Lobster (Homarus americanus) catchability in different habitats in late spring and early fall

Abstract

The effects of habitat and season on the catchability of lobsters (Homarus americanus) in baited traps were studied in September and June in Lobster Bay, Nova Scotia, by means of dive censuses followed by trapping. Moderate boulder cover characterized one site; two others had low relief (sand or mud dominated). Poisson loglinear models of the data were used to evaluate the effect of site, size, and sex on lobster catchability (q). This approach generates model-based estimates of q in units of square metres per trap. In both seasons lobster density (all sizes > 50 mm) at the two low-relief sites (means of 15–18 per 300-m² transect) was lower than that at the moderate-boulder site (means of 25–26 per transect), but trap catch rates were higher at low-relief sites. The models confirmed that lobster catchability was lower at the moderate-boulder site. Potential explanations include more shelter-seeking behaviour at the moderate-boulder site and hydrodynamic differences affecting the bait odour plume. The largest difference between seasons was higher q’s in spring for prerecruit sizes (71–80 mm CL) at all sites, perhaps due to fishery removals of larger sizes. The results have implications for lobster assessments and the planning of trap surveys of abundance.