A COMPARISON OF AERIAL, 



SHIPBOARD, AND LAND-BASED 



SURVEY METHODOLOGY FOR 



THE HARBOR PORPOISE, 



PHOCOENA PHOCOENA 



A review of the status of harbor porpoise, Phocoena 

 phocoena, in the U.S. waters of the western North 

 Atlantic identified substantial information gaps in 

 our knowledge about this species, and raised serious 

 questions about the health of the North American 

 population (Prescott and Fiorelli 1980). Significant- 

 ly, no population estimate exists for P. phocoena in 

 the western North Atlantic. Gaskin's (1977) estimate 

 of 4,000 in the Bay of Fundy region is admittedly pre- 

 liminary, and includes only a portion of the known 

 range. Prescott and Fiorelli (1980) used winter 

 stranding records from a single year to postulate a 

 minimum mid- Atlantic regional population of 726 to 

 1,525 (between Long Island Sound and Cape Hat- 

 teras), but acknowledged that no information on 

 stock or population discreteness exists for U.S. coast- 

 al waters. 



Harbor porpoise are one of the smallest oceanic 

 cetaceans, reaching a maximum size of about 2 m 

 (Gaskin et al. 1974). They are also behaviorally 

 innocuous, seldom leaping from the water, are 

 usually found in small groups of 2-4, and generally 

 avoid motor vessels (Amundin and Amundin 1974). 

 These factors frustrate attempts to study the 

 species, and it was necessary to establish and test 

 survey methodology prior to undertaking a full-scale 

 survey. An experiment was designed to estimate the 

 fraction of visible harbor porpoises observed from 

 aircraft, shipboard, and land-based survey plat- 

 forms. 



Between 4 and 12 August 1980, 30 to 34 persons 

 from College of the Atlantic, the University of 

 Guelph, and the New England Aquarium took part in 

 this experiment in Head Harbor Passage, a narrow 

 channel running NE-SW, bounded by Campobello 

 Island (N.B.) on the east and a series of small islands 

 and ledges on the west (Fig. 1). Head Harbor Passage 

 was chosen for three reasons: 1) Harbor porpoise 

 regularly inhabit the passage; 2) the passage is only 

 800 to 1,000 m wide, with many identifiable 

 landmarks, which permits accurate orientation and 

 navigation; and 3) the northwestern coast of Cam- 

 pobello Island provides easy access to land observa- 

 tion stations of nearly uniform height. 



Methods 



Four transect lines were established at 200 m inter- 



910 FISHERY BULLETIN: VOL. 81, NO. 4, 1983. 



vals for a 5 km section of Head Harbor Passage (Fig. 

 1). Each transect line was surveyed by the survey 

 vessel, the RV Beluga, a 12 m power vessel provided 

 by the College of the Atlantic, and by the survey air- 

 craft, an amphibious Cessna 185 1 provided by the 

 U.S. Fish and Wildlife Service. Because of the dif- 

 ference in survey speed, the experiment required 

 that the aircraft cover all four transects for each one 

 the boat completed. For example, while the RV 

 Beluga was enroute along Transect 3, the aircraft 

 would survey Transects 1, 2, 3, and 4, in that order, 

 and then break off until the boat had started survey- 

 ing Transect 4. At that time the aircraft would cover 

 all four transects again (Table 1). 



Six land stations were set up on the coast of Cam- 

 pobello Island at about 500 m intervals. These 

 stations were supplemented by additional stationary 

 observation points at 500 m intervals on or near 

 Spruce Island (across the passage). Two observers 

 were posted at each station, to record location and 

 movement of all harbor porpoise within sight. All 

 land stations were oriented to true northwest, in 

 order that overlapping sightings could be identified 

 later. Sighting distances were estimated by the 

 observers, based on a series of known distance cali- 

 bration trials completed the first day using the vessel 

 and a wooden life-size harbor porpoise model. Dur- 

 ing each transect, the 200 m interval made by the RV 

 Beluga provided additional distance calibrations. In 

 the final analysis of the data, only those observations 

 from the 4 km survey area in view of the six Cam- 

 pobello Island land stations have been utilized, since 

 the consistency of position and orientation of the 

 boat stations across Head Harbor Passage were more 

 variable and tide dependent. 



Vessel transects were conducted with two observ- 

 ers and a recorder stationed on the bow (approximate 

 height of eye about water = 2.5 m). Each observer 

 was responsible for surveying 95° of horizon, from a 

 point directly abeam of the survey vessel to a point 5° 

 off the opposite bow. This pattern provided an 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Table 1. — Summary of experiment on survey 

 methodology for harbor porpoise, August 1980. 



