Abstract：
Acoustic tags fitted with predation sensors, which trigger following ingestion by piscivorous predators, were used to compare direct predation rates during downstream migration (out-migration) of potamodromous (freshwater) brown trout (Salmo trutta L.) parr from their natal river into a large freshwater lake system during spring and autumn. Thirty-eight spring migrants were tagged across two study years (2021 and 2022) of which 13 individuals (34%) were predated. By contrast 40 autumn migrants were tagged (2020 and 2021) of which three individuals (7.5%) experienced predation. The overall predation loss rate for spring migrants was 0.342% day-1 and was 0.075% day-1 for autumn migrants. Most predation events during spring (77%) occurred within the lower river before tagged fish entered the lake, whilst no predation events were recorded within the river in the autumn. Predation events were significantly linked to tagging season (spring or autumn), with the probability of tags remaining untriggered (as a proxy for survival) being higher 93% (95% confidence interval [CI] [87%, 100%]) in autumn than in spring 66% (95% CI [53%, 83%]). The spring migration periods showed significantly lower river discharge (0.321 m3 /s mean daily discharge, April 1 to May 31) to those measured during autumn (1.056 m3 /s mean daily discharge, October 1 to November 30) (Mann-Whitney U-test, U = 1149, p < 0.001). Lower flows, clearer water, and longer sojourn in the river may have contributed to greater predation losses in the spring relative to the autumn.
摘要：
装有捕食传感器的声学标签，在食肉捕食者摄入后触发，用于比较春季和秋季从其出生河到大型淡水湖系统的浮游（淡水）褐鳟鱼（SalmotruttaL.）向下游迁移（向外迁移）期间的直接捕食率。在两个研究年（2021年和2022年）中，有38名春季移民被标记，其中13人（34％）被提前。相比之下，40名秋季移民被标记(2020年和2021年)，其中三人(7.5%)经历了捕食。春季移民的总体捕食损失率为第一天的0.342％，秋季移民的第一天为0.075％。春季的大多数捕食事件（77％）发生在标记的鱼进入湖泊之前的下游河流中，而秋季河内没有捕食事件记录。捕食事件与标记季节（春季或秋季）显着相关，标签保持未触发的概率(作为生存的代理)更高93%(95%置信区间[CI][87%，100%])秋季比春季高66%(95%CI[53%，83%])。春季迁移期显示出显着降低的河流流量（平均日流量0.321m3/s，4月1日至5月31日)至秋季测量的(1.056m3/s平均日排放量，10月1日至11月30日)(Mann-WhitneyU-test,U=1149,p<0.001)。较低流量,更清澈的水,相对于秋季，春季在河中逗留的时间更长可能导致更大的捕食损失。
