As outlined above, it is believed that the Turkish sturgeon fishery was based on two types of fish stock: a native population spawning in Turkish rivers (primarily A. sturio), and migratory fish spawning in other parts of the Black Sea basin. The decline of catches, reduction in available spawning areas, and very low numbers of fish now swimming into Turkish rivers suggest that the native stocks may be near extinction. If they disappear, any future commercial exploitation of sturgeon in Turkey will be entirely dependent on stocking from hatcheries in other countries, and a valuable national resource will be lost forever. To avoid this, it is recommended that a sturgeon rehabilitation programme should be initiated as soon as possible.
The rehabilitation programme should include three major components:
Hatchery construction and releases of fish to restore spawning populations of native species.
Enforcement of an effective ban on the sturgeon fishery to prevent the capture of immature, hatchery-produced fish.
Improvement of environmental conditions in the lower reaches of the major “sturgeon” rivers to enhance spawning runs.
(a) Hatchery construction and fish releases
Taking into consideration the very small numbers of broodfish remaining, and the very long period required to reach first sexual maturation in sturgeons (8–14 years for Atlantic sturgeon females), the main initial goal of the rehabilitation programme should be to increase the population to a level at which it can become self-sustaining. Experience elsewhere indicates that this requires a population of mature adults sufficient to ensure at least 10 000–20 000 fish entering the rivers for spawning each year. This level is a realistic target for Turkey if hatchery releases are maintained for at least 5 years in the absence of commercial exploitation. It must be clearly understood, however, that such a rehabilitated population will be sufficient to save the stock from extinction, but will not be large enough to permit the commercial fishery to be re-opened. It will therefore produce no financial return in the immediate future.
However, it is becoming clear from overseas experience that a commercial return from sturgeon culture can be obtained by growing-on fish to market size in captivity. By this method sturgeons of several kilogrammes can be produced in two years, and their meat commands a high price on world markets. Due to the long time required to reach sexual maturation, though production of caviar is not yet economically possible through sturgeon farming.
Objectives of the hatchery. It is recommended that a prototype hatchery be built on the chosen site below the Suat Ugurlu dam on the Yesilirmak River. The hatchery will have an annual production of 200 000 × 50 g fingerlings of A. sturio, and 50 000 × 50 g fingerlings of other species (preferably Huso huso if broodstock are available). The intensively-reared fingerlings will be marked with wire micro-tags inserted under the first dorsal scute, and released in the lower reaches of the Kizilirmak and Yesilirmak Rivers, and into lagoons in the region of Bafra (these lagoons are thought to be natural nursing areas for local sturgeons). It is estimated that a maximum of 10–12 gravid females will be required for this scale of production.
The success of the stock rehabilitation programme will be evaluated by annual surveys of survival, abundance and distribution in coastal areas. These surveys can be carried out by experimental trawling. Based on Soviet experience in the neighbouring Caspian and Azov Seas, and approximate survival rate of about 5% from 50 g to adult size is anticipated. This would provide an annual recruitment of 12 500 adults, and a total recruitement over 5 years of 62 500 fish. Such a population can be considered viable, and typically supports an annual spawning run of 10 000–15 000 fish (in sturgeons, not every fish matures at the same age, and females do not spawn every year). Once established, a spawning run of this size would provide broodstock for further enhancement of stocks and construction of additional hatcheries opening up the possibility for a regulated commercial fishery in the future.
The second objective of the sturgeon hatchery will be to evaluate the potential of the various sturgeon species for commercial grow-on to market size, to demonstrate sturgeon rearing technology to the private sector, and to initiate a domestication programme by raising fish in captivity to maturity.
Hatchery operations. Since intensive sturgeon-rearing technology is relatively new and not well known, a brief description is given below. The technology, developed in the USA, differs from conventional Soviet practice in that fingerlings are reared only on artificial diets. Their growth is therefore not limited by natural productivity in ponds, and they can be produced at any size required. It is proposed that the intensive US technology be applied in Turkey as follows:
Broodstock (in this case A. sturio) are captured in the mouths of rivers (Kizilirmak and Yesilirmak), and transported in aerated tanks to the hatchery. There, ovulation and spermiation are induced by injection of carp hypophysis or synthetic LHRH analog. Following extraction of eggs by caesarian incision, females are sutured and released. Fertilized eggs are incubated first in trout funnels to neurulation, and thereafter in MacDonald jars until they hatch. Fry are reared to about 5 g in 1.5 m diameter tanks. For the first two weeks they receive a semi-moist salmonid diet, and thereafter dry trout feed. The 5 g juveniles are graded into 4 m diameter tanks for grow-out to 50 g body weight, when they are marked and released. Spawning is expected in April-May, and fingerling release in July-August of the same year.
Optimal temperature of water for spawning and egg incubation is 10°–16°C, and for fingerling rearing 15°–22°C. Ambient temperatures within these ranges are expected at the chosen site on the Yesilirmak River.
The following assumptions and calculations were made to determine the size and design of hatchery facility required:
Broodstock. Projections for broodstock requirement were based on an ovulation success rate of 50%, average individual fecundity for Atlantic sturgeon of 400 000 eggs, egg hatchability 50%, and survival to 50 g of 40%.
Domestic stock for commercial culture will be kept in 7 m diameter, circular fibreglass tanks. Stocking density will be 70–100 fish per tank at 5 years of age. Sexual maturation of domestic males can be anticipated at 3–5 years old, and females at 5–10 years.
Fish retained for experimental production of market-sized sturgeon (6–7 kg) must be kept at the hatchery for 2–4 years. They are also held in 7 m diameter tanks.
Total requirement of 7 m diameter tanks was estimated at 6 tanks. (Imported equipment required is listed in Appendix 2).
Egg incubation. Egg incubation must be done indoors. Together with an office, laboratory, and facilities for broodstock holding during inducement of ovulation, a hatchery building of about 350 m2 will be needed. The building should be equipped with concrete floors and drains, good artificial lighting, and a potential maximum water supply of 1 000 l/min. Eggs require 10 incubation barrels (funnels) and 30 MacDonald jars.
Fry rearing. The fry rearing facility does not require a building, but should be covered by a roof. To accommodate 50 × 1.5 m diameter circular plastic or fibreglass tanks an area of approximately 500 m2 is needed. Tanks are supported on concrete blocks over a gravel bed, and supplied with 1 000 l/min of water, artificial illumination and electrical supply for automatic feeders.
Fingerling and commercial-sized fish. An outdoors area of approximately 1 500–2 000 m2 is required. This will accommodate 20 × 4 m diameter fingerling tanks, plus the 6 × 7 m commercial and broodfish tanks, on a gravel bed. A water supply of 3 500 l/min is needed.
Hatchery water supply. The total estimated maximum water requirement is 5 500 l/min. Spawning and fry rearing facilities are expected to operate from March to July, and fingerling rearing facilities from June through August. Commercial grow-out will be continuous.
The hatchery water supply line should include a water intake structure (protected by a screen), two pumps, and two plastic reservoir tanks to provide gravity flow for the entire facility. If inflow water is found to be supersaturated with nitrogen, additional small cylindrical containers filled with plastic rings will be needed for degassing. All parts of the water supply system, including pumps, must be plastic-coated (galvanized materials are not acceptable). The main drainage pipe carrying water away from the unit should be at least twice the diameter of the main supply pipe.
Ancillary equipment includes a truck with fibreglass tank(s) for fish transportation, an emergency generator, laboratory equipment (balances, oxygen meter, dissecting microscopes, water still, oven, and microcomputer with printer).
Costs. Estimates of the costs of imported equipment and materials are given in Appendix 2. Local construction costs will be site-dependent, and can be kept to a minimum if the location recommended above is chosen for development.
(a) Enforcement of the ban on the sturgeon fishery
As with seatrout, the success of a restocking programme for sturgeons depends on the enforcement of the existing laws protecting these fishes from exploitation until they become sexually mature and have the opportunity to reproduce. Sturgeon stocks are particularly vulnerable to depletion by overfishing, because of the long period required to reach maturity.
Since the largest catches of these species are taken by trawlers, which land their fish at the markets in the normal way, a sensible first step in law enforcement would be for Government fisheries inspectors to meet boats at the quay and examine the species composition of the catch. (Incidentally, the mission also noted other species of fish, e.g., turbot, being sold in the markets during the closed season.) The staff necessary for this work are already employed, and no equipment is needed. Similarly, inspectors could visit the fish markets in the major centres. Prosecution of offenders should follow initial warnings. Since the value of sturgeons (and seatrout) is so high (e.g., Beluga fetches about LT 15 000/kg for the meat alone, making a single 250 kg fish worth LT 3.75 million, or about $US 1 800) penalties will need to be correspondingly severe. It may regrettably be necessary to go so far as to confiscate one or two boats and gear before the message that Government is serious will be believed.
Enforcement measures should be preceded and accompanied by educational measures: lectures, press and TV releases, explaining to the fishermen and public why fishery protection for these species is necessary.
A successful campaign should result in sturgeons taken accidentally by trawl being returned to the water, dead or alive. Fortunately, haul time in the area is usually short (1–2 hours), and it is understood that the majority of sturgeons are alive and apparently well when brought on board the vessel. A worthwhile percentage of them may therefore be expected to survive if promptly returned to the sea.
It should be stressed that the staff responsible for fishery inspection work is already employed at each coastal regional centre, including Samsun and Rize. Government should encourage the officers to perform their duties more enthusiastically, beginning immediately, rather than waiting for a new seatrout and sturgeon enhancement programme to begin.
(c) Environmental improvement
If sturgeon spawning runs are to be re-established in the major rivers, it is necessary to ensure that environmental conditions are suitable for the fish during their spawning migration and juvenile period of life. In particular, the DSI must be careful that water discharge from the downstream dams on the Yesikirmak and Kizitirmak Rivers are not stopped or allowed to fall too low to attract mature sturgeon spawners up the rivers during the spring reproductive season, and to maintain eggs and fry during the summer. Similarly, when water is diverted to supply irrigation canals near the river mouth, sufficient water must always be allowed to remain in the main channel for the use of fish. Monitoring and control of sources of pollution in the lower reaches of the rivers is also necessary.
