Swim speed, behavior, and movement of North Atlantic right whales (Eubalaena glacialis) in coastal waters of northeastern Florida, USA

Abstract

In a portion of the coastal waters of northeastern Florida, North Atlantic right whales (Eubalaena glacialis) occur close to shore from December through March. These waters are included within the designated critical habitat for right whales. Data on swim speed, behavior, and direction of movement--with photo-identification of individual whales--were gathered by a volunteer sighting network working alongside experienced scientists and supplemented by aerial observations. In seven years (2001-2007), 109 tracking periods or "follows" were conducted on right whales during 600 hours of observation from shore-based observers. The whales were categorized as mother-calf pairs, singles and non-mother-calf pairs, and groups of 3 or more individuals. Sample size and amount of information obtained was largest for mother-calf pairs. Swim speeds varied within and across observation periods, individuals, and categories. One category, singles and non mother-calf pairs, was significantly different from the other two--and had the largest variability and the fastest swim speeds. Median swim speed for all categories was 1.3 km/h (0.7 kn), with examples that suggest swim speeds differ between within-habitat movement and migration-mode travel. Within-habitat right whales often travel back-and-forth in a north-south, along-coast, direction, which may cause an individual to pass by a given point on several occasions, potentially increasing anthropogenic risk exposure (e.g., vessel collision, fishing gear entanglement, harassment). At times, mothers and calves engaged in lengthy stationary periods (up to 7.5 h) that included rest, nursing, and play. These mother-calf interactions have implications for communication, learning, and survival. Overall, these behaviors are relevant to population status, distribution, calving success, correlation to environmental parameters, survey efficacy, and human-impacts mitigation. These observations contribute important parameters to conservation biology, predictive modeling, and management. However, while we often search for predictions, patterns, and means, the message here is also about variability and the behavioral characteristics of individual whales.

Figure 1. The study area showing the 33 lookout points used by the volunteer sighting network.

The bathymetry (gray lines) was digitized from large-scale NOAA charts, and is equivalent to 5.5, 9.1, and 18.3 m. The solid red line is the boundary of the SEUS Right Whale Critical Habitat, which is 5 nm (9.3 km) from the coast in this area. A key feature of the study area is the narrowing of the nearshore zone of shallowest waters (<10 m) and increased depth closer to shore.

Figure 2. Swim speed for three categories of right whales (MC  =  mother/calf pairs, GRP  =  groups of ≥3, SPR  =  singles and non-mother-calf pairs) in nearshore waters of Florida, 2001–2007.

Shown are the overall range, inter-quartile range (box), median (center line), mean (dot), and the number of observations (follows).

Figure 3. Swim speed for eight mother-calf pairs of right whales with at least three follows in nearshore waters of Florida, 2001–2007 (format as in Fig. 2).

Figure 4. Mother-calf interactions and behaviors: a. Calf positioned diagonally with mother's chin touching calf. b. Calf's chin resting on mother's back. c. Mother inverted (belly up), calf swimming in the opposite direction. d. Calf apparently nursing. e. Calf “romping” across mother's head. (Graphics by P. Oberlander, based on photos).

Figure 5. Sightings for female #2430 and calf during a nine-week period, 27 December 2006 to 24 February 2007, including several contributed by the Florida Fish and Wildlife Conservation Commission.

During this period the pair swam south four times and north four times, traversing 158 nm (292 km), and passing by inlets and channel entrances on several occasions (points of possible increased risk to whales). Sighting frequency is related to effort (sighting effort was less south of Ponce Inlet). The movement can be tracked by following the sequence of numbers. Key: 1-12/27/06, 2-12/28, 3-12/29, 4-12/30, 5-1/03/07, 6-1/04, 7-1/05, 8-1/07, 9-1/09, 10-1/10, 11-1/16, 12-1/21, 13-1/27, 14-1/30, 15-2/02, 16-2/05, 17-2/12, 18-2/13, 19-2/18, 20-2/20, 21-2/21, 22-2/22, 23-2/24.