Northern bluefin tuna
This is a small pelagic fish with a high commercial value. Anchovy are not longer than 20 cm and range in colour from green-blue to silver on the ventral part. This very gregarious species forms large schools, feeding mainly on zooplankton, mostly copepods, and to a lesser extent on molluscs, cladocerans, other crustaceans and appendicularians. In some cases, bigger prey such as large copepods, mysids, amphipods, cumaceans, decapod larvae, appendicularians, polychaetes and fish eggs and larvae, sporadically occur in the diet. In general, the spawning habitat of anchovy is characterized by temperatures from 17-19 ºC and two salinity peaks of 32-36 and 37.5 ppm. These temperatures are characteristic of the stratified season in the Catalan sea, while these salinities correspond to waters of continental influence and shelf-slope waters. In fact, the anchovy spawning season begins when temperatures increase at the end of spring and extends throughout the summer. The distribution of anchovy spawning is fairly continuous in the NW Mediterranean, but higher egg densities off the Ebro River mouth point to anchovys preference for areas under the influence of freshwater runoff. The cross-shelf distribution of anchovy eggs and larvae show relatively low densities of eggs in shallow areas close to the coast (<50 m depth) and maximum densities near the edge of the shelf (ca. 200 m isobath). Anchovy is an important prey for top predators such as European hake and bluefin tuna, and is targeted by purse seines and also caught by bottom trawlers in the area. Recruitment overfishing is a major concern.
This is the most abundant small pelagic fish in the area, although it is less valuable than anchovy. Sardine reach up to 30 cm in length and range in colour from yellowish-green to silver. This is very gregarious specie and data available suggests that sardine feed on zooplankton, principally copepods, cladocerans, euphausids, crustacean larvae, eggs and phytoplankton. Sardine spawns during autumn-winter, when the water column is vertically homogeneous and relatively cool as it prefers cold waters (12-14 ºC), although spawning also occurs up to 19 ºC. During spawning, salinity is in the characteristic range of shelf waters not directly related to river runoff. Sardine eggs are largely located over the shelf, from coastal areas to a depth of 100 m, but also near the shelf-break in areas where the shelf is narrow and under particular environmental conditions. Sardine is caught mainly during spring and autumn, when most individuals are between 1 and 2 years old, and landings have been found to be positively correlated with a wind mixing index, with a time lag of 18 months, but not correlated with river runoff. Like anchovy, sardine is an important prey for top predators such as European hake and bluefin tuna, and is targeted by purse seines and also caught by bottom trawlers in the area. Sardine appears to be fully exploited or overexploited.
Round sardinella is a less abundant small pelagic fish species in the Catalan Sea and it is of little commercial interest, although it is caught as a bycatch species by purse seiners and bottom trawlers. There has been a progressive increase in landings and its expansion to the northern NW Mediterranean areas has been related with the progressive increase in water temperature in the Mediterranean Sea. In accordance with its tropical origin, round sardinella spawns when surface water temperature is higher than 23 ºC and its reproductive period in the NW Mediterranean stretches over the warmest period of the year, from July to October. Distribution of round sardinella eggs and larvae indicate that spawning takes place in areas relatively close to the shore, with the highest densities at depths of less than 100 m. There is no quantitative information on its feeding.
Jellyfish belong to the same zoological group as corals and gorgonians, but are mostly pelagic as they are found in the water column. Numerous species of jellyfish can be seen in the Catalan Sea, like Pelagia noctiluca, Chrysaora hysoscella, Rhizostoma pulmo and Cotylorhyza tuberculata. Although no time series of data are available, there has been an increasing concern about jellyfish occurrence in the Catalan Sea since the late 1980s due to the fact that they are more frequently found in high densities near the coast, impairing swimming and other aquatic activities. Possible causes of jellyfish proliferations are not clear, although sporadic data from the Catalan Sea matches other information for the Mediterranean and non-Mediterranean areas where proliferations have been linked to overfishing, eutrophication and climate change.
This is a highly commercial species, mainly caught by bottom trawlers as juveniles and long lines as adults. This species is highly predatory, inhabiting the waters of the continental shelf and the upper slope. Eggs and larvae of hake are found in higher concentrations on the edge of the continental shelf and upper slope, where adults congregate to reproduce, while juveniles are located over the continental shelf; size of individuals increases with depth. The juvenile European hake in the NW Mediterranean seems to undertake nocturnal vertical movements through the water column to prey on mesopelagic fish, whereas it preys on macrobenthos and small demersal fish during the day. Adult hake inhabit the water column and feed on demersal and small pelagic fish. Recruitment and growth overfishing of this species is of concern.
Lophius piscatorius and L. budegassa are two highly commercial species, mainly benthic and located on the continental shelf. They are predatory fish, largely feeding on demersal fish and crustaceans. Anglerfish exhibit cryptic features, have large mouths and can reach lengths of 1-2 m, although much smaller specimens are found nowadays. Of high commercial importance in the Catalan Sea, they are mainly targeted by bottom trawlers and also caught using deep long lines. Although there is not a formal evaluation of exploitation status, a decline in landings has been reported in the southern Catalan Sea since the mid-1970s.
Mullus barbatus and Mullus surmuletus are two demersal species, located from the coastal area to the continental shelf where size of individuals increases with depth. Mullus barbatus is frequently 15 cm, it is found on muddy and sandy substrata and reproduces from April to August. M. surmulletus frequently reaches 20 cm, is found in rocky substratum covered by algae, seagrass and sandy bottom and it spawns from May to July. Red mullet are carnivorous, feeding on demersal crustaceans and worms. Both are highly commercial species caught by bottom trawlers and by artisanal fisheries using gill nets. Concern has been expressed by scientist from the 1990s due to they appear to be fully exploited or overexploited.
This is a demersal crustacean found from 20 to 800 m depths, living on muddy substrata in which it burrows. It is nocturnal and feeds on detritus, crustaceans and worms. Egg-carrying females are found practically throughout the year; the eggs laid around July are carried for about 9 months. The total body length of adults varies between 8 and 24 cm, usually between 10 and 20 cm. the Norway lobster is of high commercial value in the area and is mainly caught by bottom trawl. Since the 1990s, scientists have expressed their concern as Norway lobster appears to be fully exploited or overexploited.
This is a highly abundant crustacean species in the area, mainly found in muddy and sandy areas of the continental shelf below 150 m. Its carapace is wider than long, about 51 mm wide and 40 mm long. Although not a target species, it is caught in great quantities as by-catch by the bottom trawling fleet. Sometimes it is commercially used as soup crab, but mostly it is discarded. Harbour crabs are very active at night and feed on other crustaceans and small demersal fish. Ecological models have recently suggested that this species could be benefiting from heavy fishing, which is removing its predators.
This is one of the few species of demersal chondrichthyans that are still present in the southern Catalan Sea. Although there are few biological data available, catch data shows a progressive decline from the 1970s to present, and predictions from ecological models show the same pattern for biomass, mainly due to the overlap in distribution with that of bottom trawling. Maximum lengths can be up to 0.7 m and the species is mainly distributed from the coast to 170 m depth in sandy and muddy grounds. It is an oviparous species that reproduces during autumn and feeds mainly on demersal crustaceans, Liocarcinus depurator and Goneplax rhomboides, small demersal fish (mullets, gobids), and shrimps. Ecological modelling used to simulate recovery scenarios highlighted that this species would have the potential to recover relatively quickly if fishing pressure is substantially decreased, and therefore that it could be an indicator of fishing impacts.
The northern bluefin tuna lives in both the Western and the Eastern Atlantic Ocean and extends into the Mediterranean Sea and the Black Sea. This fish can live up to 30 years, is typically 2 m long, can reach 500 kg, and is dark blue above and grey below. The species preys on small fish such as sardine, anchovy, mackerel, squid and crustaceans. . The northern bluefin tuna is an important source of seafood, providing most of the tuna used in sushi. It is a particular delicacy in Japan where the price of a single giant tuna can exceed $100,000 on the Tsukiji fish market in Tokyo. As a result, some fisheries on bluefin are considered overfished, including the Mediterranean one. This is due to bluefin's slow growth rate and late maturity. The Atlantic population of the species has declined by nearly 90 percent since the 1970s and high concern has been voiced by the scientific community due to the large reported and unreported catches.
This is an endemic seabird from the Mediterranean Sea that has been listed as vulnerable by the Spanish government and in danger of extinction regionally. The southern Catalan Sea is a strategic area for the conservation of this species because it shelters three quarters of its worlds breeding population. This seabird reaches from 48 to 52 cm in length and 115 to 140 cm in height and breeds in sandy-vegetated coastal areas of the Mediterranean Sea. It feeds on small fish and crustaceans from the wetlands and on small pelagic fish that actively forage along the coast or continental shelf. Its progressively increase in the southern Catalan Sea has been related to its ability to feed on fishing discards from bottom trawling and purse seines. Conservation concern has been expressed due to by-catch of Audouin gulls, especially in surface long lines.
Although at low levels of abundance, three species of cetaceans can be found frequently in the southern Catalan Sea: fin whales (Balaenoptera physalus), bottlenose dolphin (Tursiops truncatus) and striped dolphin (Stenella coeruleoalba). Fin whales are only present in the area during their migratory events between the Strait of Gibraltar and the Liguria Sea, while resident groups of bottlenose and striped dolphins are found all year around. The diet of bottlenose and striped dolphins consist mainly of small demersal and pelagic fish with occasional squid, crabs, shrimp, and other smaller animals. Fin whales mainly feed on zooplankton, and occasionally on squids and small pelagic fish. Fin whales are considered endangered, while populations of bottlenose and striped dolphins are low and regional conservation concerns are related to mass mortality events due to viruses and detrimental effects of pollution and overexploitation.
The loggerhead turtle Caretta caretta is the most common marine turtle in the western Mediterranean, where specimens from Atlantic and eastern Mediterranean rookeries share foraging areas. Juveniles of loggerhead turtle are found in the Western Mediterranean Sea, mainly with carapace length from 30 to 80 cm. They feed on demersal invertebrates and small fish, and it has been suggested that in the western Mediterranean they take advantage of discards from fishing. This species is considered generally endangered while in the Mediterranean Sea it could be classified as critically endangered. Habitat modification, boat collision, ingestion of debris and chemical pollution are potential threats for loggerhead turtles, although scientists believe that fishing is the largest cause of mortality. Incidental catch of loggerhead turtles has been recorded in the NW Mediterranean Sea where drift-nets, bottom trawling and long lines are used.
Posidonia oceanica is an endemic flowering plant of the Mediterranean Sea, where it forms undersea meadows. It is distributed in the coastal area and it is normally in shallow waters not deeper than 10 m. Its ecological role is very important for the local ecosystems since many other species of commercial and non commercial interest find nutrients and sheltering in Posidonia meadows. Conservation issues relate to pollution, sedimentation, habitat modification and fishing impact, boat anchoring and introduction of alien species.