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

• Main Authors: Richard Crawford, Gary Thomas, Shelton Gay, Kenwyn George, Richard Thorne, Mary Anne Bishop
• Format: Dataset
• Language: unknown
• Published: Gulf of Alaska Data Portal
• Subjects: EVOSTC; Exxon Valdez Oil Spill Trustee Council; Oil Spill; Exxon Valdez; Alaska; Environmental Drivers; Satellites and Sensors; Orca Inlet; CTD; ADCP; current; hydrography; seafood waste; offal; Crawford; Thorne; Orca
• Online Access: https://search.dataone.org/view/df35d.441.2

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.