Assessing habitat utilization and rockfish (Sebastes spp.) biomass on an isolated rocky ridge using acoustics and stereo image analysis

Abstract

For those marine fish species with specific habitat preferences, a habitat-based assessment may provide an alternative to traditional surveys. We conducted a habitat-based acoustic and stereo image stock assessment survey for rockfishes (Sebastes spp.) on a rocky ridge habitat in the eastern Bering Sea. Video analysis suggested that juvenile and adult rockfishes were more abundant on the seafloor in the rocky ridge area than on the surrounding sandy flats. Over the ridges, the distribution of rockfishes was uniformly low in the water column during nighttime surveys and higher during daytime surveys. The opposite pattern was observed in the video on the seafloor between night (high density) and day (lower density), indicating that fish in the water column during the day moved to the seafloor at night. Mean biomass of adult rockfishes for the rocky ridges was 1.54 Â 10 4 tonnes based on acoustic data. The biomass of juvenile fish was estimated to be 9.2 Â 10 2 tonnes. Utilization of similar survey methodologies on a larger scale might improve assessment of rockfishes not only in Alaska, but also throughout their range where fishery-independent biomass estimates have been difficult to obtain.Résumé : Chez les espèces de poissons marins qui possèdent des préférences spécifiques d'habitat, une évaluation basée sur l'habitat pourrait être une méthode de rechange aux inventaires traditionnels. Nous avons fait un inventaire acoustique et vidéo d'évaluation des stocks des sébastes (Sebastes spp.) basé sur l'habitat dans un milieu de crête rocheuse dans l'est de la mer de Béring. L'analyse vidéo indique que les sébastes jeunes et adultes sont plus abondants sur le fond marin dans la région de la crête rocheuse que sur les plats sablonneux adjacents. Sur les crêtes, la répartition des sébastes est uniformément basse dans la colonne d'eau durant les inventaires de nuit et plus élevée durant les inventaires de jour. Un patron contraire s'observe par vidéo sur le fond marin entre les inventaires de nuit (densité élevée) et de jour (densité basse), ce qui indique que les poissons qui sont dans la colonne d'eau durant le jour se déplacent vers le fond marin la nuit. La biomasse moyenne des sébastes adultes sur les crêtes rocheuses est de 1,54 Â 10 4 tonnes d'après les données acoustiques. La biomasse des jeunes poissons est estimée à 9,2 Â 10 2 tonnes. L'utilisation de méthodes semblables d'inventaire sur une plus grande échelle pourrait améliorer l'évaluation des sébastes, non seulement en Alaska, mais aussi sur toute leur aire de répartition dans laquelle des estimations des biomasses indépendantes de la pêche sont difficiles à obtenir.[Traduit par la Rédaction]

A practical guide to the use of consumer-level digital still cameras for precise stereogrammetric <I>in situ</I> assessments in aquatic environments

“…A range of other marine biology applications also routinely use stereoimaging techniques (photo as well as video), including: fish monitoring (Ruff et al, 1995;Van Rooij et al, 1995;Li et al, 1996;Tillett et al, 2000;Harvey et al, 2003;Costa et al, 2006;Costa et al, 2009;Rooper et al, 2010;Bower et al, 2011;Torisawa et al, 2011); determination of the 3D structure of fish schools (Cullen et al, 1965;Pitcher, 1975;Dill et al, 1981;Sawada et al, 2009); determination of the influence of substrate complexity on the interaction between fish and the artificial substrate (Fischer et al, 2007); and surveys of the benthos and the sea floor (Emerey et al, 1965;Evans and Norris, 1997;Chong and Stratford, 2002;Jasiobedzki et al, 2008;Shortis et al, 2008;Svane et al, 2009).…”

Correlating environmental and biogenic factors with abundance and distribution of Pacific ocean perch (Sebastes alutus) in the Aleutian Islands, Alaska

“…Mounting evidence indicates that the presence of sponges and corals enhances structural heterogeneity in otherwise low-relief environments and can lead to increases in biodiversity and abundance of associated animals (e.g., Tissot et al, 2006; Beazley et al., 2013; Knudby et al, 2013). The morphological features of these biogenic structures may also serve as refugia for different life stages of commercially harvested species of Sebastes (Freese and Wing, 2003;Rooper and Boldt, 2005; Baillon et al, 2012) and Atka mackerel (Pleurogrammus monopterygius) (Rand and Lowe, 2011) in Alaska waters.Previous studies have also shown putative associations of rockfishes with sponge, coral, and bryozoan assemblages across a wide range of physical and oceanographic conditions (Love et al, 1991;Rooper and Martin, 2012 to concentrate near the few boulders or rocky outcrops with attached epibenthic invertebrate communities (e.g., Freese and Wing, 2003; Du Preez and Tunnicliffe, 2011). The Pacific ocean perch has been the focus of several previous studies in Alaska, and there is strong evidence that postsettlement juveniles and adults of Pacific ocean perch are found associated with sponges and corals (Krieger, 1993; Brodeur, 2001;Rooper and Boldt, 2005;Rooper et al, 2007).…”

“…Previous studies have also shown putative associations of rockfishes with sponge, coral, and bryozoan assemblages across a wide range of physical and oceanographic conditions (Love et al, 1991;Rooper and Martin, 2012 to concentrate near the few boulders or rocky outcrops with attached epibenthic invertebrate communities (e.g., Freese and Wing, 2003; Du Preez and Tunnicliffe, 2011). The Pacific ocean perch has been the focus of several previous studies in Alaska, and there is strong evidence that postsettlement juveniles and adults of Pacific ocean perch are found associated with sponges and corals (Krieger, 1993; Brodeur, 2001;Rooper and Boldt, 2005;Rooper et al, 2007).…”

“…A group composed of identifiable sponges that did not fit into 1 of the 15 morphogroups (e.g., Plakina tanaga) and unidentifiable fragments of sponges were assigned to a general category entitled "Porifera unidentified. "Corals and bryozoans are epibenthic invertebrates that also provide biogenic structure, which may serve as habitat resources for Pacific ocean perch in this part of their range (Rooper and Boldt, 2005;Rooper et al, 2007;Boldt and Rooper, 2009). To allow comparison with these and similar studies (e.g., Rooper and Martin, 2012), we grouped the coral and bryozoan taxa into single presence-absence composite "corals" and "bryozoans" factors, respectively.…”

“…The Pacific ocean perch has been the focus of several previous studies in Alaska, and there is strong evidence that postsettlement juveniles and adults of Pacific ocean perch are found associated with sponges and corals (Krieger, 1993; Brodeur, 2001;Rooper and Boldt, 2005;Rooper et al, 2007). These studies have not distinguished species of sponges, corals, or bryozoans because of the difficulty in providing consistent identifications.…”