Importance of discards from the English Nephrops norvegicus fishery in the North Sea to marine scavengers

Abstract

Discards refer to that part of the catch which is returned to the sea during commercial fishing operations. Organisms that do not survive the discarding process can provide an additional food source to scavenging species. The aim of this study was to determine whether the quantity and quality of discarded material from the intensively fished English Nephrops norvegicus fishery is such that it has a positive effect on marine scavenger populations. Field studies were used to identify marine scavenger species and estimate their abundance. Discard experiments combined with data from commercial vessels provided estimates of the partitioning of discards between aerial and marine scavengers and the spatial distribution of discarding. A bioenergetic model was devised to evaluate the importance of discards to marine scavengers. Seabirds utilised an estimated 57% of the discarded material; most discarding (83%) took place over the fishing grounds. Species identified as marine discard scavengers included Liocarcinus depurator, Asterias rubens, Neptunea antiqua, Pagurus bernhardus, Carcinus maenas, Cancer pagurus and Myxine glutinosa. The hagfish M. glutinosa was the most abundant scavenger, and made up 79% by weight of all identified marine scavengers on the fishing grounds. The energy available from discards could potentially provide the identified marine discard scavengers on the fishing grounds with 37% of their energetic requirements during the fishing season. This level of contribution is probably sufficient to allow larger populations of these scavenging species to exist than would otherwise be possible. KEY WORDS: Discards · Scavengers · Nephrops norvegicus · Bioenergetic modelResale or republication not permitted without written consent of the publisher

Consumption of discards and interactions between Black-browed Albatrosses (Thalassarche melanophrys) and Kelp Gulls (Larus dominicanus) at trawl fisheries in Golfo San Jorge, Argentina

“…As a result of prey size selection, only a fraction of the total fish biomass thrown overboard was consumed by gulls and albatrosses, as has been reported for other fisheries in Patagonia and other regions Yorio 2000a, 2000b;Garthe and Scherp 2003;Catchpole et al 2006). This suggests that care should be taken when evaluating the availability of this food resource and its effects on seabird populations.…”

Comparison of baited longlines and baited underwater cameras for assessing the composition of continental slope deepwater fish assemblages off southeast Australia

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A junk-food hypothesis for gannets feeding on fishery waste

“…The amount of fishery waste produced is substantial: approximately 7.3 million tonnes of discards are returned to the sea annually by worldwide fisheries (Kelleher 2005). This additional food source affects food web structures, as it favours scavengers throughout the water column and on the seabed (Catchpole et al 2006). For some marine top-predators such as seabirds and marine mammals, fishery wastes provide an alternative food source; they can forage on both live prey and fishery wastes, eventually favouring the latter when the former becomes scarce ( Votier et al 2004).…”