Behavioural responses of harbour seals to human‐induced disturbances

1. In Denmark, harbour seals, Phoca vitulina, were first protected in 1977, and since then a number of seal reserves have been established in Danish waters. The effectiveness of these reserves to prevent human‐induced disturbances to the seal population have, however, not been evaluated.
2. To evaluate this, experimental disturbances were conducted in one of the most important seal reserves in Denmark (Anholt seal reserve). Specifically, the behavioural responses (alert distance, flight initiation distance, flee distances and flight duration) of harbour seals to approaching pedestrians and boats were studied.
3. The project was conducted during three periods related to the breeding cycle of harbour seals. In all periods, harbour seals were alerted by boats at significantly greater distances compared with pedestrians (560–850 m and 200–425 m, respectively). Similar differences in the flight initiation distances were observed, 510–830 m for boats and 165–260 m for pedestrians. In most cases seals were alerted and began to flee when the approaching boat was outside the reserve, whereas seals did not respond to approaching pedestrians until after they had entered the reserve.
4. Harbour seals exhibited weaker and shorter‐lasting responses during the breeding season. They were more reluctant to flee and returned to the haul‐out site immediately after being disturbed, in some cases even during the disturbance. This seasonal tolerance is most likely attributed to a trade‐off between fleeing and nursing during the breeding season, and hence not an indication of habituation.
5. Based on the results of this study it is suggested that the reserve boundaries on land be placed at least 425 m from the haul‐out area and the boundary at sea should extend to at least 850 m from the haul‐out area in order to secure adequate year‐round protection from disturbances.

Copyright © 2011 John Wiley & Sons, Ltd.     

Harbour seal movements and haul‐out patterns: implications for monitoring and management

• 1. Compliance with conservation legislation requires knowledge on the behaviour, abundance and distribution of protected species. Seal life history is characterized by a combination of marine foraging and a requirement to haul out on a solid substrate for reproduction and moulting. Thus understanding the use of haul out sites, where seals are counted, as well as their at‐sea movements is crucial for designing effective monitoring and management plans.
• 2. This study used satellite transmitters deployed on 24 harbour seals in western Scotland to examine movements and haul‐out patterns.
• 3. The proportion of time harbour seals spent hauled out (daily means of between 11 and 27%) varied spatially, temporally and according to sex. The mean haul‐out duration was 5 h, with a maximum of over 24 h.
• 4. Patterns of movement were observed at two geographical scales; while some seals travelled over 100 km, 50% of trips were within 25 km of a haul‐out site. These patterns are important for the identification of a marine component to designated protected areas for the species.
• 5. On average seals returned to the haul‐out sites they last used during 40% of trips, indicating a degree of site fidelity, though there was wide variation between different haul‐out sites (range 0% to >75%).
• 6. Low fidelity haul‐out sites could form a network of land‐based protected areas, while high fidelity sites might form appropriate management units.

Copyright © 2008 John Wiley & Sons, Ltd.     

Post‐disturbance haulout behaviour of harbour seals

1. The impact of anthropogenic activity associated with marine renewable developments on harbour seals (Phoca vitulina) was investigated using controlled disturbance trials.
2. Hauled‐out seals were approached by boat until all seals had entered the water, and this was repeated approximately every 3 days (weather permitting). The time taken for seal counts to return to pre‐disturbance levels was determined by monitoring haulout sites using time‐lapse photography.
3. Mean post‐disturbance counts of hauled‐out seals returned to 52% (95% confidence interval [CI] 35–69%) of pre‐disturbance counts within 30 min. However, mean counts only returned to 94% (95% CI 55–132%) of pre‐disturbance counts after 4 hr.
4. Eight seals were tagged with Global Positioning System phone tags to provide information on haulout location and at‐sea movements, allowing investigation of how disturbance may influence haulout site choice and seal distribution.
5. Telemetry‐tagged seals displayed a high degree of haulout site fidelity. Disturbance trials did not have a significant effect on the probability of seals moving to a different haulout site.
6. When seals hauled out again within the same low‐tide period after disturbance trials, the proportion of time spent hauled out was high, indicating that when seals are motivated to haul out they will do so despite past disturbance. Motivation to haul out more on disturbance trial days was not linked to a cyclic pattern of hauling out more over consecutive low‐tide periods.
7. As there was no large‐scale redistribution after disturbance, we suggest that monitoring effort to determine the effects of short‐term increases in levels of disturbance caused by boat activity can be spatially localized. However, where disturbance is likely to be longer term or impact on important haulout sites for breeding and/or moulting, monitoring may be required over a larger geographical area.

     

Movements of fur seals following relocation from fish farms

• 1. The movement patterns of Australian and New Zealand fur seals trapped on salmon farms in south‐east Tasmania and relocated hundreds of kilometres away, were monitored using satellite telemetry. Australian fur seals released 470 km away by sea returned to farms after an average of 8.5±4.4 days (n=9 trips) and those released at 140 km returned after 3.2±0.8 days (n=4 trips). New Zealand fur seals (n=5 trips) averaged a return time of 6.8±1.2 days from 300 km.
• 2. When in south‐east Tasmania, both seal species undertook short trips to sea (mean 2.6 days) from haul‐out sites (minimum distance from farms 21 km) with 33% (1.8 days) of this time spent within 5 km of farms. Mean haul‐out duration was 1.1 days.
• 3. In summer, Australian fur seals repeatedly travelled between northern Bass Strait islands and southern Tasmanian waters following the Tasmanian east coast. Seals did not visit farms during this time.
• 4. Southern Tasmanian waters are important foraging grounds for fur seals and potential exists for a substantial number of seals to visit nearby fish farms. Farms provide predictable food resources from penned and escaped salmon, and wild fish attracted to the area.
• 5. Australian fur seals trapped at Tasmanian salmon farms regularly visited breeding colonies on islands in Victoria.

Copyright © 2008 John Wiley & Sons, Ltd.     

Evidence for long‐term spatial displacement of breeding and pupping harbour seals by shellfish aquaculture over three decades

• 1. Shellfish mariculture is increasing worldwide and often occurs adjacent to marine mammal breeding and feeding habitat. To better understand breeding pinniped vulnerability to potential shellfish mariculture disturbance and displacement effects in a US National Park, potential mechanisms were explored that may affect the proportion of harbour seals (Phoca vitulina) selecting high quality haul‐out sites near shellfish aquaculture within a large colony, and overall seal utilization of that colony in relation to other regional colonies.
• 2. Seal haul‐out sites isolated from the mainland (no predator access) had higher pup:adult ratios, indicating they are generally more important for pupping. Short‐term human disturbance did not have a significant effect on spatial use, but rather spatial use was pre‐determined by general sandbar isolation. Using multiple competing hypothesis and an information‐theoretic approach, it was found that within the estuary, after removing effects of El Niño, the proportion of seals (total seals and pups only) hauled out near mariculture sites was 8 ± 2% lower during years of higher oyster harvest. Annual oyster harvest was used as a measure of aquaculture activity that could result in direct disturbance or indirect displacement of harbour seals.
• 3. At the regional scale, oyster harvest, seal counts at a nearby colony, and loss of a major haul‐out site within the estuary, best explained pup and total seal use compared with the region. Regional population size, short‐term human disturbance rate, and other factors were not important. Concurrent with higher oyster harvest, the proportion of regional seals using the estuary declined by 7 ± 2% for seal pups (–65 ± 18 total pups), and 5 ± 2% for total counts ( ? 192 ± 58 total seals). These findings (both within the estuary and at the regional scale) were essentially identical whether modelling oyster harvest as either a continuous or categorical (low/high) variable and when using either frequentist or Bayesian statistical analyses.
• 4. Marine reserves set aside for wildlife may be less effective when the highest quality breeding and pupping sites are adjacent to regular aquaculture activities. These effects may not be detectable until additional natural variation lowers the quality of nearby habitats. Published in 2011. This article is a US Government work and is in the public domain in the USA.

     

Effects of sea‐level rise on northern elephant seal breeding habitat at Point Reyes Peninsula,California

1. Northern elephant seals (Mirounga angustirostris) historically experienced a significant population decrease to the brink of extinction owing to human exploitation, but have since recovered and recolonized former breeding/haul‐out sites. Point Reyes Peninsula, California, is one location where population increase has resulted in colony expansion.
2. Initial models identified suitable breeding haul‐outs and suggested that human disturbance, geomorphology, mean wave height, and slope were important explanatory variables. Three sea‐level rise (SLR) scenarios were run, which indicated that most current and potential haul‐out sites would largely be inundated by 2050. Because the Point Reyes coast has limited suitable habitat for the seals to colonize, conservation measures may guide management responses to SLR.
3. The resulting analyses can be used to better understand local‐scale seal responses to SLR and contribute to effective management of pinnipeds within Point Reyes National Seashore and elsewhere. Copyright © 2012 John Wiley & Sons, Ltd.

     

The importance of Southern Ocean frontal systems for the improvement of body condition in southern elephant seals

1. As top predators, it has been suggested that southern elephant seals serve as sentinels of ecosystem status to inform management and conservation.
2. This is because southern elephant seals annually undertake two large‐scale foraging migrations for 2–3 and 7–8 months to replenish resources after fasting during breeding and moulting and often rely on dynamic macroscale latitudinal fronts to provide favourable foraging through aggregating prey.
3. Yet it is largely unknown whether southern elephant seals respond to changes in frontal systems over the years, whether their foraging success is associated with specific frontal systems shifts, and how flexible southern elephant seals populations are in behaviourally adapting to changes in frontal systems.
4. This study examines the relationship between frontal systems and the resource acquisition of 64 southern elephant seals during four post‐moult and three post‐breeding migrations between 2005 and 2010.
5. Satellite‐relay‐data‐loggers provided in situ measurements concurrent with >27,500 dive profiles to define fronts and interfrontal zones between the Subtropical Frontal Zone and the Southern Boundary of the Antarctic Circumpolar Current. For >430,000 in situ measurements water mass properties could be identified.
6. Generally, southern elephant seals associate more frequently with more southerly, higher‐latitude fronts/zones. Body condition improvements related to a given frontal system or water mass vary strongly according to year, season, month and sex.
7. The variability in body condition improvements is higher in some frontal systems than in others, probably owing to shifts in the Subantarctic and Polar Front.
8. During a migration, some individuals stay within ≤3 frontal systems, whilst others change between several frontal systems and primarily improve their body condition in upper ocean waters.
9. Southern elephant seals do not trace particular water masses across frontal systems, and both surface and deep foraging strategies are used.
10. This suggests that southern elephant seals do not target particular water masses but adjust foraging and movement strategies to exploit boundary areas at which mixing and prey aggregation is high.
11. The large behavioural plasticity towards the spatio‐temporal variability in the different oceanographic regions they encounter could indicate resilience against environmental changes.

     

Measuring responses of harbour seals to potential aversive acoustic mitigation signals using controlled exposure behavioural response studies

1. Some anthropogenic activities pose acute risks for marine species. For example, pile driving could damage the hearing of marine mammals while underwater explosions can also result in physical damage or death. Effective mitigation is required to reduce these risks, but the exclusion zones specified in regulations can extend over hundreds or thousands of metres and seals pose particular problems because they are difficult to detect at sea.
2. Aversive sound mitigation aims to exclude animals from high‐risk areas before dangerous activities take place by broadcasting specific acoustic signals. Field research is needed to identify signals that might be effective in eliciting short‐term avoidance by marine species such as harbour seals (Phoca vitulina). A series of controlled‐exposure experiments (CEEs) were undertaken to measure seal movements in response to acoustic deterrent devices (ADD) and predator calls, and to assess the effectiveness of candidate signals for aversive sound mitigation.
3. Seals were fitted with UHF/GPS transmitters providing continuous high‐resolution tracks and real‐time transmissions of their locations. A tracking/playback vessel located seals at sea and transmitted either ADD signals or orca (Orcinus orca) calls over a range of distances while seals were foraging or moving between sites. Behaviour before, during and after exposure was analysed to assess responses.
4. One‐hundred and ten CEEs were assessed as being of at least ‘adequate’ quality. Of the 71 adequate trials with the Lofitech ADD, all 38 at ranges of <1 km (predicted received level 134.6 dB RMS re 1 μPa) elicited a response. The maximum response range was 3123 m (predicted RL: 111 dB RMS re 1 μPa). However, the responses observed did not always result in substantial movements away from the source, especially for seals that were travelling at the time of the exposures. More work is needed to better understand how exposure risks would be reduced in different scenarios.
5. The mean net speed of horizontal movements for seals responding to aversive sounds (1.15 m s^?1) was only 7% higher than their mean travel speed.
6. Responses to broadcasts of orca calls were highly variable.
7. The results suggest that signals similar to those generated by a Lofitech ADD could be used to reduce risks to harbour seals from pile driving and underwater explosions in coastal waters. More work will be needed to develop systems that match the requirements of industry and regulators and to explore whether these results can be generalized to offshore waters and to other phocids.

     

Effects of sea-level rise and storm-enhanced flooding on Pacific harbour seal habitat: A comparison of haul-out changes at the Russian and Eel river estuaries

1. Patterns and changes in the distribution of coastal marine mammals can serve as indicators of environmental change that fill critical information gaps in coastal and marine environments. Coastal habitats are particularly vulnerable to the effects of near-term sea-level rise.
2. In California, Pacific harbour seals (Phoca vitulina richardii) are a natural indicator species of coastal change because of their reliance on terrestrial habitats, abundance, distribution, and site fidelity. Pacific harbour seals are marine top predators that are easily observed while hauled out at terrestrial sites, which are essential for resting, pupping, and moulting.
3. Although increasing inundation from recent sea-level rise and storm-driven flooding has changed the Californian coastline, little is known about the effect of future sea-level rise and increased storm frequency and strength on harbour seal haulout site availability and quality in California.
4. Harbour seal habitat was modelled at two sandbar-built estuaries under a series of likely sea-level rise and storm scenarios. The model outputs suggest that, over time, habitat at both estuaries decreased with increasing sea level, and storm-enhanced water levels contributed significantly to habitat flooding. These changes reflect pressures on coastal habitats that have an impact on human and natural systems.

     

Genetic population structure of harbour seals in the United Kingdom and neighbouring waters

1. In the United Kingdom (UK), several harbour seal (Phoca vitulina) populations have been declining over the past decade. In order to understand the effect of these changes in abundance, this study seeks to determine the population structure of harbour seals in the UK, and in Scotland in particular, on a wider and finer spatial scale than has previously been reported.
2. Harbour seals were genotyped from 18 different localities throughout the UK and neighbouring localities in mainland Europe, at 12 microsatellite loci. Results from Bayesian and frequency based tests of population structure suggested an initial structural division into two main groups consisting of localities in northern UK and southern UK–mainland Europe, respectively.
3. These two clusters were further divided into four geographically distinct genetic clusters.
4. An overall agreement between the genetic results and the existing management areas for UK harbour seals was observed, but it is also clear that an adaptive management approach should be adopted, in which the delineation of the current management areas is maintained until further genetic and ecological information has been accumulated and analysed.