Management implications of variability in reproduction and growth of commerical [sic] marine fishes
The relation between reproductive effort and natural mortality rate was examined for 15 species of marine fish. The observed correlation relating the wet gonad somatic index (WGSI) to M was r = .831. For most species reproductive effort can be determined during a single spawning season. The described method therefore can provide a quick preliminary estimate of the rate of natural mortality.Special problems concerning the reproductive biology of copper rockfish (Sebastes caurinus), northern anchovy (Engraulis mordax) and English sole (Parophrys vetulus) were considered. It was estimated that a relatively small proportion (11.5%) of the energy consumed by copper rockfish embryos during gestation was contributed by the mother, particularly in relation to comparable estimates pertaining to black rockfish (S. melanops, 70%). It has been suggested that northern anchovy may spawn 20 or more batches of eggs per year. Alternative analysis techniques were used to show that spawning at this high rate may not be energetically feasible. Results for English sole show that the expected net somatic growth increment of a 6-year-old fish is 12 g dw compared to a seasonal weight loss of 62 g dw and a reproductive energy expenditure of nearly 30 g dw. The implications related to management strategy for English sole are then discussed.An analysis of variability in the growth and reproduction of fish of similar size and age suggests that much of the observed variability results from inherited dissimilarities in individual abilities to obtain and process food. Additional consideration of how energy allocation patterns change with size and age suggests that declining physical condition was coincidentally related with increasing relative reproductive effort, but that the two were not necessarily causally related.Finally, a method was developed which uses measures of the interannual variability in production indicators and other biological parameters to analyze how stocks respond to changes in their environment. The method was applied to a time series of Pacific herring data leading to the conclusion that fishing, poor recruitment and an increase in the rate of natural mortality have all contributed to the severe decline in stock abundance. It is also apparent that during the observed decline, the entire complex of life history parameters has undergone significant change.
- Fisheries