A review of age estimation methods in marine mammals with special reference to monodontids

Read, F.L.; Hohn, Aleta A.; Lockyer, Christina

doi:10.7557/3.4474

Cited by 24 publications

(34 citation statements)

References 176 publications

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“…The teeth from Newfoundland animals were extracted from decomposed specimens, air dried and stored whole until being sectioned for this study. Similar to other odontocetes [29][30][31], H. ampullatus dentine is laminated, with one clear and one opaque layer defining each annual GLG within the cone of the tooth [22] (Fig 2). Only teeth with a clear neo-natal line and defined GLG structure across the first five years were retained for isotope analysis, reducing our sample size to 50 individuals (N = 6 from Iceland, N = 42 from Labrador, N = 2 from Newfoundland).…”

Section: Tooth Collection and Dentine Samplingmentioning

confidence: 85%

Prolonged maternal investment in northern bottlenose whales alters our understanding of beaked whale reproductive life history

et al. 2020

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Nursing and weaning periods are poorly understood in cetaceans due to the difficulty of assessing underwater behaviour in the wild. However, the onset and completion of weaning are critical turning points for individual development and survival, with implications for a species' life history including reproductive potential. δ 15 N and δ 13 C deposited in odontocete teeth annuli provide a lifetime record of diet, offering an opportunity to investigate variation and trends in fundamental biology. While available reproductive parameters for beaked whales have largely been inferred from single records of stranded or hunted animals and extrapolated across species, here we examine the weaning strategy and nursing duration in northern bottlenose whales (Hyperoodon ampullatus) by measuring stable isotopes deposited in dentine growth layer groups (GLGs). Using a collection of H. ampullatus teeth taken from whales killed during the whaling era (N = 48) and from two stranded specimens, we compared ontogenetic variation of δ 15 N and δ 13 C found in annual GLGs across all individuals, by sex and by region. We detected age-based trends in both δ 15 N and δ 13 C that are consistent across regions and males and females, and indicate that nursing is prolonged and weaning does not conclude until whales are 3-4 years old, substantially later than previous estimates of 1 year. Incorporating a prolonged period of maternal care into H. ampullatus life history significantly reduces their reproductive potential, with broad implications for models of beaked whale life history, energetics and the species' recovery from whaling.

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Section: Tooth Collection and Dentine Samplingmentioning

confidence: 85%

Prolonged maternal investment in northern bottlenose whales alters our understanding of beaked whale reproductive life history

et al. 2020

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“…Average lengths of 240-260 cm in adults (Burgess, Lanyon & Keeley, 2012;Marsh, 1980) fit with data based on our equation, where limiting values for body weight and length of dugongs in our study were approximately 309 kg and 266 cm, respectively. In the present study, the absolute age of each animal was unknown, so the standard practice of tusk GLGs counts was used for age estimation (Marsh, 1980;Nishiwaki & Marsh, 1985;Read, Hohn & Lockyer, 2018). Then that chronological age was correlated with body morphometric indices, finding significant relationships with both body weight and length.…”

Section: Sex Differences In Growth Ratesmentioning

confidence: 86%

“…The tusks erupt later, primarily in males, but occasionally in females ( Marsh, 1980 ). The tusks are the only teeth present throughout life, and so have been used for age estimation ( Marsh, 1980 ; Mitchell, 1976 ; Read, Hohn & Lockyer, 2018 ) through counts of dentin growth layer groups (GLGs). The technique was first described by Scheffer in 1970 ( Scheffer, 1970 ) and is now broadly accepted for age estimation of dugongs ( Adulyanukosol, Amorena & Miyazaki, 1998 ; Kasuya & Nishiwaki, 1978 ; Marsh, 1980 ; Mitchell, 1976 ; Mitchell, 1978 ; Read, Hohn & Lockyer, 2018 ; Scheffer, 1970 ).…”

Section: Introductionmentioning

confidence: 99%

Age relationships with telomere length, body weight and body length in wild dugong (Dugong dugon)

Cherdsukjai

Buddhachat

Brown

et al. 2020

PeerJ

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The ability to estimate age and determine the growth status of free-ranging dugongs (Dugong dugon) is vital to providing insight into the basic biology of this endangered species. Currently, age estimation in dugong carcasses relies on counting dentin growth layer groups (GLGs) in tusks, but a disadvantage is they need to be intact. We explored whether measures of telomere length could be used as an alternative approach to age estimation in dugongs given that in other species, telomere length and age are inversely related. In this study, relative telomere length (rTL) was measured by qPCR in skin samples from 24 dugongs of varying ages determined by counts of GLGs. In addition, relationships between age by GLG counts and body weight and length and were examined. Our findings indicate that age estimated by GLGs was negatively correlated with telomere length using the logistic formula with a rate of telomere attrition of approximately 0.036 rTL/year between the ages of 5–20 years. By comparison, both body weight and length were positively correlated with GLG-based age, with growth rates of ~8.8 kg/year for weight and ~3.58 cm/year for length, respectively. After that, growth rates slowed substantially and then plateaued. The results suggest that physical maturity in dugongs occurs at 20 years of age and that measures of rTL might serve as a tool for age estimation in dugongs, living and deceased.

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“…One particular shortcoming is our approach to age estimation based on body length, which could be improved using teeth aging methods [57][58][59] in the future. In addition to these obstructions, the use of stranded and bycaught animals may introduce a bias, since a cause of death could not be diagnosed for all of the animals.…”

Section: Discussionmentioning

confidence: 99%

Fatty Acid Composition in Blubber, Liver, and Muscle of Marine Mammals in the Southern Baltic Sea

Dannenberger

Moller

Westphal

et al. 2020

Animals

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To date, only limited results on the fatty composition in different tissues of the top predators in the Baltic Sea are available. In the current study, tissue samples of blubber, skeletal muscle, and liver from 8 harbour porpoise (Phocoena phocoena) and 17 grey seals (Halichoerus grypus) in the Baltic Sea off Mecklenburg-Western Pomerania were included in the investigation. While the total fatty acid content in liver and blubber tissue revealed no differences between both species, the total fatty acid content of muscle tissue was significantly differentand showed higher concentrations in harbour porpoise muscle compared with grey seals. The most abundant fatty acids in the blubber of grey seals and harbour porpoises (18:1cis-9, 16:1cis-9, 16:0 and 22:6n-3) were present in similar quantities and ratios to each other as known from other marine top predators. If future studies can show that differences in tissue fatty acid content are caused by variation in the nutritional status, and this may lead to the development of a more objective assessment of body condition in seals and porpoises recovered via stranding schemes.

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A review of age estimation methods in marine mammals with special reference to monodontids

Cited by 24 publications

References 176 publications

Prolonged maternal investment in northern bottlenose whales alters our understanding of beaked whale reproductive life history

Prolonged maternal investment in northern bottlenose whales alters our understanding of beaked whale reproductive life history

Age relationships with telomere length, body weight and body length in wild dugong (Dugong dugon)

Fatty Acid Composition in Blubber, Liver, and Muscle of Marine Mammals in the Southern Baltic Sea

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