Development of standard weight equation and standard length categories for Emerald Bowfin
Vaskar NepalAbstract
Objective
Indices based on fish length and weight, such as proportional size distribution (PSD) and relative weight, serve as valuable tools that enable meaningful comparisons among fish populations and support assessments of management interventions. This study established species-specific standard length categories and standard weight (Ws) equations for Emerald Bowfin Amia ocellicauda, a native nongame predator facing increased commercial and recreational interest.
Methods
Length and weight data were compiled for Emerald Bowfin across 17 states and two Canadian provinces to establish PSD cutoffs, with a refined data set representing 11 states and provinces used to develop Ws equations. Proposed PSD categories for Emerald Bowfin were derived based on an updated maximum total length of 89 cm (35 inches). To model Ws, regression line percentile, linear empirical percentile (EmP), and quadratic EmP methods were evaluated using a 10-fold population-level cross-validation protocol. Models were constructed for both above-average (75th percentile) and average (50th percentile) condition targets for fish between 200 and 800 mm.
Results
Minimum total length (L) cutoffs are proposed at 20 cm (8 inches; stock), 33 cm (13 inches; quality), 43 cm (17 inches; preferred), 55 cm (22 inches; memorable), and 69 cm (27 inches; trophy) to calculate PSD indices for Emerald Bowfin. During the development of the Ws equations, linear EmP models outperformed regression line percentile approaches and provided superior accuracy without the unnecessary complexity of quadratic models. The recommended 75th percentile equation was derived as log10(Ws)=−4.945+2.980×log10(L), and the 50th percentile equation as log10(Ws)=−4.980+2.983×log10(L) for length in mm and weight in g.
Conclusions
The standard length categories and Ws equations presented here will better enable fisheries biologists to understand and manage Emerald Bowfin populations across the species' range. However, when conducting field evaluations, care should be taken to adjust target relative weight benchmarks according to the selected reference model (average vs. above-average).