of specific aspects of the biology, population dynamics and interspecific

Transcription

1 Summary The South African (Cape) fur seal Arctocephalus pusillus pusillus is the only pinniped endemic to Southern African waters, occurring mostly off the South African and the Namibian west coasts. Because of the high productivity in this region, they share these waters with a profitable fisheries industry. Since the Cape fur seal population consumes an estimated 2 million tons of food annually, with some 60% of their prey species comprising commercially valuable fish, the fisheries and the seals are generally seen as competitors for a common resource, and biological interactions (seals depriving fishermen of their livelihood) and operational interactions (seals directly interfering with fishing operations, or damaging equipment) between them are often believed to be severe. Since culling (in South Africa) has had a moratorium placed on it in 1990, and since the Cape fur seal population has been increasing at 3% annually since the seventies, numbering some 2 million individuals at present, the perception has grown that the fisheries industry will receive a substantial boost, should the fur seal population be artificially reduced, although this view is not supported by any clear evidence. Addressing this complex management issue requires improved knowledge of specific aspects of the biology, population dynamics and interspecific interactions of the Cape fur seal. To assist with this, this study entailed an examination of the reproductive organs of 159 Cape fur seal females, collected by Marine Coastal Management (formerly the SFRI), mostly at sea during annual 98

2 cruises (n = 98) but also on land at the Kleinzee breeding colony on the South African west coast (n =61). A lack of standardization has meant that only 119 females had samples of their uterine horns stored with the ovaries, requiring that reproductive history at times had to be inferred from ovarian appearance alone. Samples from each ovary of 46 females were also examined histologically. Using this material, an examination of the annual ovarian size and weight cycles were conducted. An indepth macroscopic and microscopic examination of the follicular and luteal cycles were also conducted. VVith the ages of 83 of the females having been determined to date, the information obtained from the morphological study was used to calculate a number of reproductive population characteristics. Firstly, the overall and the agespecific pregnancy rates were calculated (pregnancy being defined as successful implantation having occurred). Pregnancy rate for the current reproductive cycle was calculated at 0.902, while birth rate for the previous cycle was estimated at Age specific pregnancy rates were very erratic between ageclasses, possibly due to small sample sizes for some age classes, but appeared to be low (0.166) at 3 years, peaked at 6 years (0.909) and remained high in the oldest (13+ years) age group. The average age of puberty (where ovulation commences, as evidenced by mature follicles, CLs or CAs) was estimated at 4.34 years, dropping slightly to 4.31 years if second CAs are included in the calculation. The average age of sexual maturity (where reproduction first becomes possible, as evidenced by 99

3 successful implantation of a blastocyst, irrespective of whether or not the pregnancy was then carried to term) was estimated at 5.02 years. A comparison between gravid CLs and CLs of nonpregnancy/abortion showed that no differences could be detected until implantation. Differences increased with increasing time after implantation, but with an apparent retardation in CA resorption rate at, or before, the time of implantation in the opposite uterine horn, the differences between CAs resulting from abortions and those resulting from pregnancies became smaller. At that stage, placental scars assume greater importance in distinguishing between them. While certain errors in the study are acknowledged, the information gained has assisted in obtaining a fuller, qualitative understanding of the reproductive biology of the Cape fur seal, and has provided some quantitative information on reproductive population characteristics. This information can be used, or can be expanded upon to extend understanding of the population dynamics of the Cape fur seal for conservation and management purposes. 100

4 References Andersen, 1\11., Hjelset, A.M., Gjertz, I., Lyderson, C. & Guliiksen, B Growth, age at sexual maturity and condition in bearded seals (Erignathus barbatus) from Svalbard, Norway. Polar Biology 21 : Amoroso, E.C., Bourne, G.H., Harrison, R.J., HarrisonMatthews L., Rowlands I.W. & Sloper, J.C Reproductive and endocrine organs of foetal, newborn and adult seals. Journal of Zoology 147: Angot, M Observations sur les mammiferes marins de I'archipel de Kerguelen, avec une etude detaillee de I'elephant de mer, Mirounga leonina (L.). Mammalia 18:1111. Bengtson, J.L. & Siniff, D.B Reproductive aspects of female crabeater seals (Lobodon carcinophagus) along the Antarctic Peninsula. Canadian Journal of Zoology 59: Bester, M.N. & Kerley, G.I.H Rearing of twin pups to weaning by subantarctic fur seal, Arctocepha/us tropicalis female. South African Journal of Wildlife Research 13:8697. Bester, M.N Reproduction in the female Subantarctic fur seal, Arctocephalus tropicalis. Marine Mammal Science 11 : Bj0rge, A The reproductive biology of the harbour seal Phoca vitulina L., in Norwegian waters. Sarsia 77:

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6 Butterworth, D.S Will more seals result in reduced fishing quotas? South African Journal of Science 88: Butterworth, D.S., Duffy, D.C., Best, P.B. & Bergh, M.O On the scientific basis for reducing the South African fur seal population. South African Journal of Science 84: Butterworth, D.S., Punt, AE., Oosthuizen, W.H. & Wickens, P.A The effects of future consumption by the Cape fur seal on catches and catch rates of the Cape hakes. 3. Modelling the dynamics of the Cape fur seal Arctocephalus pusillus pusillus. South African Journal of Marine Science 16: Canivenc, R. & Bonnin, M Environmental control of delayed implantation in the European badger (Meles meles). Journal of Reproduction and Fertility, Supplement 29:2533. Craig, AM Histology of reproduction and the oestrus cycle in the female fur seal, Callorhinus ursin us. Journal of the Fisheries Research Board of Canada 21 : Coulson, J.C A study of the factors influencing the timing of breeding in the Grey seal Halichoerus grypus. Journal of Zoology (London) 194: Daniel, J.e Delayed implantation in the Northern fur seal (Callorhinus ursinus) and other pinnipeds. Journal of Reproduction and Fertility, Supplement 29:

7 David, J.H.M. 1987a. Diet of the South African fur seal ( ) and an assessment of competition with fisheries in southern Africa. In The Benguela and comparable ecosystems. Payne, AI.L., Gulland, J.A & Brink, K.H. (Eds). South African Journal of Marine Science 5: David, J.H.M 1987b. South African fur seal Arctocephalus pusillus pusillus. In Status, biology and ecology of fur seals: Proceedings of an international workshop, Cambridge, England 2327 April Croxall, J.P. & Gentry (Eds). NOAA Tech. Rep. NMFS 51 :6571. DeMaster, D.P Calculation of the average age of sexual maturity in marine mammals. Journal of the Fisheries Research Board of Canada 35: OeMaster, D.P Review of Techniques Used to Estimate the Average Age at Attainment of Sexual Maturity in Marine Mammals. In Report of the International Whaling Commission (Special Issue 6): DeVilliers, D.J. & Roux, JP Mortality of newborn pups of the South African fur seal Arctocephalus pusillus pusillus. South African Journal of Marine Science 12: DeVilliers, D.J., Oosthuizen, W.H., Roux, JP & Kotze, P.G.H Population structure of a nonbreeding colony of the Cape fur seal Arctocephalus pusillus pusillus at Cape Frio, Namibia. South African Journal of Marine Science 18: Enders, R.K., Pearson,O.P. & Pearson, AK Certain aspects of reproduction in the fur seal. Anatomical Record 94:

8 Fay, F.H b. Walrus, Odobenus rosmarus. In Handbook of marine mammals Vo1.1. The walrus, sea lions, fur seals and sea otters, pp 123. (eds. Ridgway, S.H., Harrison, RJ.). Academic Press, London. Fowler, J. & Cohen, L Practical statistics for field biology. John Wiley & Sons, Chichester, Hayama, S., Suzuki, M., Uno, H. & Yamashita, T Female sexual maturity and delayed implantation period of the Kuril seal. Scientific Reports of the Whales Research Institute 37: Harrison, RJ Reproduction and reproductive organs. In The biology of marine mammals. Edited by H.T. Andersen. Academic Press, London. pp Harrison, R.J. & Kooyman, G.L General physiology of the pinnipedia. In The Behaviour and Physiology of the Pinnipeds, pp (Eds. Harrison, R.J., Hubbard, R.C., Peterson, RS., Rice, C.E. & Schusterman, R.J.). Appleton, New York. Hewer, H.R The determination of age, sexual maturity, longevity and a lifetable in the Grey seal (Halichoerus grypus). Proceedings of the Zoological Society of London 142: Iwasa, M. & Atkinson, S Analysis of corpora lutea to estimate reproductive cycles of wild Hawaiian monk seals (Monachus schauinslandi). Marine Mammal Science 12(2):

9 Iwasa, M. & Atkinson, S Lipofuscin granular cells in regressing corpora lutea and corpora albicantia of ovaries from Hawaiian monk seals (Monachus schauinslandi). Marine Mammal Science 13(2): Johanos, T.C., Becker, B.L. & Ragen, T.J Annual reproductive cycle of the female Hawaiian monk seal (Monachus schauinslandt). Marine Mammal Science 10(1 ): Kerley, G.I.H Record for the Cape fur seal Arctocephalus pusillus pusillus from subantarctic Marion Island. South African Journal of Zoology 18: Laws, RM The elephant seal (Mirounga leonina Linn.) III. The physiology of reproduction. Scientific Reports of the Falklands Islands Dependencies Survey No pp. Laws, RM Chapter 12: Seals. In Antarctic Ecology (vol. 2) (ed. RM. Laws). Academic Press, London. Laws, RM. & Sinha, A.A Chapter 13: Reproduction In Handbook on Antarctic seal research methods and techniques (ed. RM. Laws). Cambridge University Press, Cambridge. Le Boeuf, B.J Sexual strategies of seals and walruses. New Scientist 16:3639. Lima, M. & Paez, E Growth and reproductive patterns in the South American fur seal. Journal of Mammalogy 76: Lima, M. & Paez, E Demography and population dynamics of South American fur seals, Journal of Mammalogy 78:

10 Lunn, N.J., Boyd, l.l. & Croxall, J.P Reproductive performance of female Antarctic fur seals: the inlluence of age, breeding experience, environmental variation and individual quality. Journal of Animal Ecology 63: McLaren, I.A The biology of the ringed seal (Phoca hispida Schreber) in the eastern Canadian Arctic. Bulletin of the Fisheries Research Board of Canada No pp. McLaren, l.a. & Smith, T.G Population ecology of seals: retrospective and prospective views. Marine Mammal Science 1 :5483. Mead, R.A Delayed implantation in mustelids, with special emphasis on the spotted skunk. Journal of Reproduction and Fertility, Supplement 29: Miller, C.M., Oosthuizen, W.H. & Wickens, P.A Cape fur seals trapped in trawling gear: age structure, sex ratio, seasonality and distribution. South African Journal of Marine Science 17: Moller, O.M. 1973a. The progesterone concentrations in peripheral plasma of the mink (Mustela vison) during pregnancy. Journal of Endocrinology 56: MondainMonval, M., Bonnin, M., Canivenc, R. & Scholler, R Plasma oestrogen levels during delayed implantation in the European badger (Meles meles L.). General and Comparative Endocrinology 41 :

11 Oosthuizen, W.H General movements of South African (Cape) fur seals Arctocephalus pusillus pusillus from analysis of recoveries of tagged animals. South African Journal of Marine Science 11 :2129. Oosthuizen, W.H Age determination of South African fur seals (Arctocephalus pusillus pusillus). M.Sc Thesis, University of Pretoria, Pretoria. Oosthuizen, W.H Evaluation of an effective method to estimate age of Cape fur seals using ground tooth sections. Marine Mammal Science 13: Oosthuizen, W.H. & David, J.H.M Nonbreeding colonies of the South African (Cape) fur seal Arctocephalus pusillus pusillus in southern Africa Investigational Reports of the Sea Fisheries Research Institute of South Africa 132:17pp. 0ritsiand, T The biology of the ringed seal (Phoca hispida) in the eastern Canadian Arctic. Journal of the Fisheries Research Board of Canada Bulletin 118:7981. Ouelette, J. & Ronald, K Histology of reproduction in harp and grey seals during pregnancy, postparturition and oestrus. Canadian Journal of Zoology 63: Pearson, A.K. & Enders R.K Further observations on the reproduction of the Alaskan fu r seal. Anatomical Record 111 (4):

12 Multiple births in the northern fur Zeifschrift for Saugetierkunde G.C., Spalding, D.J., MacAskie, LB. & Craig, A.M Report on Canadian pelagic fur seal Canada, BioI. MS Report, No. Pimlott, D.H. & Mossman, H.W. 1 in Fisheries Research Board 101 pp. A macroscopic ovary sectioning Journal of Wildlife Management... v.,'v& Twin seals in of Zoology (London) 1 1 Reproduction in the fur seal, Arctocephalus pusillus (Schreber). Proceedings of the Zoological Society of London 124: M.B. & Calaby, J.H UClIJI"\\.1 embryonic diapause. Journal of... l.rtrrt,rt. to delayed implantation and and Fertility, 19. Reijnders, P.J.H throughout the reproductive concentration profile harbour seals (Phoca vitulina). Journal of Reproduction and Fertility 90: man, M The pinnipeds: California Press, Berkeley. ndell, M To have or not to I sea lions and walruses. University of implantation: the example of the weasel and the stoat. Dikos 42(1):

13 Shaughnessy, P.O Cape (South African) fur seal. In Marnmals in the Seas. Food and Agricultural Organisation Fisheries Series (voi.2). pp Siniff, D.B. & Stone, S The role of the leopard seal in the trophodynamics of the Antarctic marine ecosystem. In Antarctic Nutrient Cycles and Food Webs: (Eds. Siegfried, W.R., Condy, P.R. & Laws, R.M.). SpringerVerlag, Berlin. Sirotkin, AV. & Schaeffer, H.J Direct regulation of mammalian reproductive organs by serotonin and melatonin. Journal of Endocrinology 154:15. Spotte, S The incidence of twins in pinnipeds. Canadian Journal of Zoology 60: Smith, E.A Adoptive suckling in the grey seal. Nature 217: Stevens, A. & Lowe, J.S Chapter 18: Female reproductive system. In Histology. Mosby, St. Louis. Stewardson, C.L., Bester, M.N. & Oosthuizen, W.H Reproduction in the male Cape fur seal Arctocephalus pusillus pusillus: age at puberty and annual cycle of the testis. Journal of Zoology (London) 246:6374. Tedman, R.A The female reproductive tract of the Australian sea lion, Neophoca cinerea (Peron 1816) (Carnivora: Otariidae). Australian Journal of Zoology 39: Temte, J.L Photoperiod and delayed implantation in the Northern fur seal (Cal/orhinus ursinus). Journal of Reproduction and Fertility 73:

14 Temte, J.L Photoperiod control of birth timing in the harbour seal (Phoca vitulina). Journal of Zoology (London) 233: Temte, J.L. & Temte, J Photoperiod defines the phenology of birth in captive California sea lions. Marine Mammal Science 9: Wheater, P.R, Burkitt, H.G. & Daniels, V.G Chapter 19: Female reproductive system. In Wheater's functional histology: a text and colour atlas, 3rd ed.. Churchill Livingstone, Edinburgh. Wickens, P.A, Life expectancy of fur seals, with special reference to the South African (Cape) fur seal. South African Journal of Wildlife Research 23: Wickens, P.A Interactions between South African fur seals and the purseseine fishery. Marine Mammal Science 10(4): Wickens, P.A l\iamibian sealing debacle: an environmental disaster and managerial blunder. African Wildlife 49(3):611. Wickens, P.A, David, J.H.M., Shelton, P.A & Field, J.G Trends in harvests and pup numbers of the South African Fur seal: implications for management. South African Journal of Marine Science 11 : Wickens, P.A., Japp, D.W., Shelton, P.A., Kriel, F., Goosen, P.C., Rose, S., Augustyn, C.J., Bross, C.AR, Penney, AJ. &Krohn, RG Seals and fisheries in South Africa competition and conflict. South African Journal of Marine Science 12: Wickens, P.A. & York, A.E Comparative population dynamics of fur seals. Marine Mammal Science 13:

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16 Key to Appendices Due to constraints of space, certain abbreviations were used in the appendices, which are explained further here Appendix 1: Abo Bias Abortion A blastocyst was observed in the relevent uterine horn NM No sample of uterine mucosa available, accompanying relevant ovary NonImp A corpus of ovulation is present, but has not been followed by implantation by the blastocyst NP Not pregnant, but showing signs of recently having been pregnant (e.g. has a large placental scar) RepCon Reproductive condition of the female in the breeding season during which she was collected (referring to the CL) RepHis Reproductive history of the female during the previous reproductive season (referring to the 1 st CA) ZB Zonary band Where reproductive failures have been deduced, relevant values are highlighted 113

17 Appendix 2: CLiCA nr. The number of Graafian follicles in the ovary with a CL or CA respectively (except in immature females, where the largest ovary was arbitrarily chosen as the CL ovary) CLiCA diam The size of the largest follicle in the ovary with a CL and CA respectively (except in immature females, where the largest ovary was arbitrarily chosen as the CL ovary). Appendix 3 I 4: CLiCA The ovary containing a CL or CA respectively, except in the case of immature females, where the largest ovary was chosen arbitrarily as "CL". 114

18 Appendix 1: Sizes of CLs I CAs (mm), as well as reproductive state of female Month Comments Age (yrs) 10 number Size (mm) of corpora lutea/albicantia CL RepCon. CA 1st RepHis CA 2nd CA 3rd January ZB ZB ZB 8.33.' 1' CA failure ZB Abo i I >. >. CJ ZB ZB ZB ZB ZB CA failure Nonimp ZB ZB ZB L

19 DoubleCl / Cls NM NM NM , NM NM >. >. 0) Month Comments Age 10 number Size (mm) of corpora lutea/albicantia. Cl RepCon CA 1st RepHis CA 2nd CA3rd February ZB ZB Bias ZB 3.00 CA failure Nonimp ZB ZB 5.25._ Month Comments Age 10 number Size (mm) of corpora lutea/albicantia Cl RepCon CA 1st RepHis CA 2nd CA 3rd March ZB ZB Bias ZB 3.43

20 >. >. oj Bias ZB ZB 1.90 CA failure Nonimp , ZB CA failure Nonimp. CA failure Nonimp Bias ZB ZB 4.46 ~ CA failure Z8Abo ZB 4.72.r' CA failure Nonimp APP NM CA failure APP NM APP NM 1.51 APP NM 3.12 APP NM 3.15 _.. _,...,

21 Month April Comments Immature Age ID number CL _ Size (mm) of corpora lutea/albicantia C~~dj RepCon CA 1st. RepHis CA2nd Implanted ZB! Implanted ZB Implanted 9.53 ZB Implanted ZB OJ CA failure CA failure Immature ,64 Nonimp ZB 8.67 Nonimp Implanted ZB ZB CA failure ZB Nonimp Implanted ZB 2.85 I Implanted ZB 2.79 ' Implanted ZB, _.

22 Month Comments Age ID number Size (mm) of corpora lutealalbicantia CL RepCon CA 1st RepHis CA2nd CA 3rd May Implanted 8.42 ZB CA failure Nonimp Implanted Implanted ZB CA failure Implanted 6.86 Nonimp (0 Immature Implanted Implanted ZB ZB Implanted ZB Immature Immature 3 CL absent Implanted ZB

23 Month Comments Age 10 number CL Size (mm) of corpora lutealalbicantia.. RepCon CA 1st RepHis CA2nd CA 3rd June Pregnant. f Pregnant Pregnant ZB Pregnant ZB Pregnant Pregnant Pregnant >.. o'" Pregnant ZB Pregnant CA failure Pregnant Pregnant 2.80 Nonimp. Cl failure CA failure ZBAbo ZB Pregnant ZB Pregnant 5.18 ZBAbo Pregnant 8.21 ZB

24 >. N >. Month Comments Age ID number Size (rnm) of corpora lutea/albicantia ' r CL RepCon CA 1st RepHis CA2nd CA 3 rd 1 July CA absent Pregnant Pregnant ZB Pregnant 9.19 ZB CL failure ZB ~Abo ZB 2.22 CA failure Pregnant 8.23 Nonimp Pregnant ZB _ ZBAbo ZB,. Month Comments Age ID number Size (mm) of corpora lutea/albicantia CL RepCon CA 1st RepHis CA2nd CA 3rd August Pregnant 8.91 ZB Immature CL failure ZBAbo 6.54 ZB Pregnant 7.01 ZB 4.25 ḻ Pregnant ZB Pregnant 7.99 ZB._ Pregnant 7.66 ZB Pregnant ZB 3.44 I I

25 OoubleCA Pregnant Pregnant 14.72& l B l B Month Comments Age 10 number Size (mm) of corpora lutea/albicantia Cl RepHis CA 1st RepHis CA2nd Newel October Pregnant lb 3.34 ' I'V I'V Cl fa~lure Cl failure Pregnant lb 4,92. lbabo 7.20 lbabo _ Pregnant 7.92 lb Nonimp lbnp 5.20 Nonimp Cl failure Nonimp lb ,_... Pregnant 6.64 lb I OoubleCA lbabo 9.87 Immature Cl failure lbnp Pregnant 8.97 lb lb ~ NP 3.33 lbabo _, lbabo 3.33 Nonimp. '

26 Pregnant ZB Z8NP 9.00 ZB Month Comments Age 10 number Size (mm) of corpora lutea/albicantia >. I\.) w November CL failure CL failure CL failure CL RepCon CA 1st RepHis CA2nd New CL

27 Cl fa~lure f ,16.._ _., I I I' ,, '" ~ ~ Cl failure , \ _ ~ Pregnant 9.60 Month Comments Age ID number Size (mm) of corpora lutea/albi cantia Cl RepCon CA 1st RepHis CA2nd NewCl December Pregnant 9.78 ZB 9.41

28 Pregnant Pregnant 8.40 ZB Pregnant Pregnant 1.64 Abo N (]1

29 Appendix 2: Numbers of follicles per ovary, and the size (mm) of the largest follicle in each... 0') '" Cl nr. Cl diam CAnr. CAdiam Cl nr. Cl diam CAnr. CAdiam _. January February _. '' _ a a a

30 , ' ', CL nr. CL diam ~..~ CA nr. CA diam CL nr. CL diam CA nr. ea diam March April N...J Immature Immature _

31 APP APP APP APP APP _ Cl nr. Cl diam CA nr. CAdiam Cl nr. Cl diam CA nr. CAdiam May June ~ co '" Immature Immature Immature ~ ~~

32 Cl nr. Cl diam CA nr. CA diam Cl nr. Cl diam CA nr. CA diam July August Immature ~ N < " Cl nr. Cl diam CA nr. CA diam Cl nr. Cl diam CA nr. CA diam October Nov

33 ~ _ ~, 2, ' ~~ ~ I'"'~""'''', Immature ~>~ >. c.v o ,73 30~ ~ _ o f

34 ~ v.> ~ Nov. (cont.) Cl nr. Cl diam CAnr CA diam _ ~ Dec _ CL nr CL diam CA nr CAdiam~ ~ I!

35 Appendix 3: Sizes (mm) of ovaries with corpora /utea and ovaries with corpora albicantia >. c..v N, CL CA CL CA CL CA. January February March _._ r , , , ,_ APP ~

36 f 1. APP6 APP APP " APP CL CA CL. CA CL CA... w April May June Immature Immature Immature Immature c Immature

37 r _..._'.' _._._,_ r' July 3458 CL CA '' August 4051 " CL 30.84, CA CL CA, October c.v ~ Immature " , _ r ~.,~ r" Immature _..

38 I I I I I I I I _.. Nov CL CA Nov _.. '' CL. CA CL CA r' Dec (cant.) ~ W ' _ "

39 Appendix 4: Weights (9) of ovaries with corpora /utea and ovaries with corpora albicantia >. W Q) CL CA CL CA CL January February March APP CA

40 APP APP _.. APP APP I! CL CA April May _ CL CA CL CA June ~ W...I Immature r' f ' Immature Immature Immature Immature

41 ' _... r' ~ v..> co July CL CA CL CA August Immature _ CL CA October " Immature f

42 L ~ f =r ELl L CL CA CL CA CL CA Nov Novo (cant.) Deco ,4 I I ~ (.V ( , , ' r ~ r " r _ ,4, r _