Looking at just the return on Abroader Otters, my subs found a total of 454 anomalies, of which 92 were CSCFIFFE on the second try. That means my subs got 362 chances to roll on otters, of which 7 were successful, for an overall drop chance of 2% per anomaly. I got 50 "Clear & Calm" weather results on the first anomaly (22%), and 21 "Clear and Calm" on the second anomaly (9%), for a total of 71 "Clear & Calm" results on all attempts (16% of total.) Of the 50 Clear & Calm results on the first anomaly, six produced otters, for a drop rate of 12%, and for the 21 Clear & Calm on the second anomaly, 1 produced an otter, a 5% drop rate. The overall drop rate from all Clear & Calm weathers was 10%.
Overall conclusion: the drop rate on Abroader Otters is terrible and there's not much we can do about it.