Reference |
Cowan, D.F. 1999. Methods for assessing relative abundance, size distribution, and growth of recently settled and early juvenile lobsters (Homarus americanus) in the lower intertidal zone. Journal of Crustacean Biology 19:738-751. |
Abstract |
The purpose of this study was to establish a method for repeated, year-round sampling of the abundance of young-of-the-year and juvenile lobsters, Homarus americanus, where they can be found intertidally. The primary advantage of the intertidal lobster monitoring program is the ability to overcome limitations pursuant to subtidal sampling techniques through increased temporal and spatial resolution of data collected, using sampling methods possible at low tide. Lobsters were sampled monthly throughout the years 1993-1997 by overturning rocks in one-square meter quadrants placed along fixed transects running parallel to the water’s edge 0.2-0.4 m below mean low water (MLW). Individuals were tagged using binary-coded microwire tags. Two distinct size classes of lobsters, the smaller measuring 3-15 mm in carapace length (CL), the larger measuring 16-40 mm CL, were found consistently. Monthly mean densities ranged from 0-8.6 individuals per square meter at 0.44 m below MLW. These densities are comparable to published reports of similar-sized lobsters sampled at depths of 5 m below MLS. A seasonal pattern of abundance was observed, with the highest average densities recorded in May-November. Lower abundance in December-April was most likely due to seasonal migrations of individuals of the larger size class. Preliminary results indicate that areas of the lower intertidal zone serve as nursery grounds where postlarval lobsters settle and grow for several years. The assessment method developed in this study is being used to establish a time series that may be useful in developing and testing predictive models of annual yield and recruitment of the lobster fishery. The close proximity of intertidal lobster nurseries to the terrestrial zone indicates serious implications for fisheries management and issues of habitat protection in the shoreland zone. Further investigations are needed to yield a more complete picture of the full geographical extent of use of the intertidal zone as a nursery area for lobster. |
Tag |
Coded Wire Tag (CWT) |
Objective |
Population estimates |
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