Abstract

The threats from human interaction with cetaceans within their habitats are well-known and documented worldwide.¹ Fishery interaction is considered as the most subtle and varied form of human interaction, with by-catch of small cetaceans as a very significant, if not the dominant, factor in the present management of some fisheries.² Identifying by-catch as the cause of death in cetaceans is challenging and often arbitrary,³ although studies described drowning as causing acute death of entangled cetaceans. Drowning was suggested by histopathological findings from the lungs; severe edema within alveolar spaces, rupture of alveolar walls and myosphincter of the bronchiole, combined with intra-alveolar hemorrhages, indicating death during by-catch.⁴ In human forensic medicine, typical findings in the drowning victims are well documented,^5,6,7 using conventional autopsy and virtopsy. In postmortem computed tomography (PMCT) examination of drowning cases, the findings of fluid accumulation in paranasal sinuses, frothy fluid in airways, pulmonary mosaic patterns of emphysema aquosum, hemodilution, pleural effusion of pulmonary edema can be directly demonstrated. PMCT has emerged as an effective imaging technique to augment conventional necropsy procedures in stranded cetaceans.⁸ To the best of our knowledge, the formal literature is devoid of any reference to PMCT findings in by-catch cetaceans. The study aimed to describe the PMCT findings of by-catch finless porpoises (FP) in the Bohai sea and Yangtze river.

Whole body PMCT examinations were performed in 57 by-catch FPs, Neophocaena phocaenoides and Neophocaena asiaeorientalis ssp. asiaeorientalis (29 males, 26 females, 2 unknown sex; calf to adult; 73–205 cm in length), in the Bohai sea and Yangtze river. Two FPs (Neophocaena phocaenoides), 2 Indo-Pacific humpbacked dolphin (Sousa chinensis) and an Indo-Pacific bottlenose dolphin (Tursiops aduncus) (2 males, 3 females; calf to adult; 82–250 cm in length) stranded in the Hong Kong waters were also underwent whole body PMCT with identical protocol as control. All carcasses condition was code 2. PMCT was performed on a Somatom Definition 64 slices Dual Energy CT system (n=57) or a 16-slice multi-detector row Toshiba Alexion^TM CT system (n=5).

Hounsfield unit (HU) values of content in air sinuses, respiratory tract, pleural fluid, blood in heart, spleen and liver were recorded. Volume estimation of content in air sinuses and respiratory tract were evaluated. Lung PMCT pattern and its localization were assessed. All measured variables used in the present study were adopted and modified from the study by Plaetsen et al.^7,9,10 The mean of HU values of content and volume of content in aforesaid anatomical locations in both by-catch and control group FP were cross-compared using Mann-Whitney U test (GraphPad InStat, GraphPad Software, Inc., San Diego, CA, USA). A p value <0.05 is considered as statistically significant.

Summarized results of HU values of content in aforesaid anatomical locations were presented in Table 1. Significantly higher HU values were recorded in ophthalmic sinus and peribullary sinus in the by-catch group, which might indicate fluid accumulation. Significantly lower HU values of blood in left atrium, right atrium, left ventricle and right ventricle, ascending aorta and descending aorta; and significantly lower attenuation of liver were recorded in in the by-catch group, which might indicate hemodilution.⁷ There was no significant difference in volume of content at air sinuses and respiratory tract between both groups.

Table 1. Summary of mean HU values of content in various anatomical locations, with asterisk (*) represented p<0.05, evidencing a statistical significant difference between by-catch and control group

Mosaic pattern (n=9; 16%) in lungs was identified in by-catch group only; whereas ground glass opacity (GGO) in lungs was identified in both by-catch group (n=39; 68%) and control group (n=1; 20%). Mosaic pattern could be resulted by nonuniform distribution of hypoperfused and hyperperfused areas, which might be due to multifocally scattering of aspirated water throughout the lung, hence considered as a specific finding for by-catch group. GGO could be resulted in diverse conditions, when decreases in air content occurred in lung parenchyma without totally obliterating the alveoli,⁵ hence considered as a nonspecific finding for by-catch group. PMCT provides an objective and distributable documentation of the by-catch cetacean full body in a non-invasive way, which facilitates the direct detection of hemodilution and water in the air sinuses that is rather complicated or impossible at the conventional necropsy. In conclusion, PMCT performed prior to conventional necropsy is a useful visualization and documentation tool in understanding the drowning pathophysiology in by-catch cetaceans, and possibly diagnosing death in by-catch cetaceans associated with drowning.

Acknowledgements

The authors would like to thank the Institute of Hydrobiology, Chinese Academy of Sciences and Agriculture, Fisheries and Conservation Department of the Hong Kong SAR Government for the continuous support in this project. Sincere appreciation is also extended to veterinarians, staff and volunteers from Ocean Park Hong Kong, Ocean Park Conservation Foundation Hong Kong, Institute of Hydrobiology, Chinese Academy of Sciences, and Tung Wah College for paying great effort on the stranding response and necropsy in this project. Special gratitude is owed to technicians from Zhong Nan Hospital of Wuhan University and Hong Kong Veterinary Imaging Center for operating the CT for this research.

* Presenting author
+ Student presenter

Literatures Cited

1.  Moore KT, Barco SG. 2013. Handbook for recognizing, evaluating, and documenting human interaction in stranded cetaceans and pinnipeds. U.S. Department of Commerce, NOAA Technical Memorandum, NOAA-TM-NMFSSWFSC-510, 102p.

2.  Hall MA, Alverson DL, Metuzals KI. 2000. By-catch: problems and solutions. Mar Pollut Bull. 41:204–219.

3.  Osinga N, Morick D. 2008. By-catch and drowning in harbour porpoises (Phocoena phocoena) stranded on the northern Dutch coast. Eur J Wildl Res. 54:667–674.

4.  Knieriem A, Hartmann MG. 2001. Comparative histopathology of lungs from by-caught Atlantic white-sided dolphins (Leucopleurus acutus). Aquat Mamm. 27:73–81.

5.  Christe A, Aghayev E, Jackowski C, Thali MJ, Vock P. 2007. Drowning-post-mortem imaging findings by computed tomography. Eur Radiol. 18:283–290.

6.  Levy AD, Harcke HT, Getz JM, Mallak CT, Caruso JL, Pearse L, Frazier AA, Galvin JR. 2007. Virtual utopsy: two- and three-dimensional multidetector CT findings in drowning with autopsy comparison. Radiology. 243:862–868.

7.  Plaetsen SV, De Letter E, Piette M, Van Parys G, Casselman JW, Verstraete K. 2015. Post-mortem evaluation of drowning with whole body CT. Forensic Sci Int. 249:35–41.

8.  Kot BCW, Fernando N, Gendron S, Heng HG, Martelli P. 2016. The virtopsy approach: bridging necroscopic and radiological data for death investigation of stranded cetaceans in the Hong Kong waters. Proceeding of 47th International Association for Aquatic Animal Medicine. Virginia Beach, VA, USA.

9.  Alonso-Farré JM, Gonzalo-Orden M, Barreiro-Vázquez JD, Ajenjo JM, Barreiro-Lois A, Llarena-Reino M, Degollada E. 2014. Cross-sectional anatomy, computed tomography and magnetic resonance imaging of the thoracic region of common dolphin (Delphinus delphis) and striped dolphin (Stenella coeruleoalba). Anat Histol Embryol. 43:221–229.

10. Alonso-Farré JM, Gonzalo-Orden M, Barreiro-Vázquez JD, Barreiro-Lois A, André M, Morell M, Llarena-Reino M, Monreal-Pawlowsky T, Degollada E. 2015. Cross-sectional anatomy, computed tomography and magnetic resonance imaging of the head of common dolphin (Delphinus delphis) and striped dolphin (Stenella coeruleoalba). Anat Histol Embryol. 44:13–21.