Stomach contents of small pelagic fishes in the Bay of Biscay
|Author(s)||Petitgas Pierre1, D'Elbée Jean2, Pennors Laurence1, Bourriau Paul1|
|Affiliation(s)||1 : IFREMER
2 : LAPHY
|Keyword(s)||Stomach contents, diet, small pelagic fish, Bay of Biscay|
The objectives of the integrated survey PELGAS are to monitor the Bay of Biscay pelagic ecosystem at springtime and assess the biomass of its small pelagic fish species. The survey is run each year since 2000. Survey protocols are detailed in Doray et al. 2018. The fish stomachs from which this dataset is derived were acquired on the PELGAS survey series. This dataset comprises stomach contents from 2004 to 2018 for the five dominant small pelagic fish species, anchovy (Engraulis encrasicolus), sardine (Sardina pilchardus), mackerel (Scomber scombrus), sprat (Sprattus, sprattus) and horse mackerel (Trachurus trachurus). The dataset represents a unique long-term monitoring of stomach contents characterized with a low taxonomic resolution and semi-quantitative abundance quotation. During the survey, pelagic trawl hauls are undertaken to identify echotraces to species and to measure individual fish traits. All hauls are performed during day time. The fish stomachs were sampled from the haul catch. For a given species, twenty individuals were selected at random from the catch, their stomachs dissected and preserved in formaldehyde. This was repeated at three hauls in each of the ten spatial strata defined to cover the entire Biscay shelf. Stomach sampling by species depended on the trawl haul catch and all species were not systematically sampled jointly at the same trawl haul. Also, stomach sampling intensity varied between species and years. The taxonomic analysis of stomach contents was performed in the laboratory under a binocular magnifyer by the company LAPHY . A simplified taxonomic resolution was used, which considered five icthtyoplankton groups, two copepod groups, euphausids or mysids, amphipods, two decapod groups, other crustacea, other zooplankton, phytoplankton and pulp. Taxon abundance was defined by a quotation : 0 (absence), 1 (presence : <10 individuals), 2 (abundant : between 10 and 100), 3 (very abundant : > 100). The dataset comprises trawl haul information, information on the quality of the stomach contents and abundance quotes for the list of plankton taxons.
At sea the R/V Thalassa was equiped with two two-door pelagic trawls (Brabant and Nedelec, 1988 for detailed plans). One trawl had a headline of 76 m and a foot rope of 70 m and the other trawl dimensions were 57 m x 52 m. This latter trawl was operated when bottom depths were below 50 m. The trawl was hauled close to bottom (mainly) or surface, depending on the fish school echotraces to catch. The fish stomachs were dissected onboard and preserved in formaldehyde. In the laboratory, zooplankton taxonomic groups in the stomach contents were identified under a binocular stereomicroscope.