Stomach samples from 59 harp seals have been examined for a qualitative and quantitative analysis of their feeding habits in the Barents Sea. The most frequent food items were the amphipod Parathemisto libellula (55% vol.), fish (34% vol.) and the decapod Pandalus borealis (9% vol.). Of the fish polar cod (Boreogadus saida), Nybelin's sculpin (Triglops nybelini) and Greenland halibut (Reinhardtius hippoglossoides) made up the major part. Remains of the squid Gonatus fabricii were present in 29% of the stomachs, but made up only 1% of the volume on an average

Angantyr, Lars Anker

HSN Open Archive

Feeding habits of northeast atlantic harp seals (phoca groenlandica) in the Barents Sea, August - September 1987

NORA - Norwegian Open Research Archives

l i I I tute of Marine , N-5024 Bergen, Norway ÿ apport SPS 8815 30 April 1988 FEEDING HABITS OF NORTHEAST ATLANTIC HARP SEALS (Phoca groenlandica) IN THE BARENTS SEA, AUGUST-SEPTEMBER 1987. Må ikke siteres uten etter av- tale med. Sj~pattedyrseks jonen , Havforskningsinstituttet,Bergen Not to be cited without refer- ence to the Sea Mamma1 Section, BY Institute of Marine Research, Bergen. LARS ANKER ANGANTYR Institute of Marine Research. P.O. Box 1870, N-5024 Bergen, Norway. ABSTRACT : STOMACH SAMPLES FROM 59 HARP SEALS HAVE BEEN EXAMINED FOR A QUALITATIVE AND QUANTITATIVE ANALYSIS OF THEIR FEEDING HABITS IN THE BARENTS SEA. THE MOST FREQUENT FOOD ITEMS WERE THE AMPHIPOD Parathemisto libellula (55% vol.), FISH (34% vol.) AND THE DECAPOD Pandalus borealis (9% vol.). OF THE FISH POLAR COD (Boreogadus saida), NYBELIN'S SCULPIN (Triglops nybelini) AND GREENLAND HALIBUT (Reinhardtius hippoglossoides) MADE UP THE MAJOR PART. REMAINS OF THE SQUID Gonatus fabricii WERE PRESENT IN 29% OF THE STOMACHS, BUT MADE UP ONLY 1% OF THE VOLUME ON AN AVERAGE. INTRODUCTION: Repeated invasions of harp s ea l s  on the  Norwegian coast  i n  t he  1970- i e s  and 1980-ies have caused concern about the  ecological  r o l e  of the  harp s ea l s  i n  the  Barents Sea. Previous attempts by the  I n s t i t u t e  of Marine Research, Bergen, t o  sample feeding harp s e a l s  i n  the  Barents Sea i n  1981 and 1983, were not succesful, mainly because of f a l i u r e  t o  develope techniques f o r  capturing s ea l s  i n  the  water. In  another attempt i n  August-September 1987 stomach contents were col lected from 59 harp s ea l s  i n  the  northern Barents Sea e a s t  of Svalbard (Wiig, 1987) These samples have been thoroughly examined and the  r e s u l t s  a r e  summarizes i n  t h i s  paper. I MATERIAL AND METHODS: l I Between august 20th and september 5th  a t o t a l  of 59 harp s ea l s ,  1 bearded sea1 and 4 ringed sea l s  were caught i n  the  a rea  e a s t  of Svalbard ( 7 8 ' ~  - 8 0 ' ~ ~  2 0 ' ~  - 5 0 ' ~ )  . A l l  s e a i s  were shot  i n  the  water. The s e a l s  were dissected immediately a f t e r  capture t o  minimize the  degradation of the stomach content. Stomachs were opened, r insed and the  content frozen f o r  l a t e r  examination. Lower jaws were col lected f o r  agedetermination and female reproductive organs f o r  determination of the reproductive s t a tu s .  A l l  s e a l s  were weighed and measured f o r  assessment of condition. These data have not been analyzed ye t ,  but  a l l  s ea l s  appered t o  be i n  good condition. The blubber thickness was between 3 and 6 cm i n  most s ea l s  and only three  s e a l s  had less than 3 cm of blubber measured over the  sternum. I n  the  laboratorium the drained stomach content was weighed. (The contents were drained i n  the  f i e l d  t o  minimize the  volume of the  samples). This means t ha t  only the so l i d  material  is weighed and t h i s  weight should only be seen a s  a minimum. The thawn sample was then careful ly  examined, looking through the  whole material under a dissect ing microscope. A l l  f i s h ,  crustaceans and squids were iden t i f i ed  o r  kept f o r  l a t e r  iden t i f i ca t ion .  A l l  o t o l i t h s  were kept. l The contribution of a l l  major groups were estimated a s  a volume %. l This is  ea s i e r  than t rying t o  seperate the  material  f o r  weighing, and l assuming a density of 1.0 fo r  a l l  groups the vol.  % can be d i r ec t l y  converted t o  biomass. When re fe r r ing  t o  "vol. %" i n  the  t e x t  and the  tab les  it means: the  average of a l l  the  volume percentages f o r  t ha t  group. "% of biomass'' means: the  % t ha t  group make up of the  toa1 biomass (calculated by adding the weights of a l l  the stomach contents) .  The weight of each group is  estimated from the vol.  % of the group fo r  a l l  stomachs seperately and then summarized. (Density of a l l  groups = 1 .0 ) .  l I ! Stomachparasites were collected f o r  l a t e r  iden t i f i ca t ion .  This material  w i l l  be analysed by B. Berland, Zoological Laboratorium, 1 University of Bergen. RESULTS AND DISCUSSION: The average weight of the  contents of a l l  stomachs was 259 g. Five stomachs contained less than 10 g of food. The average without these almost empty stomachs was 283 g. Since the  content had been drained before weighing i n  the  lab  these averages w i l l  underestimate the  contents i n  the stomachs. Therefore they should only be taken a s  a minimum. The da ta  can be looked a t  i n  d i f fe ren t  ways (see  tab le  1 + t ab le  2 ) ,  but i n  any case the dominating food items a r e  the  amphipod Parathemisto l i b e l l u l a ,  the fishspecies: polar cod (Boreogadus s a ida ) ,  Nybelin's sculpin (Triglops nybelini)  and Greenland hal ibut  (Reinhardtius hippoglossoides), and the decapod Pandalus boreal is .  The da ta  have not yet  been looked a t  f o r  eventual e f f e c t  of area ,  sex and age of the  sea l s .  FISH : On an average 34.4% (vol. ) of the stomach content was "fish" ( f resh  f i s h ,  fishremains and o t o l i t h s ) .  The f resh  f i s h  found i n  the  stomachs were dominated by polar  cod (6% of t o t a l  biomass, 7% vol.  and 50.6% of no. of f resh f i s h )  and Nybelin's sculpin (3% biomass and vol. ,  28.3% of of no. f resh f i s h ) .  A l a rge  number of young Greenland ha l ibu t  were present i n  some stomachs (2% biomass and vo l . ,  14.5% of no. of f resh f i s h ) ,  see  Table 1 + Table 2. I f  one looks a t  the o to l i t h s  (see  tab le  2) the  dominance of polar  cod becomes even greater  - 65.8% of the  number of f i s h  estimated from the  o to l i t h s .  Nybelin's sculpin contributed with 10.7% and Greenland ha l ibu t  with 6.4% of the  f i s h  estimated from the o to l i t h s .  Otol i ths  of Lipar is  spp. were found (8.7% of o t o l i t h s ) ,  but  s ince no other  remains of these species were found it is d i f f i c u l t  t o  assess  the  s ignif icance of these species a s  a source of food of harp s ea l s .  A small number ( l e s s  than 2% vol.  and biomass) of redf i sh  (Sebastes marinus), long rough dab (Hippoglossoides platessoides) and capel in  (Mallotus v i l losus)  were present. A 1 1  o t o l i t h s  (2.2%) from the capelin were found i n  one stomach. This sea1 was caught fu r ther  south (74 '~ .  3 0 ' ~ )  than the  r e s t  of the  sea l s .  AMPHIPODS: Parathemisto l i b e l l u l a  was present i n  95% of the  stomachs and contributed on an average 55% of the volume. It represented 58% of the  t o t a l  biomass examined. There was no s ign of other  species than P. l i b e l l u l a  among the  many Parathemisto examined. Very few other  amphipods were present (less than 0.2% v o l . ) ,  but a few gammarids and one isopod (Idotea  granulosa) were found. DECAPODS : Pandalus boreal is  made up the  major pa r t  (8.8% vol. and 12.6% of biomass) of the decapods found i n  the samples. Other decapods made up only on an average 0.5% of the volume. Among these Sabinea septemcarinatus (0.2% vol . )  was the  most dominating species. CEPHALOPODS: Remains of cephalopods were found i n  31% of the stomachs. The squid Gonatus f a b r i c i i  was present i n  29% of the stomachs, but made up only 1% of the  volume i n  average. Of the t o t a l  biomass examined it made up only 0.7%. Remains of the octopus Bathypolypus a r t i cus  was found i n  2 stomachs (one might have been Elodone c i r rhosa) .  BIVALVES : I Two stomachs contained remains of bivalves. These might have been secondary material from f i s h  eaten by the sea l s .  Anyway they only made up 0.03% of the volume. CONCLUSIONS: From the samples collected i n  1987 it seems tha t  polar  cod and the  amphipod Parathemisto l i b e l l u l a  a r e  very important food items f o r  Northeast Atlantic harp s ea l s ,  making up a t  l e a s t  60% of the  vol. and t o t a l  biomass. In  the samples from 1983 only amphipods (Parathemisto sp . )  were found (n=8, see  enclosure 1). Polar cod and Parathemistos sp. has a l s0  been found i n  stomachs from harp s ea l s  i n  the  Northwest Atlantic.  Samples from West Greenland (unpub. data)  and from Eastern Canada (Finley and Gibb, i n  press) have contained la rge  quant i t i es  of polar cod and Parathemisto sp. I n  our study only two commercially f ished species were found i n  s ign i f i can t  quant i t i es .  This was the decapod Pandalus borea l i s  (8.8% vol.  , 12.6% of biomass) and young Greenland ha l ibu t  (2.1% vol. , 1.8% of biomass). Remains of Lipar is  spp. (8.7% of o to l i t h s )  and the  squid Gonatus f a b r i c i i  were found i n  many stomachs, but contributed very l i t t l e  t o  the  volume o r  biomass (less than 1%). Therefore i t  is hard t o  say how important these species are .  It must be emphasaized t h a t  the  conclusions i n  t h i s  paper a r e  based on a r e l a t i ve  small number of s&ples from a l a rge  area. More samples a r e  needed before one can get  a good idea of the  feeding hab i t s  of harp s ea l s  i n  the  Barents Sea. More information about the  d i s t r i bu t ion  and population s i z e  of the  harp s ea l s  i n  the  Barents Sea a r e  a l so  needed before one can make calculations on the  t o t a l  consuption of the  population. Information about the da i ly  food intake of the  s e a l s  a r e  a l s0  needed. TABLE 1. DESTRIBUTION OF THE FOOD ON MAJOR GROUPS OF ANIMALS: FISH : Boreodadus saida Triglops nybelini  Reinhardtius hippo. Sebastes marinus Hippoglossoides p l .  Mallotus v i l losus  Other f i s h  Unknown 1 X of % vol. 7.0 % 2.9 % 2.1 % 0.2 % 2 Fish = 100 % 20.3 % 8.4 91 3 % of biomass 6.2 % 3.3 % 1.8 0.1 % - FISH TOTAL 34.4 % 99.9 % 27.7 % CRUSTACEA: Parathemisto l i b e l l u l a  54.9 % Gammaridae spp. 0.1 % Other amphipods 0.1 % Pandalus borea l i s  8.8 % 12.6 % Sabinea septemcarinatus 0.2 % Other decapoda 0.3 % ...................................................................... CRUSTACEA TOTAL 64.4 % 71.3 % ...................................................................... CEPHALOPODA: Gonatos f a b r i c i i  1.0 % Octapoda spp. 0.2 % CEPHALOPODA TOTAL 1.2 % 0.9 % BIVALVIA TOTAL 0.03 % - ...................................................................... "X of % vol." is  the mean of how much the species contributed t o  the  volume i n  g. Column 2 shows the d i s t r ibu t ion  i n  the  group "fishtt  when f i s h  = 100 g. Column 3 sh8ws the % of each group of the  t o t a l  biomass. TABLE 2. COMPOSITION OF THE FISH CONSUMED BY HARP SEALS. 1 2 3 FRESH FISH FISH FROM OTO. F. FISH + OTO. Polar cod (B. sa ida)  50.6 % 65.8 % 64.0 % Nyb. sculpin (T. nyb.) 28.3 % 10.7 % 12.8 % G. ha l ibu t  (R .  hippo. ) 14.5 % 6.4 % 7.4 % Redfish (S. marinus) 1.8 % 2.0 % 2.0 % L . r .  dab ( H .  p l a t e s . )  1.8 % 1.3 % 1.4 X Capelin (M.  v i l l o sus )  0.0 % 2.2 % 1.9 % Lipar is  spp. 0.0 % 8.7 % 7.7 % Other f i s h  Unknown TABLE 2. COMPOSITION OF THE FISH CONSUMED BY HARP SEALS I N  THE BARENTS SEA AUGUST-SEPTEMBER 1987. Column l shows the  composition of the f resh  f i s h  found i n  the  stomachs. Column 2 shows the composition of the  number of f i s h  calculated from the o to l i t h s .  Column 3 shows the  com- posi t ion calculated by adding the  number of f r e sh  f i s h  and the  number calculated from the o to l i t h s .  TABLE 3. LIST OF SPECIES FOUND IN STOMACHS OF HARP SEALS CAUGHT IN THE BARENTS SEA AUGUST-SEPTEMBER 1987. FISH : Polar cod (Boreogadus saida) Long rough dab (Hippoglossoides platessoides) Spotted snake blenny (Leptoclinus maculatus) Sea snails (Liparis spp.) Capelin (mallotus villosus) Greenland halibut (Reinhardtius hippoglossoides) Redfish (Sebastes marinus) Nybelin' s sculpin (Triglops nyb&ini) CRUSTACEA: Gammaridae sp. Parathemisto libellula Idotea granulosa Lebbeus polaris Pandalus borealis Pasiphaea tarda Sabinea septemcarinatus CEPHALOPODA: Bathypolypus arcticus Elodone cirrhosa (unsertain det.) Gonatus fabricii MOLLUSCA : Astarte elliptica Leda pernula ENCLOSURE 1. SAMPLES FROM THE BARENTS SEA 1981 AND 1983. BARENTS SEA AUGUST 1981. 1 harp sea1 (male, I22 cm Pong, 53 kg) was caught 17. august 1981. The stomach was empty. 8 harp s ea l s  were caught e a s t  of Svalbard and south of "Kvi t~ya" (80' N 31' E) , 11. - 18. september 1983. When the stomachs were examined three  were empty and the  rest contained 4 ,  3 ,  3 ,  3 and 6 d e c i l i t e r  of amphipods, respectively (Parathemisto sp . ,  T. Øritsland,  probably Parathemisto l i b e l l u l a ) .  no. date  sex length weight volume content amphipoder amphipoder amphipoder amphipoder amphipoder - 

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Feeding habits of northeast atlantic harp seals (phoca groenlandica) in the Barents Sea, August - September 1987

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