Ecological Realism
Similar to their predictive skill, all models’ ability to generate ecologically realistic environmental relationships and spatial predictions varied primarily by spatial dependence treatments. Response curves indicated that each model captured similar relationships between albacore presence observations and the environmental variables. However, spatially explicit models (i.e., GF and iSDM) demonstrated a broader relationship with MLD compared to the HE model. For example, the HE model response curves suggested albacore suitability was highest at shallow MLDs (~ < 10 meters; Figure 5). This relationship closely resembled the underlying MLD distributions of the logbook data (Figure S1), which suggested significantly deeper MLDs relative to the archival tag data (mean MLD: 32.7 ± 21.9 and 13 ± 4.03 for archival tag and logbook data, respectively). In contrast, the GF and iSDM models suggested high albacore habitat suitability for shallow MLDs to ~100 meters before declining with depth (Figure 5). Additionally, all models showed that response curves (i.e., from the training period) fully covered the conditions during the forecasting period, though the distributions for each environmental variable narrowed during this time (Figure 5). Despite this coverage, the distributions of environmental values differed between the training and forecasting periods. For example, SST was warmer, bathymetry shallower, and MLD nearer to the surface during the forecasting period, indicating that albacore inhabited warmer, shallower waters during MHW conditions (Figure 5).
Spatial predictions were also assessed for ecological realism. During the forecast period under MHW conditions, the models generally exhibited similar spatial patterns in predicted habitat suitability, though regional differences were apparent (Figure 6). All models identified coastal waters—particularly off the coasts of Washington, Oregon, and northern Baja California—and the North Pacific Transition Zone as highly suitable habitat. However, the HE model produced the least ecologically realistic predictions, as it forecasted higher habitat suitability across the study area compared to the spatially explicit models. Notably, the HE model predicted extensive areas of suitable habitat for albacore tuna in areas characterized by warm (positive) SST anomalies offshore of southern California, whereas the GF and iSDM models demonstrated a discernible discontinuity in suitability within this highly anomalous region (Figure 6). This overestimation in the HE model is further reflected in the distribution of predicted suitability values, where it overpredicted habitat suitability at pseudo-absence locations. In contrast, the GF and iSDM model predictions more accurately differentiated between presences and pseudoabsences, resulting in a more balanced, and likely realistic, distribution of suitability values (Figure 6). The primary differences between the spatially explicit models were in the iSDM predictions being more closely aligned with albacore occurrences in coastal Canada and absences off central California, whereas these regions were connected by a coastal band of apparent high suitability in the GF predictions. In addition, while both GF and iSDMs identified the waters off Baja California as suitable, the degree of predicted suitability was significantly higher for the GF model in this region.