FISH AND WILDLIFE TECHNICAL REPORT 25 



readings from a radar, or only one distance is available, 

 the position from the LORAN C can be checked by a com- 

 bination of depths, LORAN C lines, and bearings to a 

 land mass. 



To interpolate between two good positions, divide the 

 speed in knots by 60 and multiply by the minutes dura- 

 tion of the transect. This gives you the distance traveled 

 on each transect. This distance can then be stepped off 

 with dividers between the beginning and ending positions, 

 and each new position can then be read from the chart. 

 The positions should always be calculated as soon as possi- 

 ble after the observations. When obtaining positions from 

 a chart, the depth should also be taken and compared with 

 the depth obtained from the ship's equipment. If the ship's 

 crew are not plotting positions on a nautical chart at least 

 every 2 h, do so yourself, and be sure a position is taken 

 at every course change. Check all of your positions for 

 a logical and consistent progression. Write all the par- 

 ticulars of the fix in the field notes on the data form. 



Speed 



The speed made good can be calculated by obtaining 

 two accurate positions (preferably at least a couple hours 

 apart) and measuring the distance between the two points 

 with a pair of dividers. Move to the left or right edge of 

 the chart at the same latitude (the scale varies with latitude 

 on a mercator projection) and measure the nautical miles 

 on the latitude scale. One nautical mile is equal to 1 min 

 of latitude, and 1 of latitude is equal to 60 nmi. The speed 

 made good is obtained by dividing the nautical miles 

 traveled by the elapsed time (expressed in tenths of hours). 

 The speed made good is the distance traveled over the 

 ocean floor. Due to tides, or the action of currents, the 

 speed made good may be different from the speed through 

 the water. In most cases, the difference between the two 

 speeds is negligible, but in some passes, water may flow 

 at a rate of several knots. Birds are usually associated with 

 the water column, thus moving with it, and speed through 

 the water may give a more accurate representation of bird 

 density than speed over the bottom. Many research ships 

 are now equipped with water speed indicators, and in areas 

 of fast moving currents the speed through the water should 

 be used. Speed is always taken in nautical miles per 

 hour (knots). One knot is equal to 1.15 statute mi/h or 

 1.852km/h. 



Depth 



Depths can be read directly from a fathometer by 

 yourself or by a crew member. If positions are accurate 



and navigation charts of sufficient scale are available, 

 depths can be determined directly. However, it is always 

 best to use the fathometer. We often record the depths 

 in fathoms below the field on the transect form and con- 

 vert it to meters at a later time (1.83 m = 1 fathom). 



Temperature and Salinity 



Sea-surface temperature and salinity are obtained in 

 various ways. The ideal method is a continuously record- 

 ing thermo-salinograph, which records both temperature 

 and salinity on graph paper. Most ships measure sea 

 temperature at the water intake for cooling their engines. 

 This is often a couple of meters below the surface, but 

 mixing is generally sufficient to get reasonable readings. 

 Large ships usually record this temperature each hour. 

 Unfortunately, the reading may be done by different per- 

 sons during each day and often little care is taken when 

 reading the thermometer. Ask to see where the tempera- 

 ture gauge is located and impress on the engine room 

 personnel the importance of consistent and accurate 

 readings. The best method is to check the temperatures 

 yourself at the beginning and end of each series of 

 transects. Both water temperature and salinity can be 

 measured with inexpensive hand-held devices using water 

 samples freshly collected in a bucket over the side of the 

 ship. Take the sample on the side of the ship opposite the 

 outlet for hot water from the engines. Occasional bucket 

 temperatures should be taken to check on the more fre- 

 quently obtained intake temperatures. Depth, temperature, 

 salinity, and other environmental data are best taken at 

 the mid-point of each transect, but it is often more con- 

 venient to obtain them at the beginning. In either case, 

 be consistent throughout the survey. 



Ice 



The presence of ice is an environmental variable that 

 affects the density and distribution of birds at sea. Cover- 

 age and pattern are the most important features of ice both 

 inside and outside of the count zone. The distance to the 

 ice edge is also important, especially out to 20 mi, and 

 should be recorded whenever possible. 



Miscellaneous 



Seabirds may react to meteorological events (Manikow- 

 ski 1971) and we record barometric pressure, weather, 

 and wind speed for each transect. Sea state, swell height, 

 and tide are low priority items and are not recorded when 

 time is scarce. 



