Interannual and secular variability of larvae of mesopelagic and forage fishes in the southern California Current System

TitleInterannual and secular variability of larvae of mesopelagic and forage fishes in the southern California Current System
Publication TypeJournal Article
Year of Publication2018
AuthorsMcClatchie S., Gao J., Drenkard E.J, Thompson A.R, Watson W, Ciannelli L., Bograd SJ, Thorson J.T
JournalJournal of Geophysical Research-Oceans
Volume123
Pagination6277-6295
Date Published2018/09
Type of ArticleArticle
ISBN Number2169-9275
Accession NumberWOS:000447552600015
KeywordsCalCOFI; climate-change; distribution shifts; el-nino; ichthyoplankton; mass; modeling; ocean; oceanography; optimum multiparameter analysis; spatial; temporal; thermocline; water; water masses
Abstract

We used univariate and multivariate spatiotemporal delta models to quantify changes in the distribution of ichthyoplankton in the southern California Current System from 1951 to 2016. We focus on mesopelagic species, because they are most abundant, and on northern anchovy (Engraulis mordax), Pacific sardine (Sardinops sagax), and Pacific hake (Merluccius productus), because they are important commercial and forage fish species. Univariate models indicated that changes in the relative abundance, area occupied, center of gravity, and spatiotemporal variability of numerically dominant warm-water and cool-water-associated mesopelagic ichthyoplankton show strong species-specific differences. Multivariate models revealed that the warm-water-associated mesopelagic assemblage exhibits an increasing, nonmonotonic, secular trend of increasing relative abundance underlying interannual variability, suggesting a tropicalization of the southern California Current System. In contrast, the cool-water-associated mesopelagic assemblage shows mainly interannual variability, with little secular trend over the 65-year period. Correlation matrices of the modeled ichthyoplankton densities showed that the spatial distributions of northern anchovy and Pacific hake are highly correlated with cool-water mesopelagic ichthyoplankton, but Pacific sardine is spatially correlated with both warm- and cool-water-associated mesopelagic species. Declines of adult sardine, anchovy, and hake are occurring concurrently with tropicalization of the southern California Current System. The most parsimonious explanation for tropicalization of the ichthyoplankton is increased presence of Pacific Equatorial-influenced Water in the inshore southern California region. We modeled the distribution of ichthyoplankton in the southern California Current System from 1951 to 2016. We focus on abundant mesopelagic species and on northern anchovy (Engraulis mordax), Pacific sardine (Sardinops sagax), and Pacific hake (Merluccius productus), because they are important commercial and forage fish species. Single species models indicated that changes in abundance, area, distribution center, and variability of the most abundant mesopelagic ichthyoplankton associated with warm and cool water show strong differences between the species. Models of species groups revealed that the warm-water mesopelagic larval fishes exhibit a long-term trend of increasing relative abundance underlying year-to-year variability, suggesting tropicalization of the southern California Current System. In contrast, the cool-water mesopelagic larvae show mainly year-to-year variability, with little long-term trend. Correlations between the modeled species showed that the spatial distributions of northern anchovy and Pacific hake are highly correlated with cool-water mesopelagic larvae, but Pacific sardine is correlated with both warm- and cool-water-associated mesopelagic species. The spatial variability of hake over time is highly positively correlated with cool-water mesopelagics and with northern anchovy, but sardine fluctuate independently of the mesopelagics and both anchovy and hake. Declines of adult sardine, anchovy, and hake are occurring concurrently with tropicalization of the southern California Current System. The simplest explanation for more tropical ichthyoplankton is increased presence of Pacific Equatorial-influenced Water in the inshore southern California region.

DOI10.1029/2018jc014011
Short TitleJ Geophys Res-Oceans
Impact: 

Declines of adult sardine, anchovy, and hake are occurring concurrently with tropicalization of the southern California Current System. The simplest explanation for more tropical ichthyoplankton is increased presence of Pacific Equatorial‐influenced Water in the inshore southern California region.

Student Publication: 
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