Science Advisory Report  2013/004

Assessment of Information on Irish Moss, Rockweed, and Kelp Harvests in Nova Scotia

Summary

• Information on the status of Irish moss, rockweed, and kelp in Nova Scotia is provided, with science advice for ongoing management.

Irish Moss

• Irish moss (Chondrus crispus)populations in southwestern Nova Scotia are not considered to be under immediate threat from overharvesting or environmental factors. However, there are indications of site specific over-harvesting, and harvesting pressure appears to be increasing.
• Recommendations for protecting Irish moss populations in Nova Scotia include: establishing long term permanently closed ‘control’ sites for evaluating impacts on standing stocks and ecosystem effects; re-evaluating Chondrus standing stock for evidence of overharvest in the Lobster Bay area; enforcing the 5 mm minimum rake tine spacing throughout Nova Scotia; re-evaluating the Marine Plant Harvesting District 12 (D12) seasonal closure time to adequately protect periods of peak growth and reproductive effort, as well as seasonal habitat use of associated animals; and scientifically assessing any new harvest methods against consistent criteria prior to implementation.  

Rockweed

• Advice on rockweed (Ascophyllum nodosum) harvest rate and canopy height is best provided at the spatial scale of a sector in Nova Scotia (sub-sector in New Brunswick). 
• Advice is provided with the intent of managing recovery times of harvested rockweed and considering general ecosystem objectives related to landscape ecology for aquatic species, canopy height, and overall rockweed plant shape.
• In Nova Scotia, the present industry harvest rates of up to 25% of the harvestable biomass of rockweed have been able to maintain the commercial yield of rockweed in these harvested areas for the last 17 years.  There is insufficient information or analysis from industry or third party experiments to determine whether this rate is detrimental to the habitat value that rockweed provides to associated plants and animals.
• Published studies of rockweed indicate that harvest rates of 20% allow economic recovery of harvested beds (biomass) within one year, harvest rates of 35% lead to a recovery time of up to 3 years, and harvest rates of 50% require greater than 3 years for recovery (with a pulse harvest), regardless of scale.
• Landscape ecology theory indicates that there may be benefits from managing impacts on other species and canopy height at the scale of tens of meters.
• Recommendations for protecting rockweed populations in Nova Scotia include: establishing long term permanently closed ‘control’ sites for evaluating impacts on standing stocks and ecosystem effects; re-evaluating Ascophyllum standing stock for evidence of overharvest in the Lobster Bay area; replacing the regulated minimum cutting height of 127 mm with a minimum plant cutting height of 254 mm for all parts of Nova Scotia; revisiting the current provincial rule of 15% holdfast content in rockweed landings; scientifically assessing new harvesting methods (e.g. mechanical harvesters) prior to implementation (i.e. commercial use) in Nova Scotia; re-evaluating the need for seasonal closures to adequately protect periods of peak growth and reproductive effort, as well as seasonal habitat use of associated animals.

Kelp

• Kelp populations provide important habitat and primary production on bay wide scales, and many would consider kelp beds to be very important to the nearshore ecology of Nova Scotia, particularly with their links to commercial species of fish and invertebrates.
• There are no documented large scale impacts from the harvest of kelp in Nova Scotia due to the sporadic, almost non-existent harvest at the present time, but any major increases in current harvesting would require close scrutiny, including a bay by bay assessment of standing stocks prior to harvest.
• Recommendations for protecting kelp populations in Nova Scotia include: obtaining standing stock data (including species composition) immediately prior to any harvest of kelp; surveying kelp bed habitat utilization by invertebrate and fish species prior to harvest; limiting harvesting methods to low impact hand cutting by SCUBA, including cutting plants with a sharp instrument minimally 10 cm above the “transition zone”, i.e. just above the stipe / blade juncture; ensuring new harvest methods cut minimally 10 cm above the transition zone and are scientifically assessed prior to implementation; use of seasonal closures to adequately protect periods of peak growth and reproductive effort, as well as seasonal habitat use of associated animals; and to evaluate existing licence conditions for consistency with DFO ecosystem objectives.

This Science Advisory Report is from the September 28, 2012, Assessment of Irish Moss, Rockweed, and Kelp in Nova Scotia. Additional publications from this process will be posted as they become available on the Fisheries and Oceans Canada Science Advisory Schedule at Canadian Science Advisory Secretariat (CSAS).

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