Pre-cruise plan for R/V GYRE May-June survey, updated 16 May 2003 8

Contributing authors: Doug Biggs, Jonathan Gordon, Dan Engelhaupt, Nathalie Jaquet, John Wormuth

Summary: R/V Gyre will field a passive acoustics and visual survey and habitat characterization for sperm whales in the northern Gulf of Mexico (GOM) for 3 weeks in May-June 2003. Hereafter called Gyre Leg1, this survey will be followed by a 3 week Gyre Leg2 S-tag cruise to radio tag sperm whales. Gyre Leg1 will be staged out of Galveston TX and will be at sea from 31 May to 21 June 2003. SWSS PIs who will ride this Leg1 survey will be Doug Biggs, Jonathan Gordon, Nathalie Jaquet, Dan Engelhaupt, and John Wormuth. These PIs and their supporting teams, and Sarah Tsoflias from MMS, constitute a 25 person science party (see Table 1). It is presently planned that Gyre Leg1 will sweep the 800-1000 m isobath of the northern Gulf of Mexico from about 95°W to about 85°W, during the time that R/V Ewing is at sea and when this latter research vessel is expected to carry out concurrent passive acoustics monitoring of sperm whales in the Mississippi Canyon area and in/around one or more commercial geophysical seismic surveys in the north central GOM. As time permits or as bad weather conditions unfavorable to small boat operations may dictate (see below), Gyre Leg1 may also investigate the abundance of sperm whales and squid in one or more regions of cyclonic circulation along the eastern side of DeSoto Canyon and south along the eastern wall of the Loop Current.

Basis for Leg1 Planning:

We have attempted to factor into our planning for this cruise the political reality that MMS is extremely interested in ascertaining more clearly when and where groups of sperm whales are located off the Texas continental margin. The reason is that the oil and gas development is moving into Texas as well as Louisiana areas of the northern Gulf of Mexico continental margin. From previous SWAMP and SWSS fieldwork in summers 2000, 2001, and 2002, we know that sperm whales can be locally abundant off the Louisiana continental margin in June-July-August. In fact, most of our previous encounters with sperm whales in summers 2000, 2001, and 2002 have been concentrated from Mississippi Canyon to the western side of DeSoto Canyon. Even though the 18 sperm whales that were radio-tagged in this region in summer 2002 later ranged outside this area, sperm whales west of 90°W and east of 88°W are very much under-sampled, particularly in terms of biopsy sampling for genetics characterization (see Figure 1).

Synopsis of Leg1 Science Programs:

There are three broad options for Leg1, but since R/V Ewing is expected to concentrate on the first of these, R/V Gyre Leg1 will target options #2 and #3: 1) Focus effort on historical areas of high sperm whale abundance such as Mississippi Canyon and the nearby Mississippi River delta; 2) Expend some effort looking/listening for whales along the Texas continental margin, and then sweep along the upper slope of the northern GOM - from west to east - rather as we did last year 2002; 3) Investigate sperm whale (and squid) occurrence in oceanographic features such as cyclonic gyres, as well as in water depths of 800-1000 m.

Because Gyre Leg1 is a multi-disciplinary research effort, we are planning to carry out four subprojects: 1) Characterizing sperm whale group membership and individuals within the population by photo-id, photogrammetry and genetics; 2) Examining stock structure using genetics and coda vocalization analysis; 3) Understanding sperm whale distribution in terms of oceanographic habitat parameters; 4) Trawling for squid, primarily in areas where we know that sperm whales have been feeding and ideally at depths we know they have been feeding. Subprojects 1 and 2 are primarily daytime efforts, subproject #3 will be carried out night as well as day, and subproject #4 (squid trawling) will be carried out at night. The four subprojects are explained in more detail below.

When weather favorable to small boat operations allows, all four subprojects will be implemented in any area that we find whales. When small boats cannot be deployed and/or if whitecap conditions prevent visual teams from searching for whales, we will continue to tow the passive acoustic arrays for survey and coda vocalization analysis. We will also continue to trawl for squid at night, as long as back-deck conditions allow for safe deployment and recovery of the Isaacs-Kidd Midwater Trawl (IKMT).

Observations of Opportunity Offshore in advance of Gyre Leg1:

It is anticipated that Mr. David Dies, a sport-fishing enthusiast who last June 2002 spent 4 days in the vicinity of deepwater platform Diana-Hoover and told us that he saw dozens of sperm whales there, will again be sport fishing in this area on at least one occasion in May 2003 aboard his 45-ft boat "Mean Marine". Mr. Dies invited SWSS to send observers from Dr. Würsig's group with him for a trip of opportunity offshore in May 2003. TAMUG graduate student Heidi Petersen and her husband were planning to piggyback on such a trip of opportunity offshore with Dies to count/photograph sperm whales, under Dr. Würsig's permit, that may be seen. We had hoped the weather would allow them to go offshore with Dies May 16-17, but the offshore marine forecast was unfavorable for a trip 100 miles offshore on May 16-17. We're talking with Dies to find out whether he may go offshore May 23-24 instead.

We are also in email contact with Captain Dana Dyer, while he is at sea during May 2003 in support of the two May 2003 research cruises that precede Gyre Leg1. Because the 29 April to 16 May cruise 03G04 is doing a science program for USGS in two areas of the Louisiana slope centered on lease blocks Keithley Canyon 195 and Atwater Valley 14, Bruce Mate has given Captain Dyer the location of the 5 tagged whales that are still transmitting position information from the Louisiana slope. Captain Dyer and the other bridge watch teams will watch for these whales as their May 2003 mission time/location allows.

Any sperm whale location information we may receive from Dies and/or from Gyre in advance of Leg1 will allow us to acquire whales over the Texas and Louisiana continental margin more quickly and efficiently than last summer, when we had only anecdotal information that whales had been seen by sport-fishing boats in early summer near deepwater platform Diana-Hoover.

Strawman Station Track:

Tab 1 of the attached Excel spreadsheet called "SWSS2003GYRELeg1TimeDist.xls" gives an example of the strawman pre-cruise list of station locations and the kind of time/distance calculations we will do before we sail and that we will update as we go. Tab 2 shows a rough x-y plot of longitude-latitude coordinates of the strawman stations. At this point in our planning, the station locations are the same as those occupied last summer 2002 during Gyre Leg1. But this year we are also considering extending our search along the 800-1000 m isobaths further to the southeast, and so we have added a strawman location at 27.5°N, 85.5°W. We've done this because pre-cruise altimetry for 1, 8, 15, 22, and 29 April shows an area of strongly cyclonic circulation along the eastern wall of the Loop Current. We will continue to monitor the SSH fields in May, to allow us to decide whether to search this area as time and small-boat favorable weather may allow during the second half of the Leg1 cruise. At this point in the pre-cruise planning, we believe flexibility is more important than is any "master plan".

We're currently planning that, as was done for Leg1 in summer 2002, during Leg1 2003 the Gyre will transit south from Galveston to the 1000-m isobath. At approximately 94.75°W, in the general vicinity of the platform Diana-Hoover, we intend to spend several days searching for whales and doing squid trawling. Sperm whale survey will be undertaken using visual observers with BigEye binoculars and passive acoustic monitoring of two towed hydrophone arrays. Additionally, guided in part by feedback from the pre-cruise monitoring and the Leg1 survey itself, photo-identification and population structure activities will be conducted from two small boats each equipped with a digital telephoto camera and with a directional hydrophone. See the summary SWSS 2003 work plan and the work plan of Gordon, Jaquet, and Würsig for more information. Biopsy sampling will be conducted by Dan Engelhaupt, starting aboard R/V Gyre but possibly transferring to R/V Ewing when we get to the area of the GOM where that ship is working and if/when permits for WHOI to carry out D-Tag and CEE work are received from NOAA Fisheries.

If no whales are encountered in the western Gulf, this is still valuable data. Practically, however, should no whales or only a few whales be found after 36-48 hours of search in the far western GOM, we will begin a zig-zag patterned survey for sperm whales from west to east centered along water depths of 800-1000 m. When groups of whales are encountered, the survey will be interrupted to stay with animals for 24-48 hours for the visual/acoustic and photo-identification work.

MMS is providing 21 days of ship time for Leg1 and because we're taking two TAMU graduate students as part of the Leg1 scientific party, TAMU has added an additional 24 hours at no ship time cost to MMS. So our total time at sea will be 22 days. The strawman cruise track we've laid out in the data table and companion plot in the attached Excel spreadsheet predict that it will take 247 hours (10.3 days) or about half of the available 22 days of ship time to cover the roughly 1600 nautical mile circuit. This assumes the ship will transit at an average speed of 8.5 knots from the Galveston sea buoy south to the initial work area, and again from the last station back to Galveston sea buoy. It then assumes an average speed of 6 knots for the rest of the trip, which our experience last summer 2002 taught us is the approximate maximum tow speed for a good signal return from a towed Ecologic array. The remaining time of 11.7 days is available for small boat work and squid trawling work. During these activities, the ship will either be stopped or moving slowly and randomly in/around the local area where the whales are encountered.

Squid Trawling:

When/where we encounter groups of sperm whales, trawling for squid will be done during the nighttime hours. Dr. John Wormuth plans to use a modified 14 m2 Isaacs-Kidd Midwater Trawl (IKMT), which he will deploy from fantail using the main trawl winch. One of the features of such a large net is a long bridle to allow it to open properly. The present plan is to attach an electronics system to the depressor vane and tow the trawl on conducting cable. A potential problem is that the termination of the towing wire has to be pulled through the sheave to retrieve the net. This may cause problems with the electrical connection to the net. Wormuth is working with the Marine Operations group in Galveston to find a solution.

As a fallback, Wormuth will purchase a time-depth recorder from Sea Bird that will give him post-trawl information on depth rather than real-time data. Wormuth feels he should be able to calibrate wire out and ship speed with depth after 2 or 3 trawls by stopping the winch at various wire out intervals and getting their corresponding depths after each trawl. Wormuth also will bring a 1-m2 Multiple Opening and Closing Net and Environmental Sensing System (MOCNESS), so that if it is too rough to fish the big net off the stern, he can fish this smaller net off the starboard size.

Most of the trawling will be done when/where we encounter groups of sperm whales, although Wormuth would like to be able to make some trawls in the western Gulf and on the east side of DeSoto Canyon, even if whales are seen only infrequently there, to allow him to compare cephalopod community composition in different geographic regions of the Gulf and to contrast cephalopod community composition "in" versus "outside" groups of whales. Two IKMT trawls per night are anticipated, and a CTD cast will be done midway through the trawling period, while the catch is being sorted on deck and the net is being readied to go back in for the second collection. On most nights, trawling should be finished by approximately 3 a.m. The passive acoustic arrays then will be deployed, whales located, and the day's survey activities will commence. Wormuth intends to fish the first trawl from 400-600m and the second trawl from 600-800m, based on data from last summer's D-tag cruise that most whales dived to depths below 400 m both night and day (see Figure 2). Should other information this May-June 2003 show other diving depths (see following paragraphs), Wormuth will adjust his trawling depths.

It is planned that Dr. Aaron Thode will be aboard R/V Ewing to determine the depths to which sperm whales are diving by using passive, 3-D acoustic information from the rented SEAMAP passive acoustic array that the Ewing will tow. Dr. Thode is in email contact with Dr. Gordon to discuss whether by adding depth sensors or other telemetry to the tandem Ecologic acoustic arrays that will be towed during Gyre Leg1, Gordon may be able to make similar estimates of how deep the whales that we see and hear from Gyre are diving. When the paths of Gyre and Ewing cross, Gyre trawling activities can occur near the location of the last group of whales encountered by Ewing, unless the Ewing is engaged in CEE activities.

We will also use the acoustic backscatter information received from Gyre's 38 kHz phased array Acoustic Doppler Current Profiler (ADCP) to guide our squid trawling. Because the ADCP generates sound at 38 kHz, this sonar can potentially resolve scatterers in individual size as small as 1 centimeter (i.e., about 1/4 of the wavelength of the 38 kHz sound = 1/4 of 150,000 cm/sec divided by 38,000 cycles/sec = 1 cm). However, the signal-to-noise of the ADCP return signal below a depth of 500 m is highly dependent on ship speed. This is expected to be better at trawling speeds of 3-5 knots than at underway speed of 6 knots. TAMU graduate student Amanda Olson will review the 24 h of ADCP data collected before each night's trawling, to look for any "hot spots" of backscatter that may be present in the ADCP record at depths below the main Deep Scattering Layer (DSL). This main DSL is a prominent feature both day and night at depths of 300-400 m. If/when such higher-than-average backscatter is seen below 400 m, the trawling that night will target the principal depth of occurrence of these "hot spots".