Terry Fuller
Posts: 2429
Joined: 5 June 2003 From: Hamersley, Western Australia Status: online
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I can recall reading about studies showing when predators high in the food chain are removed en masse (think spanglies) things like urchins, starfish and marine snails increase in number and can disrupt the ecosystem causing coral to die and be replaced by algae. Greg. That's just one of the "part truths" and misrepresentations being used - and it is not as simple as that. Extract from Mark Westera's thesis http://www.chs.ecu.edu.au/org/sons/students/postgrad_students/documents/m_westera_thesis_jun-04.pdf It's 127 pages, it's a thesis, so there is a lot of detail, and it is VERY complex. It's findings are often quoted as THE justification for closing extra areas at Ningaloo. However here's the abstract. I have highlighted some bits which are very important - these are his words, his analysis of his research and his data... Some observations, like there are more fish of some species in sanctuary zones than outside them, are motherhood obvious and it would be a real worry if it wasn't true. Thesis is titled:- "The effect of recreational fishing on targeted fishes and trophic structure, in a coral reef marine park. Abstract:- Recreational line fishing is highly targeted at predatory fishes, making them vulnerable to overfishing. These same fishes play a role in trophic structure by regulating prey species. Despite increasing numbers of fishers, few studies have investigated the potential effects of recreational fishing on fish populations and subsequent trophic effects. This project investigated whether there were differences in fishes and benthos between unfished and recreationally fished areas, and whether the removal of targeted fishes influenced trophic structure. The study was conducted at the Ningaloo Marine Park, Western Australia, which had Sanctuary (no-take) and Recreation (recreationally fished) Zones. Data were collected from three regions (Mandu, Osprey and Maud) and replicated over time. Fish assemblages, benthos and trophic interactions were compared between zones at each region. At Ningaloo the lethrinids (emperors) are a top-order predatory fish and the preferred target of recreational anglers. The algal-grazing urchin Echinometra mathaei comprised 51% of macroinvertebrate abundances and was heavily preyed upon by lethrinids, being recorded in 50% of the guts of sampled fish. In all regions, Sanctuary Zones had a greater biomass of lethrinids than Recreation Zones, but there were no differences in non-targeted fishes between zones. Despite the consistent effect on lethrinids, there were inconsistencies among regions in the predator-prey relationships. At Mandu, Echinometra mathaei abundances were inversely related to lethrinid biomass, suggesting a strong predator-prey interaction. In the Recreation Zone, the abundances of E. mathaei were four times greater, and macro-algal cover was half, that of the Sanctuary Zone. Furthermore, algal composition differed between zones, and this was driven by fucoid brown algae, which dominated the diets of E. mathaei. This was interpreted as evidence of a trophic cascade resulting from the removal of lethrinids at the Recreation Zone. At Maud, different results were recorded. Abundances of Echinometra mathaei and lethrinids were both higher in the Sanctuary Zone, than the adjacent Recreation Zone. E. mathaei reside in the crevices of rock, dead coral or Echinopora coral, which provided refuge from predation and this habitat was more available in the Sanctuary Zone. It is suggested that the availability of this habitat confounded the effects of predation. Macroalgal cover was lower in the Sanctuary Zone indicating a grazing effect from E. mathaei. At Osprey there was higher cover of E. mathaei habitat in the Sanctuary than the Recreation Zone. However, there were no differences in macro-algal cover, which was consistent with a lack of difference in E. mathaei abundances. The effect of E. mathaei grazing was unlikely to have been confounded by fishes that graze macro-algae, as they did not differ between zones at any region. These results indicate that recreational fishing reduced fish populations below that of adjacent protected areas at Ningaloo Marine Park, and in one region this resulted in a trophic cascade. This may be the first study that has recorded evidence of a trophic cascade where recreational line fishing is the only means of extraction. However, the results also show that this is not a consistent response to reduced fishing pressure; in other regions, changes in predatory fish abundance did not result in differences in the abundances of their prey, suggesting no trophic cascade. The studies have contributed towards an understanding of fish-habitat interactions and provide a baseline for future monitoring of the Ningaloo Marine Park. They also have important implications for marine park managers in terms of defining their expectations when implementing Sanctuary Zones. The results also show that Sanctuary Zones have the potential to be effective tools for fisheries management." Page 98 of CHAPTER 5 - CONCLUSION, MANAGEMENT IMPLICATIONS AND FUTURE RESEARCH says "The effect of predators on prey observed at Mandu was not consistent across all regions. At Maud, high abundances of Echinometra mathaei prevailed in the Sanctuary Zone despite the higher biomass and size of predatory fishes than in the Recreation Zone. At Maud, the Sanctuary Zone was characterised by the cover of dead coral, rock and Echinopora corals that provided refuge for E. mathaei. It is likely that this difference in habitat availability mediated the effects of higher predation in the Sanctuary Zone. At the Osprey region there were no significant differences between zones in E. mathaei abundances despite potentially higher predation from lethrinids in the Sanctuary Zone, possibly because of a greater availability of refuges in the Sanctuary Zone." Some comments on research from one research group's submission were:- It should also be noted that localised fish feeding in sanctuary zones may result in artificially high numbers of fish, leading to inaccuracies when comparing sanctuary and general/recreational zones; examples include Coral Bay and Mandu. Again, this highlights the lack of baseline information for the Ningaloo MP." Mandu is the area used to justify expansions of the no take zones based on Westera's comments on the effect of removing predators such as spangled emperor. The statement "The results also show that Sanctuary Zones have the potential to be effective tools for fisheries management." needs a read of Chapter 5 - CONCLUSION, MANAGEMENT IMPLICATIONS AND FUTURE RESEARCH to be put into context. CHAPTERs 5 and 6 are well worth a read coz they show what's missing in the knowledge about Ningaloo, and the challenges facing the researchers, even if they get enough money. Also note the number of times "may", "might" "possible" "potential" and other similar qualifying words are used. Rec anglers aren't opposed to Marine Parks. Rec anglers aren't opposed to sanctuary zones. Rec anglers want sustainable fishing and good fishing experiences. Rec anglers want to protect spawning stocks and spawning aggregations (evidence - rec anglers actions on Cockburn Sound Pink Snapper) but these don't necessarily need total closures all year long. Rec anglers want to protect nursery areas. (But where are they along the Ningaloo Marine Park?) What's the impact of proposed salt works and prawn trawlers in Exmouth Gulf and fish trawlers north/east up the coast? Marine Parks and Sanctuary zones aren't the only way to achieve these. Rec anglers don't want to be the only group which has any restrictions applied. Marine Parks and Sanctuary zones limited to State waters 3 nautical miles from the coast by themselves are not SUFFICIENT to achieve these. That needs a region wide approach. Marine Parks and Sanctuary zones are NOT the right way to do Fisheries Management. If the reality is that too many fish are being caught (BIG IF) then give us the data and all thinking Rec anglers will support changes which will really fix that problem. Closing areas to fishing without managing the fishing pressure WILL lead to more pressure on the areas which stay open and can lead to collapse of the fishery DESPITE the sanctuary zones. Then in ten years there'll be a call to close off even more areas, and more areas lost to rec anglers..... TerryF ===== There'll be more.....
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