Showing papers by "Nicholas Polunin published in 1996"

Effects of fishing effort and catch rate upon the structure and biomass of Fijian reef fish communities

Abstract: An improved understanding of fishing effects is required to assess the sustainability of existing fishing practices and to determine the ecological implications of offering fishing concessions in marine reserves. The effects of fishing were investigated in six Fijian fishing grounds (qoliqoli) subject to different fishing intensities. A visual census technique was used to determine the structure and biomass of the shallow-water reef fish communities targeted by the fishers. A supervised voluntary logbook scheme was used to assess the size and composition of yield from the qoliqoli. The fish communities in the least intensively fished qoliqoli were significantly different from fish communities elsewhere. The significance of these differences was attributable to the greater biomass of invertebrate feeding and piscivorous fishes in the least intensively fished qoliqoli. Annual yields of herbivorous fishes ranged from 0.3 to 5.2% of the biomass estimated by visual census. There were no significant differences in herbivore biomass among qoliqoli subject to different fishing intensities. The biomass of invertebrate feeding fishes was significantly higher in the least intensively fished qoliqoli. The biomass of invertebrate feeding/piscivorous fishes was significantly higher in the two least intensively fished qoliqoli. In the two least intensively fished qoliqoli the estimated annual yields of invertebrate feeding and invertebrate feeding/piscivorous fishes did not exceed 4% of the biomass estimated by visual census. However, yields of these trophic groups approached 20% of biomass in the intensively fished qoliqoli where biomass was significantly lower. The fishing effects observed were primarily attributed to significant differences between the fish communities in the least intensively fished qoliqoli and all others. Thus, at higher fishing intensities, the biomass of target species provided a poor index of relative fishing pressure. The results suggest that the annual removal of 5% of fish biomass may cause significant structural changes in reef fish communities. Thus, it is important to ensure that fishing concessions and poaching activities are carefully regulated in marine reserves.

Habitat correlates of the distribution and biomass of Seychelles' reef fishes

Abstract: Relationships between quantitative measures of habitat type and the biomass of Chaetodon, Scarus and Parupeneus species were investigated across 35 reef sites in the Inner Seychelles Group. Multiple regression was used to determine the proportion of variance in biomass between sites which could be explained by depth, exposure, vertical relief, topographic complexity, live coral cover, coral rubble cover, rock cover, sand cover, underlying carbonate substrate, underlying sand substrate, underlying rock substrate and an index of fishing intensity. A significant proportion of the variance in biomass was explained by habitat variables and the index of fishing intensity for 7 of 12 Chaetodon species (23–52% of variance explained), 3 of 6 Parupeneus species (33–40%), and 10 of 13 Scarus species (14–46%). Within genera, different groups of habitat variables explained the variance in biomass for different species and, of the variables studied, only the proportion of underlying sand substrate failed to explain a significant proportion of the variance in biomass for any species. Quantitative relationships between the biomass of Chaetodon and habitat were often in accordance with those suggested by previous studies of their ecology, life-history and distribution at other Indo-Pacific locations. However, the habitat associations of the Parupeneus and some Scarus species have not been studied at other locations and clearly warrant further investigation. It was concluded that habitat was an important determinant of the distribution of many Seychelles reef fishes, but that the habitat variables examined were rarely the most important determinant of biomass. However, the inclusion of a procedure to collect habitat data provided a useful means by which to reduce the unexplained variance associated with visual census biomass estimates and therefore improves the possibility of elucidating the effects of other factors on the biomass of Seychelles reef fishes.

Fishing strategies, fishery development and socioeconomics in traditionally managed Fijian fishing grounds

Abstract: Increasing urban drift of the Fijian population coupled with an increasing proportion of Fijians in full time employment has led to escalating demands for fish and an associated rise in fish prices. Traditionally-managed reef fisheries are now exploited to meet existing subsistence needs and to supply large urban markets. The fishing strategies employed by three fishing communities were compared at different stages of their development from primitive to market economies. It was suggested that the fishing-rights owners have expanded their fisheries for economic gain, but that such expansion has, to date, had minimal impact on favoured fishing tactics and management regimes. However, the socioeconomic impact of the transition to a market economy is profound, with increasing reliance upon income from the fishery.

Trophodynamics of reef fisheries productivity

Abstract: The fish biomass of a few studied reefs varies from 2 to 24 tC km-2. Fish productivity of undisturbed tropical reefs is based on carbon sources of reefs and adjacent systems. The major primary producers of reefs are the microalgae of rocky habitats, with dominant areal coverage and high community net primary productivity (NPP). Shallow subtidal flats and reef margins support an especially high NPP. The exogenous carbon inputs to reefs derive from the plankton and other littoral ecosystems. Large external inputs are expected in areas subject to run-off and upwelling. Grazers constitute up to a quarter of the fish biomass and consume much of the microalgal NPP. There are both nocturnal and diurnal planktivores on reefs, and a Great Barrier Reef study measured import of plankton by fish to a reef front of 3 kgC m-1 year-1. Invertebrate feeders constitute the major part of the reef fish biomass and can evidently support food consumption rates in excess of 20tC km-2 year-1. Piscivores contribute 2–54% to the fish biomass of the few Indo-Pacific reefs studied and piscivory apparently exceeds 6tC km-2 year-1 on many tropical reefs. Process-orientated and biomass-based (e.g. ECOPATH) models of reef fish productivity have been synthesized. Reef fishes are major reservoirs of nutrient elements such as nitrogen. Detrital fluxes are substantial, but there is little information on pathways. Total fish productivity can exceed 20 t fresh weight km-2 year-1. There is no information on how reefs may systematically vary in fish productivity, but productivity is expected to be greater (1) in nutrient-rich waters than in nutrient-poor waters, (2) on small compared with large, reefs, (3) on reefs with adjacent productive communities compared with those without such communities, and (4) on reefs where a high proportion of the fish biomass consists of young individuals compared with those with older populations.

Developments in tropical reef fisheries science and management

Abstract: Extinction is conceivable for some species, including aquarium-fish stocks of high value and limited geographical range, but a biological basis exists for management of such small fishes. Immediate data needs are much greater for management of stocks of larger species which most reef fishing targets. The strengths and limitations of underwater visual census are now better recognized, and there is improved capacity for fish ageing, especially through otolith analysis, as a basis for growth and mortality assessments. Information technology has grown rapidly in scope, and modelling approaches offer a better foundation now for incorporating bio logical data into analytical approaches to sustainability. Reef fishery dynamics may widely be simpler than implied by their ‘multispecies‘ con dition, and in spite of their assumptions, surplus production models have proved useful in stock assessment. Empirical and exploratory approaches to sustainability, however, are more desirable than ever, as uncertainty about long-term ecosystem effects of fishing increases. Work of an experi mental nature urgently needs also to be directed at rehabilitation techni ques, especially marine fishery reserves. Successful management is, however, unlikely without local community involvement. Understandingthe scope of such participation demands a greater social science input to reef fishery studies; here as elsewhere there are encouraging trends in recent studies.

Environmental information and children: the big and the small

Abstract: A play at my elder son's school in March told the story of a group of aliens who come to Earth and are disgusted by the littering, the short-sighted chopping down of trees, crude exploitation of wild animals, and profligate use of harmful chemicals and materials, by Earth's environmentally uncanny inhabitants. That story was not entirely new to me: the songs which the children sang had been repeatedly practised in our home for weeks before the event! By the time the parts were performed on the stage of the old church hall, we were able to sing along. This participation added force to my recognition of how strong messages can be conveyed at an early stage in our lives, and how these can hopefully bring on the day more rapidly when practises which are unsound are discontinued. I do not recall such plays when I was of that age, although there was frequent encouragement to learn from the natural world, amongst others through appreciating the form of wind-dispersed seeds, the growth of crystals, or the development of a frog's egg. It seems now that the linkages between dwindling resources, a burgeoning human population and a finite planet are no longer aspects of natural history: they are ever-more immediate and increasingly-urgent pointers to a need for fuller understanding of the human condition in its ecological context. In 'The Bumblesnouts save the world', the present play performed by 5-8 year olds, the aliens, through sensitive example, stopped the shooting, halted the chopping, brought recycling where there was sheer waste and helped to ban excessive spraying. Earth's people learned to live within their carrying capacity. The Bumblesnouts thus saved the world! Encouraged by the hope that this type of education can bring, it is nevertheless worth asking how effective it will be, and where the message is not heard, what can be done to make it so. People in comfortable circumstances, like many in that hall, have time to listen to such a message, even though I do wonder whether it will cause them to alter their engrained habits. Which of them will now walk or cycle where they used to drive, or think about environmental impacts when they decide what products to buy? The next generation, my son's class-mates, may do better than their parents, but how much impact can such a child's play have amongst the less fortunate? Even here, in this corner of one of the most prosperous countries on Earth, poverty and social despondency are major issues. I believe that, were I to venture onto the streets of Newcastle upon Tyne to assess people's attitudes to environmental issues, I would be struck by the level of disinterest, or more particularly maybe, by an overriding concern for matters other than 'the environment', such as for the future of jobs, payment of a mortgage or security of a family. Quite clearly the impact of this small children's play, and other such allegories, on environmental practice in the local population as a whole is far from certain. Simply, the fact that I have the above doubt should alone be a matter for concern. If that is so here, in one part of England, what hope can there be for those corners of the world where a majority of people struggle for their livelihood? While hope abounds in the play, the question remains as to whether the signal is strong enough. The very same media which bring us messages such as that of the Bumblesnouts convey a multitude of other images to those of impressionable age. Judging from the menu to which my own children have access, particularly on television but also elsewhere, I suspect that more forceful to them are the prevalence of personal violence, of endless streets, cars and buildings, and of whole landscapes which are often devoid, it seems, of due consideration for the wider ecological linkages that sustain us. Sometimes, even eating would appear to have been dispensed with! In many parts of the world sheer struggle for survival is far more intense, and the prospects more daunting still. Education is playing its part there too, but the counter-pressures are overwhelming. Environmental conservation can only seem a rich man's iponcept to those with little to eat, little to burn, and little land to till. They often know how they would like to use their resources, but are prevented from conserving them by immediacy, lack of tenure for example and downright poverty. It is interesting to speculate that were a Bumblesnout crusade to happen there, it might defend people against outside pressures, for example by re-