<p>Rank diagnostics for <i>Q</i> = 1–8.</p>

Because these criteria did not agree, <i>Q</i> = 4 was used as an operational reference under a study-specific stability rule rather than as a uniquely selected optimum. At <i>Q</i> = 4, three components dominated by Crucian carp, Freshwater clam, and Landlocked Ayu were reproducible and closely tracked the corresponding observed shares, whereas a mixed fourth component was less stable. Repeating the stability analyses at <i>Q</i> = 5 produced the same qualitative pattern of a reproducible core and less stable additional structure.

Component correspondence also depended on data representation. Some observed shares and component scores showed spatial autocorrelation among reporting ports, whereas reconstruction error did not. NMF therefore identified a reproducible core representation of recorded catch composition without supporting a unique and uniformly stable latent structure.

These patterns describe recorded catch composition rather than stock abundance and provide a historical reference for future comparison.</p></div>