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PREDATOR-PREY I:"'TER.-\CTIO:"'S OFCOMMO~\-ICRRES (("rtu(.J(lg!dA~D FISH 1:\ THE SORTHWEST ATlAl'TIC FORAGI:'\'G STRATEGIESO~
\IL"LTtPLE SCALES
by i:.:Gail K Da\"oren
A thesis submiuedwthe School of Graduate Studies
in partial fulfillment of the requirements for thedegr~uf
Ph D
Biopsycholog)' Programme. Departments of Biology and Psychuiogy .\lemoriaJ L"ni\ersityof~e.... foundland
Submitted December 200 1
:\e.... foundland
ABSTRACT
The~orth.... est Allanllcccosy~emis .:unently undoergomg changes in~esintera..1.ions and u..:ean climate Capoelin(.\lul/om.• 1"11/11.\*':».t~dominant foragefishin the ecosyStem.. is the main prC)- item ofmari~birds. ITWIUT1&Isandpisciloorou5 tish. tn the I~s..spa....ning,;a~lin.... ere small. spa....~latl:f. shifted their distribution southerly to non-traditional areai compared to historical accounts.andabundance estimates ha\e
\aried ....-idel~During theie changes and di\ergent biomass estimates. this research .... as initiated The focus of this thesis is the multi-scale be:ha\;oura! interactions ofmarirk!
predators andpre~a marine divins bird. the ,;:ommon murre It·"uuu!XI!/.and its main pre~sp.:-cies. capoelin Thisstud~ int~atesbothcolony.b~and \essei-based techruques I sho....ed that :iQmc aggregations of capdin are stable in space and time on a number of scales fine- I 1-100 m. minute-hour ,. coarse- I 1-100 km.da~--...C'Ck)meso- io:ak tlOO-looo km. annual). a1lo .... ing mUITes to usc memol) to locate prey al,;eaduring differ~t ~odsduring their annual q-cleSocialloraging teduUques appeared to be:
Important on fine-~c;:oarse-scales IkxaJ enhancement.net ....ork foraging) .... hile no e\·ldeoce\loiSfound forsocialforagi~techniques O\eT larger~tialscales IlnfOllJ'lation Center Hypothesis) Spalial scales at ... hich mUlTes tra<:ked capel.in .... ere highly variable.
as foundinother studies e.U.ffillung predar.Ol'"-prey interactions of mobile organisms. The tracking scales ofmurres 10 capelin ....l:fe smallest during the breeding(08 -5IkIn)and pre-breeding periods (3 1- 8kmJ.compared to post-breeding 160 - 500Ian,.This variability in spatial associations between predators and their prey was likely due to different energetic requirements. lowmOlOfy constraints and search strategies used
amongt~penodsInt~r..:olon)comparisons ofpro\isioning beha\;ourb) murres r~vealed101.1. reeding ratcs of chicks at the largest murre colon:- in eastern Canada relative IoJa smaJler .::ol..ln). ""hieh resulted in the lo""est averagemassandconditionoffl~g1ing murresIIQI 0:.-l0 .!Ureponed in the literature~t)-depend~.both \\hile foraging atsea and rearing ducks at the colon). and prey distrib4..lIion around the largest colony resuh~in additional pro\'isloning constraints relative to a smaller coIon:- md di\ergent lifehisto~strategies at the t.... o colonies Poorer chick condition. and presumably lower recnJllment. ma:- ha\C rcsulted in a lack of population gro\lolhIIthelar~er.::olon). which conlains 85 .... of the common murres in the :"onhwest Atlantic Clearly. common murres int~ractIl.lth theirpr~o\'er multiple temporal and spatialscalesand these beha\-ioural interactions are manifestedIndemographic parameters
iii
ACK;-';O\\1.EDG\fE~T~
The research in Ihis thesis ",auld not ha\e been possible ",ithout a fe", key people. First.I
",auld like to thank Amold \lurphy for his remarkable competenC), tremendous suppon and for Iheenerg~he spent in tryingtounderstand my character tR-E·L·A-X)Ialso gratefull~ackno... ledge Da\id Fifield and Janet Russell who accompanied me in the field on numerous occasions ",-ith agerness and enthusiasm. The consistency of their skilL coniidencc. intelligence and good-humor was both soothing and inspiring I am also indebtedtoFran \1o\lo-bray \lo-ho has supponed and encouraged me as ",ell as helping me gainman~sciemiiic and technical skills I am similarly indebted to Richard O'Driscoll ... ho provided me with MatlabC routines to analyze a large portion of the data in this thesis and al:iO pro\-ided me with help deciphering the outcome of these statistical analyses Thanks 10 bothtoRichard and Fran also for prO\iding me with Ihc inlegrated capelin acoustic data for Chapler-Iand for the long hours of explaining acoustic data collc.::tion sy·stems and tht: intetuation software Without the oveno,ihelming emotional and professional suppon from these key people. tms re:>earch ...ould not have been possible
I also thankman~other people for both their friendship and technical SUppOIl Chamelle Burke. Sarah Jamieson. Joel Heath.. lain Stenhouse. Laura Dominguez., Stefan Ganhe.
Sabina Wilhelm. Eugene MacDonald. Phil Eustace. Greg Redmond. Chris Lang and Laura Penny Spe<;ial thankstoIhe crews of the Canadian Coast Guard "esselsSh.lmuulc.
Td':o!ilandT.:mplt!m~Jjfortheirun...avering professionalism and undying character I also gratefully acknowledge the logistical suppon in the field from Tommy Reddick
I Ro:ddid.famil~)and~Easton (Easton fami[) I Special thanks also to Da\-e Sencial forde:signi~andpro\iding the Birds and Ekasly Counter and to Becky Sjare for pro\idin~a laptop ior bird mammal surveys I also thank the Department ofToorism.
Culture and Ro:reation fort~ScientificAccessPermitS to Great and Funk Islands and ,he permit from Canadian \\ildlife $en.ice to v.ork v.ith the birds
1 also ackno",Ie:d~eSl;:\eral funding agencies tor both scholarship and research funds
~ational Scienc~and Eng.in\..'Cring Council oi"Canada (POst-graduate Scholarship.
Operatin~Granito Dr \Iome\ecchi). Mountain Equipment Co-op, Royal Bank \larine Studies Fund. The \ationaJ Chapter of Canada [ODE. Or.ille Erickson \temorial Fund.
Canadian F¢deration ofLni\ersil}' Women and thi: Memorial Lniversity of
\e'" foundland
Finall~.1appreciatiH:I~recognize members of rn} super.isory committee Dr Da\id SdU1~idertor histime:and energy provlding me ",im careful and thoughtful commenlS on m} thesis and Dr Brad deYoong for hdping me conceptuaJue and realize: my f<lrag.ing model in Chapter -' I also lhank my cQ-Sllper.isor Dr John .-\nderson for his careful SCIentific SllpponthrO'~~tmy Ph_DFmall~'.an incredibly special thanks toDrBill
\tontevoecclu for pro\iding me ",ith a solid and extraordinary personal and prOfessional rollll' model
TABLE OF CO"\"TE:-'"TS Abstra.:t
Ad:no\>, kdgc:mo:nts Table: 0fContc:ms List 0fTabJo:ls LisI0tFigurc:s Lisl oi Appt:ndicc:s Chaplt:rI -Introdu.:tion
1 ISPECIES BAo.:.GROl;-';D J: :-'ORTHWEST ATL-\.:\T1C ECOSYSTE\I I 3CHAPTER OL,U:-'CS
I -lUTER.-\.Tl-RE CITED 1 :.CO-ACTHORSHIP STATE\fE:\T
\i
wiii
:5
Chaplcr11 -Food-finding mc:chanisms of breeding common murres and the
slabilit~ofprt:~patchc:s
:0
: l(:\TRODLCTIO;"; :6
: : \fETHODS 30
: : IStudy.-\.ra 30
: : : Sur.ey \1cthods 3:
: : 3 Data :".nalysis ofSur.-c:y Data and Rc:visit Transects H
: : -I,Rc:turn and Depanure Behaviour oiMurres 36
: : : ' Data Analysis of Retum and Departure Beha..iour of\1urres 38
:::>RESl1.TS
:::> 1Abundanc~and Distribution of Capdin and\lurr~s
::3::
R~tums :::>:> Departures :::>4Wind:: :>5R~lumsand Departures
:: 3tISpla,;hdov.n and DirectDepanur~(Great Island) :: 4 DISCl"SSIO'\
:: 4 1S~archTactics
:: 4::
Summa~:: 5 L1TER...\TL"RE CITED
Chapt~rIII -Spatial associations of ..:ammon murres and capelin integrating pr«lalOr patchsd~tionandpre~beha\iour
:>Il'\TRODCCTIOi' :>:: \fETHODS
:> :: I Study Area j .::::Sun.ey Design j:::>Acoustic Estimates 3 :: 4. Physical and Biological Sampling 3 :: 5S~abirdCountS
:>::0 Collection ofSlOmach Conlenlsof\furres :>::7 Statistical .-\nalyses
39 )9 4)
;0 51 53 53 50 57 01 0)
19 19 79 81 82
'-I ,-I
85
.3 ::S Patch Seleclion \-Iodel .3:;RESLl..TS
:; .3IForaging Habitat Characteristics .3:;::Bird Characteristics .3 .3.3\turrc-Capelin Imeracliun .33-IPatchSd~tion\1odel .3.JDISCLSSIO:\
.3-l ICapelin Beha\iour .3-l ::Capelin-\Iurre lmeractiun .3 -13\Iurre Foraging Beha\iour
344Summ~
.35 LITERATL"RE CITED
Chapter [\" - Spatial associations of predators andpre~..:onstraims imposedb~
tlightlessness of ..:orrunon murres -III,\;TRODlTTIO' -I:: \tETHODS
-I::1Stud~Area -I ::::SUI"\e) Design -I::.3AC0ustic Estimates -I :: -ISeabird CountS
4 :: 5 Analysisof Scale-Dependenl Distribution Patterns -l :: bDietary Analysis
87 'I::
9:
104 107
'0'
115 115
1::-1
139 13"
141 144
147 14' 152
4:; RESLL TS
~:;I~lt.lrreDiet
~:;:~IurreDistribution
~:;:;Pr~Distribution
~:; ~ ~furre-Pr~Interaction in Continuous Se¥ments ofTransa.1.S (Fine- 155 IS.
IS.
~j~ ~lurre-Pre~Interaction (},er Sur..-eys (:\Ie-<...o-sc.aIe) 108
-I~DISCCSSIO' 110
-1-11 :\lurre Die!:>. 170
-I-l:Fino;-andCoarse-Scale .-\sso..iatioos ot' M.urresandPrey I i I -I~:; \kso-~akAssociations oi\lurres and Prey 173
-I-I-ISumm~ 177
-I 5lITER-·HCRECITED 178
Chapter \. - ClJnsequencesofforagin~nip duration on parental pro..isioning bd\a.. iour and chick condition of common murres
5 II:-'TRODL'CTIO' 5:~1ETHODS
5 : IStud:-- Area
=- : :Colony Obscl"\ations 5::;Data Analysis of Colony Obse... atioos '5 ':.-1 AI-SeaObse...·ations 5 :'5Data Analysis of At-Sea Obser..-ations
[95 195 19"
199 ::01 102
~: c Fledgling ;"'leawrements
~3RESLLTS
~3 IAmount ofPr~Delivered
~j: \Ia-ximum Foraging Distances
~j:;Parental Time Budgets
~:; 4 Splashdo.... n Beha\iour
~:;~Fledgling Condition
~-ID1SCLSSIO:--:
~-IIroraging Trip Duratiuns and ;"'Ia-ximum Foraging Distances :- -I:Pn:"lsionin~Behaviour andLifeHistor;. Slfategies :- -I3Fkdgling (ondition and Suni\al
:- -I -IPopulation Dynamics :: -I~ Summa~
~:- LITER.-\.TLRE CITED Chapter\"1 -Synthesis Discussion
oI BEH.-\.\-IOLR.-\L RESPO:\SES OF \lL"RRES TO CAPElr.\
~:'L"\1ERlCALRESPOSSESOF\fl"RRESTO CAPELr.\
03 FLTl"R.E RESEARCH
04 I\fPUC.-\T10"'S FORCOl'SERYATIO-..;
05 L1TERATl"RE (ITED
:03
:1.3
:Jc :18
::0 ::1
:35
LIST OF TABLES Table~Ia. Thestabilit~and abundance of capelin and conunon murre
aggregations inhigh-d<:nsit~sites that v.ere re\;sited around Funk Island. ·e Table~Ib The stability and abundance of capelin and conunon murre
aggregations in hig.h-density sites that v.ere reyisited around Great Island "5 Table~ ~:'\umber lJf return and depanure scans loundtobesi~ficantly
nunrandom and random at Funk Island and Great Island Table::.3 Lov.er and upper circular correlation coefficients for the mean angle
uf depanure and return directions at Funk Island and Great Island ..;7 Table::" Lov.er and upper circular correlation coefficients for the mean angle
uf \'\'ind direction~ersusthe mean angle ofretum flight diro:ctions, depanure dire\:lions trom splashdov.n areas and Ilight direct depanures lor murres from Funk Island and Great Island
Table .3 I The spatial scale of aggregation of rnurres and capelin.. the extent lJf cro.... ding within these aggregations. the distances belv.een major a~egationsand crov.ding within these aggregations and the scale of maxImum association between murres and capclin on July 18-~I Q7 Table .3':: The mean ::: SE lengths and masses of female and male capclin caught
in the l(av.1 along ""ith the \enicaJ location oCthe trawlinthe water column. to\,\, depth and densit: of capelin caught in the trawl from July
18~::8, 2000 100
Table .3.3 The mean .: SE capelin school characteristics and the characteristics 103
,,[their physical surroundings
Table 3 4 The habitat characteristics. li.sh and school type compositions of each loragingar~a.along with the persistem presence
"r
capelin schools and murres and the .. mabilit)' in capdin and murreTablej5 Lifetimetitne~functions. F(x..t. T). of an individual murre and its patch~Ie.:tiondecisions on its tirst and secondforagin~trip during a 16 hday
103
1O'J
113
157 Table 4 I Stable nitrogen and ..:arbon isolOpe concentrations.:. SD in primary
feathers of common murres and muscle tissue of capel in. the deri..ed trophic le.. els of .:ommun murres and the estimated mean proponion of .:rustaceans in the diets of common mUITes I.:. SE) collected in the :-..onh.... est Atlantic Fisheries Orltanization Di..isions 31\.. near the Funk Island seabird breeding colony
Table 4: The mean ::: SE of theagw~ationscales of common murres and acoustic scatter area from prey (capelin. total prey. non-capelinl. the densityUImorres and prey .... itrun aggregations (cro....ding). the maximum scale of association bet.... een murres and pre)'. and the density olmurres associated .... ith prey aggregations (cro.... ding) for continuous segments of transect (0.1 -:5 km. 0 I km binned datal during pre- brt:eding IMay, and post-breeding (August-September) periods in 1999 165 Table 4 3 The mean-=SE of the aggregation scales of common murres and 167
167
169 acoustic backscatter area from prey lcapelin. tota! prey. non-capelin). the density of murres and prey within aggregations Icrowding). the ma...imum scale of association~t',l,eenmurres and prey. ant! the density of murres associated wilh prey aggregations (crowding) for continuous
>e~ents oftran~ct(01 -:5 km. 0, I km binned data) in :'\onhwesl Atlantic Fisheries OrganizationDi~isions3KL(southern area) and2J Inonhem areal in August-September 1999
Tabl.: '" '" The scale of aggregation of common murres and acoustic backscatter area from prey tcapelin. total prey and non-capelin). Ihe densilYof murre5 and prey within aggregalions (cro.... dingJ, the ma.'limum scale of association bct....;:;:n murres and pre)' and the density of prey associaled .... ith murre aggregations lcro.... ding) for the ....hole survey (2 - :000km.
: km binned data) during pre-breeding I\fay) and post·breedingIAu~ust
September J periods in1999
Table 5 1 The mean:: SE mate paired durations(DDJand chick feeding rates at Great Island and Funk Island colonies in 1998 and 1999 combined :00 Table
5:
The percentages by number of knownfishspeciesdeli~eredtocommon murre chicks that were~isuallyidentified at Great Island and Funk Island in1998and1999
Table:; 3 Comparisons of parenl resting times. chick.feeding rales and chick measurements of common murres from this study andsimilarstudies in\'ol~inginterco]ony or interannual comparisons
xiii
20S
206
LIST OF FIGCRES
Fib'Ure :. I~1apof the study area sho....
mg
the Witless Bay and Funk Island seabirdbr~<iingcolonies on the east coastofi'\~""foundlandin the:'\onh.... est Atlantic 31
Figure:: The distribution and abundance of common murres and capelin around Funk1~landin : :5 km bins (a). location of :.:5kIncapelin hot
~P0ts(or above a,"erage capelin abundance scores. b). andth~Stability in presence of capelin at each hOI spot on subsequent re..isits (c) -'0 Figur~: 3 The distribution and abundance of common murres and capelin
around Great Island. WitlessBa~in::5krnbins (a). location of::5krn capelin hot spots lor above a.. erage capelin abundance scores. b). and the stabilit~in presence o( capelin at each hot spot on subsequent revisits(CI .g Figure:4 Circular plots of the proponions of common murres returning and
depaning from colonies in-IS")SC\."'tors on representative days. illustrating returning !lightdir~tionsin successi..-e sample periods (al. depanure Ilight directions from the splli5hdo.... n area in successi""e sample periods (bt"depanure flight directions from the nesting ledge in successive sample periodsIC).return and depanure llighl directions from the spla~downarea in the same sample period (d). and return and depanure flight directions from the nesting ledgeinthe same sample periods (e) -18 Figure : ..5 Distributions and densities of common mWTesflyingin all dire.."'tions
la;. nonheasl and southwest (b), and nonh.... est and southeast (c) around 54
Fun~Island
Figure:tIDistributions and densities of common mUrTestl~ingin all directions (aJ.nonh and south lb). and east and we:.1 tCI around Great Island 55 Figure'; I A map oithe study area.~ho",ingthe survey track.. seabird breeding
colonies. trawling sites. temperature, salinity sites and indicating the three ditTerent foraging sub-areas defined in chapter :.
Figure';: The distribution oi capelin (a) and murres (b) along transects and the univariate plots oilhe number oi'extra"nei~boursagainst the spatial scale of analysis for murres \ c I and capelin at specific depths (d l along
"ith the bi\-anate plots of the number of "extra" murrenei~bours[0 capelin schools against the spatial scale of analysis tel in the three main ioraging areas of common murres
Figure,;.~The propor.ion oi immature. mature and spent female and male capelin collet:ted during trawling in the three main foraging areas of
Figure:;-lThe percent of capelin with emptytoDO).less than 5000and greater [han 5000of their stomach full .-lffood in the three main foraging areas oj common murres
80
101
Figure:;:- The temperature and salinity in the study area from his'oric data in the study area in July during the 1990s ",ith the areas above and bela",
the thennocline indicated 105
Figure:;tIThe frequency of,;OO m: blOCKS along lhe entire survey route that III
.:omained increasing numbers of .:ommon murre wmpetitors laJ and the .:orrcsponding log-log plot Ib)
Figure 3 -; The outpul from the stead\ Slateforagin~model. with .:ompelitor densities in Area 2. held at I. 5. 10. and 15 ccmpetitors per 300 m: while densities in Area 1 were \aried. showing the net energy gained by the adult per ioraging trip (al by the adult per 10 h day (bJ and by' the chick per 10 h day \Cl
Figure ... I The map of the study area :>howing thet>main breeding .:olonies of
Figure
4:
The .:ruiSlt track for the \Iay 1999 SUl"\ey lal and the.~gustSeptember Iqq9sUf\e~(bl showing the location
1,)'
acoustic transects. the .:ominul,)us Sltgrnents oftranse,;:tv. here birdiOlammal counts v.ereIII
I"
140
158 condu.:ted simultaneously wilh acoustic recordingsofpr~'and the locations oftishing SItts where biological samples ""ere collecled 143 Figure 4 3 The distribution of common murres tlying lal and silting on the water
Ib) and the distribution of acoustic scatter area (S ,) due to total prey Ie) and due to capelin (d) during the \fay 1999 survey in the ;-";orthwest Atlantic Fisheries Organizalion Di\isions 3KL
Figure 4 ... The distribution of common murres flying (aJ and sitting on the ""ater (b) and the distribution of acoustic backscatter area(54.)due to tmal prey ICI and duetocapelin (d) during the \fay:000surveyinthe ;-";orthwest Atlantic Fisheries Organization Divisions 3KL
~i
159
101
102
100 Figure 4:; The distributionoffl~ingcammon murres (circles) and murre chicks
silting on the v,ater (squares. a). adult murres sitting on the v,aler (b) and the dislribution of acoustic backscalter area (5\) due to capelin (c) during the August-September sur'iey of1998in the~orthwestAtlantic Fisheries Organization Divisions~J3KL;'\'O
Figure 4_0 The distribution oftlying common murres and murre chicks silting on the v,ater la). adull murres sining on the water (b) and the distribution of acoustic backscatter area (5.\) duetototal prey lcl and due to capelin ld) during the August-September sun'ey of I'.199 in the~orth... est Atlantic Fisheries Organizalion Di\isions 2J3Kli'O Figure 5 I \tap of the study area showing the Witless Bay and Funk Island
seabird breeding colonies on the easl coastof~ewfoundland.
Figure 5 1_ The frequency of ma.'i:imum potential distances of foraging lrips preceding deli ....eries of Iish to chicks by common murres at Great Island
and Funk Island during IQq8 and]99Q :'08
Figun: 5.3 Map of the sun-e) area around Funk Island on July18-22.2000 :'09 Figure 5 4_ \Iap of the sun-ey area around Great Island on July 24.1998.May
:0
and 29. 1000. and June 1. 1000Figure 5.5 Relationship between body masses and wing lengths of common murre IledgJings al Greal and Funk Islands in 2000.
211
:58 LIST OFAPPE~DICES
Appendix 1 \ ·ariables and paramcters of the basic patch selection model tor a murre in o:ach foraging area
Appcndix:a The percenl composition by mass of each fishing set in the \fay 19Qq survey along \.\.ith the total mass of the catch
Appendi... :b The percem composition by ....eight of each fishing set in the August-September 1999sun.e~along .... ith the tOtal .... eight of the catch :bO :-\ppendi.'\.3 The number of marine birds and manunals obser.ed during ship
sun.eysinthe '\;orth\.\.est .-\lIantic Fisheries Organization Di\isions :J3K1. (August-Septcmber) and.3U t\lay, in 1998. 1999 and:ooo :b4
niii
CH...<\PTER I - Introduction
In the last t.... o decades it has been recognized that there is an increasing need to shift ITom single-species 10eco~]'S!em.le\'elmanagement. through the inclusion of multiple specIes under one conservation regime (Lud....ig et al 1993. PaulyetaI 1998. Pitcher 20011"-Ithough it is unclear ho\\. to proceed on a rigorous scientific basis. researchers are beginning to appreciate the importance ofidentil)ing patterns and understanding the underl~ingproces!'oeS Ihat intluence these panems within ecosyslems at widely val)ing spatial scales (SchneIder I(,Iq~)
Ecosystems are heterogeneous. \\.ith different processes intcractingtocreate hierarchical patterns thai change in time and space lHaury ct a! 1978. Wu and Loucks 1995) Thc spatial scale at which rerearchers study an ecosystem determines the types of processes and pancms described(Da~tonand Tegner 1<)8-11...ith smaller-scale patterns generally being masked at larger scales lWu and Loucks 19<;15) Ecosystems are characterized by small-scale pallems that are transient in space and time and. lhus. appear chaotic in nature tHaury ct aI 1<;178. Wu and Loucks 19(5) In contrast. large-scale pattcms are relali\'ely stable t Haul')'etaJ1978. Hunt and Schneidcr 1(,187. Wu and Loucks 19(5) Consequently. to accurately describe and understand thc linkages between trophic levels within an ecosystem. it is important 10 examine multiplc spatia! and temporal scales This type of research ",,-ill aid us in understanding and more adequatcly consen.-ing ecosystem- level processes under future management regimes
Foraging. strategies of predators are driven by the physiological requiremenls of Indi\~ualsandare shapedb~·locomolOry efficiency. perceptual constrainls.. learrung.
capacity and memory 1Pian 1990. Home and Schneider 19Q4). along \\'ith the distribution and beha\iour oflheir prty and inueraetions \\,ithcompetllo~tAllachin 1992. Bana and Szep 199:. 19951 The relative importance of each of these variables is species-specific and \\,ill determine the fonn of various responses ofpredato~to prey density t Pian iC>C101 Predator responses to prey density canbeboth beha\ioural. such as movements in response to prey denSity (aggregali\·e response. Hassell1966\and numerical. through changes in birth and death rales ofpredalOrs (Solomon IQ4Q) Rates at which predators consume prey (functIOnal response I. track prey (aggregative response). and reproduce I numerical response, ane all non-linear functions of prey density and distribution tSolomon 1Q4Q. Hassell I%6. Holling IQao.\1urdoch and Oaten IQ75) and are dependent on spatial scale tSchneider and Piatt 1Q86) These diverse predator responses topr~can l<2ld to comple, patterns of spatial distribution that are difficult to interpret For Instance. the scale al\l..~chmobilepredalO~track lheir prey (a&..2fegati...e response) has been found tobehighly \-ariable t Schneider and Pian 1986, E.umination of the faetol"i thai influence foraglng stralegies ofindi.."1dual predators will increase our underslanding oflhl:: causes of this ...ariabili~·in tracking scale and will pro\ide an opportunity 10 disentangle complex spatial patterns into a more interpretable contelCT..
Animals employ different behaVioural strategies to minimize energy expenditure and ausmem energy intake while foraging depending on Ihe spatial scaleatwhich they are
searching for prey' Pyke 1984. Russell et al 199:':) The use of pubhc information to locale food palches outside of\isual range Ie g Information Cente!" Hypothesis. Ward and Zaha\i 1973, or l4ithin \isual rangele_~IocaJenhancement.net...ork foraging.
Wirtenberger and Hunt 1985) maybeimportant in minimizing the~gyspent searching lor prey These social techniques.. however. may not increase~~.intake due to interference with olher compeUlors at the food patch (Sutherland 1983) Therefore. lhe tora£lng dcclsion of an indi\idual also v.ill depend on the c1lOices of iu competitors and will likely reflect the balance between cooperative and competitive interactions (Miliniski and Parker Iqq I) Criteria used to select food patches will depend on the characteristics of prey 'ol.ithin these patches le g prey density) as well as the presence ofcompetilors Paltems of distributIon of predators and their prey will retlect the importance of each criterion in meeting a predator's physiological requiremenu for SUT\ival
In Ihis thesis. 1exanu~patterns and theirunderl~in~mechanisms at a number of spalial and temporal scales v.1thm the manne ecosystem ofttle Northwest Atlantic Specifically.
I focus,:mbeha\ioural predator-prey interactions ofa marine di\ing bird. the common murrellr/UUU'¥~I.and i;:s main pre) species. capelin('\-(IlJl()lU.\,·/l'O)1l.\,I examine 00\4- the stralegies used 10 search lor prey and select prey patches influence population.1C'o'ei distribulion and variability in the spatial association panerns of predators and their prey Itracking scales)Utimatel~'.I examine how these foraginglpro\isioning strategies translale into population dynamics of predalors
I I SPECIES BACKGROL"'7'O
The common murre I('rlUuul!!t')\loas chosen for lhis Sludybecause il has been the focus of many studies on time and mer!y budgets (Cairns etillIq87.\9Q()l.responses 10pr~' tluetuations(Bur~erandPian Iqqo. \.10naghanetillIQ94. Cnleyetal lQ94), as well as many other aspects of breeding Isee Birkhead 1985) beha"iour Ie g. Burger 1997) and physiology (e g Crollet.II 1992. Croll and~cLauren1993) The common murre is a manne di\ing bird of the family Alcidae (alcid) that breeds in large coloniesathigher densities than any other a"ian species (Birkhead tQ77.IQ78)[I lays a single-egg clulch and pairs rear one chick at the colony (Gaston and Jones 1998JDuring thebrecdin~
season. these birds act as central-place foragers (Orians and Pearson [979) in that they carry food ITom foraging siles to otfspring at a breeding sile Central place foragers are
~enerallylimited by the: lime and energy expended during a round trip ITom the breeding site fOrians and Pearson1979\and.lhus. the time Spenl searching and foraging within a food palch are crucial faetOf's constraining breedingperfOI'1'TW'\Ceand foraging efficiency tClode \993) This is especially true for murresbecause their wing design is a compromise between underv.·aler night (low surface: area) and aerial flight lhigh surface area. Pennycuick1987)This results in a high \loing-Ioading..Ol"a high body mass to wing area ratio C! 06glcm;I. which placesthemclose to the flightless threshold (2 5~cm;.
Guiliemene 1994) Consequently. energy expended during flight ishighrelative to olher a\ian species (Pennycuick 1987) Consequences of this wing design are restrictions on the amount of food ingested during a foraging bout to retain the ability tofly(Sibly 1981.
Verlinden and Wiley 1989. Guillemette 1998) and low energy reserves stored in the body
(3 --Ida~'sof reserves in the "inter. I 5 -~:'days duringchick-rearin~.Gaston and Jones IQQS) Therefore. murres must eat a large percent of their body mass in fresh tOad per day(-100'0.Gabrielsen19Q41in order to meet energetic requirements for suf\.ivaL In addition. murres only deliver a single fish to their chicks at the colony after eachfora~in~
trip (single-prey loaders) and. thus. much energy is expendedtodeliver relatively little energy to chicks Tnerefore. murres are anex~lIentfocal species for the study of predator-prey interactions. due to their high energetic requirements
\Iurres are a long-lived species How individuals deal \.\ith high energy requirements depends on life history strategies (Steams19(1)and leads to various outcomes of parent- offspring conflicts (e g, timing oflledging. Ydenberg 19S9) L;1timately. individual variation in life history decisions resulls in varying body condition and suf\.;val probabilities of adults and young (Hatch 1983. Harris etal. 19(2)Life history theory poslUlates thai parents should maximize potential lifetime fitnessbybalancing present and future cOSts and benefits of reproduction (SteamsIqq~),Provisioning effon.
therefore. reflects the life history strategy ofa species tWeimerskirch etal IQ(7) Parents of long.lived species that invest heavily in indi\idual offspring (K-selected) are likely to lavour their O\.\T1 SUf\.ival over that of their offspring in any given year to prolong their lifespan and chances of future reproduction (Stearns IQqZ) InCOntrast.parents ofshon·
lived species that invest little in indi\·idual offspring (r-selected) are more likely to decide the opposite (Steams IQqZ). !\tunes have a post.hatching development strategy thai is intennediatebctw~precociaJ and semi·precociaJ (Ydenberg 1989) Chicks are reared at
the colony for approximately three lA.'eeks and depan at up to :!50'0of adult body mass (Harris and Birkhead 1(85) They are unable to fly or feed themsel\-es upon colony depanure and are accompanied by the male parent al sea for:! - 3 months (Swennen
lQ77. Bradstreet and Brown I(85)
Common murres feed on small pelagic schooling fish (Gaston and Jones 1(98) and are the pnmary 3\;an consumers of capelinIMailotlOs \',ilo.\Us)in the !\iorthwest Atlantic (Cairns etaJ 1990) Capelini~a small. short-lived (3 - 5YfJ.pelagic schooling fish lA.ith a circumpolar distribution in Arctic and sub-Arctic regions t\"ilhjalmsson 1994) In the
~orthwestAllantlc. capehn is a dommanl forage rish species and supports the upper trophicfOod.web ""ith marine birds. mammals and piscivorous fish (e g Atlantic cod (;adll.' morhllo)dependin!; on this species as prey in coastal waters. especially during the summer (Carscadden I(82) In ....e""foundland. capelin spawn during the summer primarily on or near gravel beache,; and only at one confirmed offshore spawning site on the Southeast Shoal of the Grand Banks (Carscadden IQ8:!. Carscadden et al. lQ8Q) The existence of bOlh modes of reproduction in one geographic area is uncommon and in most other regions capeJin either are beach-spawners (e g British Columbia.. Carscadden etal 1QgQ I or offshore-spa\l,ners (e g Barents Sea. Vilhjalmsson 1(94) Different spawning stocks have widelyv~;ngspa\,..ning habitat preferences (Vilhjalmsson 1(94) Females release all of their roe in one copulation event...hereas males release theirmilt over a number of events (Templeman 1(48) Copulation events generally involve contact with sediment. leading to injury tFidgeirsson 1(76) and resulting in a disproportionate
number of females sun.;\;ng spa....ning compared 10 males and. consequently. divergent life history suategtes (ShackellottaJ 1qQ4)
I: :'>'ORTHWEST .-\TLA..'\TIC ECOSYSTE\1.
The ocean climate olf~~foundlandand Labrador has been cooling since the late I960s.
reaching a hislOrical minimum in 1991 that has since reversed during the mid-I 990s cColboumeetal 1997) Trophic interactions ....;thin the \':onhwest .-\danlic ecoSY'stem are currentlyundergoin~changes due to the elimination ofa top predator. Atlantic cod ,Walters and \.1aguire 1996) The most remarkable and probably most imponant changes m<:lude the alcered distribution. biology and beha\;our of capelinMal/(J(u.,· n{fosu.f ICarscadden and Sakashima 1997. Carscadden et al :(01) During the 19905. the major post.spav,:ning concentrations of cape[in shifted fantler south into nontraditional areas lCarscadden and~akashima1997) but have recently returned to historical distributions ILilly and Simpson :000) The venical distribution of capelin in the water column also has become variable lShackelietal 1994. O'Driscoll et al :000) This is primarily revealed in the lack of consistem venical migration behaviour. whereas prior to the 1990s capelin used 10 regularlymo~'eup into surface .... alers at dusk andmo~'edeeper in the water column at dawn In addition.peakspawning has been one month later during the [990s.which was accompanied by smaller spawning fish. due to smaller age 3 fish and a higher proponion of age : fish spa\o\,ning (Carscadden and Sakashima 1997) Coincident withthese changes in the early 1990s. acoustic estimates of capelln biomass offshore have decreased significamly while estimates from research on spawning beaches have
remained consistent (Carscadden et al 200 I)S~abirdsappear to have responded to these changes in capelin biology and behaviour in complex wa)·s (e.g. Regehr and
\-tontevecchi 1997. Bryant etaI 199Q. Stenhouse and Montevecchi 1999. Massaro et al 2000. Carscadden et al submitted)
Duetothese changes and divergent biomass estimates. it has become increasingly imponant to investigate the beha\iour of capelin and its predatorstopredict how predato~will respond to these chan!Zes. both behaviourally and through altered demographic parameters (Veit e! al. 1993) Specifically. I need 10unde~tandhow the
~ha\iourof capelin and physical characteristics of capelin schools influence the multi·
scale search strategies ofpredato~along ....itht~selection of toraging habitat by predators It is also imponant to descnbe variability in the scale at which predators track capelin and identitY the faetors causing this variability This will allow ustopredict how the foraging strategiesofpredato~may change in relation 10 capelin density and abundance Finally. I need 10 understand how changes in capelin behaviour. biology and distribution affect demographic parameters of predator populations The integration of this information is the primary aim OltruS thesis. v.ith the ultimate goal of improving ecosystem-level understanding and approaches to marine conservation
I 3 CHAPTER OL'TLlNES
In Chapter 2. I examine the search beha\iour ofmurre5 Ie determine how they locate prey at sea on multiple spatial scales while rearing crucks at breeding colonies. Undemanding
ho... 5eabirds locate prey at sea is key to understanding ho... they will respond to changes in prey conditionst\"eit 1999). I teSI the relative imponance of information exchange at thecoJon~'nCRWard and Zaha\.iIQ73)and memory-based foraging in locating foraging habitats and 100d patches from the colony during chick.rearing I do this by quanti~ingthe arrival and depanure behaviour of murres from the breeding colony in conjunction with direct measures of Ihe distribution. density and spatial and temporal stabilitv of capelin aggregalions IA.lthin the foraging range of these animals (100 km:
CairnsetalIQ87. IQ9O)Many studies have tested the ICH in birds but e\.ldence of iniormation exchange at the colony on foraging sites out of visual range of the colony is unconvincing (BayerlQ81.Mock et alIQ88)and can generally be anributedtolocal enhancement (Andersson et al 1981. E,,"ans 1983. Flemming 1990. Poysa 1992. Smith 1995. \-1arzlutf et al. 1996. Buckley 1996, 19Q7) In contrast. many studies ha"'e sho"""
that birds consistently forage at specific locations (e.g Benvenuti eta1 1998. Irons 19(8) and there is some physiological e\.ldence that seabirds are capable to constructing and using complex spatial maps Ie £ Abbon et al 1999) Although there is a large literature on physicalleatures legbath~metric.hydrography) that lead to spatially predictable patchiness of seabird prey Isee Schneider 1991). few studies have determined whether prey patches are in fact stable enough for birds to use memory This is the main goal of the chapter
In Chapter 3. I e:umine the physical struet\lre of capelin schools and the scale-dependent spatial distribution of murre'S at sea in relation to capelin (tracking scale) during chick·
rearing I use information gleaned fonn the literarure to qualitatively modd the energetics ofmurn~5foraging in an area close 10 the breeding colony v.ith persistent capelin schools andin an area distant from the colony with unstable capelin sctlools I usc the theoretical framework of the Ideal Free Distribution liFO. Fretwell andLucas1970) and foragin!
theory (patch selectIon. Pyke 1984) as a basetOrmy model Linl';ng population-level distribution panems andpredator.p~spatial associations \.Vith physiological requirements ofpredalol'l pro"ldes a ..-a.Juable framework fO e:amine factors that Influence patch selectiondecisjon~of individuals {Home and Schneider 19941 I examine the consequences of interference aJ'T,ong competitol'l at prey patches throughmodelin~
Interference competition has not been studied explicitly before in akids I also describe some pre..iously unknown beha\iOllr of pre- and post-spawning capelin and continn some beha..iour of capdinpr~1OUslydescribed ITempleman IQ48. Jaan,gard 1974.
\llhjalmsson 1994) Such beha\lOUral studies arek~'in determining reasons for divergent biomass estimates of capelin and torincreasin~our underSlanding: of
no....
the changing beha..iour of capelin v.ill affect both the fonginglprO'oisioning strategies and demographic parameters of predators The integration of these sources of information is Imponant for- fannulatlng mechanistic hYPOlheses about predator-prey interactionsIn Chapter 4. I examme whether the locomotory capability of common murres15an important influence on the scale at which these mobile predators track their prey ltrackin~scale) under the framework. ofbeha\ioural predator-prey theory (e g a!!....lUegative response. Sih (984) To do this. I describe and compaTe the scale-dependent
10
panems of distribution ofmurr~in relation to their prev under two mobility regimes (I) during Ihe pre-breedingperiodwhen murres can fly and I:!} during the post-breeding or moultingperiod. ""'henmurresan~flightless and are accompanied at seabyflightless chicks I also document the relative contribution of preyIypesin murre diet during the moultmgperiodfor thefirsttime using stable Isotopic analysis I consider the perceptual constraints caused by reduced mobility (e g reduced knowledge oflocaJ prey patch Qualities and loca[ionSl, the energetic benefils of reduced mobility and how these factors interact to influence [he tracking scales of predators to their prey I also test the predictabilitv of murre and prey distributions among years and identify key marine areas used during both~riods
In Chapter:'. I examine he"" capelin distribution and beha...iour affects provisioning beha...iour. life historySlrategi~and the condition of chicks upon fledgmg and consider Ihe Implications lOr population dynamics tnumerical response) Specifically. I examine the pro...isioning constraintS on rnurres breeding at the largest andmostoffshore breeding colonyInthe :'Ioonhwest Allanuc To do this. I comparepro...isioning constrainu of common murres at IhJS large colony with those of conspec:ifics in lhe second IllT¥CSl colony in Ihe :'Ioonhwes( Atlantic I compare I I' preyIypesandfrequency of delivery (amount ofpreyt1~1maximum foraging ranges. 13t parental time budgets. (4) the at-sea behaviour of adult rnurres near each colony and (5) [he mass and condition (mass ' ""ing length) of fledglings I interpret inter-colony similarities and differences in provisioning constraints in terms of life history strategies andconseqUC'l'lCeSfor population dynamics.
"
Finally.Ipro~ideinsight into the underlying behavioural mechanisms that drive both tine- and meso-scale patterns of distribution and spatial associations bet...een predators and prey in Ihe~orthwesl-\llantlcecos~stemIalso describe how these patterns and processes influence population dynamics of predators This is timely due to recent changes in species interactions in this system. which result in the need for a bener understanding o(the linkages among trophic levels
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~aluralist123 1-13-1:'0
Smith. 1 P 1995 Foraging sociabilit\' of nesting wading birds (Ciconiiformes) at Lake Okeechobee. Florida Wilson Bulledn 107 ..07-4:'1
Solomon...\1E1Q-l9 The natural control of animal populations Journal of Animal Ecology 18 )-35
Steams. S C 19<12 The Evolution of LifeHis~Sev.' York Oxford L-ni\'eTsity Press
Stenhouse, I J &\10me\'ecchi. W:\ 1999 Indirect effects of the a\'ailability of capelin and fishery discards gull predation on breeding storm· petrels \t1arine Ecology Progress Senes 184 303-307
Sutherland. W J 1983 Aggregation and the 'ideal free' distribution Journal of Animal Ecologv 52 821-828
S...ennen. C 1977 Laboratory research on seabirds SIOZ. Texel 1-44
Templeman. VII 1948 The life history of the CaplinIM,,/lOIu,"I'//I{lsu.~0F Muller) in ...,:e...foundland waters Bulletin of the~ewfoundlandGovernment Laboratory So 171-151
L-nley. 1 D. Walton. P. Monaghan.. p.&.t.,ustin. G 1994 The effects of food abundance on breeding performance and adult time budgets of guillemots{'ria aalge Ibis 136 205-2[3
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Ward. P,&laha\i. A 1973 The importance ofcenain assembla!;es of birds as
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:!o3
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I :. CO-AL'THORSHIP STATE~tE~T
In the chap!ers of this thesis, my co-super....isors tOr Montevecchi and Dr Anderson) helped me formulate research questions and develop an integrated research program FoIIO\\.'ing this, I was solely responsible tor determining appropriate and. where necessary, designing field-based data collection methods. I was also exclusively responsible for collecting Ihe data or supervising dala collection, detennining appropriate
~talisticalanalysis techniques. analyzing the data and writing the manuscripts, The ex~ptionto this waschapler~,where the capelin acoustic data were provided in raw tonn by Dr Richard O'Driscoll (August-September 1998, IQ99) and Fran Mowbray (May 1qqq, 2000), Lpon finalizing these completed manuscripts. comments were obtained from my co-super.isors and ITom other members of my super.isory committee (Dr D Schneider and Dr B de Young). priortosubmission to the School of Graduate Studies
25
CHAPTER I1- Food-finding mechanisms of breeding common murres and the stabilityof prey patches
:: II:'\TRODLCTIO~
Belore a resource is exploited. animals must kno" where it is located (Clark and \langel 1<'}84 l Animals searching for tood patches mer a heterogeneous landscape must search on multiple scalestRussell et aJ 199:. Fauchald et aJ 2000) Therefore. the strategy used to locate prey by a predalOr "ill depend on the spalial scale over which and the temporal rate at "hich ilsfora~ngenvironmentchan~es(Pyke 198·41
",nimals provIsioning young from a central place are physically separated from their foraging environment and. thus. must lirst search for a foraging habitat. or area where food patches are likely to be found. and then search for food patches "ithin lhis habitat l \·eil 19991 Travel-time between the breeding site and food patches and toraging time
"ithin patches both limil the amount offood that young can be provisioned (Orlans and Pearson 1979) Central-place foragers may cope: with these constraints by combining different strategies For Instance. pelagic seabirds (Procellariiformesl alternale or mi.'l:
long foraging trips. where energetically efficient search strategies are used and food is pnmarily allocated to the parent. with shon foraging trips. where less efficient search strategies are used and food is primarily allocated to the chick (WeimerskirchetaL 1993.
1"94. 1997) Employing this mixed strategy doubles the frequency chicks aTe fed and allows parents to maintain their own body condilion (Chaurand and Weimerslcirch 1994.
Weimerskirch et al 1Q97) The search tactic employed controls the round-trip lime from foraging sites to the central-place and. thus. is a crucial factor ..:onslraining breeding performance (C1"de I(93) Consequently. animals may employ tactics that minimize the lime spent searching lorpr~
Information pro\ided by other individuals may increase foraging efficiency by allowing a more rapid location and exploitation of food patches (Ryer and alia 19CJI. 1992) For coloniall\" breeding seabirds. information may be exchanged at the colony about the location of distant food patches out ohisual range (4 5 km. Haney et al 19(2) of the colony (lnlormation Center Hypothesis. Ward and Zaha\"i 1<;173) or local food patches within \isua! range oithe colony (local enhancement. network foraging. Wittenberger and Hunt 1985) There is linle suppon for the Information (enter Hypothesis in birds
~e g Baver 1982. \lock et a! 19881 Most information exchange at colonies can be instead allributed 10 local enhancement. or birds cueing to the foraging acti..ities of other conspC(:ifics within \isual range of the colony (Andersson et al 1981. E\"ans 1<;183.
Flemming 1990. Poysa IQQ:. Smith 1995. Marzlutfet a! 19%.Buckl~'1996.1997) In addition.. Ihere is a growing literature showing the consistent use of eenain areas by seabirds at spatia! scales from~Tesdown to small tidal rips (Cairns and Schneider 19QO.
Hunt and Harrison 1990. Schneider 19911 Telemetry studies have also shown that indi..idual seabirds return to the same foraging sites (Benvenutietal. 1998. Hedd 1998.
(rons IQQ8) Therefore. foragers may learn from their past experience and rely on memory. rather than infonnation ex.change. 10 reduce the amount ofenergy expended
;;earching for food patches (Miliniski 1994. \1acknev and Hughes 199;) These different search tactics are not mutually exclusive and the exterll of their use may differ depending on the spatial scale animals are searching.. the behaviour of their prey. and Ihe characteristics of their toraging environment
The abundance. distribution and mobility of prey and the number of competitors in the vicinity ora colon... are the most imponant factors thaI interact to influence search tactics cAllachin 199::'. Bana and Szep 199~.1995) If food patches are dense. ephemeral and patchily distributed. the benefitS of increased foraging efficiency from information exchange outweigh costs of competition because a limited number of competitors locate food patches before they escape cDanchin and Wagner 1997) As the duration of patch persistence increases. more indi\iduals locate the patches and competition increases I Richner and Heeb 1995. Buckley 1997) At this point. competitors may distribute themselves among patches by combining past experience. or memory. in the patches and current information on the number of competitors and prey density (Ideal Free Distribution. Fretwell and Lucas 1970. Smith 199;) As Ihe number of individuals increase in a foraging habiuli. information on the position of distant and local food patches increases. This information results in increased foraging efficiencies if the search area is large or if prey is superabundant Othef\\-ise. decreased foraging efficiencies mav result due to the higher number of competitors Overa/i. Ihe search tactic employed by central-place foragers wiU reflect the balance between cooperative and competitive interactions among colony members at food patches
28
The common murre (,',,1,1UI,llgt!1is a marine di\inl; bird Ihat lay's a single-egg dUlch in dense colonies on islands (Birkhead 1977) .\1 large breeding colonies ofmurres. massi\'e tlocks of high-t1ying birds returningtothe colony are obvious and it has been suggested that naJve murres al the colony. or on the ...ater near the colony. may examine Ihese return tlight pathstogain infonnation on the location of distant foraging habitals (Gaston and Senleship 1981. Burger 1997) During the breeding season in Ne....foundland. murres teed their chicks and themselves primarily female capelin.\fal/om.~I'II/mlls(Pian 1987.
chapler:.'1 Parents deliver a singJe ti.sh to their chicks after each foraging trip Capelin is a small. schooling pelagic fish that spawns in large aggregations on coastal beaches during the summer in Se'4foundland (Templeman 1(48) Capelin schools are generally considered to be patChily distributed and ephemeral on a fine-scale (1 - 1000 ml but may be predictably located on a coarse-scale (I - 100 kmj ....ithin larger areas in different seasons I Schneider 1989. Pian 19QO: Rose and Leggett 1990. \1ethven and Piatt 1991) The stability of capelin aggregations on multiple scales in space and time. however. has not been direcrly measured
The goal of this study is to examine beha\iouraJ strategies used by common mUTTes to locate prey at sea on multiple spatial and temporal scales (Cairns and Schneider 1990) To do this. I quantify the arrival and deparrure beha\;our ofmuTTes from the breeding colony in conjunction INith direct measures of the distribution. abundanceandspatial and temporal stability of capelin aggregations INithin the foraging range of these animals (100
29
"-m. Gastor. and ;";ettleship 1981. Cairns et al 1987. 1990. Benvenuti et al 1998) Specificall\1.Iexamine the relative importan<:e ofinforrnation e....change31the colony and past experience. or memory. in locating foraging habitats on a coarse-scale and food patches ....ithin foraging habitats on a fine-scale from the colonyIdo not evaluate theuse of memory directly bUI ratherusethe temporal and spatial stability of capelin aggregations to Indicate whether seabirds could use memory to locate prey at sea. I predict thai if capelin aggregations are unstable in space and time, murres will use a higher degree ofinfonnalion e...change at the colony to locate prey. Alternalely, ifcapelin aggregations are stable or predictable, I predict thaI murres ....ill use a higher degree of memoryIalso compare the distribution and beha..iour of capelin around two breeding colonies along with the search tactics employed by murres at these colonies, which vary in population size. distance from the coast and species composition.
:::: \lETHODS
;;.::./. SlIId)'Ar.."
This study ...as conducted ini.".,,~-~OOOon and around Greal Island, Witless Bay (.rrlll';";.:;::0..9·W) and Funk Island(49045"~.53"1I'\\') on the east coast of
"e"'-foundland (Fig.:: I) In Witless Bay. apprmcimately 100,000 breeding pairs tb p ) of murres are di..ided up between three island colonies within10km of each other (Great Island 3.000 b,p, Gull Island' 1.000 b p. Green Island: 96.000 bp.) and. thus, are considered 10actas one population (chapter;) These islands are approximately 2km from shore. Funk Island is approximately 60 km from shore and holds 340,000 • 400.000
30
50
j
r I
I I
~
48 l_~_---,---r_~---r_W,it_le_SS,Ba_Y _I
46 ---j [-
58 56 54 52 50
Figure~1 \!tapof the study area sho....ing (he Witless Bay and Funk Island seabird breeding colonies on the east coast of \ie....{oundland in the ,"onhwesl
Atlantic
31
breeding pairs of murres (Canadian Wildlife Sel"\;ce unpubl data) Other species breeding at these colonies alsoteedon capelin (Cairns et al.IqS9)~ho.... ever. chese species generally do nOI feed logether (chapter 5) Therefore. Funk Island has 3 - 4 limes che number of competitors and is lanher from the coast chan Great Island. It is imponant 10 note thac Atlantic Puffins also relum 10 colonies in larg.e. high-l1ying flocks similar to common murres. and lhe sizes oflhe murre and puffin populations at each colony differs Al Greal Island..:!~-~of the birds relUming were common murres. whereas at Funk Island.
qq~~were common mUTTes ,Cairns et al19SQ\
::.::.::. Sf/n'n.I.-Il!thod~
Broad-scale vessel-based sUl"\'eys .... ere initially conducted around Great Island and Funk Island ";th the objectivc to detcnnine the location of areas where capelin and rnUTTes were hilfhly abundant in July "hen murre chicks were being reared (Fig. 2 I)SUl"\'~' roules .... ere established lhrough preliminary observations of returning tlight directions of murres IOwards each colony in 19Q7. infonnation from prc\;ous studies (e.g. Cairns et al 19Q(). Schneider et al 19Q()) and conservalions with local fishers One survey was conducted around Funk Island (SOO km) in 2000 aboard a 23 m Canadian Coast Guard
\'essel(Sham<XJk)and one more limited survey was conducted around Great Island (35 Ian)in 1998 aboard an 8 m commercial fistung vessel(MQ~~'Haun).
A Simrad EQ I00 echo-sounding~'scemwas used. operating through a hull-mounted single-beam transducer with a frequency of 38kHz.The lransduccr had a IO-degree
32
