Spatial and temporal distribution patterns of brown shrimp (Crangon crangon) derived from commercial logbook, landings, and vessel monitoring data

In this study, logbook, landings, and vessel monitoring system data of German brown shrimp (Crangon crangon L.) fishers were combined to analyse spatial and temporal distribution patterns. Landings per unit effort (LPUE) were standardized to the efficiency level of a reference vessel. The standardization altered the spatial–temporal patterns of the LPUE as the vessels differed by a factor of up to 4.7. LPUE data were separated into two size classes according to sieve fractions. Small brown shrimps were characterized by LPUE values increasing early in the year in shallow waters, especially in estuaries in July. Subsequently, peak LPUE values are reached at the end of September in all depths, but with variable spatial patterns between years. LPUE data indicate a general outward migration between early summer and winter. In winter, large shrimp shows a clear increase in LPUE with depths mainly in regions adjacent to the Dutch coast and a reversed pattern close to the Danish coast. The large size class in winter—which consists mainly of mature or egg-bearing females—showed high LPUE values along two persistent diagonal bands in the German Bight. These patterns could lead to local recruitment overfishing, if fishermen are aware of such patterns.

An external tag for fish: tagging effects in different fish size classes and its influence on growth performance and hematology of Lophiosilurus alexandri (Siluriformes: Pseudopimelodidae)

ABSTRACT This study tested an external tag for juveniles of Lophiosilurus alexandri and measured the effects of tagging in different size classes of fishes. Experiment 1 evaluated the retention rate and influence of the tag on survival and growth of three hundred fishes divided Small, Medium and Large size classes. After 90 days of experiment the fishes had 100% survival and the tag had a higher retention rate for animals of the Large size class. Experiment 2 evaluated the tag’s influence on hematology parameters of forty-two fishes at 5, 10 and 30 days post-tagging. In this experiment both tagged and untagged animals experienced 9.4% mortality. The hematocrit was higher on the 30th day for tagged animals than for untagged animals. No difference was observed for leukocytes, plasma protein, erythrocytes and mean corpuscular volume. It was concluded from Experiment 1 that the tag reduced growth performance when applied to small sized juvenile L. alexandri, and that the tag retention rate increased with increasing animal size. Among the hematological parameters studied for juveniles on the Experiment 2 the tag only influenced the hematocrit parameters, which shows that the tag can be used without considerable influence on the hematological parameters of juvenile L. alexandri.

Estudio del polen de Phaseolus chiapasanus Piper (Leguminosae: Phaseolinae)

In the course of a taxonomical revision of the genus Phaseolus and considering the recently important research realized in the Phaseolus-Vigna complex, where the palynological attributes for the genus were precised, the present paper describes the pollen of Phaseolus chiapasanus Piper. The large-size class pollen grains of Ph. chiapasanus are tricolporate, brevicolpate, pseudo-operculate; semitectate, and widely reticulate. The structure of the infratectum could be considered of the granular-collumelar type. Some of the attributes found in the polen of Ph. Chiapasanus were not known for the genus, though such attributes are commonly found in the subgenus Sigmoidotropis of the genus Vigna. Ph. chiapasanus shows a series of morphological and palynological differences that open the possibility for the creation of a new section within the genus. More detailed studies will definitely by needed to better document relationships to other species of the genus.

Commercial thinning stimulates natural regeneration in spruce–fir stands

Understanding the response of tree regeneration following commercial thinning treatments can improve planning in managed forests dependent on natural regeneration. We used long-term commercial thinning experiments in eastern spruce–fir stands of Maine, USA, to test two hypotheses: (1) commercial thinning increases the density of tree regeneration and (2) tree regeneration density increases with increasing thinning intensity. A decade after thinning, densities of softwood and hardwood regeneration were 10 times greater in thinned stands than unthinned stands. The abundance of small softwood (0.11–0.60 m tall) was highest in lower intensity thinning treatments, whereas medium (0.61–1.40 m tall) and large (≥1.41 m tall to 8.90 cm diameter at breast height) softwoods increased proportionally with thinning intensity, a pattern related to a higher rate of recruitment in more open stands created by heavier thinning. Hardwood density generally increased with thinning intensity and developed into a significant component of the large size class. Softwood regeneration density was higher in older spruce stands than younger fir stands, which may be due to greater abundance of advance regeneration, higher residual stand mortality, and greater harvest disturbance in older spruce stands. However, acceptable softwood stocking was achieved in all replicates of thinning treatments. Therefore, in addition to providing higher individual-tree growth and merchantable yield, commercial thinning in eastern spruce–fir stands also increases regeneration density. The rate of recruitment also increased as thinning intensity increased, thus stimulating understory regeneration similar to that of a shelterwood establishment cut.

Size dominance regulates tree spacing more than competition within height classes in tropical Cameroon

Does competition prevail in large size classes of trees in tropical forests? This question is fundamental to our understanding of the demography and dynamics occurring in rain forests. We investigated this question based on an undisturbed late-secondary forest on a 1-ha plot in central Cameroon. Trees were stem-mapped and classified into three size classes: understorey, midstorey and overstorey. The diameter at breast height and yearly biomass increment were determined as measures of plant growth and performance. Spatial statistics such as pair- and mark-correlation functions were used to detect scale-dependent patterns that could be caused by competition within and between the three size classes. The results revealed a random pattern and spatially uncorrelated measures of plant growth of overstorey trees. This suggests that competitive effects are of minor importance in the large size class of overstorey trees. Likewise, only weak evidence for competition between trees was found within the two lower size classes. However, negative distance correlations were found between the different size classes. We suggest that competition within height classes was relatively low due to the diversity of species with their variable niche differentiations and phenotypic plasticity that may compensate for competitive effects.

Diet, feeding behaviour and habitat utilisation of the blue stingray Dasyatis chrysonota (Smith, 1828) in South African waters

Analysis of stomach contents for Dasyatis chrysonota revealed that diet varied with size and habitat. The diet of all size classes in the surf zone was comprised primarily of Callianassa spp., Donax spp. and unidentified polychaete species. The medium and large size classes fed primarily on Donax spp., whereas the very large size class fed mainly on Callianassa spp. Polychaetes were of secondary importance as prey for the medium size class. The diet of D. chrysonota in the nearshore zone consisted mainly of Balanoglossus capensis and Callianassa spp. Balanoglossus capensis decreased from an index of relative importance (IRI) of 75.3% for the medium size class to 59.9% for the very large size class, whereas Callianassa spp. increased from 22.8% to 39.4% between the medium and the very large size classes. The offshore zone was the only area in which small size class D. chrysonota were caught. The diet of these small D. chrysonota was primarily polychaetes and amphipods. Polychaetes increased in importance in the medium size class, but declined in each successively larger size class. Conversely, Pterygosquilla armata capensis became the single most important prey item for the very large size class, comprising an IRI of 50.9%. The behaviour pattern used by D. chrysonota to locate and extract prey is described.

Season and Body Size Influence Movement of Hydropsychid Caddisfly Larvae (Trichoptera: Hydropsychidae)

Movement patterns of fifth-instar Hydropsyche slossonae larvae were investigated in artificial streams. In the first choice experiment, larvae were released into a central area and their upstream or downstream crawling or drifting was monitored. A second experiment used the same design; however, fifth instars collected during spring and fall were divided into two, nonoverlapping, relative size-classes (large and small) to determine how these factors influenced movement parameters. In both experiments, larvae always drifted more frequently than they crawled, but in experiment 2, drifting tendency declined with increasing weight in spring. In both experiments, there was no statistically detectable directional bias to crawling nor change in relative crawling direction with season or size-class. In experiment 2, drifting larvae were lighter than nondrifting larvae in the large size-class, but equal in weight in the small size-class. This result was unrelated to absolute weight, as large size-class larvae in fall were similar in weight to small size-class larvae in spring. It is possible that the relative weight differential of drifting and nondrifting larvae in one size-class but not the other may be related to sexual rather than body size differences.