Occurrence of the semi-catadromous European eel Anguilla anguilla in the Baltic Sea

Strontium (Sr) and calcium (Ca) contents in the otoliths of yellow and silver European eels [Anguilla anguilla (L.)] collected from coastal waters of the Baltic Sea and a freshwater lake in Sweden were examined by wavelength dispersive X-ray spectrometry with an electron microprobe. The mean Sr/Ca ratios from elver check to otolith edge were significantly higher for the eels from coastal waters (5.39 ± 1.09‰) than for those from the lake (0.71 ± 0.89‰). The evidence indicates that European eels in the Baltic Sea do not necessarily migrate into freshwater streams during the growth phase. Received: 30 September 1999 / Accepted: 6 April 2000     

Allozyme electrophoresis indicates high gene flow between populations of Holothuria (Microthele) nobilis (Holothuroidea: Aspidochirotida) on the Great Barrier Reef

 Genetic variation in 15 Holothuria (Microthele) nobilis (Selenka, 1867) populations on the Great Barrier Reef was studied at seven polymorphic allozyme loci. Although populations were separated by distances up to 1300 km, there were no apparent restrictions to gene flow (F _ST values were not significantly different from 0) and the maximum Nei's unbiased genetic distance was 0.003. Populations were in Hardy–Weinberg equilibrium at all loci. The estimated maximum sexual input [this is the ratio of the number of sexually produced individuals (N*) to the sample size (N _i )] and the minimum sexual input [this is the ratio of the number of genotypes (N _go ) over the sample size (N _i )] were used as estimators for the amount of asexual reproduction. Both parameters suggested that H. nobilis reproduces solely by sexual means (N*:N _i : = 1; N _go :N _i  = 0.74 to 1). The allozyme data indicated high gene flow between populations, but the possibility that allozyme frequencies may not be at equilibrium means that it was not possible to distinguish whether the patterns reflect present-day dispersal or dispersal that occurred in the past. Received: 27 March 2000 / Accepted: 29 June 2000     

Patterns of time and space utilisation in coelacanths (Latimeria chalumnae), determined by ultrasonic telemetry

Acoustic telemetry was used to examine patterns of activity and space utilisation of coelacanths, nocturnal predators which spend the day in submarine caves. Nine coelacanths (Latimeria chalumnae) were tracked, each for a period of 1 to 16 nights at Grande Comore, West Indian Ocean. Activities lasted on average 9 h, usually starting shortly after sunset and ending before sunrise. Vertically, coelacanths moved up and down at and below cave level by following the bottom contour, mainly between 180 and 400 m depth. The deepest record was 698 m, the shallowest 133 m. Most time was spent between 200 and 300 m depth. Large individuals performed deep excursions to depths below 400 m, usually once per night. The fish spent most time in water temperatures of 15 to 19 °C; they rarely ventured into waters warmer than 22 °C measured at depths shallower than 160 m depth. Horizontally, coelacanths stayed in narrow areas ranging from <1 to 10 km of coastline. Coelacanths are extremely slow drift-hunters with an estimated average swimming speed of 3.2 m min⁻¹, often travelling not more than 3 km per night. They probably take advantage of local upwelling and downwelling and slow currents occurring parallel to the steep slopes. This study shows that coelacanths are inhabitants of the subphotic zone, where they are active mainly below the depth of their daytime refuges. Received: 7 July 1999 / Accepted: 11 February 2000     

Short retention times of stomach temperature loggers in free-living seabirds: is there hope in the spring?

Stomach temperature loggers have proved useful for the study of feeding activity in free-living seabirds, but their usage has been restricted because they are frequently dislodged and lost during the seabirds' regular regurgitation of indigestible prey remains. In the present study we examine the incidence of spontaneous regurgitation (pellet production) in free-living seabirds, consider the effect this has on the likely retrieval of stomach temperature loggers and present a structural modification of the logger housings which leads to a much lower incidence of regurgitation. Systems were tested on albatrosses, cormorants, gannets and penguins. Received: 15 July 1997 / Accepted: 31 October 1997     

A correction to: biological and oceanographic insights from larval labrid (Pisces: Labridae) identification using mtDNA sequences

Previously published mtDNA cytochrome b sequences for Xyrichtys novacula (Linnaeus) and two morphologically distinct types of Xyrichtys larvae (Pisces: Labridae) included human cytochrome b sequence, presumably due to sample contamination and/or poor preservation of sample DNA. Those sequences had been used to identify the two types of Xyrichtys larvae as X. novacula, but owing to the contamination, the identifications are invalid. Fresh specimens were collected: X.␣martinicensis (Cuvier and Valenciennes), X. novacula, X. splendens (Castelnau), and Xyrichtys sp. larvae of each of the two morphotypes (dorsal-forward eye and ventral-forward eye). The cytochrome b fragment was amplified from each specimen using the polymerase chain reaction. Comparison of the sequences with human cytochrome b sequence confirmed that the new sequences were not contaminated. The interspecific differences in Xyrichtys sequences were less than previously reported, but still greater than observed in many fish genera. Distance and parsimony analyses indicated that X. novacula and X. martinicensis were more closely related to each other than to X. splendens. This conclusion differs from our previous conclusion that X. martinicensis and X. splendens were more closely related to each other than to X. novacula. Distance and parsimony analyses also demonstrated that both larval morphotypes were X. novacula and, thus, our previous conclusions regarding larval ecology and oceanographic transport remain unchanged. Received: 12 March 1997 / Accepted: 24 October 1997     

Spawning behaviour and sex hormone levels in adult and precocious brown trout (Salmo trutta L.) males and the effect of anosmia

Summary. In the present experiment the behaviour and endocrine status of males of the brown trout, Salmo trutta L., (Salmoniformes: Salmonidae) were studied when males were kept in a stream tank with a nest digging female. Groups of mature adult males and precocious intact or anosmic male parr were placed with the nesting female so that the group resembled a natural spawning situation with big anadromous fish acting as dominant males and precocious parr acting as “sneakers”. A control experiment was also run with only males without a female present. In intact parr there were significant positive correlations between the per cent of the total observation time spent with a female, milt volume, and plasma concentration of 17α, 20β-dihydroxy-4-pregnen-3-one. Anosmic parr had significantly lower volumes of strippable milt and gonadal steroid hormone levels compared with intact parr. However, no differences were found in the control experiment. Significantly fewer anosmic parr attended and courted the nesting female and those anosmic fish that attended the female had significantly lower plasma levels of gonadal hormones. Intact parr also displayed a greater number of agonistic acts against other parr without any difference in fighting ability. No differences in aggression occured in the control experiment. In adult males together with a female, post-experimental gonadal steroid hormone levels were higher than pre-experimental levels. Positive correlations between aggression and androgen hormone levels were observed in adult males. No differences in plasma hormone levels were observed between adult males and intact precocious males. The results show that olfactory occlusion results in low steroid hormone levels and milt volumes in precocious males placed in a spawning situation. The courting behaviour was also affected by anosmia. Odours from the nesting female may have caused the enhanced plasma hormone levels and stimulated the males to attend the female. Received 15 May 1997; accepted 29 June 1997.     

Eier der Flußseeschwalbe (Sterna hirundo) als Indikator für die aktuelle Belastung von Rhein, Weser und Elbe mit Umweltchemikalien

In 1995, common tern (Sterna hirundo) eggs from the big German rivers, the Rhine, Weser and Elbe were collected to study the contamination with organochlorines and mercury. We found distinct differences between the rivers: common tern eggs from the Rhine had higher concentrations of PCBs and HCHs, while eggs from the Elbe had higher residues of DDT, HCB and mercury. Also toxic PCB congeners had higher residue levels in the Rhine. Considering all organochlorines, samples from the Rhine also had the highest concentrations, while those from the Elbe were the lowest. With 5.7 μg×g^?1 fresh weight, the ΖCBs had a level endangering breeding success. Fish eating birds should be used as indicators of the contamination of the rivers with environmental chemicals and should be included in monitoring programmes.     

Modelling and assessment of South African elephant Loxodonta africana population persistence

The use of a quantitative population growth model to investigate the persistence of South African elephant populations is explored. The model provides quantitative assessments of population persistence and confidence intervals for estimated parameters based purely on population size estimates. The analysis supports the view that most of the larger populations in the region are secure. This view is further supported by a lack of density dependent effects in most of the recovering populations and the high population rates of increase observed. This predominantly positive prognosis is in contrast with that emerging from most of the rest of the African continent where the populations are under greater threat because of habitat restriction and direct human conflict. This preliminary assessment of elephant population persistence suggests that “viable” populations may lie between 400 and 6000 individuals. Although not inconsistent with information-greedy genetic and demographic models, the relationship between population growth versus genetic and demographic models should be further investigated. The implementation of a metapopulation management strategy towards these smaller populations is advocated. In addition, as all of the populations included in this analysis have been afforded some degree of protection since the 1920s, continued protection would be a prerequisite for their continued survival.