Complementing Beach Seining With Dive Surveys Improves Fine-Scale Resolution of 0-Group Gadoid Distributions in...

Many juvenile fishes use nearshore habitats as critical nursery grounds; however, the distributions of post-settlement young-of-the-year (0-group) juvenile Atlantic cod (Gadus morhua) and saithe (Pollachius virens) in Icelandic waters remain poorly understood. Catch data from beach seine surveys were combined with fish counts from dive surveys to gain high-resolution data on the depth distribution (0-21 m) and post-settlement timing of these species in nearshore habitats. Saithe were most abundant in early summer, and higher numbers were caught in beach seine tows in shallow intertidal algae than observed during dive surveys in deeper (> 5 m) waters. Conversely, Atlantic cod were distributed across the depth range but were generally more abundant in shallower water. Cod became less abundant in dive surveys following an initial peak in July but showed increasing abundance in beach seine catches later in the season. These patterns suggest that settlement occurs later for cod than saithe and that 0-group cod continue to utilize shallow habitats throughout the study period. Habitat choice, depth-related predation, or both could explain the contrasting temporal abundance trends for cod observed across the two surveys. Spatial heterogeneity, but no strong habitat associations were found-beyond depth preferences-and no other juvenile gadoid species were caught or observed, confirming that the examined depth range is primarily utilized by 0-group saithe and cod. Overall, this study contributes to understanding 0-group gadoid distributions in nearshore nursery habitats by (1) providing detailed depth-specific abundance estimates previously unavailable in this area, (2) demonstrating key differences in settlement dynamics-including depth and timing-of these species in sympatry, and (3) suggesting depth-specific predation pressures post-settlement. This information can support the development of targeted sampling for saithe and cod nursery grounds in Iceland, aiding the assessment of juvenile recruitment into adult populations of these commercially important species.