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BENSPEFISH - BENTHIC SECONDARY PRODUCTION AND ESSENTIAL FISH HABITATS IN THE MALTA FMZ

Introduction


In recent years, there has been an increasing interest by fisheries scientists in ecosystem-based fisheries management, where fish stocks are no longer considered in isolation, but as one component of an integrated ecosystem that includes the water column and the seabed (Link, 2002; Pitkitch et al., 2004).  Such a management strategy requires a good knowledge of the components of the ecosystem and how they interact together. Additionally, these habitats and their biota are often vulnerable to anthropogenic activities such as bottom fishing with trawls. Therefore, there is a need to investigate the wider ecological impacts of fishing activities on seabed habitats and organisms. Such impacts have mostly been approached from an environmental conservation perspective; however, it is equally important to consider the implications of such impacts, where they occur, for the management of demersal fisheries that are intimately linked with seabed habitats.

Previous to 2004, Malta operated an Exclusive Fishing Zone that extended to 25 nautical miles from the baselines of the Maltese Islands. With the entry of Malta into the European Union, this zone was maintained as a Fisheries Management Zone (FMZ). Due to the management regime operated by Malta within the previous EFZ since the early 1970s, demersal and benthic resources have suffered little fishing pressure, and the new management regime now operating in the Malta FMZ is designed to continue to conserve the fisheries resources within the area (Camilleri, 2003).


Map_1 

Map showing the bathymetry of the Sicilian Channel including the 25 nautical mile FMZ around the Maltese Islands (the larger blue oval) [Source: Department of Fisheries and Aquaculture, 2000].

 

The project

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 Malta Centre for Fisheries Sciences (MCFS) of the Ministry for Resources and Rural Affairs, which started in October 2006. 
The main objectives of the BENSPEFISH project are to:
1.    Locate essential fish habitats and to identify common benthic features that may attract fish to these habitats;
2.    Characterise benthic habitats including foraging areas, nursery grounds, and spawning areas important for fish in terms of their benthic assemblages and physical characteristics;
3.    Study the physical and biological response of the benthic ecosystem to different regimens of fishing disturbance within existing fishing grounds;
4.    Investigate the use of benthic secondary production on deep water fishing grounds by selected species of fish, both those of direct commercial importance and those that form part of the food chain of exploited species.
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 and GRUND trawl surveys (since 2000) and the FAO programme MedSudMed. Through the latter programme, information on benthic assemblages within this area has been collected since 2003. Samples using remote operated sampling gear, are collected from the MEDITS and GRUND stations using the trawler RV Sant` Anna.

 

Pic_2 

The Italian trawler RV Sant` Anna

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 (Bertrand et al., 2002; Relini, 1998), consisting 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.
 

Pic_3

 Scientists on board the RV Sant` Anna collecting benthic samples

 

Core samples for biotic and sediment analyses are collected using a box-corer. From each core, sub-samples are collected and stored at -20ºC 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.

 

Pic_4


Pic_5

Sampling the bottom sediment using a box corer and the resultant core sample.

 

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.

Work carried out to date

Role of environmental variables in structuring demersal assemblages

Samples and data obtained during three consecutive MEDITS surveys (2003, 2004 and 2005) within the GFCM’s Management Unit 15 (MU15), were analysed in order to study the role of environmental variables (depth, bottom temperature and sediment mean grain size) in structuring demersal assemblages within the FMZ.  After sorting, identification and quantification of biota, macrofaunal biomass data for the stations were analyzed using ordination techniques (nMDS) and relationships between environmental variables and faunal assemblages were explored by superimposing individual variables on the two-dimensional nMDS plots. The BIOENV procedure was used to determine the environmental variables that explain best the differences in demersal assemblage composition. 

 

nMDS_1

 

Non-metric multidimensional scaling (nMDS) plot with superimposed scaled values of temperature (°C) for all three years (2003, 2004 and 2005). 

Pic_6

Non-metric multidimensional scaling (nMDS) plot for the sampling stations from 2004 and 2005, based on biomass, with superimposed scaled values of mean grain size (µm). The number on each station position is the mean depth for that station.
 

This study showed that all the three measured environmental parameters (depth, temperature and sediment grain size) affect the structure of demersal assemblages, although to different degrees. The most important environmental variable was depth, followed by temperature. While mean grain size explained well the distribution of assemblages from the relatively shallow water stations (46-82m), it was not as important in the structuring of the deeper water assemblages.

These results were reported upon at the 38th CIESM congress, held in Istanbul between the 9th and 13th April, 2007 (Dimech et al., 2007b) and published in Xjenza (Dimech et al., 2005).


Spatial distribution of demersal assemblages

In the previous study, depth was identified as an important factor affecting the structure of demersal assemblages. This study was carried out to gain a better insight on the influence of depth on the spatial distribution of demersal assemblages. More than 552,000 specimens of biota were sorted, identified, weighed and counted. Biomass and abundance data were standardised per square kilometre of trawled area for each station, and analysed by agglomerative hierarchical clustering followed by nMDS ordination, using PRIMER v.6 (Clarke & Warwick, 1994).
 
The demersal fishery resources on the muddy bottoms of Maltese trawling grounds was found to be stratified in four main depth ranges:  80-160m (outer continental shelf: two subgroups), 160-270m (shelf break), 270-440m (upper slope), and 440-800m (deep slope). These results have important implications for designing monitoring surveys, since characterisation of the biotic assemblages allows for a better sampling representation of each depth-stratum/assemblage type.
The findings of this study were also reported the 38th CIESM congress held in Istanbul between the 9th and 13th April, 2007 (Dimech et al., 2007c) and accepted for publication in the international peer reviewed journal Scientia Marina (Dimech et al., 2008).

 

Demersal community structure and biomass size spectra within and outside the Maltese Fishery Management Zone (FMZ)

This study examined the protection effect of the long-established fisheries protection zone around Malta; the Malta 25 NM FMZ, by studying the demersal communities and the biomass size spectra of specific taxonomic groups.

For groups of stations on muddy bottoms at depths of 80-170m inside the FMZ (where fishing is strictly regulated) and outside the FMZ (where fishing is unregulated), abundance and biodiversity indices, and size spectra were  calculated based on data obtained during the MEDITS 2003, 2004 and 2005 research cruises. Multivariate analysis was conducted by first constructing a similarity matrix from the root-root transformed biomass data using the Bray-Curtis similarity measure, and then applying non-metric multidimensional scaling (nMDS) ordination.

The results show that species groups sensitive to trawling, such as elasmobranchs (especially, Scyliorhinus canicula and Raja clavata), were very common inside the FMZ, however, such species were practically absent outside the FMZ. This group was also that most responsible for the difference between the ‘inside’ and ‘outside’ stations. For the ‘inside’ stations, analysis of the size spectra also showed that elasmobranchs attain larger size inside the FMZ. The continental shelf inside the FMZ has more than twice the biomass and abundance (per unit area) than that outside the FMZ, and reduced biomass and abundance is a common feature of heavily trawled areas. The management regime enforced within the previous 25NM Exclusive Fishing Zone between 1971 and 2004 (which is now the Malta 25NM Fisheries Management Zone) seems to have been effective in protecting the demersal resource in the fisheries reserve on the continental shelf round Malta.

The findings of this study were reported upon at the European Symposium on Marine Protected areas (Dimech et al., 2007a).


Litter as a source of habitat islands on deep water muddy bottoms

During the MEDITS and GRUND surveys that MERG has participated in since 2003, it was noticed that on the (often abundant) litter that comes up with the haul, there is frequently a diverse biota. It would appear that several organisms use anthropogenic debris as a substratum. A study was made to characterise and quantify use of such litter by biota, since not only could these organisms be important components of the food webs of commercial fish, but a literature search showed that this phenomenon has never been studied in the Mediterranean and elsewhere.
 
Litter samples from 44 different hauls at depths of 45-700m made during the MEDITS 2005 trawl survey were collected and studied for any organisms that might be attached to them.  The litter material collected during each haul was standardised as number of items and surface area of debris per 1 square kilometre of trawled area, while the abundance of biota was standardised as per 1 square metre of rubbish surface area. The litter itself was categorised as fabric, glass, metal, plastic, pottery and sacks.  The data were analysed using univariate and multivariate (nMDS and agglomerative, hierarchical clustering) methods.  Abundance and species richness were calculated for the litter and compared with values of the same parameters obtained from samples of the sediment from the same stations, in order to analyse the contribution of anthropogenic debris to the biodiversity of muddy bottoms surrounding the Maltese islands. 

Pic_7 

An anthozoan using a beer can as a substratum

Litter was found to support a higher abundance but lower species richness than the surrounding sediment.  Metal and pottery items supported relatively high epifaunal abundances and species richness.  However, both these metrics were low for sacks, plastic and fabric. The exception was glass, which had relatively high species richness but a low abundance of epifauna.  On the basis of nMDS ordination, the high abundance and species richness supported by metals and pottery could probably be attributed to their rough surface texture relative to the other litter types, which had smooth surfaces; a smooth surface makes it difficult for biota to attach.

A paper presented these results was given at the 38th CIESM congress held in Istanbul between the 9th and 13th April, 2007 (Pace et al., 2007a).


Distribution and density of discarded limestone slabs used in the traditional Maltese lampuki fishery

The discarded limestone slabs originating from the Maltese lampuki fishery provide a substratum for biota. The amount of limestone slabs recovered in trawl nets is remarkable, and amongst the biota that such slabs supported it was interesting to note large numbers of polychaetes, especially serpulids, which are known to form part of the diet of several commercial fish species. Since no information on the distribution, density and the biota of these artefacts seems to exist, a preliminary study on the ecological effects of the slabs was made.

Discarded slabs recovered during the MEDITS 2005 survey were recorded, measured and classified into the following age categories: pre-1976, 1976-1980 and post-1980, based on the slabs’ dimensions. The density and distribution of limestone slabs were plotted on a map showing the distribution of FADs (fish aggregating devices – kannizzati) around the Maltese islands.  FADs are laid annually in September at the beginning of the lampuki season along established trajectories, which have now remained the same for several decades.
   

Pic_8 

Standardised abundance of limestone slabs at each station (circles), superimposed on a map of FAD distribution around the Maltese islands.

Even though the local lampuki fishery is several decades old, and more than 15,000 slabs are estimated to be laid annually, and in spite of the large number of slabs recovered in hauls, the abundance obtained in this study was much lower than expected.  The majority of the slabs retrieved (61%) were of recent origin (post-1980), implying that the slabs are being removed from the surface of the seabed with time.  Two plausible explanations are that either the slabs were removed by trawlers from the area studied (trawlers usually ‘clean’ an area of seabed from obstacles before commencing trawling operations), or else the slabs are gradually sinking into the sediment until completely buried. It was also found that limestone slabs were more frequent in non-FADs areas than in FADs areas suggesting that either there is illegal deployment of FADs in non-FADs areas; or that slabs are used for other purposes besides mooring kannizzati, for example, as ballast to stabilise fishing boats when empty, and are then disposed of randomly; or that slabs are transported from their point of deposition to other areas by bottom currents or by fishers when such slabs are accidentally trawled up. 

The results of this study were presented at the 38th CIESM congress held in Istanbul between the 9th and 13th April, 2007 (Pace et al., 2007b).

Work in progress

A study on the distribution and population dynamics of selected cephalopod species of the Malta FMZ is currently underway. This study will involve an assessment of the cephalopod species and their distribution and abundance based on the results from previous and future trawls surveys. Habitat preferences of different cephalopod species will be determined by correlation of abiotic factors to their distribution and abundance patterns. Studies on the population ecology of selected species, based on trawl surveys, will be carried out, in order to obtain data on spawning periods, maturity stages and sex ratios.  Such information is of utmost importance for management of the cephalopod resource in a sustainable manner.

Another study aims to determine the diets of elasmobranches since they are top predators and important scavenging species on muddy bottoms, and to correlate the diets with the relative abundance of the demersal fauna sampled during the trawl surveys. This study will be important to determine if the elasmobranch species under study utilise the demersal assemblages on muddy bottoms as their main source of food and to identify if any of these elasmobranchs are predators on commercially important species.

References

Bertrand J.A., Gil de Sola L., Papacostantino C., Relini G. & Souplet A. (2002).  The general specifications of the MEDITS surveys.  Scientia Marina 66 (Supplement 2): 9-17.

Camilleri M. (2003). Background to the establishment of the 25 mile Fisheries Conservation Zone around the Maltese islands. In: Proceeding of the APS Seminar ‘Ecosystem based fisheries management in the Mediterranean’. pp. 99-106. Malta: APS Bank Publications.

Clarke K. R. & Warwick R. M. (1994). Change in marine communities: an approach to statistical analysis and interpretation. Plymouth, UK: Natural Environment Research Council, 144 pp.

Department of Fisheries and Aquaculture (2000). Maintaining the Maltese Fisheries Management Zone. Malta: Ministry of Agriculture and Fisheries; i + 16pp.

Dimech, M., Camilleri, M., Gristina, M., Kaiser, M.J. & Schembri, P.J. 2005. Commercial and non-target species of deep-water trawled muddy habitats on the Maltese continental shelf. Xjenza; 18-23.
Dimech M., Camilleri M., Hiddink, J.G., Kaiser M.J.  & Schembri P.J. 2007a. Structure of demersal assemblages under different intensities of trawling pressure on the continental shelf around the Maltese Islands (Central Mediterranean). In: Perez-Ruzafa, A.; Hoffmann, E.; Boncoeur, J.; Garcia-Charton, J.A.; Marcos, C.; Salas, F.; Sorensen, T.K. & Vestegaard, O. (eds) European Symposium on Marine Protected Areas as a Tool for Fisheries Management and Ecosystem Conservation. Emerging science and interdisciplinary approaches. Abstracts Book p.80; EMPAFISH and PROTECT projects, Editum, Murcia: 330 pp.

Dimech, M., Camilleri, M., Kaiser, M.J. & Schembri, P.J. (2007b). Role of environmental variables in structuring demersal assemblages on trawled bottoms on the Maltese continental shelf. Rapport du Congrès de la Commission Internationale pour l'Exploration Scientifique de la Mer Méditerranée 38: 463.

Dimech, M., Camilleri, M., Kaiser, M.J. & Schembri, P.J. (2007c). Demersal assemblages on deep water trawling grounds off the Maltese Islands: management implications.  Rapport du Congrès de la Commission Internationale pour l'Exploration Scientifique de la Mer Méditerranée 38: 462.

Link J. S. (2002). Ecological considerations in fisheries management: When does it matter? Fisheries 27: 10-17.

Pace, R., Dimech, M., Camilleri, M., Mosteiro Cabanelas, A. & Schembri, P.J. (2007a). Litter as a source of habitat islands on deep water muddy bottoms.  Rapport du Congrès de la Commission Internationale pour l'Exploration Scientifique de la Mer Méditerranée 38: 567.

Pace, R., Dimech, M. & Schembri, P.J. (2007b). Distribution and density of discarded limestone slabs used in the traditional Maltese lampuki fishery.  Rapport du Congrès de la Commission Internationale pour l'Exploration Scientifique de la Mer Méditerranée 38: 568.

Pitkitch, E.K., Dantora, C.S., Babcok, E.A., Bakun, A., Bonfil, R., Conover, D.O., Dayton, P., Doukakis, P., Fluharty, D., Heneman, B., Houde, E.D., Link, J., Livingston, P.A., Mangel, M., McAllister, M.K., Pope, J.G. & Sainsbury, K.J. (2004) Ecosystem-based fishery management. Science, 305, 346–347.

Relini, G. (1998).  Valutazione delle risorse dimersali. Biologia Marina Mediterranea 5:3-19.

 

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