Bill,
I am confident that the methods were not the field techniques that I have referenced here but by the laboratory technique of observing gametes by catheterization. They are fisheries biologists and I don't think they would leave that aspect to chance. I could be wrong about that but I just don't see them eyeballing the fish and slapping a sex ID on them. The fish were PIT tagged in 1988 but were not sexed until 1991. But since they were PIT tagged in 1988 I have confidence in their Male-Female data from 1988 onward is reliable.
They did provide data for individual fish from before they were PIT tagged. But clearly this earlier data is averaged and I suspect they did apply some type of assumption assign individual fish to a sex group. They noted that the data was bimodal and I think it is likely that they used a statistical approach to allocate individual measurements to sex groups. Males grow slower and so the lower mode was probably considered to be consistent with males. To be sure, the data remained bimodal after PIT tagging and sex ID. As it turns out the males are associated with the mode with lower values of length and weight .... so it wouldn't be a bad approach when attributing weight and lengths to male and females before the PIT tagging in 1988 (age 3.5 years).
This data among others has helped me to build what I think is good model for average RW for females at various annual weight increments. Males are more problematic because I don't have good data on maximum weight increments for males and the RWs associated with those annual gains. Further I don't know maximum observed limits of male RW or male weight increment. For females, 2.2 lbs gain per year and RW 180 are practical limits. For females, can only explain less than 50% of the variation of RW from weight increment. All of the remaining variation is apparently explained by variation of length among the fish making the same weight increment. For example the regression estimates a RW for a weight increment but there will be distribution of RW for that weight increment where some individuals will have higher RW (shorter fish) and some will have lower RW (longer fish). High annual weight gains push annual length increment and RW to their limits.
One of the things I have learned is that females do not have to grow really fast to maintain 100 RW. Females growing around 1/2 lb annually will average a little higher than 100 RW (my model estimates 102). Those with higher RW are shorter than peers of the same weight ... those with lower RW are longer than peers of the same weight. Males require less weight increment to maintain 100 RW. I know this from the study above where males having an average weight increment of 0.3 lbs per annum were consistently above 100 RW. They just make smaller length increments and I think that is why they are able to maintain higher RW than females on a smaller weight increment.
Last edited by jpsdad; 09/21/24 07:51 AM. Reason: Update on more accumulated data
