spawning. Aerial surveys also afford a 

 means of studying timing of spawning activ- 

 it ies. 



The purpose of this report is (1) to 

 describe the procedures of the aerial survey 

 and (2) to record preliminary information 

 gained from surveys of the past three years. 



METHODS OF AERIAL SURVEY 



The Pacific herring spawns in inter- 

 tidal areas, and during spawning activity 

 clouds of milt appear in the water along 

 the shoreline. These milt clouds may be 

 readily observed from the air (fig. 1); they 

 have been spotted from as high as 6,500 

 feet, and are most certainly visible from 

 greater heights. Most aerial surveys are 

 conducted at altitudes between 500 and 700 

 feet. In clear weather, milt clouds have 

 been seen at three miles from these heights. 

 The exact coloration of the milt varies 

 with lighting conditions. During bright, 

 cloudless days the milt appears milky white, 

 but during overcast periods it may vary 

 from pale yellow to yellowish green. The 

 density of the milt also produces variations 

 in color. 



The rate at which milt disperses and 

 is no longer visible depends on tidal 

 action, wind, and density of deposition. 

 The schooling behavior of Pacific herring 

 is such that spawning is usually intense 

 and continuous, and dispersion of milt from 

 an area is rarely completed in a day's time. 

 After the milt has disappeared, the beach 

 utilized for spawning may be detected by 

 the presence of sea gulls actively feeding 

 on eggs. Gulls line the spawning beach in 

 countless thousands and distinctly outline 

 the areas of egg deposition. Observations 

 are classified as (1) active spawn when 

 milt is visible and (2) old spawn when 

 gulls are the only evidence of spawning. 



Aerial surveys require an observer 

 familiar with the territory and character- 

 istics of spawning beaches. Aircraft used 

 thus far for surveys (Grumman Goose and 

 Super Widgeon) cruise at speeds of 120 

 knots, and though a trained observer would 

 have little difficulty locating specific 

 landmarks, the novice might easily be con- 

 fused. When necessary, two or three passes 

 are made over the same grounds to ensure 

 accurate mileage determinations. During 



flight the observer plots the entire route 

 of the survey on reduced prints of naviga- 

 tion charts and marks beach areas used for 

 spawning. After each flight the observer 

 measures the spawning beach marked on the 

 chart and determines the mileage observed. 



Time of spawning varies in each area, 

 and to provide coverage of all major spawn- 

 ing areas, surveys are made from mid-March 

 to mid-May. Spawning in any location may 

 continue for as long as five weeks and re- 

 peated flights are necessary to adequately 

 assess egg deposition. Results of all 

 flights in a given area are compiled on a 

 single master chart. This provides a compo- 

 site picture of the spawning beach utilized 

 during the season. The 1955 master chart 

 of one of the major spawning areas is pre- 

 sented in figure 2. 



Attempts to standardize survey methods 

 have met with several obstacles of which 

 weather conditions are most important and 

 govern the days selected for survey either 

 because flying is impossible, or visibility 

 is so poor that surveys are not practical. 

 Yearly variations in time of spawning pos- 

 sible negate the necessity of flying on a 

 given day. Rather, coverage or number of 

 days and hours flown would appear to be of 

 greater importance, so that standardization 

 of flying time would provide a useful com- 

 parative index, whereas surveys on given 

 days could well distort such an index. 



Availability of aircraft has also been 

 a factor in standardizing methods. Avail- 

 able flight time has limited the extent 

 of surveys, which of necessity have been 

 centered in areas of concentrated spawning 

 activity. Thorough and complete coverage 

 has been attained in these area, but in 

 areas of very light spawning there has been 

 no standardized coverage. 



The goal of future survey work is to 

 develop a standardized method of survey from 

 which the size of spawning populations can 

 be estimated. Route and area of coverage, 

 time lapse between flights, and numbers of 

 surveys per area have yet to be established. 



SPAWNING LOCALITIES 



Rounsefell (1930) lists the reported 

 spawning areas of herring from California 

 to the Bering Sea. Aerial surveys have 



