Northwest Fisheries Science Center

2017 West Coast Groundfish Bottom Trawl Survey

Blog Entries for July 2017

Fourth Leg of the First Pass of 2017 Groundfish Survey (Part 1: F/V Excalibur)

By John Buchanan
Posted on July 11, 2017


Calendar showing date from June 26 through July 06

We departed for leg 4 of the groundfish survey late on the evening of June 26, sailing underneath the Golden Gate Bridge. Though too dark to see the bridge this year, the iconic brick-red suspension bridge is a familiar sight for Groundfish Survey biologists.

The Golden Gate Bridge as seen from below while embarking on leg 4 of the first pass of the 2016 Groundfish Survey. Photo credit: John Harms

This portion of the survey extended from San Francisco to Santa Barbara California. The scientific crew included Chief Scientist John Buchanan and back deck biologists John Harms and Aaron Chappell, and the vessel crew consisted of Capt. Mike Retherford Sr., deckhands Joey Jacques and Nate Smith, and night driver Kelsea Retherford. We encountered heavy seas (10 to 12 ft) and high winds (up to 30 kt) for the first 5 days.

During the 10 day leg, 42 station tows were completed successfully by the F/V Excalibur. Per the survey’s stratified random design, tows are allocated among three depth strata:  30 – 100 fathoms (55 – 183 m); 100 – 300 fathoms (183 – 549 m); and 300 – 700 fathoms (549 – 1281 m). That fathoms – a unit of depth commonly used by commercial fishermen – define the survey’s depth stratification is a legacy of the collaboration between NOAA and the West Coast groundfish industry that designed and developed this survey.

The F/V Excalibur’s 42 successful tows on Leg 4 were divided as follows:

Depth (fathoms)                    # tows

shallow       30-100                       15

mid-depth 100-300                      17

deep         300-700                        10

The catch associated with the various depth strata are very different. The photographs below show typical catch from tows within each depth zone (shallow, mid-depth and deep). (Photo credits: John Buchanan)

    Photo of the catch from a deep tow (~500 fathoms) containing Pacific and giant grenadier, sablefish, longspine thornyhead, Tanner crab and sea stars (Heterozonias alternatus).  

 

Photo of catch from a mid-depth tow (~250 fathoms) containing Dover sole, Pacific hake,    longnose skate, spotted ratfish, Dungeness crab, sea urchins (Brisaster sp.) and seas stars (Hippasteria sp. and Luidia foliolata).   

 

Photo from a shallow southern California tow (~100 fathoms) containing Pacific sanddab,
spiny dogfish, white croaker, half-banded rockfish and California sea cucumbers.            

 

During the second half of leg 4, the heavy seas and high winds (greater than 25 kts) subsided as we rounded Pt. Conception into the anoxic Santa Barbara basin on July 4th (see survey blog: Postcards from the Field: July 10). After an enjoyable anchorage off Goleta and UCSB, including a celebratory fireworks show, the F/V Excalibur moved offshore, outside of San Miguel Island picking up catches of sea urchins (Brisaster sp.) along with blackgill rockfish at stations in about 250 fathoms. Later, on the south side of Santa Rosa Island, Capt. Mike Retherford Sr. announced the sighting of a large shark at the surface, on the vessel’s starboard side. Further inspection revealed a ~10 ft swordfish sunning itself, likely thermoregulating after an energy-intensive vertical excursion for prey.