Empirical estimates of historical variations in the catchability and fishing power of pelagic longline fishing gear

I quantify the effects of 11 variables on the catchability and fishing power of pelagic longlines, which are used to catch tunas and billfishes in the open ocean. Extension of the depth range and the duration of longline operations have reduced the catchability of several epipelagic species, such as mako sharks (Isurus spp.), since industrial longlining commenced in the tropical Pacific Ocean in the early 1950s. Reductions in the body size of many species may also have reduced encounters with longline hooks. By contrast, the catchability of commercially valuable bigeye tuna (Thunnus obesus) increased substantially because of the longer duration and extension of the depth range of longlines. Stronger and less visible line materials and increased fishing-master experience also contributed to increased catchability. By affecting the rate of bait loss, the introduction of new bait species increased fishing power. This study highlights significant problems in deriving indices of abundance from commercial catch and effort data. Instead of relying on commercial data, assessments should use tag-recapture experiments or dedicated surveys to obtain fishery-independent estimates of abundance.     

Quantification of blue carbon pathways contributing to negative feedback on climate change following glacier retreat in West Antarctic fjords

Global warming is causing significant losses of marine ice around the polar regions. In Antarctica, the retreat of tidewater glaciers is opening up novel, low-energy habitats (fjords) that have the potential to provide a negative feedback loop to climate change. These fjords are being colonized by organisms on and within the sediment and act as a sink for particulate matter. So far, blue carbon potential in Antarctic habitats has mainly been estimated using epifaunal megazoobenthos (although some studies have also considered macrozoobenthos). We investigated two further pathways of carbon storage and potential sequestration by measuring the concentration of carbon of infaunal macrozoobenthos and total organic carbon (TOC) deposited in the sediment. We took samples along a temporal gradient since time of last glacier ice cover (1–1000 years) at three fjords along the West Antarctic Peninsula. We tested the hypothesis that seabed carbon standing stock would be mainly driven by time since last glacier covered. However, results showed this to be much more complex. Infauna were highly variable over this temporal gradient and showed similar total mass of carbon standing stock per m² as literature estimates of Antarctic epifauna. TOC mass in the sediment, however, was an order of magnitude greater than stocks of infaunal and epifaunal carbon and increased with time since last ice cover. Thus, blue carbon stocks and recent gains around Antarctica are likely much higher than previously estimated as is their negative feedback on climate change.     

Intra and interspecific association of large pelagic fishes inferred from catch data of surface longline

Synopsis This paper analyses the distribution of longline catches of swordfish, Xiphias gladius, and six species of pelagic elasmobranchs, during a fishing voyage in the tropical eastern Atlantic. Seven scales of sampling units, ranging from about 0.72 to 7.2 km were used. Observed frequencies of appearance of each species in the basic sampling unit, were compared with theoretical frequencies obtained from the Poisson and negative binomial distributions. For the study of the interspecific relationships, contingency tables were used and the degree of association was estimated using the ²test and the coefficient v of Kendall. The catch distribution of the swordfish and the devil ray (Mobula sp.) can be explained by both randomness and a slight trend to association. For the pelagic sharks, a clear trend towards intraspecific clustering was found. Catches of two species of the genus Carcharhinus showed the most positive trends to interspecific association, especially in short ranges, probably due to attraction to previously hooked fish. The possible causes of these distributions are discussed.     

Species assemblages of pelagic fish embryos in the southern North Sea between 1984 and 2000

The occurrence and abundance of the pelagic eggs of southern North Sea spring-spawning fish were analysed between 1984 and 2000. Species number varied between six (1986) and 14 (1999) and was positively correlated with sea surface temperature. With one exception, dab eggs were always the most abundant and usually highly dominant. Ranking of species depended on temperature, but no significant differences in ranking between years was discernible. Although with the increase in temperature in the 1990s a change in species assemblage was evident [species belonging to the boreal-Mediterranean (Lusitanian) group became more apparent in the species assemblage] this did not lead to an increased species diversity (Shannon Index) or a change in other community parameters. It appears that the recent developments regarding spawning stock biomass of commercial North Sea fish is reflected in the declining egg abundance of the respective commercial and larger species (i.e. cod, flounder, plaice) and an increase in abundance of the eggs of small species (i.e. long rough dab, rockling) over the years. Received in revised form: 5 November 2001 Electronic Publication     

远海50个站位沉积物中潜在木质素降解菌的分离与鉴定

【背景】微生物在海洋木质素的降解过程中发挥了至关重要的作用,然而来源海洋环境的木质素降解菌的相关研究报道却很少。【目的】从远海沉积物环境分离潜在的木质素降解菌,为木质素的可再生化学物质转化提供菌种资源。【方法】利用以木质素为唯一碳源的培养基,对50个远海沉积物样品中的木质素降解菌进行富集培养与纯化,并利用含苯胺蓝的脱色培养基筛选潜在木质素降解菌,继而通过16S rRNA基因测序与序列比对初步确定潜在木质素降解菌的分类地位。【结果】从50个沉积物样品中共分离获得菌株283株,其中潜在木质素降解菌263株,它们隶属于α-变形杆菌纲(Alphapreobacteria)、γ-变形杆菌纲(Gamaproteobacteria)、芽孢杆菌纲(Bacilli)、放线杆菌纲(Actinobacteria)和黄杆菌纲(Flavobacteriia)中的32个属。【结论】远海沉积物环境中蕴含着丰富的木质素降解菌,为海洋生物资源的开发利用提供了新的参考。     

Micro- and macrogeographic genetic structure in bryozoans with different larval strategies

Genetic structuring was examined in two marine bryozoans with different modes of reproduction and dispersal of sexually derived larvae: Alcyonidium gelatinosum=A. polyoum, which produces brooded, short-lived lecithotrophic larvae, and A. mytili, an egg broadcaster with pelagic larvae. Randomly Amplified Polymorphic DNA (RAPD) data from these species were further compared with a population of the freshwater bryozoan, Cristatella mucedo, which reproduces mainly by colony fission and production of asexual statoblasts. Microgeographic comparisons of colonies from single sites revealed higher levels of genetic divergence between A. mytili colonies (similarity coefficient, 1−S=0.60) than between those of A. gelatinosum (1−S=0.33). A macrogeographic survey of population structure was undertaken in A. gelatinosum and A. mytili populations from several geographically separated areas. Analysis of Molecular Variance (AMOVA) results showed that for A. gelatinosum, 8% of the variance was found between populations and 92% within populations, and for A. mytili, 10% of the variance was found between populations and 90% within. These values were similar between the two species, despite the differences in larval strategy, and indicate that there are high levels of population genetic subdivision in both species. Results show a general correspondence between patterns of microgeographic genetic structuring and predictions based on reproductive mode and dispersal capacity, although the species with a pelagic larva showed less genetic variation between populations than would have been predicted. Analysis of the C. mucedo population showed a highly clonal structure, as predicted and in agreement with previous studies. Such data represent the first case of a DNA-based population survey of bryozoans with differing reproductive strategies.     

Ammonium content and buoyancy in midwater cephalopods

The majority of squid families (Teuthoidea: Cephalopoda) exchange sodium for ammonium, creating a low-density fluid that imparts lift for neutral buoyancy. However, previous methods for measuring ammonium did not distinguish between NH₄⁺ and various other amine compounds. The present study, using single column ion chromatography, reassessed the cation concentrations in several midwater cephalopod species. High NH₄⁺ levels were confirmed for histioteuthid, cranchiid, and chiroteuthid and related squids. A strong relationship is reported between ammonium content and body mass in Histioteuthis heteropsis, suggesting a gradual accumulation of ammonium coincident with an ontogenetic migration to greater depths. The bathypelagic squids Bathyteuthis abyssicola and Bathyteuthis berryi, on the other hand, contained very little ammonium but rather contained large quantities of an as yet unidentified cation. The ecological significance of this compound is not yet known. Morphology in Bathyteuthid squids suggests that the unknown cation is contained intracellularly and so, unlike sequestered ammonia, does not diminish the space available for muscle tissue. Accordingly, protein measurements in B. berryi mantle muscle are on par with shallower-living muscular squids, and in situ submersible observations reveal strong locomotory abilities relative to other deep-water squids.