Okay - your pond was built and stocked in 2004. In 2016 your original stocked fish were 12 years old. IMO most all of the original BG died during the last year of old age especially if they were fed pellets. Pellet feeding IMO causes faster growth but shorter life spans of fish compared to a diet of all natural foods. A 11 to 12 year old BlueGill in northern ponds are near or past their age limit. Fish that die of old age rarely float. Now that your pond is in its 13th year expect 15% to 25% of your oldest fish to die (natural causes) each year. It is a normal natural occurrence in ponds. Fish in southern ponds typically have shorter life spans due to fast growth rates and long growing seasons compared to northern pond fish.
Here are a few pertinent excerpts from our Archives about harvest of bluegills. One should read and understand the entire discussion of harvesting bluegills. More research needs to be conducted for educating us about harvest, growth, and life span of southern bluegills.
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=273316#Post273316In WI and similar northern areas slightly better than average growth of bluegill is 1yr=2-2.5, 2 yr= 4.8-5.7, 3 yr=5.0-6.4, 4yr= 6.6-7.2, 5yr= 7.4-8.0. Ave growth of bgill in IL was also similar to the WI accelerated rates. Average MI growth rates are 1yr 3.1, 2yr 4.3, 3yr 5.4, 4yr 6.6, 5 yr 7.3, 6yr 7.7, 7yr 8.2, 8yr 8.4, 9yr 8.7, 10yr 8.9. Once a bluegill reaches 8, I think its growth rate will be only Ό to ½ per yr depending on food supply and length of growing season.
It can take up to 7 to 10 years to replace or regrow a large bgill on natural food sources in northern waters such as MI, WI or MN (also see below). Schneider 1999 and Patriarche 1968 reported bluegill lived up to 11 to maybe 14 yrs in four MI lakes. Removing larger numbers (over harvest) of bigger bluegills contributes significantly to poor size structure of a bluegill population (Coble1988).
The natural mortality of a high quality 82 acre Ohio lake for bluegill in unfished years was calculated to be a 36% mortality rate.
Regarding your redear sunish which may also be at the end of their life span
See this from:
http://animaldiversity.org/accounts/Lepomis_microlophus/#developmentLifespan/Longevity
Redear sunfish have an average lifespan of 6 years. The oldest wild-caught redear sunfish was 8 years old at time of capture. In captivity they can live to be 7 years old. (Schloemer, 1947; State of California, 2004; Twomey, et al., 1984).
The Sunfish bible by Carlander lists the oldest RES were 8 years old which was also noted as 8 yrs by G.L.Towns Redear Sunfish Management in Michigan.
