Physical oceanographic characteristics of sites in Orca Inlet, Cordova, Alaska: 2004-2005

In 1975 EPA produced effluent discharge guidelines for the seafood processor industry that required wastes to be ground to less than 1.27 cm prior to discharge. Subsequently, several negative impacts were observed around Cordova, including noticeable decreases in crab and halibut harvests and a substantial increase in numbers of gulls. We hypothesized that the change removed a food source for the large bottom-oriented animals and increased availability to the surface-oriented gulls. In 2004, we began a three year study to examine impacts of seafood waste discharge into Orca Inlet, including evaluation of alternative discharge and disposal methods. The study included model development and control-treatment experiments. We developed a dispersal model that incorporated both physical and biological transport mechanisms and demonstrated improvements over current practices. We dumped over 325,000 lbs of salmon heads and carcasses at an experimental site and monitored the biotic response. Methodologies included underwater cameras, traps, acoustic tags attached to salmon heads and visual surveys of birds and marine mammals. The results show that the heads and carcasses disperse rapidly and are efficiently incorporated into the food chain with no negative consequences, a very favorable contrast to the current EPA-mandated practice. The model also revealed that the historic practice of dumping fish carcasses was a far more effective recycling mechanism. In fact fish production may have been substantially reduced with the change in disposal practices since natural recycling is hindered by the discharge of ground waste. We conclude that it is overdue for some rethinking of fish waste practices. The policy of grinding fish waste to the same 1/2" grind size that was historically used for sewage wastes in the 1970's needs to change. We need to better understand natural recycling with regard to disposal practices. Fish processing waste is potentially a healthy source of food for marine fauna. In locations like Orca Inlet ground discharge of fish waste is not only deleterious but may also substantially reduce fish production by hindering natural recycling.

During the summer of 2004 and the spring of 2005 physical oceanographic conditions were measured in three regions of Orca Inlet, near Cordova Alaska, investigated as potential locations for the alternative disposal of fish offal from Cordova’s seafood processors. Two of the regions were surveyed in July and September 2004, including a northern site next to Salmo Point and North Island and a southern site within lower Orca Inlet adjacent to Cordova. A third region was surveyed in May 2005 along a channel that connects the southeastern and northeastern portions of the inlet. The data included profiles of currents, temperature and salinity taken over semi-diurnal tidal cycles. All three sites differ significantly in both hydrography and circulation due to a number of factors including variation in bottom depths, basin geometry, sources of freshwater input, and the strength and pattern of the tidal currents. The northern site is characterized by both high stratification from freshwater originating from glacial runoff into the Rude River and deep inflow of cold, saline water advected from Orca Bay. This region therefore becomes highly stratified in the summer and baroclinic currents occur over depth throughout the tidal cycle. The currents also exhibit significant spatial variation ranging from < 5 to 50 cm/sec due to convergences and divergences caused by both estuarine input and bathymetric effects. In contrast, lower Orca Inlet is characterized by strong, barotrophic flows (>100 cm/sec), and all inputs of heat and freshwater (including glacial sources advected from the north) are rapidly dissipated due to turbulent mixing. The northeastern channel also exhibits barotrophic flows similar in magnitude to lower Orca Inlet, but in contrast to the latter site vertical mixing produces fronts extending to depth as stratified water from Nelson Bay is advected across a shallow region and undergoes tidal mixing. All three locations would potentially serve as fish offal discharge sites if maximum dispersion is the goal. The northern site, however, may achieve better results due to its deep (80m) basin and the baroclinic nature of the currents. The higher population of ground fish in this region would also benefit more from disposal of offal at this site.

Publications:
Thorne, R.E., M.A. Bishop, R.E. Crawford, G.L. Thomas, S.M Gay III and K. George 2008. Impacts of seafood waste discharge in Orca Inlet, Prince William Sound. Exxon Valdez Oil Spill Gulf Ecosystem Monitoring and Research Project Final Report, (GEM Project 040725), Prince William Sound Science Center, Cordova, Alaska.

1975年，美国环境保护署（Environmental Protection Agency, EPA）为海鲜加工业制定了废水排放指南，要求废弃物在排放前需研磨至粒径小于1.27厘米。随后在科尔多瓦周边出现了多项负面影响，包括螃蟹和大比目鱼捕捞量显著下降，以及海鸥数量大幅增加。本研究提出如下假设：该政策移除了大型底栖动物的食物来源，同时增加了表层活动海鸥可获取的食物量。2004年，我们启动了一项为期三年的研究，以考察海鲜废弃物排放进入奥卡湾入口（Orca Inlet）的影响，其中包括评估替代排放与处置方案。本研究涵盖模型构建与控制-处理组实验。我们构建了融合物理与生物输运机制的扩散模型，并证明其相较于现行实践具有更优表现。我们在试验场地投放了超过325,000磅的鱼头及鱼体残骸，并监测其生物响应（biotic response）。研究方法包括水下摄像、诱捕装置、附着于鱼头上的声学标签（acoustic tags），以及鸟类与海洋哺乳动物的目视调查。结果显示，鱼头及鱼体残骸可快速扩散，并被高效纳入食物链，未产生任何负面影响，与美国环境保护署强制推行的现行排放实践形成了极具优势的对比。该模型还表明，历史上直接倾倒鱼体残骸的做法是效率高得多的废弃物循环利用机制。事实上，随着处置方式的改变，鱼类产量可能已大幅下降，因为研磨态废弃物的排放阻碍了自然循环过程。我们得出结论：重新审视鱼类废弃物处置规范已刻不容缓。1970年代为处理污水废弃物制定的、将鱼类废弃物研磨至0.5英寸粒径的政策亟需调整。我们需要更深入地了解与处置方式相关的自然循环过程。鱼类加工废弃物本质上是海洋动物群（marine fauna）的优质食物来源。在奥卡湾入口这类区域，研磨后排放的鱼类废弃物不仅有害，还可能通过阻碍自然循环过程大幅降低鱼类产量。

2004年夏季与2005年春季期间，我们在阿拉斯加州科尔多瓦附近的奥卡湾入口的三个区域开展了物理海洋环境参数测量，这些区域被选为科尔多瓦海鲜加工厂鱼类内脏废弃物（fish offal）替代处置的潜在场地。其中两个区域于2004年7月和9月完成勘测：分别是位于萨尔莫角（Salmo Point）与北岛（North Island）附近的北部场地，以及紧邻科尔多瓦的奥卡湾入口南部低地区域。第三个区域于2005年5月完成勘测，该区域位于连接奥卡湾入口东南与东北片区的航道沿线。本次测量数据涵盖了半日潮周期内获取的海流、温度与盐度剖面。受底质水深、盆地几何形态、淡水输入源以及潮汐海流强度与分布模式等多种因素影响，三个场地的水文特征（hydrography）与环流模式均存在显著差异。北部场地的特征为：来自鲁德河（Rude River）的冰川融水（glacial runoff）形成了较强的水体层化（stratification），同时奥卡湾涌入的低温高盐海水形成深层流入。因此该区域在夏季会形成高度层化的水体，且在整个潮汐周期内，垂向均存在斜压海流（baroclinic currents）。受河口输入与地形效应引发的辐合辐散影响，海流还表现出显著的空间差异，流速范围从小于5厘米/秒到50厘米/秒不等。与之形成对比的是，奥卡湾入口南部低地以强正压流（barotrophic flows，流速超过100厘米/秒）为特征，所有热与淡水输入（包括从北部平流而来的冰川源水体）均因湍流混合而快速消散。东北航道同样存在与奥卡湾入口南部低地量级相近的正压流，但与后者不同的是，当纳尔逊湾（Nelson Bay）的层化水体流经浅水区并经历潮汐混合（tidal mixing）时，垂向混合会形成延伸至深层的锋面。若以实现最大扩散效果为目标，这三个场地均可作为鱼类内脏废弃物的排放场地。但北部场地因其80米水深的盆地与斜压海流特性，可能获得更优的扩散效果。该区域更高的底层鱼类种群数量，也将更受益于在此处排放内脏废弃物。

相关出版物：
Thorne, R.E.、M.A. Bishop、R.E. Crawford、G.L. Thomas、S.M Gay III 与 K. George，2008年。《阿拉斯加威廉王子湾奥卡湾入口海鲜废弃物排放的影响》。埃克森·瓦尔迪兹号油溢灾难海湾生态系统监测与研究项目最终报告（GEM Project 040725），阿拉斯加州科尔多瓦威廉王子湾科学中心。