2011, 835 t, in 2012, 1711 t in 2013 and 2231 t in 2014 (more than 23.31% higher
than the previous year) (NIMRD 2015). This increase of catches during the past
years was not due to the fish fauna, but to the emergence of economic operators’
interest in the manual and beam trawl harvesting of the rapa whelk (Rapana venosa
Valenciennes, 1846), which increased the catches year by year, from about 65% of
the total catch in 2012 to 89% in 2014 (NIMRD 2015).
The low level of overall fishery catches is mainly caused by the decrease of
fishing effort (drop in the number of coastal trawlers, pound nets and, consequently,
of the staff involved in fisheries) and by the influence of hydroclimatic conditions of
fish populations, as well as by the increase of production costs and lack of a fishery
market (Maximov and Staicu 2008; Radu et al. 2013; Danilov et al. 2016). This
situation has imposed the need for the orientation of fishing activities and exploitation towards other marine living resources, such as the rapa whelk.
The gastropod R. venosa is an invasive species, reported for the first time in the
Black Sea as Rapana thomasiana (Crosse 1861) around the Novorossysky Port in
1946, although it was considered that it had settled in the Pontic basin around
1930–1940 (Daskalov and Ra ¨tz 2011). This large voracious predator quickly
colonized the shallow coastal areas of the Black Sea. It is a carnivorous species,
feeding mainly on the bivalves Mytilus galloprovincialis, Mya arenaria, Chione
gallina. At the Romanian coast it was first reported in 1963, at the mouths of the
Danube (Gomoiu 1972), from where it has expanded rapidly to the south, becoming
a common species. Today, it is common on all types of substrate (rocky, sandy,
muddy) between 3 and 45 m depth (Skolka and Gomoiu 2004).
In other Black Sea countries (Turkey, for instance), the increase in rapa whelk
abundance has triggered a commercial fishery since the early 1980s using dredge
and hookah (divers) systems. The rapa whelk represents an important input for the
economy of Turkey (Duzgunes 2001). The species was traditionally captured by
dredges, but during recent years the fishery seems to be changing to the hookah
systems because of its fishing efficiency and the high market value. The fishing
effort is steadily increasing year after year and the average size of the individuals
fished are dropping, suggesting a tendency to overexploitation of the fishery (Aydin
et al. 2016).
At the Romanian coast, fishing for R. venosa was first performed only using
divers, because this is a method which provides high selectivity of the catches and
protection of habitats. However, this method has proved to be expensive due to high
costs of operation (high costs with services rendered by divers and with boats used
during harvesting) as compared with the size of catches taken (modest catches due
to limited number of hours of immersion per day, in accordance with normative
laws, and the major influence of hydroclimatic conditions). Significantly increased
catches of rapa whelk and, implicitly, higher profitability of exploitation result from
the use of mechanized equipment for harvesting, such as, for example, the beam
trawl (not recommended to be used on rough/rocky bottoms, where there is an
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G. T ¸ iganov et al.
than the previous year) (NIMRD 2015). This increase of catches during the past
years was not due to the fish fauna, but to the emergence of economic operators’
interest in the manual and beam trawl harvesting of the rapa whelk (Rapana venosa
Valenciennes, 1846), which increased the catches year by year, from about 65% of
the total catch in 2012 to 89% in 2014 (NIMRD 2015).
The low level of overall fishery catches is mainly caused by the decrease of
fishing effort (drop in the number of coastal trawlers, pound nets and, consequently,
of the staff involved in fisheries) and by the influence of hydroclimatic conditions of
fish populations, as well as by the increase of production costs and lack of a fishery
market (Maximov and Staicu 2008; Radu et al. 2013; Danilov et al. 2016). This
situation has imposed the need for the orientation of fishing activities and exploitation towards other marine living resources, such as the rapa whelk.
The gastropod R. venosa is an invasive species, reported for the first time in the
Black Sea as Rapana thomasiana (Crosse 1861) around the Novorossysky Port in
1946, although it was considered that it had settled in the Pontic basin around
1930–1940 (Daskalov and Ra ¨tz 2011). This large voracious predator quickly
colonized the shallow coastal areas of the Black Sea. It is a carnivorous species,
feeding mainly on the bivalves Mytilus galloprovincialis, Mya arenaria, Chione
gallina. At the Romanian coast it was first reported in 1963, at the mouths of the
Danube (Gomoiu 1972), from where it has expanded rapidly to the south, becoming
a common species. Today, it is common on all types of substrate (rocky, sandy,
muddy) between 3 and 45 m depth (Skolka and Gomoiu 2004).
In other Black Sea countries (Turkey, for instance), the increase in rapa whelk
abundance has triggered a commercial fishery since the early 1980s using dredge
and hookah (divers) systems. The rapa whelk represents an important input for the
economy of Turkey (Duzgunes 2001). The species was traditionally captured by
dredges, but during recent years the fishery seems to be changing to the hookah
systems because of its fishing efficiency and the high market value. The fishing
effort is steadily increasing year after year and the average size of the individuals
fished are dropping, suggesting a tendency to overexploitation of the fishery (Aydin
et al. 2016).
At the Romanian coast, fishing for R. venosa was first performed only using
divers, because this is a method which provides high selectivity of the catches and
protection of habitats. However, this method has proved to be expensive due to high
costs of operation (high costs with services rendered by divers and with boats used
during harvesting) as compared with the size of catches taken (modest catches due
to limited number of hours of immersion per day, in accordance with normative
laws, and the major influence of hydroclimatic conditions). Significantly increased
catches of rapa whelk and, implicitly, higher profitability of exploitation result from
the use of mechanized equipment for harvesting, such as, for example, the beam
trawl (not recommended to be used on rough/rocky bottoms, where there is an
398
G. T ¸ iganov et al.