Similarities between Line Fishing and Baited Stereo-Video Estimations of Length-Frequency: Novel Application of Kernel Density Estimates

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Abstract

Age structure data is essential for single species stock assessments but length-frequency data can provide complementary information. In south-western Australia, the majority of these data for exploited species are derived from line caught fish. However, baited remote underwater stereo-video systems (stereo-BRUVS) surveys have also been found to provide accurate length measurements. Given that line fishing tends to be biased towards larger fish, we predicted that, stereo-BRUVS would yield length-frequency data with a smaller mean length and skewed towards smaller fish than that collected by fisheries-independent line fishing. To assess the biases and selectivity of stereo-BRUVS and line fishing we compared the length-frequencies obtained for three commonly fished species, using a novel application of the Kernel Density Estimate (KDE) method and the established Kolmogorov–Smirnov (KS) test. The shape of the length-frequency distribution obtained for the labrid Choerodon rubescens by stereo-BRUVS and line fishing did not differ significantly, but, as predicted, the mean length estimated from stereo-BRUVS was 17% smaller. Contrary to our predictions, the mean length and shape of the length-frequency distribution for the epinephelid Epinephelides armatus did not differ significantly between line fishing and stereo-BRUVS. For the sparid Pagrus auratus, the length frequency distribution derived from the stereo-BRUVS method was bi-modal, while that from line fishing was uni-modal. However, the location of the first modal length class for P. auratus observed by each sampling method was similar. No differences were found between the results of the KS and KDE tests, however, KDE provided a data-driven method for approximating length-frequency data to a probability function and a useful way of describing and testing any differences between length-frequency samples. This study found the overall size selectivity of line fishing and stereo-BRUVS were unexpectedly similar.

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Most cited references 5

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Habitat degradation and fishing effects on the size structure of coral reef fish communities.

Nicholas V C Polunin, Tracey Turner, Nicholas K. Dulvy … (2010)

Overfishing and habitat degradation through climate change pose the greatest threats to sustainability of marine resources on coral reefs. We examined how changes in fishing pressure and benthic habitat composition influenced the size spectra of island-scale reef fish communities in Lau, Fiji. Between 2000 and 2006 fishing pressure declined in the Lau Islands due to declining human populations and reduced demand for fresh fish. At the same time, coral cover declined and fine-scale architectural complexity eroded due to coral bleaching and outbreaks of crown-of-thorns starfish, Acanthaster planci. We examined the size distribution of reef fish communities using size spectra analysis, the linearized relationship between abundance and body size class. Spatial variation in fishing pressure accounted for 31% of the variation in the slope of the size spectra in 2000, higher fishing pressure being associated with a steeper slope, which is indicative of fewer large-bodied fish and/or more small-bodied fish. Conversely, in 2006 spatial variation in habitat explained 53% of the variation in the size spectra slopes, and the relationship with fishing pressure was much weaker (approximately 12% of variation) than in 2000. Reduced cover of corals and lower structural complexity was associated with less steep size spectra slopes, primarily due to reduced abundance of fish < 20 cm. Habitat degradation will compound effects of fishing on coral reefs as increased fishing reduces large-bodied target species, while habitat loss results in fewer small-bodied juveniles and prey that replenish stocks and provide dietary resources for predatory target species. Effective management of reef resources therefore depends on both reducing fishing pressure and maintaining processes that encourage rapid recovery of coral habitat.

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Measurement of body size and abundance in tests of macroecological and food web theory.

Simon Jennings, José de Oliveira, Tracy J. Warr (2006)

1. Mean body mass (W) and mean numerical (N) or biomass (B) abundance are frequently used as variables to describe populations and species in macroecological and food web studies. 2. We investigate how the use of mean W and mean N or B, rather than other measures of W and/or accounting for the properties of all individuals, can affect the outcome of tests of macroecological and food web theory. 3. Theoretical and empirical analyses demonstrate that mean W, W at maximum biomass (W(mb)), W when energy requirements are greatest (W(me)) and the W when a species uses the greatest proportion of the energy available to all species in a W class (W(mpe)) are not consistently related. 4. For a population at equilibrium, relationships between mean W and W(me) depend on the slope b of the relationship between trophic level and W. For marine fishes, data show that b varies widely among species and thus mean W is an unreliable indicator of the role of a species in the food web. 5. Two different approaches, 'cross-species' and 'all individuals' have been used to estimate slopes of abundance-body mass relationships and to test the energetic equivalence hypothesis and related theory. The approaches, based on relationships between (1) log(10) mean W and log(10) mean N or B, and (2) log(10) W and log(10) N or B of all individuals binned into log(10) W classes (size spectra), give different slopes and confidence intervals with the same data. 6. Our results show that the 'all individuals' approach has the potential to provide more powerful tests of the energetic equivalence hypothesis and role of energy availability in determining slopes, but new theory and empirical analysis are needed to explain distributions of species relative abundance at W. 7. Biases introduced when working with mean W in macroecological and food web studies are greatest when species have indeterminate growth, when relationships between W and trophic level are strong and when the range of species'W is narrow.

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Sperm competition and sex change: a comparative analysis across fishes.

Andrew Reynolds, Charles Goodwin, Sylvana M. Côté … (2007)

Current theory to explain the adaptive significance of sex change over gonochorism predicts that female-first sex change could be adaptive when relative reproductive success increases at a faster rate with body size for males than for females. A faster rate of reproductive gain with body size can occur if larger males are more effective in controlling females and excluding competitors from fertilizations. The most simple consequence of this theoretical scenario, based on sexual allocation theory, is that natural breeding sex ratios are expected to be female biased in female-first sex changers, because average male fecundity will exceed that of females. A second prediction is that the intensity of sperm competition is expected to be lower in female-first sex-changing species because larger males should be able to more completely monopolize females and therefore reduce male-male competition during spawning. Relative testis size has been shown to be an indicator of the level of sperm competition, so we use this metric to examine evolutionary responses to selection from postcopulatory male-male competition. We used data from 116 comparable female-first sex-changing and nonhermaphroditic (gonochoristic) fish species to test these two predictions. In addition to cross-species analyses we also controlled for potential phylogenetic nonindependence by analyzing independent contrasts. As expected, breeding sex ratios were significantly more female biased in female-first sex-changing than nonhermaphroditic taxa. In addition, males in female-first sex changers had significantly smaller relative testis sizes that were one-fifth the size of those of nonhermaphroditic species, revealing a new evolutionary correlate of female-first sex change. These results, which are based on data from a wide range of taxa and across the same body-size range for either mode of reproduction, provide direct empirical support for current evolutionary theories regarding the benefits of female-first sex change.

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Author and article information

Contributors

David Mark Bailey: Role: Editor

Journal

Journal ID (nlm-ta): PLoS One

Journal ID (iso-abbrev): PLoS ONE

Journal ID (publisher-id): plos

Journal ID (pmc): plosone

Title: PLoS ONE

Publisher: Public Library of Science (San Francisco, USA )

ISSN (Electronic): 1932-6203

Publication date Collection: 2012

Publication date (Electronic): 29 November 2012

Volume: 7

Issue: 11

Electronic Location Identifier: e45973

Affiliations

[1 ]The UWA Oceans Institute, The University of Western Australia, Perth, Western Australia, Australia

[2 ]School of Plant Biology, The University of Western Australia, Perth, Western Australia, Australia

[3 ]Centre for Marine Futures and School of Animal Biology, The University of Western Australia, Perth, Western Australia, Australia

[4 ]Western Australian Fisheries and Marine Research Laboratories, Department of Fisheries, Government of Western Australia, Perth, Western Australia, Australia

[5 ]Centre for Fish and Fisheries Research, School of Biological Sciences and Biotechnology, Murdoch University, Perth, Western Australia, Australia

University of Glasgow, United Kingdom

Author notes

* E-mail: timothy.langlois@ 123456uwa.edu.au

Competing Interests: The authors have declared that no competing interests exist.

Conceived and designed the experiments: TJL. Performed the experiments: TJL DVF CBW DLM SAH. Analyzed the data: BRF TJL. Wrote the paper: TJL BRF DVF CBW DLM SAH ESH JJM.

Article

Publisher ID: PONE-D-12-10981

DOI: 10.1371/journal.pone.0045973

PMC ID: 3510158

PubMed ID: 23209547

SO-VID: ac528794-c658-475a-9918-078008bdb3a1

License:

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

History

Date received : 19 April 2012

Date accepted : 22 August 2012

Page count

Pages: 9

Funding

The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. This research received funding from the Western Australian Marine Science Institute project to assist with the implementation of an ecosystem approach to the management of fisheries resources (TJL) and from the iVEC summer industry internship (BRF). Stereo-BRUVS data was sourced from ‘Securing Western Australia's Marine Futures’ a combined Australian and Western Australian Government Natural Heritage Trust (NHT) Strategic Project developed by South Coast Natural Resource Management, ‘Monitoring of Reef Observation Areas at the Houtman-Abrolhos Islands’ a combined Australian and Western Australian Government NHT initiative through the Northern Agricultural Catchment Council, and ‘Benchmarking of the Rottnest Island Marine Reserve’ developed by the Rottnest Island Authority. Fisheries Research and Development Corporation (FRDC 2000/137) funded line sampling for C. rubescens. Murdoch University funded line sampling for E. armatus. Pagrus auratus line sampling was funded by both Murdoch University and the Department of Fisheries.

Similarities between Line Fishing and Baited Stereo-Video Estimations of Length-Frequency: Novel Application of Kernel Density Estimates

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Most cited references 5

Habitat degradation and fishing effects on the size structure of coral reef fish communities.

Measurement of body size and abundance in tests of macroecological and food web theory.

Sperm competition and sex change: a comparative analysis across fishes.

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