Physiological stress in the smalltooth sawfish: effects of ontogeny, capture method, and habitat quality

Abstract

Similar to other elasmobranchs, the smalltooth sawfish Pristis pectinata is slow growing, matures late in life, and produces relatively few young, all factors that have contributed to its sensitivity to dramatic population declines from overfishing and habitat loss. Currently, the physiological stress response of these fish to capture or to other physiological challenges such as habitat loss, climatic changes, or pollution is unknown. In the absence of these data, conservation plans may be less effective, making populations susceptible to further declines. We examined basic stress physiology over ontogeny and as a function of capture using different fishing gears. We also examined stress parameters to test whether degraded habitat and water quality from altered habitats may have resulted in chronic stress in juveniles. Results suggested that the stress response to capture by all methods was low, particularly for blood lactate, compared to other elasmobranchs examined to date. Metabolic stress was found to change over ontogeny, with young of the year (YOY) eliciting the highest responses. Glucose, pCO 2 , bicarbonate, potassium, and hematocrit indicated that gillnet capture induced greater stress responses than longline capture. Significantly higher metabolic stress was observed in YOY and juveniles captured in the 2 nurseries most influenced by anthropogenic activities, the Peace and Caloosahatchee rivers, than in the 2 relatively pristine nurseries in Everglades National Park. Overall, the low physiological stress responses to all capture methods investigated in this study suggest that this species is resilient, which should promote optimism for recovery of the population.

Biology, ecology, and status of the smalltooth sawfish Pristis pectinata in the USA

“…Reducing the threat of injury and mortality from fisheries remains a top priority for recovering the smalltooth sawfish. Prohaska et al (2018) showed that the species is physiologically resilient and appears capable of surviving capture. Therefore, continuing to educate anglers about the presence of smalltooth sawfish and how to properly release them is essential for recovery.…”

“…data). Based on the live release of large sawfish from longline gear, it is expected that sawfish are more resilient to capture on this gear in comparison to trawls and gill nets (Prohaska et al 2018, Poulakis & Grubbs 2019, both this Theme Section). Further, lactate and HCO 3 blood levels of animals captured on longlines during permitted field activities indicate that the smalltooth sawfish is a relatively low stress species compared to other elasmobranchs (Prohaska et al 2018).…”

“…The northern 2 nurseries are located in Charlotte Harbor, an urbanized estuary that remains vulnerable to further development, where mangrovelined shorelines have been replaced by waterfront residences and seawalls , 2013, Norton et al 2012, Huston et al 2017). Prohaska et al (2018) showed that juvenile smalltooth sawfish within the Charlotte Harbor estuary have higher metabolic stress compared to sawfish from more pristine nurseries, suggesting chronic stress may be associated with living in compromised habitats. While we are unsure of how chronic stress affects body condition, behavior, or survival, juvenile sawfish appear resilient and continue to be found in that estuary.…”

Biology and ecology of sawfishes: global status of research and future outlook

“…Interdisciplinary, collaborative, habitat-use studies and detailed biological and ecological questions have been answered as part of research published in this Theme Section as a result of long-term surveys conducted within nurseries, especially regarding the smalltooth sawfish (Feldheim et al 2017, Huston et al 2017, Bakenhaster et al 2018, Hollensead et al 2018, Prohaska et al 2018. In addition to identifying geographic regions in which nurseries still exist, near-real-time, fisher-derived data have also been used to maximize tagging efforts, because juveniles exhibit high degrees of site fidelity.…”

“…In the USA and Australia, sawfishes continue to be captured in recreational fisheries, sometimes in large numbers, though the risk of mortality is likely low when they are handled and released properly (Peverell 2005, Waters et al 2014, Prohaska et al 2018. Unfortunately, reports of sawfish being retained or released after the removal of their rostra are still received, even in regions with adequate protections and extensive outreach efforts (Seitz & Poulakis 2006, Morgan et al 2016.…”