Past Research Overview
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My past research has explored community ecology, population ecology, movement ecology, and reproductive ecology through experiments, natural experiments, empirical studies, and diverse collaborations. Along the way I aimed to develop and hone a broad quantitative skillset and apply my findings to natural resource management and conservation.
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POSTDOCTORAL RESEARCH
Distribution modeling is a key step in defining species-habitat relationships and resolving higher order dynamics such as drivers of abundance, community membership, biodiversity patterns, and ecosystem structure. As such, I perennially return to distribution modeling to take advantage of the advancements, contribute to advancing modeling components, and applying these models to new taxa. Below are a few of my past and ongoing projects.
(Above) An example distribution map for one of the shark species that is caught as bycatch in the Hawaii-based tuna and swordfish pelagic longline fisheries. Warmer colors indicate a higher probability of bycatch.
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Ensemble Random Forests — How can distribution models be built when there are exceptionally few locations where a species is detected? Recent work with the NOAA PIFSC and WPRFMC has lead to the development of the Ensemble Random Forest algorithm to tackle datasets with rare and ultra-rare presences but a host of absences. This machine-learning approach is an intuitive extension to the Random Forests algorithm and has very high performance at predicting where the species is present. Published in Endangered Species Research. This model has been used to model the distribution of rare cetacean species in the Mariana Archipelago and is published in Frontiers in Marine Science.
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Benthic-oriented species -- With marine species associated with structure, it can be difficult to model their fine-scale habitat associates because tradition environmental covariates have little influence (e.g. sea surface temperature or chlorophyll-a) or have poor resolution (e.g. bathymetry). Recent work with the Red Snapper has led to the development of a big-data, high-resolution predictive distribution model for the whole Gulf of Mexico. With this model, I developed camera-based sampling designs for an independent population assessment. Further research will be looking at how the availability and quality of Red Snapper habitat influences angler catch rates.
(Above) The distribution of Red Snapper in the Gulf of Mexico (< 100 m in depth). Warmer colors indicate a higher probability of presence (not abundance). Multiple datasets from NOAA SEFSC, NOAA NOP, FWC FWRI, and NOAA SEAMAP were used to build the Random Forests predictive model that made the above map.
Ph.D. RESEARCH
Most of my PhD research was conducted in four picturesque north Florida lakes located on BJ Bar Ranch. Unlike many Florida lakes, these lakes were relatively deep (23, 20, 19, and 8 feet in maximum depth) and weakly stratified in the winter months. Two of these lakes were augmented by small and large brush piles in nearshore and offshore habitats and all the lakes were monitored before and after the augmentation. The Florida Bass population was tracked in a mark-recapture study as well as the piscine and testudine community was monitored using cameras for a year and half post-augmentation. With over 400 field days on the BJ Bar Ranch, it was hard not to deeply appreciate the opportunity to immerse myself into these rich freshwater habitats as well as be grateful for the access provided by the landowners and funding by FWC FWRI.
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Florida Bass Mark-Recapture — As part of my PhD, I was interested in how the Florida Bass population might respond to habitat augmentation. I took advantage of many students before me tagging individuals with Floy (see the yellow tags in the top video) and PIT tags to track the abundance of Florida Bass in lakes with and without the augmentation. I used day and night electrofishing (see the bottom video) as well as angling to mark new fish and recapture previously tagged individuals with the help of many friends, technicians, and volunteers. I found very little effect on Florida Bass population dynamics following augmentation in the time frame of my study. This was not terribly surprising as the brush piles did little to increase primary productivity in the systems and, thus, did not alleviate the density-dependent bottleneck on young-of-the-year fish.
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Lake Community Dynamics — The most laborious and enjoyable component of the Florida Lake research was conducting camera monitoring of each lake in areas with and without brush piles. With 642 camera surveys completed, 18 terabytes of video, and 9, 575 fish observed, there was a lot to analyze. In my dissertation, I was primarily concerned with changes in the hyper-local community throughout each lake. I observed that brush piles were strong habitat filters overall with the effect exacerbated in the speciose lake. Larger-bodied taxa were more likely to occupy brush piles than small body fish though Bluegill fry and age-0 Florida Bass did occupy the brush piles following spawning season for the respective species. For the analysis, I extended a multilevel occupancy model to a multi-species variant.
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M.S. RESEARCH
(Above) The September distribution of Basking Sharks in the Bay of Fundy. Sharks are concentrated near Grand Manan Island but have started exiting the Bay and heading south into the Gulf of Maine.
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Basking Sharks -- The Bay of Fundy is a hyper-productive gyre system in the Northwest Atlantic and has some of the strongest tidal swings in the world. Intense phytoplankton blooms are grazed heavily by Calanus finmarchicus copepods which, as the bloom wanes, diapause in the deep-waters of the bay, Grand Manan Basin. These sinking, resting copepods form a thick layer of prey that Basking Sharks travel from the warm-waters of the Caribbean to consume. My master's research was concerned with resolving the spatial dynamics of Basking Sharks within the Bay of Fundy over the course of their visiting season (June - October). A maximum entropy distribution model was used to determine the spatial patterns from 23 years of presence-only locations. You can hear more about this research with an interview I did with CBC's Paul Castle in 2013 (on the left).
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Basking shark vertical movement — Before, during, and long after my master's research on the vertical movement of Basking Sharks, a total of 42 sharks have been tagged in the Bay of Fundy with time-depth recorders. Thirteen of these tags ended up in my M.S. thesis examining the vertical movements of basking sharks in the Bay of Fundy. Years later, Dr. Heather Koopman, Dr. Andrew Westgate, Katie Bell, and myself teamed up to combine Katie's and I's M.S. thesis research along with some new analyses I developed to look at all 42 tags from 2008 to 2020. This amazing dataset is one of few to track fine-scale vertical movement of basking sharks and the first in the Bay of Fundy. The oceanic and tidal circulation makes the Bay of Fundy likely unique among basking shark hotspots and correspondingly, we found that sharks are highly plastic in their vertical movement strategies to access the changing landscape of their preferred copepod prey, Calanus finmarchicus, that diapause below 100 m throughout the bay but strongly aggregate in the Grand Manan Basin to the east of Grand Manan island and our base of operations at the Grand Manan Whale and Seabird Research Station.
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Young Zach lining up to tag his first basking shark in 2012. This was a culminating moment on one of the finest basking shark survey days I had during my M.S. In the scene, you can see the iPad we used to record data from our encounter, the archival time-depth-recorder in yellow and red laying on the bow, and, in the distance, the basking shark cruising just below the surface.
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(Above) Temperature profiles aggregated across all the shark tags in a year. 2012 stands out as much warmer from a marine heat wave.
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Basking Sharks as ocean loggers — In addition to the vertical movement of basking sharks, the biotelemetry tags recorded ocean temperature. Led by Dr. Heather Koopman and Dr. Andrew Westgate, I performed an analysis exploring how temperatures in the Bay of Fundy had increased from 2008 to 2012 before falling again in 2013. What was particularly concerning, was this warming was throughout the entire water column and indicated extreme changes in the Bay of Fundy over this time frame. Anecdotally, the extra warm summer of 2012 was incredibly different than year's past with warm-water species moving into the bay in large numbers, such as Blue Sharks, Great White Sharks, Sperm Whales, and Ocean Sunfish. In turn, it was a hard year to find classic Bay of Fundy denizens such as North Atlantic Right Whales and Basking Sharks. Fortunately, over a banter week in late August we managed to tag three sharks and saw over 30.
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B.S. RESEARCH
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American Lobster fecundity — My undergraduate thesis contributed to a larger overall investigation of the reproductive investment of American Lobsters (Homarus americanus) in the Bay of Fundy. We measured fecundity (number of eggs), egg energy content, lipid content, and fatty acid profiles. My part was determining the egg energy content which I did using a bomb calorimeter. This scientific instrument injects pure oxygen into a canister containing a sample of lobster eggs and ignites a fire using a small cotton thread. The resulting burn raises the temperature ever so slightly in the surrounding water bath which is measured precisely and converted to calories. Our results, published in 2015, showed that fecundity was declining in American Lobsters from 2008 to 2013 and that very large lobsters were likely undergoing reproductive senescence, investing less into reproduction than smaller lobsters.
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Reproductive energetics of Blue Crabs -- Between my undergraduate and master's projects, I worked on exploring correlates of reproductive investment, egg energy content, lipid content, fatty acid profiles, and zoea size, in Blue Crabs (Callinectes sapidus). We found none of the investment measurements correlated with female size and, instead, found environmental factors to likely be responsible for the variation in reproductive investment. Our results were published in 2013 in the Journal of Crustacean Biology.
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COLLABORATIONS
I have collaborated with a wide variety of researchers spanning multiple disciplines. One, on modeling the physical maturity using vertebrae fusing of the Common Bottlenose Dolphin (Tursiops tursiops) in the intensely monitored Sarasota Bay population. A second was an analysis of nanomaterial plating types on cellular growth. Both opportunities resulted in development and application of Bayesian techniques to take advantage of the way the data was collected. Other projects included Everglades Stormwater Treatment Area phosphorous dynamics and morphological differences between Common Bottlenose Dolphin ecotypes. In my PhD, I also collaborated on assessing environmental drivers of Black Crappie (Pomoxis nigromaculatus) growth with Dr. Bryan Matthias, on algal bloom dynamics of Lake Okeechobee with the late Dr. Karl Havens, and on pine rockland plant community phylogenetic structure.