CalCOFI Cruise 0903JD Marine Mammal Survey Summary

Lisa Munger, Greg Campbell, Andrea Havron, Dominique Camacho, and John Hildebrand (PI)

 

Visual

Two trained marine mammal observers were posted on the flying bridge of the David Starr Jordan (JD) to scan for cetaceans using handheld binoculars (7 power and 18 power), stand-mounted “big-eyes” (25 power binoculars), and naked eye. Visual observations were conducted during daylight hours while the ship was underway steaming at approximately 10 kn between stations. Opportunistic sighting data were also recorded while the ship was on station or occasionally during inclement weather/sea state (Beaufort 6 and above).

Sighting conditions were generally good to excellent nearshore but fair to poor offshore, with marginal conditions (Beaufort 5+) on over half the cruise, and sea state or weather leading to discontinuation of survey effort on five of the cruise days. Survey effort was curtailed in Beaufort 6+ between 83.100 and 83.90 on 3/17/09, and again the following day (3/18/09) between 83.70 and 83.60. Fog prohibited surveys the morning and evening of 3/19/09 during the transit from line 83 to line 80. Survey effort ceased on 3/21/09 at station 77.90 and did not resume, as Beaufort 7+ conditions prevailed for the remainder of the cruise.

Sightings are summarized in Table 1 and displayed in Figure 1. Species diversity was low compared to other cruises/seasons, with Dall’s porpoise (Phocoena dalli) sightings outnumbering sightings of any other species by about four to one (Table 1). The highest diversity was observed inshore along the southern lines (87 to 93), and included fin and grey whales as well as odontocetes (Figure 1).  The majority of offshore sightings were Dall’s porpoise, occurring on every line except the southernmost (line 93); a few dolphin sightings (common, Pacific white-sided, and unidentified), and one unidentified large whale were also observed offshore.

 

Acoustic

During daylight transits, a six-element hydrophone array was towed at 200 m for recording odontocete clicks and whistles from 3 to 250 kHz. At 1-2 nmi from each daylight station, an omnidirectional Navy sonobuoy was deployed to record baleen whale and low-frequency odontocete sounds, e.g. whistles, within 5 Hz to 22 kHz bandwidth.

Delphinid clicks and whistles were detected on the towed array on lines 93, 90, and the inshore portion of line 87 (Figure 2). Species sighted during acoustic detections included common and bottlenose dolphins (Delphinus sp. and Tursiops truncatus). Array recordings are pending review for Dall’s porpoise clicks, which are at frequencies above the real-time monitoring capabilities of the software currently in use.

During sonobuoy deployments, humpback whales were detected at several offshore stations on lines 80 through 93 (Figure 3). Fin whale calls were detected on one sonobuoy near the coast on line 87, corresponding to fin whale sighting locations (see Figure 1). Dolphin whistles were detected on three inshore sonobuoys (coastal and southern Channel Islands), and on two offshore sonobuoys on line 93. Sperm whale clicks were detected on one sonobuoy near the shelf break on line 77.

 

Table 1. Summary of cetacean sightings, CC0903JD. 

  

Figure 1. Cetacean sightings, CC0903JD.

Figure 2. Towed array deployments (yellow line segments) and acoustic detections from 3 to 96 kHz, CC0903JD.

Figure 3. Sonobuoy deployments and acoustic detections below 22 kHz, CC0903JD. Mn=humpback whale (Megaptera novaeangliae), Pm=sperm whale (Physeter macrocephalus)