10 



(Appendix II) . The Elizabeth Islands were not mapped, but eelgrass 

 abundance there was estimated from substrate area on maps (Appendix II) . 



Photograph interpretation 



The maps of the present-day distribution of eelgrass were based on 

 existing black and white or color vertical aerial photographs taken by 

 private and governmental agencies (Appendix I) . Most of the photographs 

 used were taken between Spring and Fall, during 1974 - 1981. Maps of 

 eelgrass based on photographs taken during the 1970 's are often 

 representative of present-day eelgrass distribution because eelgrass had 

 saturated available habitat in most areas by that time (refer to chapter 

 4) . Because older photographs may lead to underestimates of new 

 eelgrass losses or other recent changes, the dates of aerial surveys 

 used to make each map are listed in Appendix II. 



Field verification of photographs was accomplished either by skin- 

 or SCUBA diving, or surface observations from boats in 1984-1986. In 

 some embayments, interpretation of photographs was aided by information 

 from shellfish wardens, other researchers, or local residents. 



Older photographs and winter surveys were used to interpret recent 

 photographs. For example, a submerged feature unchanging in area over 

 several decades is either a rock field or peat reef, whereas a patch of 

 dense vegetation that shows gradual expansion is eelgrass because only 

 eelgrass beds change in this way. Submerged features in basins that 

 show radical movement within one or two growing seasons are probably 

 drift material. Vegetation present only on summer imagery is likely to 

 be an annual eelgrass bed. 



