Refining indices of abundance and catch allocation by accounting for available habitat

This is the authors' abstract. We don't add key points for this paper.

Many recreationally harvested demersal fishes inhabit high-relief, rocky habitat, and lack comprehensive fishery-independent surveys to inform stock assessments and management. In these situations, stock assessments often rely on fishery-dependent surveys to track patterns in abundance. To address these challenges and align methods more closely with the stock assessment process, we develop novel methods to account for changes in relative abundance, using vermilion rockfish ( Sebastes miniatus ) as a case study. We develop a habitat-weighted time series of relative abundance using maps of high-relief habitat, coupled with fine-scale catch-per-unit-effort (CPUE) data from a recreational fishery survey. We compare this approach to two alternative methods that implicitly assume equal area weights, or disregard regional abundance trends altogether, both commonly used in the absence of habitat information. We also describe a habitat-weighted, spatial index of abundance for use in allocating catch across management areas and compare it to three other methods of catch allocation. We propose that in the absence of fishery-independent surveys, habitat-weighted, fishery-dependent CPUE indices can better inform spatial and temporal indices of relative abundance, relative to methods in which habitat data are lacking. In our case study, differences among methods for catch allocation based on spatial indices of abundance were greater than differences observed for temporal indices. This result may differ among species and regions. Our work demonstrates that when only fishery-dependent data are available, the use of CPUE as a proxy for density (with habitat area weights) is more appropriate than the assumption that CPUE alone is proportional to abundance.