Redfish and Specks Benefit from Limited Weir Closings

[MathGeek]

Originally Posted by Duck Butter

1. the timing of the study is also correlating with spawning time and weirs also are open during that time (full moons in late spring/summer). Likely the fish have just spawned.

One can always take wild guesses about potential confounding factors. Redfish and black drum are not spawning during the sampling window, but specks and gafftops are. Looking at the subsample of our data taken within 48 hours of a full moon shows no significant difference in mean relative condition factors for a given year.

Originally Posted by Duck Butter

2. rod and reel catches don't show the true population, only fish susceptible to being caught, which are likely fish that are hungry and thin anyways

We've compared a lot of our data from hook and line catches to net catches in cases where data from net catches are available for comparison. The hypothesis that hook and line catches are thinner, hungrier fish (lower condition factor) has never been supported. Hook and line catches are not generally accepted as being a good representation of the length structure of a population, as all methods other than electrofishing have a lot of sampling bias with respect to lengths. However, relative condition factors in a given length class are widely accepted as not depending on the sampling method. (Others have looked at this also.)

We've got tons of data showing mean relative condition factors at or above 100% for certain species, locations, and years. If hook and line were biased toward selecting thin, hungry fish, the mean relative condition factors would almost always be under 100%, regardless of where and when they were sampled. It is also common for hook and line studies by others to find mean condition at or over 100%.

The mean condition factor of all the specks measured from Calcasieu over the four years of our study is 101%. Someone forgot to tell the fat ones not to bite.

Further, even if there was a difference between condition of hook and line catches and net sampled catches, since our methodology is the SAME every year (hook and line), the variations we see from year to year (and comparisons with other hook and line data) would still be valid.

Originally Posted by Duck Butter

3. The egg-laden females may be there but are not being caught. They are only interested in one thing - spawning. They have already fed for long periods of time to be ready for the most important event in their lives.

We do not check every fish for eggs. However, because we work at fish cleaning stations, we see many of the fish we've just sampled get filleted, and we often cut into many of of the sampled fish ourselves. There is ample evidence that there are a lot of egg-laden females in our data. You should send them a note telling them they should stop biting angler hooks to better be ready for the most important event in their lives.

The bottom line is that hook and line sampling methods are valid and widely accepted for determining relative condition factors in fish.