SmeltCam: Underwater Video Codend for Trawled Nets with an Application to the Distribution of the Imperiled Delta Smelt

Abstract

Studying rare and sensitive species is a challenge in conservation biology. The problem is exemplified by the case of the imperiled delta smelt Hypomesus transpacificus, a small delicate fish species endemic to the San Francisco Estuary, California. Persistent record-low levels of abundance and relatively high sensitivity to handling stress pose considerable challenges to studying delta smelt in the wild. To attempt to overcome these and other challenges we have developed the SmeltCam, an underwater video camera codend for trawled nets. The SmeltCam functions as an open-ended codend that automatically collects information on the number and species of fishes that pass freely through a trawled net without handling. We applied the SmeltCam to study the fine-scale distribution of juvenile delta smelt in the water column in the upper San Francisco Estuary. We learned that during flood tides delta smelt were relatively abundant throughout the water column and that during ebb tides delta smelt were significantly less abundant and occurred only in the lower half and sides of the water column. The results suggest that delta smelt manipulate their position in the water column to facilitate retention in favorable habitats. With the application of the SmeltCam we increased the survival of individual delta smelt by 72% compared to using a traditional codend, where all of the fish would have likely died due to handling stress. The SmeltCam improves upon similar previously developed silhouette photography or video recording devices and demonstrates how new technology can be developed to address important questions in conservation biology as well as lessen the negative effects associated with traditional sampling methods on imperiled species.

Linking Hydrodynamic Complexity to Delta Smelt (Hypomesus transpacificus) Distribution in the San Francisco Estuary, USA

“…However, it is possible that the maximum depth-averaged current speed was not necessarily the mechanistic driver behind the spatial variation in SI C . Since high maximum depth-averaged current speeds typically occur in channels, selection against these areas may indicate fish movement between the channels and shoals (e.g., Aasen 1999;Bennett and Burau 2015), the vertical movement of Delta Smelt in the water column (e.g., Feyrer et al 2013), or potential differences in sampling gear efficiency that lead to variations in Delta Smelt catch.…”

A Covered Cod-End and Tow-Path Evaluation of Midwater Trawl Gear Efficiency for Catching Delta Smelt (Hypomesus transpacificus)

“…This could be because of a strong surface orientation in visually feeding sub-adult Delta Smelt (Slater and Baxter 2014). Feyrer et al (2013) observed Delta Smelt throughout the water column on flood tides and only in the lower portion of the water column on ebb tides. During this study, we targeted flood tides to maximize catch.…”

Prey availability, environmental constraints, and aggregation dictate population distribution of an imperiled fish

“…, Feyrer et al. , ). Localized movement strategies (vertically or laterally) may allow smelt to hold position in desirable areas rather than be displaced by water withdrawals or substantial flow (Arthington and Balcombe , Bond et al.…”

“…, Feyrer et al. , Sommer and Mejia ), given that instantaneous velocities ranged up to 4.8 m/s and the critical swimming velocity for smelt has been estimated as approximately 0.3 m/s (Swanson et al. ).…”

“…), and movement to center or edge habitat in relationship to tides (Feyrer et al. ). Further, at least a component of the population makes determined movements depending on life stage requirements and environmental cues (Swanson et al.…”