Assessing macroscopic and histological staging of yellowfin and bigeye tuna ovaries in the north-western Coral Sea [Australian Fishing Zone].
1992
McPherson G.R.
The primary objective of this report is to describe the macroscopic development of Coral Sea yellowfin and bigeye tuna ovaries, and to assess the most appropriate techniques for fisheries observers to monitor, or sample for monitoring purposes, the maturity of these species in the Australian Fishing Zone. A nine-stage macroscopic scheme of Coral Sea yellowfin and bigeye ovaries is given. The scheme recognises an immediate post-spawning stage and includes an additional comparison to other macroscopic schemes for tunas. It relies on the examination of the interior of the ovary as many of the features of a developing ovary were masked by the opacity of the ovarian wall. Overall, macroscopic staging schemes for whole ovaries and individual oocytes were considered to be imprecise. Histological sampling of ovaries in association with gonadosomatic indices is recommended as the most appropriate method of confirming the presence of spawning activity and overall reproductive status of Coral Sea tuna. Minimum observed lengths at maturity for bigeye in the handline area and longline area respectively were 100 and 125 cm respectively.
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