Blood biochemical status of deep-sea sharks following longline capture in the Gulf of Mexico

Abstract

Prior to the Deepwater Horizon (DWH) oil spill, little research effort was focused on studying deep-sea sharks in the Gulf of Mexico (GoM). While the biology of these fishes remains virtually unknown, they are routinely captured in commercial fisheries as bycatch. In the absence of basic biological data, and with the probability of post-release survival unknown for most species, effective management plans cannot be formulated, making populations highly susceptible to overfishing. Any potential detrimental effects of the DWH oil spill, which occurred at 1500 m deep, are also unknown. Following longline capture, we characterized the physiological blood biochemical parameters related to secondary stress and compared them among seven shark species occurring on the continental shelf edge and slope in the GoM at depths ranging from 200 to 2000 m. We also investigated the relationship between blood parameters and depth as well as proximity to the oil spill site. The deep-sea sharks examined here exhibited variability in blood chemistry associated with the secondary stress response, with values falling within published records for previously studied elasmobranchs. Results suggested that there is greater relative physiological stress in shallower-dwelling sharks as well as smaller-bodied sharks. Further, the rate of core temperature warming was fastest in smaller bodied sharks, which likely contributes to greater physiological stress. The core temperatures of the larger-bodied, deeper-dwelling species were not altered as drastically as the smaller-bodied sharks after being hauled to the surface. Any chronic physiological effects of the oil spill were not detectable as there were no relevant correlations between blood chemistry metrics and proximity to the DWH oil spill site.

Keywords: Stress; elasmobranch; oil spill.

Figure 1

Map highlighting the locations of the fixed survey stations that were sampled during each research cruise, each black dot represents a station that was sampled during the larger survey, while the stations circled in red were locations where samples were collected for this study. The location of the DWH Macondo Wellhead is indicated by a black square with a red arrow.

Figure 2

Box plots of (A) total length (cm) and (B) depth (m) of capture of M. sinusmexicanus (MSIN), M. canis (MCAN), S. cubensis (SCUB), S. clarkae (SCLA), C. uyato (CUYA), C. granulosus (CGRA) and H. griseus (HGRI), letters above bars indicate significant pairwise differences within each plot.

Figure 3

Mean (± SE) of the at-vessel blood chemistry parameters (A) glucose (mmol l⁻¹), (B) lactate (mmol l⁻¹), (C) pH, (D) potassium (mmol l⁻¹) and (E) hematocrit (%) of longline-captured M. sinusmexicanus (MSIN), M. canis (MCAN), S. cubensis (SCUB), S. clarkae (SCLA), C. uyato (CUYA), C. granulosus (CGRA) and H. griseus (HGRI), letters indicate significant pairwise differences within each plot.