Growth variability of brook charr (Salvelinus fontinalis) in coastal maine

Brook charr inhabit a wide variety of habitats and exhibit considerable growth variation within and among populations. We used biannual mark–recapture electrofishing surveys and PIT tags at two streams in coastal Maine to examine spatial and temporal variability in brook charr growth. We documented considerable stream‐to‐stream and year‐to‐year variation in the growth of coastal brook charr. Based on 2892 recaptures between 2006 and 2010, we developed a suite of linear mixed models to examine variation in individual growth rates at Stanley Brook as a function of environmental variables. We distilled physical habitat data from surveys in 2010 into principle components for entry into the growth model. Growth was related primarily to an interaction between season and body length, mean water temperature, and instream location. Growth rates were highest in the summer, and smaller individuals grew more rapidly than larger conspecifics in the same stream. Individuals using habitats closer to the head of tide grew faster than those in upstream locations. Physical habitat variation was not an important control of individual growth variation within Stanley Brook. We suggest local variability in growth rates should be considered when developing management strategies for coastal populations.     

Seasonal movement,growth and survival of brook trout in sympatry with brown trout in Midwestern US streams

Seasonal patterns in growth, survival and movement of brook trout Salvelinus fontinalis were monitored in two southeastern Minnesota streams divided into study reaches based on brown trout Salmo trutta abundance. We estimated survival and movement while testing for effects of stream reach and time using a multistrata Cormack–Jolly–Seber model in Program MARK. Multistrata models were analysed for three age groups (age‐0, age‐1 and age‐2+) to estimate apparent survival, capture probability and movement. Survival varied by time period, but not brown trout abundance and was lower during flood events. Age‐0 brook trout emigrated from reaches with low brown trout abundance, whereas adult brook trout emigrated from downstream brown trout‐dominated reaches. Growth was highest in spring and summer and did not differ across streams or reaches for the youngest age classes. For age‐2+ brook trout, however, growth was lower in reaches where brown trout were abundant. Interspecific interactions can be age or size dependent; our results show evidence for adult interactions, but not for age‐0. Our results suggest that brook trout can be limited by both environmental and brown trout interactions that can vary by season and life stage.     

Role of large‐ and fine‐scale variables in predicting catch rates of larval Pacific lamprey in the Willamette Basin,Oregon

Pacific lamprey Entosphenus tridentatus is an anadromous fish native to the Pacific Northwest of the USA. That has declined substantially over the last 40 years. Effective conservation of this species will require an understanding of the habitat requirements for each life history stage. Because its life cycle contains extended freshwater rearing (3–8 years), the larval stage may be a critical factor limiting abundance of Pacific lamprey. The objective of our study was to estimate the influence of barriers and habitat characteristics on the catch‐per‐unit‐effort (CPUE) of larval Pacific lamprey in the Willamette River Basin, Oregon, USA. We sampled lampreys at multiple locations in wadeable streams throughout the basin in 2011–13 and used an information theoretic approach to examine the relative influence of fine‐ and large‐scale predictors of CPUE. Pacific lamprey was observed across the basin, but its relative abundance appeared to be limited by the presence of natural and artificial barriers in some sub‐basins. Lower velocity habitats such as off‐channel areas and pools contained higher densities of larval lamprey; mean Pacific lamprey CPUE in off‐channel habitats was 4 and 32 times greater than in pools and riffles respectively. Restoration and conservation strategies that improve fish passage, enhance natural hydrologic and depositional processes and increase habitat heterogeneity will likely benefit larval Pacific lamprey.     

Alternative growth histories in populations of Lake Superior brook trout: Critical support for partial migration

As concerns for losses of migratory species heighten globally, scientists are being challenged to characterize diversity in the migratory behaviors to support scientifically defensible conservation programs. Anecdotal observations of brook trout (Salvelinus fontinalis) inhabiting Lake Superior and its tributaries suggest the occurrence of two forms: a large lake form hypothesized to originate in streams and reside in Lake Superior for significant parts of the year and a small stream form hypothesized to be stream resident. Declines in the lake form are a conservation concern and understanding of the variation in migratory behavior is needed to assist conservation efforts. We used analyses of vertebrae and otoliths to test whether the growth histories of lake and stream caught fish differed as expected for adult and juvenile stages from a migratory population (migration), individuals differing in the age of outmigration to the lake (staggered migration), or a combination of residents and migrants (partial migration). Lake caught fish grew faster and lived longer than stream caught fish and differences in length-at-age were apparent by the end of the first year of life. There was no evidence of individuals abruptly changing growth history in a way that would suggest habitat switches later in life. Growth histories of lake and stream caught brook trout were also similar to those of migrants and residents from other brook trout populations or sub-populations. Our findings support the hypothesis of partial migration as an explanation for the diversity observed in Lake Superior brook trout and demonstrate how analyses of growth histories can help clarify migratory systems in species whose movements are challenging to track.     

Evidence of concealment behavior by adult rainbow trout and brook trout in winter

Abstract – There has been little investigation of the winter ecology of adult trout during winter, especially in regard to concealment behavior. We compared day vs night underwater counts of adult rainbow trout and brook trout from four streams. At water temperatures between 1°C and 9°C, daytime counts accounted for 44% and 16% of nighttime snorkeling counts for rainbow trout and brook trout adults, respectively. As winter progressed, nighttime counts declined more so for brook trout than rainbow trout, but the decline was not significant for either species. Nocturnalism of both species was higher in streams with colder water temperatures. We observed few fish within concealment structure; however, by electrofishing concealment habitat during the day, we captured 10 times more adult trout than we counted immediately beforehand by snorkeling. Adult trout were concealed in cobble-boulder substrate and woody debris during the day. ^Note     

Establishing survey and monitoring protocols for the assessment of conservation status of fish populations in river Special Areas of Conservation in the UK

• 1. Under the EC Habitats Directive (92/43/EEC), several rivers in the UK have been designated Special Areas of Conservation (SACs) because they support important populations of fish species. Several factors need to be considered when establishing survey protocols to assess the conservation status of fish species in these rivers.
• 2. It is important to understand the biology and habitat requirements of fish species and to design appropriate monitoring surveys that adequately assess the status of the fish populations. This information can, in turn, provide the basis for establishing sustainable conservation targets for specific stocks, a process known as condition assessment.
• 3. Favourable condition of fish species in SAC rivers is assessed using three criteria. The first relates to density of fish in various life stages against pre‐set targets, assuming that an appropriate number of sites is surveyed to account for natural spatial and temporal variations in fish populations. The second is evaluation of the demographic structure to demonstrate continued recruitment success. Third, by mapping the distribution of the target species in individual rivers and where favourable condition is only achieved where there has been no reduction in the distribution range river between surveys.
• 4. The framework described was developed from limited survey data. As more monitoring and assessment data become available, the threshold criteria for favourable condition for each species should be improved, and uncertainty in the procedures reduced.

Copyright © 2008 John Wiley & Sons, Ltd.     

Living with failure: the prey capture success of young brook charr in streams

Abstract – We examined the prey capture success of recently emerged brook charr ( Salvelinus fontinalis ) foraging in shallow, clear, still-water pools along the edges of streams. Fewer than 42% of attacks ended with ingestion either because of difficulty distinguishing suitable prey from unsuitable items or because of difficulty capturing evasive prey. Probabilities of capture upon attack and ingestion upon capture depended upon where attacks were directed in the water column, the fish's level of activity at the time of attack and its fork length, and the sampling date. In general, success was higher for larger, sedentary fish attacking prey in the lower portion of the water column than for smaller, active fish attacking prey at the water surface. The frequency of items attacked was only a moderate predictor of the frequency of prey ingested. Poor capture success is an important aspect of the early life history of brook charr in particular and probably of young salmonines in general. ^NOTE     

Morphogenesis and distribution of the endocrine pancreas in adult lampreys

The endocrine pancreas of larval lampreys appears as islets of cells isolated in the submucosa and those both continuous with, and within, the gut epithelium at the intestinal-oesophageal-bile duct junction. The islets, and occasionally follicles, are composed of only insulin-secreting (B) cells. During metamorphosis, the bile duct either completely degenerates or its epithelium transforms into a caudal endocrine pancreas while a cranial pancreas appears as a specialization and expansion of the larval pancreas. Immunocytochemistry and histochemistry demonstrates that there is a wide variation in the distribution of the pancreatic tissue in adults of lamprey species, and this variation may result from interspecific differences in morphogenetic events at metamorphosis. Despite species variability in its distribution, the endocrine pancreatic tissue in all adult lampreys is composed of equal numbers of B cells and somatostatin-secreting (D) cells, but there are no glucagon-secreting (A) cells. Immunocytochemistry reveals that B and D cells of the caudal pancreas differentiate from cells of the larval bile duct during metamorphosis of the sea lamprey,Petromyzon marinus.     

Brook trout spawning areas in lakes

Abstract— Nine lakes containing self-sustaining populations of brook trout ( Salvelinus fontinalis ) were surveyed to provide quantitative information on the abundance and distribution of redd sites. We measured rates of groundwater flow at redds in four of these lakes, and in one of these lakes we also compared the frequency of site use over four years from spawning observations. The number of redd sites in each lake ranged from 1 to 53 (mean=30) with most found relatively close to shore (∼ 1 m deep). Spawning areas per lake (16.9–829.4 m²) were not related to lake size and were often not continuous areas of littoral zone habitat. Rates of groundwater flow in lakes, averaged across redd sites in each lake, ranged from 20.0 to 107.9 ml. m.⁻² min^−1. The intensive survey of redd site use in one lake demonstrated that only 11% of sites (10 of 92) were used in all four years of observation. The mean rates of groundwater flow at sites used in all four years were significantly greater than at sites used intermittently. Data from this and other studies point to the conservation of subcatchments associated with groundwater discharge areas used by spawning brook trout as a means of maintaining self-sustaining populations.