The suitability of three anatomical structures to determine age and growth of bull trout, Salvelinus confluentus (Suckley), was assessed. Scales and pelvic fin rays collected from recaptured bull trout 96-265 mm TL were used to validate annulus formation and assess the accuracy and precision of back calculation. Ageing precision and agreement of assigned ages were compared among scales, fin rays and otoliths from bull trout 52-711 mm TL. Annulus formation was validated for 88% (14 of 16 fish) of recaptured bull trout using pelvic fin rays and 68% using scales (15 of 22 fish). Annulus formation in fin rays occurred between late April to early June, and the hyaline (non-growth) band began forming in late August. Back-calculated length was not significantly different from measured length at initial capture either for fin rays or scales (P ‡ 0.19), and absolute percent error was 7.2 ± 1.2 (mean ± SE; n = 14) for fin rays and 8.7 ± 1.9 (n = 15) for scales. Consistency of back-calculated lengths at age between tag and recapture samples for individual fish was similar for fin rays (mean absolute difference = 8.2% ± 0.9; n = 33) and scales (9.4% ± 1.4; n = 40). However, fin rays (87% precision) and otoliths (90%) provided notably higher ageing precision than scales (68%) and closer agreement of assigned ages, particularly for fish older than age 4. Pelvic fin rays appear to offer more accurate and precise age and growth determinations than scales and a non-lethal alternative to otoliths, but further work is needed to validate the accuracy and precision of ageing large, migratory bull trout. K E Y W O R D S : age validation, ageing error, back calculation, bull trout, pelvic fin rays, scales.

This technical paper presents results from pilot field trials conducted on the novel use of a biodegradable jute material to eradicate the highly invasive aquatic macrophyte Lagarosiphon major Ridley from Lough Corrib, Ireland. The results demonstrate the ability of the jute material to comprehensively kill L. major and to restore native macrophyte communities to areas of the lake that were previously overgrown with this priority invasive species. To date, eight indigenous plant species (four charophytes and four angiosperms) have been recorded growing through the loose-weave jute fabric. However, no Lagarosiphon has been recorded as doing so. This material has the potential for broader application in the management of nuisance aquatic weeds and in the restoration of native flora extirpated by these alien species.

We evaluated the species distribution, abundance, and habitat relationships of salmonids in small first‐ to second‐order headwater streams in southeast Alaska. Streams were separated into three zones based on gradient and sampled during the spring, summer, and fall. Dolly Varden Salvelinus malma were found in all streams where fish were present. They were the dominant species in moderate‐ (mean gradient = 5.5%) and high‐gradient (mean gradient = 12.9%) zones. Coho salmon Oncorhynchus kisutch fry and parr were the dominant species in the low‐gradient zone (mean gradient = 3.1%) but were present in higher‐gradient zones. Small numbers of steelhead O. mykiss parr were present in all three zones in the spring and fall. Few were captured during the summer. Coastal cutthroat trout O. clarkii were found primarily in one stream and in all three zones. The density of all species decreased as gradient increased. Anadromous Dolly Varden in spawning condition were observed in the fall up to the highest accessible locations in four streams. Salmonids use high‐gradient reaches when pools are present and accessible. Headwater tributaries comprise a large proportion of most southeast Alaska watersheds, and the combined contribution from all of these tributaries to the fish community may be large. The results from this study underscore the importance of maintaining access for fish throughout watersheds and into small high‐gradient streams.

Fin rays offer a viable alternative to scales and otoliths for determining ages of threatened salmonids, but information on potential side effects from their removal is limited. We conducted a laboratory study to assess the effects of removal of three pelvic fin rays on the survival and growth of two age‐groups of bull trout Salvelinus confluentus (age 3: 209–298 mm standard length [SL]; age 4: 294–362 mm SL). Survival was similar between fin‐ray‐excised fish (≥73%) and control fish (≥69%) at each stage during the 169‐d study (P > 0.85). Survival was also similar within age‐3 (fin ray excision: ≥39%; control: ≥30%; P > 0.42) and age‐4 bull trout (fin ray excision: ≥94%; control: ≥94%; P > 0.86), although a bacterial coldwater infection disproportionately caused higher mortality in age‐3 fish for both test groups. Growth also did not differ between treatment and control groups of either age‐3 or age‐4 fish (P > 0.38). The fin excision wound was completely healed in 56% of treatment fish by day 33 and in 96% by day 126. Excised fin rays regenerated at the rate of 0.25% per day in 92% of treatment fish, attaining nearly one‐half (42%) of the estimated total length by the end of the study; 90% regeneration was predicted to occur in about 13 months. Results suggest that removal of pelvic fin rays for aging is probably not deleterious to bull trout over the size range examined.

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