Investigations into the interactions between harbour seals (Phoca vitulina) and vessels in the inner Moray Firth : Scottish Marine and Freshwater Science Vol 7 No 24

• Main Author: Onoufriou, J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Marine Scotland Science 2016
• Subjects: Man-made structures; Seal behaviour; Phoca vitulina
• Online Access: https://dx.doi.org/10.7489/1805-1; https://data.marine.gov.scot/dataset/investigations-interactions-between-harbour-seals-phoca-vitulina-and-vessels-inner-moray

In late 2014, observations of grey seal (Halichoerus grypus) predation on conspecifics which produced similar wounds provided a plausible alternative explanation of the likely cause of spiral lacerations. At that time there was insufficient evidence to rule out interactions with vessels as a possible cause of some of these mortalities, so the requirement to investigate the temporal and spatial overlap between seals and vessels remained. A telemetry based study of the swimming behaviour of harbour seals was carried out in the Moray Firth to (1) allow a comparison of seal movements and vessel movements and (2) compare the densities of seals and shipping traffic to identify areas with high spatial overlap. A secondary aim was to provide data on seal movements between haulout areas, to identify connectivity between seal haulout sites in the Dornoch Firth Special Area of Conservation (SAC) and the potential construction site at Ardersier in the inner Moray Firth. : During the two year study in 2014 and 2015, 37 Ultra High Frequency (UHF)/GPS tags were deployed on harbour seals at two different sites at Ardersier and in the Dornoch Firth. Locations from the animals were interpolated to produce regularised locations at three minute intervals. Each location was assigned a status of ‘hauled out’ (when the animal was on land), or on a ‘trip’ (when the animal was at-sea). Each trip was associated with a specific departure and destination haulout site. Trips to and from each haulout site were then combined by smoothing all locations to produce a usage surface that was weighted by the population estimate derived from the number of seals counted at that haulout site during annual aerial surveys. All haulout sites were combined to produce estimated mean and associated 95% confidence interval usage maps on a 0.5 km x 0.5 km grid in the Moray Firth. These maps were compared with shipping activity using Automated Information System (AIS) vessel tracking data from MarineTraffic.com. AIS data provided information on vessel movements within the Moray Firth over the same period as the seal tracking study, for all vessels using an operating AIS transmitter. An estimated mean shipping usage map was developed in a similar manner to the seal usage map. The maps were combined by multiplying seal density by ship density for each grid cell to provide a total number of minutes of seal/vessel co-occurrence per year in the inner Moray Firth. Annual co-occurrence is therefore the sum, over a year, of the number of times individual seal-ship combinations occur in a 0.5 km by 0.5 km grid cell multiplied by the time step, in this case five minutes.