MONITORING THE TREND OF HARBOR SEALS IN PRINCE WILLIAM SOUND, ALASKA, AFTER THE EXXON VALDEZ OIL SPILL

Frost, Kathryn J.; Lowry, Lloyd F.; Hoef, Jay M. Ver

doi:10.1111/j.1748-7692.1999.tb00815.x

Cited by 106 publications

(113 citation statements)

References 23 publications

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“…However declines in abundance have also been observed in many areas and have been attributed to recruitment failure, competition for resources, disturbance and disease (Frost et al 1999, Thompson et al 2001, Matthews and Pendleton 2006, Lonergan et al 2007. Predicting the potential long-term effects of disease such as Phocine Distemper Virus (PDV) on harbour seal populations requires information on pre-epizootic population trajectories (Harding et al 2002, Lonergan andHarwood 2003).…”

Section: National Monitoring Programmementioning

confidence: 99%

“…Index site counts provide the opportunity to simultaneously collect covariate information, useful for enhancing aerial survey design and accuracy of population estimates. The influence of environmental covariates on estimates of population trend has been shown to be substantial and thus biologically significant (Frost et al 1999, Olesiuk 1999, Adkison et al 2003, Small et al2003 and it is recommended that covariates are integrated into abundance estimates ) and trend analyses to produce more accurate trend estimates required for the management of harbour seals. The use of mean or maximum counts by site without covariate correction can lead to a substantial bias and low power in trend determination (Adkison et al 2003).…”

Section: National Monitoring Programmementioning

confidence: 99%

“…It is critical that surveys are repeated as frequently as is financially viable to maximize our power to detect trends. Replicate counts within a survey region have been used to obtain more precise population estimates and periodic replicate surveys have been used to examine trends (Pitcher 1990, Frost et al 1999, Adkison et al 2003, Jeffries et al 2003. Studies on trend analyses of harbour seal count data suggest that even surveying annually (with 2-3 replicate surveys) it will take at least 5 years to robustly estimate annual trends greater than 5%, but as changes of more than 5% per annum are unusual in stable seal populations then realistically it will take even longer than 5 years (Adkison et al 2003, ICES 2003.…”

Section: National Monitoring Programmementioning

confidence: 99%

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The status of the harbour seal (Phoca vitulina) in Ireland

Cronin

2010

NAMMCOSP

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The status of Ireland's harbour seal population and its relationship with that of Britain and Western Europe are poorly understood. Prior to 2003, limited research efforts and poor co-ordination of survey methods fell short at providing an accurate assessment of overall distribution and population size on a regional or national scale. However, in August 2003, the Republic of Ireland's harbour seal population was assessed by means of a geographically extensive survey conducted during the annual moult, providing an up-to-date minimum population estimate and a reliable baseline for future surveys. Trends on a national scale could not be assessed due to absence of a reliable historic population estimate; however there is some evidence of local decreases and increases in harbour seal numbers in Northern Ireland and southwest Ireland respectively. Research effort to date on aspects of the ecology of the harbour seal in the Republic of Ireland is reviewed and current research and management priorities highlighted. HARBOUR SEAL ABUNDANCE AND DISTRIBUTION Minimum estimate of the Irish harbour seal populationThe population of harbour seals (Phoca vitulina vitulina) in Ireland was first enumerated by Lockley (1966) who based his minimum estimate of 1,000 on data collected incidentally, during surveys of grey seals (Halichoerus grypus), in the autumns of 1964-65. Further harbour seal specific surveys were carried out in northern Ireland by Venables and Venables (1960), Nairn (1979) and, more recently, by Wilson and Corpe (1996). The first harbour seal census of the island of Ireland was undertaken in July 1978 (Summers et al. 1980). Based on a combination of boat and aerial surveys, this gave a minimum estimate of 1,248 but absolute abundance was considered to be 1,500 to 2,000 individuals. Additional information in the Republic of Ireland was collected by Warner (1983Warner ( , 1984 and haulout counts were conducted by the National Parks and Wildlife Service (NPWS) of the Department of Environment, Heritage and Local Government at some well-known sites in the intervening years (Table 1). However, these counts have varied in location, consistency, timing and methodology and could not provide complete national or island-wide perspectives on population size and distribution. , 1997, Huber 1995, Jeffries et al. 2003, Adkinson et al. 2003, Hayward et al. 2005. While breeding season counts provide reliable estimates of abundance as well as valuable pup production data, Härkönen et al. (1999) concluded that in nonstable age-structured populations the influence of the differential haulout behaviour on estimating abundance is likely to be greater during the breeding period than during the moult period. Reijnders et al. (2003) recommended future use of moult count data to obtain a reliable and consistent index of population abundance of harbour seals in the Wadden Sea, while Thompson et al. (1997) suggest that counts made during the August moult provided more reliable population estimates for harbour seals hauling out on...

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Section: National Monitoring Programmementioning

confidence: 99%

Section: National Monitoring Programmementioning

confidence: 99%

Section: National Monitoring Programmementioning

confidence: 99%

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The status of the harbour seal (Phoca vitulina) in Ireland

Cronin

2010

NAMMCOSP

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“…The influence of covariates on estimates of harbour seal population trend has been found to be substantial (Frost et al 1999, Olesiuk 1999. Statistical models of the relationship between survey counts and environmental conditions at haulout sites have proven useful in enhancing survey design and improving the accuracy of population abundance estimates and trend analyses by adjusting counts to a standard set of environmental conditions (Watts 1996, Frost et al 1999, Adkinson et al 2003. The data that these previous models were based on were collected over a relatively short part of the annual cycle, during the breeding or moult periods namely, none of the studies to date looked at the full annual cycle.…”

Section: Harbour Seals In the North Atlantic And The Balticmentioning

confidence: 99%

A modelling framework to optimize timing of haulout counts for estimating harbour seal (Phoca vitulina) abundance

2010

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The time of year and day, the state of the tide and prevailing environmental conditions significantly influence seal haulout behaviour. Understanding these effects is fundamentally important in deriving accurate estimates of harbour seal abundance from haulout data. We present a modelling approach to assess the influence of these variables on seals' haulout behaviour and, by identifying the combination of covariates during which seal abundance is highest, predict the optimal time and conditions for future surveys. Count data of harbour seals at haulouts in southwest Ireland collected during [2003][2004][2005] were included in mixed additive models together with environmental covariates, including season, time of day and weather conditions. The models show maximum abundance at haulout sites occurred during midday periods during August and in late afternoon/early evening during September. Accurate national and local population estimates are essential for the effective monitoring of the conservation status of the species and for the identification, management and monitoring of Special Areas of Conservation (SAC) in accordance with the EU Habitats Directive. Our model based approach provides a useful tool for optimising the timing of harbour seal surveys in Ireland and the modelling framework is useful for predicting optimal survey periods for other protected, endangered or significant species worldwide.Cronin, M.A., Ingram, S.N., Zuur, A.F. and Rogan, E. 2010

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“…Understanding the effects of covariates on seal haul-out behaviour and therefore numbers at haul-out sites helps to enhance the design of surveys. Covariates can be factored into the statistical analyses to improve the accuracy of population and trend estimates (Frost et al 1999, Adkison et al 2003.…”

Section: Introductionmentioning

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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MONITORING THE TREND OF HARBOR SEALS IN PRINCE WILLIAM SOUND, ALASKA, AFTER THE EXXON VALDEZ OIL SPILL

Cited by 106 publications

References 23 publications

The status of the harbour seal (<i>Phoca vitulina</i>) in Ireland

The status of the harbour seal (<i>Phoca vitulina</i>) in Ireland

A modelling framework to optimize timing of haulout counts for estimating harbour seal (<i>Phoca vitulina</i>) abundance

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

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