Effects of diel behavior on the uncertainty and efficiency of acoustic-trawl surveys of small pelagic fishes off Northwest Mexico
Year: 2026
Type: article
Abstract: Annual acoustic-trawl (AT) surveys are conducted to manage the harvest of small pelagic fishes (SPF) off Northwest Mexico. The AT method uses species proportions and fish-length distributions from trawl catches to convert echosounder data to estimates of SPF biomasses. Here, we consider the effects of SPF diel behaviors on the accuracy and efficiency of AT sampling. We analyze echosounder data and trawl catches collected irrespective of the time-of-day during four AT surveys between 2019 and 2021. We use a multi-frequency algorithm to identify acoustic backscatter from schooling fish with swimbladders and attribute it to SPF. We compare observations of the putative SPF backscatter versus depth and time-of-day. We assume that SPF backscatter is less biased by the sea-surface ‘blind zone’ if it is deeper, and less biased by non-SPF backscatter if nearby catches have less bycatch. We also assume that trawl catches are less biased if they have higher SPF-species richness and larger length ranges. We compare these metrics across diel periods. Furthermore, geostatistical methods were applied to the Nautical Area Scattering Coefficient in order to demonstrate that vertical migration constitutes a source of uncertainty. During daytime, SPF aggregate deeply enough to be sampled by the echosounders and, during nighttime, they ascend near the surface and disperse for efficient capture. During daytime, SPF and bycatch are separated, and fewer non-SPF contribute to the catch and presumably the SPF backscatter, compared to nighttime. However, at nighttime, SPF catches are generally larger and are inferred to more accurately represent the species composition and length distribution of SPF in the area, compared to daytime catches. We conclude that, at least for the studied area and times, echosounder transects should be conducted during daytime and trawling should be conducted at nighttime to improve AT-survey efficiency and reduce uncertainty in estimates of SPF biomasses. To confirm if these conclusions are generally valid, similar analyses should be conducted in other regions.
Source: Fisheries Research
Language: English
Subfield: Aquatic Science
Domain: Life Sciences
SDG: Life below water
Open Access status: hybrid
Estimated APC paid: $3,680
OpenAlex ID: W7201985449