Mean-minus-median latitude trend intervals included zero in four US trawl samples in 1982-2019

We tested whether mean and median catch latitude changed at the same rate in two US trawl surveys and two periods. We used fixed survey strata, area and haul-effort weights, and fixed cohorts of 59 eastern Bering Sea and 62 Northeast US fall taxa. Mean-minus-median trends were +2.34, +1.70, +0.74 and -0.73 km per decade in 1982-2000 and 2001-2019. All four primary corrected intervals included zero. Only the early Northeast interval was within a chosen -5 to +5 km per decade band. Typical absolute location gaps were about 19-20 km across taxon-years. Early Bering Sea intervals excluded zero under some sensitivity choices, including removal of four years flagged in later documentation. Thus the main null result does not show equal trends. Survey boundaries, catchability, selected taxa, known early data concerns and short series limit inference. We did not measure climate or pollution exposure. The package preserves source hashes, a raw-data rebuild, derived evidence, code, uncertainty and checks.

species distributions · observation bias · marine biodiversity · mean latitude · median latitude · climate indicators · trawl survey · null result