Shikoku Diving Map: Kashiwajima, Kannoura & Muroto Compared
2026-03-16
Kochi Prefecture in Shikoku has three major dive sites: Kashiwajima west of Cape Ashizuri, Kannoura east of Cape Muroto, and Muroto near Cape Muroto itself. Despite being in the same prefecture, visibility differs dramatically — Kashiwajima averages 4–5m higher than Kannoura and Muroto. We analyzed 2,433 real observations to understand why.
13.1m
Kashiwajima
1,544 obs
9.1m
Kannoura
747 obs
8.8m
Muroto
142 obs
Detailed 3-Site Comparison
| Site | Annual Avg | Best Month | Best Vis | Worst Month | Worst Vis | Obs |
|---|---|---|---|---|---|---|
| Kashiwajima | 13.1m | Sep | 16.2m | Apr | 10.5m | 1,544 |
| Kannoura | 9.1m | Jan | 11.8m | Jun | 6.8m | 747 |
| Muroto | 8.8m | Dec | 12.1m | Jul | 5.9m | 142 |
Why Kashiwajima Is 4–5m Higher: Kuroshio Access
Kashiwajima: Direct Kuroshio Benefit
Kashiwajima sits just west of Cape Ashizuri, Shikoku's southernmost point, where the Kuroshio Current arrives directly. The Kuroshio carries nutrient-poor oceanic water that suppresses phytoplankton growth, raising visibility. The area hosts Japan's highest coral species diversity, reflecting its tropical-like marine environment.
Reference: Ministry of Environment 'Coral Reef Monitoring' (https://www.env.go.jp/nature/biodic/coralreefs/)
Kannoura & Muroto: Farther from the Kuroshio
Kannoura and Muroto are located east of Cape Muroto. The Kuroshio approaches Shikoku closest near Cape Ashizuri then flows toward the Kii Peninsula, so the east side of Cape Muroto receives less Kuroshio benefit. Instead, nutrient-rich coastal water dominates, supporting more plankton and lower visibility.
Reference: JMA 'Kuroshio Current Path' (https://www.data.jma.go.jp/gmd/kaiyou/data/shindan/b_2/kuroshio_stream/kuroshio_stream.html)
Simply put, Kashiwajima is 'right next to the Kuroshio' while Kannoura and Muroto are 'on the other side.' Though only about 100km apart as the crow flies, ocean current influence differs dramatically.
Monthly Pattern Differences
Kashiwajima: September Best (16.2m)
Peaks in September when summer Kuroshio influence is most stable. April is lowest (10.5m) but spring turbidity impact is less severe than Izu Peninsula. Annual range of 5.7m is relatively stable.
Kannoura: Winter Best (Jan 11.8m)
Opposite to Kashiwajima, Kannoura peaks in winter. Worst in summer (June 6.8m). With stronger coastal water influence, it follows a Honshu-like pattern where visibility improves in winter as plankton decreases.
Muroto: Winter Best (Dec 12.1m)
Similar winter-peak pattern to Kannoura. December reaches 12.1m, the only month exceeding 10m. July is lowest (5.9m). With only 142 observations, trends may shift as more data accumulates.
AI Prediction Accuracy
Our site-specific AI model achieves 66% prediction accuracy for Kannoura. Kashiwajima uses the general AI model with moderate accuracy. Muroto's 142 observations are insufficient for reliable predictions yet, but accuracy should improve as data accumulates.
Planning Your Shikoku Dive Trip
For Best Visibility: Kashiwajima
Annual average 13.1m, peaking at 16.2m in September. Japan's highest coral diversity. About 3.5 hours by car from Kochi City — distant but worth it. Consider staying overnight in Sukumo.
For Kannoura/Muroto: Visit in Winter
Opposite to Kashiwajima, winter is best. Kannoura in January reaches 11.8m, Muroto in December hits 12.1m. Summer drops to 6–7m, giving little reason to visit then. Muroto offers unique geological dive topography near the cape.
Access
Kashiwajima: ~3.5h drive from Kochi Airport. Kannoura: ~2.5h from Tokushima or Kochi Airport. Muroto: ~2h from Kochi Airport. Kannoura is also accessible from Kansai via Nankai Ferry.
About the Data
Aggregated from 1,544 Kashiwajima, 747 Kannoura, and 142 Muroto real dive log observations. Muroto figures are reference values due to limited data. Monthly patterns use full historical averages. Visibility is the mean of daily min/max values. Kuroshio influence analysis references JMA ocean current data.
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