = 108, P = 0.010). The preycategory that varied most obviously with predator length inthe southern ground in Season 3 was myctophid fish. Thisaccounted for >65% of total prey biomass in the smalltoothfish (<450 mm) and was absent in the diet of the largestfish caught >750 mm) (Fig. 1A). Cephalopods wereuncommon in smaller toothfish (<550 mm) but accountedfor ~40% or more of total prey biomass in toothfish largerthan 550 mm (Figs 1A and 1B). The depth at which toothfishwere caught within each fishing ground in each fishingseason did not significantly influence the diet data.

The time of day when fish were caught had no influenceon their diet (in 758 samples for which time of capture wasknown). For within-season and within-ground analyses,there was no effect of time of capture on diet, with theexception of Season 1, ground 2 (P <0.05; but non-significant with the period 1100–1400 hours excluded) andSeason 3, ground two (P <0.05, but nonsignificant with theperiod 0200–0600 hours excluded). Overall, the resultssuggest that day or night sampling had no influence on thecomposition of toothfish diet.

Comparison between fishing grounds and seasons

The prey biomass of toothfish differed significantlybetween grounds during Season 2 (Mantel’s test, P <0.05)and Season 3 (P <0.001). In Season 2, fish accounted for74% prey biomass in the northern ground, and 64% preybiomass in the southern ground (Table 4). Although thebiomass of macrourid fishes in the prey was similar foreach ground, bathylagid fish accounted for 28% of the preybiomass (37% IRI) in the southern ground, compared withonly 8% (4% IRI) in the northern ground (Table 4). Morid

==

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1_,2,1

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mm,mmmm,mm bbb

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jh

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52 S. D. Goldsworthy et al.

fish accounted for 17% of prey biomass in the northernground, and were absent from the diet of fish in thesouthern ground. Both the overall biomass and the speciescomposition of cephalopods also differed between thefishing grounds (Table 4). Cephalopods accounted for33% prey biomass in the southern ground (principally fromthe family Gonatidae, Onychoteuthidae (Moroteuthis sp.)

and Mastigoteuthidae, and only 20% in the northernground (principally Chiroteuthidae, Onychoteuthidae(Moroteuthis sp.) and cirrate octopods). Crustaceans(entirely prawn-like crustaceans) were uncommon in thediets of toothfish from the southern ground (2%), andmore numerous (6%, but mostly Lithodes crabs) in thenorthern ground (Table 4).

Table 2. Prey category by lowest possible taxonomic level and aggregated prey groups for toothfish caught around Macquarie I.

Prey group Prey category by lowest taxonomic level

Fish Bathylagidae Bathylagus sp.Myctophidae Electrona subaspera, E. carlsbergi

Gymnoscopelus braueri, G. fraseri, G. microlampas, G. nicholsiKrefftichthys anderssoniLampanyctus achirus

Macrouridae Coryphaenoides sp.Cynomacrurus piriei

Moridae Halargyreus johnsoniiLepidion sp.

Nototheniidae Dissostichus eleginoides Lepidonotothen squamifronsParanotothenia magellanica

OFish SqualidaeNemichthyidae, Labichthys yanoiMicrostomatidae, Nansenia sp.Astronesthidae, Astronethes sp.Stomiidae, Stomias sp., Borostomias sp.Chauliodus danaeIdicanthidae, Idiacanthus atlanticusScopelarchidae, Scopelarchoides sp.Melanonidae, Melanonus gracilisMelamphaidae, Poromitra sp.PsychrolutidaeEpigonidae, Rosenblattia sp., Epigonus sp.Gempylidae, Paradiplospinus antarcticusArchiropsettidae

Cephalopoda Chiroteuthidae Chiroteuthis sp.Cirrate octopods Cirroteuthidae, Stauroteuthidae, OpisthoteuthidaeGonatidae Gonatus antarcticusMastigoteuthidae Mastigoteuthis sp.Onychoteuthidae Moroteuthis ingens, M. knipovitchi, Kondakovia longimanaOCeph Unidentified octopod

Brachioteuthidae, BrachioteuthisCranchiidae, Galiteuthis glacialis, Taonius sp.Histioteuthidae, Histioteuthis eltaninae, H. macrohistaVampyroteuthidae, Vampyromorpha sp.

Crustacea Lithodidae Lithodes murrayiPrawn-like crustacea Caridea

NematocarcinidaeEuphausiidae, Gnathophausia sp.MysidaeSergestidae

OCrust AmphipodaOstracodaMaxillopodaIsopoda

Diet of Patagonian toothfish 53

In Season 3, fish accounted for more of the prey biomassin the northern ground (76%) than in the southern ground(52%) and, in contrast to Season 2, bathylagid fish were thedominant fish prey in the northern ground (36% biomass,49% IRI)) but were less important in the southern ground(9% mass, 4% IRI) (Table 4). Nototheniid fish accounted formost of the fish prey biomass in the southern ground (18%biomass, 5% IRI), although myctophids were mostcommonly taken (9% biomass, 22% IRI). Nototheniid (9%biomass, 1% IRI) and myctophid fish (2% biomass, 1% IRI)were less common in the diet in the northern ground inSeason 3 (Table 4). Cephalopods (mostly Gonatidae, 26%biomass, 16% IRI) accounted for 41% of the prey biomass inthe southern ground in Season 3, but only 18% (mostlygonatid and mastigoteuthid squid) in the northern ground(Table 4). Similar to Season 2, crustaceans (mostly prawn-like crustaceans) accounted for only a small percentage ofthe prey biomass in Season 3 in the southern (7% biomass,11% IRI) and northern (2% biomass, 1% IRI) grounds.

As well as there being differences in the diets of toothfishbetween fishing grounds within each season of fishing,toothfish diet also differed significantly within fishinggrounds among seasons (Table 4). In the southern ground,

the relative biomass of fish and crustaceans in the diet oftoothfish changed markedly between years, although thebiomass and species composition of cephalopods changedlittle (Table 4). The total and relative biomass of various fishtaxa changed markedly between fishing seasons, especiallyin the bathylagids (4–37% IRI), macrourids (0.1–14% IRI),myctophids (0.8–22% IRI) and nototheniids (0.0–8.1% IRI)(Table 4). Prawn-like crustaceans were common in the dietin the southern ground in all years (17–43% IRI), althoughtheir relative and total biomass in the diet varied markedlybetween years (Table 4). In the northern ground, althoughthe total and relative biomasses of fish, cephalopods andcrustaceans were similar between years, the composition ofprey species, particularly bathylagid (4–49% IRI), mac-rourid (2–9% IRI) and morid (3–11% IRI) fishes differedmarkedly between seasons (Table 4).

Table 3. Occurrence of prey groups and major prey types (fish, cephalopods, crustaceans) in the stomachs of toothfish from

Macquarie I. (seasons and grounds combined)Contribution of various prey items in the diet is expressed as the

percentage frequency of occurrence (%F), percentage frequency by number (%N), percentage frequency by mass (%M) and index of

relative importance (IRI)

Prey group %F %N %M IRI

FishBathylagidae 14.4 15.6 13.9 13.6Myctophidae 10.0 7.3 3.2 3.4Macrouridae 4.2 2.0 7.6 1.3Moridae 3.0 4.4 4.8 0.9Nototheniidae 2.4 1.2 8.7 0.8Ofish 3.7 4.2 5.4 1.1Unident. Fish 36.0 20.4 14.6 40.3

CephalopodsGonatus 8.0 5.0 16.2 5.4Mastigoteuthis 5.0 3.3 1.9 0.8Moroteuthis 1.6 0.8 4.3 0.3Chiroteuthis 1.3 0.6 1.6 0.1Cirrate octopods 4.5 2.4 0.7 0.5OCeph 3.6 1.8 2.2 0.5Unident. Ceph 13.7 7.9 4.6 5.5

CrustaceansPrawn-like crustaceans 28.0 19.2 9.0 25.3Lithodidae 1.6 0.8 1.0 0.1OCrust 2.0 2.2 0.0 0.1Unident. Crust 2.1 1.0 0.3 0.1

Fish 64.9 55.0 58.1 71.4Cephalopods 34.6 21.9 31.6 18.0Crustaceans 32.7 23.1 10.3 10.6

Fig. 1. Changes in the composition of prey biomass with respect totoothfish total length (1, <450 mm; 2, 450–550 mm; 3, 551–650 mm;4, 651–750 mm; 5, 751–850 mm; 6, >850 mm) in the southern fishingground at Macquarie I. in the 1998/99 fishing season: (A) fish preygroups; (B) cephalopod prey groups; (C) major prey categories.

54 S. D. Goldsworthy et al.

Tab

le 4

.O

ccur

ren

ce o

f p

rey

grou

ps

and

maj

or p

rey

type

s in

th

e st

omac

hs

of t

ooth

fish

fro

m t

he

sout

hern

and

nor

ther

n fi

shin

g gr

ound

at

Mac

quar

ie I

slan

d o

ver

thre

e fi

shin

g se

ason

sC

ontr

ibut

ion

of v

ario

us p

rey

item

s in

the

diet

is e

xpre

ssed

as

perc

enta

ge f

requ

ency

of

occu

rren

ce (

%F

), p

erce

ntag

e fr

eque

ncy

by n

umbe

r (%

N),

per

cent

age

freq

uenc

y by

mas

s (%

M)

and

inde

x of

rel

ativ

e im

port

ance

(IR

I)

Pre

y gr

oup

Sou

ther

n fi

shin

g gr

ound

Nor

ther

n fi

shin

g gr

ound

1995

/96

1997

/98

1998

/99

1997

/98

1998

/99

%F

%N

%M

IRI

%F

%N

%M

IRI

%F

%N

%M

IRI

%F

%N

%M

IRI

%F

%N

%M

IRI

Fish B

athy

lagi

dae

12.7

10.4

6.7

4.7

37.5

23.9

27.9

37.4

7.7

6.0

8.5

3.9

4.8

10.0

8.2

4.0

25.9

29.7

35.8

49.0

Myc

toph

idae

4.7

5.6

2.4

0.8

18.8

9.8

4.8

5.3

24.8

16.8

8.6

22.1

13.7

10.4

4.3

9.1

8.4

4.0

2.2

1.5

Mac

rour

idae

1.2

0.6

2.0

0.1

21.9

7.6

25.5

13.9

2.6

1.2

3.1

0.4

7.3

4.3

22.6

8.9

7.2

2.4

8.7

2.3

Mor

idae

0.5

0.4

1.4

0.0

0.0

0.0

0.0

0.0

1.7

1.2

1.4

0.2

10.5

6.1

16.9

10.9

5.4

11.9

6.6

2.9

Not

othe

niid

ae1.

20.

68.

10.

20.

00.

00.

00.

06.

83.

217

.95.

12.

41.

36.

90.

93.

01.

28.

70.

9O

fish

2.1

1.1

6.0

0.3

0.0

0.0

0.0

0.0

2.6

1.2

4.8

0.5

6.5

3.5

5.7

2.7

7.2

11.2

4.6

3.3

Uni

dent

. Fis

h38

.225

.519

.837

.628

.19.

86.

28.

732

.516

.07.

727

.029

.819

.99.

640

.039

.215

.69.

728

.6C

epha

lopo

dsG

onat

us8.

34.

922

.95.

025

.013

.015

.313

.612

.810

.425

.516

.20.

84.

31.

40.

26.

02.

66.

91.

6M

asti

gote

uthi

s1.

20.

60.

90.

018

.812

.03.

55.

69.

45.

60.

21.

92.

44.

82.

80.

810

.85.

34.

33.

0M

orot

euth

is1.

20.

62.

80.

13.

11.

110

.80.

72.

61.

612

.71.

31.

60.

95.

00.

41.

80.

62.

80.

2C

hiro

teut

his

0.5

0.2

1.1

0.0

0.0

0.0

0.0

0.0

2.6

1.2

2.0

0.3

2.4

1.3

5.4

0.7

1.8

0.6

0.3

0.0

Cir

rate

oct

opod

s1.

20.

70.

10.

09.

44.

31.

41.

01.

71.

20.

20.

118

.511

.73.

512

.83.

61.

60.

30.

2O

Cep

h1.

40.

92.

30.

13.

11.

12.

20.

26.

03.

20.

40.

85.

63.

91.

71.

46.

02.

03.

30.

9U

nide

nt. C

eph

19.6

12.9

6.9

8.4

3.1

1.1

0.0

0.1

6.0

3.6

0.5

0.9

4.8

3.0

0.1

0.7

12.7

5.0

4.2

3.3

Cru

stac

eans

Pra

wn-

like

cru

stac

eans

40.6

32.3

16.0

42.5

37.5

16.3

2.4

13.5

23.9

15.6

4.2

16.6

8.1

10.0

0.7

3.9

12.0

4.6

1.0

1.9

Lit

hodi

dae

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

3.4

1.6

2.1

0.4

5.6

3.0

5.0

2.1

1.8

0.6

0.4

0.1

OC

rust

1.2

1.7

0.0

0.0

0.0

0.0

0.0

0.0

6.8

8.8

0.1

2.1

0.0

0.0

0.0

0.0

2.4

0.8

0.0

0.1

Uni

dent

. Cru

st1.

91.

00.

40.

10.

00.

00.

00.

03.

41.

60.

10.

23.

21.

70.

10.

31.

20.

40.

20.

0

Fish

55.4

44.2

46.5

56.2

81.3

51.1

64.3

69.1

74.4

45.6

52.1

66.8

78.2

55.4

74.3

78.5

79.5

76.0

76.3

87.4

Cep

halo

pods

30.4

20.8

37.1

19.7

53.1

32.6

33.2

25.8

35.0

26.8

41.4

22.0

46.0

29.9

20.0

17.7

40.4

17.6

22.1

11.6

Cru

stac

eans

42.0

35.0

16.5

24.1

37.5

16.3

2.4

5.2

35.9

27.6

6.5

11.2

24.2

14.7

5.8

3.8

17.5

6.3

1.6

1.0

Diet of Patagonian toothfish 55

Discussion

The results indicate that subadult and adult toothfish feedingon the shelf around Macquarie I. prey on a wide variety oftaxa, from demersal fish and crustaceans to mesopelagicfishes and cephalopods. The major prey items in terms ofbiomass and IRI included the bathypelagic fish Bathylagussp., the squid Gonatus antarcticus and prawn-likecrustaceans (nematocarcinids, euphausiids, sergetids andmysids). Also important were nototheniid, macrourid, morid

and myctophid fish. Diet varied considerably among years,and even over the short geographic distance (about 50 km)between the two fishing grounds, suggesting that toothfish atMacquarie I. are opportunistic predators. This variabilitywas most apparent in the fish component of the diet, wherethe importance of Bathylagus, morid, macrourid, myctophidand nototheniid fishes varied considerably among seasons,and within and between grounds within seasons. However,we found no evidence that this variability was related to thesize of toothfish, or to the depth and time of day at which

Table 5. Comparison of diets of toothfish from five localities throughout the southern Atlantic (Argentine Shelf and South Georgia), southern Indian Ocean (Iles Crozet and Kerguelen) and southern Pacific Ocean (Macquarie Island), as indicated by percentage

frequency of occurrence

Argentine shelf/slopeA

South Georgia <300 mA

South Georgia >1000 mA

Iles CrozetB Iles KerguelenC Macqaurie IslandD

n 231 155 3272 74 1514 1423% stomach contents 58.4 83.1 6.9 41.9 50.8 60.6

FishBathylagidae 14.4Myctophidae 0.7 1.9 11.5 27.2 10.0Macrouridae 2.1 0.9 4.2Moridae 2.1 1.3 3.0Merluccidae 3.5Gadidae 4.9Zoarcidae 5.6 2.2Nototheniidae 25.7 37.8 0.5 19.2 13.0 2.4Channichthyidae 39.5 0.5 26.1Bathydraconidae 0.9Ofish 0.3 3.8Unident. fish 50.7 7.6 54.0 5.8 23.0 36.1

CephalopodsGonatus 8.0Mastigoteuthis 5.0Moroteuthis 1.6Loligo 2.8Illex 2.8Semirossia 0.7Kondakovia 14.7 0.1Chiroteuthis 1.3Octopus 0.7Cirrate octopods 4.5Unident. octopod 1.3Oceph 2.0Unident. Ceph. 0.8 7.7 1.0 13.7

CrustaceansPrawn-like crustacea 2.7 3.8 0.1 28.1Euphausia 20.1 7.7 3.2Lithodidae 7.1 1.6Amphipods 23.1 1.4Isopods 1.9Ocrust 4.2Unident. Crust 2.9 12.1

Fish 95.1 86.5 60.3 na na 65.0Cephalopods 6.9 0.8 14.7 7.7 1.0 34.7Crustaceans 0.0 22.7 21.8 na na 32.8

AGarcía de la Rosa et al. (1997); BDuhamel and Pletikosic (1983); CDuhamel (1981); DThis study.

56 S. D. Goldsworthy et al.

they were caught. The extent to which toothfish predate orscavenge prey at Macquarie I. is unknown.

Elsewhere, toothfish length and age are thought toincrease with water depth, with juvenile fish feedingpelagically and older fish feeding more benthically and indeeper water as they mature (Gon and Heemstra 1990;García de la Rosa et al. 1997). We found evidence for thisonly in Season 3 and only in the southern ground, withsmaller toothfish preying principally on pelagic myctophidfish, which were absent from the diet of larger toothfish.

Diets of toothfish have been published for most of thegeographic range (Table 5). Most were recorded fromsamples within depth ranges similar to that at Macquarie I.,and in continental shelf waters. Although most describedonly the frequency of occurrence of prey taxa, such dataindicate some regional differences in toothfish diet. Of noteis the greater dependence on fish prey, and lower abundanceof cephalopods in the diets of toothfish in the southernAtlantic and Indian Oceans than at Macquarie I., and theabsence of crustaceans in the diets of toothfish on theArgentine shelf (Table 5). Notable differences occur in thecomposition of the fish component of the diet. Bathylagidfish are the most important fish prey at Macquarie I., but areabsent from the diets of toothfish elsewhere, whilenototheniid and channichthyid fishes occur most frequentlyin the diets of toothfish in the southern Indian and AtlanticOceans (Table 5). Some of these dietary differences can beaccounted for by biogeographical differences in the range ofprey species. For example, channichthyid fish do not occurat Macquarie I. and Iles Crozet (Williams 1988) and henceare absent from the diet of toothfish there. However, theimportance of bathylagid fish in the diets of toothfish atMacquarie I. but their complete absence from the diet inother subantarctic regions, is not consistent with the widesubantarctic distribution of this genus (Gon and Heemstra1990). The fish diet of toothfish from the Argentine shelfalso differs from the other subantarctic regions in that itincludes species from more temperate regions (Table 5).

Given the marked interannual differences in toothfish dietobserved at Macquarie I., there should be caution ininterpreting regional difference across their range if multi-year data are absent. However, there have been severalstudies of the diet of toothfish undertaken around SouthGeorgia and Shag Rocks (Tarverdiyeva 1972; Zhivov andKrivoruchko 1990; García de la Rosa et al. 1997), and thesestudies indicate broad dietary similarities. Most notable isthe importance of nototheniid, followed by channichthyidand myctophid, fishes; however, the proportion of the dietmade up by these fishes varies somewhat between studies,depending in particular on whether fish were sampled fromshelf or slope waters. Further, the frequency of benthic andpelagic crustacean species taken (about 14–40% frequencyof occurrence) varies between studies, with cephalopodsgenerally occurring in <15% of stomachs.

It is unfortunate that most of the studies that haveinvestigated toothfish diet have described only the frequencyof occurrence of prey items. Such analyses tend tooverestimate the importance of prey with small biomass andunderestimate the importance of prey with large biomass. Forexample, prawn-like crustaceans occurred in 28% oftoothfish stomachs investigated at Macquarie I. and were oneof the most commonly observed prey items, but accounted foronly 10% of total prey biomass. Given the generally highlydigested state of toothfish stomach contents, and the potentialbiases of the standard measures of prey importance(frequency of occurrence, number and mass), measures suchas the IRI may provide a better indication of the importance ofvarious prey taxa in toothfish diet (Cortés 1997; but seeHannson 1998).

Acknowledgments

This study was supported by the Australia FisheriesResearch and Development Corporation (FRDC Project No.97/122) and the Austral Fisheries Company. We thank thecrew of the Austral Leader (Austral Fisheries), fishingobservers (D. Heran, M. Scott, S. Kalish, M. Tucker,M. Strauss, M. Baron, C. Sutherland) and the crew of theCSIRO research survey, Tony Koslow, Rudy Kloser and TimLamb. George Jackson (Institute of Antarctic and SouthernOcean Studies, University of Tasmania) helped with theidentification of some cephalopods. We thank AndrewConstable, Cathy Bulman and Franzis Althaus forcommenting on the manuscript.

References

Clarke, M. R. (1986). ‘A Handbook for the Identification ofCephalopod Beaks.’ (Clarendon Press: Oxford.) 273 pp.

Cortés, E. (1997). A critical review of methods of studying fish feedingbased on analysis of stomach contents: application to elasmobranchfishes. Canadian Journal of Fisheries and Aquatic Sciences 54,726–38.

Duhamel, G. (1981). Caracteristiques biologiques des principalesespèces de poissons du plateau continental des Iles Kerguelen.Cybium 5,19–32.

Duhamel, G., and Pletikosic, M. (1983). Donnés biologiques sur lesNototheniidae des Iles Crozet. Cybium 7, 43–57.

Fischer, W., and Hureau, J.-C. (1985). FAO species identification sheetsfor fishery purposes, Southern Ocean, CCAMLR Convention Areas48,58 and 88. Vol I and II. (FAO: Rome.) 471 pp.

García de la Rosa, S. B., Sánchez, F., and Figueroa, D. (1997).Comparative feeding ecology of Patagonian toothfish (Dissostichuseleginoides) in the southwestern Atlantic. CCAMLR Science 4,105–24.

George, E. L., and Hadley, W. F. (1979). Food and habitat partitioningbetween rock bass (Ambloplites rupestris) and smallmouth bass(Micropterus dolomieui) young of the year. Transactions of theAmerican Fisheries Society 108, 253–61.

Goldsworthy, S. D., He, X., Lewis, M., Williams, R., and Tuck, G.(2001). Diet overlap and prey consumption among Patagoniantoothfish, seals and seabirds around Macquarie Island. MarineEcology Progress Series 218, 283–302.

Diet of Patagonian toothfish 57

http://www.publish.csiro.au/journals/mfr

Gon, O., and Heemstra, P. C. (1990). ‘Fishes of the Southern Ocean.’(JLB Smith Institute of Ichthyology: Grahamstown, South Africa.)462 pp.

Hannson, S. (1998). Methods of studying fish feeding: a comment.Canadian Journal of Fisheries and Aquatic Sciences 55, 2706–7.

Kock, K.-H. (1992). ‘Antarctic Fish and Fisheries.’ (CambridgeUniversity Press: Cambridge.) 359 pp.

Konforkin, I. N., and Koslov, A. N. (1992). Prespawning and spawningbiology of Patagonian toothfish (Dissostichus eleginoides) aroundSouth Georgia (Subarea 48.3). Document WG-FSA–92/13.(CCAMLR: Hobart, Australia.) 16 pp.

Manly, B. F. J. (1991). Randomization and Monte Carlo methods inbiology. (Chapman and Hall: New York.) 281 pp.

Mantel, N. (1967). The detection of disease clustering and a generalizedregression approach. Cancer Research 27, 209–20.

Mora, S., Salas, J. C., and Oyarzun, C. (1986). Antecedentes sobre lafauna acompañante en la pesquería de Dissostichus eleginoides(Smith, 1898) en la VIII Región. Biota 1. 72 pp.

Tarverdiyeva, M. I. (1972). Daily food consumption and feedingpatterns of the Georgian cod (Notothenia rossi marmorata Fisher)and the Patagonian toothfish (Dissostichus eleginoides Smitt) (Fam.Nototheniidae) in the South Georgia area. Journal of Ichthyology12, 684–92.

William, R. (1988). The nearshore fishes of Macquarie Island. Papersand Proceedings of the Royal Society of Tasmania 122, 233–45.

Williams, R., and de la Mare, W. K. (1995). Fish distribution andbiomass in the Heard Island Zone (Division 58.5.2) CCAMLRScience 2, 1–20.

Williams, R., and McEldowney, A. (1990). A guide to the fish otolithsfrom waters off the Australian Antarctic Territory, Heard andMacquarie Island. ANARE Research Notes No. 75.

Zhivov, V. V., and Krivoruchko, V. M. (1990). On the biology of thePatagonian toothfish, Dissostichus eleginoides, of the Antarctic partof the Atlantic. Journal of Ichthyology 30, 142–6.

Manuscript received 15 May 2000; revised 20 December 2000 and 9July 2001; accepted 7 November 2001