Using RAMP to estimate fisheries discard mortality in the southern New England flatfish complex

Yellowtail flounder NOAA

Winter flounder NOAA

Windowpane flounder NOAA

RAMP curves were estimated for yellowtail flounder, winter flounder, and windowpane flounder in the southern New England flatfish complex (Barkley et al. 2012).  Fish were treated with experimental trawl and air exposures and sublethal and lethal effects on reflex impairment noted.  Seven reflex actions were tested and responses were combined into RAMP scores.

RAMP curves were calculated (see also for anatomy of a RAMP curve):

RAMP was determined to be a useful method for predicting discard mortality in the flatfish complex and can be used for rapid, real time, onboard sampling of discard mortality rates:

"Implications

The utility of RAMP is the ability to test the reflexes of fish caught and use the RAMP score to predict mortality using the reflex impairment-mortality relationship. Creating reflex impairment-mortality relationships opens up the possibilities to expand RAMP sampling and to gain a more accurate representation of the total commercial discard mortality rates. These reflex methods can be applied to a subsample of fish during commercial fishing trips to allow for a more representative discard mortality estimate. The RAMP methods are also not limited to a particular gear type, so fish caught in the large-mesh otter trawl fishery as well as fish caught in the scallop fishery can be assessed using the same reflexes and can be compared to the same reflex impairment-mortality relationship. This allows for the estimation of discard mortality over a wide spectrum of gears, tow-times, and time on deck.

Summary of conclusions

- The suite of seven reflexes is a reliable indicator of survivability in yellowtail and winter flounder.

• Tow-time was not as important as a stressor on flounder as air exposure. 
• The results indicate that the discard mortality of yellowtail and winter flounder may be reduced onboard fishing vessels by limiting the amount of time the fish are on a dry deck.
• Windowpane flounder are less hearty then yellowtail and winter flounder, and may not be able to survival discarding.
• The reflex impairment-mortality relationships developed from this project for yellowtail flounder and winter flounder can be used to estimate the discard mortality rate of fish, based on at-sea RAMP sampling over multiple gear types."

Realtime knowledge of discard mortality rates can be used in adjusting fishing practices to decrease and avoid discard mortality, as well as for testing new fishing gears designed to reduce bycatch capture and discarding.