Edited by: David Peel, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia
Reviewed by: Aldo S. Pacheco, National University of San Marcos, Peru; Ladd M. Irvine, Oregon State University, United States
This article was submitted to Marine Conservation and Sustainability, a section of the journal Frontiers in Marine Science
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During winter months, humpback whales (
The humpback whale (
Ship strikes are a major cause of mortality for humpback whales worldwide (
Along the eastern seaboard of the United States, in the Mid-Atlantic region, is the entrance to the largest estuary in the country, the Chesapeake Bay (
Map of the primary study area, which includes waters in and around the mouth of the Chesapeake Bay off Virginia Beach, Virginia as well as the Port of Virginia and Naval Station Norfolk. Shipping channels are outlined in black and the North Atlantic right whale Seasonal Management Area is shaded. The 37-km Chesapeake Bay Bridge-Tunnel spanning the mouth of the Bay is also shown.
Heat map showing vessel traffic movement in and out of the Chesapeake Bay for the year 2016. The red color indicates the highest density of vessel traffic. Yellow indicates a moderate volume of vessel traffic, and blue indicates the lowest density of vessel traffic. Image provided by
Understanding the occurrence and behavior of humpback whales within the Chesapeake Bay’s high-traffic region is critical to mitigating potentially harmful impacts on the species. Funded through the United States Navy Marine Species Monitoring Program, in 2015 scientists at HDR Inc. began a long-term study of humpback whales that utilize the waters in and around the mouth of Chesapeake Bay to address questions of habitat use and identify potential conflicts associated with anthropogenic activities. Specifically, this project sought to document the behavior and movements of humpback whales, the level of overlap with high-traffic areas, evaluate site fidelity, and examine any discernable movement and habitat use patterns while taking into account age class and gender.
From January 2015 to February 2017, field effort occurred in each of the 3 years during the winter and early spring. Each field season is referred to herein as, e.g., the 2015/2016 season. Surveys were conducted using an 8.2-m fiberglass hybrid-foam-collar vessel that departed from Lynnhaven Inlet in Virginia Beach, Virginia. Field days were chosen based on optimal sea conditions (Beaufort Sea State of 3 or less and swell height less than 2 m) and time of year (November–March), when sightings of humpback whales in the area are most numerous. Field effort was conducted during daylight hours although start and end time varied based on suitable weather. The primary area of interest was in and around the mouth of the Chesapeake Bay (
All baleen whales observed were approached to confirm species and record group size, behavioral state, estimated age class, and GPS location. Age class for humpback whales was approximated by using the 8.2 m vessel as a reference. When approaching broad side to a whale, whales that were estimated to be a similar-size (± approximately 2 m) to the vessel were considered to be juveniles. Those estimated to be >2 m longer than the vessel were categorized as non-juveniles (i.e., either sub-adults or adults). Although subjective, these length estimates are in line with a study by
Argos satellite-linked tags from Wildlife Computers (Redmond, Washington) in the Low Impact Minimally Percutaneous External-electronics Transmitter (LIMPET) configuration (
Using the Argos locations obtained post-filtering, a ‘total distance’ was calculated for each tagged whale by summing the cumulative distances between each Argos location. This distance was then divided by the number of days the tag transmitted to provide an ‘average distance per day’ that an individual whale traveled. The ‘max distance from initial location’ was calculated as the furthest straight line distance between the first location and the farthest location, and the ‘mean distance from initial location’ was calculated as the mean distance of all Argos locations from the first tag location.
For the three SPLASH10-F-333 tags, the number of dives recorded were binned according to pre-determined depths. The dive-depth bins were defined as <5, 5–10, 10–15, 15–20, 20–25, 25–30, 30–35, and 35–50 m. Dive duration was also categorized in pre-determined 30 s time bins when greater than 1 min and less than 7 min. Dives shorter than 1 min and longer than 7 min were their own bin. Given these parameters, a dive to 22 m that lasted 4 min and 10 s would be logged in the 20–25 m depth bin and the 4–4.5 min duration bin. One histogram message was generated daily via Argos that contained the information for each of the dive-depth and dive duration bins.
Photo sorting and matching were performed in ACDSee Pro v. 7 and 9
A hierarchical state-space model (hSSM) was applied to the tag data from all tagged whales in order to gain inference on animal behavior and residency. As with other state-space approaches, the track is smoothed into equal time intervals, with the estimated locations taking Argos location error into account. The R package ‘bsam’ (
To determine the appropriate time interval for the hSSM predictions, the average time between received locations amongst all tags was calculated. This average time was the smallest interval considered between predicted locations in candidate models. Tag deployments shorter than 4 days (
Model diagnostics were examined to ensure that Monte Carlo Markov chains (MCMC) were mixing and that all movement and individual effect parameters were converging as expected. Tracks were examined
The model attempted to assign estimated locations into one of two behavioral states based on the two-dimensional movement of the animal, travel and area restricted search. Travel is characterized by faster movement and fewer direction changes whereas area restricted search (ARS) is characterized by slower movement and frequent turns. Area restricted search is often associated with foraging activity, and in this study behavioral observations of feeding whales, as well as their proximity to prey aggregations, support this assumption. Behavioral states were assigned following
Animal locations, both filtered Argos and modeled hSSM locations, were overlaid with major shipping lanes to determine the degree of overlap as a proxy for risk of ship strike. Initially, the “shipping lane study area” was defined by the Traffic Separation Scheme which defines inbound and outbound commercial traffic boundaries for the Chesapeake Bay. However, as tag locations showed movements out of the defined area but still within other shipping channels around the Bay, the area was extended using additional nautical charts and datasets, including the Traffic Separation Scheme, Coastal Maintained Channels in United States Waters (United States Army Corps of Engineers), and Shipping Fairways, Lanes, and Zones for United States Waters (National Oceanic and Atmospheric Administration) as guidelines. These revised boundaries are, hereafter, collectively referred to as shipping channels and were used to determine the percentage of animal locations that occurred within and outside of them.
Seventy-two field days were conducted between January 02, 2015 and March 21, 2017 (
Summary of field effort and humpback whales sighted, photo-identified, satellite-tagged, and biopsied over three consecutive field seasons from 2015 to 2017.
Season | ||||
2014/2015 | 2015/2016 | 2016/2017 | Totals | |
No. field days | 16 | 27 | 29 | 72 |
First field date | 2-Jan-2015 | 1-Dec-2015 | 1-Nov-2016 | — |
Last field date | 31-May-2015 | 9-May-2016 | 21-Mar-2017 | — |
Total effort (min) | 6,847 | 9,877 | 11,830 | 28,554 |
Total trackline distance (kms) | 1,485 | 2,456 | 2,857 | 6,797 |
Sightings (individuals) | 41 (57) | 96 (136) | 168 (249) | 305 (442) |
Unique IDs | 31 | 37 | 59 | 127 |
Unique IDs seen in previous seasons | N/A | 8 | 20 | 28 |
Satellite tags deployed | 0 | 9 | 26 | 35 |
Biopsy samples collected | 12 | 11 | 28 | 51 |
Survey vessel trackline (gray line) and sightings of baleen whales for all field effort from December 2015 to February 2017, with humpback whales shown as green dots, minke whales shown as purple triangles, and fin whales shown as blue triangles.
All hierarchical state-space model (hSSM) locations (red dots) in the immediate vicinity of the shipping channels at the mouth of the Chesapeake Bay from 33 satellite tagged humpback whales included in the hSSM. Green dots show tag deployment locations from all 35 tagged whales.
Based on size estimates, all tagged humpback whales were judged to be juveniles or sub-adults and none were associated with a calf. Of the 51 biopsies obtained, 30 were collected from whales that were satellite tagged. Gender analysis was performed on a subset (
Details of satellite tag deployments and results from GIS and hSSM analysis of 35 humpback whales from 2015 to 2017.
PTT ID | Age-class | Sex | Date deployed | # days transmitted | Number of locations post-filtering (Argos/hSSM) | Within shipping lane (%) (hSSM) | Total distance (Km) | Mean distance (Km)/day | Max distance from initial location (Km) | Mean distance from initial location (Km) |
157916 | Juvenile | Male | 12/7/2015 | 14.2 | 212/114 | 16.7 | 714 | 50.3 | 42 | 12 |
157915 | Juvenile | Unknown | 12/9/2015 | 10.5 | 163/85 | 25.9 | 611 | 58.2 | 83 | 23 |
157917 | Juvenile | Male | 12/9/2015 | 12.1 | 149/96 | 11.5 | 786 | 65.0 | 506 | 104 |
157918 | Juvenile | Female | 12/10/2015 | 5.6 | 76/45 | 15.6 | 252 | 45.0 | 21 | 8 |
157919 | Juvenile | Male | 12/20/2015 | 11.5 | 163/93 | 29.0 | 497 | 43.2 | 13 | 5 |
157920 | Sub-adult | Male | 12/20/2015 | 17.6 | 210/142 | 2.8 | 943 | 53.6 | 242 | 81 |
157921 | Juvenile | Male | 2/6/2016 | 21.4 | 231/171 | 41.5 | 1360 | 63.6 | 344 | 40 |
157922 | Juvenile | Male | 2/6/2016 | 3.3 | 10/N/A | – | 219 | 66.4 | 115 | 34 |
157923 | Juvenile | Male | 2/9/2016 | 20.7 | 305/166 | 39.8 | 1139 | 55.0 | 189 | 22 |
158676 | Sub-adult | Female | 11/1/2016 | 2.7 | 62/N/A | – | 238 | 88.1 | 32 | 15 |
158677 | Sub-adult | Male | 11/1/2016 | 6.7 | 163/54 | 11.1 | 722 | 107.8 | 212 | 55 |
158678 | Sub-adult | Male | 11/1/2016 | 6.0 | 144/48 | 4.2 | 650 | 108.3 | 136 | 34 |
158675 | Sub-adult | Female | 11/3/2016 | 3.5 | 211/28 | 14.3 | 885 | 105.4 | 205 | 71 |
158679 | Sub-adult | Male | 11/3/2016 | 8.4 | 78.67 | 10.4 | 361 | 103.1 | 158 | 62 |
158680 | Sub-adult | Female | 11/18/2016 | 8.4 | 215/68 | 5.9 | 465 | 55.4 | 120 | 51 |
158681 | Juvenile | Female | 12/13/2016 | 9.3 | 253/75 | 44.0 | 536 | 57.6 | 20 | 8 |
158682 | Juvenile | Female | 12/21/2016 | 8.4 | 206/67 | 25.4 | 494 | 58.8 | 29 | 12 |
158683 | Juvenile | Female | 12/21/2016 | 12.9 | 292/103 | 35.9 | 727 | 56.4 | 21 | 9 |
166671 | Juvenile | Unknown | 12/28/2016 | 19.6 | 498/157 | 33.1 | 1210 | 61.7 | 49 | 13 |
166672 | Juvenile | Female | 12/28/2016 | 7.2 | 160/58 | 37.9 | 431 | 59.9 | 24 | 8 |
166673 | Juvenile | Unknown | 1/1/2017 | 38.7 | 724/310 | 16.5 | 1868 | 48.3 | 94 | 26 |
166674 | Juvenile | Unknown | 1/5/2017 | 19.2 | 319/152 | 10.5 | 1386 | 72.2 | 158 | 41 |
166675 | Juvenile | Male | 1/11/2017 | 10.0 | 84/N/A | – | 234 | 23.4 | 53 | 20 |
166676 | Juvenile | Unknown | 1/16/2017 | 9.2 | 254/74 | 35.1 | 629 | 68.4 | 104 | 19 |
166677 | Juvenile | Unknown | 1/19/2017 | 11.5 | 265/93 | 6.5 | 759 | 66.0 | 111 | 41 |
166678 | Juvenile | Unknown | 1/19/2017 | 18.4 | 487/147 | 61.9 | 1072 | 58.3 | 40 | 13 |
166680 | Juvenile | Unknown | 1/21/2017 | 24.7 | 705/197 | 2.0 | 1694 | 68.6 | 179 | 97 |
166679 | Juvenile | Unknown | 1/25/2017 | 17.2 | 471/138 | 58.0 | 1066 | 62.0 | 26 | 8 |
166681 | Sub-adult | Unknown | 2/1/2017 | 11.6 | 303/93 | 52.7 | 836 | 72.1 | 53 | 8 |
166682 | Juvenile | Unknown | 2/2/2017 | 21.9 | 547/175 | 51.4 | 1541 | 70.4 | 41 | 12 |
166683 | Juvenile | Unknown | 2/2/2017 | 19.2 | 512/153 | 43.1 | 1106 | 57.6 | 39 | 9 |
166685 | Juvenile | Unknown | 2/14/2017 | 43.8 | 862/350 | 9.1 | 2754 | 62.9 | 238 | 128 |
168686 | Juvenile | Unknown | 2/17/2017 | 7.6 | 184/66 | 10.6 | 422 | 55.5 | 66 | 27 |
168687 | Juvenile | Unknown | 2/17/2017 | 10.5 | 200/88 | 21.6 | 656 | 62.5 | 40 | 11 |
168688 | Juvenile | Unknown | 2/24/2017 | 5.2 | 99/41 | 48.8 | 338 | 65.0 | 24 | 13 |
The number of Argos locations obtained post-filtering ranged from 10 to 862 (mean = 280) per tag (
All 35 tagged whales had filtered Argos locations within the shipping channels at the mouth of Chesapeake Bay. Approximately one quarter of all locations were within the shipping channels (
Fifteen of the 26 (57.7%) tagged animals from the 2016/2017 season had Argos locations inside the Chesapeake Bay [west of the Chesapeake Bay Bridge-Tunnel (CBBT), a 37-km man-made structure that spans the mouth of the Chesapeake Bay with portions above and below water] (
Movements out of the primary study area included offshore travel to the north (New York), south (North Carolina), and east (offshore to 178 km), where whales spent time in both the shallow waters over the continental shelf as well as deeper waters (>3,100 m) east of the continental shelf break (
Mean predicted behavioral state from the hSSM for 33 tagged whales along the eastern seaboard from Cape Hatteras, North Carolina to Long Island, New York, showing travel (red dots), area-restricted search (purple dots), and indeterminate behavior (orange dots).
A total of 9,781 dives were recorded from the three SPLASH tags. Nearly all (96.4%) dives were to depths of 20 m or less, with the majority (87.2%) to 15 m or less (
Total number of dives (100×) for three satellite-tagged humpback whales (identified by PTT ID) grouped by 5-m depth bins. Maximum large-ship draft is noted by the black line.
Total number of dives (100×) for three satellite-tagged humpback whales (identified by PTT ID) grouped into 1-min dive duration bins.
Re-sightings of humpback whales were noted both within- and between-seasons. Of the 106 cataloged individuals, 66 were seen on more than one occasion (excluding same-day re-sightings). Of those seen more than once, within-season re-sightings (from the 1st day observed to the last day observed) ranged from 1 to 94 days (mean = 29; median = 25). Eight individuals were re-sighted between the 2014/2015 and 2015/2016 seasons, and 20 individuals observed during the 2016/2017 season were seen in previous seasons. Using photographs obtained from the cataloging effort, obvious evidence of vessel interaction, such as propeller scarring, was apparent on at least nine of the 106 (8.5%) cataloged humpback whales.
Two tags were omitted from the hSSM analyses completely (157922 and 158676) due to deployment durations of less than 4 days, a low number of reported locations, and no discernable behavior. On average 62 min passed between received locations, with the maximum gap being almost 1 day. As such, 1 h was the minimum time interval considered for an hSSM. However, the finest temporal scale model that converged successfully was a 3-h model. The selected model converged using 30,000 burn in samples and 15,000 samples. The 15,000 samples were thinned to retain 1,000 in total. A qualitative review of the tracks did not show excessive smoothing between Argos locations, with one exception. One tag, 166675, was also removed from the analysis after reviewing the results and the hierarchical model was rerun without it. This tag had a different duty cycle and few reported locations with long gaps between, which resulted in a modeled track that was artificially over-smoothed. Diagnostics for the updated model performed similarly to the one with the dropped tag. Overall the final model performed acceptably: all parameters converged, MCMCs were mixing, and autocorrelation between chains was low.
Visual inspection of hSMM results was also used to validate the outputs. Generally, the model predicted the behavior that would be expected from reviewing the Argos data qualitatively. Despite the study area being a complex estuarine system, location predictions did not cut across land significantly; as such, no locations were dropped from the model output. Indeterminate locations were most often found as animals were transitioning between traveling and ARS behaviors. Of 3,714 modeled locations, 458 (12.3%) were identified as traveling, 211 (5.7%) were indeterminate, and the remaining 3,045 (82.0%) were identified as ARS (
On January 02, 2016 a humpback whale was observed and photographed within the shipping channels without any apparent injuries (
A second humpback whale was first observed and tagged (157919) on December 20, 2015 (
A third humpback whale was first observed and tagged (166675) on January 11, 2017 (
Results from satellite tagging and photo-ID during 3 years of effort show both within-season and between-season site fidelity in the study area for individual whales and a high level of occurrence within the shipping channels. Because Argos satellite locations have error associated with them, ranging from <250 m to >1,500 m (
The hSSM analysis provided valuable insight regarding the behavior of all but the shortest (or sparsely reporting) tagged humpback whales in this study. Humpback whales showed variable movement patterns, though the most common was ARS centered around the mouth of Chesapeake Bay, highlighting that this is an important foraging area for this population. This is where most of the tags were deployed and it may also be that tags were shed before significant movement was undertaken. Other movement strategies observed when examining all tracks included looping down near the Outer Banks of North Carolina to presumably feed and then returning north, foraging further inside the bay, and long-distance directed movements northwards along the coast and the shelf break before engaging in ARS in other locations.
Because tag deployments were on the order of days to weeks, it is important to take into account the potential for tagging bias with these results. Whales may be more likely to occur in close proximity to where they were tagged, at least initially (e.g.,
Many humpback whale sightings, and subsequently tag locations, occurred within the deeper shipping channels suggesting these may be areas of preferred prey aggregations. A fishery for Atlantic menhaden (
Dive data from the three SPLASH10-F-333 tagged whales revealed that the majority of dives were to depths of 15 m or less. The current maximum draft for commercial and military vessels extends to 15 m. The spatial overlap of humpback whales in this study area with transiting ships, results in an increased likelihood for interactions (
During the winter months, when humpback whales are most likely present, large ships moving into and out of the Chesapeake Bay are required to reduce their speed to 10 knots in order to be compliant with the North Atlantic right whale SMA guidelines (
Approximately half of the humpback whales examined to date as part of the UME had evidence of human interaction, either due to ship strike or entanglement (
In total, nine of the 106 (8.5%) humpback whales in our humpback whale catalog have scars or injuries indicative of propeller or vessel strikes. While it is impossible to conclude if these injuries occurred outside of the study area, the evidence from this study highlights different instances where humpback whales were observed in the study area without injuries and re-sighted within the same season with vessel-related injuries. Such examples support the notion that those injuries likely occurred in the primary study area near the mouth of the Chesapeake Bay and suggests that animals are at an increased risk of deleterious interactions with localized shipping traffic.
More than three-quarters of the humpback whales identified and satellite tagged during the first 3 years of this study were estimated to be juveniles. The large percentage of juveniles observed matches both historic stranding data (e.g.,
Interactions with vessels, both large and small, are a significant cause for concern for humpback as well as other baleen whale species encountered in the study area. Although the satellite tagging effort focused on humpback whales, other baleen whale species, including minke whales and ESA-listed fin whales, were also documented in the study area. ESA-listed North Atlantic right whales are also known to occur near the mouth of the Chesapeake Bay (
While much of the tagging data corroborates sighting location ‘hot spots’ in and around the shipping channels, the amount of time some tagged individuals spent west of the CBBT was somewhat unexpected. This is an area where live observations of humpback whales have not previously been reported in the literature, and only occasional sightings have been anecdotally reported by local fisherman or tour operators. The extensive network of bridge pilings appear to create a physical barrier with regards to passage by whales to waters west of the CBBT. Observations of whales passing through the unobstructed non-pile shipping channel openings directly over the CBBT tunnels are not unexpected given their preference to remain in the deeper channels to forage. Although less field effort was conducted in waters west of the CBBT, it should be considered an area of interest in future years given the high traffic rate of large vessels, reduced speed restrictions, and extent of marine-based military training exercises occurring in this part of the Bay. Increased presence of humpback whales west of the CBBT may be attributed to a combination of possible factors, including, but not limited to: a short-term distributional shift related to overall oceanographic conditions causing prey to become more concentrated farther into the Bay than in previous years, better documentation of whale presence through increased field effort or an increased number of deployed satellite tags, or simply an overall increase in the number of humpback whales in the study area.
The number of sightings of humpback whales and other baleen whales (including ESA-listed fin whales), as well as the level of interaction between whales and vessel traffic to-date, support the need for further documenting habitat use and movement patterns in this region. Satellite-tag data have signified that the mouth of the Chesapeake Bay is an important habitat for humpback whales during winter months. The hSSM results suggest that many of the modeled locations centered at the mouth of the Bay represent foraging behavior for these whales, which is further supported from visual observations and stable isotope analyses. This segment of the population clearly engages in diverse feeding and movement strategies, which also needs to be taken into account when mitigating anthropogenic impacts and determining effective management actions. At the time of deployments, the SPLASH10-F-333 tags used in this study were programed to collect only binned depth data. Research is ongoing, and future tagging effort will incorporate behavioral dive profiles to give a more detailed picture of how humpback whales spend time beneath the shallow waters of the Chesapeake Bay. A small unmanned aerial system has also been added to the study with the goal of obtaining more precise length estimates and therefore improving and validating age class estimations. Future hSSM analyses will focus on temporal patterns of use, increasing sample size with more tag deployments, simulating longer tracks, and exploring individual space use further. Additional United States Navy-funded collaborative efforts will also involve deploying digital acoustic recording tags to collect information on received levels of ship noise, as well as determining behavioral states and assess possible avoidance responses. All of this information will provide a better understanding of the occurrence and behavior of humpback whales within these heavily transited waters.
The waters around the mouth of the Chesapeake Bay are a busy area for transiting commercial and military ships, as well as recreational boats. Seasonal speed restrictions established as part of the North Atlantic right whale SMA limit the speed of large vessels only at the mouth of the Bay, but speed restrictions are not in place in other areas that humpback whales actively utilize nor do they pertain to vessels <19.8 m. Extending the SMA farther into the Bay and farther offshore has the potential to improve protection for humpback whales, as well as other baleen whale species utilizing this habitat.
Data generated by this study are represented or included as summarized data in the article/supplementary material. Sighting data is available through OBIS SEAMAP and tag location data are available for viewing through both Movebank and the Animal Telemetry Network.
All tagging and survey methods were conducted under a scientific research permit #16239 issued to Dan Engelhaupt by the National Marine Fisheries Service under the Marine Mammal Protection Act. Prior to tagging, procedures were reviewed and approved by an Institutional Animal Care and Use Committee as part of the Animal Welfare Act.
JA, DE, and AE: field work, analysis, and writing. AD: analysis and writing. TP, MR, and JB: field work and writing.
JA, DE, and MR were employed by HDR Inc. AE was self-employed via Amy Engelhaupt Consulting. AD was self-employed via CheloniData. TP was self-employed. JB was employed by NAVFAC.
We thank personnel from Naval Facilities Engineering Command for their assistance in the field, including Jackie Bort Thornton, Danielle Jones, Cara Hotchkin, Brittany Bartlett, and Jamie Gormley. Will Cioffi of Duke University performed the humpback whale gender analysis. We thank Alexis Rabon and Sarah Mallette from the Virginia Aquarium along with the captains and crew of the Atlantic Explorer, as well as Kristin Rayfield and the captains and crew of Rudee Flipper Tours for coordination of real-time humpback whale sightings. Grant Miller-Francisco assisted with GIS. Ladd Irvine, Aldo Pacheco, and Bob Kenney provided valuable reviews of this manuscript. We thank the Wildlife Computers team for product support and assistance. All research activities were conducted under National Marine Fisheries Service Scientific Permit 16239 held by DE, with the exception of tagging effort in December 2015 which was conducted under Scientific Permit 14450 held by Keith Mullin of Southeast Fisheries Science Center.