Six students defend thesis research this spring 2019

By June ShresthaIchthyology Lab.

I’m happy to share that we’ve had six students defend their theses thus far in 2019! Please join me in congratulating the students, and read below to learn a little more about their research.

  • Jessica Jang, Pacific Shark Research Center
  • Melissa Nehmens, Pacific Shark Research Center
  • Stephen Pang, Ichthyology Lab
  • Patrick Daniel, Physical Oceanography
  • Heather Barrett, Vertebrate Ecology
  • Sierra Helmann, Biological Oceanography

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Jessica Jang

Pacific Shark Research Center

Reproductive Strategies of the Big Skate (Beringraja binoculata, Girard 1855) with evidence of multiple paternity.

Jessica Jang

  • Jessica collected Big Skate egg cases from California to Washington and looked at whether Big Skate egg cases size dimension and embryo numbers differed in captive and wild populations.
  • Captive population had smaller egg cases and less embryos per egg case compared to the wild. Embryos in captivity were much smaller than from the wild. Big Skate egg cases sizes and embryo numbers peaked at 42 degrees north, suggesting that area is the most prolific due to upwelling conditions.
  • Big Skates are one of two species of the 300+ known skates that exhibit multiple embryos within in an egg case. Using genetics, Jessica found that several males may sire within an egg case and female Big Skates can store sperm with a minimum of 3 months.

Melissa Nehmens

Pacific Shark Research Center

Life History of the Southern Lanternshark, Etmopterus granulosus, from the Southwestern Indian Ocean

Melissa Nehmens

  • Melissa used microsatellite markers to look at reproductive and population genetics of the Southern Lanternshark, Etmopterus granulosus. Interestingly, she found that the Southern Lanternshark does not fit preconceived paradigms about elasmobranchs and reaffirms that life history studies need to be conducted to avoid inaccurate assumptions.
  • She found that monogamy is the predominant mating system with a frequency of polyandry at 33%, suggesting the mating system is likely dynamic, and based on what is most beneficial at a given time
  • As a species that is frequently caught as bycatch, it would be expected that the population would be in a numerical decline and be reducing in genetic diversity. Though little data is available to numerically assess Southern Lanternshark, the genetics do not show a reduction in genetic diversity.
  • She also examined telomere length in different age classes to determine if telomeres shorten with relation to individual size. This method was used to see if this could potentially push traditional ageing studies away from chronological age to a biological age.

Stephen Pang

Ichthyology Lab

The effect of sex ratio on the reproductive biology of two sex changing fish (Lythrypnus dalli and Rhinogobiops nicholsii)

Stephen Pang

  • Stephen examined how size-selective fishing (i.e., targeting the largest individuals in a population) impacts the reproductive output of protogynous hermaphrodites. These species change sex from female-to-male so this size-selective tendency is also sex-selective since it preferentially removes males from the population. This is predicted to lead to male limitation.
  • He used bluebanded and blackeye gobies as model species in the hopes that he’d be able to scale my results up to more recreationally- and commerically-important fishes
  • He found that male limitation is not present in either species. Despite previous modeling work predicting sperm limitation, that work has mostly revolved around aggregate spawning species. Stephen thinks that he may not have seen sperm depletion/limitation in bluebanded or blackeye gobies due to their pair spawning mating strategy
  • Stephen concluded that populations of protogynous hermaphrodites need to be managed holistically and need to take into account things like intrasexual competition, mate choice, and other components of their mating system

Patrick Daniel

Physical Oceanography Lab

Contributions of wind- and wave-induced transport to nearshore phytoplankton variability in Northern California

Patrick Daniel
  • Off of the Bodega Headland in Northern California, the abundance of nearshore phytoplankton can increase rapidly at rates faster than would be explained by growth and are correlated with increases in offshore wave height. Patrick analyzed a a 5-year time series of intertidal chlorophyll data in order to explain the physical drivers responsible for the high frequency variability.
  • He found that upwelling alone doesn’t explain the events, as the increases in offshore equatorial winds occurred simultaneously with increases in nearshore phytoplankton. Instead, phytoplankton abundance was correlated with increases in Stokes drift, a wave-induced surface transport.
  • The timing of events suggests that Stokes drift is reinforced by alongshore winds, which impart energy to the wave spectrum, resulting in strong onshore transport of phytoplankton to the nearshore during periods of high wave energy.

Heather Barrett

Vertebrate Ecology Lab

The energetic cost of human disturbance on the southern sea otter (Enhydra lutris nereis)”

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  • Heather collaborated with Sea Otter Savvy to investigate the energetic cost of human disturbance to the southern sea otter (Enhydra lutris nereis). Human disturbance to wildlife is a growing concern in conservation policy and management. As outdoor recreation increases there is a consequent rise in human-wildlife encounters. Thus, linking behavioral response to the energetic cost of the response could further our understanding of the true cost of the disturbance, and provide sound scientific basis for management. This is particularly a concern for sea otters due to their high metabolic costs, sensitive energetic budget, and threatened status.
  • The project objectives were to use a newly developed Hidden Markov Model used to predict sea otter activity to determine the:
    • 1) Frequency and severity of human disturbance to sea otters in California;
    • 2) Factors that influence sea otter response and vulnerability to disturbance (i.e. pup presence, kelp canopy, group size, and time of day);
    • 3) Daily energetic cost due to human disturbance using specific disturbance scenarios.
  • Heather found that the degree of activity change due to human disturbance is specific to location and stimulus distance. The closer to a sea otter, the potential for disturbance increased exponentially. She also determined that kelp canopy and group size increase the likelihood of sea otters resting, thus increasing their vulnerability to increased activity due to a disturbance (i.e. resting otters are at higher risk to increase activity). Daily energetic costs were estimated (using previously recorded metabolic rates) and also supported that the energetic cost increases when stimuli are closer.
  • In conclusion, disturbance to sea otters has an energetic cost, and the model is a useful tool that can provide quantifiable viewing distances or disturbance thresholds to inform management and policy decisions.

Sierra Helmann

Biological Oceanography Lab

Resolution of the Chlorophyllide a Problem in the Routine Measurement of Chlorophyll a

Sierra Helmann


Congratulations to all that defended this spring, and stay tuned to hear who defends this summer/fall!

In the mean time, catch up on the research from students that defended in 2018 fall2018 spring/summer, 2017, and 2016

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