Juvenile length-at-age data reveal that spanner crabs (<Emphasis Type="Italic">Ranina ranina</Emphasis>) grow slowly

The spanner crab (Ranina ranina) is a widespread and abundant brachyuran in offshore sand substrata of the Indo-Pacific region. Little is known of this species biology, population dynamics and ecology, despite it being the target of commercial fishing operations in many areas. Previous studies of R. ranina growth using length-frequency analysis of samples collected with commercial fishing gear have derived widely divergent estimates of growth parameters. The estimated time taken to reach 100 mm rostral carapace length (minimum legally exploited size in Queensland, Australia) in those studies has ranged from 1.75 to 8.83 years for females and from 1.08 to 3.58 years for males. Our data show that the commercial fishing apparatus used in those studies is size selective and catches only adult crabs. The resulting size bias in samples collected using that apparatus precludes the application of length-frequency-based techniques to estimate growth parameters from those samples. We devised a new dredge to collect samples of juvenile R. ranina and to calculate juvenile growth rates from modal progression in those samples. We combined those data with estimated mean maximum lengths (L) of 121.7 mm for females and 155.9 mm for males from commercial catch data to model other von Bertalanffy growth parameters using bootstrap methods. Those modelled parameters (K=0.29, T₀=–0.24 for females; K=0.23, T₀=–0.25 for males) indicate that R. ranina grows more slowly than most previous estimates suggest, with females requiring an average of 6.35 years and males 4.31 years to reach 100 mm rostral carapace length. This slow growth is consistent with the slow metabolism of R. ranina, and indicates that this species would be likely to recover slowly from overexploitation.Communicated by G.F. Humphrey, Sydney     

Attrition and housing improvements: A study of post-disaster housing after three years

This research is part of an effort to monitor houses built for victims of hurricane Fifi in 1975. After 3 years (1978) we interviewed the residents to determine the rate of continued occupancy and the amount of housing improvement and the correlates of both. We found that a significant number of small families, Protestants, and families that had not participated in the construction of the housing had moved. From what we could determine, moving was primarily related to seeking work and improving one's financial position.
Nearly 90% of the permanent occupants had improved their houses with either indigenous or manufactured materials. Non-improvement of houses was concentrated among families with few members. The largest number of unimproved houses was located in the project that sewed the poorest victims and contained the cheapest housing.     

Design of a rapid-sampling vertical-tow net

Design and operation of a new sampler for zooplankton are described. The sampler facilitates reliable duplicate samples; it can be closed at a defined depth during vertical towing, and can be rapidly reloaded for repeated tows.     

A mathematical model of PCB bioaccumulation in plankton

In batch experiments exposing individual plankton constituents to Aroclor 1254 PCB, the rate at which the organism approaches partitioning equilibrium appears to be partly size-dependent while the extent of PCB accumulation is species-specific. The sorptive desorptive kinetics of PCB in these experiments can be described mathematically by a first-order expression. Employing this expression in a model plankton food web permits examination of the role of feeding and sorptive processes in determining PCB body burden under various environmental conditions. When ingestion rates exceed desorption and excretion rates, a consuming organism accumulates PCB above levels predicted by equilibrium partitioning relationships. Feeding-induced oscillations in PCB body burden could thus obscure the reduction of soluble PCB concentration which determine a “baseline” PCB body burden. Unless referenced to a specific set of biological and environmental conditions, the importance of direct partitioning from water vs. food uptake appears to be a moot topic.     

Effectiveness of high back belt positioning booster seats in side impacts

OBJECTIVE: The objective of this study is to evaluate the potential of high back booster seats to provide effective protection to children in side impacts. METHOD: This article presents a series of side impact sled tests at a velocity change of 30.5 km/h and a peak deceleration of 15.2 g, using the Hybrid III 6-year-old dummy in two styles of commonly used high-back booster seats: a conventional polystyrene booster seat and a convertible child restraint/booster seat. A series of tests were also performed using alternative anchorage systems in combination with the boosters. Simulated side impact tests were conducted at 90 degrees and 45 degrees. RESULTS: The booster seats tested were found to be too short for the 6-year-old dummy and head contact with the side door occurred in all 90 degree tests, resulting in high HIC values. The greatest potential for achieving effective protection in side impact in this test series was observed when the convertible child restraint/booster was used in combination with a rigid anchorage system. Using this system, the body of the dummy was kept farther away from the door which resulted in a softer head impact with the side door. CONCLUSIONS: Results from this work indicate that current booster seats offer poor torso containment and no head protection for children within the recommended age range. They also showed that the level of protection provided by belt positioning booster seats can be improved through the use of rigid anchorage systems. However, for this potential to be fully realized, belt positioning booster seats must offer better containment of the occupant during the impact.     

Sex ratios,mating behavior and sexual size dimorphism of the northern water snake,Nerodia sipedon

Competition among males to mate is generally associated with male-biased size dimorphism. In this study we examine mating behavior in the northern water snake (Nerodia sipedon), a species in which males are much smaller than females despite substantial competition among males to mate. Competition among males was a consequence of a male-biased operational sex ratio due to slightly higher female mortality from a birth sex ratio of 1 : 1, and, in 1 year, more synchronous and longer mating activity by males. Approximately one-third of both males and females appeared not to mate in a given year. Larger males were generally more likely to attempt mating, but size did not explain the variance in the number of aggregations in which individual males participated. Within aggregations, males that were successful at achieving intromission were larger than unsuccessful males in 1 of 2 years. Variation in condition (mass relative to length) and relative tail length were not generally useful predictors of either mating effort or success in males. Because large size was often advantageous to males, sexual size dimorphism appeared not to be a consequence of sexual selection favoring smaller males. Because sexual dimorphism was evident at birth, and both males and females matured sexually at about 4 years, sexual dimorphism was not simply a consequence of one sex growing at the maximum rate for longer. Female fecundity increased with size, and sex differences in size-fecundity relations may underly the pattern of sexual size dimorphism. However, because multiple mating by females is common, sperm competition is likely to be important in determining male reproductive success. Therefore, allocation of energy to sperm rather than growth may also prove to be an important influence on male growth rates and sexual size dimorphism.     

Active salinity choice and enhanced swimming endurance in 0 to 8-d-old larvae of diadromous gobies,including Sicydium punctatum (Pisces), in Dominica,West Indies

We studied the early life history of diadromous gobies in Dominica, West Indies, from May 1989 to May 1991, emphasising Sicydium punctatum Perugia. The transition of newly hatched larvae from upriver nest sites to the sea was studied in laboratory experiments. Newly hatched larvae are negatively buoyant but avoid settling to the bottom by active swimming during drift to the sea. Laboratory experiments evaluated salinity preferences and effects on swimming endurance. Larvae in haloclines actively selected low to intermediate salinities. Initially (0 to 5-d post-hatch), larvae minimized exposure to salinities >10 ppt, but later (5 to 8-d) occupied increasingly saline water. Larvae in no-choice freshwater or seawater treatments ceased activity at 4 to 5 d, but in haloclines larvae remained active up to 8 d post-hatch. Salinities <10 ppt are important for early survival of sicydiine gobies. Implications for larval survival and transport are discussed.