Larval fish diversity on the Scotian Shelf

Abstract

We examined larval fish diversity on the Scotian Shelf using data, representing 91 genera, collected during the Scotian Shelf Ichthyoplankton Program from 1978 to 1982. Two diversity indices (genus richness (GR) and Shannon's entropy (H)) were relatively lower from December to February-March and relatively higher and stable from April to September-October. Taxon composition changed seasonally. Total median log abundance (log10(number of individuals + 1)·1000 m-3) was low from December to February, increased in March, was stable from April to June, and declined from July to October. Our results suggest that the abundance trends of most taxa were not coincident with either a spring or fall bloom of calanoid copepods. Log GR was significantly positively related to H (r = 0.62, p < 0.001, n = 1853). A negative exponential best described the relationship between log GR and log abundance (R2 = 0.77; log GR = 1.37(1 – e-(1.13)(log abundance)), p < 0.001, n = 2357). Shannon's H was not related to log abundance in winter or in summer-fall and was negatively correlated in spring-summer (r = -0.12, p = 0.003, n = 593). Thus, diversity increases with abundance but the composition is dominated by relatively fewer genera at higher levels of abundance. Western - Sable Island banks had higher levels of GR and abundance in all seasons. Additional banks were diverse and productive during warmer months.