Investigating and mitigating uncertainties in the assessment of Scottish Nephrops norvegicus populations using simulated underwater television data

Abstract

Campbell, N., Dobby, H., and Bailey, N. 2009. Investigating and mitigating uncertainties in the assessment of Scottish Nephrops norvegicus populations using simulated underwater television data. – ICES Journal of Marine Science, 66: 646–655. Nephrops norvegicus is a commercially significant decapod crustacean that excavates and inhabits burrows in muddy sediments throughout the Northeast Atlantic and Mediterranean Sea. Because of its variable emergence behaviour, traditional surveys are considered a poor indicator of the status of its populations, and underwater television (TV) survey methods have been developed. The approach involves towing a TV camera over patches of muddy sediment and counting the number of Nephrops burrow complexes within a known area. Assuming a 1:1 rate of occupancy, the average population density can be estimated. This is raised to the known area of suitable sediment to give a measure of population size. Recently, underwater TV surveys have been used to provide absolute measures of abundance for a number of Nephrops stocks in the North Sea and Northeast Atlantic. It is therefore imperative to identify, quantify, and control for uncertainties in this process. Previous workers have suggested that visual recognition of Nephrops burrows and “edge effects”, where single openings of burrow complexes at the sides of the viewed transect are counted, are important sources of uncertainty. This study shows edge effects to be responsible for an overestimation of population size of between 4 and 55%, depending on the width of the field of view and the mean size of the burrow complex. This overestimation is countered to some extent by variability in burrow entrance structure, which leads to Nephrops burrows going unrecognized. The scales of these errors are discussed in relation to observed sediment softness, sediment distribution, and burrow dimensions from sites around Scotland.

Indexing and selection of well-lit details in underwater video mosaics using vignetting estimation

“…In these sequences the main scientific purpose is taking population census of the commercially significant species of lobster, Nephrops norvegicus. The census is performed by marine biologists counting manually from the survey video, the respective dwelling burrows of the creatures [1]. These surveys were conducted by a sled (equipped with lights and camera) being pulled along the seabed in a straight line by an above boat.…”

“…Video has become an important survey tool in numerous underwater scientific research missions, such as taking population census [1], assessing the biological environment [1], archaeological analysis [2], and seabed classification [1] etc. Due to the poor visibility conditions that exist underwater, these surveys employ high intensity lights and are usually recorded in close proximity to the seafloor.…”

The Saga of the Management of Fisheries in the Adriatic Sea: History, Flaws, Difficulties, and Successes toward the Application of the Common Fisheries Policy in the Mediterranean

“…Importantly, there seems to be a stock-specificity to the relationship between burrow density and sediment composition which has been found to hold true over time (Campbell et al, 2009). This aspect, added to the fact that Nephrops is a sedentary species (Chapman and Rice, 1971), means that Nephrops is generally characterized by spatially segregated populations (or stocks) with little or no exchange between them (Bell et al, 2007).…”

A Review of the Tools Used for Marine Monitoring in the UK: Combining Historic and Contemporary Methods with Modeling and Socioeconomics to Fulfill Legislative Needs and Scientific Ambitions

“…Real-time analysis can be carried out e.g., when looking for specific features of interest or for stock assessment (ICES, 2007;Campbell et al, 2009), determining the presence of target nonindigenous species and for groundtruthing of acoustic MBES data where visual confirmation of predicted transitions in sea bed composition is required (Kenny et al, 2003). Cameras are also employed in Sediment Profile Imagery (SPI) for in situ assessment of the interface between sediment and overlying water (Birchenough et al, 2013) and baited remote underwater video systems (BRUV) can be used to supplement or replace more traditional collection survey methods (Roberson et al, 2017).…”