Population age structure and mortality rates of jackass morwong (Nemadactylus macropterus) in Eastern Bass Strait,Australia |
| |
| Institution: | 1. Centre for Maritime and Ocean Studies, Chaguramus Campus, University of Trinidad and Tobago, Trinidad and Tobago;2. Biomedical Engineering Unit, O''Meara Campus, University of Trinidad and Tobago, Trinidad and Tobago;1. Recruitment Processes Program, Resource Assessment and Conservation Engineering Division, Alaska Fisheries Science Center, NOAA, National Marine Fisheries Service, 7600 Sand Point Way NE, Seattle, WA 98115, USA;2. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, 104 CEOAS Administration Building, Corvallis, Oregon 97331, USA |
| |
| Abstract: | The catch-curve method was used to estimate the instantaneous rate of total mortality (Z) of jackass morwong (Nemadactylus macropterus) in south-east Australian waters. Age-frequency distributions were obtained for fish collected from eastern Bass Strait during the 3 years. March 1982–February 1985. Fish were obtained from: (1) demersal research fishing surveys stratified by depth; (2) commercial landings from eastern Bass Strait; (3) commercial landings from the adjacent New South Wales fishery.Jackass morwong were found in water 65–299-m deep, and almost half the biomass was in water 90–179-m deep. Our estimate of the total biomass (from the survey results) of the part of the population in eastern Bass Strait was 15 700 t. The oldest male morwong caught was 11 years old, the oldest female 13 years old. From the survey data, total mortality (Z) was estimated as 0.45 for males, which is equivalent to an annual survival rate (S) of 0.64, and as 0.47 for females, equivalent to an S of 0.63. There was substantial annual variation in estimates of Z. For the survey results, the annual mortality rate estimated for males was significantly different from that for females.The instantaneous rate of fishing mortality (F) estimated from population biomass and mean commercial landings was very low (about 0.024; sensitivity analysis indicated a possible range of 0.012–0.072), and indicated that about 2% (by number; range 1–6%) of the part of the population in eastern Bass Strait was harvested annually.Z values estimated from samples of commercial landings were consistently larger than Z estimated from the survey samples. Using estimates of Z from commercial landings data resulted in high values of M (the instantaneous rate of natural mortality), which were inconsistent with the longevity of the species and the proportion of older fish found in the population. We believe this to be due to bias in the way commercial landings sample the population, and to be an inherent bias in the use of age-frequency data from commercial landings unless some correction for size-selectivity due to commercial fishing gear and fishing behaviour can be made. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
