The role of infaunal and epibenthic scavengers in the decomposition of fisheries’ discards

Type: 
Internship position (6 ECTS)
programme: 
EMBC+
Beam trawl fisheries, as all bottom-contacting trawls, induce mortality on benthic communities and thereby generate carrion. The induced mortalities and the increased food availability create a shift to benthic communities consisting of species with fast turnover rates and the ability to scavenge on a broad spectrum of prey, i.e. opportunistic generalists. Gear developments and the introduction of new legislation, such as the Landing Obligation, may lead to subtle reductions in mortalities and changes in the food availability from trawling. The role of returning unwanted catches to the sea, known as discarding, is under-investigated when it comes to its availability of discards as a food source to marine scavengers in the sea. The main reason is the difficulty to investigate the fate of a discarded item once it has sunken under the water surface. Experimental manipulations that investigate the contribution of a discarded item to the diet of marine scavengers require designs that are logistically complex to realise at sea. Detailed information on the consumption of the discards is difficult to obtain from at-sea experiments, e.g. the scavenging community cannot be controlled for. Laboratory tests may complement the information from field trials with high-resolution data from replicated experiments. The student will learn in this internship how laboratory experiments are designed and set-up to complement field trial data. The student will take samples at sea to build a mesocosm experiment in the lab. The investigation of the effect of discards on the feeding behaviour of scavengers requires that both ‘dead’ discards and ‘living’ scavengers can be accommodated in the laboratory accommodation. Standardisation and control for experimental manipulations should be carefully designed in order to have a clear treatment effect. How long does it take for epibenthic scavengers to be hungry and start feeding on the offered discards? How long does feeding last? How many fish or which sizes of fish can be accommodated in the tanks without massive oxygen loss in the system? How does the species composition of the extracted samples from the sea trial and the decomposition of the discards in the lab alter the conditions of the sea water and hence of the viability of the experimental accommodation? Is there mortality of the accommodated infaunal community? How much feed should be added? Can we use a camera system to monitor the scavenging behaviour or can we visually monitor this behaviour depending on the feeding time of the accommodated scavengers? Do they scavenge gradually during the day or are the selected scavengers (starfish, edible crab…) greedy and fill their stomachs at once? The internship will investigate how the existing experimental set-up can be modified to address the questions related the investigations of scavenging behaviour on dead discards, based upon experiences of research at Ghent University and the Institute for Agricultural of Fisheries Research (ILVO).
Number of students: 
1
academic year: 
2015-2016
contact person first name: 
Jochen Depestele
Other people involved: 
Ulrike Braeckman (Ulrike.Braeckman@UGent.be) Jan Vanaverbeke (Jan.Vanaverbeke@UGent.be, jvanaverbeke@naturalsciences.be)
Reference Number: RP-39472