Date of Award

Winter 1-31-2023

Document Type

Thesis: Open Access

Degree Name

MS Marine Science

Department

Environmental and Ocean Sciences

Committee Chair

Andrew Thompson

Committee Member

Steven Searcy

Committee Member

Rasmus Swalethorp

Committee Member

Nathalie Reyns

Abstract

Discerning the causes of population boom and bust cycles for coastal pelagic species (CPS) has been a major focus of fisheries management research for over a century. Year-class strength is contingent on larval survival and condition, which can be influenced by larval size at age and growth rate. These two factors, in turn, can be affected by maternal investment and environmental variables such as water temperature, salinity, oxygen, and chlorophyll a. We evaluated each of these factors from 127 two to eight week-old Northern Anchovy (Engraulis mordax) larvae off the coast of San Diego to San Francisco, California (USA) collected from 2009-2019. Sagittae otoliths were analyzed to determine larval age (otolith ring-count), size-at-hatch as an index of maternal investment (otolith core diameter) and growth rate (otolith increment width). Size at age was determined by computing the residuals between age and the following larval condition measurements: standard body length (SL), muscular height at the anal fin (MHA), and muscular height at the pectoral fin (MHP). Linear regressions revealed that SL, MHA, MHP and average recent otolith growth (average of last 3 increment widths) were significantly correlated, indicating that fish that were larger at age were also growing faster. Generalized Linear Mixed Models (GLMM) demonstrated that fish age (survival) was positively correlated to core diameter, and negatively correlated with water temperature and chlorophyll a; SL was positively correlated with core diameter, negatively correlated with salinity and latitude; MHA was positively correlated with core diameter, negatively correlated with latitude, and largest at slightly above average temperatures (residual= 0.25); and MHP was positively correlated with core diameter and negatively correlated with chlorophyll a. Average recent growth rate was not significantly correlated with core diameter or any environmental factor. However, lifelong growth rate trajectories showed that fish were growing faster in years with high recruitment. This preliminary finding supports that larval growth rates could have important implications for year-class strength; however further analyses are needed. Overall, maternal investment, intermediate water temperature, low chlorophyll a and low salinity optimized larval survival to older ages and morphological condition. Future fisheries studies should analyze the relationship between larval condition and recruitment success as well as understanding what drives maternal investment and how it is best measured.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a CC BY License.

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