An Optical Imaging System for Capturing Images in Low-Light Aquatic Habitats Using Only Ambient Light

Camille Pagniello,Ana Širović,Edward Parnell,Jack Butler,Paul Roberts,Jules Jaffe,Addison Sherwood,Annie Rosen

doi:10.5670/oceanog.2021.305

Abstract

It is preferable that methods for monitoring fish behavior, diversity, and abundance be noninvasive to avoid potential bias. Optical imaging facilitates the noninvasive monitoring of underwater environments and is best conducted without the use of artificial lighting. Here, we describe a custom-designed optical imaging system that utilizes a consumer-grade camera to capture images in situ in ambient light. This diver-deployed system can be used to collect time series of occurrences of animals while concurrently obtaining behavioral observations for two weeks to a month (depending on the sampling rate). It has also been configured to be paired with a passive acoustic system to record time-synchronized image and acoustic data. The system was deployed in a protected kelp forest off southern California and captured >1,500 high-quality images per day over 14 days. The images revealed numerous fish species exhibiting biologically important behaviors as well as daily patterns of presence/absence. The optical imaging system is a cost-effective tool that can be easily fabricated and improves upon many of the limitations of previous systems, including deployment length and image quality in low-light and limited-visibility conditions. The system provides a relatively noninvasive way to monitor shallow marine habitats, including protected areas, and can augment traditional survey methods by providing nearly continuous observations and thus yield increased statistical power.

Highlights

Optics-based technology has become a powerful monitoring method for marine ecologists and managers (Bicknell et al, 2016)
Behavioral observations using optical imaging systems (OISs) should be made without artificial lighting, as many fish species exhibit behavior patterns that are regulated by ambient light levels (Potts, 1990), so artificial lighting can alter behavior (Nightingale et al, 2006)
We review the capabilities of this new system and provide results from a deployment in the kelp forests within the South La Jolla State Marine Reserve (SMR)

Summary

Introduction

Optics-based technology has become a powerful monitoring method for marine ecologists and managers (Bicknell et al, 2016). Cameras are relatively noninvasive when compared to other monitoring methods (Chaudoin et al, 2015), and they permit in situ observations of behavior (Bouchet and Meeuwig, 2015; Parnell et al, 2017), diversity (Favaro et al, 2012), and abundance (McLean et al, 2010) of a wide variety of marine animals. Most battery-powered OISs that sample nearly continuously are only capable of a few hours of image or video capture (e.g., Favaro et al, 2012; Mallet and Pelletier, 2014; Wilby et al, 2016). To capture high-quality images during crepuscular periods, OISs for studies of fish are often equipped with artificial lights (e.g., Harvey et al, 2012; Fitzpatrick et al, 2013; Myers et al, 2016). Others who have not used artificial lighting do not record any observations during the hours near sunrise and sunset (Chaudoin et al, 2015)

Methods

Findings

Conclusion