title: Recreational Fish-Finders--An Inexpensive Alternative to Scientific Echo-Sounders for Unravelling the Links between Marine Top Predators and Their Prey.
abstract: Studies investigating how mobile marine predators respond to their prey are limited due to the challenging nature of the environment. While marine top predators are increasingly easy to study thanks to developments in bio-logging technology, typically there is scant information on the distribution and abundance of their prey, largely due to the specialised nature of acquiring this information. We explore the potential of using single-beam recreational fish-finders (RFF) to quantify relative forage fish abundance and draw inferences of the prey distribution at a fine spatial scale. We compared fish school characteristics as inferred from the RFF with that of a calibrated scientific split-beam echo-sounder (SES) by simultaneously operating both systems from the same vessel in Algoa Bay, South Africa. Customized open-source software was developed to extract fish school information from the echo returns of the RFF. For schools insonified by both systems, there was close correspondence between estimates of mean school depth (R2 = 0.98) and school area (R2 = 0.70). Estimates of relative school density (mean volume backscattering strength; Sv) measured by the RFF were negatively biased through saturation of this system given its smaller dynamic range. A correction factor applied to the RFF-derived density estimates improved the comparability between the two systems. Relative abundance estimates using all schools from both systems were congruent at scales from 0.5 km to 18 km with a strong positive linear trend in model fit estimates with increasing scale. Although absolute estimates of fish abundance cannot be derived from these systems, they are effective at describing prey school characteristics and have good potential for mapping forage fish distribution and relative abundance. Using such relatively inexpensive systems could greatly enhance our understanding of predator-prey interactions.
authors.affiliation: Percy FitzPatrick Institute, DST/NRF Centre of Excellence, University of Cape Town, Cape Town, South Africa.
authors.forename: Alistair M
authors.initials: AM
authors.lastname: McInnes
authors.affiliation: Computational Biology Group, Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa.
authors.forename: Arjun
authors.initials: A
authors.lastname: Khoosal
authors.affiliation: Department of Medicine, University of California San Diego, La Jolla, California, United States of America.
authors.forename: Ben
authors.initials: B
authors.lastname: Murrell
authors.affiliation: Branch: Fisheries Management, Department of Agriculture, Forestry and Fisheries, Rogge Bay, South Africa.
authors.forename: Dagmar
authors.initials: D
authors.lastname: Merkle
authors.affiliation: Department of Statistical Sciences, University of Cape Town, Cape Town, South Africa.
authors.forename: Miguel
authors.initials: M
authors.lastname: Lacerda
authors.affiliation: DST/NRF Centre of Excellence at the Percy FitzPatrick Institute of African Ornithology, Department of Zoology, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa.
authors.forename: Reason
authors.initials: R
authors.lastname: Nyengera
authors.affiliation: Branch: Fisheries Management, Department of Agriculture, Forestry and Fisheries, Rogge Bay, South Africa.
authors.forename: Janet C
authors.initials: JC
authors.lastname: Coetzee
authors.affiliation: Raggy Charters, Port Elizabeth, South Africa.
authors.forename: Loyd C
authors.initials: LC
authors.lastname: Edwards
authors.affiliation: Percy FitzPatrick Institute, DST/NRF Centre of Excellence, University of Cape Town, Cape Town, South Africa.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Ryan
authors.affiliation: Branch: Fisheries Management, Department of Agriculture, Forestry and Fisheries, Rogge Bay, South Africa.
authors.forename: Johan
authors.initials: J
authors.lastname: Rademan
authors.affiliation: Branch: Fisheries Management, Department of Agriculture, Forestry and Fisheries, Rogge Bay, South Africa.
authors.forename: Jan J
authors.initials: JJ
authors.lastname: van der Westhuizen
authors.affiliation: DST/NRF Centre of Excellence at the Percy FitzPatrick Institute of African Ornithology, Department of Zoology, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa.
authors.forename: Lorien
authors.initials: L
authors.lastname: Pichegru
mesh_terms: D000349:Africa; D000818:Animals; D059001:Aquatic Organisms / Q000502:physiology*; D004455:Echolocation; D005399:Fishes / Q000502:physiology*; D005843:Geography; D016014:Linear Models; D011235:Predatory Behavior / Q000502:physiology*; D011998:Recreation; D012984:Software; D014159:Transducers