Physiological condition and hook injury survival
The IPHC is developing condition indices for Pacific halibut, to better inform our understanding of the influence of physiological condition on the performance of Pacific halibut in relation to seasonal spawning, migration, disease response, and post-capture release survival. A paramount aim in ecological studies is the development of methods that assess the nutritional and physiological statuses of living organisms. The relevance of these types of studies relies on the influence of body conditions on the performance of the organism (Brosset et al. 2015a). For instance, an animal with a relatively healthier physiological condition is considered to have improved fitness for activities such as reproduction, migration, etc. (Brosset et al. 2015b). Most commonly, the physiological status of an organism is related to its energy availability, which is also referred to as its energy storage. All in all, it has been generally concluded that an individual with greater stored energy has improved or better physiological condition (Mesa and Rose 2015).
Bycatch and discard mortality of Pacific halibut, as defined by the incidental catch of fish in non-target fisheries and by the mortality that occurs in the directed fishery (i.e. fish discarded for regulatory reasons), respectively, represent important sources of mortality that can result in significant reductions in exploitable yield in the directed fishery. Due to regulatory requirements, all Pacific halibut that are caught as bycatch or that are below the minimum commercial size limit (U32) in the targeted fishery cannot be retained and must be returned to the sea without sustaining additional injury (Trumble et al., 1993). The entire discarding process involves: first, the capture of the fish (by hooking in the case of the longline fishery); second, the handling of the fish by members of the fishing boat and; finally, the release of the fish back into the ocean. Along the discarding process (Figure 1), Pacific halibut will receive injuries and will be subjected to a variety of influencing factors that will affect their survival potential after release. Individual variability in terms of survival (or its opposite, mortality) after release to the sea will be expected depending on the severity of injuries and stresses incurred during the discarding process as well as on the biological characteristics of the fish (e.g., physiological condition or status). IPHC is actively involved in studies investigating the types and relative levels of injuries and stresses that fish are exposed to during the discarding process in relation to the biological characteristics of the fish, with the goal of developing better estimates for the probability of survival (or mortality) during the entire discarding process.
Brosset, P., Ménard, F., Fromentin, J.M., Bonhommeau, S., Ulses, C., Bourdeix, J.H., Bigot, J.L., Van Beveren, E., Roos, D. and Saraux, C. 2015a. Influence of environmental variability and age on the body condition of small pelagic fish in the Gulf of Lions. Marine Ecology Progress Series. 529: 219-231.
Brosset, P., Fromentin, J.M., Ménard, F., Pernet, F., Bourdeix, J.H., Bigot, J.L., Van Beveren, E., Roda, M.A.P., Choy, S. and Saraux, C. 2015b. Measurement and analysis of small pelagic fish condition: A suitable method for rapid evaluation in the field. Journal of Experimental Marine Biology and Ecology. 462: 90-97.
Mesa, M.G. and Rose, B.P. 2015. An assessment of morphometric indices, blood chemistry variables and an energy meter as indicators of the whole body lipid content in Micropterus dolomieu, Sander vitreus and Ictalurus punctatus. Journal of fish biology. 86(2): 755-764.
Trumble, R.J., Neilson, J.D., Bowering, W.R., and McCaughran, D.A. (1993). Atlantic halibut (Hippoglossus hippoglossus) and Pacific halibut (Hippoglossus stenolepis) and their North American fisheries. Can. Bull. Fish. Aquat. Sci. 227.