Aims: The ECOPredS project investigates predator-prey interactions between killer whales and their prey, including grey and harbour seals, in Scotland. A key question to the project is the impact of predation on harbour seal populations, which have seen regional declines in the east and north coasts of Scotland. Our ultimate goal is to inform the conservation and management of both the predator and prey species.
Research questions: the project aims to fill knowledge gaps in the following areas:
- What is the composition of killer whale diet, both in terms of proportion of different species and seal age class (adult vs pup)? How much does the diet composition vary by season and region? Does it mirror prey availability or indicate any prey preference?
- How much prey is consumed in total? How do theoretical estimates of food requirements compare to the observed predation rates by killer whales? What does the level of consumption mean for harbour seal populations?
- Do seals show any risk-balancing behaviours in areas and times of high predation risk, such as increased time spent at, or near, haul-out sites?
- How do killer whales search, detect, and capture seals? What are the key ecological, social, and/or anthropogenic factors influencing foraging effort and feeding success?
- Do killer whales in Scotland show any signs of prey limitation? How do their fat store body condition (inferred from body shape) compare to other killer whale populations around the world?
Study area: the project focuses on inshore predator-prey interactions, which often involve seal prey and are readily available to land-based visual observation. These interactions typically occur within few metres or hundreds of metres of the shoreline, but from land-based vantage points, sightings of killer whales can be made as far as 5 km distance. We also carry out passive acoustic monitoring (PAM). PAM complement visual observation efforts by listening at all weather conditions, day and night, and at less land-accessible locations. To-date, dedicated field work involving both visual and acoustic data collection has focused on Shetland and Orkney.
Data collection and integration: as well as collecting new data, the project brings together and analyzes existing data from collaborators and citizen scientists. The project is currently focusing on three data-driven approaches:
- Visual observations of killer whale foraging behaviour and body shape
- Analysis of seal behaviour and distribution in relation to killer whale presence
- Passive acoustic monitoring (PAM) near coastal haulout sites
Approach 1 collects behaviour observations and morphometric (body shape) data of killer whales to estimate their hunting effort, prey composition, and body condition while foraging in nearshore areas. This involves both land-based and drone-based observations, and estimating the proportion of predation events involving different prey types (species, age class). The observational data will also inform about killer whale hunting tactics and time allocation to different areas and behaviours.
Approach 2 aims to investigate how seal behaviour might influence their risk of being detected and encountered by killer whales. For example, seals may have different haulout patterns in areas and times (of day/year) with frequent killer whale visitation. So far, the project can address this using existing data from collaborators, namely SMRU telemetry data and killer whale sightings from the public. We also conduct surveys of seal haulout sites to understand fine-scale variation in their distribution.
Approach 3 aims to monitor the acoustic environment and predator-prey sound production in key areas where interactions are expected to occur. This will be achieved by using data from existing acoustic recorders, and deploying new hydrophones that can be left to record in a station for a couple of months at a time. Killer whales in Shetland have been recorded to produce pulsed calls, echolocation clicks and whistles, but they may be more quiet when hunting for seals. Harbour seal males produce breeding calls to attract mates, which may also attract killer whales.