Surveys of larval herring began in the North Sea in 1946 and have continued with few interruptions until the present day. In 1967, coordination of the international survey effort was assumed by a Working Group of the International Council for the Exploration of the Sea (ICES), and from
1972 onwards the data have been archived in a data base at the Marine Laboratory in Aberdeen. Until 1986, Larval Abundance Indices (LAIs) were calculated for each assessment unit from catches of larvae smaller than 10 mm, and spawning-stock biomass estimated by reference to historical regressions
of LAIs against spawning biomass derived from Virtual Population Analysis (VPA). The regressions were updated each year. From 1986 onwards, a Larval Production Estimate (LPE) was calculated for each assessment unit in addition to an LAI. The LPE was determined by back-calculating the abundance
at hatching date and size, from abundance at capture date and size using estimates of growth and mortality rates, and integrating over the spawning area and period. The LPE method utilised data on all size classes of larvae captured, rather than solely larvae smaller than 10 mm. The LPE method
performed better than the LAI when compared to other assessment data for the North Sea over the period from 1972 to 1989. A comparison of spawning-biomass estimates calculated directly from LPEs by reference to fecundity data, with those derived from acoustic surveys, revealed similar trends
but an inconsistency in the absolute levels which could not be readily explained.
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