A positive change in catch-minus-detection latitude slopes did not persist with a survey step in Northeast US trawls in 1982-2019

We tested whether the difference between catch-weighted and detection latitude trends changed between 1982-1999 and 2000-2019. We used fixed strata, area weights, positions and persistent taxa in two US trawl surveys. The median taxon-paired change was +2.51 km per decade in the eastern Bering Sea and +8.75 in the Northeast US fall survey. Two-test adjusted block bootstrap intervals were -7.69 to +12.62 and +1.37 to +16.12. The Northeast interval included zero when the split moved to 2001 or when a 2009 survey step was fitted. Bering intervals included zero in all checks. Thus the positive Northeast main-model change did not give stable regional replication. The test follows a published descriptive pattern and uses the same records. Short periods, selected taxa, detection error and survey changes limit inference. No causal climate effect is measured. Original code, regional estimates, a figure, source hashes and external-data retrieval instructions are included.

species distributions · observation bias · trawl surveys · biomass · detection · period sensitivity · OceanAdapt