Great work performing your survey and recording/sharing your data. To begin, lets discuss the population the surveys suggest and some other considerations regarding potential biases that can increase the uncertainty of the population estimate. In your first survey you marked 69 unique fish. In the second survey, you caught 61 fish of which 7 fish were recaptures. These values suggest that your total population of fish is 601. In a .73 acre pond, that is 823 total fish per acre. Of the 601 estimated, you identified 124 unique fish (roughly 20.6% of your estimated population).

With mark and recapture, the larger the number of your samples (especially the second survey), the more reliable and less uncertain the estimate. I do consider this to be a good sampling but given the second survey comprises less than 11% of the population, it has a higher uncertainty than if the second sampling had been 22% of the population. In fact, the uncertainty would be halved by doubling the number of second survey samples. There will always be some level of uncertainty when the sample number of the second survey is less than the total population but the purpose of this statistical method is to make a good estimate of the population with acceptable levels of uncertainty WITHOUT having to count each one. By and large, mark and recapture does this so long as biases are not extreme in the sampling method(s).

It is especially important that the second survey be unbiased. Especially with respect to the first survey. Both of your surveys are by fishing with the same method (earthworms on a small hook). So there is little bias introduced by the method but it isn't bias free. Generally we agree that some fish after being caught are more difficult to catch again. This effect, would introduce a bias to overestimate a population. An electrosurvey eliminates this uncertainty because it ability to produce samples doesn't depend on vulnerability to angling. Even so, to be a good survey for mark and recapture, it must not introduce bias that affects the sampling of marked fish. Let's say the marked fish were caught at 25 ft depths but the electrosurvey only worked in water of 12 ft depths, then the electrosurvey would introduce a negative bias on recaptures (thus increasing population estimates).

Another important bias is geospatial bias. This would be especially important for fish that are not ranging considerably. If there is a equal chance that any fish in the population could be sampled in the sample areas then this would minimize bias. Also, if the second survey gives no preference to geospatial areas (being no more biased toward other areas than where the marked fish were captured) then this would minimize bias. If fish are territorial and not likely be impartial to location, then there is possible geospatial bias where the geospace of the samplings have been limited. For example, if your surveys occured in 1/3 of the geospatial extents of the BOW AND the fish are territorial, then you may have a great population survey that are limited to the extents of sampling area. In doing your sampling, these considerations should be given thought and decisions made regarding trust of the findings and adjustments if deemed prudent.

For now, I think we can move forward with estimate of the population that your surveys imply. While I do think they could underestimate your populations, I also know that careful future sampling will prove to make that evident. For example, if the proportion of unmarked fish is higher than anticipated, that would suggest the surveys underestimated the population. You describe the BOW as being fertile with much chara and (some duckweed). Chara favors water of good alkalinity. Duckweed favors high fertility. So I think there is a really good chance that your pond carries more than mark and recapture presently suggests. Also, you mentioned not having good access to all of the pond. Geospatial bias may have affected the population estimate. Presently, your survey suggests a standing weight of adult panfish of around 150 lbs per acre. Give some thought to geospatial bias and let me know if you are satisfied that all or most of the pond was sampled without geospatial bias.