The use of sedimentary fish remains for interpretation of long-term fish population fluctuations

Abstract

Abstract The varved marine sediments of Saanich Inlet, British Columbia, retain a detailed record of fish remains. We examine methods to process and interpret sedimentary fish remains and explore sources of bias in transfer and preservation through time. In high-resolution box cores spanning the last 130 years, scales outnumber vertebrae. A consistent record across replicates is recognizable once outliers are removed. Pacific herring and hake remains make up over 90% of the identifiable remains. Cores from ODP leg 169S covered the entire Holocene; scale recovery is poor, so the record is based on fragmented bones. Bones associated with the backbone, gill arches and fins yield the best taxonomic information. In both core sets, low-frequency signals are resolved using a five-sample running mean. Because the data series in the short cores are autocorrelated, spectral analysis is the best approach to identify high-frequency signals that explain much variance in the scale data. High cross-spectral coherencies confirm a basin-wide signal in scale deposition. The herring scale deposition data are compared to recent fishery biomass estimates and confirm similarities in timing of low-frequency trends and signals. Experiments with herring in large tanks explore the transfer of scales from fish to the ocean floor; shedding and predation are found to provide a regular rain of scales to the sediments. Overall, the sedimentary fish remains record in basins with good preservation shows promise as a means to identify generalized long-term fish histories through the Holocene as well as a more specific Pacific herring and hake story over the last century.