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    This file provides daily/per station summaries of daytime and nighttime acoustic data (omitting data recorded within 1 hour of sunrise and sunset), specifically per day and night mesopelagic average nautical area scattering coefficient (NASC 200-1000 m), average total NASC (0-1000 m), and weighted mean depths (WMD) of mesopelagic and total NASC. Migration amplitude is the difference in day and night WMD, day to night ratio is the ratio of daytime to nighttime total NASC (0-1000 m) and migration ratio is calculated from the relative drop in mesopelagic backscatter (NASC 200-1000 m) during night. For details of calculations see Klevjer et al. 2016. Note that the provided positions correspond to the fixed Malapina station at that date, not the start and end point of the data collection.

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    This dataset presents the diet composition of tuna during autumn migrations to the Iceland Basin south of the continental shelf for the year 1998 and 1999 (area Va and XII defined by ICES). Each line in the dataset represents a different prey item found in the stomach of one tuna fish with a specific ID number. Therefore, several lines represent the total number of prey item found in one tuna stomach. For the stomach content analysis, the data were separated by geographical areas recorded in the column G called “area”. Tuna were also classified according to their size distribution defined in the column “groups”. A total of 36 prey species or higher taxa are described in 421 stomach samples: 17 teleost fishes, 4 squid, 1 octopus, 11 crustaceans and 2 other invertebrate species. The most important prey species are European flying squid (Todarodes sagittatus), barracudinas (Paralepididae) and gonate squid (Gonatus sp.). The identification of prey items was performed by identification of individual prey items, and of sagittal otolith and of beak pairs for fish and squid respectively, when preys were heavily digested.

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    We present data of Atlantic bluefin tuna (Thunnus thynnus) diet published in Ólafsdóttir et al (2016). Each line corresponds to the observation of one prey individual in a single tuna stomach and contains data on the predator (tuna ID number in database, length, weight and sex) and on the prey (Micromesistius poutassou, Gonatus fabricii, Todarodes sagittatus, Scopelogadus beanii, Notoscopelus kroeyeri, Maurolicus muelleri and Paralepidae), together with cruise information (latitude, longitude and date of collection). Therefore, several lines can contain data of a single tuna stomach which can be identified by the “Specimen ID (predator, MFRI database)” column. The size, weight and length of each prey was recalculated based on regression between beak/otolith size and total length of the prey estimated from survey samples collected in Icelandic waters. These regressions are available under "Further details".