Kurle Carolyn M, Worthy Graham A J
Alaska Fisheries Science Center, National Marine Fisheries Service, National Marine Mammal Laboratory, 7600 Sand Point Way NE, 98115, Seattle, WA, USA.
Physiological Ecology and Bioenergetics Laboratory, Texas A&M University at Galveston, 5001 Avenue U, Suite 105, 77551, Galveston, TX, USA.
Oecologia. 2001 Jan;126(2):254-265. doi: 10.1007/s004420000518. Epub 2001 Jan 1.
We investigated the feeding ecology and foraging location of migrating and nursing northern fur seal (Callorhinus ursinus) adult females and migrating juvenile males from the Pribilof Islands, Alaska, using carbon (δC) and nitrogen (δN) isotope analysis of fur seal skin and whole potential prey. Post-parturient and lactating females had mean δN values significantly (0.8‰) higher than pregnant, migratory females, and δC values that were not significantly different. Two opportunistically collected, migrating, nulliparous females had mean δC values 1.1‰ lower than migrating, pregnant females, and δN values that were not different. Pregnant, migratory females had mean δC values significantly (1.5‰) higher than migratory juvenile males, and mean δN values significantly (0.6-1.6‰) higher than migratory juvenile males. The exception was one group of juvenile males from St. Paul Island with mean δN values that were not significantly different from migrating females. The mean δN values of pregnant females indicate they were feeding at a higher trophic level than juvenile males during migration. The higher mean δC values for pregnant females suggest they were feeding coastally during the spring migration, while juvenile males and nulliparous females were feeding offshore. The higher δN values for post-parturient, lactating females over migrating, pregnant females point to either a trophic shift in diet over time, or a more likely N-enrichment due to negative nitrogen balance caused by the nutritional stress of lactation and the feeding/fasting regime experienced by females. Similar mean δC values for migrating and breeding-season females indicate that both groups were feeding in coastal, on-shelf domains during their respective time periods. Similar mean δN values for nulliparous and pregnant females indicate they were feeding at similar trophic levels despite indications of feeding in separate ecosystems during migration. Using a δN shift of 2-3‰ per trophic level, we made general inferences about the trophic levels at which northern fur seals were feeding. The interpretation of our δN data indicates that migrating pregnant females, lactating females and the majority of migrating juvenile males consumed prey with mean δN values between 14.2‰ and 15.2‰, 15.1‰ and 16.1‰, and 13.6‰ and 14.6‰, respectively. Probable fur seal prey was analyzed as well. Walleye pollock showed progressive N and C-enrichments with age. Mean δN and δC values of 3- to 4-year-old fish were ~6.0‰ and 1.1‰ higher, respectively, than values for 0-age pollock. Atka mackerel also showed isotopic enrichment with age. The δN and δC values of large fish were 0.8‰ and 0.3‰ higher, respectively, than values for smaller fish.
我们利用对海狗皮肤和所有潜在猎物进行碳（δC）和氮（δN）同位素分析，研究了来自阿拉斯加普里比洛夫群岛的成年雌性和未成年雄性海狗在迁徙和哺育幼崽期间的觅食生态和觅食地点。产后和哺乳期雌性海狗的平均δN值显著高于怀孕和迁徙期的雌性海狗（高0.8‰），而δC值没有显著差异。两只机会性采集的正在迁徙的未生育雌性海狗的平均δC值比正在迁徙的怀孕雌性海狗低1.1‰，δN值没有差异。怀孕和迁徙期的雌性海狗的平均δC值显著高于迁徙期的未成年雄性海狗（约高1.5‰），平均δN值显著高于迁徙期的未成年雄性海狗（约高0.6 - 1.6‰）。例外的是来自圣保罗岛的一组未成年雄性海狗，其平均δN值与正在迁徙的雌性海狗没有显著差异。怀孕雌性海狗的平均δN值表明它们在迁徙期间的觅食营养级高于未成年雄性海狗。怀孕雌性海狗较高的平均δC值表明它们在春季迁徙期间在沿海觅食，而未成年雄性海狗和未生育雌性海狗在近海觅食。产后和哺乳期雌性海狗的δN值高于怀孕和迁徙期的雌性海狗，这表明要么是随着时间推移饮食中的营养级发生了变化，要么更有可能是由于泌乳的营养压力以及雌性海狗经历的进食/禁食模式导致负氮平衡，从而使氮含量增加。迁徙期和繁殖期雌性海狗的平均δC值相似，表明这两组海狗在各自时期都在沿海陆架区域觅食。未生育和怀孕雌性海狗的平均δN值相似，表明尽管在迁徙期间它们在不同生态系统中觅食，但它们的觅食营养级相似。利用每营养级2 - 3‰的δN变化，我们对北方海狗的觅食营养级进行了大致推断。对我们的δN数据的解读表明，正在迁徙的怀孕雌性海狗、哺乳期雌性海狗和大多数正在迁徙的未成年雄性海狗所消耗猎物的平均δN值分别在14.2‰至15.2‰、15.1‰至16.1‰和13.6‰至14.6‰之间。我们还分析了可能是海狗猎物的鱼类。狭鳕随着年龄增长，氮和碳含量逐渐增加。3至4岁鱼的平均δN值和δC值分别比0龄狭鳕高约6.0‰和1.1‰。阿特卡鲭鱼也随着年龄增长出现同位素富集。大鱼的δN值和δC值分别比小鱼高0.8‰和0.3‰。
