From Landlocked to Longlining: A Summer with Sharks Puts Stress into Perspective

Claire E. Robinson Department of Biology, Tennessee Technological University, 1 William L Jones Drive, Cookeville, TN 38505. E-mail: [email protected]

A Great Hammerhead Shark Sphyrna mokarran captured by longlining. Photo Credit: GCRL.

A Great Hammerhead Shark Sphyrna mokarran captured by longlining.
Photo Credit: GCRL.

Research experience can powerfully ignite students’ curiosity, expose them to potential career paths, and ultimately prepare them for the world of science. Unfortunately, as a biology undergraduate with a strong passion for marine science in the landlocked state of Tennessee, it is difficult to apply my education and gain practical field experience. However, thanks to the Summer Field Program at the University of Southern Mississippi’s Gulf Coast Research Laboratory (GCRL) in Ocean Springs, Mississippi, I was able to get my feet wet. In the summer of 2014, I participated in a long-line survey research project concerning the Atlantic Sharpnose Shark Rhizoprionodon terraenovae with my Elasmobranch Biology class. The project aimed at understanding certain physiological parameters relating to stress. The research we conducted was incredibly fascinating. However, this study was just a small part of the course. We spent plenty of time in the classroom and lab learning about anatomy, taxonomy, ecology, behavior, etc. Throughout the four-week class, we jetted out to sea multiple times to try our luck at catching sharks.
Measuring an Atlantic Sharpnose Shark Rhizoprionodon terraenovae captured by longlining. Photo Credit: GCRL.

Measuring an Atlantic Sharpnose Shark Rhizoprionodon terraenovae captured by longlining. Photo Credit: GCRL.

From our fieldwork, we caught multiple species, including Atlantic Sharpnose Shark, Blacktip Shark Carcharhinus limbatus, Great Hammerhead Shark Sphyrna mokarran, and even Bull Shark C. leucas. We used a one-mile longline, bearing 100 circle hooks baited with mackerel, deployed for one hour. At the midpoint of the longline, we measured water quality parameters (e.g., dissolved oxygen, temperature, salinity). Individual captured sharks were measured, weighed, and tagged before release. We also extracted blood from a subsample of 14 male R. terraenovae individuals for hematological analyses of lactate and glucose levels. The lactate and glucose levels, along with the rest of the data collected, were utilized for further individual interpretation. Using these hematological measurements, we observed correlations between the lactate and glucose levels that varied according to the length and mass of the individuals. Overall, larger individuals had higher lactate levels and lower glucose levels in their bloodstream. The process we were measuring was stress-induced anaerobic glycolysis. Stress-induced anaerobic glycolysis occurs when glycogen is used in white muscle cells to produce adenosine triphosphate in the absence of oxygen. Lactate production is catalyzed when this occurs (Klimley 2013). Over time, lactate production and buildup can cause severe health issues, including blood acidosis (Skomal 2007; Frick et al. 2012). Stress-inducing events such as reproduction, long-line capture, and predation can cause this phenomenon to occur. Our results indicated a positive correlation between body size and lactate levels. From these data, we inferred that the larger individuals were on average older than the smaller ones, suggesting lactate buildup over time. Older individuals have had more time to experience stressful encounters, perhaps causing their bodies to accumulate lactate more than younger, less experienced individuals. Lactate accumulation in some species of large pelagic fishes can cause negative long-term effects such as internal physical trauma, homeostatic disruptions, and abnormal physiological function (Skomal 2007). Long-line and rod-and-reel capture can negatively affect sharks’ health, causing them to undergo stress and expend considerable energy during capture and handling. Reducing stress is paramount in minimizing lactate accumulation; however, recreational and commercial shark fishing is a part of human culture worldwide. Recent research suggests that we are contributing to the demise of several elasmobranch species, not only in this way, but also in many other ways: shark fin soup, tourism, habitat degradation and loss, and bycatch (Dulvy et al. 2014). My class members collaborated to brainstorm unique interpretations of the data. The project gave us experience out in the field as well as at our computers, where we learned the meticulous process of scientific writing. Most of all, it gave us the freedom to explore the various ranges of data interpretation from research. The class and the people I worked alongside throughout last summer impacted me in a profound way. It firmly reassured me that marine biology was the path for me. More than anything else, I gained a priceless perspective on the coast that I would not have gotten otherwise in Tennessee. The memories of my charmingly geeky coastal summer will forever be some of my favorites: full of stress, yet full of excitement; full of seasickness (unfortunately), yet full of discovery. I implore any aquatic biology fanatic to explore their options on further education outside of their home institution. It’s your education; take control of it. Broadening your scientific experiences beyond the classroom and beyond your backyard can only be beneficial for you as a fledgling scientist in this field. As for me, I am here in Ocean Springs again this summer as an intern, broadening my horizons and developing connections far away from my landlocked home. So let me ask you: what are you doing next summer? REFERENCES Dulvy, N. K., S. L. Fowler, J. A. Musick, R. D. Cavanagh, P. M. Kyne, L. R. Harrison, J. K. Carlson, L. N. K. Davidson, S. V. Fordham, M. P. Francis, C. M. Pollock, C. A. Simpfendorfer, G. H. Burgess, K. E. Carpenter, L. J. V. Compagno, D. A. Ebert, C. Gibson, M. R. Heupel, S. R. Livingstone, J. C. Sanciangco, J. D. Stevens, S. Valenti, and W. T. White. 2014. Extinction risk and conservation of the world’s sharks and rays. eLife. DOI: 10.7554/eLife.00590. Frick, L. H., T. I. Walker, and R. D. Reina. 2012. Immediate and delayed effects of gill-net capture on acid–base balance and intramuscular lactate concentration of Gummy Sharks, Mustelus antarcticus. Comparative Biochemistry and Physiology 162A:88–93. Klimley, A. P. 2013. The biology of sharks and rays. The University of Chicago Press, Chicago. Skomal, G. B. 2007. Evaluating the physiological and physical consequences of capture on post-release survivorship in large pelagic fishes. Fisheries Management and Ecology 14:81–89.