Development of rehabilitation strategies and accurate assessment of anthropogenic impacts relies on a thorough understanding of a species’ life history. In the case of the lake sturgeon Acipenser fulvescens, a better understanding of the juvenile life history stages is needed to improve conservation efforts for this imperiled species. Home range size and seasonal movement of juvenile lake sturgeon in the Winnipeg River, Manitoba, were examined using mark–recapture and acoustic telemetry. Over a 30‐month period (May 2006–October 2008), 5,671 juvenile lake sturgeon (213–879 mm fork length [FL]) were marked with Floy tags and the movements of 23 juvenile lake sturgeon (364–505 mm FL) were monitored by means of acoustic transmitters. Despite the potential for movement over 49 km of naturally connected riverine habitat, the results indicated that juvenile lake sturgeon exhibited strong site fidelity. As determined from the mark–recapture data set, 90.8% of recaptured fish were recaptured less than 2.0 river kilometers (rkm) from their original capture location. Similarly, acoustic telemetry data indicated that 50% of the tagged fish moved 1.5 rkm or less from their initial release locations. Finally, the results of both methodologies indicated that juvenile lake sturgeon rarely move through rapids characterized by high water velocities (>1.5 m/s), complex turbulent flows, boulder and bedrock substrates, and various cross‐sectional water depths ranging from 1.0 m to approximately 15.0 m in either an upstream or downstream direction. These results suggest that the year‐round habitat requirements for juvenile lake sturgeon can be met in relatively short sections of a large river. Furthermore, owing to strong site fidelity and a lack of movement through rapids, macroscale habitat use in juvenile lake sturgeon occupying large rivers may be dependent on dispersal at either the larval or young of the year life history stages.
An increased understanding of the juvenile life history stage of the lake sturgeon, Acipenser fulvescens, has been recognized as a key requirement for improving conservation efforts for this once abundant species. The objectives of the current study were to develop an effective methodology for capturing juvenile lake sturgeon in a large riverine environment; to describe the physical habitat characteristics (depth, water velocity and substrate) associated with the areas where juvenile lake sturgeon were captured; and to determine basic population parameters (length, body mass and condition factor) for juvenile lake sturgeon captured in those areas. Gillnets (mesh sizes 25-108 mm) were used to sample the Winnipeg River, a large river in the northern extent of the species range, from 12 June to 6 November 2006. A total of 2154 juvenile (<530 mm FL) lake sturgeon were captured, which represented over 74% of the total fish catch. Moderate (51-108 mm) and small (25 mm) mesh gill nets were found to be efficient for sampling juvenile lake sturgeon, with the former capturing a wider range of sizes and the latter capturing fewer fish but resulting in decreased mortality. Juvenile lake sturgeon were captured at high densities in discrete areas characterized by water depths >13.7 m, detectable water velocities >0.20 m s )1 , and various substrate types.
An examination was made of whether social interactions can have a beneficial effect through the attenuation of the stress response in a social species. In the first experiment, one larger (mean +/-s.e. 194.0 +/- 12.5 g) and seven smaller (32.0 +/- 2.6 g) juvenile lake sturgeon Acipenser fulvescens were placed in tanks to determine whether a classic dominance effect would be established based on body size (n = 6). Large fish did not establish a territory or aggressively interact with smaller fish, as there were no significant differences in nearest-neighbour distances and an absence of aggressive behaviour (biting, chasing and pushing). In the second experiment, it was hypothesized that the presence of conspecifics would have a beneficial effect through an attenuation of the stress response. Fish in groups or isolation were stressed by a brief aerial exposure (30 s), and blood plasma was measured at regular time intervals (0, 20, 40, 60, 120 and 240 min) following the stressor via an implanted cannula (n = 9-11). The presence of conspecifics did not affect the peak cortisol response, however, the overall cortisol response was shorter in duration compared to fish in isolation. Furthermore, secondary stress variables (plasma ions and glucose) showed differences between fish in groups and isolation. The results of these experiments suggest that social interaction plays an important and beneficial role in regulating the stress response in cohesive social species such as A. fulvescens.
Adaptive management and recovery initiatives for longlived, late-maturing species such as Lake Sturgeon, Acipenser fulvescens, are complicated by temporal lags. By the time anthropogenic impacts on critical periods (spawning, larval hatch, age-0 survival) would be manifested in adult populations, decades might have passed. However, recruitment patterns and population trajectory responses (both positive and negative) can be identified by examining the juvenile life stage. This study describes and evaluates a gill net method for sampling juvenile Lake Sturgeon between 250 and 800 mm fork length (FL) resident in Boreal Shield rivers in relative proportion to their abundance. The method is based on previous observations of deepwater preference (>10-15 m), and employs mesh sizes of 25.4, 50.8, 76.2, 127.0 and 152.4 mm stretched measure. Selectivity curves were generated based on 1040 Lake Sturgeon captures from six reaches of the Winnipeg and Nelson rivers, Canada. A normal (common spread) curve approximated a normal distribution centered on~390 mm FL, and relative selection exceeded 0.65 across the 250-800 mm FL range. For the Slave Falls Reservoir (Winnipeg River), Spearman's rankorder correlation (q) for zone-specific cohort-frequency distributions in adjacent sampling years ranged from 0.85 to 0.93, while the score for the entire reservoir was 0.95, suggesting inter-annual consistency. The method allows for rapid and robust assessments of relative abundance and cohort strength for juvenile Lake Sturgeon within large Boreal Shield river systems, and facilitates biological comparisons among reaches and over time. Incidentally, cohort frequency results derived herein indicate that juvenile recruitment in regulated Boreal Shield rivers can be erratic, irrespective of size of the spawning stock. Such a pattern could be an inherent characteristic of the species that needs to be accounted for when developing adaptive management and species recovery plans. U.S.
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