Jurgenne H. Primavera

Effect of aquaculture on world fish supplies

Global production of farmed fish and shellfish has more than doubled in the past 15 years. Many people believe that such growth relieves pressure on ocean fisheries, but the opposite is true for some types of aquaculture. Farming carnivorous species requires large inputs of wild fish for feed. Some aquaculture systems also reduce wild fish supplies through habitat modification, wild seedstock collection and other ecological impacts. On balance, global aquaculture production still adds to world fish supplies; however, if the growing aquaculture industry is to sustain its contribution to world fish supplies, it must reduce wild fish inputs in feed and adopt more ecologically sound management practices.

Coastal Ecosystem-Based Management with Nonlinear Ecological Functions and Values

A common assumption is that ecosystem services respond linearly to changes in habitat size. This assumption leads frequently to an “all or none” choice of either preserving coastal habitats or converting them to human use. However, our survey of wave attenuation data from field studies of mangroves, salt marshes, seagrass beds, nearshore coral reefs, and sand dunes reveals that these relationships are rarely linear. By incorporating nonlinear wave attenuation in estimating coastal protection values of mangroves in Thailand, we show that the optimal land use option may instead be the integration of development and conservation consistent with ecosystem-based management goals. This result suggests that reconciling competing demands on coastal habitats should not always result in stark preservation-versus-conversion choices.

Non‐linearity in ecosystem services: temporal and spatial variability in coastal protection

Natural processes tend to vary over time and space, as well as between species. The ecosystem services these natural processes provide are therefore also highly variable. It is often assumed that ecosystem services are provided linearly (unvaryingly, at a steady rate), but natural processes are characterized by thresholds and limiting functions. In this paper, we describe the variability observed in wave attenuation provided by marshes, mangroves, seagrasses, and coral reefs and therefore also in coastal protection. We calculate the economic consequences of assuming coastal protection to be linear. We suggest that, in order to refine ecosystem-based management practices, it is essential that natural variability and cumulative effects be considered in the valuation of ecosystem services.

Development and conservation of Philippine mangroves: institutional issues

The decline of Philippine mangroves from half a million hectares in 1918 to only 120 000 ha in 1994 may be traced to local exploitation for fuelwood and conversion to agriculture, salt beds, industry and settlements. But brackishwater pond culture, whose history is intertwined with that of mangroves, remains the major cause of loss. The paper discusses the institutional issues — aquaculture as development strategy, low economic rent of mangroves, overlapping bureaucracy and conflicting policies, corruption, weak law enforcement and lack of political will — relevant to this decline. Recommended policies are based on these institutional factors and the experiences in mangrove rehabilitation including community-based efforts and government programs such as the 1984 Central Visayas Regional Project. These recommendations include conservation of remaining mangroves, rehabilitation of degraded sites including abandoned ponds, mangrove-friendly aquaculture, community-based and integrated coastal area management, and provision of tenurial instruments.

Genetic diversity of wild and cultured Black Tiger Shrimp (Penaeus monodon) in the Philippines using microsatellites

Abstract Six microsatellites were used to study (1) the genetic diversity of wild Penaeus monodon shrimp from four geographic regions (Palawan, Quezon, Capiz and Negros Occidental-W) in the Philippines, and (2) its association with the status of mangroves and intensity of shrimp culture systems in these regions. Two cultured populations (Negros Occidental-C and Antique) were used for comparison. All six microsatellite loci were polymorphic. A total of 184 different alleles were found over all loci. The total number of alleles per locus ranged from 6 to 54, with allele size ranging from 159 base pairs (bp) to 400 bp. The observed heterozygosity of the six loci ranged from 0.47 to 1.00. The number of genotypes per locus ranged from 5 to 70. F st values showed significant genetic differentiation among the four wild populations. Genetic differences between wild populations were also detected by pairwise comparison based on genotypic and allelic frequencies. Genetic differentiation among wild populations exhibited a positive correlation with mangrove status and intensity of culture systems at P =0.083. The Negros Occidental-W population, which originated from an area with the most severe mangrove loss and the most intensive culture systems, was the most significantly differentiated population. It also showed less genotypes per locus than the other three wild populations, suggesting a decrease in genetic diversity in this population. The population from Capiz, a province with a wide area of extensive culture ponds and few remaining secondary mangroves was the second most differentiated population. The Quezon population, which originated from an area with a few extensive culture ponds and less mangrove destruction, was not genetically different from the Palawan population, which was from a pristine site with mostly primary mangroves and no major aquaculture industry. The cultured populations showed less genetic diversity and were significantly different from the four wild populations based on pairwise F st values and pairwise comparisons of allelic and genotypic frequencies. The results suggest that (a) there was a significant genetic differentiation among the wild P. monodon populations in the Philippines, and (b) the cultured populations were significantly differentiated from the natural populations. More replicate samples from each of the geographic regions are needed to conclusively determine the possibility of an association between genetic differentiation and the status of mangroves and/or intensity of shrimp culture systems.

Induced maturation and spawning in five-month-old Penaeus monodon Fabricius by eyestalk ablation☆

Abstract Pond-reared sugpo (Penaeus monodon Fabricius) females from coastal fry harvested after 4 months were unilaterally ablated and stocked in an indoor concrete tank with an equal number of males. The first two spawnings were obtained 22 d after ablation with the eggs hatching into viable nauplii. Five months (12–15 d from spawning to first postlarva, 14–16 d from first postlarva to coastal fry, and 4 months rearing in ponds) is the shortest age on record at which P. monodon females can be successfully ablated.

Are mangroves worth replanting? The direct economic benefits of a community-based reforestation project

SUMMARY Competition for coastal land use and overexploitation have reduced or degraded mangrove coverage throughout much of their distribution, especially in South-east Asia. Timber production was the initial motivation for early mangrove reforestation projects. Morerecently,benefitsfromprotectionagainsterosion and extreme weather events and direct improvements in livelihoods and food security are perceived as justifications for such restoration efforts. This study examines the socioeconomic impacts of a communityled reforestation project in the Philippines through a survey of the local fishers. Revenues from mangrove fisheries,tourismandtimberresultinanannualbenefit to the community of US

Studies on the egg quality of Penaeus monodon Fabricius, based on morphology and hatching rates

315ha −1 yr −1 .T his fi gure is likelytobeconsiderablymoreifthecontributionofthe mangrove to the coastal catch of mangrove-associated species is included. This estimate only includes direct benefits to the community from mangroves, and not intangible benefits such as coastal protection, which paradoxically is perceived by the community as one of the most important functions. More than 90% of all fishers, regardless of where they fished, thought the mangrove provided protection from storms and typhoons and acted as a nursery site and should be protected. Those fishing only in the mangrove perceived more benefits from the mangrove and were prepared to pay more to protect it than those fishing outside. This study concludes that replanting mangroves can have a significant economic impact on the lives of coastal communities. Acknowledgement of the value ofreplanted mangroves compared with other coastal activities and the benefits they bring to the more economically-vulnerable coastal dwellers should support better informed policy and decision-making with regard to coastal habitat restoration.

Morphometric relationship of length and weight of giant tiger prawn Penaeus monodon according to life stage, sex and source

Abstract Eggs of Penaeus monodon are classified into five different types on the basis of morphological criteria and hatching rates — A1 eggs undergo normal development with 58% hatching rate; A2 eggs show delayed and/or abnormal development with 32% hatching rate; and B, C and D eggs are unfertilized and do not hatch. Wild (unablated) females have the highest proportion of A1 eggs and highest hatching rate, followed by ablated wild stock; ablated pond stock show the lowest proportion of A1 eggs and the lowest hatching rate. There is a highly linear relationship between the percentage of A1 eggs and the hatching rate in spawnings from ablated females of both pond and wild stock. Discussion concentrates on the development of these egg types, comparison with other studies and the importance to hatchery operations of these findings.

Observations on artificial fertilization of eggs and the embryonic and larval development of milkfish, Chanos chanos (Forskal)☆

Abstract Regression analysis was performed on length–weight and length–length measurements of Penaeus monodon ( n =3270 individuals) including carapace length, body length, total length and body (wet) weight of different life stages (nursery, growout and broodstock), sexes (female and male) and sources (pond and wild). Regression lines differed among the life stages and between the sexes and sources at the broodstock stage. Nursery and growout P. monodon showed a greater weight gain per unit length than broodstock. With bigger females, size dimorphism appeared only at the broodstock stage; males and females showed similar sizes in nursery and growout. Equations (including a , b and r ) for interconversions of length and weight are reported for the different stages, sources and sexes.