Data for: Dynamic coastal pelagic habitat drives rapid changes in growth and condition of juvenile sockeye salmon (Oncorhynchus nerka) during early marine migration

Migrating marine taxa encounter diverse habitats that differ environmentally and in foraging conditions over a range of spatial scales. We examined body (RNA/DNA, length-weight residuals) and nutritional (fatty acid composition) condition of juvenile sockeye salmon (Oncorhynchus nerka) in British Columbia while migrating through oceanographically variable waters. Fish were sampled in the stratified northern Strait of Georgia (NSoG); the highly mixed Johnstone Strait (JS); and the transitional zone of Queen Charlotte Strait (QCS). In 2015, body and nutritional condition were high in the NSoG but rapidly declined to reach the lowest levels in JS where prey availability was low, before showing signs of compensatory growth in QCS. In 2016, juvenile salmon had a significantly lower condition in the NSoG than in 2015, although zooplankton biomass was similar, condition remained low in JS, and no compensatory growth was observed in QCS. We provide evidence that differences in juvenile salmon condition between the two years were due to changes in the food quality available to juvenile fish. We propose that existing hypotheses about fish survival need to be extended to incorporate food quality in addition to quantity to understand changes in fish condition and survival between years.

Methods
Zooplankton was collected using a vertical Bong net (250 µm mesh size, mouth diameter 0.5 m). The net was deployed from near-bottom depth at a maximum of 300 m depth to surface. Zooplankton was preserved in 5% buffered formaldehyde-seawater solution. Zooplankton was identified to the lower taxonomic level possible. For detailed methods, see the associated article.

Fish were collected from a 6m motorized vessel at distances of 5-60m from shore, using a purse seine designed for manual deployment and retrieval (bunt: 27 x 9 m with 13 mm mesh; tow 46 x 9 m 76 mm mesh). White muscle tissues were collected post-catchment from flash-frozen organisms.

RNA:DNA ratios were measured at the University of British Columbia (UBC) using a VarioSkan Flash Microplate Reader (ThermoFisher Scientific). For detailed methods see Garzke et al (2022). RNA:DNA ratios were measured in triplicates and sample averages were calculated from triplicates not exceeding a coefficient of variance above 15%.

Fatty acids follow the notation C20:5n.3 corresponding to eicosapentaenoic acid (EPA), where 20 is the number of carbon atoms, 5 is the number of double bonds, and 3 is the position of the first double bond from the omega end.

Fatty acids were analyzed at the Fisheries and Oceans Canada (DFO) Pacific Science Enterprise Centre. FAs were converted to fatty acid methyl esters using a direct transesterification method, separated using an Agilent CP-Sil 88 column (50 m, 0.25 mm diameter), and quantified with a gas chromatograph (SCION 436) equipped with a flame ionization detector.

These data represent all chromatogram peaks attributed to FAs based on external standards (Nu-Chek Prep GLC-37, GLC-463; Cayman Chemical 18:4n-3; Matreya PUFA Mix No. 3) and by comparing reference samples analyzed at another lab (M.T. Brett, University of Washington). Overall, 81.2 ± 0.08% (mean ± sd) of the chromatogram area was identified and attributed to FAs. FAs were quantified based on a known quantity of an internal standard, C19:0, that was added to each sample. For detailed methods see Garzke et al (2022).

For each sampling date, fatty acids are presented as μg of total fatty acids of mg DW of the analysed muscle tissue.

Oceanography data (SST and SSS), were collected from CTD profiles using a RBR maestro and SeaBird 19plus V2 CTD. Samples represent the average of the upper 10m of the water column.

洄游性海洋类群会在不同空间尺度下遭遇环境与摄食条件各异的多样生境。本研究针对不列颠哥伦比亚省（British Columbia）洄游过程中身处海洋环境多变水域的幼年红大马哈鱼（juvenile sockeye salmon, Oncorhynchus nerka），对其躯体状况（RNA/DNA比值、体长-体重残差）与营养状况（脂肪酸组成）展开了调查。研究采样共设置三类区域：层化状态显著的乔治亚海峡北部（northern Strait of Georgia, NSoG）、混合作用强烈的约翰斯通海峡（Johnstone Strait, JS），以及夏洛特皇后海峡（Queen Charlotte Strait, QCS）的过渡带。

2015年，NSoG区域内的幼鱼躯体与营养状况良好，但在猎物可获得性较低的JS区域，该状况迅速恶化至最低水平，随后在QCS区域出现补偿性生长的迹象。2016年，NSoG区域内的幼鱼状况显著低于2015年同期：尽管浮游动物生物量与2015年相近，但JS区域的幼鱼状况仍处于低位，且QCS区域未观测到补偿性生长。本研究证实，两年间幼鱼状况的差异源于幼鱼可获得食物的品质变化。我们提出，现有鱼类存活相关假说需进一步拓展，除食物数量外还应纳入食物品质维度，以解析不同年份间鱼类状况与存活率的变化规律。

方法
浮游动物采样采用垂直波网（vertical Bong net，250 μm网目孔径，网口直径0.5 m），从最大水深300 m的近底层至表层下放采集。采集所得浮游动物经5%缓冲甲醛海水溶液固定后，鉴定至尽可能低的分类阶元。详细采样方法参见相关研究论文。

研究人员依托6米机动船，在离岸5~60 m的水域使用适配人工收放的围网（purse seine，囊袋尺寸27×9 m，网目孔径13 mm；拖网尺寸46×9 m，网目孔径76 mm）采集幼鱼。捕获后立即取白色肌肉组织，经液氮速冻保存。

RNA:DNA比值测定于不列颠哥伦比亚大学（University of British Columbia, UBC）完成，使用VarioSkan Flash微孔板阅读器（VarioSkan Flash Microplate Reader，ThermoFisher Scientific）。详细方法参见Garzke等人2022年的研究。该比值设置3次生物学重复，变异系数不超过15%的重复组方可用于计算样本平均值。

脂肪酸采用C20:5n.3的标注方式，对应二十碳五烯酸（eicosapentaenoic acid, EPA），其中20代表碳原子数，5代表双键数，3代表距Omega端首个双键的位置。

脂肪酸分析于加拿大渔业与海洋部（Fisheries and Oceans Canada, DFO）太平洋科学企业中心完成。采用直接酯交换法将脂肪酸转化为脂肪酸甲酯，使用Agilent CP-Sil 88色谱柱（50 m，内径0.25 mm）进行分离，随后通过配备火焰离子化检测器的气相色谱仪（SCION 436）完成定量。

本研究的脂肪酸峰识别依托外标（Nu-Chek Prep GLC-37、GLC-463；Cayman Chemical 18:4n-3；Matreya PUFA Mix No.3）完成，并通过比对其他实验室（华盛顿大学M.T. Brett团队）的参考样本进行验证。最终，色谱图总面积的81.2±0.08%（平均值±标准差）可被识别并归为脂肪酸。脂肪酸定量基于添加至每个样本的内标C19:0的已知浓度完成。详细分析方法参见Garzke等人2022年的研究。

每个采样日期的脂肪酸数据以每毫克干重（DW）肌肉组织中总脂肪酸的微克数（μg）表示。

海洋学数据（海表温度SST、海表盐度SSS）通过RBR maestro与SeaBird 19plus V2 CTD采集中的CTD剖面获取，采样数据为水体上层10 m的平均值。