The First Record of Bigscale Logperch and Range Expansions of Smallmouth Buffalo, White Crappie, and Gizzard Shad in Arizona

Bigscale Logperch Percina macrolepida is reported and substantiated for the first time in Arizona. A single specimen was collected during a routine survey of Cow Springs Lake on September 26, 2017, preliminarily identified as Percina sp . , preserved, and retained for species identification. We verified the specimen was a Bigscale Logperch through genetic analysis. Review of published literature and the U.S. Geological Survey Nonindigenous Aquatic Species Database suggests that this is the first known occurrence of Bigscale Logperch in Arizona. Further, three additional non-native species were detected during our sampling events on June 21 and September 26, 2017—Smallmouth Buffalo Ictiobus bubalus , White Crappie Pomoxis annularis , and Gizzard Shad Dorosoma cepedianum —representing the first collection of these species in the Little Colorado River basin that we are aware of. We recommend further evaluation of the ecology, distribution, and abundance of these four non-native species to better understand their effect on the native fishes of the watershed and the likelihood of establishment in the watershed and elsewhere in Arizona.

Potential Effects of Age, Population, and Latitude on Precision of Scale and Otolith Age Estimates of White Crappie in Minnesota

We calculated between-reader precision of ages estimated with scales and whole otoliths (sagittae) of White Crappie Pomoxis annularis for 10 Minnesota populations, and determined effects of population and mean age on precision. For all samples combined, two experienced readers counted the same number of annuli on 91% of the scales and 92% of the whole otoliths. Mean coefficients of variation equaled 1.8% between scale readers and 3.0% between whole otolith readers. We detected no systematic age-bias between readers of each structure. Agreement between scale readers differed among populations, ranging from 67 to 100% among populations (median = 89%), but agreement also decreased with increasing scale age in six of these populations. Agreement between readers of whole otoliths was unaffected by increasing age of White Crappie, but agreement ranged from 39 to 100% among populations. When compared with other studies, latitude had no influence on precision of whole otolith ages because precision in the Minnesota populations differed little from precision reported for populations in Kentucky and Mississippi. Latitude could be affecting precision in scale age estimates because precision was usually better for the Minnesota populations than for populations in Oklahoma, Kentucky, and Mississippi; however, differences in viewing methods and reader competencies could also explain geographical differences.

Spatial structuring within a reservoir fish population: implications for management

Spatial structuring in reservoir fish populations can exist because of environmental gradients, species-specific behaviour, or even localised fishing effort. The present study investigated whether white crappie exhibited evidence of improved population structure where the northern more productive half of a lake is closed to fishing to provide waterfowl hunting opportunities. Population response to angling was modelled for each substock of white crappie (north (protected) and south (unprotected) areas), the entire lake (single-stock model) and by combining simulations of the two independent substock models (additive model). White crappie in the protected area were more abundant, consisting of larger, older individuals, and exhibited a lower total annual mortality rate than in the unprotected area. Population modelling found that fishing mortality rates between 0.1 and 0.3 resulted in sustainable populations (spawning potential ratios (SPR) >0.30). The population in the unprotected area appeared to be more resilient (SPR>0.30) at the higher fishing intensities (0.35–0.55). Considered additively, the whole-lake fishery appeared more resilient than when modelled as a single-panmictic stock. These results provided evidence of spatial structuring in reservoir fish populations, and we recommend model assessments used to guide management decisions should consider those spatial differences in other populations where they exist.