scholarly journals A note on the age at sexual maturity of humpback whales

2020 ◽  
pp. 71-73
Author(s):  
Peter B. Best
Keyword(s):  
Sexual Maturity ◽  
Gulf Of Maine ◽  
Accumulation Rate ◽  
Age Determination ◽  
Biological Data ◽  
Humpback Whales ◽  
Natural Mortality ◽  
Growth Layer ◽  
Younger Age ◽  
Layer Groups

The conclusion of researchers in the 1950s that humpback whales reached sexual maturity at about age five was largely influenced by their interpretation of baleen tracings, and to achieve consistency with these tracings the accumulation rate of ear plug laminations (growth layer groups: GLGs) was assumed to be two per year. However, ovulation and natural mortality rates calculated by these researchers under the same assumption produced estimates that are difficult to reconcile with other biological data or with more recent estimates using individual re-sighting data. Such disparities are reduced or disappear when an annual accumulation rate is used, in which case their ear plug data would have indicated a mean age at sexual maturity of 9–11 years. Recent estimates of the age of female humpback whales at first calving using longitudinal studies of photoidentified individuals have produced conflicting results, some (from southeastern Alaska) being compatible with the earlier age-determination studies, others (from the Gulf of Maine) suggesting a much younger age.

Age at attainment of sexual maturity in humpback whales, Megaptera novaeangliae

1992 ◽  
Vol 70 (7) ◽  
pp. 1470-1472 ◽  
Author(s):  
Phillip J. Clapham
Keyword(s):  
West Indies ◽  
Sexual Maturity ◽  
Gulf Of Maine ◽  
Megaptera Novaeangliae ◽  
Humpback Whales ◽  
Annual Growth Rate ◽  
Growth Layer ◽  
The West ◽  
Similar Range ◽  
Layer Groups

Twelve female humpback whales (Megaptera novaeangliae) in the southern Gulf of Maine produced first-observed calves at ages ranging from 5 to 7 years. These data confirm that most females of this species attain sexual maturity at an average age of approximately 5 years. Observations in the West Indies of two males, aged 6 and 7 years, engaged in breeding-related behavior that is characteristic of mature animals suggests that males attain sexual maturity within a similar range of ages to females, although they may not be able to successfully engage in intrasexual competition until later in life. These data imply that the examination of ear plugs to determine the age of dead humpback whales should be based upon an assumed annual growth rate of two growth layer groups, not one.

Age, Growth, and Maturity of Bottlenosed Dolphin (Tursiops truncatus) from Northeast Florida

1973 ◽  
Vol 30 (7) ◽  
pp. 1009-1011 ◽  
Author(s):  
D. E. Sergeant ◽  
David K. Caldwell ◽  
Melba C. Caldwell
Keyword(s):  
Tursiops Truncatus ◽  
Accumulation Rate ◽  
Age Determination ◽  
Growth Layer ◽  
Translucent Zone ◽  
Bottlenosed Dolphin ◽  
Males And Females ◽  
Absolute Age

It is confirmed that one growth layer consisting of one opaque and one translucent zone is laid down annually in the dentine of the teeth of bottlenosed dolphin (Tursiops truncatus), allowing absolute age determination, although the seasonal sequence of dentine deposition is not yet clear. On this basis females from northeast Florida were found to mature at about 12 years and males at 13 years, both sexes living to about 25 years of age. Females accumulated up to 14 corpora albicantia in the ovaries, indicating an accumulation rate of about one per annum. Birth occurred at 100-cm length. Males and females matured at about 245- and 235-cm length, respectively, and attained asymptotic lengths of about 270 and 250 cm.

A comparison of age determination techniques for the harbour porpoise, Phocoena phocoena L.

1989 ◽  
Vol 67 (7) ◽  
pp. 1832-1836 ◽  
Author(s):  
Peter Watts ◽  
David E. Gaskin
Keyword(s):  
North Atlantic ◽  
Age Determination ◽  
Harbour Porpoise ◽  
Phocoena Phocoena ◽  
Growth Layer ◽  
Single Cross Section ◽  
Living Bone ◽  
Layer Groups ◽  
Annual Deposition ◽  
Age Estimates

The maximum life-span of the harbour porpoise has been estimated at 13 years (based upon dentinal growth layer groups in the teeth) and at 21 years (based upon growth layers in the periosteal bone of the mandible). We used both techniques to estimate the ages of 120 harbour porpoises from the western North Atlantic, in an attempt to determine the relative reliability of each technique. Dentinal layering was the better predictor of body length. Mandibular layering was highly variable even within a single cross section in most specimens, as a result of both common bifurcation of the layers and destruction of the inner layers by growth and remodelling of the living bone. Furthermore, mandibular layers appear to be deposited at a rate of 2 layers/year, double the deposition rate of dentinal growth layer groups. Age estimates which assume annual deposition of mandibular layers therefore overestimate true age.

Variability of Dentin Deposits in Tursiops truncatus

1980 ◽  
Vol 37 (4) ◽  
pp. 712-716 ◽  
Author(s):  
Clifford A. Hui
Keyword(s):  
Tursiops Truncatus ◽  
Age Determination ◽  
Growth Layer ◽  
Posterior Teeth ◽  
Annual Cycles ◽  
Left And Right ◽  
Layer Groups

Dentin is deposited in approximately annual cycles in Tursiops truncatus for at least the first 11 yr. There were no consistent differences in the dentinal layer count between the left and right sides nor between the mandible and maxilla in the teeth of nine animals studied. The posterior teeth, however, have a greater number of growth layer groups (GLGs). The differences in the number of GLGs among teeth of the same individual increase unpredictably when there are more than about 15 GLGs in the posterior teeth. Only minimal age may be determined using dentinal counts.Key words: age determination, dentin, dolphins, odontocetes, teeth, Tursiops

scholarly journals Age determination methods in harbour seals (Phoca vitulina) with a review of methods applicable to carnivores

2010 ◽  
Vol 8 ◽  
pp. 245 ◽  
Author(s):  
Christina Lockyer ◽  
Beth Mackey ◽  
Fiona Read ◽  
Tero Härkönen ◽  
Ilk Hasselmeier
Keyword(s):  
Best Practices ◽  
Marine Mammals ◽  
Tooth Extraction ◽  
Age Determination ◽  
Detailed Examination ◽  
Phoca Vitulina ◽  
Growth Layer ◽  
Harbour Seals ◽  
Determination Methods ◽  
Layer Groups

The development of age determination methods in marine mammals is reviewed with particular reference to the use of teeth Growth Layer Groups (GLGs) formed in the dentine and cement of carnivores. Using this background, practices for sampling, tooth extraction and collection, storage and different methods of preparation of teeth as well as reading and counting GLGs are discussed and evaluated for the harbour seal (Phoca vitulina). The paper includes comments on best practices for counting GLGs with new examples from known-age seals, and also a detailed examination of confounding factors in interpreting GLGs such as mineralization anomalies and the phenomena of accessory lines, “false annuli” and “paired laminae” which have not been discussed previously. The paper concludes with recommendations for undertaking age estimation in harbour seals from sampling through final GLG interpretation with special emphasis on standardization of methods with other researchers.

GROWTH LAYER GROUPS (GLGs) IN THE TEETH OF AN ADULT BELUKHA WHALE (DELPHINAPTERUS LEUCAS) OF KNOWN AGE: EVIDENCE FOR TWO ANNUAL LAYERS

1987 ◽  
Vol 3 (1) ◽  
pp. 14-21 ◽  
Author(s):  
Arthur D. Goren ◽  
Paul F. Brodie ◽  
Stephen Spotte ◽  
G. Carleton Ray ◽  
H. W. Kaufman ◽  
...  
Keyword(s):  
Delphinapterus Leucas ◽  
Growth Layer ◽  
Layer Groups

scholarly journals Growth of the skull of the bottlenose dolphin, Tursiops truncatus, in the Southwest Atlantic Ocean

10.5597/00229 ◽  
2017 ◽  
Vol 11 (1-2) ◽  
pp. 199-211 ◽  
Author(s):  
André Silva Barreto
Keyword(s):  
Bottlenose Dolphin ◽  
Tursiops Truncatus ◽  
Growth Equation ◽  
Growth Layer ◽  
Southwest Atlantic ◽  
Development Patterns ◽  
Skull Measurements ◽  
The One ◽  
Layer Groups ◽  
Mature Size

Defining the age of attainment of physical maturity is important for many studies, including identification of stocks, populations or species. In order to identify the age when the skull of the bottlenose dolphin, Tursiops truncatus, reaches maturity, skulls of fifty-three specimens found stranded along the coasts of southern Brazil, Uruguay and northern Argentina (27o35’S, 48o34’W-36o49’S, 55o19’W) were analyzed. Sixty skull measurements were taken to compare the growth rate of the different functional apparatuses. Age was estimated by counts of growth layer groups in the dentine of decalcified, stained longitudinal sections of teeth. Von Bertalanffy’s equation was applied to assess the growth and determine the age at maturity of each apparatus. Generally the maturation of skull starts at age two and stabilizes at age five, and the age of reaching the mature size varies amongst different characters. The braincase is the most precocious apparatus, while the feeding is the one that last stabilizes. The development patterns observed for the hearing, vision and breathing apparatuses were similar. Statistic analysis revealed significant differences among the ages at maturity, but not for von Bertalanffy’s growth equation parameters for each functional apparatus. For the studied population it is suggested that skulls can be considered mature in animals with more than five years. 

Potential Rates of Increase of a Harbour Porpoise (Phocoena phocoena) Population Subjected to Incidental Mortality in Commercial Fisheries

1991 ◽  
Vol 48 (12) ◽  
pp. 2429-2435 ◽  
Author(s):  
Thomas H. Woodley ◽  
Andrew J. Read
Keyword(s):  
Gulf Of Maine ◽  
Intrinsic Rate ◽  
Frequency Equation ◽  
Harbour Porpoise ◽  
Population Increase ◽  
Intrinsic Rate Of Increase ◽  
Natural Mortality ◽  
Phocoena Phocoena ◽  
Rate Of Increase ◽  
Incidental Mortality

We estimated the potential intrinsic rate of increase (r) of the harbour porpoise (Phocoena phocoena) population in the Bay of Fundy and Gulf of Maine using empirical data on reproductive rates (mx) and several hypothetical survival (Ix) schedules. Schedules of Ix, to maximum ages of 12 and 15 yr, were calculated from two potential natural mortality (nx) schedules combined with several schedules of incidental mortality (hx) estimates. The most realistic results were obtained when nx of non-calves were calculated from Caugley's (1966. Ecology 47: 906–918) smoothed age-frequency equation for Himalayan thar (Hemitragus jemlahicus) and applied in conjunction with a range of calf natural mortality estimates, this model indicates that harbour porpoises have a limited capacity for population increase, and populations are unlikely to sustain even moderate levels of incidental mortality (4% of the population per year). Extending the maximum age used in the models from 12 to 15 yr does little to increase estimates of r for the harbour porpoise population, and hence their susceptibility to incidental mortality.

scholarly journals Validation of Age Estimation in the Harp Seal, Phoca groenlandica, Using Dentinal Annuli

1983 ◽  
Vol 40 (9) ◽  
pp. 1430-1441 ◽  
Author(s):  
W. D. Bowen ◽  
D. E. Sergeant ◽  
T. Øritsland
Keyword(s):  
Outer Layer ◽  
Age Estimation ◽  
Transverse Section ◽  
Age Determination ◽  
Middle Layer ◽  
Harp Seal ◽  
Growth Layer ◽  
Phoca Groenlandica ◽  
Incremental Growth ◽  
Absolute Age

We investigated the validity and accuracy of age estimation in harp seals, Phoca groenlandica, using a sample of 155 known-age teeth from seals age 3 mo to 10 yr. Under transmitted light, transverse sections of harp seal canine teeth showed distinct incremental growth layers (IGLs) in the dentine. The first growth-layer group (GLG), representing Ist-year growth, consists of two IGLs: an outer layer of opaque dentine, bounded by the neonatal line, and an inner layer of translucent dentine. Subsequent GLGs, each representing 1 yr of growth, generally consist of three IGLs: an outer layer of interglobular dentine deposited during the annual molt in April, a middle layer of opaque dentine formed during the northward spring migration (May–June), and an inner layer of translucent dentine formed from July to March. We show that dentinal GLGs can be used to estimate the absolute age of harp seals. The accuracy of the method decreases with age. Only 72.4% of estimates of 0-group seals were correct using only transverse sections. These errors were virtually eliminated (99.0% correct age determination) when the tooth root was examined. Based on a single examination of a transverse section, the probabilities of correctly estimating age are 0.983, 0.889, 0.817, and 0.553 at ages 1, 2, 3, and 4 + yr, respectively, when clearly inaccurate tag-tooth associations are omitted. The respective probabilities are only slightly higher when age is based on the average of five blind readings, being 1.0, 0.889, 0.833, and 0.625. Beyond age 3 yr, existing data are insufficient to estimate reliably the accuracy of age determined by counting GLGs.

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