ABSTRACT:We assessed seasonal histological changes as markers of health status in mussels Mytilus spp. sampled from Southampton Water, Hampshire, UK and the River Exe, Devon, UK between November 2004 and October 2005. A total of 29 health parameters related to pathogens, inflammatory and non-specific pathologies, and reproductive and physiological condition were recorded monthly from individual mussels collected from these 2 sites. We then assessed the diffential prevalence of these health parameters according to species. M. edulis, M. galloprovincialis and their hybrids were identified using the Glu-5' gene and the ME15 and ME16 primer sets that distinguish alleles specific to M. edulis (180 bp), M. galloprovincialis (126 bp) and hybrids (180 bp/126 bp). Although no overall annual differences were observed between species with respect to median levels of adipogranular (ADG) tissue and reproductive status, specific differences in reproductive status were observed within individual months. During these months (August to October), M. edulis exhibited a relatively lower reproductive status compared to M. galloprovincialis and hybrids. With respect to all remaining health parameters (pathogens, inflammatory and non-specific pathology), principal components analysis revealed no overall differences between species throughout the year. However, greater differences were observed between species during the autumn and winter than during the spring and summer, thus indicating that species differences may be exacerbated by season. This study highlights how species can affect the accurate interpretation of histopathology data collected during biological effects monitoring programmes. Whether species can also affect the biomarker response of Mytilus mussels to contaminated environments remains to be shown. The results are discussed in the context of biological effects monitoring utilising mussels.

The lower perennial corridor of the Little Colorado River in Grand Canyon, Arizona, is numerically dominated by endemic desert fishes and therefore significant for conservation of these species. From 2000 to 2012, the U.S. Fish and Wildlife Service conducted monitoring of native fishes in the Little Colorado River near its confluence with the Colorado River. The primary focus of these efforts was to estimate the spring and fall abundance of native fishes, especially the federally endangered humpback chub Gila cypha. Because humpback chub in Grand Canyon are influenced by operations of Glen Canyon Dam, our efforts provide managers of the Glen Canyon Dam Adaptive Management Program with abundance estimates and trends of humpback chub in the Little Colorado River, the most important tributary in Grand Canyon for spawning and production of this species. From 2001 to 2006, the spring abundance estimates of humpback chub ≥150 and ≥200 mm remained relatively low (≤3,419 and ≤2,002 fish, respectively), thereafter significantly increasing to highs of 8,083 and 6,250, respectively, by spring 2010. Also from 2000 to 2006, the fall abundance estimates of humpback chub were substantially below those abundances estimated after 2006. In addition, flannelmouth sucker Catostomus latipinnis and bluehead sucker Catostomus discobolus showed post-2006 increases in relative abundance, suggesting a systemwide event occurred that was beneficial to native fishes. Most of the increases of humpback chub occurred during the spring season in the reaches of the Little Colorado River between 5 and 13.57 km upstream from the confluence. Successful production of age 0 year classes of humpback chub may be partially driven by hydrograph dynamics of the Little Colorado River, whereas water temperatures and predation pressures in the mainstem Colorado River likely influence survivorship of native fishes into subadult and adult life stages.

No abstract