Humans

Ecosystems provide us with nutrition, subsistence, employment, income, lifestyles, cultural identity, and even spirituality.

We must understand the roles oceans play in our lives, and how ecosystem functions and processes impact individuals and societies. To this end, NPRB has funded a variety of social, economic and management research.

Humans research topics are consistent with those outlined in the NPRB Science Plan. (Photo: Morgen Young/NPRB)

Research Highlights

Project 711: Trawl modification can reduce crab mortality

(March 2010) The potential for unobserved mortality of crabs encountering bottom trawls, but not brought aboard the fishing vessel, greatly influences management of Bering Sea fisheries.

Project 711, Quantification of unobserved injury and mortality of Bering Sea crabs due to encounters with trawls on the seafloor, addresses the lack of data on the mortality rates of such crabs for Tanner, snow, and red king crabs, the three principal commercial crab species of the Bering Sea.

Right: (top) Diver Heloise Chenelot holds two male king crabs (Shawn Harper); (bottom) Tanner crab (Jan Haaga, NOAA-AFSC)

Pilot fieldwork had established recapture net designs and handling, as well as procedures for holding crabs onboard.Reflex and reflex impairment observations of captive animals provided information needed for field assessments of crab condition.

Crab mortality varies depending on which part of a bottom trawl is involved. Left: Typical bottom trawling net setup. See larger image

Highest rates of mortality were caused by footrope wings (15-32%) and lowest by the sweeps (4-9%).

Small gear modification = large drop in crab mortality

Recent progress has shown that simply raising trawl sweeps just 2-3 inches above the seafloor reduced red king crab mortality by 71%, from 9.1% to 2.6%. Tanner and snow crab mortalities approached zero with the modification. The sweep covers the greatest seafloor area and is thus important to fishery managers' consideration of requiring these modifications for bottom trawlers targeting flatfish in the Bering Sea. Read the January 2010 progress report highlighting these early results

The fishing industry has been very supportive of this project and has been the primary focus of outreach. Project results have been presented at various venues, including:

• A series of presentations to the North Pacific Fishery Management Council and its committees regarding sweep modification regulations
• A gear development workshop, held at the flume tank at Memorial University, St. Johns, Newfoundland
• Workshops for the Pollock Conservation Cooperative, and for Bering Sea and Gulf of Alaska bottom trawlers
• Annual skippers' meetings at the Groundfish Forum and the Best Use Cooperative