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Trawl Surveys


BENSPEFISH is a collaborative research project between the Marine Ecology Research Group (MERG) at the Department of Biology of the University of Malta, and the Agriculture and Fisheries Regulation Department (previously known as the Malta Centre for Fisheries Studies) within the Ministry for Resources and Rural Affairs, which started in October 2006.  BENSPEFISH forms part of a wider study on the benthic habitats and biotic assemblages of actual and potential fishing grounds in the Malta FMZ within the ambit of the (MEDITS, GRUND and MedSudMed programmes. The project involves a long-term study involving benthic sampling for faunal and sediment analysis using remote operated sampling gear, as well as analysis of the benthic invertebrates collected during the ongoing trawl survey programmes. Samples are collected from the MEDITS and GRUND stations using the Italian research trawler RV Sant` Anna.


The Italian research trawler RV 'Sant Anna' (photo © Mark Dimech)

The MEDITS and GRUND sampling stations are distributed within five pre-determined depth zones (or depth strata) as follows:

i. Depth Zone A 10-50m

ii. Depth Zone B 51-100m

iii. Depth Zone C 101-200m

iv. Depth Zone D 201-500m

v. Depth Zone E 501-800m

Trawl samples are collected using the standard MEDITS and GRUND gear which consists of a trawl net of width 20m and height 1m. Normally, each trawl haul lasts ca 45 minutes, depending on the depth and substratum type, and trawl speed is ca 3 knots. The entire faunal component from each haul is sorted into commercial and non-target species, after which fauna of interest are identified, counted, measured and weighted on deck, or are preserved for future study. 


Scientists on board the RV 'Sant Anna' collecting benthic samples (photo © Mark Dimech)

Core samples for biotic and sediment analyses are collected using a box-corer. From each core, sub-samples are collected and stored at -20˚C to be used for granulometric analysis, and organic carbon and organic nitrogen determinations. The cores are analysed for macrofauna (both epifauna and infauna) by sieving through a 0.5 mm mesh net to remove the mud fraction, after which the remaining sample is fixed in 10% formaldehyde in seawater and stored in 70% ethanol. All the macrofauna is identified as far as possible and counted. 

The use of benthic secondary production on deep water fishing grounds by selected species of demersal fish is studied through dietary analysis of stomach contents in order to determine the feeding habits of the selected species, the differences in feeding habits related to size, weight, sex, and maturity stage of the fish, and the differences in feeding habits related to changes in depth and bottom type.  Through such studies the effects of fishing intensity on feeding habits of the selected species can also be explored. 


Sampling the bottom sediment using a box corer and the resultant core sample (photo © Mark Dimech)



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Last Updated: 30 November 2011

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