The Georgian Coast Guard seized the Russian Grot fishing boat along with the Ukrainian SUAR-2 boat January 10. Both vessels, with crews of eight and 10 respectively, were towed to the Georgian port of Poti.
"We suggested paying 10,000 lari ($5,800) in bail, but our request was declined," said Nugzar Tkebuchava acting for Captain Sergei Rybkin. "The court upheld the prosecution's demand and ordered a two-month custody pending the trial."
The Russian crew members have been released on bail, $1,100 each, the lawyer said.
Sergei Mestnikov, the captain of the Ukrainian boat, was also left in custody for two months under the Poti court ruling Friday. His crewmen were freed after paying $1,100 in bail each.
Authorities said earlier the sailors could be charged with illegally crossing the maritime border, illegally fishing in Georgian territorial waters and violating international maritime regulations. They could face up to five years in prison.
The Georgian border police earlier claimed to have discovered six metric tons of illegal catch on board the Grot, which is registered at Russia's southern port of Novorossiisk.
Both vessels were fishing off the coast of Abkhazia, which has proclaimed independence from Tbilisi but has not been recognized as a state by the world. Georgian law says Abkhazian ports and coastal waters are closed for international navigation, except for vessels with humanitarian cargoes.
Russia's Foreign Ministry said ahead of the court session earlier Saturday that it hoped Georgian authorities would show "understanding" and restraint in handling the case.
"We expect the Georgian side to treat the incident with understanding, to show restraint in its statements and action and to free the crew and the captain of the fishing boat," said official Foreign Ministry spokesman Mikhail Kamynin.
The incident could mark a further escalation in an ongoing political and economic standoff between the two ex-Soviet neighbors.