Multispecies resource management of economically important marine plant communites of eastern Canada

Abstract

The annual 45,000 t harvest of six marine plant taxa, consisting principally of the alga Chondrus crispus, is worth $ 5 million annually to maritime fishermen. The harvesting techniques enable capture of associated biota and alter the abiotic structure of the habitat. Methods developed to assess ecological impact include permanent transects which are sampled for vegetation composition and dry biomass. C. crispus represents 80% of the plant biomass in commercial beds; 27 other genera comprise the remainder. Thirty-five associated invertebrate species include only one of direct economic importance, the lobster, Homarus americanus. On commercial Chondrus beds off western Prince Edward Island, lobsters were captured in basket dragrakes up to 5.4 h-1 during 1975 and 1976. Of the total lobster catch, the percentage injured by Chondrus dragrakes was 2.7% in 1975 and 1.3% in 1976. Chondrus dragrakes, as used in southwestern Nova Scotia, disrupt the drumlin substrate. Controlled dragraking for 2-h periods disrupted 0.25% to 1.5% of the bottom area. One month of normal harvest activity displaced 0.5% to 2.9% of the bottom of surveyed sites. A harvest of 1000 t of Laminaria spp. is projected for 1979. Dragrakes harvest entire plants averaging 5.0 ± 2.3 m in length. The residual population averaged 2.3 ± 1.9 m. Indirect effects of kelp harvesting on the benthic community are the subject of ongoing research. © 1980 Biologische Anstalt Helgoland.