Impacts On Populations

Most traders argue that the collection of marine ornamentals for the aquarium trade has no negative impact on reef fish populations. This is likely to be true for fisheries that are fairly small in comparison to the available resource base (fish population). A study in the Cook Islands showed that the total catch per unit effort remained constant between 1990 and 1994114, an indicator that fish populations on these islands were probably being harvested sustainably. In Australia, through the use of permits, the aquarium trade fishery is such that current levels of exploitation are sustainable41. However, Australia is an unusual case, as the Great Barrier Reef is the largest reef system in the world. The available habitat and the interconnectivity of fish populations provide resilience to adverse effects from a comparatively small marine

A typical collector's boat, called bancas, in the Philippines.

ornamental fishery41. Nevertheless, no matter how large a fishery is, not all fish are equally available or equally attractive to the industry and the most common fish are not necessarily those most favoured by hobbyists. Consequently, the effects of collecting for the aquarium fish trade should be measured with respect to their potential to deplete particular species or locations rather than viewed in terms of their global impact41.

Several countries in Asia and South America, for example, have begun to implement collection restrictions of certain ornamental fish species due to fears of reduction beyond recovery of population numbers115 and possible restructuring of reef communities due to sustained collection pressures on favoured species18,47. Although no marine species collected for the aquarium trade is known to have been driven to global extinction,

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studies carried out in Sri Lanka , Kenya1, the

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Philippines ' , Indonesia and Hawaii and anecdotal information from Australia41 all reported localized depletion of a number of target aquarium species of fish (e.g. butterflyfish, angelfish), due to heavy collecting pressure. However, there is a need for improved information on fishing effort121, catch and location, as well as more research on the effects of collection of fish for the aquarium trade. To date, most evaluations of direct impacts of the aquarium trade on reef fish (coral and invertebrates) populations come from visual censuses of fish densities, calculations of potential yield from

Cleaner fish, Labroides dimidiatus

Cleaner fish, Labroides dimidiatus

Cleaner fish and shrimp have stimulated discussion regarding the impact of marine ornamental fisheries on ecological processes. The two main groups of cleaner fish, which remove parasites and other material such as mucus and dead tissue125 from other reef organisms, are gobies and wrasses, but juvenile species of angelfish have also been observed feeding this way6. Many of these species are popular marine ornamental species (e.g. the French angelfish Pomacanthus paru, grey angelfish Pomacanthus arcuatus) with reports of the bluestreak cleaner wrasse, Labroides dimidiatus, being traded in large numbers - at least 20,000 a year from Sri Lanka44. GMAD importers' data (exporters' data from 1996-2003 in parenthesis where applicable) for the years 1988-2002 showed 33 individuals (173) exported from Fiji, 7,258 (23,597) from Indonesia, 62 from Kenya, 3,164 (3,707) from the Maldives, 30 from the Netherlands (re-export), 831 (23,159) from the Philippines, 97 from Singapore (re-export), 5,347 (11,100) from Sri Lanka and 132,092 from an unknown origin. Exporters' records also showed 43 individuals exported from the Marshall Islands, 51 from Palau, 78 from Saudi Arabia and 412 from the Solomon Islands.

modelling, estimated exports from custom records, or observations by experienced biologists and commercial fishers, often without quantitative validation37. The most thorough attempt at quantifying the impact of coral harvesting on species distribution and abundance was carried out in the Philippines. Results of the study, which compared coral community parameters at two sites, one where no collection occurred, the other heavily harvested, showed that coral collection had resulted in a reduction of coral cover (31 per cent) and coral density (64 per cent)122. Six commonly collected corals experienced declines in abundance, by more than 70 per cent122. Although coral exports have since been banned from the Philippines, it is possible that similar impacts would be observed at

Labroides dimidiatus tend to be more abundant at sites with greater numbers of sedentary fish, fewer predators, fewer fish aggregating in large schools and where the species richness of the fish community is higher125. Due to their role in maintaining the health and diversity of their 'clients', concerns have been raised about the impact on population levels of the species and reef health in general of removing large quantities of Labroides dimidiatus for the aquarium trade57. Most experimental removals of cleaner fish have failed to show

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significant effects , although parasite load was shown to increase four-fold on selected clients within 12 hours of being deprived of access to cleaner fish129.

A recent study which analysed the causal link between cleaner fish presence/absence and reef fish diversity at Ras Mohammed, Egypt, demonstrated that Labroides dimidiatus has a significant effect on local reef fish diversity with a more rapid increase in diversity being recorded when cleaner fish are added to individual reef patches130. Indeed, the removal of Labroides dimidiatus had no effect on fish abundance within the first few weeks, but a significant decline in fish diversity was recorded after a 4-20 month time period. On the other hand, the immigration or addition of Labroides dimidiatus individuals to reef patches led to an immediate, i.e. within 2-4 weeks, significant increase in fish diversity.

In addition to playing a key role in reef health - the removal of Labroides dimidiatus in large quantities for the aquarium trade is likely to have negative impacts on reef diversity - this species tends to fare poorly in aquarium conditions unless kept with a large community of fishes, and is not likely to accept substitute foods, so aquarists are advised to avoid it131.

heavily exploited sites in Indonesia. No comparable study to date has been carried out for Indonesia.

The only systematic study assessing the effects of harvesting fish for the aquarium trade on resource

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populations was carried out in Hawaii ' . The study reported that eight of the ten species most targeted by collectors showed declines in abundance at harvesting sites relative to control sites (i.e. where no collection of organisms was taking place). The magnitude of the overall decline was highest for Achilles tang (Acanthurus achilles) (57 per cent) and lowest for pebbled butterflyfish (Chaetodon multicinctus) (38 per cent). However, temporal effects such as yearly fluctuations in recruitmentxv of common species (e.g. yellow tang (Zebrasoma flavescens))

might be substantial for the time frame of such a study and thus results need to be evaluated with care. The study also showed that, although the three most heavily collected species were herbivorous (Zebrasoma flavescens, spotted surgeonfish (Ctenochaetus strigosus) and Acanthurus achilles), and suffered significant reductions in abundance at collection sites, no increases in algae abundance were recorded when compared with control sites120.

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