Assessing discarding at sea using a length-structured yield-per-recruit model

Discarding at sea is a common practice in fisheries. Part of the catch is often discarded because fish are too small to be marketed, or are bycatch. Regulations such as trip limits or quota limitations also provide fishermen with a strong incentive to discard fish that are above their quota and to high grade to maximize profits. Almost all fish discarded at sea die. However, the impacts of discarding at sea have not been evaluated in many fisheries. Because the probability of a fish being discarded is usually dependent upon its length, a length-structured model is appropriate for evaluating discarding. In this study, we propose an approach to evaluating the impacts of discarding at sea using a length-structured yield-per-recruit model. As an example, the proposed approach was applied to data from the Oregon flatfish fishery.