Ecological habitat partitioning and feeding specialisations of coastal minke whales (Balaenoptera acutorostrata) using a designated MPA in northeast Scotland

Abstract

In the design of protected areas for cetaceans, spatial maps rarely take account of the life-history and behaviour of protected species relevant to their spatial ambit, which may be important when modelling population trends or assessing susceptibility to anthropogenic threats. In the present study, we examined the distribution and feeding behaviours of minke whales by age-class (adults versus juveniles) from long-term studies in the Moray Firth in northeast Scotland, where a Marine Protected Area (MPA) has recently been designated. Data were collected from dedicated boat surveys between 2000 and 2019, during which 657 encounters with 774 whales of confirmed age-class (444 juveniles and 330 adults) were recorded from 50,041 km of survey effort, resulting in 224 individual follows. Feeding/foraging whales were documented in 84% of the encounters. Adults and juveniles were occasionally seen together, but their distributions were not statistically correlated, and GIS revealed spatial separation by age-class―with juveniles preferring shallow, inshore waters with sandy-gravel sediments and adults preferring deeper, offshore waters with steep benthic slope. Whilst adult minkes employed a range of “active” prey-entrapment specialisations, showing seasonal flexibility in their targeted prey with interindividual variation, juveniles almost exclusively used “passive” (low energy) feeding methods, targeting low-density patches of inshore prey. These findings corroborate the need to incorporate demographic/behavioural data into spatial models when identifying priority areas for protected cetaceans and may be important to adaptive management objectives for the species in the Moray Firth MPA.

Inferring species interactions from co-occurrence networks with environmental DNA metabarcoding data in a coastal marine food-web

“…Only a small proportion of co-occurrences were attributable to trophic interactions in the present analyses. Our food webs showed that most predators within the study area feed on multiple prey species (Figures 1 and 2), thus reducing the likelihood of detecting trophic interactions due to dietary plasticity (Robinson et al, 2023; Thurman et al, 2019). Some trophic interactions may not be described in the literature and are subsequently categorised as non-trophic interactions in our analyses.…”

“…The North Sea represents a "wasp-waist" system, where a few key forage fish species, i.e., sandeels (Ammodytes spp. ), herring and sprat (clupeids), exert control over the abundance of predators, i.e., marine mammals, predatory fishes, seabirds, through bottom-up interactions, and control the abundance of zooplankton prey through top-down interactions (Fauchald et al, 2011;Lynam et al, 2017;Robinson et al, 2023). The abundance and quality of sandeels, the dominant bait fish in the North Sea, has, however, been declining in recent decades, contributing to failures in seabird breeding (MacDonald et al, 2019;Wanless et al, 2005).…”

“…Within the southern Moray Firth, in the northwestern North Sea, the Southern Trench was recently designated as a marine protected area (MPA) for the protection of coastal minke whales which use these waters as a targeted feeding area during the summer months (NatureScot, 2020; Robinson et al, 2023). Here, we investigate spatiotemporal changes in the complexity and structuring of this ecosystem, employing co-occurrence networks and food webs.…”

Environmental DNA reveals fine scale spatial and temporal variation of prey species for marine mammals in a Scottish marine protected area

“…We analysed temporal trends in the community through partitioning the data by sampling month, and spatial trends by dividing the samples into categories based on their distance from shore; near (<1.2 km), middle-near (between 2.5 and 7 km), middle-far (between 7 and 10 km), and far (> 10 km up to 16.1 km) (Drummond et al, 2021;Fraija Fernández et al, 2020). These categories were defined based on previous observations that juvenile minke whales were most frequently sighted inshore (<2.5 km), whilst adults more frequently occurred further offshore (>10 km) (Robinson et al, 2023).…”

“…The dominant minke whale prey species, such as sandeels and clupeids, were the most abundant vertebrate species detected with our primer sets (Figure 3). Abundances vary throughout the foraging season which would account for the dietary plasticity exhibited by these whales (Robinson et al, 2023). Sandeels were most abundant during June and July, when they are foraging in the water column, but declined from August onwards, when they return to burrows in the sediment (Henriksen et al, 2021) (Figure 2.5).…”