Effects of fishing pressure on the fish resources of the Port Moresby barrier and fringing reefs

Are marine reserves effective in management of reef fisheries

Coastal fisheries in the South Pacific are reviewed, including descriptions of fisheries, catch composition, catch rates and fisheries biology studies conducted on target stocks. The most widely targeted coastal fish stocks are reef fishes and coastal pelagic fishes. Small pelagic species are important for subsistence and small-scale commercial fisheries. Previously, small pelagic resources were important as a source of live bait for pole-and-line tuna fishing, but this method is declining and only one large bait fishery is left in the region in the Solomon Islands. The pole-and-line bait fisheries represent the only large-scale industrial fisheries to have operated in the coral reef lagoons of the Pacific. Estuarine resources are of major importance only in the large islands of Melanesia but are the staple diet of a relatively large proportion of the total South Pacific population. Deep slope fish stocks form the basis of only two commercial fisheries in the region and expansion of deep slope fishing comparable with the 1970s and 1980s is unlikely to occur again. Commercial fisheries development is currently orientated towards small- and medium-scale long-line fisheries for offshore pelagic resources, where high value tunas and billfishes are caught for export markets. The total coastal fisheries production from the region amounts to just over 100000 tyr -l , worth a nominal US$262 000 000. About 80% of this production is from subsistence fishing. Just under half the total annual commercial catch comes from fishing on coral reefs, which includes a small tonnage of deep slope species. Invertebrates are the most valuable inshore fisheries resources and these include sea-cucumbers, trochus and pearl oyster. Lobsters and mangrove crabs form the basis of small-scale commercial fisheries, as also do penaeid shrimps, except in PNG where they are caught in large quantities through trawling. Mariculture of shrimps is becoming increasingly popular in the region and is a major industry in New Caledonia. The greatest influence on coastal fisheries in the Pacific through the next decade is likely to come from southeast and east Asia, where the demand for high value coastal fishes and invertebrates has led to large scale depletions and has motivated entrepreneurs to seek stocks in the neighbouring Pacific islands.

background

Coastal fisheries in the pacific islands

Overfishing is considered one of the three most significant threats to coral reef ecosystems. Exponentially increasing human populations in the tropics have placed enormous demands upon reefs as a food source. At high intensities, termed ecosystem or Malthusian overfishing, fishing causes major direct and indirect effects on the community structure of fishes and other organisms. It reduces species diversity and leads to local extinctions not only of target species but also of other species not fished directly. Conceivably it could also lead to global extinctions. Loss of keystone species, such as predators of echinoderms, through fishing, can lead to major effects on reef processes, such as accretion of calcium carbonate. Ultimately, sustained heavy fishing may lead to loss of entire functional groups of species, resulting in impairment of the potentially important ecosystem functions provided by those groups. Overfishing has been shown to interact with other agents of disturbance to reduce the ability of reefs to recover from natural occurrences such as hurricanes. Effective management of fishing will require a deeper understanding of the effects of exploitation than we now possess. Research initiatives are underway to examine the responses of fish populations to fishing, generally responses to protection from fishing. There is, however, an urgent need to look beyond fish communities and to consider the entire reef ecosystem. Studies that integrate population and community biology with ecosystem processes will provide a much better understanding of the effects of biodiversity loss on reef function and will improve our ability to manage these complex systems.



Efecto de la pesca sobre la estructura ecosistemica de los arrecifes de coral



Resumen: La sobrepesca es considerada como una de las tres amenazas mas significativas para los arrecifes de coral. En los tropicos, las poblaciones humanas en incremento exponencial han impuesto demandas enormes sobre los arrecifes como fuentes de alimentos. A intensidades de pesca altas, denominadas sobrepesca ecosistemica o Maltusiana, la pesca causa importantes efectos directos e indirectos en la estructura de la comunidad de peces y otros organismos. La sobrepesca reduce la diversidad de especies y lleva a la extincion local tanto de las especies pescadas como de otras especies no pescadas en forma directa. En forma concebible puede tambien llevar a extinciones globales. La perdida de especies clave por medio de la pesca, tales como predadores de equinodermos, puede tener ejectos importantes sobre los procesos biologicos del arrecife, tales como la acumulacion de carbonato de calcio. En ultima instancia, la pesca intensiva sostenida puede llever a la perdida de grupos funcionales de especies enteras, lo que resulta en la pedida de las funciones ecosistemicas potencialmente importantes provistas por estas especies. Se ha demostrado que la sobrepesca interactua con otros agentes perturbadores para reducir la habilidad de los arrecifes para recuperarse de fenomenos naturales como los huracanes. El manejo pesquero efectivo requerira de un entendimiento mas profundo de los efectos de la explotacion. Se estan llevando a cabo iniciativas de investigacion para examinar las respuestas de las poblaciones de peces a la pesca, se trata generalmente de estudios sobre la respuesta de las poblaciones a la proteccion de la pesca. Existe sin embargo, una necesidad urgente de mirar mas alla de las comunidades de peces y considerar a la totalidad del ecosistema. Los estudios que integran la biologia de poblaciones y comunidades con los procesos ecosistemicos, proveerian de un mejor entendimiento de los efectos de la perdida de la biodiversidad sobre las funciones de los arrecifes y mejorarian nuestra habilidad para manejar estos sistemas complejos.

Effects of Fishing on the Ecosystem Structure of Coral Reefs

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.

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

Coral reefs are the most diverse ecosystem in the sea. Throughout the world they are being over-fished, polluted and destroyed, placing biodiversity at risk. To date, much of the concern over biodiversity loss has centred on local losses and the possibility of global extinction has largely been discounted. However, recent research has shown that 24% of reef fish species have restricted ranges (< 800 000 km2), with 9% highly restricted (< 50 000 km2). Restricted-range species are thought to face a greater risk of extinction than more widespread species since local impacts could cause global loss. We searched for information on status in the wild and characteristics of 397 restricted-range reef fish species. Fish body size, habitat requirements and usefulness to people were compared with those of a taxonomically-matched sample of more widespread species. We found that on average species with restricted ranges were significantly smaller (mean total length 19.1 cm versus 24.4 cm), tended to have narrower habitat requirements and were less used by people. Greater habitat specificity will tend to increase extinction risk while, if real, more limited usefulness (equivalent to exploitation) may reduce risk. Fifty-eight percent of restricted-range species were considered common/abundant in the wild and 42% uncommon/rare. Population status and threats to 319 species for which data were available were assessed according to the categories and criteria of the IUCN red list of threatened animals. A number of species were found to be rare, were exploited and had highly restricted ranges overlapping areas where reef degradation is particularly severe, placing them at a high risk of extinction. Five species were listed as Critically Endangered, two of them possibly already extinct in the wild, one as Endangered and 172 as Vulnerable. A further 126 species fell into Lower Risk categories and 11 were considered Data Deficient. Given the intensity of impacts to reefs, the broad geographical areas affected and the large numbers of restricted-range species, global extinctions seem likely. Urgent management action is now crucial for the survival of several species of reef fishes.

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Effects of fishing pressure on the fish resources of the Port Moresby barrier and fringing reefs

Citations

Are marine reserves effective in management of reef fisheries

Coastal fisheries in the pacific islands

Effects of Fishing on the Ecosystem Structure of Coral Reefs

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

The threatened status of restricted-range coral reef fish species

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