title: Seabird diving behaviour reveals the functional significance of shelf-sea fronts as foraging hotspots.
abstract: Oceanic fronts are key habitats for a diverse range of marine predators, yet how they influence fine-scale foraging behaviour is poorly understood. Here, we investigated the dive behaviour of northern gannetsMorus bassanusin relation to shelf-sea fronts. We GPS (global positioning system) tracked 53 breeding birds and examined the relationship between 1901 foraging dives (from time-depth recorders) and thermal fronts (identified via Earth Observation composite front mapping) in the Celtic Sea, Northeast Atlantic. We (i) used a habitat-use availability analysis to determine whether gannets preferentially dived at fronts, and (ii) compared dive characteristics in relation to fronts to investigate the functional significance of these oceanographic features. We found that relationships between gannet dive probabilities and fronts varied by frontal metric and sex. While both sexes were more likely to dive in the presence of seasonally persistent fronts, links to more ephemeral features were less clear. Here, males were positively correlated with distance to front and cross-front gradient strength, with the reverse for females. Both sexes performed two dive strategies: shallow V-shaped plunge dives with little or no active swim phase (92% of dives) and deeper U-shaped dives with an active pursuit phase of at least 3 s (8% of dives). When foraging around fronts, gannets were half as likely to engage in U-shaped dives compared with V-shaped dives, independent of sex. Moreover, V-shaped dive durations were significantly shortened around fronts. These behavioural responses support the assertion that fronts are important foraging habitats for marine predators, and suggest a possible mechanistic link between the two in terms of dive behaviour. This research also emphasizes the importance of cross-disciplinary research when attempting to understand marine ecosystems.
authors.affiliation: Marine Biology and Ecology Research Centre, Plymouth University, Plymouth PL4 8AA, UK; Marine Physics Research Group, Plymouth University, Plymouth PL4 8AA, UK.
authors.forename: S L
authors.identifier: 0000-0002-5409-4458
authors.initials: SL
authors.lastname: Cox
authors.affiliation: Plymouth Marine Laboratory , Prospect Place, Plymouth PL1 3DH , UK.
authors.forename: P I
authors.initials: PI
authors.lastname: Miller
authors.affiliation: Marine Biology and Ecology Research Centre , Plymouth University , Plymouth PL4 8AA , UK.
authors.forename: C B
authors.initials: CB
authors.lastname: Embling
authors.affiliation: Plymouth Marine Laboratory, Prospect Place, Plymouth PL1 3DH, UK; Institute of Marine Sciences, University of California, Santa Cruz, CA 95064, USA; National Oceanic and Atmospheric Administration (NOAA), Southwest Fisheries Science Centre, Environmental Research Division, 99 Pacific Street, Suite 255A, Monterey, CA 93940, USA.
authors.forename: K L
authors.identifier: 0000-0003-0843-0956
authors.initials: KL
authors.lastname: Scales
authors.affiliation: Environment and Sustainability Institute , University of Exeter , Penryn TR10 9FE , UK.
authors.forename: A W J
authors.initials: AW
authors.lastname: Bicknell
authors.affiliation: Marine Physics Research Group , Plymouth University , Plymouth PL4 8AA , UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Hosegood
authors.affiliation: RSPB , Ramsey Island, St David's, Pembrokeshire SA62 6PY , UK.
authors.forename: G
authors.initials: G
authors.lastname: Morgan
authors.affiliation: Marine Biology and Ecology Research Centre , Plymouth University , Plymouth PL4 8AA , UK.
authors.forename: S N
authors.initials: SN
authors.lastname: Ingram
authors.affiliation: Environment and Sustainability Institute , University of Exeter , Penryn TR10 9FE , UK.
authors.forename: S C
authors.identifier: 0000-0002-0976-0167
authors.initials: SC
authors.lastname: Votier
keywords: diving behaviour; foraging ecology; marine predator; ocean front; oceanography; seabird