IPHC oceanographic monitoring program 2015

Transcription

1 IPHC oceanographic monitoring program 2015 Lauri L. Sadorus and Jay Walker Abstract This was the seventh consecutive year that the International Pacific Halibut Commission s (IPHC) profiler project collected oceanographic data from the U.S. West Coast northward to British Columbia, into the Gulf of Alaska, Bering Sea, and Aleutian Islands during the IPHC stock assessment survey. In addition to the standard setline survey grid, additional survey stations were added in the Bering Sea to sample the eastern Bering Sea flats which had not been surveyed by IPHC since The IPHC has been operating profilers since 2000 on a limited basis and coastwide since A total of 1,240 successful casts were made this year out of a possible 1,368. Introduction Since the expansion of its survey in 1997, the International Pacific Halibut Commission (IPHC) has annually conducted fishing operations at more than 1,000 stations ranging geographically from the U.S. west coast to the Bering Sea. Since 2009, a water column profile has been attempted at each station during the survey. Sampled stations can vary from year to year. In addition to the standard grid, stations are temporarily added because of a particular question or concern in areas not normally surveyed. Area 2A, for example, has had several groups of temporary stations fished along with the standard survey in recent years. In 2011 and 2014, the Puget Sound region (southern Salish Sea) was included in the 2A survey to ground-truth the predicted density of halibut in the region relative to that observed on the outer coast of Area 2A. In 2013, stations were added in northern California due to a recently-developed halibut sport fishery in the area and the subsequent need to assess the halibut density there, and another 12 were added for one year in 2014 because it was unclear if the southern terminus of the commercially exploitable halibut biomass had been located. Beginning in 2014, a multi-year survey expansion plan was initiated whereby traditional range and depth limits of the survey are exceeded in various regions coastwide. In 2015, the expansion included stations on the eastern Bering Sea flats and those results will serve to calibrate the IPHC survey with the National Marine Fisheries Service groundfish trawl survey. All survey stations are located on the continental shelf and, except for the Bering Sea flats area, are arranged on an equidistant 10-nmi grid. As such, the IPHC operates the largest consistent sampling program of any research agency in the north Pacific (see Henry et al. (2016) for detailed survey information). Changes in the physical and chemical makeup of the ocean waters affect the health and distributions of marine populations. This area of investigation has gained momentum in recent years as scientists and stakeholders try to understand the direct and indirect effects on fisheries. Coupling oceanographic observations with catch estimates from the IPHC setline survey over time is a necessary next step to understanding the impacts of these changing conditions on the halibut resource. In the late 1990s, the IPHC began considering the feasibility of collecting environmental data alongside halibut catch data on the setline survey. In 2000, a Sea-Bird 1 Seacat SBE-19 water 1 Sea-bird Electronics Inc NE 20 th Street. Bellevue, Washington, USA. 398

2 column profiler equipped with sensors to measure depth, temperature, and salinity was purchased by the IPHC and deployed aboard a longline vessel chartered for the annual setline survey. The profiler was then deployed on different vessels and in different areas successfully for several years. In 2005, a dissolved oxygen (DO) sensor was added to the profiler and proved well-suited for the project s purposes. In 2007, the IPHC received a grant from the Oregon Department of Fish and Wildlife Restoration and Enhancement Program to purchase a second Sea-Bird Seacat SBE- 19plus (an updated version of the SBE-19) dedicated to the IPHC survey stations off the Oregon coast. This new profiler was equipped with additional sensors to measure dissolved oxygen (SBE- 43), ph (SBE-18), and chlorophyll a concentration (WET Labs 2 ECO-FLRTD). The successful deployment of these two profilers aboard multiple vessels over multiple years and areas provided proof of concept that these oceanographic data could be collected with minimal disruption to the core survey operations. To that end, the IPHC received a grant from the National Oceanic and Atmospheric Administration (NOAA) in late The grant allowed for the purchase of 14 Sea-Bird Seacat SBE19plus V2 water column profilers, laptop computers for each, as well as annual maintenance and data processing costs for four years. The grant expired in September 2012 and ongoing maintenance costs are currently borne by the IPHC. Methods Instruments The Seacat profiling units collect a suite of data throughout the water column, including: pressure (depth), conductivity (salinity), temperature, dissolved oxygen (DO), ph, and fluorescence (chlorophyll a). The sensors are protected by a stainless steel cage, 96 cm tall and specially designed for each unit. The primary units (pressure, conductivity, temperature) are equipped with titanium housings which are rated for depths to 7,000 m. The auxiliary sensors have maximum depth ratings ranging from 1,000-7,000 m, which is sufficient for all standard IPHC survey stations. Part of the survey expansions that started in 2014 included stations with an estimated average depth as deep as 730 m (from 500 m traditionally). To err on the side of caution, the profilers are deployed at standard survey stations and expansion stations up to 500 m depth only. To adapt the profiler for deployment from a halibut fishing vessel, a system was designed using weights and floats that permits the profiler to descend rapidly enough through the water column to collect valid data and also ensures that the unit will not crash into or become permanently attached to the ocean bottom (Hare 2001). A sustained descent rate of 1-2 m/s is the target, and the weight of the assembly in the water is sufficient that, if the unit is allowed to free fall, the target descent rate is achieved. A 15-meter anchor line is attached to the bottom of the profiler cage using a section of gangion line as a weak link (in case the anchor cannot be freed from the bottom). A 40-pound longline anchor or cannonball is attached to the end of the 15-meter line. To the top of the cage, two floats are attached that effectively offset the weight of the anchor in water. The floats are attached to standard buoy line which is almost neutrally buoyant. 2 WET Labs, 620 Applegate Street, Philomath, Oregon, USA. 399

3 Deployment A profiler unit was deployed at each eligible survey station, just prior to hauling the fishing gear. To deploy the unit, the anchor was lowered into the water followed by the profiler and cage, and then the buoy line and buoys. After a minimum 90-second acclimation period at the surface, the line was released, and the full setup allowed to free fall to the bottom. Each profiler took measurements from the surface to depth at a rate of four per second and a pump ensured consistent water flow past the sensors. Once the anchor hit the bottom, the remainder of the unit ceased descent shortly afterward, due to the strong positive buoyancy of the floats. On board the vessel, it was usually evident when the anchor hit bottom because of a noticeable slackening of the line. At that time, the vessel s gurdy was engaged and the profiler was immediately hauled back aboard. Once on deck, a series of protocols were executed to clean the sensors and store the unit until the next deployment, as outlined in the Seacat manual (IPHC Unpub.). Data capture Each profiler was shipped into the field with a dedicated laptop computer. Approximately once per day, the profiler was connected to the computer, data were uploaded, and the profiler unit was then reset for the next day s casts. The data were sent remotely or via data storage cards back to the Seattle office after each trip. To facilitate quicker retrieval and processing of the data, beginning in 2013, a cloud storage service was used to transmit the data more efficiently to the IPHC office. Specifically, when the vessels arrived in port after each trip, the samplers (whenever possible) connected the laptops to the internet whereby data were automatically uploaded to a secured storage location in the cloud and were immediately accessible to office staff. Results Two of the profilers were lost at sea early in the program, with the result being that since 2011, IPHC has been operating with 12 SBE19plusV2 and one SBE19plus units. In 2015, an additional profiler (SBE19plusV2 model) with auxiliary sensors was purchased and the SBE19plus was upgraded to a V2 model, bringing the compliment of profilers to 14. During the annual factory maintenance, all profilers were outfitted with new rubber caps in an attempt to minimize moisturerelated shut down of the instruments. This step appeared to serve its purpose and mid-cast shut downs were not a common problem in 2015 as had been the case in recent years. Data collection In 2015, a total of 14 fishing vessels were chartered to complete the IPHC setline survey (Henry et al. 2016) and each vessel was outfitted with a Seacat19plus V2 profiling unit, a laptop computer, and accessory gear. Out of a possible 1,368 stations coastwide, 1,240 useable casts of environmental data were collected (Table 1), resulting in a 91% success rate. Occasionally, data collection was unsuccessful or not attempted, and there were several reasons for this. The vessel captain and lead biologist together decided whether it was prudent to launch the profiler, given the conditions at each station. Poor weather and strong tides were the most common reasons given for aborted casts. On stations where tides were strong but the station was otherwise deemed viable, the samplers were allowed to incorporate an additional pound weight to the bottom of the assembly to achieve a more vertical descent. 400

4 The laptop computers, most purchased in 2008, have exceeded their expected lifespan, due largely to the careful handling of these units by the field staff. A replacement schedule began in 2015 with the replacement of three laptops. Additional replacement units are expected to be purchased over the next several years. Currently, both the port and survey programs are betatesting field tablets for data capture which may eventually be used for profilers as well, but laptops will likely be kept active for the foreseeable future either as the primary data capture or backup system. Environmental conditions The sample area encompasses a wide range of environmental conditions. The highest chlorophyll concentrations were detected in the eastern Aleutian Islands, Shelikof Strait, and the U.S. west coast with less intense concentrations elsewhere. Off the U.S. west coast, there were a few very deep stations where near-bottom waters were hypoxic (< 1.4 ml/l), but the hypoxic zone typically seen near bottom at the more shallow stations since 2002 was not detected during the survey for the second year in a row. Coastwide, the lowest near-bottom DO concentration detected (0.533 ml/l) was in the western Gulf of Alaska at 506 m depth. Both the coldest and the warmest near-bottom conditions coastwide were found in the Bering Sea at expansion stations. The coldest water was north of St. Matthew Island at C and the warmest was at the shallow, nearshore stations in northern Bristol Bay at about 14 C. A complete set of figures displaying isosurface plots for each environmental variable collected can be viewed in the online appendices. Data processing and availability A primary goal of this project is to make the survey profiler data available to scientists worldwide. The IPHC is working with the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) at the University of Washington and NOAA s Pacific Marine Environmental Laboratory to process the oceanographic data and make them publicly accessible. The complete set of data is now available at: Processing of the 2014 and 2015 datasets is in progress. Acknowledgments The success of the profiler project depends on the efforts and cooperation of many people. We would like to acknowledge the IPHC survey program staff for competently incorporating the profiler project into the survey protocols, Nathan Willse for making sure the gear was ready for the field, IPHC sea samplers for their hard work and attention to detail in collecting the data, the survey vessel captains and crews for making sure the Seacats were safely retrieved after every cast, and Peggy Sullivan at NOAA/JISAO for her tireless work on the data and website. 401

5 References Hare, S. H Deployment of a water column profiler from a halibut longliner during IPHC survey operations. Int. Pac. Halibut Comm. Report of Assessment and Research Activities 2000: Henry, E., Soderlund, E., Henry, A. M., Geernaert, T. O., Ranta, A. M., and Kong, T. M Standardized stock assessment survey. Int. Pac. Halibut Comm. Report of Assessment and Research Activities International Pacific Halibut Commission. Unpub. Oceanographic sampling on IPHC setline surveys, Seacat manual Operation manual. International Pacific Halibut Commission. 58 p. 402

6 Table 1. Number of profiler casts completed during the 2015 standardized stock assessment survey, by survey region and vessel. Stations Survey region Profiled Possible Vessel name(s) Oregon Pacific Surveyor Washington Pacific Surveyor Vancouver Star Wars II Goose Island Star Wars II St. James Pender Isle Charlotte Pender Isle Ketchikan La Porsche, VanIsle Ommaney Bold Pursuit Sitka Bold Pursuit Fairweather Bold Pursuit Yakutat Seymour Prince William Sound Waterfall Seward Waterfall Gore Point VanIsle Portlock La Porsche Albatross Clyde Shelikof Clyde Trinity Clyde Semidi Van Isle Chignik Free to Wander Shumagin Free to Wander Sanak Polaris Unalaska Kema Sue 4A Edge Free to Wander 4D Edge Kema Sue Adak Norcoaster Attu Norcoaster St. George Saint Peter St. Paul Saint Peter St. Matthew Kema Sue Total regions: 33 1,240 1,368 Total vessels:

7 Appendices (available via the website for full color viewing) This section contains a series of plots produced using Ocean Data View (Schlitzer 2010) software illustrating oceanographic conditions in summer 2015 as measured by Sea-Bird profilers during the IPHC standardized setline survey. Appendix 1 contains information for the U.S West coast, Appendix 2 for the Gulf of Alaska, and Appendix 3 for the Bering Sea and Aleutian Islands. Temperature, salinity, dissolved oxygen, and ph are calculated using the deepest measurements at each station - typically 5-10 m off bottom. Chlorophyll a concentration is calculated using measurements at 25-m depth. The data are illustrated as iso-surface plots, which are continuous surfaces that use the observed point values to interpolate values at locations between those observations. Survey stations (i.e., where measurements were actually taken) are denoted as black dots. Note that these data have not yet been thoroughly analyzed and are considered preliminary. Appendix 1: U.S. West Coast and British Columbia Appendix 2: Gulf of Alaska Appendix 3: Bering Sea and Aleutian Islands To view the complete document including the full color maps, please visit the IPHC website: Reference Schlitzer, R., Ocean Data View, 404