Temporal and Spatial Patterns of Interspecific Abundance–Occupancy Relationships Across Western Atlantic Fishery Ecosystems

Interspecific abundance–occupancy (A-O) relationships were estimated for species representing the Gulf of Maine, Georges Bank, southern New England and the Mid-Atlantic ecosystems for the finfish and shellfish assemblage from 1963 to 2009 using the National Marine Fisheries Service’s annual bottom-trawl survey. Occupancy was considered the proportion of stations with at least one individual present and abundance was estimated as the mean annual number of fish captured per station. Interspecific relationships over all species were fitted by year in order to estimate assemblage structural changes over time in relation to environmental and anthropogenic factors. A-O relationships were fitted using a log-linear model whose parameters are indices of the strength of the relationships and goodness-of-fit statistics represent the quality of the annual fits over the time-series. A combination of break point and jackknife-after-bootstrap analysis will be conducted to determine the probability of "state" changes in the interspecific slopes.  Preliminary results for Georges Bank indicate that the quality of the fits for species' assemblages within years decreased over the time series and were correlated significantly with total landings. These results also suggest that the 1970s and 1990s were periods of higher than average chance of breakpoints in the time series of interspecific slopes. Temporal and spatial trends in A-O relationships and breakpoints will be compared across ecosystems to determine coherency in system responses to exploitation.