Separate haul halves agreed on 50-78 percent of annual movement signs in four US trawl samples in 1982-2019

We tested how haul selection changes a marine distribution measure used in climate studies. We divided hauls within each year and fixed survey stratum into two separate halves, 500 times. We used 30 eastern Bering Sea taxa and 15 Northeast US fall taxa in 1982-2000 and 2001-2019. Median agreement on annual north-south movement signs was 56, 50, 78 and 50 percent. Northeast linear trend signs agreed in every split in both periods. Only the late Bering sample had a positive sea surface temperature slope with a four-test adjusted interval above zero. That interval included zero with a stricter common-taxon filter. Thus annual movement signs were less stable than Northeast trend signs under this procedure. The split ranges are conditional design checks, not confidence intervals or independent survey replication. Shared catchability bias, selected common taxa, survey boundaries, few annual pairs and surface temperature as a bottom-water proxy limit use. This study does not identify a climate or pollution cause. The package gives original code, aggregate evidence, exact raw hashes and an external retrieval recipe.

species distributions · observation bias · trawl survey · sample splitting · climate indicators · sea surface temperature