Commercially Important Crabs, Shrimps and Lobsters of the North Pacific Ocean

Table of Contents [pdf, 1 Kb] Summary [pdf, 85 Kb] Introduction [pdf, 0.8 Mb] Major Species and Stocks of Crabs in the PICES Region [pdf, 1.23 Mb] Major Species and Stocks of Shrimps in the PICES Region [pdf, 0.5 Mb] Oceanography [pdf, 0.4 Mb] Sampling and Data Analysis [pdf, 0.38 Mb] Acknowledgements [pdf, 0.27 Mb] References [pdf, 0.33 Mb] Appendices [pdf, 0.3 Mb] Plates 1-5 [pdf, 0.95 Mb] (Document contains 83 pages)

Effects of underwater explosions on oysters, crabs and fish: a preliminary report.

Investigation on the effects of explosive shock on marine life. Necessary that the "commercial" effects, the actual damage to commercially important stocks of fish and shellfish, be evaluated. Equally important are the "biological" effects, the immediate physical effects of shock waves on animals and the indirect effects on future stocks. Indirect effects might include the diversion of migratory stocks from an area, or actual damage to the habitat, rendering it unfit for sedentary or non-migratory native species. Interruption of the food chains in an area by destruction of forge forms or vegetation. (PDF contains 43 pages)

Freshwater crabs in Africa

Freshwater crabs are a strangely neglected component of the world's inland aquatic ecosystems. Despite their wide distribution throughout the tropical and warm temperate zones of the world, and their great diversity, their role in the ecology of freshwaters is very poorly understood. This is nowhere more true than in Africa, where crabs occur in almost every freshwater system, yet even fundamentals such as their higher taxonomy are yet to be determined. This review will attempt to stimulate interest in this fascinating group of organisms by summarising what little we do know about freshwater crabs in Africa. The author describes habitat, reproduction, diet, population density, terrestrial activity and economical importance of African freshwater crabs. The article concludes with an assessment of threats and conservation. In an appendix the author describes the five families of freshwater crabs which are recognised in Africa.

Climate-related hydrological regimes and their effects on abundance of juvenile blue crabs (Callinectes sapidus) in the northcentral Gulf of Mexico

The abundance of juvenile blue crabs (Callinectes sapidus) in the northcentral Gulf of Mexico was investigated in response to climate-related hydrological regimes. Two distinct periods of blue crab abundance (1, 1973–94 and 2, 1997–2005) were associated with two opposite climaterelated hydrological regimes. Period 1 was characterized by high numbers of crabs, whereas period 2 was characterized by low numbers of crabs. The cold phase of the Atlantic Multidecadal Oscillation (AMO) and high north-south wind momentum were associated with period 1. Hydrological conditions associated with phases of the AMO and North Atlantic Oscillation (NAO) in conjunction with the north-south wind momentum may favor blue crab productivity by influencing blue crab predation dynamics through the exclusion of predators. About 25% (22–28%) of the variability in blue crab abundance was explained by a north–south wind momentum in concert with either salinity, precipitation, or the Palmer drought severity index, or by a combination of the NAO and precip

Prediction of discard mortality for Alaskan crabs after exposure to freezing temperatures, based on a reflex impairment index

Millions of crabs are sorted and discarded in freezing conditions each year in Alaskan fisheries for Tanner crab (Chionoecetes bairdi) and snow crab (C. opilio). However, cold exposures vary widely over the fishing season and among different vessels, and mortalities are difficult to estimate. A shipboard experiment was conducted to determine whether simple behavioral observations can be used to evaluate crab condition after low-temperature exposures. Crabs were systematically subjected to cold in seven different exposure treatments. They were then tested for righting behavior and six different ref lex actions and held to monitor mortality. Crabs lost limbs, showed ref lex impairment, and died in direct proportion to increases in cold exposure. Righting behavior was a poor predictor of mortality, whereas reflex impairment (scored as the sum of reflex actions that were lost) was an excellent predictor. This composite index could be measured quickly and easily in hand, and logistic regression revealed that the relationship between reflex impairment and mortality correctly predicted 80.0% of the mortality and survival for C. bairdi, and 79.4% for C. opilio. These relationships provide substantial improvements over earlier approaches to mortality estimation and were independent of crab size and exposure temperature.

Prosomal-width-to-weight relationships in American horseshoe crabs (Limulus polyphemus): examining conversion factors used to estimate landings

Horseshoe crabs (Limulus polyphemus) are valued by many stakeholders, including the commercial fishing industry, biomedical companies, and environmental interest groups. We designed a study to test the accuracy of the conversion factors that were used by NOAA Fisheries and state agencies to estimate horseshoe crab landings before mandatory reporting that began in 1998. Our results indicate that the NOAA Fisheries conversion factor consistently overestimates the weight of male horseshoe crabs, particularly those from New England populations. Because of the inaccuracy of this and other conversion factors, states are now mandated to report the number (not biomass) and sex of landed horseshoe crabs. However, accurate estimates of biomass are still necessary for use in prediction models that are being developed to better manage the horseshoe crab fishery. We recommend that managers use the conversion factors presented in this study to convert current landing data from numbers to biomass of harvested horseshoe crabs for future assessments.

Abundance of adult horseshoe crabs (Limulus polylphemus) in Delaware Bay estimated from a bay-wide mark-recapture study

Estimates of the abundance of American horseshoe crabs (Limulus polyphemus) are important to determine egg production and to manage populations for the energetic needs of shorebirds that feed on horseshoe crab eggs. In 2003, over 17,500 horseshoe crabs were tagged and released throughout Delaware Bay, and recaptured crabs came from spawning surveys that were conducted during peak spawning. We used two release cohorts to test for a temporary effect of tagging on spawning behavior and we adjusted the number of releases according to relocation rates from a telemetry study. The abundance estimate was 20 million horseshoe crabs (90 % confidence interval: 13−28 million), of which 6.25 million (90% CI: 4.0−8.8 million) were females. The combined harvest rate for Delaware, New Jersey, Virginia, and Maryland in 2003 was 4% (90% CI: 3−6%) of the abundance estimate. Over-wintering of adults in Delaware Bay could explain, in part, differences in estimates from ocean-trawl surveys. Based on fecundity of 88,000 eggs per female, egg production was 5.5×1011 (90% CI: 3.5×1011, 7.7×1011), but egg availability for shorebirds also depended on overlap between horseshoe crab and shorebird migrations, density-dependent bioturbation, and wave-mediated vertical transport.

Potential causes of mortality for horseshoe crabs (Limulus polyphemus) during the biomedical bleeding process

Biomedical companies catch and bleed horseshoe crabs for the production of Limulus amebocyte lysate (LAL), a product used for protecting public health (Berkson and Shuster, 1999). LAL is a clotting agent, derived solely from horseshoe crab blood cells, which is used to detect the presence of pathogenic gramnegative bacteria in injectable drugs and implantable medical and dental devices (Mikkelsen, 1988; Novitsky, 1991). In addition, LAL is used in many diagnostic tests for such illnesses as gram-negative bacterial meningitis and typhoid fever (Ding and Ho, 2001). Because the LAL test allows one to detect femtogram levels of endotoxin (Ding and Ho, 2001), it is the most effective test for detecting endotoxin contamination, and its increasing use in medical and pharmaceutical laboratories makes it a highly valued product.

The eggs of marine crabs - an unexploited resource

Marine crabs belonging to the family Portunidae form bycatch of shrimp trawlers in India. They are sold at low prices and consumers discard eggs and consume the meat. The paper details the nutritional value of eggs of Portunus pelagicus.

Testing a Device to Exclude Ovigerous Blue Crabs, Callinectes sapidus, from Commercial Pots

North Carolina fishery managers are considering methods to offer greater protection to the blue crab, Callinectes sapidus, spawning stock while maintaining a viable commercial fishery for female blue crabs in high salinity estuaries. We tested how effectively wire rectangles, or excluders, of two internal sizes, 45x80 mm and 45x90 mm, would prevent entry of ovigerous female (sponge) crabs into pots relative to control pots (without excluders) while maintaining sizes and catch rates of male and nonsponged female hard crabs. Field sampling among three pot designs (two excluder sizes and control pots) was conducted in Core Sound, N.C., during 2004–06. Median sizes (carapace widths) of mature female crabs were not different among the three pot types. However, median sizes of male crabs and sponge crabs were greater in control pots than pots with either size of excluder. Catch rates of mature female crabs from control pots were greater than from pots with 45x85 mm excluders. Catch rates of legal male and sponge crabs from control pots were greater than from pots with either size of excluder. Results indicate that using excluders involves a tradeoff between reducing catches and sizes of sponge crabs while also reducing sizes and catches of legally harvestable nonsponge crabs; moreover, the reduction in total catch and sizes would be greater for legal male crabs than for legal nonsponged female crabs. In high salinity waters close to North Carolina’s existing no-harvest blue crab sanctuaries, where females typically dominate catches of hard crabs, the benefit of using excluders to prevent entry of sponge crabs may outweigh a potentially modest decrease in landings of nonsponged females.