Heidi Pearson, PhD is Associate Professor of Marine Biology

Recent Submissions

  • Assessing the dynamics of common dolphin (Delphinus delphis) mother-calf pairs along the south coast of Portugal using unmanned aerial vehicles

    Castro, Joana; Cid, André; Quirin, Alicia; Matos, Fábio L.; Rosa, Rui; Pearson, Heidi (John Wiley & Sons, Inc., 2024-02-13)
    Maternal grouping dynamics involve trade-offs between: (1) infant protection from predation (predation hypothesis), (2) infant protection from male harassment (infant safety hypothesis), and (3) reducing scramble competition for prey resources (foraging-type scramble competition hypothesis). Using unmanned aerial vehicles, we assessed grouping dynamics in common dolphin (Delphinus delphis) groups containing mother-calf pairs to address these hypotheses. We analyzed social aspects and structural group elements using generalized additive mixed models and modeled group formation using multinomial generalized estimating equations. Calf proportion was higher in very compact groups and in groups of 10–20 individuals but decreased in larger groups. The frequency of socio-sexual behaviors increased in larger groups and decreased in groups with higher calf proportion. Calf distance to its nearest neighbor decreased with increasing group size and cohesion. With a higher proportion of calves, scatter (versus parallel) formation was less frequent. A calf's nearest neighbor was most often (55.4%) a nonmother. Calves showed a preference for being in the front center of the group. These results offer strong support for the predation and infant safety hypotheses and partial support for the foraging-type scramble competition hypothesis. This work provides insight into the adaptive function of maternal strategies in a small delphinid.
  • Dusky dolphin (Lagenorhynchus obscurus) habitat use in a mussel farming region and changes over time

    Piwetz, Sarah; Pearson, Heidi; Honkus, Krysta A.; Würsig, Bernd (Taylor & Francis, 2024-04-01)
    Information on marine mammal habitat use in coastal areas can provide a better understanding of anthropogenic effects on species. Admiralty Bay, New Zealand has extensive near-shore mussel farms and is an important dusky dolphin (Lagenorhynchus obscurus) foraging habitat. Prior dusky dolphin research indicated a declining trend in regional abundance from the late 1990s to mid-2000s. We describe dusky dolphin behaviour, habitat patch use and movement patterns in Admiralty Bay in 2011–2012 and compare findings to previous research to capture long-term trends. Sampling methods included small-boat group follows and photo-identification and shore-based theodolite tracking. Dolphin encounter rate, mean group size, and individual resighting rate showed a negative trend from previous years. Coordinated prey ball herding, a foraging technique documented in previous years, was rarely observed during this study. Dolphins were more likely to forage near farms (excluding specialised prey herding), though they seldom entered farms. Near shore, swimming speed was slower, reorientation rate was higher, and linearity was lower in the presence of farms than in their absence. This research builds upon prior studies, suggesting a continued decline in dusky dolphin presence, and highlights differences in habitat patch use in a human-altered ecosystem.
  • Use of hormones in assessing reproductive physiology of humpback whales (Megaptera novaeangliae) from Juneau, Alaska

    Atkinson, S.; Melica, V.; Teerlink, S.; Mashburn, K.; Moran, J.; Pearson, Heidi (Elsevier, 2023)
    Humpback whales (Megaptera novaeangliae) in Southeast Alaska have been studied for over 50 years, and are largely considered a recovery success since the cessation of commercial whaling. Reproductive physiology is an important factor to consider in studying population health and can provide important insights into the drivers contributing to population abundance fluctuations. Validated assays for progesterone and testosterone were used on blubber biopsies from humpback whales (N = 33 whales, 71 samples) near Juneau, Alaska, in 2020 and 2021. Long-term sighting histories were used to confirm detected pregnancies with calf sightings the following year. Blubber samples were divided into two seasonal bins (early and late summer). Pregnant females sampled in both early and late summer of both 2020 and 2021 showed elevated progesterone concentrations compared to other reproductive states (p < 0.05). Progesterone concentrations in adult male whales (0.3 ± 0.2 ng/g) were not significantly different from lactating or resting female whales. Blubber testosterone concentrations in adult male humpback whales ranged from 0.05 to 1.1 ng/g, and mean concentrations were approximately double those of female whales in any reproductive state. Pregnancy was detected in 5 of 11 and 4 of 9 adult females in 2020 and 2021 respectively, yielding summer season pregnancy rates for sexually mature females at 0.45, and 0.44, respectively. Calving rates were 0.36 and 0.22 in 2020 and 2021, respectively, and the annual growth rate for this subpopulation was calculated at 2.6 % per annum. One female had successful pregnancies for four consecutive years. These results demonstrate the synergistic value of combining immunoreactive assays and long-term sighting histories to further knowledge of reproductive physiology in individual humpback whales, which can be expanded to assessing the health of a population or ecosystem.
  • Macronutrient composition of sea otter diet with respect to recolonization, life history, and season in southern Southeast Alaska

    LaRoche, Nicole; King, Sydney; Fergusson, Emily; Eckert, Ginny; Pearson, Heidi (John Wiley & Sons, Inc., 2023-05-02)
    The sea otter (Enhydra lutris) population of Southeast Alaska has been growing at a higher rate than other regions along the Pacific coast. While good for the recovery of this endangered species, rapid population growth of this apex predator can create a human-wildlife conflict, negatively impacting commercial and subsistence fishing. Previous foraging studies throughout the sea otter range have shown they will reduce invertebrate prey biomass when recolonizing an area. The goal of this study was to examine and quantify the energy content of sea otter diets through direct foraging observations and prey collection. Our study area, Prince of Wales Island in southern Southeast Alaska, exhibits a gradient of sea otter recolonization, thus providing a natural experiment to test diet change in regions with different recolonization histories. Sea otter prey items were collected in three seasons (spring, summer, and winter) to measure caloric value and lipid and protein content. We observed 3523 sea otter dives during the spring and summer. A majority of the sea otter diet consisted of clams. Sea otters in newly recolonized areas had lower diet diversity, higher energetic intake rates (EIR, kcal/min), and prey had higher energy content (kcal/g). Females with pups had the highest diet diversity and the lowest EIR. Sea otter EIR were higher in the fall and winter vs. spring and summer. Sea cucumber energy and lipid content appeared to correspond with times when sea otters consumed the highest proportion of sea cucumbers. These caloric variations are an important component of understanding ecosystem-level effects sea otters have in the nearshore environment.
  • A deep learning approach to photo–identification demonstrates high performance on two dozen cetacean species

    Patton, Philip T.; Cheeseman, Ted; Abe, Kenshin; Yamaguchi, Taiki; Reade, Walter; Southerland, Ken; Howard, Addison; Oleson, Erin M.; Allen, Jason B.; Ashe, Erin; et al. (John Wiley & Sons, Inc., 2023-07-13)
    1. Researchers can investigate many aspects of animal ecology through noninvasive photo–identification. Photo–identification is becoming more efficient as matching individuals between photos is increasingly automated. However, the convolutional neural network models that have facilitated this change need many training images to generalize well. As a result, they have often been developed for individual species that meet this threshold. These single-species methods might underperform, as they ignore potential similarities in identifying characteristics and the photo–identification process among species. 2. In this paper, we introduce a multi-species photo–identification model based on a state-of-the-art method in human facial recognition, the ArcFace classification head. Our model uses two such heads to jointly classify species and identities, allowing species to share information and parameters within the network. As a demonstration, we trained this model with 50,796 images from 39 catalogues of 24 cetacean species, evaluating its predictive performance on 21,192 test images from the same catalogues. We further evaluated its predictive performance with two external catalogues entirely composed of identities that the model did not see during training. 3. The model achieved a mean average precision (MAP) of 0.869 on the test set. Of these, 10 catalogues representing seven species achieved a MAP score over 0.95. For some species, there was notable variation in performance among catalogues, largely explained by variation in photo quality. Finally, the model appeared to generalize well, with the two external catalogues scoring similarly to their species' counterparts in the larger test set. 4. From our cetacean application, we provide a list of recommendations for potential users of this model, focusing on those with cetacean photo–identification catalogues. For example, users with high quality images of animals identified by dorsal nicks and notches should expect near optimal performance. Users can expect decreasing performance for catalogues with higher proportions of indistinct individuals or poor quality photos. Finally, we note that this model is currently freely available as code in a GitHub repository and as a graphical user interface, with additional functionality for collaborative data management, via Happywhale.com.
  • Bellwethers of change: population modelling of North Pacific humpback whales from 2002 through 2021 reveals shift from recovery to climate response

    Cheeseman, Ted; Barlow, Jay; Acebes, Jo Marie; Audley, Katherina; Bejder, Lars; Birdsall, Catlin; Bracamontes, O. S.; Bradford, Amanda L.; Byington, Josie; Calambokidis, John; et al. (The Royal Society, 2024-02-28)
    For the 40 years after the end of commercial whaling in 1976, humpback whale populations in the North Pacific Ocean exhibited a prolonged period of recovery. Using mark–recapture methods on the largest individual photo-identification dataset ever assembled for a cetacean, we estimated annual ocean-basin-wide abundance for the species from 2002 through 2021. Trends in annual estimates describe strong post-whaling era population recovery from 16 875 (± 5955) in 2002 to a peak abundance estimate of 33 488 (± 4455) in 2012. An apparent 20% decline from 2012 to 2021, 33 488 (± 4455) to 26 662 (± 4192), suggests the population abruptly reached carrying capacity due to loss of prey resources. This was particularly evident for humpback whales wintering in Hawai‘i, where, by 2021, estimated abundance had declined by 34% from a peak in 2013, down to abundance levels previously seen in 2006, and contrasted to an absence of decline in Mainland Mexico breeding humpbacks. The strongest marine heatwave recorded globally to date during the 2014–2016 period appeared to have altered the course of species recovery, with enduring effects. Extending this time series will allow humpback whales to serve as an indicator species for the ecosystem in the face of a changing climate.
  • Biologically important areas II for cetaceans within U.S. and adjacent waters - Gulf of Alaska Region

    Wild, Lauren A.; Riley, Heather; Pearson, Heidi C.; Gabriele, Christine M.; Neilson, Janet L.; Szabo, Andy; Moran, John; Straley, Janice M.; DeLand, Sarah (Frontiers Media S. A., 2023-05-05)
    We delineated and scored Biologically Important Areas (BIAs) for cetacean species in the Gulf of Alaska region. BIAs represent areas and times in which cetaceans are known to concentrate for activities related to reproduction, feeding, and migration, and also the known ranges of small and resident populations. This National Oceanic and Atmospheric Association (NOAA)-led effort uses structured expert elicitation principles to build upon the first version of NOAA’s BIAs for cetaceans. Supporting evidence for these BIAs came from aerial-, land-, and vessel-based surveys; satellite-tagging data; passive acoustic monitoring; Indigenous knowledge; photo-identification data; and/or prey studies. A total of 20 BIAs were identified, delineated, and scored for six species: beluga whale (Delphinapterus leucas), fin whale (Balaenoptera physalus), gray whale (Eschrichtius robustus), humpback whale (Megaptera novaeangliae), North Pacific right whale (Eubalaena japonica), and sperm whale (Physeter macrocephalus). Of the 20 total BIAs, there were two small and resident populations, one migratory, and 17 feeding areas; no reproductive BIAs were identified. An additional five watch list areas were identified, a new feature to the second version of BIAs. In addition to more comprehensive narratives and maps, the BIA II products improve upon the first version by creating metadata tables and incorporating a scoring and labeling system which improves quantification and standardization of BIAs within and across regions. BIAs are compilations of the best available science and have no inherent regulatory authority. They have been used by NOAA, other federal agencies, and the public to support planning and marine mammal impact assessments, and to inform the development of conservation measures for cetaceans.
  • A collaborative and near‑comprehensive North Pacifc humpback whale photo‑ID dataset

    Cheeseman, T.; Southerland, Ken; Acebes, Jo Marie; Audley, Katherina; Barlow, Jay; Bejder, Lars; Birdsall, Caitlin; Bradford, Amanda L.; Byington, Josie K.; Calambokidis, John; et al. (Springer Nature Limited, 2023-06-23)
    We present an ocean-basin-scale dataset that includes tail fuke photographic identifcation (photo-ID) and encounter data for most living individual humpback whales (Megaptera novaeangliae) in the North Pacifc Ocean. The dataset was built through a broad collaboration combining 39 separate curated photo-ID catalogs, supplemented with community science data. Data from throughout the North Pacifc were aggregated into 13 regions, including six breeding regions, six feeding regions, and one migratory corridor. All images were compared with minimal pre-processing using a recently developed image recognition algorithm based on machine learning through artifcial intelligence; this system is capable of rapidly detecting matches between individuals with an estimated 97–99% accuracy. For the 2001–2021 study period, a total of 27,956 unique individuals were documented in 157,350 encounters. Each individual was encountered, on average, in 5.6 sampling periods (i.e., breeding and feeding seasons), with an annual average of 87% of whales encountered in more than one season. The combined dataset and image recognition tool represents a living and accessible resource for collaborative, basin-wide studies of a keystone marine mammal in a time of rapid ecological change.
  • Climate Soundscapes

    Sandoval, Artemio Katooneh; Pearson, Heidi C. (Con Brio Chamber Series, 2022-11-19)
    Con Brio Chamber Series Presents CLIMATE SOUNDSCAPES Friday, November 18, 2022, 7:30 PM Kunéix Hidi Northern Light United Church Saturday, November 19, 2022, 2:00 PM Atrium at the APK State Library, Archives and Museum
  • Whales in the carbon cycle: can recovery remove carbon dioxide?

    Pearson, Heidi C.; Savoca, Matthew S.; Costa, Daniel P.; Lomas, Michael W.; Molita, Renato; Pershing, Andrew J.; Smith, Craig R.; Villaseñor-Derbez, Juan Carlos; Wing, Stephen R.; Roman, Joe (Elsevier Ltd., 2022-03)
    The great whales (baleen and sperm whales), through their massive size and wide distribution, influence ecosystem and carbon dynamics. Whales directly store carbon in their biomass and contribute to carbon export through sinking carcasses. Whale excreta may stimulate phytoplankton growth and capture atmospheric CO2; such indirect pathways represent the greatest potential for whale-carbon sequestration but are poorly understood. We quantify the carbon values of whales while recognizing the numerous ecosystem, cultural, and moral motivations to protect them. We also propose a framework to quantify the economic value of whale carbon as populations change over time. Finally, we suggest research to address key unknowns (e.g., bioavailability of whale derived nutrients to phytoplankton, species- and region-specific variability in whale carbon contributions).
  • Integral functions of marine vertebrates in the ocean carbon cycle and climate change mitigation

    Martin, A.H.; Pearson, Heidi C.; Saba, G.K.; Olsen, E.M. (Cell Press, 2021-05-21)
    In the last decade, the ocean has absorbed a quarter of the Earth’s greenhouse gas emissions through the carbon (C) cycle, a naturally occurring process. Aspects of the ocean C cycle are now being incorporated into climate change mitigation and adaptation plans. Currently, too little is known about marine vertebrate C functions for their inclusion in policies. Fortunately, marine vertebrate biology, behavior, and ecology through the lens of C and nutrient cycling and flux is an emerging area of research that is rich in existing data. This review uses literature and trusted data sources to describe marine vertebrate C interactions, provides quantification where possible, and highlights knowledge gaps. Implications of better understanding the integral functions of marine vertebrates in the ocean C cycle include the need for consideration of these functions both in policies on nature-based climate change mitigation and adaptation, and in management of marine vertebrate populations.
  • Assessing the Behavioural Responses of Small Cetaceans to Unmanned Aerial Vehicles

    Castro, J.; Borges, F. O.; Cid, A.; Laborde, M. I.; Rosa, R.; Pearson, Heidi C. (Multidisciplinary Digital Publishing Institute, 2021-01-05)
    Unmanned Aerial Vehicles (UAVs), or drones, have recently emerged as a relatively affordable and accessible method for studying wildlife. Vertical Take-off and Landing (VTOL) UAVs are appropriate for morphometric, behavioural, abundance and demographic studies of marine mammals, providing a stable, nonintrusive and highly manoeuvrable platform. Previous studies using VTOL UAVs have been conducted on various marine mammal species, but specific studies regarding behavioural responses to these devices are limited and scarce. The aim of this study was to evaluate the immediate behavioural responses of common (Delphinus delphis) and bottlenose (Tursiops truncatus) dolphins to a VTOL UAV flown at different altitudes. A multirotor (quadcopter) UAV with an attached GoPro camera was used. Once a dolphin group was located, the UAV was flown at a starting height of 50 m directly above the group, subsequently descending 5 m every 30 s until reaching 5 m. We assessed three behavioural responses to a VTOL UAV at different heights: (i) direction changes, (ii) swimming speed and (iii) diving. Responses by D. delphis (n = 15) and T. truncatus (n = 10) groups were analysed separately. There were no significant responses of T. truncatus to any of the studied variables. For D. delphis, however, there were statistically significant changes in direction when the UAV was flown at a height of 5 m. Our results indicate that UAVs do not induce immediate behavioural responses in common or bottlenose dolphins when flown at heights > 5 m, demonstrating that the use of VTOL UAVs to study dolphins has minimal impact on the animals. However, we advise the use of the precautionary principle when interpreting these results as characteristics of this study site (e.g., high whale-watching activity) may have habituated dolphins to anthropogenic disturbance.
  • Behavioral observations and stable isotopes reveal high individual variation and little seasonal variation in sea otter diets in Southeast Alaska

    LaRoche, Nicole; King, Sydney L.; Rogers, Matthew C.; Eckert, Ginny L.; Pearson, Heidi C. (Marine Ecology Progress Series, 2021-10-28)
    Two complementary approaches were used to assess year-round variation in the diet of sea otters Enhydra lutris around Prince of Wales Island (POW) in southern Southeast Alaska, a region characterized by mixed-bottom habitat. We observed sea otters foraging to determine diet composition during the spring and summer. Then, we obtained sea otter vibrissae, which record temporal foraging patterns as they grow, from subsistence hunters to identify year-round changes in sea otter diets via stable isotope analysis of carbon (δ13C) and nitrogen (δ15N). We compared the stable isotopes from sea otter vibrissae and sea otter prey items that were collected during spring, summer, and winter. Overall, year-round sea otter diet estimates from stable isotope signatures and visual observations from spring and summer were dominated by clams in terms of biomass, with butter clams Saxidomus gigantea the most common clam species seen during visual observations. Our results indicate that these sea otters, when considered together at a regional level around POW, do not exhibit shifts in the main prey source by season or location. However, sea otter diets identified by stable isotopes had a strong individual-level variation. Behavioral variation among individual sea otters may be a primary driving factor in diet composition. This study provides quantitative diet composition data for modeling predictions of invertebrate population estimates that may aid in the future management of shellfisheries and subsistence hunting and the development of co-management strategies for this protected species.
  • Examining the Role of Marine Mammals and Seabirds in Southeast Alaska’s Marine Ecosystem Dynamics

    Rhodes-Reese, Melissa; Clay, David; Cunningham, Curry; Moriles-Miller, Janet; Reese, Cheryl; Roman, Joe; Warren, Joseph D.; Pearson, Heidi C. (Frontiers Research Foundation, 2021-12-22)
    Primary producers are the foundation of marine food webs and require reliable nutrient sources to maintain their important role with ecosystems. While marine mammals and seabirds can play critical roles in marine nutrient cycling, their contributions are often overlooked. The fjord systems of Southeast Alaska support a high diversity of marine mammals and seabirds in addition to some of the most valuable fisheries in the US. Nonetheless, there is still relatively little known about nutrient sources and fluxes in this region which is a critical component of fisheries management. The goal of our study was to advance knowledge of the role of mammals and seabirds in marine nutrient cycling and to understand how changing marine mammal and seabird populations may alter ecosystem dynamics. We analyzed nutrient levels in marine mammal scat, seabird guano, and seawater samples collected in Berners Bay, Southeast Alaska, to determine the influence of marine mammals and seabirds on nearshore nutrient concentrations. Utilizing qualitative network models (QNMs), we then examined how a simulated Berners Bay ecosystem would respond to an increase in marine mammals, seabirds, and nutrients. Researchers are increasingly utilizing QNMs as a first step in the development of ecosystem-based fisheries management plans as their adaptable nature is well suited to address rapidly changing climatic conditions. Our direct nutrient measurements and QNM results indicate that marine mammals and seabirds have the potential to provide substantial contributions to marine nutrient concentrations in the region and that these valuable ecosystem services should not be overlooked.
  • Recycling Attitudes and Behavior among a Clinic-Based Sample of Low-Income Hispanic Women in Southeast Texas

    Pearson, Heidi C.; Dawson, Lauren, N.; Breitkopf, Carmen Radecki (2012-04-06)
    We examined attitudes and behavior surrounding voluntary recycling in a population of low-income Hispanic women. Participants (N = 1,512) 18–55 years of age completed a self-report survey and responded to questions regarding household recycling behavior, recycling knowledge, recycling beliefs, potential barriers to recycling (transportation mode, time), acculturation, demographic characteristics (age, income, employment, marital status, education, number of children, birth country), and social desirability. Forty-six percent of participants (n = 810) indicated that they or someone else in their household recycled. In a logistic regression model controlling for social desirability, recycling behavior was related to increased age (P,0.05), lower acculturation (P,0.01), knowing what to recycle (P,0.01), knowing that recycling saves landfill space (P,0.05), and disagreeing that recycling takes too much time (P,0.001). A Sobel test revealed that acculturation mediated the relationship between recycling knowledge and recycling behavior (P,0.05). We offer new information on recycling behavior among Hispanic women and highlight the need for educational outreach and intervention strategies to increase recycling behavior within this understudied population.

    Schuler, Alicia, R.; Pearson, Heidi C. (Cognizant, LLC, 2020-01-03)
    An increasing number of visitors to Juneau, AK, alongside a predictable population of humpback whales (Megaptera novaeangliae), has supported the substantial growth of its whale-watching indus- try. The industry provides benefits to the community through economic gains, while the experi- ence can foster environmental awareness and support for protection of whales and the environment. However, the sustainability of the industry could be jeopardized if increasing whale-watching vessel pressure affects the health of its resource, the whales. This study investigates whether participation in whale-watching tours in Juneau, AK can support conservation of whales and the environment. Participant knowledge, attitudes, intentions, and behaviors were obtained from 2,331 respondents in surveys before, after, and 6 months after a whale-watching tour during the 2016 and 2017 seasons. Following a whale watch, the percentage of participants that indicated whale watching as a knowl- edge source increased (p = 0.022), awareness of guidelines and regulations doubled (p < 0.001), and strong support for regulations increased (p = 0.016). Six months later, these responses remained significantly higher than before the whale watch. Despite knowledge of distance threshold increasing after a whale watch (p = 0.003) and 6 months after (p = 0.021), getting close to whales remained an important factor in a participant’s whale watch. Participants had a higher likelihood of strongly sup- porting guidelines and regulations if they indicated that boats can have a negative impact on whales or were aware of guidelines and regulations. Lastly, participants that acknowledged negative effects on whales from boats had higher overall proenvironmental attitudes. This study indicates that incor- porating messages that facilitate participant awareness of guidelines/regulations and the purpose of those measures can support conservation and protection of local whale populations through manag- ing participant expectations and ultimately encouraging operator compliance.
  • Humpback Whale Movements and Behavior in Response to Whale-Watching Vessels in Juneau, AK

    Schuler, Alicia, R.; Piwetz, Sarah; Clemente, Jacopo Di; Steckler, David; Mueter, Franz; Pearson, Heidi C. (2019-11-20)
    The whale-watching industry in Juneau, Alaska relies primarily on the presence of North Pacific humpback whales (Megaptera novaeangliae). To meet demands from the rapidly growing tourism industry, the number of whale-watching vessels in this region has tripled over the last 18 years. As a result, increased vessel presence could have negative effects on humpback whales, ranging from short-term behavioral disturbance to long-term impacts. The current humpback whale viewing regulations are outdated and may not be as effective as they were 18 years ago, when both the whale-watching industry and humpback whale population were smaller. The present study assessed how humpback whale movement and behavioral patterns were affected by (1) vessel presence and number of vessels present, and (2) time spent in the presence of vessels. The study also determined how humpback whale behavioral state transitions were affected by vessel presence. A total of 201 humpback whale focal follows were conducted during summer 2016 and 2017. Based on linear mixed effects models, whales in the presence (vs. absence) of vessels exhibited 38.9% higher deviation in linear movement (p = 0.001), 6.2% increase in swimming speed (p = 0.047) and a 6.7% decrease in inter-breath intervals (IBI) (p = 0.025). For each additional vessel present, deviation increased by 6.2% (p = 0.022) and IBI decreased by 3.4% (p = 0.001). As time spent in the presence of vessels increased, respiration rate increased (p = 0.011). Feeding and traveling humpback whales were likely to maintain their behavioral state regardless of vessel presence, while surface active humpback whales were likely to transition to traveling in the presence of vessels. These short-term changes in movement and behavior in response to whale-watching vessels could lead to cumulative, long-term consequences, negatively impacting the health and predictability of the resource on which the industry relies. Current formal vessel approach regulations and voluntary guidelines should be revisited to reduce vessel pressure and mitigate potential negative effects of this growing whale-watching industry.
  • Oceanographic Determinants of the Abundance of Common Dolphins (Delphinus delphis) in the South of Portugal.

    Castro, J.; Couto, A.; Borges, F. O.; Laborde, M. I.; Pearson, H. C.; Rosa, R.; Cid, A.; Pearson, Heidi C. (MDPI, 2020-08)
    Off mainland Portugal, the common dolphin (Delphinus delphis) is the most sighted cetacean, although information on this species is limited. The Atlantic coast of Southern Portugal is characterized by an intense wind-driven upwelling, creating ideal conditions for common dolphins. Using data collected aboard whale-watching boats (1929 sightings and 4548 h effort during 2010–2014), this study aims to understand the relationships between abundance rates (AR) of dolphins of different age classes (adults, juveniles, calves and newborns) and oceanographic [chlorophyll a (Chl-a) and sea surface temperature (SST)] variables. Over 70% of the groups contained immature animals. The AR of adults was negatively related with Chl-a, but not related to SST values. The AR of juveniles was positively related with SST. For calves and newborns, although the relationship between SST and AR is similar to that observed for juveniles, the effect could not be distinguished from zero. There was no relationship between Chl-a levels and the AR of juveniles, calves and newborns. These results corroborate previous findings that common dolphins tend to occur in highly productive areas demonstrating linkages between their abundance and oceanographic variables, and that this region may be a potential nursery ground.