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ICES PAPER MARINE MAMMAL CTTEE C.M.l989/N:ll

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FEEDING HABITS OF NORTHEAST ATLANTIC HARP SEALS PHOCA GROENLANDICA ALONG THE SUMMER ICE EDGE OF THE BARENTS SEA

1 2 3

C h r i s t i a n Lydersen , Lars Anker Angantyr , Øystein Wiig , and Torger Ø r i t s l a n d

I n s t i t u t e of Marine Research,

P. O . Box 1870 Nordnes, N-5024 Bergen, Norway

1 P r e s e n t a d d r e s s : U n i v e r s i t y of Oslo, I n s t i t u t e of Biology, P. O . Box 1051 Blindern, N-0316 Oslo 3 , Norway

i P r e s e n t a d d r e s s : Greenland F i s h e r i e s Research I n s t i t u t e , Tagensvej 135, DK-2200 Copenhagen N , Denmark

P r e s e n t address: Norwegian P o l a r Research I n s t i t u t e , P. O. Box 158, N-1330 Oslo Lufthavn, Norway

ABSTRACT

Stomachs from 58 harp s e a l s Phoca g r o e n l a n d i c a from t h e n o r t h e r n p a r t s of t h e Barents Sea were c o l l e c t e d between August 20 and September 5

1987. F i f t y s i x of t h e stomachs c o n t a i n e d i d e n t i f i a b l e c o n t e n t s . The amphipod Parathemisto l i b e l l u l a was t h e most common food items, found i n 98% of t h e s e a 1 stomachs and c o n s t i t u t e d 57.9% of t o t a l volume.

Fishes were found t o be t h e second most i m p o r t a n t p r e y group, with a r c t i c cod Boreogadus s a i d a a s t h e dominant s p e c i e s followed by Nybelin's s c u l p i n T r i g l o p s n y b e l i n i and Greenland h a l i b u t R e i n h a r d t i u s hippoglossoides. Decapods, mainly Pandalus b o r e a l i s , were a l s o common a s prey of harp s e a l s . No s e x o r age r e l a t e d d i f f e r e n c e s i n c h o i c e of food were found. From knowledge of d e p t h s a t l o c a t i o n s s e a l s were c o l l e c t e d and precence of f r e s h b e n t i c f i s h i n t h e s e a 1 stomachs, harp s e a l s were assumed t o be a b l e t o c o l l e c t food a t d e p t h s below 300 m.

Introduct lon.

The harp seal Phocagruenlandica i s an important species of the marine ecosystem i n the Barents Sea. I ts impact on the system i s dependent on the size of the population and i t s food habits. No recent estimate of the populatlon size exist. In 1978 the population was estlmated to number 800.000 seals w i t h an annua1 increase of about 5% (Benjaminsen 1979).

During the early 1980's the population size was believed to exceed 1 mill, while the population size the last years probably has decreased (Ulltang and 0ien 1 988).

Markussen and 0 r i tsland ( 1985) estimated a population of 1 mill. harp seais in the Barents Sea needing 1.4 to 4.2 mill, tons of food every year depending on prey organism, Know ledge of the feeding habits of harp seals is, however. scarce. Most of the available information i s based on material collected during the breeding season (Sivertsen 1941, Myers 1959,

Sergeant 1973, Bowen 1985)) and most of the quanti tative information originates from the northwest Atlantic stock. The present paper reports on feeding habits of harp sea1 collected along the summer ice edge of the

I Barents Sea.

Material and rnethods.

Stomachs of 58 harp seals were co1 lected at the ice edge in the northem parts of the Barents Sea (790 1 5'-79055' N, 27035'-4450'E) i n the period from August 20 to September 5 1987. The seals were shot in the water and imrnediately dissected on the deck. The stornach contents were rinsed through a sleve w i t h mesh size 1 mm and then frozen. Teeth and sex organs were sampled for age detennination and evaluation of stage of sexual

niaturity. Water depth at most of the hunting sites was recorded using the echo-sounder onboard the research vessel.

In

the lab the stomach contents were sorted to the lowest possible taxionomic level. Total wet weight of the contents and volume percentages ( V ) of the major prey groups were registered. A non-trace frequency of occurrence ⁽⁰⁾ was calculated for the main prey groups, accordlng to Bigg and Perez ( 1 985). Prey represented by trace eiements only, l i k e beaks of squid and otol ithu of f ish, were excluded from these calculat ions and were only examined for qualitative purposes. In order to evaluate the relative importance of dt f ferent preys, an abundance factor (A) was calculated as:

A = V x O .

Sizes of testis or presence of corpora lutea or albicantia in ovaries were used to evaluate the stage of sexual maturity. The age determination was performed reading growth lairs in the dentine of cross sections of the canine teeth.

Resul

ts.

Two of the collected stornachs were empty. The mean drained wet

weight of the rest of the stornachs was 273 ⁱ 2539 (SD) w i t h a range from 0.1 - 13269. The main prey groups and their relative contribution to the diet of the harp seals are shown i n Table 1.

I t appears that amphipods i s the most important prey group. The

amphipod group consists almost entirely of Parathemisto //be//u/a (Tab.2).

Fish consti tute the second most important prey group, and i s dominated by polar cod (Bofeogadussaaida ). More benthic fish like Greenland halibut

( Reinhardtius hf&wg/ossoides and Ny be l i n's scu l p i n ( T f k ~ / ~ p s nybe/ini) were also common. The largest fract ion of the f ishbgroup consisted of

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partly dlgested fish whlch was not ldenttfted t o specles level. Thls fractlon i s not included i n Table 2 and contstitutes 63.7% of the fish volume In Table 1. SOme specles were Only found as traces In single sea1 stomachs and were excluded in Table 2. They Include the copepode

Pafeuccnc7etag/acia/is, the isopode /datt?agranu/ma, and the bivalves Astarte e//iptica and L eda pernula.

The harp seal sample conslsts of 23 females and 35 males. The mean age o f females was 7.21 4.7yrs (range 1 - 16 yrs) and of males 8.11 4.5yrs (range 1 - 15 yrs). In order t o test for age and/or sex related dlfferences i n dlet, we grouped the stomach contents or adult males (N=23,+2 empty stomachs), subadult males (N= 121, adult females (N= l l), and subadult females (N=12) respectlvely (Flg. I ) . No slgnlflcant dlfrerences In dlet were found between males and females (~2=0.190, p=0.66), or between adul t s and subadul t s (~2=0.365, p-0.55). W t t h l n the 4 groups in ~ i g . I , subadult females and adult females were dlfferlng the most in cholce of food. Thls d l f ference was, however, not slgnlf lcant (~2=2.3 l 8, p=O. 1 3 ) .

The mean depth recorded where stomachs contalned freshly eaten benthlc f lsh (N= 1 2) was 256m I 6 1 m, w l t h a maxlmum recorded depth of 340m.

Durlng summer perlods large herds of harp seals are normal l y observed

In the open waters between the coast of Flnmark (northem Norway) and the Svalbard

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Franz Josef Land archlpelagoes. Durlng our f l e l d work,

a

l o t of ef f o r t

was

used trylng t o detect some of these herds in order to

lncrease the posslbllity of gettlng a large sample slze. A l i attempts In

detecting herds of harp seals fal led t o succeed. Along the ice edge,

however, in the northern PartS of the Barents 5ea, single individuals and scattered groups of harp seals were observed, and finally the sampling was concentrated in this area.

Bigg and Perez ( 1 985) proposed a modified volume method which

incorporates measure of volume and frequency of occurrence of different food i tems i n order to assess marine mamma1 food habi ts. The abundance factor calculated i n the present work i s a modification of that method. The non-trace frequency of occurrence i s incorporated i n order to moderate the effect on the volume precentage

of

one large prey organism i n a single stomach.

The inf ormat ion on diets o l harp seals i s scarce. Myers ( 1 959) found f lsh remains w I th herrings ( Clupea harengus) as the dominant species i n a sample of 1 85 harv seals from Canadian waters. Sergeant ( 1 973) states that pelagic fish, especially capelin (Ma//otus vi//osus). plus pelagic and benthic crustaceans were the most important preys. He collected some harp seals summering in the cold waters between northwest Greenland and the Canadian arctic archipelago. A l though smal l sample

sl

ze, these seals were mainly eating arctic cod and various crustaceans including R

/jbe//u/a. Bowen ⁽ 1 985) has analysed aval lable data on f eeding of the ,

northwest Atlantic harp sea1 population and concludes that they mainly

f eed on pelagic f l shes dominated by capel i n and arctic cod, andton a variety of invertebrates where euphausids and shrimps are the most dom i nant.

Of the Information on diets of the northeast Atlantic populat.t'bh' Smirnov ( 1 924) states without any further information on nurnb4eof seals, age, sex etc.,that pelagic crustaceans and polar cod followed by capelin,_&rring andpaagic molluscs are-the most important preys11- ^-

Sivertsen ( 1 941 1 found that ysung of the year harp seals after weaning starts feeding on pelagic crustaceans, especial ly the euphausids

7-hysanoessa Mermts and Thysanoessa raschr'fand the am ph i pod Anmyx nugax. Yearl ings had a dif ferent diet including capel i n and shrimp species Ilke 5p1;rontocarts turgida and Grangon craflgo~ Information on adult dlets were based on 2 anlmals w i t h contens In their stomach containing 7:

raschii and 6: crangn.

The resuits

or

the present paper seem to correspond t o the resuits of the analyses of harp seals from the cold waters between Greenland and Canada reported by Sergeant ( 1973).

One slngle haro sea1 was shot In the southern Barents Sea, but was excluded from our sample slnce collected dlstantly from the rest of the sample. ~ h i s seai, however, had eaten capel in, lndlcatlng thts specles as

a

potentlal prey for harp seals

In

the Barents Sea.

I t seems when comparlng results from lnvestegatlons of stomachs from ^l dlfferent sea1 specles foragelng, a t ieast partly, pelaglcally In assoclatlon ^l l wlth the ice edge both in European and Canadlan Arctic, that pelagic

~

crustaceans lncludlng R /rDe//u/a and arctic cod are the most slgnif lcant preys (Lowry e t al. 1 980, Bradstreet and Cross 1 982, G jertz and Lydersen

1 986, Smith 1 987, Lydersen e t al. 1 989). ⁱ

l

Sergeant ( 1 973) suggests dlvlng abilltles of harp seals down to 250 m based on reglstrations of fresh bethlc I l s h in stomachs of seals collected

In

areas of known depths. We

co1

lected haro

seals contalnlng

fresh

benthlc

f lsh on depths deeper than 300m. R hfppg//ossoldes was one of the?

specles

we

considered benthlc. Thls specles Is, however, found t o have a bathypelagic mode of -11 fe (Chumakov. 1 9691 f eedlng lin-the water

column

(Haug and ~ u i i iksen 1982)., and might therefore seem unsuited as indicator of foraging depths of harp seals. Most of the R h/;a,?ag/i7ssaides in the Svalbard area are however, caught on depths below 200m (Gode and Haug

1987) and Chumakov ( 1969) states that R h@pag/assoides sink to the bottom during day time which is when most seals were collected. Thus the present study indicates that the harp sea1 might feed on depths down to at least 300m.

As a conclusion, amphipods,mainly P /ibe//u/' were found to be the most significant food item of harp seals feeding along the ice edge in the northern parts of the Barents Sea. Fishes were found to be the second most important prey group, w i t h arctic cod as the dominant species followed by

T v e / # ? / and R h@,mg/ossuides. No signi ^f icant sex or age related

differences in choise of prey were found. The seals might be able to search for food at depths down to ^300m.

Aknowledgement.

This project was f inanced by "Fondet for Fiskeleting og Forserk" through the Institute of Marine Research, Directorate of Fisheries in Bergen, Norway. We would like to thank Yu. I. Nazarenko and the crew onboard

"Veslekari" for a l l help rendered us during the field work.

Ref

erences.

BENJAMINSEN, T. 1979. Pup productlon and sustalnable y l e l d of Whlte Sea harp seals. Fisk. Dir. Skr. Ser. HavUnders. 16: 5 5 1-559.

BIGG,

M. A., and PEREZ, M. A. 1 985. Mod1 fled volume:

a

frequency

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volume method t o assess marine mamma1 food habl ts. /n Marine mammals and f lsherfes. fdftedby J. R. Beddlngton, R. J. H.

Beverton and D. M. Lavlgne. George A l len & Union. London. pp 277-283.

BOWEN, W. D. 1985. Harp seal feedlng and lnteractlons w i t h commercfal fisheries i n the north-west Atlantic.

/n

Marine mammals and flsherles. Edftedby J. R. Beddlngton, R. J. H. Beverton, and D.

M. Lavlgne. George A l len & Unw in. London. pp. 1 35- 1 52.

BRADSTREET, M. S. W., and CROSS, W. E. 1 982. Trophlc r e l a t lons a t high arc t l c ice edges. Arctic. 35: 1 - 1 2.

CHUMAKOV, A. K. 1 969. The Greenland hal l but ( Relnhardtlus

h~~~og/ossofdes(Walbaum)) in the Iceland area - the hallbut flsherles and tagglng. J. Ichthyol. (Vopr. Ikht.) 9: 909-91 2.

GJERTZ, I, and LYDERSEN, C. 1 986. The rlnged sea1 ( Phoca hfspida) spring d l e t In northw estern Spt tsbergen, Svalbard. Polar Research 4:

53-56.

GODB, O. R., and HAUG, T. 1987. Migration and recruitment t o the commercial stock of Greenland hai ibut, Keinri;rBfius

h~;apag/ossaides( Wal baum), in the Svalbard area. FiskDir. Skr.

Ser. HavUnders., 18: 3 1 1 -328.

HAUG, T., and GULLIKSEN, B. 1982. Size, occurrence, growth, and food of

Greenland halibut, R~inhardtiush~;op~~~as~aide~(Walbaum~ in coastal waters of western Spi tzbergen. Sarsia 68: 293-297.

LOWRY, L.F., FROST, K., and BURNS, J. J. 1 980. Variabi l i t y in the diet of ringed seals, P h ~ ~ a h i ~ p i d ' , in Alaska. Can. J. Fish. Aquat. Sci.

37: 2254-226 1.

LYDERSEN,C., WERTZ, 1, and WESLAWSKI, J. M. 1989. Stomach contents of autumn-f eeding marine vertebrates from Hornsund, Svalbard.

Polar Record. 25: 107- t 1 4.

MARKUSSEN, N. H., and ORITSLAND, N. A. 1985. Grønlandselens matbehov 11 1.

Videreutvikling og anvendelse av simuleringsmodellen SEAERG. Biologisk I n s t i t u t t . Avd. f r o generell fysiologi.

Universitetet i Oslo. 6 1 pp.

MYERS, B. J. 1959. The stomach contents of harp seals ( Phoca groenlandica Erxleben) from the Magdalen Islands, Quebec. Can. J. 2001. 37:

378.

SERGEANT, D. E. 1973. Feedlng, grow th, and productlvl ty of northwest Atlantic harp seals ( Pag~i/usgmen/andicus). J. Fish. Res.

Board Can. 30: 17-29.

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P-

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SI VERTSEN, E. 1 94 1. On the biology of the harp seal Phocc7 groen/andlca Erxl. Hvalrådets Skr. No. 26.

SMIRNOV, N. 1924. On the eastern harp-sea1 Phoca (Pagophoca) groenlandlca var. oceanlca Lepechin.. Troms0 Museums Arshefter 47 No. 2.

SMITH, T. G. l 987. The rlnged seal, Phoca hlspfda, of the Canadlan western arct

lc.

Biil l. Flsh Res. Board Can. No. 2 1 6.

ULLTANG, O., and N. 0IEN. 1988. Bestandsutvikllng og status for gronlandssel og klappmyss, Fiskets Gang 6/7: 8- l 0.

Table t . Distribution of major groups of preys from stomachs of harp seals collected i n northern parts of the Barents Sea auturnn 1987.

Voiume percent ( V ) referres t o volume of prey group compared t o total volume of all preys. Occurrence (0) i s the number of seals w i th prey group i n stomach cornpared t o the total nurnber of seals.

The abundance factor (A) i s V x O.

Prey group Volume percent Occurrence Abundance factor

( V ) ( 0 ) (A)

Fish 28.0 0.70 19.6

Amph i pods 57.9 0.98 56.7

Decapods 13.1 0.66 8.6

Cephalopods 1 .O 0.29 0.29

Table 2. Distribution of prey species within each

main

ptey group from stomachs of harp seals csllectedl in northern parts of the Barents Sea autumn 1987. Volume percent ( V ) referres to volume of one prey species compared to total volume of all preys.in that group Occurrence

(O)

is the number of seals with prey species in stomach compared to the total number of seals. Abundance factor (A) is V

x

0.

Prey species Volume percent Occurrence Abunduice

frctor

(V)

( 0 )

(A)

Fish:

Boteogadus saida 56.1 0.36 20.2

Triglops nybelini 23.2 0.27 6.3

Reinhardtius hippoglossoides 1 6.9 O. 18

3

.O

Other fish 3.8 0.12 0.5

induding:

Sebastes marinus

Hippoglossoides platessoides Leptoclinus maculatus

Benthose ma glaciale Liparis sp.

Arnphipods:

Parathemisto libellula 99.6

Gammarus spp. 0.2

Other amphipods 0.2

Deapods

Pandalus boreal 1s 95.0 Sablnea septemcarclna tus 2.0

O t her decapods 3.0

includlng:

Lebbeus polaris Pasiphaea tarda Ce phrlopods Gonatus fabrlcll Oc t opods

including:

Bathypolipus arcticus Elodone cirrhosa

Fig.1. Results from analysis of -stomach contents a f harp seals of different age and sex groups collected i n the Borents Sea summer 1987.