Handle with care: establishing catch limits for fish stocks experiencing episodic natural mortality events

Harmful blooms of the dinoflagellate Karenia brevis, known as "red tides," are responsible for major episodic fish kills in the Gulf of Mexico. In response to management concerns, we conducted a management strategy evaluation to examine whether decision-making reactivity to event occurrence or precautionary catch limit reductions could aid in achieving fishery objectives. Simulated stock dynamics were representative of Gulf of Mexico Red Grouper Epinephelus morio, and assessment of simulated data involved estimation of time-varying natural mortality. We found that both unresponsive yet precautionary catch limits and reactive decision making could improve achievement of fishery objectives, although practical impediments to reactive strategies abound. Where catch limit reductions were introduced to buffer against scientific uncertainty, a trade-off was evident that required recognizing constraints in stock assessment reliability (given the complexities of estimating time-varying natural mortality) and balancing these constraints against desirability for high catch rates. Our study provides a narrative on the ways in which management guidance can be structured to address uncertainty about future occurrences of episodic natural mortality events.