Atlas of fish at the delta
Although it is little known, fish fauna at the Delta is exceptional, not only because of the amount but also, and perhaps more importantly because of the variety. The atlas of fish at the Delta is a management tool to raise awareness of the delta estuary fish heritage, including freshwater environments and bays which have remained almost unknown till now.
The unique ecology at the Ebro Delta is characterized by diverse environments and species living in a relatively small area. Estuary ecosystems are greatly influenced by currents of seawater and freshwater which in turn produce great variations of physical-chemical elements present in these waters.
Fish communities in estuaries are very diverse and are formed with marine, limnetic and migrating species. Furthermore the total number of species has changed enormously over the years due to those which have disappeared and the introduction of new species, but obviously this number changes depending on the presence of occasional species.
More than forty species of fish have been recorded so far in these delta waters (Queral, 2001). Some of which are in grave danger of extinction both nationally and internationally. This is the case with the Spanish toothcarp (Aphanius iberus), which has one of its biggest communities at the Delta, or the Valencia toothcarp (Valencia hispanica). The three-spined stickleback (Gasterosteus aculeatus) and freshwater blenny (Salaria fluviatilis) are to be found in many areas but are endangered on the Iberian Peninsula, however, communities are still present at the Delta.
Aquatic delta ecosystems have suffered intense modifications over the last 150 years. Rice cultivation, which today takes up more than 60% of the delta surface area, has caused the disappearance of large areas of marshland. This crop also implies a severe alteration in the seasonal flow of water and its physical-chemical properties (conductivity), and also some important amounts of fertilizers and other phytosanitary products.
Since the construction of large dams, the Ebro River has almost stopped interacting with its delta plain. Man has constantly tried to get rid of ecosystems such as cavities, and others which are still with us today, those with a larger volume of water have been reduced considerably. However, all of these modified and altered aquatic environments have been filled with introduced species of fish.
Some, such as the common carp (Cyprinus carpio), have been present at the Delta for decades or even centuries, but introducing and establishing new species is an ongoing process. In the last decade alone, a minimum of four new foreign species have been established (Pseudorasbora parva, Misgurnus anguillicaudatus, Fundulus heteroclitus and Xiphophorus maculatus), and different exotic species have been seen although acclimatization has not been confirmed.
One of the prior conditions for developing fauna management and conservation programmes, is knowledge of the species living in a determined geographical area. This way, inventory and quantification of fish communities and their habitats becomes an almost essential prerequisite for preserving fish fauna.
The distribution atlas is one of the most widely used methods for finding out about the distribution of species. With respect to compiling an atlas, ichthyology has received rather unfavourable treatment compared to other taxonomic groups, and even with the increase of studies carried out at the Ebro delta in recent years, information on fish fauna is still scarce compared to the ecological importance and wealth of fish fauna present. Despite this, there are specific studies (Demestre et al., 1977 and Sostoa, 1983) which give us a more general view of ichthyologic fauna. However, none of these studies include the environments around the bay.
With this situation in mind and that of the lack of updated information on fish communities at the Delta as a whole, it was decided that an atlas on fish at the Ebro delta be developed, and that it include those in freshwater areas as well as those around the bay, all within the delta environment but which are somewhat forgotten in terms of their scientific communities. The main aim was to create an updated list of fish species and obtain an idea of the approximate structure of the fish population.
Among these main aims of the Atlas, these are the most important:
- Create an updated list of species present in the aquatic delta environments.
- Create a database for collecting and recording information.
- Create an inventory and maps of aquatic habitats with presence of fish at the delta.
- Discover the approximate local distribution of each species in each of the specified environments.
- Establish vulnerable areas for conservation of fish fauna and decide which have priority.
The fish Atlas is real and you can see it at: http://parcsnaturals.gencat.cat/web/.content/home/delta_de_lebre/novetats/2015/ATLES_PEIXOS_WEB.pdf