This paper not to· be cited without prior refererice to ihe autliors
:mte~ation3.J. Cciuneil for~~~~\::l";··'~:;U.~.l!~:I'"
. . C:M. 1996/N: 5
the Exploration oftbe Sea D 1b' lot h ("' I<
Marlße M~als Committee
-
~
_.
~...
j
•
,
•
"
,
•
•
'..
"
."
,
' •• '
•
POST WEANING VARIATIONS IN BODY CONDITION AND FIRST
INDEPENDENT FEEDING OF NORTHEAST ATLANTic HARP
(PHOCA GROENLANDlCA) AND ~O.()DED (CYSTOPHORA CRlSTATA)
.
SEALS
".
•
.
.
"
,
,
,
'
.
.
.
.
.
Tore Hatig*, Kjell T. Nilssen*, Per E. Grotries**, Lotta Liridblciin*
Kjellqwist*
•
"-'<,'
and Sten A.
* Norwegiait InStitute afFisheries arid Aquaeulture, PO Box 2si 1, N-9002
Troms", Norway
.... .
. ..
. .
**NorWegi~ College ofFishenes Science, University ofTromS", N-9037 Trams", Norway .
ABSTRACT
e
,,".-
Daia were eollected forharp s~s Pho~a gToellltindica ofthe Barents Sea (or the "Bast lee")
stock in 1990-1995, aitd froffi luirP arid hooded se3ls Cysiophora cristata betongißg io the
Greenland Sea (or "West lee") stockS in 1995, arid questions eoneerning various eeologiCal
aspeCts of the wly life. stages of the two species were addressed. Pups of both harp .änd
hooded seals were able to firid prey and feed independeritly. shörtly after weanirig. In the EaSt
lee the first food. of harp sCa! pups waS mainly euphausüds ("kiill") ThystiJloessa sp. arid
amphipods of the
Parathemisto. Parathemisto sp.; particularly P. /ibe/lu/a, dorninated
the diet of hoth harjJ. aitd höcided seal pups in the West lee, but the diet also contamed
of minor iInportance as food for seal
sympagic amphipods of the genus Gammarus. Krill
pups in the West lee. The change in body conditiori ofEast lee hafp seal pups froffi we3nirig
(mid March) to June indicated that considerable amounts of blubber energy, deposited duIiIlg
suckling, were mobilized.. This suggests that the wly food int3.lce was insufficient to meet the
energy requirements cf the weaned pups faemg the tränSition from life on the pack ice to
exiStence in the open wäter environment. The patterns of poor spring älid early sumnier body
eoridition, followed by. a subsequent räpid improvement during late summer and iliJriJffin
seemed to occur riot only amcingst pups-of-the-year, but 3.Iso arriongst har}> seats in therr
seeond arid third years oflife.
genus
was
2
-
.
INTRODUCTION
Three stocks ofharp seals Phoca groelllandica irihabit the North Atlalitie Ocean (Sergeant
1991). Two stocks are distributed in the riortbeaSt AthÜltie, with whelpirig and moUltirig iaking
place offthe east cOaSt ofGreenlarid
(the Greeniaricl
Sea or West lee stock) and in the White
.
. ' , '
Sea (the Barents Sea or Ea8t lee st~ek), respectiveiy (see Fig. 1). Stlldies orihe ajuu,iaI eycle of
distribution, nutrition, condition arid n~produCiion ofBarents Sea harp seals were carried out in
the pericid 1990-1994 (Haug et al. i994, Nilssen 1995, KjellqwiSt
,
,
et al. 1995).
'
The harp seal pups ofthe East and West ic~ commence independent feedmg in habitats that
differ frorn each other (see Sergeant 1991). The East Ice pups are usually born on the 40-90
'crn truck winter ice, ofthe current year, and they start independent feeding in the southeaStem
parts ofthe Barents Sea in relatively shallow waters (30-:100 rn deep).In the West lee, the harp seals whelp ori the finge ofthe winter ice (usually ~nciw covered floes ofapproXimateiy 1
in thicklless) that lies seaward to the heavier multi year icc ofthe east Greenhmd pack. Most
ofthe West Ice is located in areas where water depths range between 1000 and 3000 m. The
niain pupping period for hai-p seals ofthe West Ice stock is approximately one month later than
that ofthe East lee, most ofthe jnips usually heirig born in late March (Sergeant 1991,
0ritsland & 0ien 1995).
The main pupping seasori for hooded seals in the West lee is ~d March (Rasmussen 1960,
-
,
.
0ritslarid 1964, ~ritslarid & 0ien 1995). Since hafp arid hooded seals are preseni in the same
areas orthe West lee throughout the breedirig seäson, pups ofboth species may corriinerice
feeding independently in a sitUation that results iri competition. The adult hai"p seals ofthc
West lee have a diet ihat dUrers frorn that ofhood~d seals (potelov, NÜssen & Raug,
~ripublished niateriäl).. It woulrl he ofiriterest to establish whether the ~e is t~e for'thc pups
ofthese iwo species.
ira ~ompeiitiori exists, ihe'siic ofa year-däss orone species might
infltience year-class strength ofthe other.
.
"
Questions conceming ecologicat aspects of the early life bistor)' of phocid seais have, however,
heen litde studied. Some information conceming energy transfer from mothers to pups dtirlng
lactation, first neonatal gTowth, arid thc post weaning fast ofthe harp seal, and other phocid
speeies, iric1uding hooded seals Cystophora cristata, is avai1~ble (Stewart: &. Lavigne 1980,
e
'.",
3
1984, Worthy &. LilVigne 1983a, b, 1987, Kovaes & LaVigne 1986, 1992, Kovacset a/. 1991,
Nord"}' ~t ai. 1993), arid the dietary eompositiciri cifyoung luirP seals has been cximined iit
varlous
arw (Läwson & Sterison 1995, Lawson et a/. 1995, NIlssen et a/. 1995a). Älthough
there are some data rehiting to tbe ehanges of blubber thiekness arid weight ofharp seal pups
fram the East lee (Sivertsen 1941, Timoshenko 1995), the feeding habits ofhaip seal pups in
the northeast AtIaittie 8reaS are viriualiy unkßown. It has, however, been suggested thai they
feed on erustaeeäns arid fish bath mthe East Ire and West lee (Sivertsen 1941, RaSmussen
1957).
Defieieneies in Jcitowledge abaut pup eeology Ied us to address inereased attention towards tbis
.tYPe of st1ldy. Atiention was direeted towards the .studY ofBarents Sea harp seal pups, with thc
aim cifgaining ariy understanding of meehariisrris thai may iIifluenee thc survival of haij seal
pups dunng iheir first year orllfe. Such infoimation could be eXpIainiItg thc Iarge variations in
year-class stren~h thät have been obserVed in tiüs stock (see KjelIqWist et al. 1995,
Timoshenko 1995).
,~
,
"\
"
MATE~SANDMETHODS
Sampling ur
e
seals
"C-',,"
The sarnpliIig ofBarents Sea harp seals in 1990-1994 yielded rlatä from pups-of-the year (145
individuals), and fTom i and 2years old änimals (45 and 41 iItdividuais, respectiveIy), wiuch
were ali induded in
. (see NÜssen
the body condition analyses, in Jurie, September, OCtober arid February .
ct al. 1994, 19953., b). Therefore, to cover tbe eritire yeär, the appropriäte period
for coIh~ctio~ ofsupplemeniary seal pup rlata in 1995 was March-May, i.e. in the period from
weamng until the pups started to feect irideperideniiy.
In 1995 the ccilleCtion ofpups waS carried o~t rluring the commercial hunting season.
Perinission was obta.med to catch uj) 10 1,500 härp seal pups (750 from t~e East lce and 750 .
from tbe West lee), arid up to 750 hooded seal pups fr6in the West lee. All püps shoulrl be
weaned, i.c., the hart> s~aI pups shouici be niggedjäck~ts (moultirig young) ärid beaters
4
(moulted young) while the hooded seal pups should all be weaned bluebaekS. In order to study
the development ofthe pups after weamng it was neeessary to obtain a temporal distribution of
eatehes, and this was aehieved by setting a maximum allowable quota per week.
One vessel (MIS Harmoni) operated in the East lee (Fig. 1) duririg the periods, 23 March - 13 .
April and 24 April- 10 May 1995. During the first perlod, 156 ragged jaekets and 89 beaters·
were colleeted. When the vessel made its second trip to the East lee there was Httle ice in the
traditional eateh areas (see Fig" 1), and only 4 beaters were eaught.
Two vessels (MIS Poiarjinlgst and WS Polarstar) operated in the West lee (Fig. 1) from 8
Apiii to 12 May 1995. Duririg this period, 338 raggedjaekets,
22 beaters, and 364 bluebacks
wen~ obtairied.
Measurements and biological collections
Two scientists eollected sampIes on eaeh ofthe three NOrWegian sealing vessels that operated
durlng the 1995 season. All sampIes were eolleeted in aeeordanee with t.he guidelines
established during 1990-1994. For eaeh pup.samples records were taken ofspeeies, date, time
ofthe day, position, sex and stage of development.
All pups were weighed to the nearest kg, and standard body length was measured to the
nearest em in a straight line from the tip ofthe snout to the tip ofthe tall, with the animal
laying on its beicie. The dorsal blubber thiekIless (at a knife-cut in the mid-liße between the front
flippers) was measured to the nearest mm.
The stomach and large intestine of each pup w~s removed, arid frozen ror subsequent aDa1ysis
in the laboratory.
Analyses of body condition
The condition was cletermined as index C = -.J LI W *d, where L is standard body length in cm,
W is total body mass in kg and d is the dorsal blubber thiekIless in cm. This indeX was
e
5
introdueed by Ryg et izl. (1990), and it has proved to be useful in studies of seasonal variations
in body eoridition of adult harp seals (Chabot
Analyses
et al. 1995, NIlssen et al. 1995e).
of stomach arid intesÜne contents
In the laboratory, the stomac~ and intestines were thawed and then Cut operi. The weight of
storiiaeh eonterits was reeorded, aitd the intestirial contents were flushed out using fresh water.
Crustaeeans were separated from fish and identified to the lowest possible taxon aeeording to
Enekell (1980). A emde estimate ofthe riumber of erustaeeans was obtained byeoimting
earapaees. Otoliths from thc stomaeh and intestines were eollected aitd identified to thc lowest
possibie taxon using the keys developed by i-Iärkörien (1986). Thc number offish of each
species present in the stomachs arid intestines was calculated by halvirig the number ofotolithS.
Indices conürionlyused in stomach anaIyses oftop predators (Hyslop 1980, Pierce &. Boyle
1991) were used to estinülte the dietary contribution of different prey items: 1) the percentage
of oceurrenee of a given dieiary componerit, defined as the pereentage ofstomachS cr
intestines that contained orie or more individuals ofthis eomporierit; 2) the relative frequency
. ofoeeurrenee ofa prey species caleuiated as a numerieal fraction oftotal numbers ofan prey
eategories (% numencal frequency).
e
·.".
RESULTS
Body cöndition
FAst Ice - harp seals
1'0 address the question ofseasonal vanation in body oondition ofharp seal. pups fr6Iri the East
lee stock, data froni 231 animals (aged benveen 3 months and 3 years) eollected in 1990-1994
waS cambincd with that colleeted
m1995 (249 pups). The raggedjaekets häd the thickest
dorsai blubber (approXimately 48 min). Blubber thiekness decreased from the time ofweanmg
in March until June, when the dorSal blu~ber was oOly about
17 mm thick
(Fig. 2). The
6
blubber increased in thickßess during thc course of summer, but never regained the levels
observed just after weaning. A dorSal blubber tiückIless of 39-40 rinn was maintairied from
October until April. Variations in ihe conditiori index C (Fig; 3) resemble those ofthe dorsal
blubber: The patterns obserVed far varhiiions in dorsal blubber thicknes~ lind conditian iIidex
during the fust year oflife seem io be maint~ed also through thc second arid third year (Figs
2 arid 3).
West lce - hinp seals
Thc body condition data for the 338 raggedjackets and 22 beaters colleeted rluring 1995 are
,
.
,
shown in Fig. 4. Body coriditiori index tended to decreaSe in the period 10 - 30 April.
e
'~"
weSt lce - hooded seals
Atötal of 326 West Ice bluebacks were analysed with respect to condition index (Fig. 5).
-
There was HUle change in mean coriditiori iridex during April, but the aiümais taken in May
exhibited significaritly lower conclition indices trum those taken earlier.
Pup dietS
EDst lce - hinp seals
All but orie stomach öfhaip seal pups taken in thc East Ice in
March and April 1995 were
empty. Thc stomach with coriteiit contai~ed milk. Ocly few ofthe intestines ofthe pups
colleeted during the first period (20-26 March) were emptY, and this held true for both ragged
jackets (9.9%) and beaters (16.5%) (Table 1). In the second perlod (24-30 April), only 4
beaters were caught, two ofwhich had empty iritcstines. Much oftbe iritestirial content was
unidentifiable and was most probably thc remains ofriüIk. Ofthe 9 identifiable prey itemS,
kri11
.
..
Thysalloessa sp. was fourid in the iritestines of25.2% ofthe raggedjackets arid of nearly 50%
ofthe beaters. Also amphipods ofthe genus Parathemisto oceurred 1h~quently, in 20.5% ofthe
raggedjackets arid in more than 50% ofthe beaters. In 29% ofthe pups, both P. libeI1ula arid
kri1l occurred simultaneously, while rion co-occum:~rit preserice were ob~erved in 7~ ofthe
pups for botlt prey items. Of other icientified prey species, the amphipod Gemmiare/lUs homari
occurred in c. 8% ofthe beäiers. In tenns ofnÜtnericai frequency, lciill contributed moSt (42-
."".
e
"
7
67%) to the seal pup diets, fotlowed by Piirathemisto sp. whieh eontributed 32-56% (Fig. 6).
Other pr~y appeared io be ofnegligible iIriportariee.
.
West /ce - Jiaip seals
Stomaehs and intestines ofharp seal pups Sampled in the West lee were examined in thfee
perlods ('fable 2). Stomaehs were usually emptY, but the irieideriee ofenipty iriteStines was low
(0-15.4%). Ten prey tYPes were obserVed in the stomaehSfmtestines ofthe West lee ragged
jaekets arid beaters. Arnphipöds ofthe geriusParathemiSto occurred in 44.4-100% oftbe
iritestines, arid P. libeIiula was pcirticU1ariy common, oceurring in 55.6-100% ofthe intestines.
Arriphipods ofthe genus Gammanis si>. weree also encountered frequentiy, with thc species G..
•
wiiidtzkii being particularly abundant (fourid in 38.5-100% ofthe inÜ~stiries). The prey grouP.s
, . '
desigmited Parathemisto sp. and GammarUs sp. may weH 8lso mClude reIllains of P. libe//ula
~
arid G. wi/kitzkii, which could riöt be identified to species. Other arnphipods oceurred qUite
ftequeritIy in the intestines (Eusiros sp. and represeritatives froin the fainily Lysianassidae)
while kriiI was rare. Contents from stomaehs resemblecl those obserVed in the in1(~siiries.
Parathemisto iibe//ula was tbe dominant prey species by nuinerlcal frequericy, contributmg 43-
.
.
60% (Fig. 7), arid amphipods oribe genus Parathemisto had a
numerlcal contribuiion ef 64-
,92% to the diei. The coritribut~on oftbe genus Gammanis was sIllall (4-28%), and ether food
items seemed to be ofminor impoitarice.
West lce - hooded seals
All but one hcioded seal pups wen~ eXamiried in three periods froin io to 30 April (Table 3).
The blueback coHected in the penod 3-9 April ba.d umdeniifiabh~ reinains in tbe iniestiries.
Most ofthe stomachs were erriptY (70.9-87.2%), hut the frcquency ofempty intt~stmes was
much lower (0-38.5%). At least 14 different prey items were recorded. Crustacea.ns domi.itated
the intestinal contents, but cephaiopods and flsh ha.d 8lso beeri conSumed. Parathemisto
/;beIiuia was the most frequent prey species, occurring in 10:3-25.7% öfthe StoinachS arid
46.2-86'.7% ofthe intestines. Gammarus wiiidtzkii was also of some impoitarice, occurring in
5.1~8.go.lo ofthe stomachs and 15.4-33.3% ofthe irites~es. Co-occurrence ofParathemisto
and Gdmmarus was observed in 20% ofthe sampies. Some prey items thai were absent froin
. early sarnples weer found later; e.g.,
the amphipods Eusinis sp.; krin, umdeniified decapods,
the cephaIop()d Gonathüsfabricii and fish (in partieUlar tlie polar eoel, Boreogadus saida). In
8
tenns ofnumericai frequencyofoccurrence (Fig. 8),' Parathemisto /ibel/u/a dominated with a
coniributiori of 78.2-92.5% to the blueback stornach ami intestinal content. The total
eontriblltion ofthe genus Parathemisto was io 82.3-95.3%, whitS! ~hat ofGcimmcirus sp.
varied between 1.9-8.1%.
,
.
DISCUSSION
In their studies ofneonatai growth in harp seals, Stewart & Lavigne (i980) observed that
body weight declined considerably dunng thc post-weaning period, arid they attribüted most öf
ibis weight decrease to a loss from the core ofthe animais. Energy loss from the blubber laye~
seemed to be less conspiciIolls, and Stewart & Lavigne (Ioe.eit.) aiiributed
this to the necessity.
ofmairitenance of the biubber hiyer to reduee heat loss ",heri tbe yoting began to rorage in the .
aquatic environment. Later stUdies have, however, revwed that, although core reserves of
eriergy may be ofimportance in the earllest phases ofthe po~tWeaning faSt, the weaned pups
must reiy on the blubber layer as the most impoitarii source of energy during fastmg (Woithy
& Lavigne 1983a, b, 1987). Results from recen! studies
on haij seaI pups, indicate thai
catabolism of subcutaneous blubber energy represenied the major energy source (ca 80%) in
the post weamng period (Nordoy
et al. 1993).
The present observations on changes in condition index arid dorsal biubber thickness ofharp
seai pups from the Easi lee are in agreement with previous field and iaboratory observationS,
and indicate that substantial amourits of stored blubber are mobilized
mthe period from .
weanmg (ritid March) to mid lurie. Thus, atthough the pups may be able to find prey arid fee~
independeritIy shortly after weanmg, ii appears tbat food intake is insUfficient to meet the
energy requirements needed in the transition from the pack ice to a life in more open water.
Poolingofmaierial eollecited in 1990-1995 may give a false piCture ofseasonal ehanges in
the patterns we observed äfe:
East lee harp seais by SivefSten (1941). A pattern of poor
hody condition if substantial year-to-yecu- variations occur, hut
similar, to those obtained for
'spnng arid early summer conditio'ri followed by ari iniprovement durlng hite sUmmer arid
- - - -
-----------------
9
,
,
autUmn'seerns to OCcUf not only in young-of-the-Year. but also in
arid thini year oflife.
,
.
harp seals in their se~o~d
similai- obserVations ~ave been made on adult EaSt lee harp seals
.
(Nilsseri et izi. 1995e). and seasonal variation in bödy mass. blubbe~ tluciOless: eondition inde~
änd energy mtake have also been obserVecl iri eaptlve subadult and aclult haip seals (Renoufet
al. 1993; Lager
et al. 1994).
The signillcanee cf
eai-iy independent feedmg as an energetic supplement is not known. It iSt
for exainple. üneertalri wiu~ther surnval ofthe pups is eompleteIy depenclent upon the blubber
stores established duririg sucklirig or whether they are ahle to eoinpensate for an unsuccesful
suclding periöd by increasing feedirig soon äfter weanmg. Thc energy defleit impösed by
exeessive depletion ofthe blubber iäycr would presiimably be eXacerbated by increäSed heat
loss. riecessiiatmg
an elevation in metabolie rate to maintairi ~hennal homeostasis in thc cold
aquatic .envii-omnent (Broclie & Paasche 1982. Worthy &. L3.Vigrie 1987). Mobilisätion of
energy reserves ston~d in the bödy eore may reduce this effect (Nordri}r ~t al. 1993). but the .
period from weanmg until mid June seems to be eriticät for tbe pups. Their abilitY to perfOnTI
int~itsive feerling sufficieni to deposit energy stores appear to be good after iurie.
The trend towards decreased eondition in West Ice harp seat pups in the post weanmg penod
is gerierally consistent With the obserVatioris made in the E3.St lee. hut it is diffieult to ättach
ariy signifieance to the apparanily lower condition indices ofraggecljackets in the West ice as
••
compäI'ed with the Ea8t lee on the basis of data froni a smgIe year.
As ha8 been oDserved previously (Sivertsen 1941; Nüssen et al. 1995b). most ofthe stomacbs
examinecl in March-April were empty. This eouid be mdicative ofrapid digestion by härP seat
..
_
'
'.
.
."
'_,,'.
.
~
i.
."
,-
puPS. and may also refleet ä. moderate feedmg intensitY during this period. EXämination of
intestinal cOritents reveaIed ihai the firSt food ofhärj) seal pups was restrlcted aIriiost
exciusiveIy to crustaceanS. aIthough there was considerable species väriaiion betWeen thc nVo
areaS investigated.
Tbe early post-weaning diet ofEast Ice hai-p seal pups was dominated by twc> tYPes ofpn~y:
euphausücls (kriiI) and aniphipods ofthe genus PiUtitheinisio.
. arid kriIl in p~icular.
The importance cf erustaceans•
as fust food for East lee häip seaIs was emphasized by SiverSten (1941).
10
Wrule krill seems to be an imjjc;>rtant prey for the youngest aniriials, jjaitieularly during t~e
first peri~d after weamng, Parath'emisto sp. has proven to be a prey of majo~ impoitanee for .
both pups lind older harp seals ofthe EaSi lee stock during the int~nSive feedlng period mhit~
summer arid autt.im.O. (Nilssen et al. 1995a).
The post-weaning diet ofWest lee harp seal pups waS also ehlliciett~rized by a dommanee of
arnphipods ofthe genus Paratheinisto. Unlike in the East lee, krill appeared to be ünimpöitarit,
but amphipods of the gerius Gammarus, mpartieular G. wilkitzkii, eoniribuied significantly to
the diet ofthe harp seal pups in the West lee. Infoimation about the feecfuig habits ofragged
jaekets and beaters from the West lee is eXtremely scilree, although Rasmussen (1957)
reported to have observed beaters retumirig fröm dives With polar rod in their mouthS iri April.
No fish speeies were reeorded in the diet ofhai'p seal pups in our stUdy.
•
Ginnmafuswilkitzkii is an aiJtöehthonous sympagie amphipod ofArctie areas (see GuIiiksen &
umrie 1991), arid its frequent oceurrenee in the diet ofWest lee haJp seal pups suggest that .
the pups may penorm their first feeding exrorsions beneath iee floes. Aeeording to Guiliksen
& L"nne (loe.eit.), G. wilkiizkii is prevwent in the perennial sea iee zone, arid tbis may explain
why the spedes was present in the diets ofihe harp seai pups sampied in the multi year sea ice
areas ofthe weSt lee but was absent from the diets ofpups Sampled
mthe seasonal sea ice
areas ofthe BaSt lee. Giveri its high degree of eo-occurrenee with G. wilkiizkii in harp seai
stomachsrmtestines, and its frequent occurrenee elose to the suifaee of sea iee, Parathemisto
iibellula rnay also have been taken by the seal pups as they foraged undemeath the iee floes.
However, P. libe1Iula is elassifierl aS belonging to the sub iee fauna; due both to its laek of
physieal associatiori Witlt tlte lower layerS ofsea iee arid to its frequent pehigie oeeurrenee in
cold water
areas (Ouiliksen & Lmme 1991; Laririe &. GullikSen 1991). This prey couid,
therefore, hRve been oonsumed by seals fomging in open waters.
The results ofthe present investigation corifirm previous findings that crustaceans, P. libellula
in particular, are ofmajor iniportance as food for harp seals at certain tinies ofthe year
(Sivertsen 1941~ Sergeant 1973; Ndssen 1995, NLlssen et al. 19953, LiridStrßm et aI. 1996).
The coinposition ofthe diet ofthe harP seal pups öf the East Ice stock remains unkßoWn for
. the period June to September, in September the diet is a inixtüre of P. /ibeilula, krill, capelln
•
11
arid polar eorl, arid in Oetober thc diet mainly eömpnscs capeliri and polar eod (NÜssen et al.
1995a, Liridstr"m et al. i996). Martensson et ai. (1994) have shown that eapiive iuu-p seal
pups were unable to niaintam body mass wheri fed a enistaeean diet ad libitum, lind they
suggested that the seals would have to supplement the diet with flsh in order to maintain
j
"
,
.
•
•
gfoWth. Our observations indicate thät pups feeding on erustaceans iri the post-weaning period
lose eoridition from March to june. An increaSe in the eoritribution offish to the diet in
summer and autiimn may häve led to the increased body conditiori observoo from Jurie
oriwards. Also, the substantial inerease in energy density tllat oCcUrs both in crustaceans arid in
planktivormls fish durlng the surrinier arid auttiilm may have been a contributory faetor (see
,.
,
.
"0' .
'" . ' , '
.
.
'
Percy 1993. Martensson et al. 1996).
e
As was observed for the harp seai pups, the bluebaeks also started to food independeritly soori
after wearung. The blueback diet appeared to be very sirriiiar to tbat ofthe West lee harp seal
pups: a dominänce of Parathemisto (almost exciusively P. libe//ula), with some C(mtrlblltion
from Gammarus sp. (mainly G. wilkitzlai). This may ißcllccite that the feedmg behaviouf of the
härp lind hooded seat pups is similar, and the possibilitY ofiriterspecific competition can not be
excluded niay be inferred. In ihe last part ofthe investigation pericid there is some weak
evidenee that non-erustäeean prey items (polar eod arid the cephalopod GonatUs fahneii) may
increase iri aburidariee on the diet.
,.
'
ACKNOWLEDGEMENTS
We should like to express sincere tharikS" to the field assistants I. Berg, B.Bergn"dt, K.A
Fagerheim, RHaugen, A. Konradsson, B. M1kkelsen, N.E. SkRvberg, to the crews on board
the se8Iers, to G.L.Andersen for laboratory treatment of biological saritples, to Professor W.
Vader for help in species determina.tion, and to Professors B. Gulliksen and M. Jobimg and Dr
E.S. NordaJ for comments on the manuscripi. The work was supporiect economiCaIly by the.
NOrWegiari Couricil ofResearch, project 1081471110.
12
REFERENCES
Brodie, P.F. & Paasche, Al 1982. Density-dependent condition and energetics ofmarine
mamma! populations in multispecies fisheries management. Pp. 35-38 in Mercer, M.C. (ed.)
Multispecies approaches to fisheries management. Can. Spec. Publ. Fish. Aquat. Sei. 59.
Chabot, D., Stenson, G.B. & Cadigan, N.B. 1995. Short- and long-term fluctuations in the size
and condition ofharp seal (Phoca groenlandica) in the Northwest Atlantic. NAFO SCR
Doc. 95142, Serial No. N2551: 27 pp.
Enckell, P.H. 1980. Kräftdjur. Bokförlaget Signum i Lund. 685 pp.
Gulliksen, B. & Lenne, 0.1. 1991. Sea ice macrofauna in the Antarctic and the Arctic. 1. Mar.
Syst. 2: 53-61.
Härkönen, T. 1986. Guide to the otoliths 0/ the bonyfishes 0/ the northeast Atlantic. Danbiu
ApS, Hellerup, Danmark: 256 pp.
Haug, T., Nilssen, K.T., 0ien, N. & Potelov, V. 1994. Annual distribution of Barents Sea
harp seals, Phoca groenlandica. Polar Res. 13: 163-172.
Hyslop, E.J. 1980. Stomach content analysis - a review ofmethods and their application. J.
FishBiol.17:411-429.
Kjellqwist, S.A, Haug, T. & 0ritsland, T. 1995. Trends in age composition, growth and
reproductive parameters ofBarents Sea harp seals, Phoca groenlandica. ICES J. mar.Sci.
52: 197-208.
•
•
13
Kovacs, K.M. & Lavigne, D.M. 1986. Matemal investment and neonatal growth in phocid
seals. J. Anim. Eeol. 55: 1035-1051.
Kovacs, K.M. & Lavigne, D.M. 1992. Mass-transfer efficie:mcy between hooded seal
(Cystophora eristata) mothers and their pups in the GulfofStLawrence. Can. J. ZooI. 70:
1315-1320.
Kovacs, K.M., Lavigne, D.M. & Innes, S. 1991. Mass-transfer efficiency between harp seal
(Phoea groenlandiea) mothers and their pups during lactation. J. Zooi., Land. 223: 213221.
Lager, AR., Nord"}', E.S. & Blix, AS. 1994. Seasonal ehanges in food intake ofharp seals
(Phoca groenlalldiea) at 69 0 N. Mar. Mamm. Sei. 10: 332-341.
Lawson, I.W. & Stenson, G.B. 1995. Historie variation in the diet ofharp seals (Phoca
groenlandiea) in the northwest Atlantie. Pp 261-269 inBlix, A.S., Wall"e, L. & Ulltang, 0.
(eds) Whales, seaIs,flsh and man. Elsevier Scienee B.V.
Lawson, I.W., Stenson, G.B. & MeKinrion, D.G. 1995. Diet of harp seals(Phoea
groenlandiea) in nearshore waters ofthe northwest Atlantie during .1990-1993. Can. J.
Zool. 73: 1805-1818.
Lindstmm, U., Harbitz. A., Haug, T. & Nilssen, K.T. 1996. Do harp seals Phoea groelliandica
exhibit particular prey preferences? ICES CM 19961N: 2: in press.
L"nne, 0.1. & Gulliksen, B. 1991. On the distribution ofsympagie macro-fauna in the
seasonally iee eovered Barents Sea. Polar Biol. 11: 457-469.
Märtensson, P.-E., Lager Gotaas, AR, Nordoy, E.S. & Blix, AS. 1996. Seasonal changes in
energy density ofprey ofnortheast Atlantie seals and whales. Mar. Mamm. Sei. 12: in press.
•
14
Märtensson, P.-E., Nord"}', E.S. & Blix, AS. 1994. Digestability ofcrustaceans and capelin in
harp seals (Phoca groenlandica). Mar. Mamm. Sei. 10:
3~5-331.
Nilssen, K.T. 1995. Seasonal distribution, condition and feeding habits ofBarents Sea harp
seals (Phoca groenlandica). Pp 241-254 in BIix, AS., Wa1lße, L. & Ulltang, 0. (eds)
Whales, seals, Jish and man. Elsevier Science B. V.
Nl1ssen, K.T., Ahlqwist, I., Eliassen, l.E., HilUg, T. & LindbIom, L. 1994. Studies offood
availability and diets ofharp seals, Phoca groenlandica, in the southeastem Barents Sea in
February 1993. ICES CM 19941N: 12: 24 pp.
Nilssen, K.T., Grotnes, P.E., Haug, T. & Potelov, V. 1995c. Seasonal variation in body
condition of adult Barents Sea harp seals (Phoca groenlandica). In press in Proceedings
from the NAFOnCES Symposioum The Role ofMarine Mammals in the Ecosystem,
Dartmouth, Canada, September 1995.
Nilssen, K.T., Haug, T., PoteIov, V., Stase*ov, V.A & Timoshenko, Y.K. 1995b. Food
Habits ofharp seals (Phoca groenlaruJica) during lactation and moult in March-May in the
southem Barents Sea and White Sea. ICES J. mare Sei. 52: 3341.
Nilssen, K.T., Haug, T., PoteIov, V. & Timoshenko, Y.K. 1995a. Food habits and food
availability ofharp seals (Phoca groenlandica) during earIy summer and autumn in the
northem Barents Sea. Polar Biol. 15: 485-493.
Nord"}', E.S., Aakvaag, A & Larsen, T.S. 1993. Metabolie adaptions to fasting in harp seal'
pups. Physiol. Zool. 66: 926-945.
0ritsland, T. 1964. Klappmysshunnens forplantingsbiologi. Fisken Hav. 1964(1): 1-15.
0ritsland, T. & 0ien, N. 1995. Aerial surveys ofharp and hooded seal pups in the Greenland
Sea pack-ice. Pp. 77-87 inBlix, AS., WalWe, L. & Ulltang, 0. (eds) Whales, seals,Jish,
and man. Elsevier Science B. V.
•
•
15
Percy, J.A. 1993. Energy consumption and metaholism during starvation in t~e Aretic hyperiid
..
.
amphipod Themisto libellula Mandl. Polar Bio/. 13: 549-555.
Pierce, GJ. & Boyle, P.R 1991. A review ofmethods for diet analysis ofpiscivorous marine
mammals. Oeeanogr. Mar. Biol. Annu. Rev. 29: 409-486.
Rasmussen, B. 1957. Exploitation and protection ofthe east Greenland seal herds. Norsk
Hvalfangsttid 46: 45-59. .
Rasmussen, B. 1960. Om klappmyssbestanden i det nordlige Atlanterhav. Fisken Hav.1960(1):
1-23.
Renouf, D., Gales, R & Noseworthy, E. 1993. Seasonal variation in energy intake and
condition ofharp seals: Is there a harp seal morph? Problems for bioenergetic modelling. J.
Zool., Land 230: 513-528.
Ryg, M., Lydersen, C., Markussen, N.H., Smith, T.G. & 0ritsland, N.A. 1990. Estimating the
blubber content ofphocid seals. Can J. Fish. Aquat. Sei. 47: 1223-1227.
Sergeant, D.E. 1973. Feeding, growth and productivity ofnorthwest Atlantic harp seals
•
(Pagophilus groenlandicus). J. Fish. Res. Bd, Can. 30: 17-29.
Sergeant, D.E. 1991. Harp seals, man and ice. Can. Spee. Publ. Fish. Aquat. Sei. 114: 1-153.
Sivertsen, E. 1941. On the biology ofthe harp seal Phoca groenlandica Erx. Investigations
carried out in the White Sea 1925-1937. HvalrMets Skr. 26: 1-164.
Stewart, RE.A. & Lavigne, D.M. 1980. Neonatal growth ofnorthwest Atlantic harp seals,
Pagophilus groenlandicus. J. Mamm. 61: 670-680.
..
16
Stewart, RE.A & Lavigne, D.M. 1984. Energy transfer and female eondition in nursing harp
seals, Phoea groen/andiea. Ho/are!. &0/. 7: 182-194.
Timoshenko, Y.K. 1995. Harp seals as indicators ofthe Barents Sea ecosystem. Pp. 509-523
in Blix, AS., Wallee, L. & Ulltang, 0. (oos) Whales, sea/s,fish andman. Elsevier Scienee
B.V.
Worthy, G.Al & Lavigne, D.M. 1983a. Energeties offasting and subsequent growth in
weaned harp seal pups, Phoca groenlandica. Can. J. Zoo/. 61: 447-456.
Worthy, G.AJ. & Lavigne, D.M. 1983b. Changes in energy stores during postnatal
development ofthe harp seal, Phoca groenlandiea. J. Mamm. 64: 89-96.
Worthy, G.AJ. & Lavigne, D.M. 1987. Mass loss, metabolie rate, and energy utilization by
harp and gray seal pups during the postweaning fast Physio/. Zoo/. 60: 352-364.
•
•
17
Table 1. Frequencies of empty intestines and identified species ofprey in intestines ofEast lee
harp seal pups (raggedjackets and beaters) captured in 1995 during the two periods 20-26
March and 24-30 April, respectively. N = number ofintestines examined. "Others" include
remains such as molluscs, hair and algae.
20-26 March
ragged
jackets
beaters
24-30 April
beaters
N
151
85
4
Empty
9.9
16.5
50
6.0
20.5
0.7
6.6
0.7
8.2
54.1
8.2
4.7
3.5
0
50
0
0
0
25.2
49.4
50
0.7
1.3
3.5
7.1
50
0
0
1.2
0
6.0
15.3
0
59.6
23.5
0
Crustaceans
. Amphipoda
Parathemisto libellula
Parathemisto sp.
Gammarellus homari
Lysianassidae indet.
Amphipoda indet.
Euphausiacea
Thysanoessa sp.
Decapoda
Decapoda indet.
Unidentified crustacea
Pisces
Unidentified fish remains
Others
Digested remains
..
18
Table 2. Frequencies of ernpty stomachs and intestines and identified species ofprey in
stornachsfmtestines ofWest Ice harp seal pups (raggedjackets and beaters) captured in
1995 during the periods 10-16 April, 17-23 April and 24-30 April, respectively. N = nurnber
of intestines examined. UOthers" include remains such as hair and algae.
10-16 April
17-23 April
ragged jackets beaters
storn.
N
intest. intestines
24-30 April
rag.jack. beaters
rag.jack.
intestines
intestines
73
73
1
26
6
9
87.7
2.7
0
15.4
0
0
0
0
0
11.5
16.7
11.1
5.5
4.1
5.5
2.7
0
1.4
1.4
52.1
47.9
43.8
26.0
6.8
27.4
8.2
100
100
100
0
0
0
0
57.7
57.7
38.5
26.9
11.5
26.9
7.7
100
100
66.7
33.3
16.7
50.0
16.7
55.6
44.4
44.4
33.3
11.1
33.3
0
0
0
0
0
0
0
7.7
11.5
16.7
0
0
0
Others
1.4
2.7
0
3.8
0
11.1
Digested rernains
1.4
32.9
0
11.5
0
22.2
Ernpty
Crustaceans
. Copepoda
Copepoda indet.
Amphipoda
Parathemisto libellu/a
Parathemisto sp.
Gammarus wilkitzkii
Gammarus sp.
Eusirus sp.
Lysianassidae indet.
Amphipoda indet.
Euphausiacea
Thysanoessa sp.
Unidentified crustacea
e
•
•
19
•
Table 3. Frequencies of ernpty stornaehs and intestines and of stornachsfmtestines contiüning
identified groups ofprey ofWest lee hooded seal pups (bluebacks)captured in 1995 dunng
the periods 3-9 April, 10-16 April, 17-23 April and 24-30 April, respeetively. N = nurnber
of stornachslintestines examined. "Others" include rernains such as hair and algae.
3-9 April
10-16 April
storn. intest. storn. intest.
1
N
24-30 April
storn. intest.
storn. intest.
181
15
39
0
0
87.2
38.5
70.9
19.6
80.0
0
0
0
2.5
0
0.6
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
25.7 67.0
10.1 33.0
8.9 16.8
1.7
3.4
4.5 14.0
0.'6
2.8
0
0.6
20.0
6.7
6.7
0
0
0
0
0
0
0.6
0
6.7
0
o·
0
0
0
0
0
2.6
2.2
1.7
6.7
6.1
0
0
13.3
6.7
Cephalopods
Gonathusjabricii
0
0
0
0
1.7
2.8
6.7
13.3
Pisces
Boreogadus saida
Gadoidea indet.
Unidentified fish
0
0
0
0
0
0
0
0
0
2.6
0
0
1.7
0
0
6.1
0.6
0.6
0
0
0
6.7
6.7
0
Others
0
0
1.9
2.6
16.2
2.2
13.3
6.7
Digested rernains
0
100
0
5.1
0
5.0
0
0
Ernpty
•
17-23 April
100
Crustacea
Copepoda
Copepoda indet.
Amphipoda
Parathemisto libellula
Parathemisto sp.
Gammaros wilkitzkii
Gammarus sp.
Eusirus sp.
Lysianassidae indet.
Amphipoda indet.
Euphausiacea
Thysanoessa sp.
Decapoda
Decapoda indet.
Unidentified crustacea
10.3 46.2
2.6 25.6
5.1 15.4
5.1
0
0
2.6
0 2.6
0
0
0
86.7
66.7
33.3
13.3
o 26.7
0
0
0 6.7
•
20
GREENLAND
..... Ap..
e
Fig. 1. Map showing the 1995 catch positions ofthe seal pups (filled circ1es) in the
southeastem Barents Sea (the "East lee") and in the Greenland Sea (the "West Ice").
Approximate localisations ofthe ice edge at the beginning, in the middle and by the end of
the period ofinvestigation are indicated (Source: The Norwegian Meteorological Institute,
PO Box 43 Blindem, N-0313 Os10, Norway).
•
•
21
N=ISS/90 4 44
1312
76 12
22
7
4
5
2
34
50
_ 45
e
E
E
';' 40
fI)
CD
c:
.Q
~
35
-.... 30
s:::.
CD
.c
.c
::s
JS
16
!!
25
0
0
20
15
Mar Apr lun
9S 9S 91
I
SepOet
9019192
o-lYR
Feh
Apr lUD
93
91
I I
91
Sep
90191
1-2YR
Feh Apr lun
91
93
I I
Sep
90191
91
2-3YR--1
Fig. 2. Seasonal variation in dorsal blubber thickness (mean ± 95% CI) ofyoung harp seals
during their first three yea.rs of life in the East lce and Barents Sea. Data collected during
different yea.rs are pooled. Open squares = ragged jackets; filled squares = beaters; N =
number of pups.
•
22
N=ISSI90 4 44
100
13 12
76 12
22
7
4
5
34
2
90
80
)(
CD
"C
70
oE
c
0
60
:e
"C
c
0
0
50
40
30
20
Mar Apr lun
95
I
95
91
SepOct
9019192
o-lYR
Feh Apr lun
93
91
',
91
Sep
90191
1-2YR
Feh Apr lun
93
"
Sep
91 91
90191
2-3YR-.-J
Fig. 3. Seasonal variation in body condition index (mean ± 95% CL see text for definition of
the index) ofyoung harp seals during their first three years oflife in the Bast lce and
Barents Sea. Data from different years are pooled. Open squares = ragged jackets; filled
squares = beaters; N = number of pups.
23
•
N=
133
150 55
20 2
100
e ><
.=
80
+
CD
"C
-r
•
60
c
+
•
0
:e
"C
c
0
(.)
40
•
20
o
11-13 Apr
14-20Apr
21-28 Apr
Periods
Fig. 4..Weekly variation in body condition index (mean ± 95% CI, see text for definition of
the index) ofharp seal pups in the West lce during April 1995. Crosses = raggedjackets;
filled circles = beaters; N = number ofpups.
24
N=
)(
Cl)
-c
--
c:
c:
0
E
-c
c:
0
()
100
90
80
70
60
50
40
30
20
10
0
69
236
18
+
+
+
3
=F
+
9-15 Apr 16-22 Apr 23-30 Apr
9-13 May
Periods
Fig. 5. Weekly variation in body condition index (mean ± 95% CI, see text for definition of
the index) ofhooded seal pups in the West lce during April and May 1995. N = number of
pups.
e
J
25
,
~
-100
~
u
Z
~
=
:J
80
U
u
o
~
o
60
t>
z
~
:J
40
CI
~
~
~
..
~ 20
~ Parathemisto
~
HIlI Thysanoessa sp.
§il Other crustacea
• Various
>
....
~
~
~
0
RJ
BI
20-26 MARCH
B2
24-30 APRIL
Fig. 6. Relative numericai frequency ofoccurrence ofprey speeies in intestines ofEast lce
harp sCal pups (ragged jackets: RJ; beaters: B) during two periods (1 = 20-26 March; 2 =
24-30 APril) in 1995. N ~ number ofintestines examined.
ap.
26
.-----
N=9
,
N=73
11 Parathemisto Üb.
~ Parathemisto sp~
sp.
~ ~ammarus
~ Other crustacea
• Various
BI
RJI3
RJS
RJIl RJI2
.
24-30 APRIL
10-16 APRIL
17-23 APRIL
"~
~"
Fig. 7. Relative Iuimerica1 fh;;quencY ofoccurrenee of prey species in stomaehS (8) and
üitestines (1) ofWest lee hart> seal pups (raggedjaekets: RJ; beaters: B) duiing three
periods (1 = 10-16 April; 2 = 17-23 April; 3 == 24-30 April) in 1995. N = luimber of .
stomaehslintestines examined.
•
J
27
•
ID
~
fYjJ
Paraihemlsio lib.
Parathemisto 51>.
Gammarus
sp.
..
.
",'
'
l1§ Other crustacea
• Various
SI .
"",
11
c·_~·,
82
,
10-16 APRIL
12
,.
17-23 APRIL
83
13
24-30 APRIL
Fig.8. Relative numericai frequency ofoccurrence ofprey species in StomäehS (S) and
,
intestines (I) ofWest lee hooded seal pups duririg thfee penods (1 ~ 10-16 April; 2 = 17-23
.APrlI; 3 = 24-30 Apru) in 1995. N = number ofstomaehSJinteStmes exariüned.