Prey preferences of adult sea bass Dicentrarchus labrax in the northeastern Atlantic: implications for bycatch of common dolphin Delphinus delphis

Abstract

Spitz, J., Chouvelon, T., Cardinaud, M., Kostecki, C., and Lorance, P. 2013. Prey preferences of adult sea bass Dicentrarchus labrax in the northeastern Atlantic: implications for bycatch of common dolphin Delphinus delphis – ICES Journal of Marine Science, 70: 452–461. In the northeastern Atlantic, adult sea bass (Dicentrarchus labrax) is one of largest fish living on the shelf, and this species has important commercial value. However, pelagic trawl fisheries that target sea bass have negative operational interactions with common dolphins (Delphinus delphis). Our goal was to determine the diet of adult sea bass in the Bay of Biscay from stomach-content and stable-isotope analyses, and explore the dietary overlap between sea bass and common dolphins. We found that sea bass primarily target small pelagic fish, most notably mackerel (Scomber scombrus), scads (Trachurus spp.), anchovy (Engraulis encrasicolus), and sardine (Sardina pilchardus). These four species also dominated the diets of common dolphins. This overlap in feeding preferences could increase the risk of dolphins being caught by trawl fisheries while feeding among sea bass, and may be an underlying mechanism to explain the high rate of common dolphin bycatch observed in the pelagic trawl fishery for sea bass in the Bay of Biscay. Understanding the foraging ecology and trophic interactions of predator species is an essential step for identifying and resolving management issues in the northeastern Atlantic and other marine ecosystems.

Dwellers in dens on sandy bottoms: Ecological and behavioural traits of <em>Octopus vulgaris</em>

“…Adult sea bass in the northeastern Atlantic primarily target small pelagic fish, most notably mackerel (Scomber scombrus), scads (Trachurus spp. ), anchovy (Engraulis encrasicolus), and sardine (Sardina pilchardus) (Spitz et al 2013). Therefore, we consider that predation pressure by natural octopus predators at that site is not a main factor limiting their density and distribution.…”

Trophic ecology of commercial-size meagre, Argyrosomus regius, in the Bay of Biscay (NE Atlantic)★

“…Stomach content analysis described the diet in terms of prey occurrence, relative abundance, calculated mass and size distribution, following a standard procedure for marine top predators (Pierce and Boyle, 1991;Pusineri et al, 2005;Spitz et al, 2013). Diagnostic hard parts were recovered from stomachs and stored dry for fish bones and otoliths or in 70% ethanol for cephalopod beaks and crustacean remains.…”

“…A strong advantage of the use of SIAR in isotopic modeling is its ability to account for variation in trophic enrichment factors (TEFs), as well as variation in prey and predator isotopic signatures. Hence, SIAR has become the most popular tool for interpreting preypredator relationships from stable isotope signatures (Jaeger et al, 2009;Mèndez-Fernandez et al, 2012;Spitz et al, 2013). Here, in order to create accurate mixing models, the potential preys were first grouped into five forage species types according to their habitat and ecology.…”

“…The five groups were denoted as: pelagic fish from the shelf, demersal and benthic fish from the shelf, coastal fish, cephalopods, and crustaceans. These groups and associated isotopic values were the ones used in Spitz et al (2013) for adult sea bass diet in the Bay of Biscay, and were previously checked for statistical differences in d Table S1, Fig. S2).…”

“…S2). These differences are largely explained by the documented spatial variations of isotope values in the Bay of Biscay (Chouvelon et al, 2012), which actually drove the determination of such groups by Spitz et al (2013) to be relevant for SIAR. As SIAR models are sensitive to assumptions regarding TEFs, we performed two mixing models using slightly different TEFs for fish muscle tissue from the literature (Pinnegar and Polunin, 1999;Sweeting et al, 2007a,b).…”