The role of epibenthic predation in the mortality of discarded plaice

Type: 
Master Thesis subject (30 ECTS)
programme: 
EMBC+
Over two-thirds of the catches of beam trawlers are returned to the sea. Returning unwanted catches to the sea is a practice in commercial fisheries which is known as discarding. European fishery managers are attempting to reduce discards through the introduction of a new legislation, the ‘landing obligation’. The landing obligation bans the discards of certain quota-regulated species, but allows for exceptions if the discarded species have a high probability of surviving the discarding process. The discards of European plaice (Pleuronectes platessa) are high in the Belgian beam trawl fisheries (up to half of the catch), but the probability that a discarded plaice survives the catching and discarding process varies considerably across seasons, fish conditions and fishing practices. These survival probabilities have been tested in holding facilities on-board fishing vessels and in laboratory conditions. The tests were conducted in the absence of both avian and benthic predators. Tests in holding facilities have highlighted that plaice specimens were injured or stressed from the catching and discarding process. These elevated stress and/or injury levels may increase predation risks when the fish are returned to their natural habitat. A multitude of experiments have investigated avian predation, but few experiments have investigated the predation risk by benthic scavengers. This thesis will examine this risk for a selection of epibenthic scavengers, such as common starfish (Asterias rubens), edible crab (Cancer pagurus) and velvet swimming crab (Necora puber) and assess the effect of elevated stress and/or injury level on the predation risk of discarded plaice. The key benthic predators and plaice specimens will be collected from catches of beam trawls and brought to the lab to set up a ‘mesocosm’ experiment. The main focus will be directed towards the effect of stress/injury level of plaice on predation risk. However, the risk levels will also be determined by the predator density (number of predators per area) and interspecific competition (single versus multi-species interactions). This thesis will focus on the predation risk for different levels of stress and injuries of ‘discarded’ plaice, while controlling for the effects of predator density and species composition. Such an experiment will highlight whether the survival probabilities in holding facilities are representative of the survival in the natural habitat, or whether the risk of predation is being increased by the catching and discarding process in beam trawl fisheries.
prerequisites: 
At least part of the thesis will be conducted in Oostende, because of the availability of lab facilities.
Number of students: 
1
academic year: 
2016-2017
contact person first name: 
Jochen Depestele
Other people involved: 
Ulrike Braeckman (Ulrike.Braeckman@UGent.be) Jan Vanaverbeke (jvanaverbeke@naturalsciences.be)
Reference Number: RP-39681