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Relative infaunal bivalve density assessed from split beam echosounder angular information

Sánchez-Carnero N., Rodríguez-Prez D., Zaragozá N., Espinosa V., Freire J.

Oceanologia

2014

No. 56 (3)

497--521

Management of shellfish resources requires a spatial approach where mapping is a key tool. Acoustic techniques have been rarely used to map infaunal organisms with a patchy distribution. We propose and test the use of split-beam echosounder angular information to assess razor shell presence and relative density. Our statistical approach combines textural analysis of angular echograms, standard unsupervised multivariate methods and hierarchical classification through dendrograms to identify groups of locations with similar clam densities. The statistical analyses show that the classification is consistent with groundtruthing data and that results are insensitive to boat motion or seabed granulometry. The method developed here constitutes a promising tool for assessing the relative density of razor clam grounds.

Status of exploited Baltic flounder stocks in the southern Baltic area (ICES SD 26)

Draganik B., Ivanow S., Tomczak M., Maksimov B.Yu., Psuty-Lipska I.

Oceanological and Hydrobiological Studies

2007

Vol. 36, No.4

47-64

Flounder is the target of directed fisheries in coastal waters and is a bycatch of cod fishing. Flounder were fished in the Baltic region ICES Subdivision 26 (SD 26) by Polish and Soviet fleets until 1991. Since that time political and economic changes have altered the exploitation structure of that area, leading to increased fishing effort and flounder catches. This report, which is based on Polish, Russian and Lithuanian data, presents a review of long term changes in flounder fisheries in SD 26, and describes the current status of flounder exploitation there. The extended Survival Analysis (XSA) method was used to assess the stock. The results indicate that the flounder stock in SD 26 is in good condition and that the spawning stock biomass (SSB) is at a consistently high level. However, the estimated mean fishing mortality (F^), with reference to Biological Reference Points, indicates that the stock is being exploited too intensely to be sustainable.