Annual net primary production calculated from eastern Canadian Irish moss fishery data

Abstract

Western Prince Edward Island Irish moss (Chondrus crispus) has been intensively dragraked since 1966 . As well, most unattached fronds removed by wave surge, ice, etc . are brought to shore by waves and currents, where they are harvested eagerly . Accurate annual fishing yields were recorded between 1966 and 1981 inclusive . Given that herbivore densities are reduced, likely due to the intensive raking, and that mean annual bycatch (non-Irish moss seaweeds) (23 .4 %) and commercial bed sizes (873 ha) were known, the fishing yields thus were considered a unique database from which to calculate net primary production (NPP) . Factors used to convert from wet to dry wt (DW), and from dry wt to carbon were 0 .22 an 0 .31, respectively . Calculated mean annual NPP values were as follows : 2 .101 ± 0 .654 t (DW) ha -1 y -1 ; 210 .1 g DW m-2 yr -1 and 63 .0 g CM-2 yr -1 . These values are much lower than those calculated for northwest Atlantic kelp and rockweed but similar to that determined for northeast Atlantic Gracilaria verrucosa . The interannual variability pattern for NPP was similar for both the wild Irish moss harvest and that of experimental Chondrus crispus outplants placed in one of the 14 commercial beds .