BIODIVERSITAS ISSN: 1412-033X Volume 17, Number 2, October 2016 E-ISSN: 2085-4722 Pages: 808-813 DOI: 10.13057/biodiv/d170258 The length-weight correlation and population dynamics of razor clams (Solen regularis) in Surabaya east coast, Indonesia NINIS TRISYANI 1,2,♥ , ENDANG YULI HERAWATI 3 , MAHENO SRI WIDODO 3 , DADUK SETYOHADI 3 1 Doctoral Program, Faculty of Fisheries and Marine Science, Universitas Brawijaya. Jl. Veteran, Malang 65145, East Java, Indonesia. 2 Department of Fisheries, Faculty of Engineering and Marine Science, Universitas Hang Tuah. Jl. Arif Rahman Hakim No. 150. Surabaya 60111, East Java, Indonesia. Tel.: +62-31-5945864,  email: nisuht@yahoo.com 3 Faculty of Fisheries and Marine Science, Universitas Brawijaya. Jl. Veteran, Malang 65145, East Java, Indonesia Manuscript received: 29 April 2016. Revision accepted: 7 October 2016. Abstract. Trisyani N, Herawati EY, Widodo MS, Setyohadi D. 2016. The length-weight correlation and population dynamics of razor clams (Solen regularis) in Surabaya east coast, Indonesia. Biodiversitas 17: 808-813. Solen regularis is a pelecypod species living in intertidal areas at sandy substrate. In Surabaya east coast, Solen regularis is exploited by the locals for consumption, both as fresh seafood or processed one. This research aims to analyze the length-weight correlation of the clams and the population dynamics, conducted from August 2014 to July 2015 in Surabaya east coast. The results show that the correlation is explained in the equation W = 0.038L 2.798 with the correlation coefficient of 0.9. Also, the allometric growth pattern is proven negative as the increase in body length is faster than that in weight. Growth is measured with von Bertalanffy growth model Lt = 8.0 ( 1-e (-0.7 (t+0.003) ) and the result from the parameter analysis using ELEFAN I method in FISAT II software show that L ∞ = 8.0 cm and k = 0.7/year. The estimated weight at t 0 in Pauly’s empirical formula is -0.003 cm. Mortality rates are shown as follows: natural mortality (M) is 2.05/year, fishing mortality (F) is 2.01/year, and total mortality is 4.05/year. Exploitation rate (E) is 0.50/year indicating that the exploitation of Solen regularis is in optimal condition. The B/R and Y/R value is 1.4%/year. It can be suggested from the findings of the research that knowledge on population dynamics may be useful for the utilization and management of Solen regularis in order to preserve its environmental and ecological sustainability. Keywords: Growth, mortality, razor clams, Solen regularis, Surabaya east coast INTRODUCTION Solen spp. or also known as razor clam or kerang bambu (Indonesian) or kerang lorjuk (Maduranese) is a species of mollusk clams widely consumed and highly traded as a commodity in international markets (Baron et al. 2004). This species varies in several species, such as Solen dactylus living along the coasts with muddy sandy substrate in Oman Sea and Persian Gulf (Bruyne 2003), Solen regularis in the western part of Sarawak, Malaysia (Rinyod and Rahim 2011), and Solen marginatus in the coasts of Atlantic, Europe, northwestern part of African coasts, and Mediterranean Sea buried under the sand and/or tidal areas, both in intertidal and sub tidal parts at mud substrates and the sands (Hmida et al. 2012). In Indonesia, Solen spp. can be found in the Maduranese coast of Pamekasan District (Nurjanah et al. 2008), Eastern coast of Surabaya (Trisyani et al. 1999; Trisyani and Irawan 2008), and Kejawanan Beach, Cirebon (Subiyanto et al. 2013). The locals call this type of clam lorjuk or kerang bambu. The findings from investigation conducted by the Indonesian Institute of Sciences (LIPI) show that Solen regularis is widely found in the Surabaya east coast, and the DNA analysis using RAPD indicates that Solen regularis in the Surabaya east coast exhibits 13.1% of similarity with Solen sp. found in Pamekasan coast (Trisyani and Budiman 2015). The higher demands for Solen spp. as comestibles have led to the more intensified fishing for this species which is feared as the possible cause of decreasing population of the clam. This problem, however, has not been officially identified because of the absence of data for fishing production and industry. A research carried out by Trisyani and Irawan (2008) shows that Solen sp. found along the eastern coast of Surabaya lives in the muddy sand substrate with the organic content of approximately 0.22-0.54 ppm, water temperature of about 28-31ºC, salinity around 26-31 ppt, and soil pH at 7.0-8.5. The clams are fished using dredging tools and sticks whose ends are immersed into a mix of chalk and soap. Substrate is dredged and sticks are pushed into the hole to pull the clams out. As the stick end touches the clams, they are immediately captured by hand. Trisyani and Hadimarta (2013) have conducted a research and found that Solen’s reproduction cycle by observing their Gonad Maturity Level (GML). It is discovered that the GML of the clams in the Surabaya east coast reaches the mature level (GML III) in Mays and starts the insemination (GML IV) in Junes. Gonad growth declines until the resting phase (GML 0) in Septembers, and in Octobers, GML gradually refrains to the mature levels (GML II and GML III). As the GML rises, it is followed by an increase in the diameter of the oocytes with the equation of GML = 0.522 ± 0.528 of oocyte diameter with correlation of 79.2 % Previous researches related to the razor clams growth have been conducted by Baron et al. (2004) on Ensis