Thesis Defense by Jen Chiu – August 17th, 2018

Diets and stable isotope signatures of Yellowtail Rockfish (Sebastes flavidus) in central California

A Thesis Defense by Jen Chiu

Fisheries & Conservation Biology Lab

Friday, August 17th, 2018 at 12pm

MLML Seminar Room

Jen Chiu is a Master’s student under Dr. Rick Starr in the Fisheries and Conservation Biology Lab.  She graduated from the University of California, Santa Barbara with a B.S. in Ecology and Evolution and a minor in Asian American Studies.  During her time at UCSB, she assisted with research focusing on the non-consumptive effects of predators on prey in the intertidal zone, coupled with the effects of climate change and habitat complexity.  Prior to beginning her graduate work at MLML, she assisted with fisheries ecology research in the Gulf of Mexico, as well as studied the distribution and biomass of benthic invertebrates in the San Francisco Bay.  In addition to her conducting her thesis work, Jen has been a part of the California Collaborative Fisheries Research Program (CCFRP) throughout her entire time at MLML.  She currently serves as the Lead Field Scientist for MLML and the Statewide Coordinator for the program, where she is responsible for managing the MPA monitoring efforts of all academic partners across the state.  She plans to continue her involvement with CCFRP after her defense.

Thesis Abstract:

Studies of fish diets can be used to improve the understanding of feeding habits, trophic distributions, and the predatory role of a species in an ecosystem.  Identifying the spatial and temporal variability in the diets of fishes can provide useful information for stock assessments and fisheries management. Yellowtail Rockfish (Sebastes flavidus) are an important part of the U.S. west-coast commercial groundfish fishery, and abundant along the central California coast.  The most recent studies of Yellowtail Rockfish diets occurred over 20 years ago and originated primarily from studies in Oregon and Washington.  To provide more current information on trophic ecology from California, I examined the food habits of Yellowtail Rockfish collected near Cordell Bank, the Farallon Islands, and Half Moon Bay in 2013 and 2014 using gut content and stable isotope analyses. Yellowtail Rockfish analyzed in this study were semi-pelagic predators, feeding primarily on tunicates, crustaceans, and teleosts.  Based on δ15N values, fish caught in 2013, on average, were feeding at lower trophic levels than those caught in 2014.  δ13C values indicated that fish caught at the northern-most sites were feeding on more pelagic-influenced carbon sources, while those caught at the southern-most sites were feeding on more benthic-influenced carbon sources.  Yellowtail Rockfish in central California can be described as opportunistic feeders because predation patterns were temporally localized, and diets consisted mostly of transitory prey sources.  The Yellowtail Rockfish diet information presented in this study fills data gaps of a key life history component, and will be useful for future stock assessments.

Watch Jen Chiu’s Thesis Defense below:

Thesis Defense by Evan Mattiasen – June 6th, 2018

Effects Of Hypoxia on the behavior and physiology of juvenile state temperate reef fishes (genus: Sebastes)

A Thesis Defense by Evan Mattiasen

Ichthyology Lab

Wednesday, June 6th, 2018 at 4pm

MLML Seminar Room

Thesis Abstract:

The progression of climate change is predicted to cause large-scale changes to ocean chemistry (i.e., shifts in temperatures, salinity, ocean acidification, etc.) within the California Current. Forecasts from climate models and oceanographic observations indicate an increase in the frequency and duration of hypoxic events in the coastal zone, which have the potential to affect marine biodiversity and fisheries. Many studies have shown that exposure to extreme low dissolved oxygen (pO2) conditions can have deleterious effects on fish in early life stages, such as inhibition to growth and reproduction. Rockfish (Sebastes spp.) are a diverse group of species composed of fishes with varying life history characteristics. This study aims to determine how exposure of two species of young-of-the-year (YOY) juvenile rockfishes will perform under chronic exposure to varying dissolved oxygen levels. Copper rockfish (Sebastes caurinus) and Blue rockfish (Sebastes mystinus) are two closely related species that differ in early life history traits. Copper rockfish have a short pelagic duration that begins with parturition in the spring and ends with recruitment to the kelp forest canopy after 1-2 months. Blue rockfish have a longer pelagic duration that begins in the winter and ends with recruitment to the benthic kelp forest habitat after 3-6 months. I compared how behavior and physiology were affected under chronic exposure to low pO2 at four treatment levels (ambient = 9.0 mg O2 L-1, moderate = 6.0 mg O2 L-1, low = 4.0 mg O2 L-1, hypoxic = 2.0 mg O2 L-1). Behavioral tests were aimed at identifying changes in exploratory behavior (i.e., escape response trial), predator detection through olfactory perception (i.e., olfactory choice test), and changes in turning preference (i.e., behavioral lateralization). Physiological tests focused on determining changes in hypoxia tolerance (critical oxygen tension, pCrit), the capacity for aerobic activity (i.e., aerobic scope), and ventilation rates. Changes in growth rates of both species were also measured. The findings of this study indicate that both species express sensitivity to low pO2; however, the strength of the response differed between species. Copper rockfish exhibited decreased growth rates and reduced absolute lateralization following chronic exposure to the lowest oxygen levels. Behavioral tests did not differ with treatment for blue rockfish. Additionally, growth rates for Blue rockfish followed the opposite trend of Copper rockfish where individuals in the lowest oxygen treatment grew more than those in the control treatment. Both species exhibited decreases in aerobic scope and increases in ventilation rates with decreasing oxygen levels. Copper rockfish had a lower tolerance of hypoxia and weaker acclimation response compared to Blue rockfish as measured by critical oxygen tension threshold (pCrit). A lower pCrit for fish exposed to low oxygen conditions indicates the potential for acclimation to those conditions. Despite the physiological changes that occurred for both species in low oxygen conditions, these results provide evidence of acclimation to chronic hypoxia. Species with a greater capacity for acclimatization are potentially those with life history characteristics where larvae/juveniles have a higher probability of exposure to low oxygen conditions, leading to either acclimatization in the field or pre-adaptation to hypoxia over multiple generations. The differences expressed by each species suggest that acclimatization to changing ocean conditions may vary across closely related species, leading to winners and losers under future ocean conditions. Overall, increases in strength and frequency of coastal hypoxia events may have severe impacts on juvenile stage rockfishes that reside in kelp forests. While this study highlights adaptations to low oxygen, extended exposure to hypoxia decreased fitness of individuals through metabolic and aerobic depression, and changes to behavior. The information gathered in this study is critical for advancing the understanding of how these economically valuable species will fair in the future, and the information presented here will help inform policy makers to protect populations at risk.

Watch Evan Mattiasen’s Thesis Defense below: