Environmental Biology of Fishes最新文献

Examining variation in reproduction (estimates of maturity and adult skip spawning) over time and space provides vital information on stock structure for managing coast-wide species; however, it is equally important to identify the drivers of variability, i.e., fishing pressure, genetics, and oceanographic conditions. The 2021 lingcod, Ophiodon elongatus, stock assessments used separate population models, north and south of 40°10′ N, based on evidence of distinct population clusters and historical fishery trends. We collected 1035 lingcod ovaries along the US West Coast over seven years (2013–2019) to evaluate trends in reproduction and inform stock management decisions. We estimated biological (physiological maturity) and functional (potential spawners) length (L₅₀) and age (A₅₀) at 50% maturity across eight regions: coast-wide, between management areas (north and south of 40°10′ N), genetic stocks (north and south of 38°17′ N), and among important biogeographic regions including Cape Mendocino, California (north of 40°10′ N), the Central coast (40°10′–34°26′ N), and Pt. Conception, California (south of 34°26′ N). Regional biological L₅₀ and A₅₀ maturity estimates (43.36–52.75 cm and 1.66–2.88 years) were smaller than functional maturity (46.31–56.65 cm and 1.89–3.23 years). Overall, regional analyses showed a decline in size and age at 50% maturity with decreasing latitude, with females south of Pt. Conception reaching maturity at much smaller sizes and younger ages than their northern counterparts. These regional estimates of maturity add to the growing body of literature that seeks to determine the best spatial management plan for lingcod sub-populations.

Headwater streams, located upstream of the river network, play a crucial role in river ecosystems. However, the increasing conversion of natural habitats into agricultural land leads to extensive alterations in landscape composition, posing serious threats to natural stream ecosystems and biodiversity. This research focuses on the headwater streams of the Xin’an River in the Wannan Mountains, China. The study merged information on habitat conditions from two types of habitats (disturbed and natural segments) to evaluate the impact of agricultural land use on the beta diversity of fish assemblages. The results indicated that the disturbed segments exhibited intermediate land-use intensities, slightly higher habitat heterogeneities, and a higher number of native invasive species compared to the natural segments. Differences in local-scale habitat conditions and regional-scale land use drove the species composition discrepancy (taxonomic beta diversity) between disturbed and natural segments. This study provides evidence of how agricultural land use impacts fish assemblage diversity in headwater streams and underscores the significance of sustainable management and conservation for preserving endemic assemblages in these streams.

Understanding the spatial ecology of fish is critical for effective conservation and management. Gar (Lepisosteidae spp.) are an ancient lineage of freshwater fishes that have long been thought of as having high site fidelity with limited large-scale movements. We acoustically tagged Longnose Gar (L. osseus) in a large freshwater embayment (Hamilton Harbour) and tracked the movements of 12 individuals within this system and throughout the coastal waters of Lake Ontario for up to 4 years. Three distinct movement patterns were observed: migrants (N = 7), which moved throughout much of western Lake Ontario and had a maximum displacement of 184 km (linear distance); residents (N = 3), which remained in or near the original tagging location (an industrial slip with year-round warmwater outfall); and sporadic migrants (N = 2), which showed both migratory and resident behavioural patterns in different years. Seasonally, gar were most active during the summer and then fall, with more restricted home ranges and movements during winter suggestive of more quiescent behaviour. This study represents the first use of acoustic telemetry to track Longnose Gar movements year-round in a large lake and confirmed that a majority of tracked fishes make large-scale movements in Lake Ontario. Such results reframe the presumption that gar are more resident fishes with restricted space use.

Daytime habitat use by Japanese eel (Anguilla japonica) at the yellow eel stage (total length ≥ 15 cm) and the newly recruited glass/elver stage in spring (total length 5–7 cm) was examined in three sites of different types of streams in southwestern Japan. Although habitat use by yellow eels was examined in summer and winter, no distinct difference was found between the two seasons. Yellow eels preferred lower current velocity in all the three sites in both seasons. Cover use by yellow eels differed among the three sites having different cover-type availability. In a coarse-substrate mountain stream, the majority of yellow eels used cobble/boulders as cover, whereas in the other two fine-substrate streams, where coarse substrates were rare, large parts of yellow eels burrowed into fine sediments. In addition, undercut bank and bank vegetation were substantially used and preferred by yellow eels depending on the study site, suggesting the importance of natural bank habitat. The majority of glass/elver eels used sand substrates with current velocity < 10 cm·s⁻¹ in all the three sites, suggesting their clear preference for such habitat. However, the preference for sand shown in this study contrasts with a general trend established by previous experimental studies that glass/elver eels prefer stony substrates over sand. Our results contrary to the general trend could be attributed to glass/elver eels displaying a stronger preference for slow currents over stony substrates, implying that current velocity has a dominant effect in habitat use by glass/elver eels under natural conditions.

Rapid climate change and invasive species introductions threaten ecological communities across the globe. Freshwaters are particularly vulnerable and impacted, especially when these stresses coincide. We document the migration of an invasive piscine predator, the Sacramento pikeminnow (Ptychocheilus grandis), within its introduced range, the South Fork Eel River, California, USA. Snorkel surveys and temperature monitoring in 2015–2019 showed that pikeminnow migrate upstream during spring and early summer, with earlier migration in warmer years. We developed a statistical temperature model to forecast the timing and extent of upstream migration by pikeminnow under varying combinations of discharge and air temperature. Modeled river temperature increased with air temperature and downstream and decreased with discharge. In years with low discharge and high air temperature, we predict pikeminnow will move upstream earlier, increasing spatial and temporal overlap in their summer range with native fishes. Managing conditions that reduce pikeminnow co-occurrence with native fishes (i.e., decreasing river temperature) could increase amount and duration of predator-free habitat for native fishes. We predict invasive pikeminnow will have larger impacts on invaded riverine communities with global warming and increasing drought severity. Knowledge of life history and phenology, for pikeminnow and other organisms, can guide effective management as conditions change and help to limit adverse impacts of introduced organisms on native species.