The Impact of Fisheries Discards on Scavengers in the Sea

Assessing the diet and trophic level of marine fauna in a fishing ground subject to discarding activity using stable isotopes

“…This could counter balance any potential effect of discard consumption (identified in many of these species in the Bay of Bourgneuf using gut content metabarcoding [ 38 ]) on their TL. This would also be consistent with previous studies showing that gadoids and many perciformes such as Callionymidae, Scombridae or Sparidae are frequently observed to scavenge upon both discards and carrion generated by trawling [ 15 , 18 , 63 ], but remains at this step speculative. Alternatively, scavenging behaviors revealed in other studies may not correspond to consistent long-term strategies, which would therefore not reflect in their isotopic composition.…”

“…The natural diet of Raja undulata is largely dominated by crustaceans [ 66 ], which contrasts with the substantial contributions from pelagic fish (PSC) and demersal fish and cephalopods (DFC) revealed here by mixing model analysis. Scavenging on discards was also noted for Rajidae [ 22 ] and cephalopods [ 18 ].…”

“…undatum [ 19 , 70 ], crabs, hermit crabs and spider crabs [ 17 , 19 , 71 ] and with gut content metabarcoding of a bentho-demersal community in the Bay of Bourgneuf, revealing potentially important discard ingestion in all of these taxa [ 38 ]. Decapods constitute the dominant invertebrate Order attracted by or consuming discards, based on a review of 43 observational studies [ 18 ]. Most decapods are opportunistic omnivores and the spatial variability in prey availability is the primary determinant of their trophic strategies [ 68 , 69 ].…”

“…While fisheries discards may benefit obligate scavengers, consumption by other facultative or non-typically scavenging species is considered to be certainly underestimated [ 9 ]. Multiple studies have shown that some benthic or demersal species may benefit from dead or damaged fauna linked to fishing as a source of food [ 15 – 17 ], but there is little information about their level of reliance upon discards on the long term, with large-scale model based ecosystem assessments providing contrasting results [ 18 , 19 ]. One limitation is that empirical studies on discard consumption have relied mainly on underwater video recording [ 17 , 20 , 21 ] or traditional gut content analysis [ 22 , 23 ], which only provide a snapshot of the diet and do not assume consistency of feeding strategies over time.…”

Using ecological trajectories to track long‐term taxonomic and functional changes in benthic shallow soft‐bottom communities (Bay of Saint‐Brieuc, English Channel)

“…The diversity of temporal dynamics suggests a complex gradient of sensitivity to organic matter enrichment and the implication of additional driving factors. Indeed, (1) discards from scallop dredging could promote opportunistic species and scavengers leading to increases in their abundances (Depestele et al, 2019), and (2) by capturing nutrients, green tides are particularly suspected to buffer the influence of nutrient enrichment on macrofauna as discussed by Ponsero & Le Mao (2011) and Sturbois et al (accepted) concerning the neighbouring intertidal area.…”