Trends in the Reproductive Phenology of two Great Lakes Fishes

To assess potential effects of climate change on Great Lakes fish populations, we evaluated trends in the reproductive phenology of Yellow Perch <i>Perca flavescens</i> (spring spawner) and Lake Trout <i>Salvelinus namaycush</i> (autumn spawner). For Yellow Perch in Lake Michigan, the estimated reproductive midpoint date (50% of mature females ripe or spent, 50% not yet spawned) took place 6.2 d/decade earlier in the spring near Milwaukee from 1988 to 2012 and 1.8 d/decade earlier in Green Bay from 1980 to 2012. At both locations water temperatures at the spawning sites on the midpoint date showed no trends, but mean water temperatures during the spring at the spawning site and midlake increased over the study period. This suggests that Yellow Perch spawning areas were warming sooner in the spring and that Yellow Perch were spawning earlier to maintain a consistent spawning temperature. Lake Trout phenological patterns were more complex. For Lake Trout in Lake Michigan near Milwaukee, there was a marginally significant trend for spawning to take place 2.1 d/decade later in the autumn from 1983 to 2006. However, water temperatures at the spawning site at the midpoint date did not change and autumn temperatures at the site and at midlake did not show a warming trend. For Lake Trout in Lake Superior near the Apostle Islands, the midpoint date did not change from 1988 to 2012. Water temperatures at the spawning site on the midpoint date and during the autumn also showed no trends, but midlake summer and autumn water temperatures increased significantly. Overall, Yellow Perch in Lake Michigan have shifted reproductive timing in a manner consistent with a warming climate, but the relationship of climate change to reproductive phenology remains unclear for Lake Trout in Lake Michigan and Lake Superior. Received December 15, 2014; accepted August 7, 2015

为评估气候变化对五大湖鱼类种群的潜在影响，本研究对黄鲈（Yellow Perch，*Perca flavescens*，春季产卵物种（spring spawner））和湖鳟（Lake Trout，*Salvelinus namaycush*，秋季产卵物种（autumn spawner））的繁殖物候（reproductive phenology）趋势展开了评估。针对密歇根湖的黄鲈：1988年至2012年，密尔沃基附近海域的繁殖中点日期（reproductive midpoint date，即50%成熟雌性个体已产卵或排卵、50%尚未产卵的时间节点）以每10年6.2天的速率提前；1980年至2012年，绿湾海域则以每10年1.8天的速率提前。两处采样点的繁殖中点日期当日的水温均无显著变化，但研究期内该产卵场春季平均水温及湖中部平均水温均呈上升态势。这表明黄鲈的产卵区域春季升温更早，黄鲈因此提前产卵以维持稳定的产卵水温。

湖鳟的物候模式则更为复杂。1983年至2006年，密尔沃基附近密歇根湖海域的湖鳟产卵时间以每10年2.1天的速率推迟，该趋势仅具有边际显著性。但该产卵场繁殖中点日期当日的水温并无变化，且该场所以及湖中部的秋季水温均未呈现升温趋势。针对使徒群岛附近苏必利尔湖的湖鳟，1988年至2012年其繁殖中点日期未发生改变；该产卵场繁殖中点日期当日及秋季的水温均无显著趋势，但湖中部夏季与秋季的水温呈显著上升态势。

总体而言，密歇根湖的黄鲈繁殖时间调整模式与气候变暖的影响相符，但气候变化与密歇根湖及苏必利尔湖湖鳟繁殖物候之间的关联仍不明确。本文于2014年12月15日收稿，2015年8月7日录用。