ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on May 17, 2007
ICES Journal of Marine Science: Journal du Conseil 2007 64(5):973-980; doi:10.1093/icesjms/fsm062
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The effects of stock enhancement of pikeperch (Sander lucioperca) in Iranian coastal waters of the Caspian Sea
1 Caspian Sea Bony Fish Research Centre, PO Box 66, Bandar Anzali, Iran
2 Sea Fisheries Institute, Ko
taja 1, 81-332 Gdynia, Poland
Correspondence to S. Abdolmalaki: tel: +98-181-3224055; fax: +98-181-3223070; e-mail: abdolmalaki2001{at}yahoo.com
Abdolmalaki, S., and Psuty, I. 2007. The effects of stock enhancement of pikeperch (Sander lucioperca) in Iranian coastal waters of the Caspian Sea. – ICES Journal of Marine Science, 64: 973–980.Annual landings of pikeperch (Sander lucioperca) in Iranian coastal waters of the Caspian Sea in the early years of its exploitation, the late 1920s and early 1930s, reached some 3000 t. However, after 1935, catches declined drastically through overfishing, declining sea level, and the destruction of spawning grounds in the Anzali Lagoon. In 1990, Iran initiated a programme of artificial culture to enhance the local stock. The aim of the programme was and still is to restore the formerly abundant population of this predatory fish and to increase the profitability of the beach-seine fisheries of fishers who had stopped deploying gillnets, which pose a threat to the valuable species of sturgeon in the Caspian. Analysis of the age composition of pikeperch catches indicates that the use of beach-seines does not prevent overfishing of young pikeperch released as fingerlings in the same calendar year in which the fishing season started. No undersized fish are discarded back into the sea, because there is market demand for even the smallest fish, and a lack of communication exists between the programme beneficiaries and the management and research units. Some 15 years after it was initiated, the effectiveness of stock enhancement at a level of 4–6million fry per year remains uncertain.
Keywords: Caspian Sea, multispecies fishery, pikeperch, Sander lucioperca, stock enhancement
Received 28 April 2006; accepted 21 March 2007; advance access publication 17 May 2007.
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Introduction |
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 Top Introduction Material and methodsResultsDiscussionReferences |
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The pikeperch (Sander lucioperca) is found in freshwater and brackish water, and is a semi-anadromous, cool-water species found in the Caspian watershed (Ural, Volga, Kura, and Sefid Roud rivers) and in the basins of the Black, Azov, Aral, and Baltic Seas (Craig, 2000). It seems to prefer salinities <12. Pikeperch occurrence in the Caspian Sea is restricted to estuaries and coastal zones (Kazancheyev, 1981). As a predator and commercially valuable species, pikeperch constitute an important component of the Caspian ichthyofauna, both ecologically and commercially.
Catches of pikeperch first recorded in the Caspian in the late 1920s indicated that it constituted about one-third of the total taken from the coastal zone of the southern Caspian Sea, some 3000–4000t annually (Razavi, 1999). Shortly thereafter, catches decreased suddenly to some 30 t annually, and they have never again reached the initial level. The cause of the sudden disappearance of the pikeperch stock from the southern Caspian Sea has not been determined conclusively. Ivanov (2000) maintained that the stock of Caspian Sea pikeperch was depleted by excessive catching that led to overfishing. Another cause for the decline and inability to recover is assumed to be the degradation of spawning grounds and habitats, a progressive occurrence from the 1930s. The Caspian Sea is a unique saltwater basin not connected to the open ocean (at least not until recently, when the Volga–Don canal system was opened); therefore, factors that limit areas accessible to pikeperch include fluctuating water levels and salinity variation in coastal estuaries. Among other factors that limit the size of the pikeperch stock, Kushnarenko (2001) also noted the volume of freshwater input, oxygen concentration, the input into the estuaries and sea of organic material, and illegal catches or poaching.
The Caspian Sea is about 422000 km2 in area, with 6397 km of coastline; of the latter, more than 900 km is in Iran. The level of the Caspian Sea, which is below sea level, fluctuates considerably as a consequence of climate change in the drainage basins and, to a large extent, variation in the inflow of freshwater from the Volga river in particular. During the first three decades of the 20th century, the level of the Caspian Sea remained about 26 m below that of the Baltic Sea. This was followed by a period of fluctuation during which a minimum of –28.4 m below the Baltic Sea level was recorded. The most recent rise in level began in 1978 and reached –26.9 m by 1994. The level continues to rise and some low coastal areas have been inundated (Golubtsov and Lee, 2000).
Historically, the most important area for pikeperch spawning in Iran has been the Anzali Lagoon (Region Anzali; Figure 1). The lagoon used to be a freshwater ecosystem created by significant decreases in the level of the Caspian Sea combined with considerable river discharge from the inland watershed. However, for a variety of reasons, the open water area of the Anzali Lagoon decreased substantially during the 20th century, and by 1989 it was only about 22.5% of its estimated size in the late 1930s (Hol
ik and Oláh, 1992).
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Although the precise cause is not known conclusively, natural pikeperch spawning in the Anzali Lagoon stopped completely, and it has not been observed there for several decades. Bearing in mind the size of historical catches of the species, and assuming that the carrying capacity had not changed, the Iranian fisheries administration in 1990 initiated a pikeperch stock-enhancement programme. Since then, the Anzali Lagoon has been stocked systematically with fingerlings brought from spawners held at Aras, a border reservoir that lies between Iran and Azerbaijan (Abdolmalaki and Ghaninezhad, 1999). The aim of this work is to assess the effects of that restoration programme in Iran's Caspian Sea coastal zone 15 years after it was initiated.
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Material and methods |
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TopIntroductionMaterial and methodsResultsDiscussionReferences |
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Sampling
Catches made in each beach-seine haul are recorded by fisheries officers and archived at the General Fishery Offices of the coastal states of Iran before being forwarded to the Caspian Sea Bony Fish Research Centre in Guilan, Bandar Anzali. Based on unpublished statistics from fishing harbours and the Iranian Fisheries Company, catches by poachers are added to the final catch statistics.
To gather biometric data and catch statistics from beach-seine cooperatives, groups of officers were mobilized in the five fishing regions throughout the fishing season. Sampling was conducted randomly once or twice a week. Biometric data included date and place of capture, fish fork length (FL, to the nearest 0.5 mm), and total fish weight (to the nearest 50 g). Scales for later age determination were collected from all fish sampled, and for age determination, it was assumed that all fish had been born on 1 June. As the fishing season in the study region (23 September to 9 April) begins and ends in different years, the catch year noted in the tables and used in the calculations is that in which the season began.
Statistical analysis
FAST software (Slipke and Maceina, 2001) was used to analyse length- and weight-at-age data and to determine the parameters for the von Bertalanffy growth function (von Bertalanffy, 1938). Instantaneous natural mortality (M) was estimated using Pauly's (1980) empirical formula, for which the mean annual surface water temperature (T) was taken to be 14.5°C.
Separable virtual population analysis (SVPA) techniques were applied to calculate the coefficients of pikeperch fishing mortality, stock abundance, stock biomass, and spawning-stock biomass (SSB) in the period 1990–2004. For this purpose, the average weights-at-age in the stock and in the catch were assumed to be identical. M was estimated to be 0.31 for all age groups, and it was assumed that selectivity was 1 for fish aged 2 years and older. Recruitment age was assumed to be the second year of life. The value of fishing mortality F for the last age group and in the last year of the study were synchronized to the mean annual catch per unit effort from gillnet catches and selectivity for fish in the first year of life, using the Solver function in Excel.
In order to estimate SSB, the maturity coefficients applied to fish in subsequent years of life were 0.3, 0.7, and 0.9 for fish aged 2, 3, and 4 years, respectively. It was also assumed that neither gear selectivity nor fishing strategy varied throughout the study period.
The effects of minimum landing length on yield-per-recruit (N0 = 100) of the pikeperch being exploited were simulated with FAST software, which computes yield (in weight) with the Jones modification of the Beverton–Holt equilibrium yield equation found in Ricker (1975). For detail, the reader is referred to Slipke and Maceina (2001).
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Results |
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TopIntroductionMaterial and methodsResultsDiscussionReferences |
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The fishery
Iranian fisheries are a mixture of large-scale industrial and artisanal fisheries. Three types of fishing gear are used in the Caspian Sea: beach-seines (local name, pareh) for bony fish close inshore, lift nets (a cone net with a bright light to attract the fish) for kilka (Clupeonella spp.), and gillnets for sturgeon (Acipenser spp. and beluga, Huso huso). For reasons of conservation, fishing for sturgeon is now restricted to a state-owned, carefully monitored, company. Iran's fishing fleet in the southern Caspian has shrunk significantly in recent years by way of a government buy-back scheme aimed at eliminating the use of gillnets by privately owned and operated fisheries. The State's fisheries organization revokes gillnet licences and issues permits for beach-seine cooperatives. Some representatives of the inhabitants of coastal cities have requested more beach-seine cooperatives in their regions of authority, and the number of cooperatives increased from 68 in 1989 to 151 in 2004 (Table 1), while the number of fishers increased from 6000 to about 12 000, respectively. About 85–100 people are involved in fishing in each beach-seine cooperative. Each beach-seine is about 1000 m long, and is hauled by tractors. Codend width and length are 10–15 and 100 m, respectively, and the minimum legal mesh size in the codend is 30 mm, although fishers also use smaller mesh.
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Licences are free, and fishers are not required to declare their catch. Although there is a minimum landing length (34 cm FL for pikeperch), there is no custom of sorting and discarding undersized fish back into the sea, and fish of all sizes are either consumed by the families of fishers or sold at market.
In addition to licensed fishers, there is an unknown number of poachers. There are no permanent fish landing sites and no control at all over the fish catch. Although gillnets are officially prohibited, some 6000 persons are currently involved in this means of illegal fishing. The Iranian fishing company has established an enforcement office responsible for confiscating illegal gillnets (Table 1 lists the number of nets confiscated annually), and management measures are enforced by the Iranian coastguard.
Catches
The species distribution of the catches from the southern Caspian Sea has been recorded since 1927 (Table 2). Initially, local fisheries were supported by pikeperch and Caspian kutum (Caspian roach; Rutilus frisii kutum) stocks. Then pikeperch catches virtually collapsed overnight, from some 3000 t annually in 1935 (Figure 2), and decades of stability at low levels marked the catches of all fish species. The worst period for the fisheries of the southern Caspian were the 1960s; in 1961 just 2100 t of fish were caught. The species structure of the catches also changed, and the biggest landings in Iran were those of sturgeon—the most valuable species. In the decades following, landings of mullet (Liza auratus and L. saliens) and Caspian kutum increased successively, reaching 8000 t per year recently. Changes in gear types have had a fundamental impact on the changes in species structure of the catches; the main species caught by today's beach-seine fishery are kutum and mullet (generally about 75% of the total catch by weight). Although gillnets are used to target sturgeon, that catch too is dominated by kutum.
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Most pikeperch are caught in beach-seines (Table 1). Although the pikeperch bycatch in gillnet catches (both legal and poached) is generally not large, the situation is not uniform from year to year (D. Ghaninezhad, pers. comm.). Historically and recently, the main pikeperch fishing ground in Iranian coastal waters has been the Anzali Region.
Pikeperch landings recorded between 1965 and 1970 seemed to indicate some recovery of the stock, but this trend was short-lived, and pikeperch catches in the 1980s once again became incidental and oscillated around several tonnes annually.
After 1989, when 16 000 fingerlings were released, pikeperch landings started to grow slowly, and 1994 and 1998 stand out as years in which relatively good catches were recorded (Figure 2). Information on the local pikeperch stock available to the authors failed to explain these peaks, so we assume that the inflated landings of those 2 years resulted from errors in the recording of catches. Consequently, further calculations covering those years were smoothed by using the mean catches of the years before and after those 2 years in the analytical series.
Population characteristics and evaluating resources
The length–weight relationship was W = –0.020606L2.85. The estimated parameters of the von Bertalanffy equation were L
= 55.05 cm, K = 0.15, and t0 = –2.59, and M was 0.31.
More than 90% of the pikeperch caught with beach-seines were smaller than the minimum legal length (Figure 3). Mean fish weight was generally greater at the beginning of the study period. The mean age of pikeperch in the catches changed little between 1990 and 2004, apart perhaps from a slightly rising trend over the whole period (Table 3).
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The age distribution of pikeperch caught with beach-seines varied from year to year (Table 4). At the beginning of the study period and in 2003, the catch was dominated by fish of age group 1. Between 1997 and 2002 and again in 2004, the catch was dominated by fish of age groups 2–4, but we could find no evidence of a change in fishing strategy during those years.
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Two periods can be distinguished based on SSB (Figure 4) and catches: up to 1997, apart from the outlier in the catches in 1994 (Figure 2; Table 2), both values remained stable at
10 t, subsequently tending to increase. Similarly, recruitment (of second year pikeperch) did not begin to increase until six years after stocking started. Recruitment was particularly good during 1999. During that season, the fish recruited to the exploitable stock had been released in Anzali Lagoon in 1998 with a weight greater than that of fingerlings released in other years (Table 5). Recruitment has fluctuated subsequently, but it was very low in the last year of this study (2004). Analysis of the age distribution of the exploited population (Table 4) indicates that the generation born in 2003 was caught intensively in its first fishing season.
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Despite varying recruitment, SSB and catches remained stable until 2004. With the exception of one outlier, fishing mortality Fbar(2–5) remained uniform despite increased fishing effort until 2003 (Figure 5). The high fishing mortality in 1991 and 2004 was linked to the significant catch share of very young fish in those years.
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The relation between the abundance of fish of age group 1 in the catches and the quantity of fingerlings released into the sea in the same calendar year at the beginning of the fishing season (Figure 6) confirms that the greater individual body weight of the fingerlings released into the sea in 1998 gave them a significant advantage in terms of survival possibility. Increasing the quantity of fingerlings released with a lower individual weight in subsequent years did not achieve the same results.
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The yield-per-recruit plot by level of exploitation (u) allows us to determine the optimal length of recruits to the fishable population (Figure 7). However, we stress that the smallest fish recorded during the study period was just 12 cm FL, and that the mean length of fish exploited in the first year of life was 23.1 cm, in the second year, 27.5 cm, and in the third year, 31.3 cm FL. In terms of optimum levels of stock production, recruitment of the youngest fish, which happened in 10 of the 15 catch seasons analysed, is not advantageous and leads to growth-overfishing.
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Discussion |
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TopIntroductionMaterial and methodsResultsDiscussionReferences |
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The Iranian waters of the Caspian Sea are under the constant influence of changes stemming from both cyclic fluctuations in sea level and anthropogenic pressure (Salmanov, 1999; Ivanov, 2000). Sadlayev et al. (1965) first alerted the Iranian Fisheries Company to the destruction of pikeperch stocks in Iranian waters and suggested that improving the water quality in Anzali Lagoon might help. However, pikeperch stocks then were not considered as valuable (relatively) as they are now. Notwithstanding, those comments in the 1960s were pertinent, because they drew the attention of the authorities to the need for better water quality management and at the same time highlighted the fact that excessive catches were destroying the reproductive capacity of stocks and leading to overfishing (Roux, 1961; Vladykov, 1964).
Pikeperch stocks have decreased not only in Iranian waters, but also in those of other coastal states of the Caspian Sea. Similar to the situation with Iranian catches, the largest catches on the Russian coast were registered in the 1930s (Ivanov, 2000). Naturally, large pikeperch catches during that period were linked to sea level, a rise in which results in an increase in the area of coastal shallow water and the expansion of cyprinid species that are the main prey of pikeperch in the Caspian Sea (Yanovskaya, 1985). On the other hand, relatively high salinity limits the distribution range and growth rate of pikeperch. In comparison with other pikeperch populations inhabiting a similar climate, the value of L estimated here (55.05 cm FL) is substantially less than that of pikeperch from the Volga river delta (79.0 cm FL; Belyaeva et al., 1989), Aras Lake (Iran) (73.3 cm FL; Akbarzadeh, 2006), and Egirdir Lake (Turkey) (95.4 cm FL; Balik et al., 2004).
Currently, catches are dependent on the Iran Fisheries Company's programme to release fingerlings produced artificially into rivers. Fishers operating in Anzali Lagoon report that pikeperch spawners have not been seen there for at least 20 years. As the cause of the disappearance of the stock in the 1930s has not been determined conclusively, it is difficult to say whether the disadvantageous conditions in Anzali Lagoon or the low spawning stock size inhibit natural spawning.
The lack of significant dependence between the quantity of fingerlings released and the abundance of fish in the first year of life estimated by SVPA indicates substantial uncertainty regarding the scope and causes of fingerling mortality. Not surprisingly, the fingerlings with heavier body weights released in 1998 influenced the abundance of that year class in catches. There is obviously a trade-off here between the cost of holding fingerlings in culture to a larger size and the subsequent economic return. Additionally, it would seem essential to study the availability of food resources for fingerlings in the Anzali Lagoon during the release period.
In many parts of the world, pikeperch stocking is practiced in inland waters and marine bays (Steffens et al., 1996; Hansson et al., 1997; Balik et al., 2004). The species is amenable to introduction into the wild, and determining its optimal rearing conditions has been the focus of much research (Szkudlarek and Zak
, 2007). Moreover, pikeperch populations spread easily and can colonize neighbouring waters provided there is relatively good access (Linfield and Rickards, 1979). In marine coastal waters, however, the reintroduction or stock enhancement of certain species has encountered obstacles (Bell et al., 2006). Despite initial conjecture, such obstacles are not only biological, even though factors including density-dependence, greater mortality, and an inability to switch from formulated to natural food or its unavailability at the site and time of release can impact the success of a restocking programme. The results of long-term stocking in small basins in Lao PDR have indicated just how important a role the local community can play in such initiatives (Garaway et al., 2006). As long as the fishers that exploit the resources are not interested in the relation between protecting young pikeperch and the potential benefits of catching larger fish in subsequent years and do not participate in stocking programmes either financially or physically, the human factor will be a source of substantial uncertainty of equal magnitude to biological or environmental factors.
Pikeperch is just one of several species targeted by the Iranian multispecies beach-seine fishery. The gear is traditionally used by small fishing communities inhabiting marine and estuarine coastlines (Lamberth et al., 1994; Stergiou et al., 1996; Cabral et al., 2003; Gray and Kennelly, 2003). In addition to its immediate economic significance, the use of such gear has an impact on the integration of the local community. From the point of view of protection of resources, the most important issue in a multispecies fishery is the small mesh size that renders a gear highly effective but non-selective. In pikeperch fisheries, the beach-seine does not protect the fish in their first year of life that are released into the sea in the same year in which the fishing season begins. In comparison with management methods such as limiting fishing effort or implementing catch limits, minimum mesh size of gear is the easiest factor to control in traditional, widespread fisheries (Gulland, 1982). The heavy mortality of discards when they are not sorted in water (Cabral et al., 2003; Gray and Kennelly, 2003) means that, even if the legal minimum landing length is enforced, it will not impact the level of catch mortality. In the case of Iran, the effectiveness of control is currently limited by such factors as inadequate resources, little fisheries-specific training for coastguard staff, and the lack of a strategic approach to enforcement activities, including no intelligence gathering (Taghavi, 2000). Therefore, the current situation demands that the minimum mesh size in the codend be increased, and that this parameter be monitored with greater effectiveness.
It must be emphasized that when Iranian fishery management views the issue of beach-seine catch licenses as a rescue measure that decreases illegal sturgeon catches, and the monitoring units are liberal in their enforcement of regulations, the costs incurred to increase the pikeperch stock may remain ineffective. Increasing potential production, and therefore population abundance, does not automatically lead to increased effectiveness. This statement has been put forward many times, recently by both Bell et al. (2006) and Garaway et al. (2006), and it refers quite plainly also to the enhancement of the pikeperch stock in Iranian coastal areas. Releasing fingerlings with a greater mean weight could result in better success of stock-enhancement initiatives. The success of pikeperch stocking, however, appears to depend just as much on increasing adaptive social learning as it does on having an appropriate management strategy.
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Acknowledgements |
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This work was supported by the Iranian Fisheries Research Organization (IFRO). We thank A. A. Khanipoor, Director of the Caspian Sea Bony Fish Research Centre, for his support and encouragement, D. Ghaninezhad, Head of stock management, for advice on data analysis, colleagues in the Guilan, Mazandaran, and Golestan Research Centres for providing the data for the analysis, two reviewers of an early draft for comments that helped us refocus our thoughts, and the several people who helped us smooth the English, and provided valuable comments and assistance with the artwork.
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References |
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