INNSENDTE ARTIKLER The status of Danube beluga sturgeon (Huso huso): Past, present and future Av Carolyn M. Rosten, Dalia Onara, Kate Hawley and Radu Suciu Carolyn M. Rosten1 is a researcher with the Norwegian Institute for Water Research (NIVA), Pirsenteret, Havnegate 9, 7462 Trondheim, Norway. Dalia Onara is a scientific researcher with the Danube Delta National Institute (DDNI), Sturgeon Research Group, 165 Babadag Street, RO-8800, Tulcea, Romania. Kate L. Hawley is a research assistant with NIVA. Radu Suciu is leader of the Sturgeon Research group at the DDNI and CITES Scientific Authority for Acipenseriformes of Romania. Status for Donau beluga drett og utsettelse av stør er også trådt i stør (Huso huso): kraft for å bedre fiskebestanden i områ­ Fortid, nåtid og fremtid det. En av de største utfordringene ligger Støren i Donau er i stadig tilbakegang, og i forebyggingen av illegalt fiske, gitt den langsiktige forandringer i populasjons­ gode markedsverdien på stør, og forval­ størrelse og struktur av størarter er blitt tingsprogrammet utarbeider stadige nye observert. I dette manuskriptet er beluga strategier for å håndtere utfordringene. stør (Huso huso) brukt som en flaggskips­ Som et ledd av dette ble Danube Sturgeon art for en casestudie av stør i Donau. Den Task Force (DSTF) opprettet i 2012 for å rumenske regjeringen brukte i 2006 doku­ ta denne utfordringen i årene som mentasjonen fra disse kritiske forandrin­ kommer. gene til å tvinge igjennom midlertidige fiskestanse på størarter, samt imple­ Summary mentere regionale overvåkingsstrategier. Sturgeons of the Danube River are in Overvåkingsprogrammet for juvenil stør decline. Long term changes in both som ble implementer på grunnlag av population size and structure of sturgeon dette har samlet ny og vital data på antall species have been observed. Beluga stur­ fisk samt nedstrøms migrasjonsmønster geon (Huso huso) as the flagship species for juvenil stør i Donau. Suksessfull opp­ of the Danube are used in this manuscript as a case study species. In 2006 the Roma­ 1 Author to whom correspondence should be addressed. nian government used documentation of Tel: +47 22 18 51 00; Fax: +47 22 18 52 00; these critical changes to enforce a fishing E-mail: [email protected]. moratorium on sturgeon species and VANN I 04 2012 523 INNSENDTE ARTIKLER implement a regional monitoring stra­ powerdams Iron Gate I & II at river tegy. The juvenile sturgeon monitoring kilometres 942 and 863 in 1970 and 1984 programme implemented as part of these respectively (Hensel & Holcik 1997). changes has collected vital new data on These barriers divide the lower and mid the numbers and downstream migration Danube halving the historic spawning of Danube sturgeon. Juvenile sturgeon migrations of sturgeons which were have also been successfully produced and documented extending as far upstream released as part of the supportive stock­ as Vienna (Bacalbasa­ Dobrovici 1997). ing programme. The greatest challenge The lower Danube extends downstream lies in the prevention of illegal fishing, from the Cerna River at river kilometre given the extreme value of sturgeon. The (rkm) 955 (Hensel and Holcik, 1997), with management programme is constantly the Romanian stretch reaching from the evolving to deal with the challenges of Iron Gates II dam at rkm 859 to the Danube conserving Danube sturgeon and in 2012 delta when the river meets the Black Sea. the Danube Sturgeon Task Force (DSTF) Many neighbouring countries border was created to take this challenge forwards. along the banks of the Danube (Ukraine, Moldova, Bulgaria and Serbia in the Lower Introduction Danube), figure 1. All countries borde­ Six species of sturgeon once migrated ring the river downstream of Iron Gate along the Danube for spawning: The ana­ II participate in the sturgeon fishery. The dromous species beluga; Huso huso, Rus­ river is, at its widest point, 1 km wide sian sturgeon; Acipenser gueldenstaedtii, and reaches maximum depths of up to stellate sturgeon; A. stellatus, and the 60 m. At the entrance to the Danube delta European Atlantic sturgeon; A sturio and the river splits into three main branches the river resident ship sturgeon; A nudi- forming the delta, figure 1. It also splits ventris (Bacalbasa­ Dobrovici 1997). and re­joins at several places along its Only the beluga, Russian, stellate and length. sterlet; A. ruthenus remain and as with During the 20th Century, world demand sturgeon populations throughout the for sturgeon meat and caviar has inflated world, all species are in sharp decline. the economic value of sturgeon fishing, The Danube river system has long with the value of beluga caviar estimated been subjected to anthropogenic influ­ at $1000 per 100 grams (Suciu, 2005). ence from a number of sources altering This, when coupled with the develop­ the entire ecosystem. The fish commu­ ment of intense fishing pressure follo­ nity, in particular sturgeon species, has wing a lack of fishing controls after the been greatly impacted by these changes. Romanian revolution in 1989 (Kynard et Loss of habitat has occurred throughout al 2002), has caused the sharp decline in the system and in particular, historical recent documented catches of sturgeon. spawning grounds are no longer acces­ In 2006 all sturgeon fishing was sible due to the construction of the hydro­ banned for ten years by the Romanian 524 VANN I 04 2012 INNSENDTE ARTIKLER Figure 1. Map of the Danube course through Romania giving the position of the two Iron Gate dams. government, with the exception of a few ery renowned throughout the world. His­ individuals to be used for a supportive torical catches of sturgeon are closely stocking programme and afterward related to the development of human returned live to the Danube. These settlements and fishing techniques on the strong measures were made possible Danube. Sturgeon have been harvested after documentation of changes in both on a commercial scale since the 4th and 5th the size and structure of the sturgeon Centuries and from the Middle Ages populations in recent years. This sophi sticated gear was constructed taking manuscript takes beluga sturgeon, the advantage of the anadromous movements flagship species of the Danube Commis­ of these fish. One such method was the sion in Vienna, as a case study and dis­ construction of fishing weirs; fence traps cusses the changes in the population and made of wooden branches, spanning the the management approaches which were river and intersected with small gates for developed to aid the recovery of the species. river traffic to pass through, figure 2. These would be operated by a team of Past – Historical beluga 100­200 people, catching 1000­2000 stur­ population geons daily (Bacalbasa­Dobrovici 1997). The sturgeon stocks associated with the Such fishing methods resulted in a docu­ Danube have, over the centuries, formed mented decline of beluga as early as the the basis of a significant commercial fish­ 16th century and initiated international VANN I 04 2012 525 INNSENDTE ARTIKLER Figure 2. Historical method of sturgeon capture on the Danube consisting of fence traps spanning the entire river. These were very efficient capture methods and caught 1000-2000 sturgeon daily at times. Picture taken from Kunike (1979). disputes between upstream and down­ period (1920­2006) that records from the stream nations, culminating in the col­ Danube have been available, figure 3. A lapse of migratory sturgeon fishing in large crash occurred in the early 1940s, Austria during the 18th Century (Hensel coinciding with the Second World War & Holcik, 1997). and a reduction in fishing and therefore Limited sources of historical data fisheries records at that time. Stocks have exist for Danube sturgeon populations. also been in slow decline since the build­ However Antipa (1909) made meticulous ing of Iron Gate dams I and II. records of mean weight and sex ratio In addition to population size, popu­ data. These were compared to data lation structuring of beluga in the Danube record ed as part of new, more detailed has altered during recent history. In the Romanian fishery catch statistics collec­ early 20th century (1903­1904) the sex ratio ted since 2003. Only catch statistics from of beluga was strongly skewed towards 2003 to 2005 are available because the males during summer and autumn sturgeon fishing ban was implemented months, gradually increasing towards a by the Romanian government in 2006. 50:50 balance during winter and spring, The beluga sturgeon stock has been suggesting earlier arrival of males prior relatively variable during the whole to spawning, figure 4. Fishery statistic 526 VANN I 04 2012 INNSENDTE ARTIKLER Figure 3. Annual commercial catch of beluga sturgeon (Huso huso) in the lower Danube river / Romania. data from 2003 to 2005 suggest the same T = 3.18, p < 0.01). Interrogation of pattern of a bias towards males, evening length frequency of returning adult out as the spawning period approached. beluga and comparison with length at However, males were apparently 10 – 20 age taken from Ambroz (1960) demon­ % more abundant throughout the year strates an apparent lack of first time than 100 years previously, despite greater spawners in the population (first­time variation in the data due to lower sample spawning traditionally occurred at age size. These statistics were used to bring 13­15 years in females and younger in about the 10 year sturgeon moratorium, males (Otel 2007), particularly affecting though later communications with fis­ females (Figure 6). Lengths of returning hermen suggested that these records beluga during 2003­2005 suggested few might be biased, since it was still possible first returns of females below age 13, and to sell caviar on the internal black males below 12 or that the length at age market which indicates that the females of returning adults had increased. (particularly large specimens) were under reported in the fishery statistics.