Department of Natural Resources, College of Agriculture and Life Sciences, Cornell University, Ithaca, New York, 14853, USA.
Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, 14853, USA.
Ecol Appl. 2017 Apr;27(3):956-965. doi: 10.1002/eap.1498. Epub 2017 Mar 16.
Each year, millions of hatchery-raised fish are stocked into streams and rivers worldwide, yet the effects of hatchery-raised fish on stream nutrient cycles have seldom been examined. We quantified the influence of supplemental nonnative fish stocking, a widespread recreational fishery management practice, on in-stream nutrient storage and cycling. We predicted that supplemental, hatchery-raised brown trout (Salmo trutta) stocking would result in increased N and P supply relative to in-stream biotic demand for those nutrients and that stocked fishes would remineralize and store a significantly greater amount of N and P than the native fish community, due to higher areal biomass. To test these predictions, we measured the biomass, nutrient (NH -N and soluble reactive phosphorus [SRP]) remineralization rates, and body carbon, nitrogen, and phosphorus content of the native fish community and trout stocked into four study streams. We then estimated fish growth rates to determine species-specific nutrient sequestration rates in body tissues for both stocked and native fish and measured ammonium and phosphorus uptake rates to determine the relative influence of net fish nutrient remineralization on stream nutrient cycles. When brown trout were stocked in these systems at density levels that were orders of magnitude higher than ambient native fish density, they provided a sizeable source of NH -N that could account for up to 85% of demand for that nutrient. Stocked trout had minimal effects on in-stream SRP cycles even at high release densities, likely due to low per capita SRP excretion rates. A unique feature of our study was that we evaluated the temporal component of the stocked trout nutrient subsidy by estimating the number of fish removed from the system through natural mortality and angler harvest, which indicated that the stocked trout subsidy lasted approximately 6-8 weeks after stocking. By combining population models with areal nutrient excretion rates and estimates of biotic nutrient uptake, we showed that trout stocking provided a strong pulsed nutrient subsidy.
每年，全球都有数以百万计的人工养殖鱼类被放养到溪流和河流中，但人工养殖鱼类对溪流养分循环的影响很少受到关注。我们量化了补充非本地鱼类放养的影响，这是一种广泛的娱乐性渔业管理实践，对溪流中养分储存和循环的影响。我们预测，补充的、人工养殖的虹鳟（Salmo trutta）放养将导致相对于这些养分的溪流生物需求增加 N 和 P 的供应，并且由于较高的面积生物量，放养鱼类将再矿化和储存大量的 N 和 P。为了验证这些预测，我们测量了四个研究溪流中本地鱼类群落和放养的鳟鱼的生物量、养分（NH -N 和可溶性反应磷 [SRP]）再矿化率以及体碳、氮和磷含量。然后，我们估计了鱼类的生长速度，以确定放养和本地鱼类体组织中特定物种的养分固存率，并测量了铵和磷的吸收速率，以确定鱼类养分再矿化对溪流养分循环的相对影响。当虹鳟在这些系统中以比环境中本地鱼类密度高出几个数量级的密度放养时，它们提供了大量的 NH -N，可占该养分需求的 85%。即使在高释放密度下，放养的鳟鱼对溪流 SRP 循环的影响也很小，这可能是由于人均 SRP 排泄率低所致。我们研究的一个独特特征是，我们通过估计通过自然死亡率和垂钓者收获从系统中移除的鱼的数量来评估放养鳟鱼养分补贴的时间成分，这表明放养鳟鱼补贴在放养后持续了大约 6-8 周。通过将种群模型与面积养分排泄率和生物养分吸收估计相结合，我们表明鳟鱼放养提供了强烈的脉冲养分补贴。
