Sensitivity of wear rates in the micro-scale abrasion test to test conditions and material hardness

Micro-scale abrasion (ball cratering) tests were performed with different combinations of ball and bulk specimen materials, under different test conditions, such as load and abrasive slurry concentration. Wear modes were classified into two types: with rolling particle motion and with grooving particle motion. Wear rates observed with rolling particle motion were relatively insensitive to test conditions, whereas with grooving motion they varied much more. It is suggested that rolling abrasion is therefore a more appropriate mode if reproducible test results are desired. The motion of the abrasive particles can be reliably predicted from the knowledge of hardnesses and elastic properties of the ball and the specimen, and from the normal load and the abrasive slurry concentration. General trends in wear resistance measured in the micro-scale abrasion test with rolling particle motion are similar to those reported in tests with fixed abrasives with sliding particle motion, although the variation in wear resistance with hardness is significantly smaller. © 2004 Published by Elsevier B.V.

Estimates of growth and comparisons of growth rates determined from length- and age-based models for populations of purple wrasse (Notolabrus fucicola)

Growth of a temperate reefa-ssociated fish, the purple wrasse (Notolabrus fucicola), was examined from two sites on the east coast of Tasmania by using age- and length-based models. Models based on the von Bertalanffy growth function, in the standard and a reparameterized form, were constructed by using otolith-derived age estimates. Growth trajectories from tag-recaptures were used to construct length-based growth models derived from the GROTAG model, in turn a reparameterization of the Fabens model. Likelihood ratio tests (LRTs) determined the optimal parameterization of the GROTAG model, including estimators of individual growth variability, seasonal growth, measurement error, and outliers for each data set. Growth models and parameter estimates were compared by bootstrap confidence intervals, LRTs, and randomization tests and plots of bootstrap parameter estimates. The relative merit of these methods for comparing models and parameters was evaluated; LRTs combined with bootstrapping and randomization tests provided the most insight into the relationships between parameter estimates. Significant differences in growth of purple wrasse were found between sites in both length- and age-based models. A significant difference in the peak growth season was found between sites, and a large difference in growth rate between sexes was found at one site with the use of length-based models.

Injury Rates of Red King Crab, Paralithodes camtschaticus, Passing Under Bottom-trawl Footropes

The rate of injuries sustained by red king crab, Paralithodes camtschaticus, during passage under several types of bottom trawl footropes was examined using a modified bottom trawl in Bristol Bay, Alaska. Crabs were recaptured and examined for injuries after passing under each of three trawl footropes representing those commonly used in the bottom trawl fisheries of the eastern Bering Sea. Using the injury rate from tows with a floated footrope which minimized crab contact to account for handling injuries, injury rates of 5, 7, and 10% were estimated for crabs passing under the three commercial trawl footropes.

Blue Crab, Callinectes sapidus, Retention Rates in Different Trap Meshes

Percent escapements of blue crabs, Callinectes sapidus, by size and sex were determined for commercially available 38.1 mm square and hexagonal meshes and for five experimental squares. Commercial trap mesh sizes retained excessive numbers of sublegal blue crabs. Based on the criteria of maximizing sublegal crab escapement without an unacceptable loss of legal blue crabs, the 44.4 mm square (as measured from the inside of adjacent corners) was optimum and superior to either trap mesh used by fishermen.

Comparisons of Shark Catch Rates on Longlines Using Rope/Steel (Yankee) and Monofilament Gangions

During the months of June through September in 1991 and 1992, 71 shark longlines were fished in the Chesapeake Bight region ofthe U.S. mid-Atlantic coast with a combination of rope/steel (Yankee) and monofilament gangions. A total of 288 sharks were taken on 3,666 monofilament gangions, and 352 sharks were caught on 6,975 Yankee gangions. Catch rates between gear types differed by depth strata, by month, and by species. Analyses were divided between efforts in the nursery ground ofthe sandbar shark, Carcharhinus plumbeus, in Chesapeake Bay and efforts outside the Bay. Mean catch per unit effort (CPUE) ± SE, as sharks caught per 100 hooks fished, was significantly (P<0.05) lower for Yankee gangions. Mean CPUE's for sandbar sharks in the nursery ground were 20.6 ± 3.8 for Yankee gangions and 26.0 ± 3.0 for monofilament gangions, and mean CPUE's for all species combined outside the Bay were 3.7 ± 0.7 for Yankee gangions, and 6.9 ± 1.2 for monofilament gangions.

Differences in Dolphin Mortality Rates in Night and Day Sets for the U.S. Eastern Tropical Pacific Tuna Purse Seine Fishery

Because dolphins sometimes travel with yellowfin tuna, Thunnus albacares, in the eastern tropical Pacific (ETP), purse seiners use the dolphins to locate and capture tuna schools. During the process of setting the purse seine nets, dolphins often become entangled and drown before they can be released. Data for the U.S. purse seine fleet in the ETP during 1979-88 show that dolphin mortality rates in sets made during the night are higher than mortality rates in sets made during the day. Even with efforts to reduce nightset mortality rates through the use of high intensity floodlights, night set mortality rates remain higher. The data are also used to simulate a regulation on the fishery aimed at eliminating night sets and show that dolphin mortality rates would decrease.