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Separating two herring stocks from growth data: long‐term changes in survey indices for Western Baltic Spring Spawning Herring ( Clupea harengus ) after application of a stock separation function
Author(s) -
Gröhsler T.,
Schaber M.,
Larson N.,
Oeberst R.
Publication year - 2016
Publication title -
journal of applied ichthyology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.392
H-Index - 62
eISSN - 1439-0426
pISSN - 0175-8659
DOI - 10.1111/jai.12924
Subject(s) - herring , clupea , baltic sea , stock (firearms) , fishery , biology , north sea , spatial distribution , spring (device) , oceanography , geography , remote sensing , archaeology , mechanical engineering , fish <actinopterygii> , engineering , geology
Summary In the Baltic Sea, herring stocks are surveyed and managed according to a spatial allocation based on ICES (International Council for the Exploration of the Sea) subdivisions. In the western Baltic, the distribution areas of two stocks overlap: the Western Baltic Spring Spawning Herring ( WBSSH ) and the Central Baltic Herring ( CBH ). Survey results of length‐at‐age data indicate in Subdivision ( SD ) 24, which is a part of the WBSSH management area, that a considerable fraction of CBH is present and correspondingly erroneously allocated to WBSSH stock indices. Accordingly, a stock Separation Function ( SF ) based on growth parameters was established to identify the fraction of CBH in the WBSSH area. In the present study, the SF was applied to 8 years of data from the GERman Acoustic Survey ( GERAS ), which is conducted annually in autumn in ICES subdivisions 21‐24. Results showed a distinct fraction of CBH in SD 24, and exclusion of the CBH greatly improved the quality of the GERAS index used in the assessment of the WBSSH stock.