No abstract

The integration of multiple tissues in physiological and ecological analyses can enhance methodological approaches, increase applications for data and extend interpretation of results. Previous investigations of the stress response in fish have focused primarily on cortisol levels in a single matrix—blood plasma—which confines interpretations of cortisol levels to a short temporal frame. Epidermal mucus has been proposed as an alternative or complement to plasma that may provide a view to cortisol levels over a different temporal window allowing comparative assessment. Here, we explore the potential for multi-tissue cortisol analysis using both plasma and epidermal mucus in Pacific halibut (Hippoglossus stenolepis). The relative timing at which cortisol increased and decreased in the two matrices as well as cortisol concentrations at estimated peak levels were compared in two trials after (i) inducing cortisol synthesis by adrenocorticotropic hormone (ACTH1–24) administration and (ii) inducing cortisol elimination using cortisol (hydrocortisone, 98%) injection. The ACTH treatment elicited a peak plasma cortisol response approximately 12 hours post-injection, while mucus cortisol concentrations peaked later at approximately 62 hours post-injection. Exogenous cortisol treatments suggested relatively little transfer of cortisol from plasma to mucus, potentially reflecting differential effects of endogenous and exogenous cortisol. Our results suggest the potential utility of mucus as a sampling matrix that provides an extended window for detection of the stress response as compared to plasma. Results also suggest the utility of a multi-tissue approach to cortisol analysis with potential applications to applied fisheries research. Increased understanding of the relative scale of the cortisol response to stress (e.g. capture) will allow researchers and managers to better interpret the physiological condition and survival outcome of fish subjected to regulatory discard.

Cross‐contamination of epidermal mucus was assessed at three sampling locations on the bodies of Pacific halibut Hippoglossus stenolepis by inducing contact between fish coated with labelled synthetic mucus and non‐treated fish. Results indicate a positive relationship between sampling site exposure and sample contamination and that mucous sample cross‐contamination can be mitigated by sampling in a location protected from external contact.

The advancement of conservation practices in global trawl fisheries has been impeded in part by a lack of a collective understanding of the most relevant and broad-scale knowledge-needs, along with the identification of potential barriers to addressing these knowledge-needs. Using both an online survey and an in-person workshop, we engaged a diversity of fishing industry stakeholders including scientists, technology companies, trawl net makers, and fishermen working with North Pacific, United States, trawl fisheries to identify and prioritize areas in which further knowledge is required for successful implementation of conservation engineering practices. In addition, we identified barriers to addressing these knowledge-needs. Knowledge-needs related to fishing gear performance were identified among the top priorities, including several areas targeted at improving fishing efficiency that could further advance the sustainability of well-managed trawl fisheries. To better understand the composition and behavior of target versus non-target catch, workshop participants identified the importance of closing data and technology gaps. This highlights areas for potential collaboration between fishermen, researchers, and technology companies to address research prioritized by the end-user. Further, results from the workshop emphasized a need for industry-driven training and workshops focused on elevating fishermen skill for newer entrants through peer-learning and knowledge-sharing to achieve objectives like better non-target avoidance and increased fishing efficiency of the target species. Addressing these prioritized knowledge-needs, by first working toward overcoming the industry-identified barriers, may aid in increasing uptake of conservation practices, thereby contributing to the long-term sustainability of these fisheries and associated social-ecological systems.