Biometric relationships between age-0 walleye Sander vitreus total length and external morphometric features

Abstract

In fishes, predation often is size-specific, with decreasing predation risks associated with larger body size. However, consumed fishes observed during diet analysis are often partially digested with only a variety of different body parts identified, making it challenging to determine original body size at consumption and size-specific predation risk. Therefore, the objective of this study was to assess linear relationships between total length and 10 body components of age-0 walleye Sander vitreus. Ten morphometric features (spinal column: first anterior vertebrae before the caudal bone to the first vertebrae posterior of the cranium (SC), length between anterior edge of the rostrum and posterior margin of operculum margin (RO), length between anterior edge of the rostrum to the origin of the dorsal fin (RD), gape height (GH), length of the base of the anal fin (AF), height of the caudal fin (CF), orbit height (OH), orbit width (OW), base of anterior (AD), and posterior (PD) dorsal fins) were measured from 61 age-0 walleye ranging from 119 to 275 mm total length. Walleye total length was positively related to all ten morphometric features: spinal length (R2 = 0.90), gape height (R2 = 0.84), orbit width (R2 = 0.52), and orbit height (R2 = 0.56), base length of anterior dorsal fin (R2 = 0.85), base of posterior dorsal fin (R2 = 0.80), base of anal fin (R2 = 0.73), length between rostrum and first dorsal fin (R2 = 0.91), caudal height (R2 = 0.46), and rostrum to posterior margin of the operculum (R2 = 0.95). Most age-0 walleye (87%) consumed by predators had at least one morphometric feature that was measurable, with 42% of the measurable features having coefficient of determination value of at least 0.80 with total length. Length-frequency histograms developed from total lengths estimated from morphometric features were all similar to direct total length measurements, indicating that they provided a reliable metric of size distribution. Establishing biometric relationships for morphometric features that can be directly measured provide an alternative to back-calculation of prey size and provide information that aids in understanding complex relationships between recruitment, predation, and prey size.