Removing anchovy reduced the spatial convergence estimate for ten larvae per catch in southern California in 2014-2019

We tested whether a reported spatial convergence of fish larvae remained after control for station pairs, light states and catch counts. In CalCOFI spring catches, the 2017-2019 minus 2014-2016 Sorensen contrast at ten larvae was -0.0465 in the north and -0.1261 in the south. Omitting 2016 changed the northern sign. All southern year-omission estimates stayed negative. An added exploratory check removed northern anchovy and used identical catches for full and removed count sets. The southern contrast changed from -0.1181 to -0.0067, a 94 percent reduction in magnitude. The northern contrast became more negative. The reduction did not repeat in 1996-2001. This shows that one taxon can strongly affect this finite-catch diversity measure. It does not show a causal effect of anchovy or the warm event. Few years, selected catches, mixed taxon labels, shared water masses and unmeasured detection limit inference. Code, aggregate evidence, source hashes, numerical checks and figures are included. External raw data and record-level panels are excluded.

CalCOFI · marine warming · observation bias · northern anchovy · spatial dissimilarity · rarefaction · day-night sampling · temporal replication