AbstractsBiology & Animal Science

The exercise physiology of snapper (Pagrus auratus): implications for the better commercial harvesting of an iconic New Zealand finfish

by Sarah Elizabeth Coxon

Institution: University of Canterbury
Department: Biological Sciences
Year: 2014
Keywords: Snapper; Pagrus auratus; exercise physiology; swimming performance; Ucrit; temperature; hypoxia; fisheries
Record ID: 1301096
Full text PDF: http://hdl.handle.net/10092/9430


Worldwide, an increasing demand for fish and fisheries products, together with socioeconomic pressure for industry expansion, is placing considerable pressure on wild fish stocks – more than 80% of which are considered by the Food and Agriculture Organisation of the United Nations (FAO) to be either maximally- or over-exploited. Adding value to the existing catch and/or improving the sustainability of current wild capture methods may offer a means of providing industry growth while negating the need for increased landings. In particular, the peri-mortem condition of a fish plays an integral role in the condition of the tissues post-mortem and hence in product quality, with harvesting techniques that result in stress or fatigue yielding a lower quality product. An understanding of the physiology of the target species and its response to harvest is therefore essential to implementing targeted improvements in harvesting technologies. For species harvested using trawl-based technologies, this includes knowledge of their exercise physiology, in particular their swimming capacity, since this is a key determinant of the interaction between fish and trawl gears, and hence of the nature and severity of stress experienced and of the condition of fish at landing. This thesis describes a series of discrete studies relating to the exercise physiology of juvenile snapper, Pagrus auratus, an iconic New Zealand finfish that comprises important recreational and commercial fisheries. In particular, we sought to characterise the capacity of snapper for sustained swimming activity, including how performance may differ between fish of different size or with environmental temperature; to determine the consequences of exhaustive exercise for both subsequent swimming activity, an important determinant of survival in escaping or discarded catch, and for tissue biochemistry, which ultimately determines product quality in harvested fish; to validate the use of laboratory-based simulations for the study of capture-related stress by comparing the response of laboratory-exercised snapper with commercially caught fish; and to determine the tolerance of snapper to environmental hypoxia, and further, the possible consequences of hypoxia for swimming capacity and for recovery in fish retained for subsequent rested-type harvest. The capacity of snapper for sustained swimming activity was characterised through the use of incremental exercise tests to determine critical swimming speeds, Ucrit. Juvenile snapper (94-107 mm length, 16-157 g mass) demonstrated a strong swimming capacity, with individual fish attaining critical swimming speeds of up to 7.1 body lengths per second (bl s⁻¹). Swimming performance demonstrated an allometric association, with absolute critical speeds increasing with fish size, whilst relative performance favoured smaller fish. The relation was described by the function Ucrit (m s⁻¹) = 0.003412 [length (mm)] + 0.2669. Critical swimming performance also exhibited variation in response to environmental variables. Thermal…