Development of long-term larval indices for Atlantic herring (Clupea harengus) on the northeast US continental shelf

Abstract

Abstract Richardson, D. E., Hare, J. A., Overholtz, W. J., and Johnson, D. L. 2010. Development of long-term larval indices for Atlantic herring (Clupea harengus) on the northeast US continental shelf. – ICES Journal of Marine Science, 67: 617–627. The incorporation of data from ichthyoplankton programmes into the stock assessment process has lagged far behind the use of data from comparable adult-monitoring programmes. This can in part be attributed to a mismatch between established analytical approaches to larval-index development and the inconsistencies in sampling for many long-term ichthyoplankton datasets. Along the northeast US continental shelf, ichthyoplankton surveys have been carried out by the Northeast Fisheries Science Center (NMFS/NOAA) multiple times annually since 1971, but the spatial and seasonal allocation of sampling has varied substantially. Here, we present a non-linear least-squares approach to larval-index development. We use the age structure and abundance of larvae on each survey to derive the larval index, along with parameters describing the survival of larvae and the seasonal cycle of hatching. Application to Atlantic herring (Clupea harengus) revealed a large drop in the index around 1976, an increase in the index through the late 1980s, and another large drop in 2004. This index was correlated with the stock assessment estimate of Atlantic herring spawning-stock biomass from 1971 to 2003, but differed substantially during 2004. Our results demonstrate that our approach to larval-index development is flexible to the inconsistencies in sampling effort.