Four temperature slope intervals included zero for fish larva pair diversity in two California sectors in 1978-2022

We tested whether warmer spring surface water predicts higher within-tow fish larva diversity. The outcome is the chance that two distinct larvae have different taxon labels. It needs only two larvae. We used 2,086 CalCOFI spring bongo tows in two sectors and two periods, 1978-1999 and 2000-2022. Models controlled station, time trend, season, daylight and sampled volume. The four slopes were +2.09, +8.09, +1.74 and +7.31 percentage points per C. All four intervals adjusted for four tests included zero. Removing anchovy gave no clear slope difference. Removing major warm-event years reversed the later southern slope. A diagnostic with catch-size control gave one clear positive interval, but changed the target relation. A 20-larva rule retained 1,429 tows. The pair measure retained 657 more tows but did not establish a common warmth link. Wide intervals, taxon labels, coarse seasonal temperature, selective capture and only 21-22 sampled years limit inference. Separate sectors share ocean conditions and one survey. No pollutant or causal climate-change effect was tested. Code, aggregate results, checks, figures and exact source hashes are included. External tables and record-level extracts remain outside the bundle.

CalCOFI · fish larvae · Gini-Simpson diversity · sea surface temperature · observation bias · anchovy · regional comparison · null result · reproducible methods