Maizuru Bay surveys did not establish higher autumn richness at 30 fish and matched bottom temperatures in 2002–2023

We tested whether autumn fish surveys recorded more species than spring surveys at similar bottom water temperatures in Maizuru Bay, Japan. We used open visual census tables from 2002–2023. Within each year, we selected disjoint March–June and September–December pairs with bottom temperatures of 12–24°C and a difference of no more than 1°C. We calculated exact expected richness for 30 counted fish and gave each year equal weight. The 63 pairs covered all 22 years. Spring richness averaged 8.01 species and autumn richness averaged 7.50. The autumn minus spring difference was −0.51 species, with a nominal 95% three-year block interval of −1.47 to +0.35. Checks at 20 and 50 fish and with surface-temperature matching also had intervals that included zero. The annual contrast changed through time. An exploratory linear time model gave a mean interval of −0.98 to −0.02. Thus, evidence for a lower autumn mean depends on the time model. Neither model supports a positive full-period autumn difference. Bottom matching left autumn surface temperature 4.81°C lower on average. The result does not establish equal seasonal richness or a temperature cause. It applies to selected surveys on one coastal transect. The package preserves source data, provenance, the local plan, code, all results, figures, and independent and clean-repeat checks.

fish · species richness · rarefaction · seasonal change · temperature matching · Maizuru Bay · open data