UC San Diego

The Santa Barbara Basin (SBB) fish assemblage over the last two millennia was examined using fish otoliths recovered from sediment cores. In Chapter 2, the hypothesis that otolith shape and elemental composition can be used to accurately discriminate between common southern California Current System fish taxa was tested. Digital images of 905 sagittal otoliths, representing 6 major taxonomic-based groups, were used to develop geometric (GEO) and elliptic Fourier (EF) shape measurements and a subset of 143 otoliths also analyzed for trace elements (ELM). Results indicate that random forest analysis was superior to discriminant function analysis and GEO features outperformed EF and ELM features for classification. Highest classification accuracy (96.3%) resulted from using the 10 strongest discriminatory features, which included a mixture of GEO, EF, and ELM features.

In Chapter 3, fossil otoliths (n = 1188) recovered from 3 Kasten and one box core sampled in the SBB were classified to taxonomic group by expert opinion (EO) and, after measuring shape and elemental features, by using the classification models developed in Chapter 2. Results of the EO and feature-based classification methods agreed strongly for the most abundant taxa and indicated that Myctophidae (52.7%) and Bathylagidae (31.5%) have dominated the forage fish assemblage in the SBB over the last two millennia. Less abundant taxa include Merlucciidae (6.9%), Sebastidae (4.8%), and Engraulidae (3.9%). Taxa displayed similar periods of variability on the decadal (50-90 years) and century scale (200 +/-50 years).

In Chapter 4, the relation of climate and SBB fish assemblage was investigated by comparing the otolith deposition rate (ODR) record with proxies of climate over the same period. Results indicate coherence between the ODR of Myctophidae, Bathylagidae, Engraulidae, and Sebastidae, which display significant correlation with temperature-based climate indices. The coherent pattern in several fish populations and basin-wide climate variability observed over off the coast of Southern California demonstrate the role of climatic forcing in regulating forage fish populations over the past two millennia. Our results provide baseline composition data and an increase understanding of natural variability of SBB fish populations.