Comparison of six tag types in sea-trout tagging experiments in the Baltic Sea

In the international Baltic Sea trout tagging experiment 27 753 hatchery reared sea trout smolts were tagged in Denmark, Finland, Poland and Sweden in 1979 and 1980. The fish were tagged with the original Carlin tag, two modified Carlin tag types (Canadian and Finnish polythene), streamer and Floy tags and Polish tags attached with Monel metal wire. The tag returns were affected by the place of release and smolt quality. The best results were obtained in the case of tags attached with double wire or thread -original Carlin, Canadian and Finnish polythene. The poorest results were obtained with streamer tags.

Using experiments and expert judgment to model catchability of Pacific rockfishes in trawl surveys, with application to bocaccio (Sebastes paucispinis) off British Columbia

The time series of abundance indices for many groundfish populations, as determined from trawl surveys, are often imprecise and short, causing stock assessment estimates of abundance to be imprecise. To improve precision, prior probability distributions (priors) have been developed for parameters in stock assessment models by using meta-analysis, expert judgment on catchability, and empirically based modeling. This article presents a synthetic approach for formulating priors for rockfish trawl survey catchability (qgross). A multivariate prior for qgross for different surveys is formulated by using 1) a correction factor for bias in estimating fish density between trawlable and untrawlable areas, 2) expert judgment on trawl net catchability, 3) observations from trawl survey experiments, and 4) data on the fraction of population biomass in each of the areas surveyed. The method is illustrated by using bocaccio (Sebastes paucipinis) in British Columbia. Results indicate that expert judgment can be updated markedly by observing the catch-rate ratio from different trawl gears in the same areas. The marginal priors for qgross are consistent with empirical estimates obtained by fitting a stock assessment model to the survey data under a noninformative prior for qgross. Despite high prior uncertainty (prior coefficients of variation ≥0.8) and high prior correlation between qgross, the prior for qgross still enhances the precision of key stock assessment quantities.

Experiments in gear configuration to reduce bycatch in an estuarine squid-trawl fishery

Three experiments were performed in an estuarine squid-trawl fishery in New South Wales, Australia, to test modifications to trawl nets. Lateral mesh openings were experimentally increased and physical bycatch reduction devices (BRDs) were placed in codends. These modifications aimed to reduce nontargeted catches of fish, while maintaining catches of the targeted broad squid (Photololigo etheridgei) and bottle squid (Loliolus noctiluca). Compared to conventional codends made with 41-mm diamond mesh, codends made with different posterior circumferences and larger 45-mm mesh had no significant effect on the catches of any species. The best performing configurations involved the installation of BRDs designed to separate organisms according to differences in behavior. In particular, versions of a composite square-mesh panel reduced the total weight of bycatch by up to 71% and there was no significant effect on the catches of squid. The results are discussed in terms of the probable differences in behavior between fish and squid in codends. After this study, a square-mesh panel BRD was voluntarily adopted throughout the fishery.

Estimates of commercial longline selectivity for Pacific halibut (Hippoglossus stenolepis) from multiple marking experiments

The term “selectivity” refers to the relationship between the size (or age) of a fish and its vulnerability to a given kind of fishing gear. A selectivity schedule, along with other parameters, is normally estimated in the course of fitting a stock assessment model, and the estimated schedule can have a large effect on both the estimate of present stock abundance and the choice of an appropriate harvest rate. The form of the relationship is usually not known and not well determined by the data, and equally good model fits can often be obtained with different plausible specifications of selectivity. Choosing among the model fits and associated abundance estimates in this situation is problematic (Sigler, 1999; Sullivan et al., 19

Farming experiments and transfer of technology of bivalve culture along the southwest coast of India

The Central Marine Fisheries Research Institute (CMFRI) in India developed bivalve farming technologies in the 1970s, but these were not widely adopted at the time. In 1993, CMFRI undertook an action research program to encourage farming of edible oysters (Crassostrea madrasensis), mussels (Perna viridis and Perna indica), clams (Paphia malabarica) and pearls (Pinctada fucata) along the southwest coast of India. Successful demonstration of the viability of bivalve farming led to the initiation of commercial farming of mussels and generated interest among farmers and entrepreneurs in developing production of pearls and farming of edible oysters. Given the high potential for the mollusc aquaculture, both for the local and export market, issues such as demarcation and issuance of lease right on aquaculture zones in public waterbodies by the government, organization of marketing systems and provisions for technical and financial support to farmers need to be addressed.

A computer software package for assessing and managing risks posed by experiments with genetically modified fish and shellfish

Assessment and management of risk is needed for sustainable use of genetically modified aquatic organisms (aquatic GMOs). A computer software package for safely conducting research with genetically modified fish and shellfish is described. By answering a series of questions about the organism and the accessible aquatic ecosystem, a researcher or oversight authority can either identify specific risks or conclude that there is a specific reason for safety of the experiment. Risk assessment protocols with examples involving transgenic coho salmon, triploid grass carp and hybrid tilapia are described. In case a specific risk is identified, the user is led to consider risk management measures, involving culture methods, facilities design and operations management, to minimize the risk. Key features of the software are its user-friendly organization; easy access to explanatory text, literature citations and glossary; and automated completion of a worksheet. Documented completion of the Performance Standards can facilitate approval of a well designed experiment by oversight authorities.