Marine cage culture and the environment: twenty-first century science informing a sustainable industry

Technological innovation has made it possible to grow marine finfish in the coastal and open ocean. Along with this opportunity comes environmental risk. As a federal agency charged with stewardship of the nation’s marine resources, the National Oceanic and Atmospheric Administration (NOAA) requires tools to evaluate the benefits and risks that aquaculture poses in the marine environment, to implement policies and regulations which safeguard our marine and coastal ecosystems, and to inform production designs and operational procedures compatible with marine stewardship. There is an opportunity to apply the best available science and globally proven best management practices to regulate and guide a sustainable United States (U.S.) marine finfish farming aquaculture industry. There are strong economic incentives to develop this industry, and doing so in an environmentally responsible way is possible if stakeholders, the public and regulatory agencies have a clear understanding of the relative risks to the environment and the feasible solutions to minimize, manage or eliminate those risks. This report spans many of the environmental challenges that marine finfish aquaculture faces. We believe that it will serve as a useful tool to those interested in and responsible for the industry and safeguarding the health, productivity and resilience of our marine ecosystems. This report aims to provide a comprehensive review of some predominant environmental risks that marine fish cage culture aquaculture, as it is currently conducted, poses in the marine environment and designs and practices now in use to address these environmental risks in the U.S. and elsewhere. Today’s finfish aquaculture industry has learned, adapted and improved to lessen or eliminate impacts to the marine habitats in which it operates. What progress has been made? What has been learned? How have practices changed and what are the results in terms of water quality, benthic, and other environmental effects? To answer these questions we conducted a critical review of the large body of scientific work published since 2000 on the environmental impacts of marine finfish aquaculture around the world. Our report includes results, findings and recommendations from over 420 papers, primarily from peer-reviewed professional journals. This report provides a broad overview of the twenty-first century marine finfish aquaculture industry, with a targeted focus on potential impacts to water quality, sediment chemistry, benthic communities, marine life and sensitive habitats. Other environmental issues including fish health, genetic issues, and feed formulation were beyond the scope of this report and are being addressed in other initiatives and reports. Also absent is detailed information about complex computer simulations that are used to model discharge, assimilation and accumulation of nutrient waste from farms. These tools are instrumental for siting and managing farms, and a comparative analysis of these models is underway by NOAA.

Incidental capture of loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) sea turtles by the pelagic longline fishery off southern Brazil

Incidental capture in fishing gear is one of the main sources of injury and mortality of juvenile and adult sea turtles (NRC, 1990; Lutcavage et al., 1997; Oravetz, 1999). Six out of the seven extant species of sea turtles — the leatherback (Dermochelys coriacea), the green turtle (Chelonia mydas), the loggerhead (Caretta caretta), the hawksbill (Eretmochelys imbricata), the olive ridley (Lepidochelys olivacea), and the Kemp’s ridley (Lepidochelys kempii) — are currently classified as endangered or critically endangered by the World Conservation Union (IUCN, formerly the International Union for Conservation of Nature and Natural Resources), which makes the assessment and reduction of incidental capture and mortality of these species in fisheries priority conservation issues (IUCN/Species Survival Commission, 1995).

Reproductive biology of male franciscanas (Pontoporia blainvillei) (Mammalia: Cetacea) from Rio Grande do Sul, southern Brazil

The reproductive biology of male franciscanas (Pontoporia blainvillei), based on 121 individuals collected in Rio Grande do Sul State, southern Brazil, was studied. Estimates on age, length, and weight at attainment of sexual maturity are presented. Data on the reproductive seasonality and on the relationship between some testicular characteristics and age, size, and maturity status are provided. Sexual maturity was assessed by histological examination of the testes. Seasonality was determined by changes in relative and total testis weight, and in seminiferous tubule diameters. Testis weight, testicular index of maturity, and seminiferous tubule diameters were reliable indicators of sexual maturity, whereas testis length, age, length, and weight of the dolphin were not. Sexual maturity was estimated to be attained at 3.6 years (CI 95% =2.7–4.5) with the DeMaster method and 3.0 years with the logistic equation. Length and weight at attainment of sexual maturity were 128.2 cm (CI 95%=125.3–131.1 cm) and 26.4 kg (CI 95% =24.7–28.1 kg), respectively. It could not be verified that there was any seasonal change in the testis weight and in the seminiferous tubule diameters in mature males. It is suggested that at least some mature males may remain reproductively active throughout the year. The extremely low relative testis weight indicates that sperm competition does not occur in the species. On the other hand, the absence of secondary sexual characteristics, the reversed sexual size dimorphism, and the small number of scars from intrassexual combats in males reinforce the hypothesis that male combats for female reproductive access may be rare for franciscana. It is hypothesized that P. blainvillei form temporary pairs (one male copulating with only one female) during the reproductive period.

Age and growth of the estuarine dolphin (Sotalia guianensis) (Cetacea, Delphinidae) on the Paraná Coast, southern Brazil

Teeth of 71 estuarine dolphins (Sotalia guianensis) incidentally caught on the coast of Paraná State, southern Brazil, were used to estimate age. The oldest male and female dolphins were 29 and 30 years, respectively. The mean distance from the neonatal line to the end of the first growth layer group (GLG) was 622.4 ±19.1 μm (n=48). One or two accessory layers were observed between the neonatal line and the end of the first GLG. One of the accessory layers, which was not always present, was located at a mean of 248.9 ±32.6 μm (n=25) from the neonatal line, and its interpretation remains uncertain.The other layer, located at a mean of 419.6 ±44.6 μm (n=54) from the neonatal line, was always present and was first observed between 6.7 and 10.3 months of age. This accessory layer could be a record of weaning in this dolphin. Although no differences in age estimates were observed between teeth sectioned in the anterior-posterior and buccal-lingual planes, we recommend sectioning the teeth in the buccal-lingual plane in order to obtain on-center sections more easily. We also recommend not using teeth from the most anterior part of the mandibles for age estimation. The number of GLGs counted in those teeth was 50% less than the number of GLGs counted in the teeth from the median part of the mandible of the same animal. Although no significant difference (P>0.05) was found between the total lengths of adult male and female estuarine dolphins, we observed that males exhibited a second growth spurt around five years of age. This growth spurt would require that separate growth curves be calculated for the sexes. The asymptotic length (TL∞), k, and t0 obtained by the von Bertalanffy growth model were 177.3 cm, 0.66, and –1.23, respectively, for females and 159.6 cm, 2.02, and –0.38, respectively, for males up to five years, and 186.4 cm, 0.53 and –1.40, respectively, for males older than five years. The total weight (TW)/total length (TL) equations obtained for male and female estuarine dolphins were TW = 3.156 × 10−6 × TL 3.2836 (r=0.96), and TW = 8.974 × 10−5 × TL 2.6182 (r=0.95), respectively.

Reproduction of blacknose shark (Carcharhinus acronotus) in coastal waters off northeastern Brazil

The blacknose shark, Carcharhinus acronotus, is a relatively small carcharinid, typically inhabiting continental shelf areas in the western Atlantic Ocean, from North Carolina throughout the Gulf of Mexico (Bigelow and Schroeder, 1948) and along the South American coast to Rio de Janeiro (Compagno, 1984). The abundance of this shark in nearshore areas throughout its distribution makes it accessible to commercial fishing, mainly from inshore hook-and-line and gill-net fisheries (Trent et al., 1997; Mattos and Hazin1).

A note on the culture of Chanos chanos (Forskal) at Brackishwater Fish Farm, Kaninada

The culture of Chanos chanos to marketable size within a three months period, is described. Procedures involved include phased manuring coupled with proper water management to keep up enhanced primary productivity. Results show that, under monoculture, with low-input technology it is possible to produce 3,000 kg fish per hectare per year.

Prawn culture and policy options: technology import and culture through fishermen vis a vis industry

Recent developments in aquaculture has created an awareness that prawn culture is a dollar spinner, in which industry can step in to earn foreign exchange by producing an expensive food iten which has a high market demand abroad. The Government has to take a policy decision whether the prawn culture should be done through small fishermen to improve their socio-economic condition or through private industry with the high technology input and predefined objectives of export trade. Perhaps a simultaneous operation of the two could be allowed best in the interest of India. Perhaps in the interest of quick development and adoption of high production technology, through fishermen organization, the development is encouraged through the implimentation of welfare and area development schemes. In some selected areas private industry may be encoureged to use high production technology to develop prawns.

Present status and problems of mussel culture in India

Two species of mussels, the green mussel (Perna viridis) and the brown mussel (Perna indica) were cultured using the seed collected from the natural beds of the east and west coasts of India. The results of culture experiments are consolidated and the present status is reviewed. Although the culture experiments gave encouraging results, problems such as mooring of rafts in highly turbulent coastal waters, large scale seed requirements, control of predation, legal problems and marketing of end products require urgent attention before undertaking commercial operations. Some of the major problems of mussel culture are outlined for formulating effective management policies and their implementation for commercial mussel farming in India.

Rice-fish culture: status and potential for increased production in the southwestern states of India

The scope of increasing production through rice-fish integration, suitable for coastal districts of Kerala, Karnataka, Goa and Maharashtra, is reviewed. The method of adopting the lowlying freshwater rice fields to raise 2 rice crops along with 4-species fish culture, followed by a third non-cereal summer crop in a year, is discussed. A calendar of operation and economics of the system are presented.

Scope for commercial culture of tilapia

The suitability of tilapia species for fish culture and the potential for the development of commercial culture operations in India are discussed. Sex regulation, monosex tilapia polyculture, chromosome manipulation and sex reversal, nutrition and feed formulation are examined in detail.