Causes and Consequences of Phenotypic Plasticity in Reproductive Traits for Rockfishes (Sebastes Spp.) of the California Current Ecosystem

Phenotypic plasticity in life history traits is common for marine fish as part of a life history strategy evolved to cope with spatiotemporal variation in ocean environmental conditions. Knowing how and why phenotypic plasticity in life history traits occurs improves predictions of growth, reproductive potential, and population dynamics as ocean conditions change through time or vary through space. Here, I use the live-bearing rockfishes (Sebastes spp.) of the California Current Ecosystem to explore environmental and energetic causes of reproductive plasticity and consequences for spatiotemporal variation in reproductive potential. Within the genus, intra- and inter-specific variation in the frequency of reproduction exists. Most rockfish produce a single larval brood annually once mature. However, a subset of species (and individuals of those species) reproduce with greater frequency in the southern region of the California Current Ecosystem, where ocean conditions most differ. Temporally, warm climate events negatively impact fish body condition and gonad size. I hypothesize that spatiotemporal variation in the ocean environmental conditions of the California Current influences variation in maternal energy reserves and the reproductive output of fish, with respect to maternal size. To test this, I use empirical study and theory. In Chapter 1, I find larger body size and greater food resources for the rosy rockfish (Sebastes rosaceus), a species capable of multiple broods, increases the frequency of reproduction and thus annual fecundity in optimal, stable laboratory feeding conditions. In Chapter 2, I use a 20+ year time series of rockfish from central California to find strong inter-annual variation in size-dependent fecundity relationships, and a greater capacity of large females to increase offspring production during years of favorable ocean conditions compared to small, mature females. In Chapter 3, I develop a state-dependent model to better understand the energy dynamics of reproduction and the evolutionary causes of spatial variation in reproductive traits. I find latitudinal variation in the life history traits of rockfish is adaptive to maximize expected lifetime egg production in different biogeographic regions of the California Current. These regions from north to south differ in seasonality, ocean productivity, and temperature. Strong seasonality in the north favors a single brood reproductive strategy to cope with food scarcity in the late winter that causes an annual period of net energetic losses. Multiple brooding is favored for environments with weaker seasonality as an opportunity to increase annual reproductive output after females obtain an asymptotic size, stop growing, and reallocate energy from growth to reproduction. However, the maximum female size is expected to differ by region and to depend on the mean amount of food in the environment. Therefore, due to weaker seasonality, poorer ocean productivity, and warmer temperatures in the southern region of the California Current, females are expected to be smaller, have small-sized broods, and be less productive compared to females in the north. This is despite the expectation for increased multiple brooding. My dissertation improves the knowledge of how and why spatiotemporal variation in the frequency of reproduction occurs among rockfishes of the California Current Ecosystem. Importantly, phenotypic plasticity in life history traits influences spatiotemporal variation in growth and reproductive output and should be accounted for when considering how future changes in ocean environmental conditions will influence fisheries productivity and population dynamics for these economically important species.