EUROFLEETS2 Funded Project “MULLET” Results

Multiple Level Effects of Trawling

Project Acronym &Title: MULLET – Multiple Level Effects
of Trawling

Area: Celtic Sea

Research Vessel: RV Celtic Voyager, Marine Institute, Ireland

Chief scientist: Marija Sciberras, School of Ocean Sciences,
Bangor University, UK

Other project partners: Instituto Español de Oceanografía,

Date: 17 – 25 May 2015

RV Celtic Voyager © Marija Sciberras

MULLET cruise team © Marija Sciberras MULLET sampling location © Marija Sciberras

Marija Sciberras, Bangor University, UK

“This work provides an assessment of trawling impacts across
multiple trophic levels simultaneously and allows us to improve
our knowledge of the secondary effects of trawling on benthic
community and ecosystem processes at a spatial scale that is
relevant to fisheries. This work has also provided us with the
opportunity to expand links between Bangor University in the UK
and the Spanish Oceanographic Institute (IEO) and Mediterranean
Institute for Advanced Studies (IMEDEA) in Mallorca, Spain. I am
most thankful for the brilliant and very dedicated crew members
of the RV Celtic Voyager and the scientific crew who joined this
cruise; everyone was a real pleasure to work with.”

Main Objectives

The MULLET project had set out to achieve the following:

i. to quantify the effect of fishing for Nephrops norvegicus (aka
Norway lobster or langoustine) using otter trawl gears on the
invertebrate community that occurs within this actively fished
fishing ground;

ii. to assess whether bottom trawling affects the fitness of fish
species that feed on seabed invertebrates by changing their food

Scientific crew sorting the fish catch © James Monnington

Work progress and main achievements

Our team of benthic marine ecologists from Spain and the UK embarked
on an 8-day research survey on the RV Celtic Voyager visiting sites
in a Nephrops fishing ground in the Celtic Sea. Despite bad weather,
the rough seas did not dampen our excitement and twenty sampling
stations in the Celtic Sea at depths averaging 100m were visited. At
each station we used a combination of sampling gear (Day-grabs and
demersal otter trawl) to collect samples of the benthic invertebrate
and fish community. Whilst at sea, our team was busy processing
invertebrate samples and identifying, counting and measuring the
length and weight of all the fish species collected in the catches.
Additionally, stomach samples for the benthivorous fish (megrim,
haddock and grey gurnard) were collected so as to relate fish prey
spectrums with the food available in the environment across the
gradient of trawling effort in the fishing ground.

Preliminary analysis of the invertebrate data suggested
significantly higher abundance of polychaetes (marine worms) in
highly fished areas compared to lightly fished areas. In general,
polychaetes are characterized by short regeneration times and fast
growth rates making them more resilient to frequent anthropogenic
disturbance such as bottom fishing relative to other species groups.
Preliminary analysis of total fish abundance indicated higher
biomass at areas of medium trawling intensity; however variation was
high among different fish species. For example, megrim abundance
decreased with increasing trawling intensity but haddock abundance
appeared to peak at medium-trawling intensities. Further analysis
that include stable isotope analysis of fish tissue samples at the
Spanish Oceanographic Institute (IEO) and Mediterranean Institute
for Advanced Studies (IMEDEA) and analysis of fish diet at Bangor
University are ongoing.

The cruise benefitted two students who are currently carrying out
their research projects at Bangor University; Robert Bajada who is
carrying his studies at the Masters level and James Monnington who
is carrying out his studies at the doctorate (PhD) level.


Day grab to sample benthic invertebrates
© Marija Sciberras


Sediment Profile Imaging camera to determine invertebrate activity
in the sediment
© Marija Sciberras

RV Celtic Voyager operating the otter trawl net

© James Monnington

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