Spring 2008 Cruise Report

Richard Thorne

The herring survey effort during spring 2008 consisted of two cruises.  The first cruise had a juvenile herring emphasis and was a two-vessel survey.  The MV Auklet served as the acoustic survey vessel, while the FV Kyle David was the biological sampling vessel.  The second cruise was a single-vessel survey on the Kyle David and focused on adult herring.  

During the first cruise, acoustic surveys were made in Simpson Bay, Port Gravina, Port Fidalgo, Eaglet Bay, Whale Bay, Sawmill Bay and Zaikof Bay (Figure 1).  Biological collections were made in Simpson Bay, Eaglet Bay, Whale Bay, Sawmill Bay and Zaikof Bay.  Simpson Bay was surveyed on March 16.  A sizeable concentration of fish was observed in the inner bay (Figure 2).  The ADF&G RV Solstice sampled these fish the next night and caught mixed juvenile herring, ages 1, 2 and 3.  Port Gravina was sampled on March 17.  Fish were only detected within St. Mathews Bay (Figure 3).  This concentration was estimated at 3-5 thousand tons.  Port Fidalgo, specifically the area around Two Moon Bay and Snug Corner Cove was surveyed on March 18.  Few fish were observed.  Eaglet Bay was surveyed on March 19.  Herring were observed at the head of the bay and in Cascade Bay (Figure 4).  The Kyle David captured juvenile herring at this location, along with some smelt (yet to be identified).  Whale Bay was surveyed March 20 (Figure 5).  Herring were detected, and later confirmed to be primarily age 0 fish.  Sawmill Bay was surveyed March 21.  About 1.5-2.0 thousand metric tons were observed (Figure 6).  Samples indicated mixed juvenile herring.  After a weather day, Zaikof Bay was surveyed March 23.  Very few fish were observed.  Synoptic observations of seabirds and marine mammals were made throughout the cruise.  Steller sea lions were observed inside St. Mathews Bay and Sawmill Bay.  No whales were observed in the survey areas.  The only whale activity was detected around Shelter Bay during transit of Lower Knight Island Passage.

The second cruise focused on Port Gravina and Port Fidalgo, the areas where most adult herring have been observed for the past several spring periods.  The herring concentration in Port Gravina was still primarily limited to St Mathews Bay.  Very few fish were observed in the normal spawning areas from Red Head to Olsen Bay.  The herring concentration in St Mathews Bay was subject to predation by about 20 Steller sea lions (Figure 7) and 3 whales.  The whales foraged all the way to the head of St Mathews Bay (Figure 8). Two major aggregations of herring were located in Port Fidalgo.  One was off Irish Cove, the other outside of Two Moon Bay.  Both aggregations were large, about two square kilometers in area (Figures 9 and 10).  Preliminary estimates place the biomass from the two aggregations at about 5 thousand tons.  The aggregations were the subject of intense predation by 20-50 Steller sea lions and 5-10 whales.  This offshore distribution normally occurs in mid-March, rather than late-March.  It appears that the spawning migration of herring in Prince William Sound during 2008 is delayed by one to two weeks compared to normal years.  As a result, the 2008 surveys are likely to produce underestimates of the adult herring biomass.

Figure 1-Track of MV Auklet during first herring cruise in March 08

Figure 2-Echogram from transect of herring schools in Simpson Bay, March 16, 2008

Figure 3-Echogram from transect of herring in St Mathews Bay, March 17, 2008

Figure 4-Echogram from transect into Cascade Bay in Eaglet Bay, March 19, 2008

Figure 5-Echogram of age-0 herring layer in Whale Bay, March 20, 2008

Figure 6-Echogram of herring schools from transect in Sawmill Bay, March 21, 2008

Figure 7-Steller sea lions in St Mathews Bay, March 29, 2008

Figure 8-Whale cruising the shoreline at the head of St Mathews Bay, March 29, 2008

Figure 9-Large herring aggregation off Two Moon Bay, Port Fidalgo, March 28, 2008

Figure 10-Large herring aggregation off Irish Cove, Port Fidalgo, March 28, 2008