Habitat utilization and vertical movements of white marlin (Tetrapturus albidus) released from commercial and recreational fishing gears in the western North Atlantic Ocean: inferences from short duration pop-up archival satellite tags

Researchers have applied numerous techniques to improve billfish stock assessments, including habitat‐based models that incorporate behavioral and oceanographic parameters to standardize historical catch‐per‐unit‐effort time‐series data. These methods have allowed researchers to account for significant changes in the depths of pelagic longline (PLL) gear deployments over time. This study presents habitat‐use data recovered from high‐resolution 5‐ and 10‐day pop‐up satellite archival tags (PSATs) attached to 47 surviving white marlin released from commercial and recreational fishing gears offshore of the U.S. East Coast, the northern Caribbean, and Venezuela between 2002 and 2004. Data recovered from transmitting tags indicated that white marlin spent nearly half of their time associated with warm, near‐surface waters (<10 m). All fish displayed frequent short duration (mean: 39.8 min) vertical excursions from surface waters to depths averaging 51 m. Qualitative and multivariate classifications of data from completely transmitted movements of surviving white marlin revealed two major types of descents: one pattern was characterized by deep ‘V’‐shaped excursions of relatively short duration (mean: 23.4 min) while the other featured descents that were more broadly ‘U’‐shaped and confined to a specific depth range for an extended period of time (mean: 75.8 min). Based on the frequency, persistence, and patterns of these vertical movements, white marlin appear to direct a considerable proportion of foraging effort well below surface waters, a behavior that may account for relatively high catch rates of white marlin on some deep‐set PLL deployments.     

Culturing freshwater pearl mussel Margaritifera margaritifera: a breakthrough in the conservation of an endangered species

• 1. The freshwater pearl mussel Margaritifera margaritifera L. is globally endangered and is threatened by commercial exploitation, pollution and habitat loss throughout its range. Captive breeding would be a valuable tool in enhancing the status of M. margaritifera in the UK.
• 2. We have developed a semi‐natural system for successfully infecting juvenile brown trout with glochidial M. margaritifera, and culturing juvenile mussels in experimental tanks where glochidial M. margaritifera can excyst from fish gills and settle into sediment.
• 3. Infected fish had less than 1% mortality. Levels of infection varied among fish. Two yearly cohorts of juvenile M. margaritifera were identified from samples of sediment taken from each experimental tank. Individuals range in size from 1.4 mm (2000 cohort) to >3 mm in length (1999 cohort).
• 4. The number of juvenile M. margaritifera present in the two experimental tanks are estimated to be between 3600 (tank A) and 0 (tank B) for the putative 1999 cohort and between 6000 (tank A) and 13 000 (tank B) for the putative 2000 cohort.
• 5. This pioneering method for large‐scale cultivation of juvenile M. margaritifera is intermediate between the release of infected fish into rivers and the intensive cultivation systems developed in continental Europe and the USA for other species of unionid. This is the first time that large numbers of M. margaritifera have been cultured and represents a significant breakthrough in the conservation of this globally endangered Red Data List species. The method is straightforward and is most cost‐effective when undertaken alongside established hatchery processes.

Copyright © 2006 John Wiley & Sons, Ltd.     

Freshwater mussel assemblage structure in a regulated river in the Lower Mississippi River Alluvial Basin,USA

• 1. This paper documents a diverse, reproducing freshwater mussel community (20 species) in Lower Lake — an impounded, regulated portion of the Little Tallahatchie River below Sardis Dam in Panola Co., Mississippi, USA.
• 2. Despite being regulated and impounded, the lake has a heterogeneous array of habitats that differ markedly in mussel community attributes. Four distinct habitat types were identified based on current velocity and substrate characteristics, representing a gradient from habitats having lotic characteristics to lentic habitats. All four habitat types supported mussels, but habitats most resembling unimpounded, lotic situations (relatively higher current velocity and coarser substrate) had the highest mussel abundance and species density (10.1 mussels m^?2, 1.8 species m^?2, respectively). Lentic habitats (no flow, fine substrate) were characterized by lower abundance and species density (2.0 mussels m^?2, 0.8 species m^?2, respectively), but supported mussel assemblages distinctive from lotic habitats.
• 3. Evidence of strong recent recruitment was observed for most species in the lake and was observed in all four habitat types.
• 4. Although impounded and regulated, Lower Lake represents one of the few areas of stable large‐stream habitat in the region. The presence of a diverse, healthy mussel community in this highly modified habitat suggests that a large component of the regional mussel fauna is relatively resilient and adaptable and is limited primarily by the absence of stable river reaches. Management actions that increase stream stability are likely to result in expansion of the mussel fauna and restoration of a valuable component of ecosystem function in this region.

Published in 2006 by John Wiley & Sons, Ltd.     

Movements by wild brown trout in a boreal river: response to habitat and flow contrasts

Abstract  Radio transmitters were implanted in wild brown trout, Salmo trutta L., in the River Måna at low summer water flows ( n  = 18), higher flow in summer ( n  =   20), and variable, peaking flows in autumn ( n  =   20), and tracked two to four times day and night for 4–5 weeks. Individuals were caught and released in a 4-km uniformly channelised section, and in a 4-km natural diverse river section. Substantial individual variation in home range and total movement (924–85 818 m² and 295–7014 m) suggested flexibility to adapt to local environmental conditions. Fish were stationary most of the time (median movement 0 m), but some individuals undertook few and apparently sporadic longer movements, sometimes involving shifts in home range. No consistent diurnal pattern in movements was found. Trout in the uniform habitat section appeared to have larger home ranges and moved more than trout in the natural section. Differences were, however, not statistically significant in most comparisons, due to large individual variation. Similarly, larger home ranges and movements between trials related to higher flow were found, but differences were generally not significant. No consistent effects of sudden, extreme peaking flows on area use or movements by the brown trout were observed.     

Model uncertainty in the ecosystem approach to fisheries

Fisheries scientists habitually consider uncertainty in parameter values, but often neglect uncertainty about model structure, an issue of increasing importance as ecosystem models are devised to support the move to an ecosystem approach to fisheries (EAF). This paper sets out pragmatic approaches with which to account for uncertainties in model structure and we review current ways of dealing with this issue in fisheries and other disciplines. All involve considering a set of alternative models representing different structural assumptions, but differ in how those models are used. The models can be asked to identify bounds on possible outcomes, find management actions that will perform adequately irrespective of the true model, find management actions that best achieve one or more objectives given weights assigned to each model, or formalize hypotheses for evaluation through experimentation. Data availability is likely to limit the use of approaches that involve weighting alternative models in an ecosystem setting, and the cost of experimentation is likely to limit its use. Practical implementation of an EAF should therefore be based on management approaches that acknowledge the uncertainty inherent in model predictions and are robust to it. Model results must be presented in ways that represent the risks and trade‐offs associated with alternative actions and the degree of uncertainty in predictions. This presentation should not disguise the fact that, in many cases, estimates of model uncertainty may be based on subjective criteria. The problem of model uncertainty is far from unique to fisheries, and a dialogue among fisheries modellers and modellers from other scientific communities will therefore be helpful.     

THE USE OF TIMBER IN MINING

The paper considers briefly the history of the use of timberunderground and the general problem of support and goes on todiscuss the two main uses for timber in mining, i.e. on roadwaysand at the coal face, where the two principal methods of workingare pillar and stall working and longwall working. Species whosetimber is useful for supports are listed and the various kindsof supports given together with the chief factors affectingtheir behaviour. Replacement of timber by steel is discussed,and in considering the outlook for home-grown timber props emphasisis laid on the need to supply only the best types properly preparedand seasoned.