Benthic Habitats and the Effects of Fishing

Linking Fisheries to Benthic Habitats at Multiple Scales: Eastern Scotian Shelf Haddock

John T. Anderson, Jim E. Simon, Don C. Gordon, and Peter C. Hurley

doi: https://doi.org/10.47886/9781888569605.ch44

Abstract. Historical distributions (n = 32y) of age-1 juvenile haddock Melanogrammus aeglefinus from the eastern Scotian Shelf population varied linearly with year-class strength, indicating a dependence on demersal habitats. Distributions of haddock ages 2–5 were weakly density dependent, indicating weaker associations with benthic habitats. The preferred areas (≥75%) of occurrence for age-1 haddock changed with the spatial scale of analysis. As bin size was reduced from 1,342 km2 (400 nm2) to 755 km2 (225 nm2) to 336 km2 (100 nm2) to 84 km2 (25 nm2), the boundaries of preferred areas shifted in location and the total area increased in size. As the spatial scale of bin size was reduced, the frequency of missing data increased, making it difficult to determine the true nature and extent of high-preference areas. The historical data indicated that preferred areas occur at the smallest scale analyzed of approximately 100 km2. Therefore, preferred areas (≥75% occurrence) and nonpreferred (≤25% occurrence) areas 10 km by 10 km were selected on three banks of differing size for directed studies. Acoustic surveys were carried out in the selected study areas using a normal incidence echosounder to determine fine-scale (16–18 m) bathymetric structure. These areas ranged in mean depths from 42 to 84 m. Bathymetric relief (m/km) was always greater in preferred areas within each bank. Spatial auto-correlation of bathymetric relief had smaller decorrelation scales for preferred areas within banks. Preferred areas for age-1 haddock were always more rugged at finer spatial scales than nonpreferred areas, indicating that preferred habitats may be more complex. There was a bank-scale dependency in surface structure where smaller banks were less rugged at finer spatial scales. We hypothesize that there may be a bank-dependent scaling of habitats where larger banks have a greater variety of habitats that span a greater range of spatial scales.