Stocking density and its influence on the productivity of red cusk eel, Genypterus chilensis (Guichenot, 1848), in shallow raceways

We compared the growth properties of red cusk eel Genypterus chilensis with initial mean weight ± standard error, 106.2 ± 6.1 g reared in shallow raceways at three different stocking densities (28.5, 46.1, and 60.7 kg m-3) in a 226-day long growth trial at a constant temperature of 17°C. There was a trend towards higher specific growth rates at the highest density. Final mean weights were 333 ± 12, 352 ± 12, and 354 ± 15 g, at the 30, 45, and 60 kg m-3 density, respectively. Overall, the growth rates were higher in the 60 kg m-3 density group than the two other density groups. The daily feeding intake (%) was higher in the medium (0.51), and high (0.55) density groups compared the low-density group (0.45). Feed conversion efficiency (FCE) did not differ between the density groups. A significant size rank correlation was maintained in all density groups throughout the study. Calculated productivity increased almost linearly with increasing stocking density and was found to be 32, 34, and 39 g m-2 d-1 at 30, 45, and 60 kg m-3, respectively. The results show that the optimum density conditions for farming juvenile red cusk eel, both concerning growth rate, feed conversion, and productivity is at densities equal to or higher than 60 kg m-3.

Linguistic Laws in Speech: The Case of Catalan and Spanish

In this work we consider Glissando Corpus—an oral corpus of Catalan and Spanish—and empirically analyze the presence of the four classical linguistic laws (Zipf’s law, Herdan’s law, Brevity law, and Menzerath–Altmann’s law) in oral communication, and further complement this with the analysis of two recently formulated laws: lognormality law and size-rank law. By aligning the acoustic signal of speech production with the speech transcriptions, we are able to measure and compare the agreement of each of these laws when measured in both physical and symbolic units. Our results show that these six laws are recovered in both languages but considerably more emphatically so when these are examined in physical units, hence reinforcing the so-called ‘physical hypothesis’ according to which linguistic laws might indeed have a physical origin and the patterns recovered in written texts would, therefore, be just a byproduct of the regularities already present in the acoustic signals of oral communication.

On the physical origin of linguistic laws and lognormality in speech

Physical manifestations of linguistic units include sources of variability due to factors of speech production which are by definition excluded from counts of linguistic symbols. In this work, we examine whether linguistic laws hold with respect to the physical manifestations of linguistic units in spoken English. The data we analyse come from a phonetically transcribed database of acoustic recordings of spontaneous speech known as the Buckeye Speech corpus. First, we verify with unprecedented accuracy that acoustically transcribed durations of linguistic units at several scales comply with a lognormal distribution, and we quantitatively justify this ‘lognormality law’ using a stochastic generative model. Second, we explore the four classical linguistic laws (Zipf’s Law, Herdan’s Law, Brevity Law and Menzerath–Altmann’s Law (MAL)) in oral communication, both in physical units and in symbolic units measured in the speech transcriptions, and find that the validity of these laws is typically stronger when using physical units than in their symbolic counterpart. Additional results include (i) coining a Herdan’s Law in physical units, (ii) a precise mathematical formulation of Brevity Law, which we show to be connected to optimal compression principles in information theory and allows to formulate and validate yet another law which we call the size-rank law or (iii) a mathematical derivation of MAL which also highlights an additional regime where the law is inverted. Altogether, these results support the hypothesis that statistical laws in language have a physical origin.

Mechanics of foraging success and optimal microhabitat selection in Alaskan Arctic grayling (Thymallus arcticus)

Most fishes residing in temperate streams in the Northern Hemisphere are drift-feeders. Despite this fact, little is known about the mechanisms of drift-feeding itself. We used Alaskan Arctic grayling (Thymallus arcticus), an abundant boreal drift-feeder, to examine the effects of water velocity on several aspects of drift-feeding behavior and test predictions of the Grossman et al. (2002) net energy intake model for microhabitat choice. Water velocity had a negative effect on prey capture, a positive effect on holding velocity, and little effect on reactive distance. We also found that dominance was a better predictor of prey capture success than size rank, although neither of these variables influenced holding velocity or reactive distance. The Grossman et al. (2002) model successfully predicted holding velocities of grayling in one Alaskan stream, but not another. Model failure might have occurred due to higher turbulence, increased predation, or interspecific competition with Dolly Varden (Salvelinus malma). These results help inform the study of habitat selection in drift-feeding fishes as well as management and conservation of Arctic grayling.

Variations in body-size spectra of periphytic ciliates at different depths: a case study in coastal waters of the Yellow Sea

Body-size spectra are inherent characteristics of organisms that can be used to summarise the functional structure of a community and thus be used in both ecological studies and biomonitoring programs. In order to determine the effect of water depth on body-size spectra of marine periphytic ciliate communities, a 1-month baseline survey was conducted at four depths (1, 2, 3.5 and 5m) in coastal waters of the Yellow Sea, northern China. Based on equivalent spherical diameters (ESD), 50 species were categorised into seven body-size ranks: S1, 2–17μm; S2, 22–27μm; S3, 29–36μm; S4, 37–49μm; S5, 53–71μm; S6, 84–92μm; S7, 127–153μm. These seven body-size ranks were composed of four trophic functional groups: algivores (A), bacterivores (B), predators (R) and non-selectives (N). Body-size rank S1 was composed primarily of the B functional group; S2 was composed of the N and R functional groups, S3 and S4 were composed of the A, B and N functional groups, S5 and S6 were composed of the A functional group and S7 was composed of the R functional group. The medium body-size ranks (S4 and S5) were dominant at 1 and 2m, whereas the smallest body-size rank (S1) was dominant at 3.5 and 5m. Canonical analysis of principal coordinates revealed a clear vertical variation in body-size spectra at the four depths. Body-size diversity indices peaked at 2–3.5m and fell sharply at 5m. Body-size diversity indices peaked at 2–3.5m and fell sharply at 5m. Body-size distinctness, as measured by the paired-index (ellipse) test, showed an increasing trend of departure from the expected pattern from surface to deeper layers. These results suggest that the body-size spectra of periphytic ciliates may be significantly shaped by water depth and thus may be used as bioindicators of the ecological integrity and quality of water at different depths in marine ecosystems.

BASIC THEORY FOR A CLASS OF MODELS OF HIERARCHICALLY STRUCTURED POPULATION DYNAMICS WITH DISTRIBUTED STATES IN THE RECRUITMENT

In this paper we present a proof of existence and uniqueness of solution for a class of PDE models of size structured populations with distributed state-at-birth and having nonlinearities defined by an infinite-dimensional environment. The latter means that each member of the population experiences an environment according to a sort of average of the population size depending on the individual size, rank or any other variable structuring the population. The proof of the local existence and uniqueness of solution as well as the continuous dependence on initial continuous is based on the general theory of quasi-linear evolution equations in nonreflexive Banach spaces, while the global existence proof is based on the integration of the local solution along characteristic curves.