Utilisation of invertebrates discarded from the Nephrops fishery by variously selective benthic scavengers in the west of Scotland

Abstract

Demersal trawl fisheries generate large quantities of discards which temporarily increase the amount of carrion available to benthic communities and lead to a faster energetic turnover. This study examines the availability of discarded material to the benthos, assesses consumption times of different items and identifies scavengers attracted to those invertebrates most frequently discarded from Clyde Sea Nephrops trawlers. In field and laboratory trials, heavy-shelled dead whelks (Buccinum undatum, Neptunea antiqua) sank faster than softer-bodied species like cephalopods (Allotheuthis subulata, Rossia macrosoma) or echinoderms (Ophiura ophiura, Asterias rubens), making most discards available to the benthos (at ca. -60 m CD [chart datum]) within minutes after discarding. SCUBA and time-lapse camera observations in the Clyde Sea and Loch Sween indicated bait utilisation times between 24 and 48 h. Fast-moving animals like brachyuran crabs were the first to arrive at discard bait piles whose composition mimicked typical discards from the Clyde Sea Nephrops fishery. Bimonthly deployments of traps baited with invertebrate discards in the north of the Clyde Sea showed that A. rubens, followed by Pagurus bernhardus, Liocarcinus depurator and whelks, were the most abundant megafaunal scavengers. Fine-meshed funnel traps deployed inside those creels yielded up to 2819 amphipods per trap, with Scopelocheirus hopei and Orchomene nanus accounting for most of the catch. Together with whelks, A. rubens and Carcinus maenas, O. nanus showed a clear preference for crustacean bait. By contrast, Pagurus bernhardus was more attracted to A. rubens and, in 1 trial, to O. ophiura bait. Traps deployed in the south of the Clyde Sea yielded generally lower numbers and species diversity in the catch, with Nephrops being the most abundant megafaunal scavenger. It showed a preference for L. depurator and conspecific bait. While the results show that a range of epibenthic species readily utilise invertebrates discarded from Clyde Sea Nephrops trawlers, it is unknown to what extent discards subsidise benthic communities as information on the ecological energetics of the species involved locally is currently lacking. KEY WORDS: Carrion · Discards · Nephrops norvegicus · Scavengers · Trawling · ScotlandResale or republication not permitted without written consent of the publisher

Fate of discards from deep water crustacean trawl fishery off the south coast of Portugal

“…These values are comparable with results from other authors. Bergmann et al (2002) in west Scotland and in the North Sea, reported major consumption between 24 and 48 h. Ramsay et al (1997) with immersion times that were longer than this study (16.5-76 h) found consumption from 0.00 to 0.47, values lower than those found in our study where complete consumption was found in some traps. Bozzano & Sardá (2002), using a time-lapse camera set at 100-319 m and immersion periods from 9.5 to 30.6 h, found that the attached bait was almost completely consumed during the longer immersion periods.…”

“…Both S. hopei and N. (C.) borealis were reported to be important scavengers in the Clyde Sea (Nickell & Moore 1991), the North Sea , and the Mediterranean (Bozzano & Sardá 2002). S. hopei, along with other amphipod and isopod species, was attracted to baited traps in the Irish Sea (Ramsay et al 1997) and together with another lyassianidae amphipod, Orochomene manus, was an important scavenger in west Scotland (Bergmann et al 2002). Large parcels of fish at 1310 m in the Santa Catalina Basin were scavenged mainly by fish and ophiuroids, but also by two species of lysianassid amphipods (Smith 1985).…”

Catch me in winter! Seasonal variation in air temperature severely enhances physiological stress and mortality of species subjected to sorting operations and discarded during annual fishing activities

“…However, data from surveys show a rather stable situation for the Northern Adriatic Sea (Raicevich, 2004). The hypothesis of a trade-off between energetic costs, associated with the fishing disturbance, and energetic benefits, due to discard supply can be put forward: the scavenging behavior of L. depurator (Bergmann et al, 2002) would, indeed, allow populations of this species to exploit the supplementary, low-energy expenditure, source of food given by individuals of other species discarded by fishing activities. A similar hypothesis has been proposed also for the scavenging starfish Asterias rubens in the North Sea (Ramsay et al, 2000).…”

The trophic position of the Atlantic blue crab Callinectes sapidus Rathbun 1896 in the food web of Parila Lagoon (South Eastern Adriatic, Croatia): a first assessment using stable isotopes.

“…The green crab, similarly to C. maenas, is a voracious shore predator, preying especially on molluscs (Sanchez-Salazar et al, 1987), and is an active scavenger (Moore & Howarth, 1996;Bergmann et al, 2002). It is characterized by trophic habits similar to those shown by adult blue crabs (Hines, 2007); however, its size at maturity is much smaller than that of the blue crab (Berrill, 1982;Kennedy & Cronin, 2007), it is less aggressive and thus http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 11/05/2018 23:10:53 | more susceptible to negative competitive and predatory interactions (Rossong et al, 2012).…”