The improved management of small-scale cage culture in Asia: final technical report

The purpose of the project is to develop sustained small-scale cage fish culture in inland and coastal waters through improved understanding of the social, institutional and resource environment of resource poor groups. Two Asian countries, Bangladesh (inland systems) and Vietnam (marine), were studied with this workshop bringing together both sides of the project together with representatives of collaborative institutions, government departments and universities. Addressing the overall aim of producing guidelines for the planning and extension of cage aquaculture in Asia a combination of group work and plenary discussion was conducted producing the following outputs. 1) An assessment of cage aquaculture potential, 2) Development options for small-scale cage culture, 3) A review of tools and methodologies and 4) Policy initiatives for sustainable cage culture development. Key issues raised were the use of outputs as a guide to be adapted to regional circumstances to facilitate farmer and extension worker discussion and not as a rigid methodology. The degree of linkage between development, research and government institutions was also considered a crucial factor in benefiting the research and development of cage culture at the local, regional and national level and vital in affecting the future policies by both development and government institutions. [PDF contains 242 pages]

Assessing the quality of water quality assessments: An analytical quality control protocol for benthic diatoms

In this paper, the background to the development of an analytical quality control procedure for the Trophic Diatom Index (TDI) is explained, highlighting some of the statistical and taxonomic problems encountered, and going on to demonstrate how the system works in practice. Most diatom-based pollution indices, including the TDI, use changes in the relative proportions of different taxa to indicate changing environmental conditions. The techniques involved are therefore much simpler than those involved in many studies of phytoplankton, for example, where absolute numbers are required.

Population structure of pink salmon (Oncorhynchus gorbuscha) in British Columbia and Washington, determined with microsatellites

Population structure of pink salmon (Oncorhynchus gorbuscha) from British Columbia and Washington was examined with a survey of microsatellite variation to describe the distribution of genetic variation. Variation at 16 microsatellite loci was surveyed for approximately 46,500 pink salmon sampled from 146 locations in the odd-year broodline and from 116 locations in the even-year broodline. An index of genetic differentiation, FST, over all populations and loci in the odd-year broodline was 0.005, with individual locus values ranging from 0.002 to 0.025. Population differentiation was less in the even-year broodline, with a FST value of 0.002 over all loci, and with individual locus values ranging from 0.001 to 0.005. Greater genetic diversity was observed in the odd-year broodline. Differentiation in pink salmon allele frequencies between broodlines was approximately 5.5 times greater than regional differentiation within broodlines. A regional structuring of populations was the general pattern observed, and a greater regional structure in the odd-year broodline than in the even-year broodline. The geographic distribution of microsatellite variation in populations of pink salmon likely ref lects a distribution of broodlines from separate refuges after the last glaciation period.

Demographics by depth: spatially explicit life-history dynamics of a protogynous reef fish

Distribution and demographics of the hogfish (Lachnolaimus maximus) were investigated by using a combined approach of in situ observations and life history analyses. Presence, density, size, age, and size and age at sex change all varied with depth in the eastern Gulf of Mexico. Hogfish (64–774 mm fork length and 0–19 years old) were observed year-round and were most common over complex, natural hard bottom habitat. As depth increased, the presence and density of hogfish decreased, but mean size and age increased. Size at age was smaller nearshore (<30 m). Length and age at sex change of nearshore hogfish were half those of offshore hogfish and were coincident with the minimum legal size limit. Fishing pressure is presumably greater nearshore and presents a confounding source of increased mortality; however, a strong red tide occurred the year before this study began and likely also affected nearshore demographics. Nevertheless, these data indicate ontogenetic migration and escapement of fast-growing fish to offshore habitat, both of which should reduce the likelihood of fishing-induced evolution. Data regarding the hogfish fishery are limited and regionally dependent, which has confounded previous stock assessments; however, the spatially explicit vital rates reported herein can be applied to future monitoring efforts.

Soft Flesh in Sablefish, Anoplopoma fimbria, of Southeastern Alaska: Relationships with Depth, Season, and Biochemistry

The condition of soft-textured flesh in commercially harvested sablefish, Anoplopoma fimbria, from southeastern Alaska was investigated by National Marine Fisheries Service (NMFS) scientists from the Alaska Fisheries Science Center’s Auke Bay Laboratories (ABL) in Alaska and the Northwest Fisheries Science Center in Seattle, Wash. Sablefish were sampled by longline, pot, and trawl at five sites around Chichagof Island at depths of 259–988 m in the summer of 1985 and at depths of 259–913 m in the winter of 1986. At the time of capture and data collection, sablefish were categorized as being “firm” or “soft” by visual and tactile examination, individually weighed, measured for length, and sexed. Subsamples of the fish were analyzed and linear regressions and analyses of variance were performed on both the summer (n = 242) and winter (n = 439) data for combinations of chemical and physical analyses, depth of capture, weight vs. length, flesh condition, gonad condition, and sex. We successfully identified and selected sablefish with firm- and soft-textured flesh by tactile and visual methods. Abundance of firm fish in catches varied by season: 67% in winter and 40% in summer. Winter catches may give a higher yield than summer catches. Abundance of firm fish catches also varied with depth. Firm fish were routinely found shallower than soft fish. The highest percentage of firm fish were found at depths less than 365 m in summer and at 365–730 m in winter, whereas soft fish were usually more abundant at depths greater than 731 m. Catches of firm fish declined with increasing depth. More than 80% of the fish caught during winter at depths between 365 and 730 m had firm flesh, but this declined to 48% at these depths in summer. Longlines and pots caught similar proportions of firm and soft fish with both gears catching more firm than soft fish. Trawls caught a higher proportion of soft fish compared to longlines and pots in winter. Chemical composition of “firm” and “soft” fish differed. On average “soft” fish had 14% less protein, 12% more lipid, and 3% less ash than firm fish. Cooked yields from sablefish with soft-textured flesh were 31% less than cooked yields from firm fish. Sablefish flesh quality (firmness) related significantly to the biochemistry of white muscle with respect to 11 variables. Summer fish of all flesh conditions averaged 6% heavier than winter fish. Regulating depth of fishing could increase the yield from catches, but the feasibility and benefits from this action will require further evaluation and study. Results of this study provide a basis for reducing the harvest of sablefish with soft flesh and may stimulate further research into the cause and effect relationship of the sablefish soft-flesh phenomenon.