Growth and population parameters of the world?s northernmost harbour seals Phoca vitulina residing in Svalbard, Norway

Lydersen, Christian; Kovacs, Kit M.

doi:10.1007/s00300-004-0656-7

Cited by 30 publications

(50 citation statements)

References 45 publications

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“…3 and 4). Growth curves for older seals based on body masses and standard lengths of live-captured, drugged individuals show that there is sexual size dimorphism in the Svalbard harbour seals (Lydersen and Kovacs 2005). The asymptotic values for both body mass and standard lengths are greater for males than for females (Table 1).…”

Section: Growthmentioning

confidence: 99%

“…Krog and Bjargov (1973) speculated as to whether the harbour seals in Svalbard would give birth to more than the average number of white coated pups because of the cold climate of the region. However, several hundred harbour seal pups have been observed in Svalbard Børseth 1992, Lydersen andKovacs 2005) and no white coated pups have been recorded.…”

Section: Puppingmentioning

confidence: 99%

“…However, the harbour seals from the three studies discussed above were all measured during the same period of the year, so the fact that the Svalbard seals generally are fatter is not due to seasonally biased sampling. One possible reason for Svalbard harbour seals having thicker blubber could be that Svalbard's waters are colder than those in the southern areas where these other populations are found, and that the Svalbard harbour seals therefore need a thicker blubber layer to stay within their thermoneutral zone (for more details: see Lydersen and Kovacs 2005). Colder water could also be an explanatory factor for the size dimorphism between the sexes in the Svalbard harbour seals.…”

Section: Growthmentioning

confidence: 99%

“…hormones to estimate the time of the onset of sexual maturity for the Svalbard harbour seals (Lydersen and Kovacs 2005).…”

Section: Harbour Seals In the North Atlantic And The Balticmentioning

confidence: 99%

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Status and biology of harbour seals (<i>Phoca vitulina</i>) in Svalbard

Lydersen

Kovacs

2010

NAMMCOSP

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Harbour seals in Svalbard are the northernmost population of this species. This small population is comprised of ca. 1,000 individuals, most of which reside along the west coast of Prins Karls Forland (78°20'N). Satellite tracking studies have shown that adults are resident. Birthing occurs in the latter half of June. Newborns weigh about 11 kg and gain an average of 0.7 kg/d during the nursing period. Haulout patterns in Svalbard harbour seals are influenced by date (season), time of day, tidal cycle and temperature. Moulting takes place in early fall, first among juveniles, then in adult females and finally in adult males. Feeding studies show that polar cod (Boreogadus saida) is the dominant prey in terms of numbers, while Atlantic cod (Gadus morhua) is the dominant prey based on biomass, at least during the early autumn. Growth curves display significant sexual dimorphism with asymptotic values for standard length and body mass being greater for males. Testosterone levels in males showed an abrupt increase at 6 years of age, while estradiol levels in females increased abruptly from age 4 years. The reproductive rate for adult females was 0.93. Longevity of Svalbard harbour seals is very short compared with populations from other areas.Lydersen, C. and Kovacs, K. M. 2010. Status and biology of harbour seals (Phoca vitulina) in Svalbard. NAMMCO

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Section: Growthmentioning

confidence: 99%

Section: Puppingmentioning

confidence: 99%

Section: Growthmentioning

confidence: 99%

“…hormones to estimate the time of the onset of sexual maturity for the Svalbard harbour seals (Lydersen and Kovacs 2005).…”

Section: Harbour Seals In the North Atlantic And The Balticmentioning

confidence: 99%

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Status and biology of harbour seals (<i>Phoca vitulina</i>) in Svalbard

Lydersen

Kovacs

2010

NAMMCOSP

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“…Four of the 10 seals tagged weighed < 60 kg and were considered to be juveniles (Härkönen & Heide-Jorgensen 1990, Lydersen & Kovacs 2005.…”

Section: Resultsmentioning

confidence: 99%

Using mobile phone telemetry to investigate the haul-out behaviour of harbour seals Phoca vitulina vitulina

Cronin¹,

Zuur²,

Rogan³

et al. 2009

Endang. Species. Res.

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Information on the haul-out behaviour of pinnipeds is essential for increasing the accuracy of population estimates necessary for the effective conservation of protected species, as well as improving survey design. The haul-out behaviour of 10 harbour seals Phoca vitulina L. in southwest Ireland was examined using a novel telemetry system based on global systems for mobile communications technology. The data on the haul-out patterns of tagged individuals were examined using generalised additive modelling to determine potential factors of influence, such as the tide, the time of day and the time of year. The behaviour varied among seals, with time ashore reaching a maximum during post-moult in October and decreasing to a minimum in February. A strong tidal influence on haul-out behaviour was evident. Tagged seals hauled out more frequently at low tide. There was variation between individuals in the influence of time of day on haul-out behaviour. A cyclic pattern with lunar periodicity was evident in seals tagged in October, and the pattern varied between tidal periods. There was an overall large variation in patterns of behaviour over the tagging period, both between individuals and between tidal periods for each individual. This cautions against making inferences on the haul-out behaviour of the 'population' based on the behaviour of a small number of tagged individuals. The present study provides detailed information, heretofore unavailable, on the haul-out behaviour of individual harbour seals and on the behaviour of the species in Ireland, and it has important implications for population assessment for conservation purposes across the species' entire geographical range. KEY WORDS: Generalised additive modelling · Haul-out behaviour · Lunar influence · Telemetry Resale or republication not permitted without written consent of the publisher Contribution to the Theme Section 'Biologging technologies: new tools for conservation'

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Age–length relationships in UK harbour seals during a period of population decline

Hall

Mackey

Kershaw

et al. 2019

Aquatic Conservation

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1. The abundance of harbour seals (Phoca vitulina) in the UK as a whole has increased over the past 10 years, after a 30% decline during the preceding 10 years and two major viral epidemics. However, population trends vary greatly among regions, with those on the east coast of Scotland and in the Northern Isles experiencing dramatic declines since the early 2000s and populations on the west coast being either stable or increasing. The reasons for these differences in population dynamics are unknown.2. Determining whether there has been a change in somatic growth among populations can assist in assessing potential causes for abundance declines, as shifts in juvenile growth rates or maximum length at maturity may indicate changes in environmental conditions. Resource limitations are likely to result in slower growth and later age at sexual maturity, whereas causes of acute mortality could have the opposite effect.3. Here, analysis of the most comprehensive length-at-age dataset for UK harbour seals found no evidence for major differences, or changes over time, in asymptotic length or growth parameters from fitted von Bertalanffy growth curves, across all regions, with the exception of one pairwise comparison; males from East Scotland were significantly shorter than males from all other areas by an average of almost 9 cm. However, the power to detect small changes was limited by measurement uncertainty and differences in spatial and temporal sampling effort. 4. Asymptotic lengths at maturity across all regions were slightly lower than published lengths for harbour seal populations in Europe, the Arctic, and Canada, with females being on average 140.5 cm (95% confidence interval 139.4, 141.6 cm) and males 149.4 cm (95% confidence interval 147.8, 151.1 cm) at adulthood. 5. Reliable estimates of changes in growth over time are important for understanding environmental constraints on a population, but knowledge of the underlying drivers of change is essential for the design of robust conservation and mitigation plans.

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Growth and population parameters of the world?s northernmost harbour seals Phoca vitulina residing in Svalbard, Norway

Cited by 30 publications

References 45 publications

Status and biology of harbour seals (<i>Phoca vitulina</i>) in Svalbard

Status and biology of harbour seals (<i>Phoca vitulina</i>) in Svalbard

Using mobile phone telemetry to investigate the haul-out behaviour of harbour seals Phoca vitulina vitulina

Age–length relationships in UK harbour seals during a period of population decline

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