News Archive

Two UWA Oceans Institute Students won first and second prizes at the recent AMSA(WA) Honours Prizes.

Jordan Goetze 1st prize and Bryce McLaren 2nd prize.

The winners of the 2010 Australian Marine Science Association(WA) Honours Prizes are

Jordan Goetze 1st  University of Western Australia

Bryce McLaren 2nd University of Western Australia

Nick Breheny 3rd Murdoch University

Evidence of artisanal fishing impacts and depth refuge in assemblages of reef fish of a Fijian Island

Jordan Goetze University of Western Australia

Protection from fishing generally results in an increase in the abundance and biomass of targeted fishes within marine reserve boundaries. Natural refuges such as depth may also protect targeted species, yet few studies have looked at the effects of depth concomitant with marine reserves. There is also limited research into the effects of protection on assemblages of coral reef fish in developing countries where fishing is mostly small-scale and artisanal. The effects of protection and depth on assemblages of reef fish in the Kubulua district of Vanua Levu Island, Fiji were studied using baited remote underwater stereo-video systems. Videos were collected from shallow (5-8 m) and deep (25-30 m) sites inside and outside of the Namena reserve (60.6 km2, 13 years old) and Namuri reserve (4.25 km2, 4 years old). The relative abundances of 341 species and biomass of 258 species of fishes was recorded. In the shallow waters of the Namena reserve species richness was 34% greater than surrounding fished areas, while in deep waters of the reserve, species richness was only 9% greater than comparable fished areas. Differences in the composition of fish assemblages existed between protected and fished areas in the deep, but not in the shallow, suggesting a depth refuge is not leadingto an increase in the biomass or abundance of fishes outside the Namena reserve. Targeted fish species belonging to the food fish grades A, B and C (highest price to lowest) of the Kubulua district were more abundant in the Namena reserve than surrounding fished areas, while the remaining non-targeted species were not. No differences in the species richness, abundance or biomass of targeted and non-targeted species were observed inside and outside of the Namuri reserve, most likely due to its smaller size and age, compared to the Namena reserve. This study suggests that artisanal fishing impacts on the structure of assemblages of fishes, but differences may only be detected in large reserves that have been established for a long period of time. Observed effects of protection also vary with depth, highlighting the importance of incorporating multiple depth strata in the design of marine reserves and sampling over this full depth range when monitoring.

Assemblages of reef fish at Rottnest Island: the effect of protection and a comparison of stereo-video techniques

Bryce William McLaren University of Western Australia

The Rottnest Island marine environment has a unique mixture of tropical and temperate organisms. Due to its close proximity to Perth it has a high level of recreational use, requiring rigorous management decisions to ensure sustainability and minimise conflict between multiple users. In 2007 the two existing sanctuary zones (Kingston Reef and Parker Point) were extended and three new partial sanctuary zones were created. In collaboration with the Rottnest Island Authority a combination of baited remote underwater stereo-video (stereo-BRUV) and diver operated stereo-video (stereo-DOV) techniques were used to obtain fishery independent data on reef fish assemblages at comparable sites inside and outside of the five protected areas. In contrast to a previous study of Kingston Reef Sanctuary Zone there were no consistent differences in the composition of the assemblages of reef fishes; however, there were some differences in the relative abundances and biomass of some non-target species inside and outside the protected areas. Environmental data were used to investigate the small scale biogeography of the fish populations around the island. Wave exposure (calculated as fetch) and temperature (as a gradient from Kingston Reef to West End) were correlated with biomass data from both stereo-video methods using multivariate regression. The results showed that exposure and temperature significantly influenced the fish assemblages. The implications of this for future monitoring are discussed. To evaluate the sampling design of this benchmark study the statistical power of the two stereo-video techniques were compared using the estimated variance of three conspicuous fish species. This showed that stereo-BRUV generally had a higher statistical power to detect changes in their populations. A cost-benefit analysis also showed that stereo-BRUV was generally more cost-efficient than stereo-DOV transects for detecting any change in the fish assemblage. Based on previous studies of sanctuary zones in comparable regions, most of the sanctuary zones at Rottnest Island are too new to expect any differences to exist. However, the level of partial protection within these zones may also be a contributing factor. The previous study of the Kingston Reef Sanctuary Zone was done approximately five years ago, during summer. Therefore the contrasting results of this study may be due to fish assemblages changing within that time or an effect of seasonal variation. The minimal effect of exposure on fish assemblages suggests that the sampling design is appropriate Continued monitoring is recommended to encompass both summer and winter sampling.. While stereo-DOV methods have their advantages, it may be more cost effective to focus sampling purely on stereo-. However, the small size of the sanctuary zones restricts the number of stereo-BRUV replicates, and thus the statistical power to detect differences, less so than stereo-DOV. Given the different limitations of these two methods, a combination of these techniques may be required to achieve the most complete description of assemblages of reef fish at Rottnest Island. Continuing to collect data from the two complementary methods will also make results more comparable to other studies, and allow the monitoring to be adapted to future management questions that have not yet arisen.

Media references

Janine MacDonald (UWA Public Affairs) (+61 8) 6488 5563 / (+61 4) 32 637 716

[email protected]