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Accion concertada para el estudio biologico y pesquiero de gambas profundas del mediterraneo y mares adyacentes


In this report are presented the results of the Seminars and Workshops of the 'Concerted Action for the Biological and Fisheries Study of the Mediterranean and Adjacent Seas Deep Shrimps'. Specialists in red shrimps fisheries and biology, as well as invited speakers of other science domains, attended the Seminars. They gave key talks on the biology of red shrimps and on geological and oceanographic aspects related to the ecology of red shrimps. The state of the art on current knowledge on the biology, ecology and fisheries of red shrimps in the Mediterranean was presented and future lines of research were identified.
Analysis of fisheries data using Yield per Recruit models, for areas where detailed information is available, indicates that the resource of Aristeus antennatus is slightly over-exploited. For this species, it is the female fraction of the population which is most affected by fishing, as females predominate in the population at commercial fishing depths (usually from 500 to 800 m). Aristaeomorpha foliacea is also slightly overexploited, but in this case, as no segregation by sex is found, fishing affects the entire population.

The knowledge on the basic biology of both species is locally satisfactory, in general, although specific issues requiring further research were identified (these are listed in the 'Conclusions and Recommendations' section). The broad geographical distribution of the two main species, Aristeus antennatus and Aristaeomorpha foliacea, is known for the Mediterranean and adjacent Atlantic waters. However, the lower end of the depth distribution is not known for many areas, due to the lack of deep (beyond 1000 m) samplings in most areas.

Temporal variations in the abundance and location of the resource are also important. Fluctuations in the abundance of Aristeus antennatus have been detected over several time scales, from day-night migrations along submarine canyons to seasonal and long-term cycles of changes in abundance (6 to 7 years). The wide fluctuations in an antennatus populations and the existence of different population structures by habitats are potential sources of uncertainty, especially regarding the computation of growth parameters. These differences originate problems in the application of assessment models, leading to significant errors. The current opinion among scientists puts the maximum age for this species in the range between 4 and 8 years, which is a too wide range and a source of controversy.

The environmental factors that were identified as determining the complex spatio-temporal dynamics of deep shrimps were the following:
- Bottom geomorphology: presence of large-scale features such as canyons and channels may determine the large scale distribution of the resource.
- The dynamics of sediment movement along canyons and near-bed flows may affect the distribution and temporal evolution of red shrimps at several scales.
- The hydrology of the area (movements of water masses and currents) coupled with the bottom morphology originates transient phenomena which may be responsible for the fluctuations of red shrimp abundance over short and medium temporal scales. The local oceanographic conditions may account also for the local abundance and relative proportions of species of red shrimps.
- In relation to the previous three points, the overlaying production conditions and particle fluxes to the deep sea are important in determining the availability of food resources for deep-water shrimps.

Multi-disciplinary studies on the distribution, seasonality and migrations of deep shrimp resources in relation to environmental factors are necessary in order to contribute to a better understanding of the evolution of the resource and to implement sound assessment and management strategies.

Future lines of research identified during the CA are summarised as follows:
- The hypotheses advanced during the Seminars on possible links between environmental factors and spatio-temporal variations on red shrimp resources need to be further elaborated and tested.
- Basic research in aspects of the biology and ecology of red shrimps is necessary. Specifically, detailed studies on trophic ecology, early stages of development and differential ecological preferences of the main red shrimp species (Aristeus antennatus and Aristaeomorpha foliacea) are fundamental.
- Two main areas of methodological research were highlighted: The use of time- and space-explicit models to study the complex dynamics of red shrimp resources, and research on adequate models allowing to improve estimates of population parameters (such as growth parameters) required when applying assessment methods.
- To apply correctly current assessment models, it is necessary to monitor more extensively the fishing activity and to obtain reliable catch statistics. The use of scientific observers aboard commercial vessels is essential to optimise the use of official statistics.

During this Concerted Action, the scientific guidelines were concretely presented at various thematic sessions, discussing the ideal methodological approach to each subject.

Mobility. A correct management strategy has to incorporate a deep knowledge of the mobility patterns of red shrimps, considering both their population structure and their space-time dynamics.
Methodology: Determine the spatial and temporal population structure of red shrimp inside and outside submarine canyons over the 400-900 m depth range. Preliminary research on the possibilities of successful mark-recapture methods.

Causes of Mobility. The causal mechanisms of mobility in red shrimps have to be investigated. The knowledge acquired during the CA point to hydrographic, geomorphological and trophic factors as central to explain the mobility patterns.
Methodology: 1) Establish the relationship between water masses and red shrimp presence. 2) Link the geomorphological structure and activity of canyons with red shrimp presence. 3) Determine the structure of benthic food resources and their use by deep-water shrimps.

New explorations. The eastern Mediterranean and the deep sea harbour virgin stocks which have been little explored yet. An integrated study including biological and fishery aspects is required, in view of the sustainability of the resource, as deep-water resources are very sensitive to new exploitation.
Methodology: Prospecting surveys in areas of the Aegean and Ionian seas where the presence of red shrimps has been established. Experimental prospecting surveys along a longitudinal axis across the Mediterranean at depths greater than 1000 m.

Fisheries biology and resource management. Precise knowledge on the reproductive life span and growth of the animal is essential in conducting a sound management of the resource. The current deficiencies in the precision and accuracy of effort and catch data should also be overcome.
Methodology: Estimates of growth parameters by using alternative mathematical models. Investigate the use of new biochemical methods. Study the eco-physiology and reproductive metabolism of deep-water shrimps and their relation to environmental factors such as photoperiod. Obtain reliable local maps of abundance, effort and accompanying species in representative ports of the Mediterranean.

In summary, in the present Concerted Action, it has been established that:
1. The bio-ecology of deep-water shrimps, which are the object of an important fishing industry, is at a relatively low state of knowledge, especially regarding their complex life-cycles, behaviour and auto-ecology.
2. Research effort is required to establish the grounds of an efficient regulatory management. Studies of the bio-ecological characteristics of red shrimp fisheries need to be promoted
3. In this context, we propose an integrated and multidisciplinary workframe. The study includes the definition of the most important subjects and the ideal methodology. The scientific scope of the study, the geographical frame and the scientific, technical and administrative co-ordination are also analysed.

All aspects underlined in the course of this Concerted Action should be studied in concrete geographical areas where the existing background is a guarantee of success in the research. Research actions should also be undertaken simultaneously and co-ordinately. A pragmatic approach to the research actions includes Vertical Actions and Horizontal Actions. The Vertical Actions should be conducted in specific areas of well-defined scientific and technical characteristics and should be complementary among them, and extrapolable to other areas if required. Horizontal Actions should be developed homogeneously on all the areas and should employ simultaneous research and standardised methodology.
Deep shrimp resources in the Mediterranean are mainly constituted by red shrimp species: The Peneids Aristeus antennatus and Aristaeomorpha foliacea, and Pandalids of the genus Plesionika. The fisheries for red shrimps represent a sizeable amount of the demersal trawl fishing in Italy and Spain, in volume and economic value, and to a lesser extent in Portugal and France. The red shrimp resource is also locally abundant off northern Africa (Tunisia and Algeria) and Greece. In Greece, although no directed red shrimp fishery exists at the moment, scientific trawl surveys have shown the existence of important red shrimp resources deeper than 500 m.

Red shrimp fishing in Spain and Italy is a highly selective activity, targeting primarily Aristeus antennatus and Aristaeomorpha foliacea. In Italy, the proportion of both species in the catch varies to a great extent locally and seasonally. In the Spanish Mediterranean only Aristeus antennatus is of commercial importance. In Portugal and France, red shrimps are subject to a mixed fishery with other deep-water crustaceans and in Greece they are not exploited.

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