Anne Kirstine Frie

Trends in age-at-maturity and growth parameters of female Northeast Atlantic harp seals, Pagophilus groenlandicus (Erxleben, 1777)

We analyzed and compared trends in age-at-maturity and body growth in the Greenland Sea and Barents Sea stocks of harp seals, Pagophilus groenlandicus, from the early 1960s to the early 1990s. Mean and median age at sexual maturity (MAMPM and MdAM) were estimated from Richards curves fit to age-specific proportions mature. No long-term trends were found in the Greenland Sea seals, where a common value of MAMPM (5.6 years) and MdAM (4.8 years) could be fit to samples from 1959 through 1990. There were also no significant changes in length-at-age of molting females between 1964 and 1987. For Barents Sea harp seals, MAMPM increased significantly from 5.4 years in the period 1962– 1972 to 6.6 years in 1976–1985 and 8.2 years in 1988–1993, concurrently with a decline in body growth rates. Tests on MdAM also showed an increasing trend, but the grouping of samples was slightly different. Estimates of MAMPM for the Barents Sea stock were similar to previously published back-calculated values of MAM, but simulations showed that this method is sensitive to the age distribution of the sample, thus complicating comparisons between samples with different age structures. The high values of MAMPM and low growth rates in the Barents Sea stock in the late 1980s to early 1990s coincided with severe depletion of important prey species in the Barents Sea, reports of mass invasions of harp seals along the Norwegian coast and indications of reduced body condition. All these are consistent with a hypothesis of reduced per-capita resource levels within the distribution area of Barents Sea harp seals at that time, but no cause-and-effect relationship for the longterm trend in age-at-maturity can be established.

Age-dependent prevalence of anti-Brucella antibodies in hooded seals Cystophora cristata

Investigations of hooded seals Cystophora cristata have revealed high prevalences of Brucella-positive seals in the reduced Northeast Atlantic stock, compared to the increasing Northwest Atlantic stock. This study evaluated the relation between Brucella-serostatus in seals in the Northeast Atlantic stock and age, sex, body condition and reproduction. Bacteriology documented which animals and organs were B. pinnipedialis positive. No relationship was observed between Brucella-serostatus and body condition or reproductive traits. Pups (<1 mo old) had a substantially lower probability of being seropositive (4/159, 2.5%) than yearlings (6/17, 35.3%), suggesting that exposure may occur post-weaning, during the first year of life. For seals >1 yr old, the mean probability of being seropositive decreased with age, with no seropositives older than 5 yr, indicating loss of antibody titre with either chronicity or clearance of infection. The latter explanation seems to be most likely as B. pinnipedialis has never been isolated from a hooded seal >18 mo old, which is consistent with findings in this study; B. pinnipedialis was isolated from the retropharyngeal lymph node in 1 seropositive yearling (1/21, 5%). We hypothesize that this serological and bacteriological pattern is due to environmental exposure to B. pinnipedialis early in life, with a subsequent clearance of infection. This raises the question of a reservoir of B. pinnipedialis in the hooded seal food web.

Harp seal ageing techniques—teeth, aspartic acid racemization, and telomere sequence analysis

Abstract Lower jaws (containing the teeth), eyes, and skin samples were collected from harp seals (Pagophilus groenlandicus) in the southeastern Barents Sea for the purpose of comparing age estimates obtained by 3 different methods, the traditional technique of counting growth layer groups (GLGs) in teeth and 2 novel approaches, aspartic acid racemization (AAR) in eye lens nuclei and telomere sequence analyses as a proxy for telomere length. A significant correlation between age estimates obtained using GLGs and AAR was found, whereas no correlation was found between GLGs and telomere length. An AAR rate (kAsp) of 0.00130/year ± 0.00005 SE and a D-enantiomer to L-enantiomer ratio at birth (D/L0 value) of 0.01933 ± 0.00048 SE were estimated by regression of D/L ratios against GLG ages from 25 animals (12 selected teeth that had high readability and 13 known-aged animals). AAR could prove to be useful, particularly for ageing older animals in species such as harp seals where difficulties in counting GLGs tend to increase with age. Age estimation by telomere length did not show any correlation with GLG ages and is not recommended for harp seals.

Accuracy of the Aspartic Acid Racemization Technique in Age Estimation of Mammals and the Influence of Body Temperature

The aspartic acid racemization (AAR) technique has been applied for age estimation of humans and other mammals for more than four decades. In this study, eye lenses from 124 animals representing 25 mammalian species were collected and D/L ratios obtained using the AAR technique. The animals were either of known age or had the age estimated by other methods. The purpose of the study was to: a) estimate the accuracy of the AAR technique, and b) examine the effect of body temperature on racemization rates. Samples from four of the 25 species covered the range of ages that is needed to estimate species-specific racemization rates. The sample size from a single species of known age, the pygmy goat ( Capra hircus, n = 35), was also large enough to investigate the accuracy of ages obtained using the AAR technique. The 35 goats were divided into three datasets: all goats (n = 35), goats >0.5 yrs old (n = 26) and goats >2 yrs old (n = 19). Leave-one-out analyses were performed on the three sets of data. Normalized root mean squared errors for the group of goats >0.5 yrs old were found to be the smallest. The higher variation in D/L measurements found for young goats 0.5 yrs old was for three age groups of the goats: 0.934 yrs for young goats 8 yrs ( n = 4). Thus, the age of an adult or an old animal can be predicted with approximately 10% accuracy, whereas the age of a young animal is difficult to predict. A goat specific racemization rate, as a 2 k Asp value, was estimated to 0.0107 ± 3.8 x 10 -4 SE ( n = 26). The 2 k Asp values from 12 species, four estimated in this study and another eight published, were used to examine the effect of core body temperature on the rate of racemization. A positive relationship between AAR and temperature was found ( r 2 = 0.321) but results also suggest that other factors besides temperature are involved in the racemization process in living animals. Based on our results we emphasize that non-species-specific racemization rates should be used with care in AAR age estimation studies and that the period of postnatal growth of the eye lens be considered when estimating species-specific D/L 0 values and ages of young individuals.