Research

RESEARCH INTERESTS

Cetacean foraging ecology and population structure, climate-prey-predator relationships, marine resource and fisheries management, international marine conservation and policy

RESEARCH METHODS

Stable isotope analysis, predictive habitat modeling, passive acoustics, statistical and spatial modeling, hormone analysis

Research Areas:

Arctic Science Policy

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Integrating scientific knowledge into the formation of policy is always a challenging exercise in translation. In the Arctic, there is an urgent need to accelerate this process as the region undergoes rapid physical and environmental change—at rates faster than the rest of the globe. Arctic governance is adapting to these dramatic changes, but governance decisions will be steered only by the most rigorous and up-to-date scientific understanding if scientists engage in a sustained and consequential manner. For science to play a central role in the formation of robust policies, it must be part of a cyclical, iterative exchange. In the same way that pressing human-health problems require an integrative bench-to-bedside exchange, termed translational research, Arctic scientists must understand policy considerations and engage in the adaptive management stages of policy review and revision, not solely problem description and data delivery.

This work is published in BioScience.

Humpback whale reproduction physiology

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The primary objectives of this study, led by Casey Clark, were as follows: (i) to test the efficacy of blubber progesterone assays as a tool for diagnosing pregnancy in humpback whales (Megaptera novaeangliae); (ii) to estimate the pregnancy rate of humpback whales in Monterey Bay, California; and (iii) to investigate the relationship between stable isotopes and reproductive status of these whales.

Progesterone concentrations of female whales fell into two distinct groups, allowing for diagnostic separation of pregnant and non-pregnant individuals. Pregnancy rate varied between years of the study (48.4%% in 2011 and 18.5% in 2012), but fell within the range of other estimates of reproductive success for this population.

Stable carbon and nitrogen isotope ratios were examined to investigate the impacts of pregnancy on these values. We propose a new theoretical framework to describe the physiological and isotopic changes that occur during the reproductive cycle of this migratory species (Figure above). This frameworks considers the effects of pregnancy on δ15N, resulting from tissue synthesis and reduced excretion of nitrogenous waste, as well as on δ13C through increased mobilization of lipid stores to meet the energetic demands of pregnancy.

This work is published in Conservation Physiology.

Humpback whale foraging responds to ocean climate

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Large, migratory predators are often cited as sentinel species for ecosystem processes and climate related changes, but their utility as indicators is dependent upon an understanding of their response to environmental variability. In this study, we examine humpback whale response to environmental variability through stable isotope analysis of diet over a dynamic twenty year period (1993-2012) in the California Current System (CCS).

The above conceptual diagram displays the proposed relationship between oceanographic forcing, prey abundance and humpback whale foraging. A positive phase of the North Pacific Gyre Oscillation (blue line) is correlated with increased upwelling and more abundant krill populations resulting in lower trophic level humpback whale diets (color bar on right side of diagram and position of whale). As the NPGO switches to a negative phase, upwelling is reduced, krill populations decline while sardine and anchovy populations increase driving the diet of humpback whales to be at a higher trophic level.

This work is published in Global Change Biology.


Dall’s porpoise acoustic-based habitat modeling

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Most information on Dall’s porpoise distribution to date has been collected during visual line-transect surveys. Though they are effective, visual surveys are hindered by inclement weather, rough seas and missed sightings, and are limited to observing animals only at the sea surface.

Passive acoustic surveys provide an alternative means of detecting vocal animals underwater, with less limitations due to poor weather conditions. Using data collected on a 2008 ship-based survey in the California Current, we develop the first habitat-based models of Dall’s porpoise distribution using acoustic detections and compare them to models built with visual data. In addition, we produced a combined model utilizing both methods. The results showed promise for incorporating acoustics into habitat models but also identified important caveats that should be considered in future modeling utilizing acoustic detections.

This work is currently Submitted.


Global review of humpback whales

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In preparation for the NMFS review of humpback whale under the Endangered Species Act, Dr. Jennifer Jackson and I prepared this comprehensive summary on the status of the species in each ocean basin. This report summarizes the distribution, abundance, trends, genetic diversity, habitat requirements, threats and recovery from exploitation for each population.

This work was published as a technical memorandum by NOAA.

 

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