Analysis of the Colonizing Success of Lessepsian Migrants
143
compete with the local Atlantic lizard fish Synodus saurus which is rare and
noncommercial, but with the hake M erluccius. The two fishes share the same food
and frequently the same bottoms. The above-mentioned authors reach the conclusion that Saurida takes advantage of dry warm winters and M erluccius of the
rainy cold winters. Ben-Yami and Glaser (1974) also reach the conclusion that the
two species have divided the shelfbetween them, in such a way that in the summer
the lizard fish predominates shallow bottoms and is barely overlapping with the
hake, while in the winter, the hake advances into the shallow areas. Saurida is
generally caught down to maximum 80 m. M erluccius appears in the summer
chiefly below tbis depth. It seems therefore that Saurida might have occupied the
shallower parts of a depth range previously occupied only by the hake. The food
of the two species is rather similar, composed mainly of anchovy, and lately of two
Lessepsian migrant fish: Leiognathus klunzingeri and U peneus asymmetricus. BenYami and Glaser (1974) reach the conclusion that the sudden appearance of
Saurida did not increase the trawl catches but merely displaced M erluccius to
deeper bottoms. According to Gorgy (1966), the hake is found along the Egyptian
shores only deeper than 100 m. Since the 1954-56 invasion, Saurida has maintained its numbers and has not descended below 13% of the total trawl catches
(Fig.41).
Ben-Tuvia (1973) mentions that before the appearance of Saurida in commercial amounts in 1955, the catches of the immigrant food fish Leiognathus klunzingeri were bigger. This conclusion would in a way contradict the previous conclusion about the penetration of Saurida into the same food niche. An additional
prey such as Leiognathus may have reasonably increased the available food basis
for the two competing species Saurida and M erluccius.
Speaking of the near-shore fishes, Ben-Tuvia (1973) mentions that Siganus
rivulatus may make up as much as 50% of the fishes caught in fish poisonings.
Popper (personal communication) considers that S. rivulatus thrives at the expense of the local fish Sargus. Among the barracudas the immigrant Sphyraena
chrysotaenia makes up presently one half of the catches, while the two local
species S. sphyraena and S. viridensis constitute the other half (Ben-Tuvia, 1973).
Since here too the local species have not disappeared, the logical explanation is
that the migrants fitted themselves into the food niche of the natives, by better
exploitation ofthe available food or due to the enrichment in the food basis itself
by the addition of migrant species.
In the case of the immigrant shrimp and portunid swimming crabs immigration has resulted in a better exploitation of apreexistent food basis. There are six
species of commercial shrimp in the Levant basin; four of them are Lessepsian
migrants: Penaeus japonicus, P. semisulcatus, Metapenaeus monoceros and M.
stebbingi; two ofthem Penaeus kerathurus and Parapenaeus longirostris are Atlantic species. According to Tendler (personal communication) the migrant shrimp
make up 80% of the Israel shrimp-catches. Along the Anatolian coast another
Lessepsian migrant shrimp becomes commercially important: Trachypenaeus curvirostris (Geldiay and Kocatas, 1972). According to' these authors Penaeus japonicus is usually more abundant at Iskenderun than P. kerathurus.
If one analyzes the tables of the bathymetric distribution of benthic invertebrates as given by Gilat (1964, 1969) for four profiles along the coast of Israel and
143
compete with the local Atlantic lizard fish Synodus saurus which is rare and
noncommercial, but with the hake M erluccius. The two fishes share the same food
and frequently the same bottoms. The above-mentioned authors reach the conclusion that Saurida takes advantage of dry warm winters and M erluccius of the
rainy cold winters. Ben-Yami and Glaser (1974) also reach the conclusion that the
two species have divided the shelfbetween them, in such a way that in the summer
the lizard fish predominates shallow bottoms and is barely overlapping with the
hake, while in the winter, the hake advances into the shallow areas. Saurida is
generally caught down to maximum 80 m. M erluccius appears in the summer
chiefly below tbis depth. It seems therefore that Saurida might have occupied the
shallower parts of a depth range previously occupied only by the hake. The food
of the two species is rather similar, composed mainly of anchovy, and lately of two
Lessepsian migrant fish: Leiognathus klunzingeri and U peneus asymmetricus. BenYami and Glaser (1974) reach the conclusion that the sudden appearance of
Saurida did not increase the trawl catches but merely displaced M erluccius to
deeper bottoms. According to Gorgy (1966), the hake is found along the Egyptian
shores only deeper than 100 m. Since the 1954-56 invasion, Saurida has maintained its numbers and has not descended below 13% of the total trawl catches
(Fig.41).
Ben-Tuvia (1973) mentions that before the appearance of Saurida in commercial amounts in 1955, the catches of the immigrant food fish Leiognathus klunzingeri were bigger. This conclusion would in a way contradict the previous conclusion about the penetration of Saurida into the same food niche. An additional
prey such as Leiognathus may have reasonably increased the available food basis
for the two competing species Saurida and M erluccius.
Speaking of the near-shore fishes, Ben-Tuvia (1973) mentions that Siganus
rivulatus may make up as much as 50% of the fishes caught in fish poisonings.
Popper (personal communication) considers that S. rivulatus thrives at the expense of the local fish Sargus. Among the barracudas the immigrant Sphyraena
chrysotaenia makes up presently one half of the catches, while the two local
species S. sphyraena and S. viridensis constitute the other half (Ben-Tuvia, 1973).
Since here too the local species have not disappeared, the logical explanation is
that the migrants fitted themselves into the food niche of the natives, by better
exploitation ofthe available food or due to the enrichment in the food basis itself
by the addition of migrant species.
In the case of the immigrant shrimp and portunid swimming crabs immigration has resulted in a better exploitation of apreexistent food basis. There are six
species of commercial shrimp in the Levant basin; four of them are Lessepsian
migrants: Penaeus japonicus, P. semisulcatus, Metapenaeus monoceros and M.
stebbingi; two ofthem Penaeus kerathurus and Parapenaeus longirostris are Atlantic species. According to Tendler (personal communication) the migrant shrimp
make up 80% of the Israel shrimp-catches. Along the Anatolian coast another
Lessepsian migrant shrimp becomes commercially important: Trachypenaeus curvirostris (Geldiay and Kocatas, 1972). According to' these authors Penaeus japonicus is usually more abundant at Iskenderun than P. kerathurus.
If one analyzes the tables of the bathymetric distribution of benthic invertebrates as given by Gilat (1964, 1969) for four profiles along the coast of Israel and