Adriatic Sea (North Central) - Key Species
European anchovy (Engraulis encrasicolus)
European anchovy is a small pelagic fish with a high economic value. It is no longer than 20 cm in length and ranges in colour from green-blue to silver in the ventral part. This is very gregarious specie that forms big schools and mainly feeds on small zooplankton, mostly copepods, and to a lesser extent on molluscs, cladocerans, other crustaceans and appendicularians. Bigger prey sporadically occur in the diet, such as large copepods, mysids, amphipods, cumaceans, decapod larvae, appendicularians, polychaetes and fish eggs and larvae. In general, the spawning habitat of anchovy is characterized by an optimal temperature range of 17-19 ºC and two salinity peaks (32-36 and 37.50/00). These temperatures are characteristic of the stratified season. In fact, anchovy spawning season begins when temperatures warms at the end of spring and extends throughout the summer. European anchovy is important prey for top predators of the area such as European hake and bluefin tuna, and it is targeted by purse seines and mid water trawlers. Recruitment overfishing of this species is a big concern.
Sardine (Sardina pilchardus)
Sardine was the most abundant small pelagic fish in the area, although its economic value is less than anchovy and nowadays population size has decreased dramatically. Sardine reach 30 cm in length and range in colour from yellowish-green to silver. Sardine is a very gregarious species. Available data suggest that sardine feed on zooplankton, principally copepods, cladocerans, euphausids, crustacean larvae, eggs and also on phytoplankton. Sardine spawns during autumn-winter, when the water column is vertically homogeneous and relatively cool as it prefers cold waters (12-14ºC), although spawning also occurs in water up to 19ºC. During spawning, salinity is in the characteristic range of shelf waters not directly related to river runoff. Like anchovy, sardine is an important prey for top predators of the area such as European hake and bluefin tuna, and it is targeted by purse seines and also caught by mid water trawlers. The status of sardine is worrying as it is considered to be fully to overexploited.
Sprat (Sprattus sprattus)
Sprat is a small, herring-like, marine fish with silver grey scales and white-grey flesh and is found in European waters and the Mediterranean, usually inshore forming schools, sometimes entering estuaries (especially as juveniles) and tolerating salinities as low as 4 ppt. It feeds on planktonic crustaceans and spawns at depths of 10-20 m. This species was relatively abundant in the north-central Adriatic Sea but has shown a progressive decrease to close to extinction in the late 1990s. Although no time series of data are available, this decline could be related to a progressive increase in water temperature in the Mediterranean Sea and therefore this species is being forced to move to the more northern areas of its former distribution.
Jellyfish
Jellyfish belong to the same zoological group as corals and gorgonians, but they are mostly pelagic as they are found in the water column. Numerous species of jellyfish are found in the north-central Adriatic Sea, like Pelagia noctiluca and Aurelia aurita. Although time series of data are not available, there has been increasing concern that jellyfish are being more frequently found at high densities near the coast, impairing swimming and other aquatic activities. Possible causes of jellyfish proliferations are not clear, although they have been related to eutrophication, climate change and disruption of the food web by fishing.
European hake (Merluccius merluccius)
This is a highly commercial species, mainly caught by bottom trawlers. European hake is highly predatory, inhabiting the waters of the continental shelf. Juvenile European hake prey on mesopelagic fishes, macrobenthos and small demersal fish. Adult hake inhabit the water column and feed on demersal and small pelagic fish. There is a strong concern about recruitment and growth overfishing of this species.
Red mullet (Mullus barbatus and Mullus surmuletus)
Mullus barbatus and Mullus surmuletus are two demersal species mainly located from the coastal area to the continental shelf where size of individuals increases with depth. Mullus barbatus grows to 15 cm, is found on mud and sandy bottoms and reproduces between April and August. M. surmulletus reaches 20 cm in length, is found on rocky substratum covered by algae, seagrass and sandy bottoms, and spawns between May and July. Red mullet are carnivorous, feeding on demersal crustaceans and worms. Both are highly commercially important and caught by bottom trawling and by artisanal fisheries using guild nets. Since the 1990s, red mullet appear to be fully exploited or overexploited.
Flatfishes
Several species of flatfishes are abundant in the wide continental shelf area of the north-central Adriatic Sea. They range from small to large in size and have relatively short life spans. Flatfish are of high commercial value and are mainly caught by bottom trawling and beam trawling. Their populations are directly impacted by trawling, and ecological models and time series of relative biomass suggest that their abundances are decreasing with time.
Mantis shrimp (Squilla mantis)
Squilla mantis is chiefly found and fished in the Mediterranean Sea. It grows up to 200 mm long and it is generally dull brown in color, but has two brown eye spots, circled in white at the base of the tail. This species digs burrows in muddy and sandy substrata near the coast. It remains in its burrow during the day and comes out at night to hunt, and in the winter to mate. Mantis shrimp is particularly abundant where there is significant run-off from rivers, and where the substrate is suitable for burrowing. It feeds mainly on small benthic invertebrates such as worms, bivalves and snails. The species is mainly caught by beam trawling and bottom trawling. Populations are directly impacted by trawling, and ecological models suggest that they could be negatively impacted under high fishing pressure, however conclusions that can be drawn from available catch and biomass data for this species are not clear.
Norway lobster (Nephrops norvegicus)
This is a demersal crustacean found from 20 to 800 m depth on muddy bottoms in which it burrows. It is nocturnal and feeds on detritus, crustaceans and worms. Egg-carrying females are found practically throughout the year; eggs laid around July are carried for about 9 months. The total body length of adult animals varies between 8 and 24 cm, usually between 10 and 20 cm. The Norway lobster is of high economic value in the area and is mainly caught in bottom trawls. Since 1990, the species appears to be fully to overexploited.
Scallops
Scallops, like the Mediterranean scallop (Pecten jacobaeus) or the queen scallop (Chlamys opercularis), are target species that fetch high commercial values. They are caught with beam trawls and hydraulic dredges and have decreased in the Adriatic Sea due to high fishing pressure. Although trends in data on biomass are not clear, regional catch data show declines of scallops, probably due to intensive fishing and the long life spans of scallops.
Starry ray
Several demersal chondrichthyans, like the Starry ray, are present in the north-central Adriatic Sea, although their abundances have notably decreased from the 1970s, mainly due to overlapping distribution with bottom trawling activities. Although few data are available, catch data show a progressive decline from the 1970s to present, and predictions from ecological models show the same pattern for biomass.
Cetaceans
Although at low population levels, two species of cetaceans can be found frequently in the north-central Adriatic Sea: the bottlenose dolphin (Tursiops truncatus) and the common dolphin (Delphinus delphis). The diet of bottlenose and common dolphins consist mainly of small demersal and pelagic fish with occasional squid, crabs, shrimp and other smaller animals. Populations of bottlenose and common dolphins are small and regional conservation concerns are related to mass mortality events due to viruses and negative effects of pollution and overexploitation.
Loggerhead turtle (Caretta caretta)
The loggerhead turtle Caretta caretta is the most common marine turtle in the Mediterranean, where specimens from Atlantic and eastern Mediterranean rookeries share foraging areas. Juveniles of loggerhead turtle are found in the Western Mediterranean and the Adriatic Sea, mainly with carapace length from 30 to 80 cm. They mainly feed on demersal invertebrates and small fish, and it has been suggested that in the western Mediterranean they take advantage of organisms discarded during fishing. This species is generally considered 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 this species, although fishing by-catch is most likely the largest cause of mortality in the Adriatic area, mainly due to incidental catch by bottom-trawlers and mid-water trawlers.
Maerl
Maerl is a collective name for two or three species of red algae in the Corallinacease, especially Phymatolithon calcareum in the Adriatic Sea. It accumulates as unattached particles and forms extensive beds in suitable sublittoral sites. There are numerous features of maerl that contribute to its value as a habitat for other marine species. For example, it provides a surface to which other seaweeds can attach. Other organisms then can feed on these seaweeds or it can be grazed itself by organisms. It also provides attachment sites for animals which in turn are food for others and its loose structure provides shelter, e.g. for small gastropods. The infauna in maerl beds includes many bivalves and they are very important nursery areas for scallops. Maerl habitats are extremely sensitive to bottom trawling. In the north of the Adriatic Sea there used to be important expanses of maerl but they have dramatically declined.
Northern Bluefin Tuna (Thunnus thynnus)
The northern bluefin tuna is a species of tuna fish living in both the Western and Eastern Atlantic Ocean and extending into the Mediterranean Sea and the Black Sea. This fish can live to 30 years, is typically 2 m long, and can reach 500 kg. 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 of bluefin are considered overfished, including the Mediterranean one. This is due to the slow growth rate and late maturity of bluefin tuna. The Atlantic population of the species has declined by nearly 90 percent since the 1970s and severe concern has been voiced by the scientific community due to its large reported and nonreported catches. The bluefin species are consequently listed as ones to "Avoid" on the Monterey Bay Aquarium's Seafood Watch program.
Basking shark (Cetorhinus maximus)
This is the second largest fish, after the whale shark. It is slow moving and a filter feeder preying mainly on zooplankton and small fish. Basking shark is mainly a coastal-pelagic shark, prefering waters between 8 and 14°C (46 and 57° F). It is often seen close to land and will enter enclosed bays, follows concentrations of plankton in the water column and is therefore often visible on the surface. It is highly migratory and a cosmopolitan species found in all the world's temperate oceans. However, this species is currently of conservation concern as it is classified as vulnerable in the IUCN red list. This is mainly due to a combination of low resilience and overfishing (direct or due to by-catch). The Adriatic Sea stills shelters several individuals of basking sharks, especially in the northern areas.
Mediterranean monk seal (Monachus monachus)
The Mediterranean monk seal is believed to be the world's rarest pinniped and one of the most endangered mammals of the world. This species is classified as critically endangered in the IUCN red list. The global population is estimated to be of 150 - 250 individuals remaining in the whole Mediterranean Sea, and, of this, about 20 individuals are left in the Adriatic Sea (Yugoslavia coast). Its present endangered situation can be mostly attributed to persecution by fishermen during the 1990s and also to habitat modification due to them breeding in coastal areas now occupied by humans. This species grows from 80 cm as newborns to an average length of 2.40 m as adults. The males can weigh up to 320 kg, the females are slightly smaller. Their fur is black (males) or brown to dark grey (females) with a paler belly which is close to white in males. Pups are born with black natal fur, often with a white patch beneath. The reproductive maturity is reached at around four years of age, and total age is over 20 years.