State of the Black Sea Whiting (Merlangius merlangus euxinus) (Nordmann, 1840)

Transcription

1 State of the Black Sea Whiting (Merlangius merlangus euxinus) (Nordmann, 1840) 1. Basic Identification Data Scientific name: Merlangius merlangus euxinus Common name: Whiting ISCAAP Group: 32 Geographical sub-area: 29 Stock assessment method: trawl survey, VIT and YPRLEN 2.1 Authors: Gheorghe RADU and Valodea MAXIMOV with consultancy for data from STECF/BS stock assessment working group Affiliation:National Institute for Marine Research and Development Grigore Antipa Constanta 2. Stock identification and biological information 2.1 Stock unit In the Black Sea, the whiting is one of the most abundant species among the demersal fishes. It does not undertake distant migrations, spawning mainly in the cold season within the whole habitat area. The whiting produces pelagic juveniles, which inhabit the upper 10-meter water layer for about a year. The adult whiting is cold-living, preferring temperatures 6-10º С. Fishes at the age less than 6 years are predominant in the whiting populations, the older year classes are found in catches individually. It occurs all along the shelf, dense commercial concentrations are formed by 1-3 year old fishes in the water down to 150 m depth, most often at m depths (Radu G.&Radu E.,2008). Such concentrations on the shelf of Bulgaria, Georgia, Romania, the Russian Federation and Ukraine not do from every year, appearing at periods of 4-6 years - in the years of appearance of highly productive year classes. (Ivanov L. and Beverton R.J.H., 1985)

2 Fig Whiting migration routes in the Black Sea area (Radu G., 2003) Fig Whiting migration routes in the Black Sea Romanian area The problem of units for whiting stocks in the Black Sea has not been settled yet. Fisheries experts from the Black Sea Commission specify the stock as shared that is although this fish does not make long migrations; its whole stock (or two different stocks Eastern and Western) is exploited by each Black Sea country in their waters and for its adequate assessment the analysis of the regional data is required. So, the problem of quantity and location of whiting stock units in the Black Sea is not solved. At present whiting stocks belong to the groups of shared ones. 2.2 Growth and maturity The determination of the biologic parameters represents an important objective for the establishment of the demographic structure, the growth parameters, as well as other parameters required for the study of recruitment, mortality, effective and biomass, divided into age classes. In the Black Sea for the grounds with relatively slight fished off whiting population was characteristic of predominance of larger-sized fishes than in the grounds with wide shelf (Shlyakhov, 1983). In in the grounds of intensive Turkish trawl fisheries one can observe tendency to reduction of mean length of fishes which became equal or even less than in Ukrainian waters. It is not quite typical and in our opinion it is the evidence of excessive intensity of fishery. Turkish scientists came to the same conclusion (Genç et al., 2002). In front the Bulgarian coast whiting catch length composition ranged between 50 and 230 mm and individual weight between g. The highest percent belongs to the mm group, followed by mm and mm. The length group mm, accounts around 6% of the whiting by-catch. The rest of the length groups are very weakly presented in the landings (Maximov et al., 2009). The analysis performed by (Raykov et al., 2008), show that highest value for L asymptotic of the whiting was calculated in Ukranian waters (39 cm) with the lowest growth rate (k = 0.106), accordingly. In Bulgarian and Romanian marine area the values are very similar and lower, as regards the asymptotic length (Radu G et al., 2006, 2010, 2011). Overall, in the last years, the whiting population on the Romanian littoral was homogenous, the length ranging between 40 and 230 mm/ g, the dominant classes being those of mm/ g. The average body length was mm, and the average weight 10.58g (Maximov et al., 2009), (Radu G et al., 2006, 2010,

3 2011). The analysis of age components during the entire Romanian fishing season emphasized the presence of individuals aged between 0;0 + to 5;5 + years, with a domination of individuals aged between 2;2 + years and 3;3 + years. Table Maturity give and Natural mortality of whiting at Romanian littoral Age Maturity M Ogive Table2-1: Maximum size, size at first maturity and size at recruitment at Romanian littoral in Somatic magnitude measured (LH, LC, etc)* Lt Units* cm Sex Fem Mal Both Unsexed Maximum size Reproduction December-March observed Size at first maturity season Reproduction areas Recruitment size 4.5 Nursery areas Shelf Depth bigger than 50m Table2-2: Growth and length weight model parameters Growth model Length weight relationship Sex Units female male both unsexed L cm K 0.16 t Data source Romanian data a b M (vector by length or age) M age sex ratio (% females/total) 57%

4 7 6 Female Male Total % No. individuals Length class (mm) Fig Structure on length classes for whiting in 2011, total catches in Romanian area 5; 5+ years, 2% 3; 3+ years, 7% 4; 4+ years, 1% 0; 0+ years, 4% 1; 1+ years, 40% 2; 2+ years, 46% Fig Structure on age classes for whiting in 2011, total catches in Romanian area

5 3. Fisheries information 3.1 Description of the fleet Table Romanian whiting catches in Country Year Vessel length Gear Mesh size range Fishery GSA Species Catche (t) Discards (t) ROM 2008 VL2440 OTM 14D16 DEMF SA 29 WHG ROM 2008 VL1824 OTM 14D16 DEMF SA 29 WHG ROM 2008 VL1218 OTM 14D16 DEMF SA 29 WHG ROM 2008 VL0612 FPN 14D16 MDPSP SA 29 WHG ROM 2009 VL0612 FPN 14D16 MDPSP SA 29 WHG ROM 2010 VL0612 FPN 14D16 MDPSP SA 29 WHG ROM 2010 VL0006 FPN 14D16 MDPSP SA 29 WHG ROM 2011 VL2440 OTM 14D16 MDPSP SA 29 WHG ROM 2011 VL0612 FPN 14D16 MDPSP SA 29 WHG ROM 2011 VL0006 FPN 14D16 MDPSP SA 29 WHG Catches as used in the assessment Catches as used in the assessment 2011 data (N) Age BG GE RO RF TR UK TOTAL Total Catches as used in the assessment average data (N) Age BG GE RO RF TR UK TOTAL Total Historical trends In Bulgaria, Georgia, Romania, the Russian Federation and Ukraine whiting is very rarely the target species for fisheries and yielded as by-catch during trawl fisheries for other fish species or while non-selective fisheries with fixed nets in the coastal sea areas. Official statistics in all Black Sea countries does not reflect the true capture of whiting which is much higher than reported one.

6 In the total mean annual catch of whiting by Black Sea countries (except Turkey) according to the data of official statistics submitted to FAO was less than 0.6 thousand tons. It should be noted that with target trawl fisheries for sprat and other fishes whiting is by-caught in larger quantities that it is specified in official reports of the countries. Thus in the waters of Ukraine during sprat fisheries with midwinter trawls in whiting by-catch was assessed in the range of thousand tons (Shlyakhov, Charova, 2003). Sprat catches with small by-catches quantity of whiting are sometimes not registered and they are recorded in statistics as sprat. Recording is made in case of increased by-catches (more than 10-20%). This situation is common in the waters of Bulgaria, Georgia, Romania and the Russian Federation. Turkey is the only country in the region, where the annual target trawling fisheries for this fish is conducted. In its annual catches varied from 6 thousand tons to 19 thousand tons, making on average 10.8 thousand tons. As compared with , when mean annual catch of whiting was equal to 17.6 thousand tons, the tendency towards reduction of both its catches and CPUE is observed. Also, the whiting represents a complementary catch of the Romanian and Bulgarian fishermen. The level of fishing productivity is different from year to year, depending on the fishing effort (number of boats, nets, effective fishing days) and on the evolution of the hydro-climatic conditions and the anthropogenic factors (Radu G et al., 2006, 2010, 2011). Table 3.2 Whiting catches in the Black Sea area (BSC2011, BS stock assessment working group, 2011,2012) Year Bulgaria Georgia Romania Russian Federation Turkey Ukraine Total

7 3.3 Management regulations Not considering in details the similarity and differences of various measures of Black Sea whiting fisheries in various countries it should be noted that fishing in Turkey is conducted without limitation of annual catch or the fishing efforts. The mesh size of bottom trawls is designed to catch whiting being 40 mm and minimum commercial size 13.0 cm (TL). By the ruling of General Directorate of Fisheries in 2010, the use of monofilament strings was prohibited. Trawling is permitted only in the season between September and April, in the open areas outside the 3 miles zone from the coast. Regulations of the Commercial Fisheries in the Black Sea Basin currently in force in Ukraine have determined the following requirements: minimum commercial size of whiting 12 cm (SL); the allowable by-catch of its juveniles not more than 20% of total biomass of catch during non-target trawl fisheries and not more 30% by counting during the target fisheries with trawls (with mesh size not less than 12 mm). The annual regulation of whiting fisheries includes determination of the limits for whiting s harvesting on the basis of its stock value and TAC. In Romania are not special regulations for whiting (Radu, 2011, Radu &Nicolaev, 2010). 3.4 Reference points Reference Points F YPR SSB/R TSB/R F-zero F F-max F at 50% of MSP Mean F = for the period Mean F = for Fisheries independent information 4.1 Swept area method Brief description of the chosen method and assumptions used In the Romanian waters was used the bottom trawl 22/27-34 with horizontal opening of 13m. The average speed of the vessel was of knots, the trawling time was standardized at 60 minutes. Have been registered the following elements: geographical coordinates for trawling points, water depth (m), the average trawling speed (knots), time of trawling, total catch and structure on species. For every trawling was taken one random sample for small size species and for big species like turbot and dog-fish each specimens were registered and measured. Having data regarding horizontal opening of the trawl, trawling speed and time have been calculated the surveyed area, catch per surveyed area, extrapolated catch per square Nm for each species and biomass Spatial distribution of the resources

8 1 2 Fig Distribution of the whiting agglomerations at Romanian littoral in spring 2009 and Fig Distribution of the whiting agglomerations at Romanian littoral in autumn 2009 and 2010

9 Fig The distribution of the whiting agglomerations in demersal trawl survey, in spring and autumn 2011, Romanian area Historical trends Table The biomass whiting agglomerations (t) in the Romanian waters Year Spring 11,853 7,410 26,171 Autumn 4,921 20,948 16,307 Along Georgian coasts after the disintegration of the USSR whiting biomass assessments were not made, but on the basis of monitoring the scientists from this country make conclusion that in the period from the early 1990s until the mid-2000s the whiting abundance as well as of other bottom fishes increase (Komakhidze, Diasamidze, Guchmanidze, 2003). In Romanian waters in whiting remained the most abundant among bottom fishes although its mean annual catch reduced as much as four times as compared with Partially it was caused by reduction of fishing efforts as compared with previous period (Nicolaev et al., 2003). The stock biomass was assessed 4,900-26,000 tons by swept area method (bottom trawl surveys) (Radu G.,2011). In the Russian sector of the Black Sea trawl survey show that stocks of whiting and other Gadidae (Gaidrosparus mediterraneus) are estimated about thousand tons and the annual TAC for whiting averages 2 thousand tons (Volovik, Agapov, 2003). Along the Turkish coasts the total trawlable biomass of whiting in local areas were estimated by A. İşmen (2003). In 1992 the highest biomass between Sinop and Sarp (eastern Black Sea), which is an area, closed to trawl fishing 30 thousand tons. In 1990 the biomass of whiting between Sinop and İğneada (western Black Sea) was estimated within the range of thousand tons. Even if for the period of similar direct assessments of whiting biomass were made, they were not published. In in the waters of Ukraine whiting biomass changed from 43 up to 70 thousand tons, on average 54 thousand tons, and for the subsequent decade from 40 up

10 to 68 thousand tons, on average 52 thousand tons (Shlyakhov, Charova, 2006). These data testify rather high inter-annual fluctuations but rather stable average level of whiting biomass in the specified areas where whiting specialized fisheries is almost absent and trawling fisheries are not conducted on the grounds with the densest whiting distribution. By this reason the most realistic assessments of the stock abundance seem to be estimates according to the data of trawl surveys or surveys produced on the basis of analysis of fisheries with obligatory correction for unregistered catch. With the exception of last year's estimates of the Black Sea EWG STECF, for last 15 years only one regional research was undertaken (Prodanov et al., 1997) that made possible to produce assessments of abundance and biomass of whiting in the Black Sea by VPA method for the period of on the basis of analysis of regional biological and fishing data. According to Bulgarian scientists (Prodanov and Bradova, 2003), whiting biomass in the western part of the Black Sea excluding the western Turkish coastal waters in 1997 was assessed by VPA as 121 thousand tons, which was comparable with the long-term mean after decline in / Prodanov K, Bradova, N. (2003). 5 Ecological information 5.1 Protected species potentially affected by the fisheries 5.2 Environmental indexes 6 Stock assessment 6.1 Name of Model VIT and YPR-LEN 3.1 We used the VIT program for estimation of abundance and fishing mortality and YPR-LEN (NOAA Fisheries Toolbox Version 3.1) for obtaining the reference points for dogfish in the Black Sea. The program VIT is conceived for the analysis of fisheries where the available information is limited. VIT is designed for the analysis of marine populations, exploited by one or several gears, based on single species' catch data (structured by age or size). The main assumption underlying the model is that of steady state, because the program works with pseudo-cohorts and it is therefore not suitable for historical data series. The program uses the catch data and ancillary parameters for rebuilding the population of the species and the mortality vectors affecting it by means of Virtual Population Analysis (VPA). Once the virtual population has been rebuilt, an analysis of the fishery can be carried out with the aid of several tools: Comprehensive VPA results, Yield-per-Recruit analysis based on the fishing mortality vector, analysis of sensitivity to parameter values and transition analysis. The latter permits non-equilibrium analysis of how a shift in exploitation regime is reflected in the fisheries. All these tools can be applied to specific studies of competition among fishing gears Model assumptions The VIT software was applied to assess population parameters based on pseudocohort analyses of average data and 2011 data. In both variants the main share in total catch was represented by Turkey. The two scenarios were run with the following parameters: L = cm k = 0.23 t0 =

11 a = b = M = Scripts Results Table Summary results for data Summary data Whiting (Program VIT) --- Total BG Ge RO RF TR UK Catch mean age Catch mean length Mean F Global F Total catch E E E E E E E+06 Catch/D% Catch/B% B/R SSB/R Y/R Y/R BG Y/R GE Y/R RO Y/R RF Y/R TR Y/R UK Current Stock Mean Age Current Stock Critical Age Virgin Stock Critical Age Current Stock Mean Length Current Stock Critical Length Virgin Stock Critical Length Number of recruits, R E+11 Mean Biomass, Bmean E+12 Spawning Stock Biomass, SSB E+12 Biomass Balance, D E+12 Natural death/d Bmax/Bmean Turnover, D/Bmean Table Summary results for 2011 data Summary data for whiting BS Total BG GE RO RF TR UK Catch mean age Catch mean length

12 Mean F Global F Total catch E E E E E E E+07 Catch/D% Catch/B% B/R SSB/R Y/R Y/R BG Y/R GE Y/R RO Y/R RF Y/R TR Y/R UK Current Stock Mean Age Current Stock Critical Age Virgin Stock Critical Age Current Stock Mean Length Current Stock Critical Length Virgin Stock Critical Length Number of recruits, R E+11 Mean Biomass, Bmean E+12 Spawning Stock Biomass, SSB E+12 Biomass Balance, D E+12 Natural death/d Bmax/Bmean Turnover, D/Bmean Table Reference points for Black Sea whiting 2011 Reference Points F YPR SSB/R TSB/R F-zero F F-max F at 50% of MSP Mean F = for the period Mean F = for 2011

13 Fig Fishing mortality related with Y/R and SSB/R Fig Fishing mortality related with Catch Numbers

14 Fig Fishing mortality related with Y/R Fig Fishing mortality related with Spawn numbers

15 Fig Fishing mortality related with %MSP 6.2 Robustness analysis 6.3 Assessment quality 7 Stock predictions 7.1 Short term predictions As the estimated F =0.375 exceeds Fmsy= 0.352,we classify the stock of whiting in the Black Sea as being exploited unsustainably. Given that this is not a highly migratory species we may conclude that the resident population is more exploited in the southern part (Turkish waters) than in the rest of the Black Sea - an effect that has been demonstrated by Prodanov et al. (1997) who performed separate VPA analyses of the western/northern and eastern/southern components of the whiting stock. If we consider the recommendation of the EWG as FMSY 0.4, the two results obtained by me Fc (2011) = and Fc ( ) = oscillate around of the value of Fmsy = 0.4. We can consider that the stock is fully exploited. 7.2 Medium term predictions 7.3 Long term predictions 8 Draft scientific advice Gaps that need to be addressed in the near future include: Several gaps were identified such as: limitations in performing of scientific surveys,

16 insufficient training in assessment methods, lack of harmonisation in data collection and age reading, insufficient knowledge of stock units, and lack of monitoring programs for assessing the IUU and discards. Management advice and recommendations - Recommends to organise workshop(s) for inter-calibration of age readings between different laboratories and scientists in the region, and harmonisation of the frameworks and methods of sampling of commercial fisheries and scientific surveys. - Reducing fishing mortality; - Regional management measures. References Genç Y., Mutlu C., Zengın M., Aynın İ., Zengın B., Tabak İ., Doğu Karadeniz deki Av Gücünün Demersal Balık Stokları Üzerine Ektisinim Tesbiti, Tarım Köyişleri Bakanlıgi, TAGEM, Trabzon Su Ürüleri Mekez Araştırma Enstitüsü, Sonuç Raporu Proje No: TAGEM/IY/97/17/03/006, ss:114 (in Turkish) Komakhidze A., Diasamidze R., Guchmanidze A., 2003 State of the Georgian Black Sea demersal ichthioresources and strategy for their rehabilitation and management. In: Workshop on Demersal Resources in the Black & Azov Sea. Published by Turkish Marine Research Foundation, Istanbul, TURKEY, B. Öztűk and S. Karakulak (Eds.), Maximov V., Raykov V.S., Yankova M., Zaharia T., Whiting Merlangius merlangus euxinus population parameters on the Romanian and Bulgarian littoral between ; Journal of Environmental Protection and Ecology, p. Nicolaev et al., 2003 Nicolaev S., Maximov V., Anton E., 2003 Actual state of Romanian marine demersal fisheries In: Workshop on Demersal Resources in the Black & Azov Sea. Published by Turkish Marine Research Foundation, Istanbul, TURKEY, B. Öztűk and S. Karakulak (Eds.), Prodanov, K., K. Mikhaylov, G. Daskalov, K. Maxim, E. Ozdamar, V. Shlyakhov, A. Chashchin, A. Arkhipov, Environmental management of fish resources in the Black Sea and their rational exploitation. Studies and Reviews. GFCM. 68. Rome, FAO. 178p. Prodanov K, N. Bradova Stock Assessment of the Whiting (Merlangius merlangus) in the Western Part of the Black Sea During Proc., Institute of Oceanology 4: Radu G., 2003 Management of Fisheries and Other Living Marine Resources, National Report and Data Sheets in Romania. Workshop on Responsible Fisheries in the Black Sea and the Azov Sea, and Case of Demersal Fish Resources, April , Şile, İstanbul, BSEP Programme, Country Report, TÜDAV/BSEP/ UNDP/GEF Radu G., Nicolaev S., Radu E., Anton E., 2006 Evolution of main indicators of marine living resources from the Romanian Black Sea sector in 2004 and st Bilateral Scientific Conference Black Sea Ecosystem 2005 and Beyond 8-10 May 2006, Istanbul, Turkey Radu, Gh. & Radu, E Determinator al principalelor specii de pesti din Marea Neagra. Editura VIROM, Constanta, 558 p. (In Romanian). Radu G., E. Anton, Mariana Golumbeanu, State of the Romanian Black Sea Fisheries in the Last Decade. International Conference on Fishery and Aquaculture - A View Point Upon the Sustainable Management of the Water Resources in the Balkan Area May, 2010, Galati ROMANIA ISSN: ; Radu G., Romanian Fishery Report th regular FOMLR AG meeting of the

17 BSC, Black Sea Commission Permanent Secretariat Premises, Istanbul, Turkey, th of September, 2011; Radu G., S. Nicolaev, The regulation of Black Sea fish stocks. International Association for Danube Research- IAD Danube News Editor DANUBE NEWS Alumnus: Swiss Federal Institute of Aquatic Science and Technology (Eawag), Ueberlandstrasse 133; CH-8600 Dübendorf, Switzerland; Radu G., S. Nicolaev, V. Maximov, E. Anton, The Dynamics of Marine Fisheries at the Romanian Coast During The joint 3rd biannual Black Sea Scientific Conference and up-grade BS-Scene Project Joint Conference. Black ea Outlook Conference 31 October 4 November Raykov, V., Yankova, M Growth dynamics and mortality estimation of the Horse Mackerel (Trachurus mediterraneus ponticus, Aleev) migrating along the Bulgarian Black Sea Coast. Proceedings of first Biannual Scientific Conference Black Sea Ecosystem and Beyond 8-10 May 2005, Istanbul, Shlyakhov V. A Biology, distribution and fishery of whiting (Odontogadus merlangus euxinus (Nordmann) in the Black Sea. - USSR, Moscow, Proceedings of VNIRO "Biological resources and prospects of fishery of new species fishes and invertebrates", 1983, с (in Russian) Shlyakhov, V., Charova, I The Status of the Demersal Fish Population along the Black Sea Cost of Ukraine. In: Workshop on Demersal Resources in the Black & Azov Sea. Published by Turkish Marine Research Foundation, Istanbul, TURKEY, B. Öztűk and S. Karakulak (Eds.), Shlyakhov, V., Charova, I., 2006 Scientific data on the state of the fisheries resources of Ukraine in the Black Sea in st Bilateral Scientific Conference Black Sea Ecosystem 2005 and Beyond 8-10 May 2006, Istanbul, Turkey,