Thesis (Ph.D.) - University of St Andrews, May 2007.

Studies have been made on age determination, reproduction, growth and population structure in the harbour seal (Phoca vitulina richardi). They are based upon gross and histological examinations of reproductive tracts, growth measurements, and associated canine teeth of 42 prenatal and 319 postnatal specimens collected between 1964 and 1965. In postnatal seals cementum annulations were used as the criterion of age. Two annulations are deposited annually, a translucent "dense, inorganic" band during the winter and spring and an opaque "less dense, more organic" band during the summer and fall. Their formation may result from an internal rhythm. In southeastern Vancouver Island (southern British Columbia) parturition occurs primarily during July, lactation then lasts 6 weeks with ovulation shortly thereafter in September. Implantation is delayed for 2 to 2½ months and birth is about 230 days later. The male's main breeding season begins at least 4 months in advance of the female's but ends shortly after. Extensive clines in the timing of the reproductive cycle of both sexes are found in the Pacific and Atlantic Oceans. First ovulations occur at 2 to 5 years of age with peak periods at 2 and 3 years. About 88.9% of all adult females produce young each year. Males mature at 5 and 6 years of age. Prenatal males and females grow at similar rates. Postnatal males, however, grow slightly faster and larger being about 10% longer and 36% heavier at asymptotic sizes. Sex ratios are about 1 : 1 from implantation until males reach sexual maturity at 5 years, their mortality rate then increases resulting in a gradually increasing percentage of females in older age groups. Males generally do not live longer than 20 years and females seldom more than 30 years. In a random kill sample the average annual sex ratio is 46.9% males, and 49.6% of all females and 33.7% of males are mature. From bounty return records and reproductive and population data a minimum population estimate of 75,000 seals is made for British Columbia. This is a density of about 4.4 seals per mile of coastline. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (PhD)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Robert A. Garrott. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 1987. / Bibliography: leaves 153-177. Also available on the World Wide Web.

Thesis (Ph. D.)--Montana State University--Bozeman, 2006. / Typescript. Chairperson, Graduate Committee: Jay J. Rotella. Includes bibliographical references.

VHF radio-telemetry was used to study individual and seasonal variation in common seal haul-out behaviour in a study area in Orkney, Scotland. The timing of the annual cycle was also described and seasonal changes in behaviour, distribution and abundance were related to the constraints of breeding and the moult. There were consistent seasonal trends in site-use, with some sites being used during the breeding season, and others during the winter. Sex differences in site-use also occurred during the summer, with mothers and pups being seen regularly at some sites, and males predominating at others. A high degree of individual, sex-related and seasonal variation in haul-out behaviour was found. In general, seals spent most time in inshore waters, and hauled out frequently, during the summer. For males, this was especially marked during the moult, whereas females came ashore most regularly during the pupping period. Outside the breeding season, seals left the study area for longer periods, of several days, but regularly returned between trips to haul out. These longer winter trips are believed to represent periods of more intense feeding activity, and it is suggested that the constraints of breeding and the moult restrict seals to shorter feeding trips during the summer. Changes in haul-out behaviour during the moult resulted in common seals being most abundant on land in August. Behaviour was also less variable during the moult, and it is suggested that population surveys should be made at this time of year. An aerial survey was made over Orkney in August 1985 and, in conjunction with telemetric data on haul-out frequency, the results were used to produce a preliminary estimate of the size of the population in this area.

Feeding habits of fur seals (Callhorinus ursinus), sea lions (Eumetopias jubata) and harbour seals (Phoca vitulina) have been examined along the British Columbia coast. Collections were made out to 35 miles from shore. All pertinent published and unpublished data have been combined with the object of assessing the effect of pinniped predation upon commercially valuable fish stocks. A total of 126 harbour seal stomachs, 2,113 fur seal stomachs and 393 sea lion stomachs were available. Comparative anatomy of the digestive tract was examined and notable differences were found in the relatively longer digestive tract and late eruption of permanent teeth in the sea lion. Published data indicate that fur seals, sea lions, and harbour seals eat an amount of food equal to 6%of their body weight per day with a range of 2% to 11%. All samples were grouped as to season and area of collection and comparative seasonal feeding habits were discussed. The effect of the reproductive period upon feeding habits was examined: there is little evidence regarding fur seal feeding habits on the rookeries except for conflicting observations made on harem bulls; the majority of the sea lion rookery population fasts for a few days only, during pupping; harbour seals on the Skeena River appear to fast for at least part of June. There is no evidence of interspecific competition between the three species studied on the British Columbia coast. Sea lions and harbour seals each year eat an estimated amount equivalent to 1.6% of the annual commercial salmon catch and 2.7% of the annual commercial herring catch. Predation at this level is believed to be of negligible importance in the reduction of existing salmon and herring stocks. Insufficient data from waters greater than 35 miles from shore precludes an assessment of fur seal predation upon ocean salmon. Further offshore collections should be made. / Science, Faculty of / Zoology, Department of / Graduate

The mechanisms of osmotic and ionic regulation in marine mammals are of interest because of the apparent lack of "fresh" water in their environment. Previous investigation on the harbor seal, (Phoca vitulina, L.), generally indicated that the seal can obtain all the water it requires from its food. However, some dispute still exists as to whether the seal may ingest sea water along with its food and conserve water by concentrating ions and excreting them with a net water gain. The effects of a 16-hour period with no fluids and also of intubation with varying amounts of distilled water and varying amounts and concentrations of sea water were determined. The concentrations of sodium, chloride and potassium ions as well as the osmotic pressures of plasma and urine were measured for the periods before and after intubation. The results of this study are discussed with respect to published data and proposed mechanisms of osmotic and ionic regulation by the kidney. The findings indicate, as suggested by others, that the seal does not gain any substantial amount of water from sea water ingestion. / Science, Faculty of / Zoology, Department of / Graduate

Gross and histological analyses of reproductive tracts from multiparous, nulliparous, and non-pregnant females of Pribilof Islands (eastern Pacific) origin have been used to determine the histology and physiology of the estrus cycle, the age of sexual maturity, and certain causes of prenatal mortality. The ovaries alternate in function, one ovary ovulating in one breeding season, the opposite ovary ovulating in the next. An undetermined factor suppresses follicular development in the ovary containing a corpus luteum of pregnancy; suppression maintains for 6 months after parturition. Graafian follicular development is greatest in July, with an average 15 follicles in the ovary destined to ovulate. About 4 of these will enlarge abruptly prior to ovulation; one will reach ovulation size (10 mm or greater in diameter) and rupture; the rest will become atretic. Mating occurs 3-5 days after parturition in mid-July. If fertilization is accomplished, the resulting blastocyst remains free in the uterus until early or mid-November, when it implants in the mucosa. The newly formed corpus luteum is actively secretory for a month after ovulation. During this time, follicular development is suppressed in both1 ovaries, and the uterine mucosa is progesteronic. From the end of August, the corpus luteum is regressive; the luteal cells are vacuolated, and secretion is minimal. This is reflected in a recrudescence of follicular activity in the ovary containing the corpus luteum, and regression of the associated uterine mucosa. Immediately prior to implantation the corpus luteum resumes secretion, and the mucosa is prepared for implantation. Placentation is established during December. Luteal degeneration begins in January and is progressive until parturition, when the corpus luteum appears to be non-secretory. Luteal degeneration has no affect on the pregnant uterine horn; it is assumed that the placenta secretes sufficient hormone to replace the luteal hormones. Prenatal mortalities take 3 forms: "missed” pregnancies, abortions, and resorptions. On the basis of histological examinations, "missed" pregnancies are ultimately due to failure of implantation. Three conditions are responsible: failure of fertilization, failure of implantation, or malfunction of the reproductive tract which precludes pregnancy. Abortion results in the expulsion of a conceptus from the uterus before term; resorption is a gradual process of dissolution of the conceptus within the uterus. On the basis of histological evidence, three causative agents of abortion and resorption are evident: degeneration of the corpus luteum after implantation, malfunction of the uterine mucosa, and intra-uterine mortality of the conceptus. Annovulatory cycles, dominated by Follicle Stimulating Hormone, occur among females 1 to 3 years of age. A cycle increasingly dominated by Luteinizing Hormone and culminating in ovulation occurs among the majority of 4-year-old females. The follicular cycle resulting in the first ovulation is later than subsequent cycles; the peak of first ovulations occurs around August 25th. On the basis of gross examinations, 60% of females ovulate for the first time at 4 years of age. Since the pregnancy rates of 5-year-old females are consistently about 50%, probably a number of 4-year-olds do not mate, either because ovulation occurs after the breeding season, or because breeding males are not available. Gross and histological analyses of reproductive tracts from nulliparous females of Robben and Commander Islands (western Pacific) origin have been used to compare the reproductive potential of two breeding populations of fur seals,; Pregnancy rates among females 4 years of age of Robben and Commander Islands origin are approximately 50%; those of 4-year old-females of Pribilof Islands origin are approximately 5%. The disparity in the age of reproductive maturity between females of the two populations is based on a physiological delay of one year in the maturation of the endocrine system controlling reproduction among females of Pribilof Islands origin. / Science, Faculty of / Zoology, Department of / Graduate

The structural and functional organization of the pinniped eye, as represented by the harbour seal, Phoca vitulina, is much more complex than previously realized. The retina of the harbour seal is similar to that of the harp seal, in that it shows little zonation of the inner nuclear layer, possesses large horizontal cells, and has similar nuclear densities within the different retinal layers throughout the retina. The outer nuclear layer is the thickest of all the retinal layers. Photoreceptor cells of types B and C were observed with a ratio of roughly 1:23 respectively. This ratio and photoreceptor density along with a well-developed and extensive tapetum, indicates a highly light-sensitive retina. The existence of retinal folding in marine mammals is also questioned and discussed. Refractive observations obtained through retinoscopy show that the harbour seal eye is very myopic and astigmatic in air, and hypermetropic with no discernable astigmatism in water. The axis of least corneal curvature is horizontal; current theories predict that the stenopeic pupil would thus correct for astigmatism in air. The functional significance of the astigmatism, which is in the order of 7 to 13 diopters, has not been adequately determined to date, however. These observations are in agreement with those recently reported for the harp seal. Behavioural studies have also confirmed the high sensitivity of the harbour seal eye to light, as suggested by the histological observations. Two captive harbour seals were trained to select a two-bar pattern over a one-bar pattern in both air and water, discriminating for the presence of a gap. Their abilities to carry out this task were measured as the gap in the two-bar pattern was gradually reduced in size. The light intensity of the white parts of the stimulus cards was 284-369 candela/m² . Under these conditions, the harbor seal can detect a gap as small as 1 mm at a distance of 1.7 m in both air and water. These studies fail to provide values of the visual acuity of the harbour seal in the strict sense, however, owing to the physics of the pattern utilized. Rather, they indicate a measure of the absolute sensitivity of the eye to light. / Science, Faculty of / Zoology, Department of / Graduate