Sharks and stress! How does water quality influence capture and handling stress in bull and bonnethead sharks?

Methods

Summary

Field Study Sites and Environmental Measures

This study was conducted as part of a larger project evaluating blood gas analysis to assess capture and handling stress of carcharhinid sharks in three bays (Faka Union, Fakahatchee, and Pumpkin Bays) within the Ten Thousand Islands off the southwest coast of Florida from 2007 to 2011 (Hyatt et al. 2012; 2016).  This project was performed in collaboration with an on-going shark population assessment for waterway mitigation under previously established sampling protocols (Shirley et al. 2005; Steiner et al. 2007).  Each bay was sampled one evening per month, from two hours before until two hours after sunset.  Sampling occurred during all months of the year.  Bay temperature (°C), salinity, and DO (mg/L) were measured once per evening with a handheld multimeter (YSI 85, Yellow Springs Corp., Yellow Springs, OH). 

Shark Capture and Blood Processing

One gillnet and two longlines were utilized at the same location, with the two longlines running parallel to the gillnet, approximately 15 m off each flank.  Longlines consisted of two 10-hook 100 m floating mainlines of 8 mm braided nylon rope anchored at both ends.  Each gangion contained one float while the mainlines, anchored at both ends, had four floats, one at each end and two in the middle.  Gangions were constructed of 1 m of 500 pound test monofilament with 20/0 Mustad circle hooks or 15/0 Mustad circle hooks baited with frozen or fresh mullet (Mugil spp.).  The gillnet was 91.4 m of 12.7 cm stretch mesh 0.57 mm (30 pound test) monofilament anchored at both ends.  The float line had floats every 1.5 m and the lead line had lead weights every 20 cm.  Surface buoys were used at both ends to mark the location of the net.  Gillnets and longlines were monitored continuously atop a nearby anchored houseboat to allow rapid removal of sharks after capture.  Baited longlines were hypothesized to draw sharks into the gillnet.  Movement of surface floats on the gillnet indicated shark capture; workers timestamped each capture event, subsequently boarded an attached 7.6 m outboard motorized mullet skiff, detached from the houseboat, and approached the gillnet to retrieve the shark.  The shark was brought on to the skiff and placed in a 1.5 m diameter plastic pool with continuous flow-through sea water for monitoring, processing, and assisted swimming, if needed.  Immediately upon landing a shark, a blood sample (approximately 1 ml) was obtained via caudal venipuncture using a heparin washed 3 ml syringe and a 22 g 19 mm 0.75 in) or 38 mm (1.5 in) needle (depending on shark size).  The blood draw was also timestamped.  Blood gas analysis was obtained through the use of the i-STAT portable clinical analyzer (Abaxis, Union City, CA) and an i-STAT CG4+ disposable cartridge measuring pH, pCO₂ (mm Hg), and lactate concentration ([lac], mmol/L).  pH and pCO₂ were body temperature corrected automatically by the i-STAT based on measured water temperature as the assumed body temperature input into the analyzer (Abbott Point of Care Inc. 2013a, 2013b).  Blood gas analysis performed on the i-STAT has been validated for use in some sharks at a given temperature to provide reliable results similar to a bench-top analyzer (Gallagher et al. 2010).  However, since the temperature corrections of the i-STAT are based on mammalian conversion factors and constants, the corrections for sharks may not be considered absolute, but can be considered relative corrections allowing for practical application and ease of use in the field setting (Mandelman and Skomal 2009; Brooks et al. 2012).   After blood draw, morphometrics and tagging, sharks were subsequently released.  If during any time a shark that was on the boat was not active, the shark was ram ventilated over the side of the boat while at an idle speed.

Statistical Analysis

There is some controversy in the field regarding the effect of temperature on the measurement and calculation of blood gas analysis parameters, aside from effects that temperature may have on the physiological stress response of the organism.  Dr. Anderson will evaluate the effects of temperature on measurements via graphical analysis and the comparison of regression models; making informed decisions concerning temperature correction equations to employ as guided by results in consultation with the literature.  Then, he will test the normality of data distributions of independent and dependent variables; these results will help the statistician decide if data transformations are required before conducting further analysis; and which type of transformations are appropriate to conduct.  From there, principal components analysis will inform the nature of relationships among both independent and dependent variables in the data set.  Independent variables which are found to be closely related to one another (for example, it’s conceivable that temperature and DO may be tightly inversely related) can guide Dr. Anderson to select the most important variable in the dyad or group for further analysis, or to model principal components which represent combinations of variables.  Finally, the multiple polynomial regression technique will employ the ordinary least squares (OLS) regression technique to fit a polynomial model to the data.  OLS regression equations are modeled by determining the equation that minimizes the sum of the squared distances between the sample’s data points and the values predicted by the equation.  Modeling polynomial effects allows for the examination of possible curvilinear responses of the dependent variables (blood gas analytes) to independent variables (water quality parameters). 

Dissemination

The analytical approach involves a series of dependent and complementary analyses that help the scientists understand a comprehensive picture of the relationships of water quality to the stress response in sharks.  It is in the manuscript to be prepared for publication in a peer-reviewed journal where the scientists will clearly explain the statistical methods used, and where the results will be consolidated and presented in text format with accompanying figures and tables.  The results presented in the manuscript will be a synthesis of the patterns of relationships that have been explored.  The peer-reviewed scientific journal, Journal of Coastal Research, will be targeted for submission. 

Literature Cited

Abbott Point of Care Inc. 2013a. pCO2 and calculated values for HCO3, base excess and anion gap. Article 714182-00P.

Abbott Point of Care Inc. 2013b. pH.  Article 714181-00M.

Brooks, E. J., J. W. Mandelman, K. A. Sloman, S. Liss, A. J. Danylchuk, S. J. Cooke, G. B. Skomal, D. P. Philipp, D. W. Sims, and C. D. Suski. 2012. The physiological response of the Caribbean reef shark (Carcharhinus perezi) to longline capture. Comparative Biochemistry and Physiology, Part A: Molecular & Integrative Physiology 162(2):94-100.

Gallagher, A. J., L. H. Frick, P. G. Bushnell, R. W. Brill, and J. W. Mandelman. 2010. Blood gas, oxygen saturation, pH, and lactate values in elasmobranch blood measured with a commercially available portable clinical analyzer and standard laboratory instruments. Journal of Aquatic Animal Health 22(4):229-234.

Hyatt, M. W., P. A. Anderson, and P. M. O'Donnell. 2016. Behavioral release condition score of bull and bonnethead sharks as a coarse indicator of stress. Journal of Coastal Research (In press).

Hyatt, M. W., P. A. Anderson, P. M. O'Donnell, and I. K. Berzins. 2012. Assessment of acid-base derangements among bonnethead (Sphyrna tiburo), bull (Carcharhinus leucas), and lemon (Negaprion brevirostris) sharks from gillnet and longline capture and handling methods. Comparative Biochemistry and Physiology, Part A: Molecular & Integrative Physiology 162(2):113-120.

Mandelman, J. W., and G. B. Skomal. 2009. Differential sensitivity to capture stress assessed by blood acid–base status in five carcharhinid sharks. Journal of Comparative Physiology B Biochemical Systemic and Environmental Physiology 179(3):267-277.

Shirley, M., P. O'Donnell, V. McGee, and T. Jones. 2005. Nekton species composition as a biological indicator of altered freshwater inflow into estuaries. Pages 351-364 in S. A. Bortone, editor. Estuarine Indicators. CRC Press, Boca Raton.

Steiner, P. A., M. Michel, and P. M. O'Donnell. 2007. Notes on the occurrence and distribution of elasmobranchs in the Ten Thousand Islands estuary, Florida. American Fisheries Society Symposium 50:237-250.