It is important to understand what animals eat for many reasons; for example, we can’t accurately predict population dynamics without understanding who eats how much of what and when. If animals were people, we could just ask them what they were eating. Instead, we have to discern trophic habits in other ways. I use chemical tracers – including bulk stable isotope ratios and fatty acid profiles – to elucidate feeding habits of aquatic macro-organisms.

In my first dissertation chapter, I used carbon and nitrogen stable isotopes to quantify spatial and temporal trophic variability in the fish community in Lake Hövsgöl in northern Mongolia.  Lake Hövsgöl is the nineteenth largest lake in the world by volume, and characterized by a low degree of human impact: it is subject to limited commercial and recreational fishing and minimal development.  I found that pelagic fish in this system demonstrated more carbon isotopic variability than did benthic fish and that spatial variability generally exceeded temporal (interannual) variability. Interestingly, the isotopic variability observed in this system was generally larger than that observed in comparable systems.

In my second chapter, I compared stomach contents data (which provide a short-term snapshot of what an animal has eaten recently) with carbon and nitrogen stable isotope and fatty acid data (which provide longer-term diet information) to assess individual diet specialization in three highly mobile pelagic predators: striped marlin (Kajikia audax), blue marlin (Makaira nigricans) and dolphinfish (Coryphaena hippurus).  I found that individuals of these species did not demonstrate individual diet specialization, perhaps because their mobile habits meant that they were subject to less density-dependent competition than other more stationary species.

In my final dissertation chapter, I used carbon, nitrogen, and sulfur stable isotope ratios to assess the trophic niche of sea nettle jellyfish (Chrysaora quinquecirrha) and ctenophores (Mnemiopsis leidyi) in Barnegat Bay, NJ.  I found that the sea nettles are likely intraguild predators, consuming both zooplankton and ctenophores, but that their presence did not dramatically change the food web dynamics.T.

Publications

T Young, J Pincin, P Neubauer, S Ortega-García, OP Jensen. 2018. Investigating diet patterns of highly mobile marine predators using stomach contents, stable isotope, and fatty acid analyses. ICES J Marine Science 75(5), 1583–1590. doi:10.1093/icesjms/fsy025. [link]

T Young, O Jensen, B Weidel, S Chandra. 2015. Natural trophic variability in a large, oligotrophic, near-pristine lake.  Journal of Great Lakes Research 41(2): 463-472. [pdf] [cover photo]

Presentations

6th International Billfish Symposium, Dania Beach, FL, Sep 2016, Poster: “Do highly mobile predators demonstrate individual diet specialization?” (T Young, S Ortega-Garcia (presenter), J Pincin, P Neubauer, O Jensen)

American Fisheries Society, 145^th Annual Meeting, Portland, OR, Aug 2015, Poster: “Are striped marlin ‘true’ generalists? A three-pronged approach” (T Young, J Pincin, S Ortega-García, P Neubauer, O Jensen)

Ecological Society of America, 100^th Annual Meeting, Baltimore, MD            Aug 2015, Oral presentation: “Individual diet specialization in striped marlin”
(T Young, J Pincin, S Ortega-García, P Neubauer, O Jensen)

5th International Billfish Symposium, Taipei, Taiwan Oct 2013, Poster: “Investigating seasonal diet variation in striped marlin (Kajikia audax) using three complementary methods” (T Young, S Ortega-Garcia (presenter), J Pincin, O Jensen)

Manasquan River Marlin & Tuna Club, Annual Spring Kick-Off Dinner, Brick, NJ, April 2012, Poster: “From sardines to sportfishing: Using stable isotope and fatty acid analysis to better understand tradeoffs between commercial and recreational fisheries in Magdalena Bay, Mexico” (T Young, S Ortega-Garcia, J Pincin, O Jensen)

American Council for Mongolian Studies, 2014 Annual Meeting, Philadelphia, PA, March 2014, Poster: “Trophic variability in a simple, pristine lake: What are the implications for studying change in other lakes?”  (T. Young, B. Weidel, S. Chandra, O. Jensen)

Ocean Sciences, 2014 Meeting, Honolulu, HI, February 2014, Poster: “Trophic variability in a simple, pristine lake: What are the implications for studying change in other lakes?”  (T. Young, B. Weidel, S. Chandra, O. Jensen)

Society for Conservation Biology, 26^th International Congress, Baltimore, MD, July 2013, Poster “Trophic variability in a simple, pristine lake: What are the implications for studying change in other lakes?”  (T. Young, B. Weidel, S. Chandra, O. Jensen)

American Fisheries Society, 142^nd Annual Meeting, St. Paul, MN, August 2012, Oral presentation: “Interannual trophic variability in a pristine north temperate lake” (T. Young, O. Jensen, B. Weidel, S. Chandra)

Ecological Society of America, 97^th Annual Meeting, Portland, OR, August 2012, Oral presentation: “Interannual trophic variability in a pristine north temperate lake” (T. Young, O. Jensen, B. Weidel, S. Chandra)

Mongolia Ecological Research Symposium, Tuckerton, NJ, February 2012, Oral presentation: “Making connections: Examining trophic relationships in a pristine Mongolian lake with high school students in Philadelphia using stable isotope analysis” (T. Young, M. Brickle, M. Clark, O. Handoko, A. Huynh, A. Nguyen, A. Nguyen, A. Lam, D. Lewis, N. Marsico, M. Muhammad, S. Small, K. Wint)