•

• J THIS PAPER 15 NOT TO BE C1TED WITHOUT PRIOR REFERENCE TO TRE AUTHOR International Council for Qt 1976/N: 11 , . ~h~ Exploration of the Sea Marine Hamtn31s COmInittce GREY SEAL PUP PRODUCTION IN 1960 - 1975 \ ,

CF Summers

Institute for ~~rine Environmental Research, Seals Research Division c/o BritishAntarctic Survey, Cambridge

INTRODUCTION

Smith (1966) published the first detailed account of the size and distribution of Grey scal , Halichocrus ~rypus, brecding nssemblies in Orkney.\'Vaughan (1969) addedto and revised Smith's data. This paper presents'further extension and revision of the data and includes estimates ~f thc"number lof P;Xps taken by licensed hunters. . . ~ • HETHODS ,, Counts cf Grey sea~ pups were made during the breeding season around the ti~e of peak numbers ashore (Coulson & Hickling, 1964), either directly or from aerial photographs. However it is not possible even from ground counts, to co~struct a birth-iate curvc in the fashion of Coulson & Hickling (1964) and S~~ers, Burton and Andcrson (1975). These authors applied colour dye tQ the:pups/and assumed that the number of undyed animals I represented'the:increITßnt between counts. The use of colour,dye in Orkney would bc incompatible with the local' fishery for pup pelts. 'Consequently production has bccn dcrived from the;'count data by assuming the relationship bctwceri,numbcrs ßshore and productivity as described by Summers, nonner & vaI1 Haaften (in;press). Beca~se none of the published data from Orkney explain,how production estimates were derived from census data, all data froo'; 1960 onwards heId by SRD has' been reworked. '. ~, . " RESULTS AND DISCUSSION

Orkney breeding localities are shown in Fig 1; production estimates are sumoarised iri Table 1 and:Fig 2~ No estiIT~tes are given for the years 1962 ~ 1963 because hunting started before peak numbers could be assessed, or fof,,1972 when vcry fcw localities,were countcd. The killing of Grey seal pups in Orkncy"as a fishery protection mcasure was first licensed in 1962. -: Pup hunting'statistics provided by the Department of Agricul ~ure and Fisheries for are presented in Table 2. Total production in Orkney increased'at over 3% annually up to the late 1960's at which time the ycar'classes depleted by pup hunting, started to be recruitcd to tre br~eding population (Fig 2). ~ j

, " i ~ f ,.' ~. ". I • '. Local,trends lnproduct~v~ty have, however, shown marked,d~fferences (Fig 3).,Vau8han (1969) suggcstcd'that hunan disturbance iS,thc major factor in"dctcrniriing the distribution of thc brecding stock~ Far exarnple productiviiy at N, Fara fell dramatically in 1969 whcn an observer party spent three w~eks on the island during the pupping season, while the islands;of and nearby'Sweynholm were only minor breeding localities during" the eai:-ly 1960' s w~en Gairsay was inh~bitedo The Greenholms have

1 - #.

• sho~~ a steady decline in productivity since 1962. Since this timeboth the Firth and Spurness Sound became initially more productivebut';' by thc lnte 1960's productivity of Westray Firth had declined",,~,This was exacerbated by the increase in the proportion of the total Orkney hunting quota taken from the Westray Firth after 1968 when new owners of Little Linga refused to made the island available for hunting. lt seems likely therefore that these changes .in productivity at the Greenholms, Spurness Sound and Westray Firth, and the relatively recent establishment of breeding localities at the Point of Spurness, Lingaholm, Holm of Hüip, , Calf of and Stroma result from redistribution of the stock in response' to hunting.

REFERENCES

COULSON,J.C. and HICKLING, G., (1964). The breeding biology of the Grey seal Halichoerus grypus, (Fab.) on the Farne lslands, Northumberland. J. Anim. Ecol. 33, 485-512 SMITH, E.A., (1966):- A review of the world's Grey seal population. • J. Zool., Lond., 150, 463-489. SUMMERS, C.F., BONNER:-W. N. and van HAAFTEN, J. L., (in press). Changes in the seal populations of the . Proc. lCES Symp. Changes in the fish stocks of the North Sea and their causes. Rapp. P.-v. Reun. Cons. perm. int. Explor. Mer. SUMMERS, C. F., BURTON, R. W. and ANDERSON, Sheila S., (1975). Grey seal (Halichoerus grypus) pup production at : A study of birth and survival statistics collected in 1972. J. Zooi., Lond.~ '175, 439-451 - VAUGHAN, R. W. (1969). Grey seal numbers in Orkney. Mamm. Soc. Br. Isles, • Bull., 32: 11-15

- 2 - .. FIG" 1 Grey seal breeding localities in Orkney. For key to localities see Table 1 •

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, \ .... 5 10 15 20 o• , , I , 'km

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TABLE GREY SEAL PUP PROOrCTION IN ORK1~Y (1960 - 1975)

J. 1960 1961 1964 1965 1966 1967 1968 1969 1970 1971 1973 1974 1975 .(> 1 Muckle Greenholm 880 645 1120 805 825 720 780 680 895 705 605 ·630 580 2 Little Greenholm 240 365 590 460 570 560 390 375 400 440 260 240 290 GREEllHOLMS 1120 1010 1710 1265 1395 1280 1170 1055 1295 1145 865 870 870 a 3 Little Linga 300 315 195 350 430 495 500 720 650 885 650 600 605 4 Holms of Spurness 120 165 35 185 185 130 370 250 180 210 310 195 360 5 Point of Spurness 10 55 60 80 25 60 6 Lingaholm 20 40 60 190 245 85 55 7 Holm of Huip 30 40 115' I 180 155 SPURNESS SOUND 420 480 230 535 615 .625 890 1020 975 1385 1400 1085 1235

8 Holm of Fara 565 385 . 30 145 345 345 330 275 '220 410 450 640 610 9 North Fara 160 205 210 225 350 40 130 120 50 100 90 10 Ruskholm 260 320 260 310 110 315 245 260 280 130 20 165 80 11 Wartholm 50 40 20 35 10 10 10 5 5 20 15 0 5 WESTRAY FIRTH 875 745 470 695 6'15 895 935 580 615 680 535 905 785 a 12 Sweynholm 80 ) a 110 105 20 95 115' 180 150 75 30 150 13 Grassholm 5 90 25 ) 50 80 90 55 125" 95 30 d GAIRSAY AREA 80 120 105 150 160 185 ·110~: 150 240 275 180

160 185 155 125 180 150 165 240 14 150a 185 140 90 130a 65 90 75 15 5 5 20 25 20a 10 35 45 55 85 16 Pentland Little Skerry 120 60 30 105 60 45 . 65 25 105 45 65 90 60 PENTLAllD FIRTH 275 250 265 220 210 215 285 225 285 310 280 345 375 17 AUSKERRY 130 125 225 ORKllEY 2690 2485 2680 2835 3000 3165 3440 3065 3280 3670 3450 362i: 3740° ......

a estimate, no adequate data b including 20 at (20) c including 40 at (20) Calf of Eday and 30 at (19) Stroca d occasional births recorded at (18) Gairsay •

• FIG 2.. Grey seal production in Orkney 1960 - 1975. The exponential log n:i: 0.033t+ 5.8408 (r 0.89; p<: 0.01) is fitted for • e = the years prior to the recruitment of hunted year classes

o o o

3500 o o • o

o

3000

_2500

•

2000

1960 1965 1970 1975 TABLE 2 h"IDfBERS OF PUPS TAKEN UNDER LICENCE IN ORK1"'EY (1962 - 1975)

1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1~75

GREENHOLMS 307 420 436 433 454 351 390 354 386 315 400 486

Little Linga 44 98 120 120 Spurness (Holms & Pt) 16 30 50 46 64 51 100 125 74 Lingaholm 30 10 112 Holm of Huip 50 SPURNESS SOUND 60 98 120 120 30 50 46 94 61 212 125 124

N'Fara/Faraholm 80 150 210 212 270 380 380 a 50 72 Ruskholm/Wartholm 164 192 162 148 190 195 140 80 40 40 70 40 WESTEAY FIETE 164 192 162 198 270 267 290 290 252 310 450 420 b c EIsewhere 30 8 20e Unspecified 6 d d ORKNEY 736 943 531 710 754 751 754 668 726 746 699 837 975 1050

......

," a including a few from Grassholm b Sweyholm/Gairsay/Borayholm c Sweyholm/Gairsay d islands hunted were Greenholms/Little Linga/N Fara/Faraholm/Ruskholm/Wartholm/N Ronaldsay/ plus Holms of Spurness in 1963 e Calf of Eday

• • • FIG 3 Fluctuations in Grey seal pup production in the Orkney a .localities affected by hunting • 11 ••.. ••• • •• •• •• •• •••• •• •• •• •• ••• • 1500 : ~ ~ 1.. • _._.~ .... \ r \ ~.... '. .... ~ .... t.. I\ ... ",. -.. : -·.1' .,. ... ~:e.....~ .I l: •..•... .l" I ..•• , ./ . .. I" : ~ : ~. ~ .••.. .• ••., ...... ' ..•. ~ .. ,," .... 1000 /...... ~ '. ••.....

500

1960 ]965 ]97Q 1975

KEY

...... ••.. Greenholms

------Spurness Sound

Westray Firth