Are passive acoustics an appropriate method to accurately represent a soniferous Atlantic croaker (Micropogonias undulatus) population?

Abstract

It was observed that the fundamental frequency of Atlantic croaker sounds is inversely correlated with the length of the fish. We used fundamental frequency as a method to estimate the average length of the croaker population at any given time. Croaker were collected using an otter trawl and simultaneously counted and measured acoustically with a 200‐kHz split‐beam echosounder at two sites within the Pamlico Sound estuary, NC from June to November 2008. Passive acoustic recorders [long‐term acoustic recording system (LARS) recordings 10‐s wave files < 10 kHz at 15‐min intervals] were deployed near each trawling site to obtain in‐situ recordings of croaker over the same period. Based on captive fish recordings, a linear regression analysis related total length to fundamental frequency, where TL = 305.323 mm−(0.270 Hz−1)f0(r2 = 0.84). This equation was then used to estimate croaker lengths from LARS recordings. Lengths of fish collected in the trawls, compared with the estimate from the passive LARS recordings and the echosounder surveys, were significantly smaller (P > 0.0001). Thus suggests that size‐selectivity of the trawl underestimates the average size of fish and that acoustic methods (active and passive) provide a more accurate size estimate for croaker populations.