Abstract
It has been speculated that some deep-sea fishes can display large vertical migrations and likely doing so to explore the full suite of benthopelagic food resources, especially the pelagic organisms of the deep scattering layer (DSL). This would help explain the success of fishes residing at seamounts and the increased biodiversity found in these features of the open ocean. We combined active plus passive acoustic telemetry of blackspot seabream with in situ environmental and biological (backscattering) data collection at a seamount to verify if its behaviour is dominated by vertical movements as a response to temporal changes in environmental conditions and pelagic prey availability. We found that seabream extensively migrate up and down the water column, that these patterns are cyclic both in short-term (tidal, diel) as well as long-term (seasonal) scales, and that they partially match the availability of potential DSL prey components. Furthermore, the emerging pattern points to a more complex spatial behaviour than previously anticipated, suggesting a seasonal switch in the diel behaviour mode (benthic vs. pelagic) of seabream, which may reflect an adaptation to differences in prey availability. This study is the first to document the fine scale three-dimensional behaviour of a deep-sea fish residing at seamounts.
Highlights
The behavioural ecology behind the migrations and habitat use of marine fishes intrigued scientists from the very first forays of ocean discovery, but our knowledge acquired since has been very much skewed towards inshore fishes and their habitats
In this paper we present the results of a combined passive and active acoustic telemetry experiment designed to verify that habitat use of highly mobile fishes at seamounts is based on their ability to undergo vertical migrations in the water column and that they do so as a response to environmental conditions and prey availability
Active telemetry Each of the four fish generated a minimum of 36 hours tracking that spanned 17 days (Table 1), during which they displaced an average 11 km/day at an average 0.41 km/hour but with substantial individual differences in horizontal movements
Summary
The behavioural ecology behind the migrations and habitat use of marine fishes intrigued scientists from the very first forays of ocean discovery, but our knowledge acquired since has been very much skewed towards inshore fishes and their habitats. It is speculated that some deep-sea fishes are thought to be capable of moving between the flanks and adjacent midwater zones of seamounts - biodiversity rich, underwater mountains in the open ocean - and display vertical migrations of several hundreds of meters [1,2,3,4]. Such behaviour would allow them to better explore the full suite of benthopelagic food resources that can be found around seamounts. Neither has the ability of such fishes to migrate between the various ecological niches at a seamounts’ dynamic habitat (benthic versus pelagic, summit versus slope)
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