Interactions Between Tourism Vessels and Humpback Whales in the Gulf of Tribugá, Colombia

Abstract

Whale-watching is a growing ecotourism activity in Colombia that offers economic benefits but may pose behavioral risks to humpback whales (Megaptera novaeangliae) if not properly managed. Although preventive recommendations exist to promote sustainable practices, their effectiveness remains largely unquantified in the Colombian North Pacific. This study evaluates adherence to whale-watching regulations and describes humpback whale behavioral responses to vessel presence in the Gulf of Tribugá, a key breeding and calving area. Data were collected from tourism vessels during July and September 2023, documenting 236 whales across 99 groups—71% of which included calves. The predominant whale response to vessels was neutral (74%), while evasive behaviors occurred in 22% of encounters, particularly among mother–calf pairs. Surface-active behavior was infrequent (22%) and most observed in calf–escort groups, serving as a supplementary indicator of behavioral state. Compliance with whale-watching recommendations varied: although most encounters involved a single vessel (57%) and averaged 16 min in duration, only 14% of vessels maintained the recommended minimum distance of 100 m. These findings highlight persistent gaps in regulatory adherence and underscore the need for strengthened enforcement and adaptive management to ensure sustainable whale-watching practices in Colombia’s North Pacific.

1. Introduction

Humpback whales (Megaptera novaeangliae Borowski, 1791) are charismatic marine mammals that inhabit oceans worldwide. These cetaceans exhibit a conspicuous range of surface-active or aerial behaviors, including breaching, flippering, and lobtailing, observed in both their feeding and breeding grounds [1]. This acrobatic repertoire is believed to serve multiple functions, including the removal of external parasites, courtship, communication, and social dynamics [2,3]. Furthermore, these behaviors are believed to be energetically costly [4]. Their frequent occurrence on breeding grounds—where adults typically fast and would be expected to conserve energy—suggests that such displays may play a significant role in the species’ communication repertoire [5].

In Colombia, humpback whales from Stock G are found along the Pacific coast between June and November [6]; however, some individuals have been observed as early as May, with others lingering through December [7]. These months provide favorable conditions for mating, breeding, and calf-rearing during the austral winter [8]. Due to their coastal habits [9] and proximity to areas of high human activity, these whales face multiple threats [1] and are considered the marine mammals inhabiting the largest risk area globally [10]. Although the species is classified as Least Concern worldwide [11], its conservation status in Colombia is Vulnerable [12]. Humpback whales in the region face numerous threats, including unregulated whale-watching practices, which exacerbate conservation challenges [10,13].

Whale-watching is a rapidly expanding industry worldwide [1,14], providing economic benefits and fostering cultural values within local communities [15,16]. It is considered a cornerstone of the economy along the Colombian Pacific coast [17]. Additionally, whale-watching activities have contributed to scientific knowledge on humpback whales [18], making the species one of the most extensively documented cetaceans [13,19]. In the Colombian Pacific Ocean, whale-watching began in 1994 in Bahía Málaga [20] and has since expanded to multiple locations, including Isla Gorgona, Gulfs of Tribugá and Cupica, and Tumaco Bay [21]. Since 2001, preventive guidelines for sustainable and responsible whale-watching have been developed, including The Responsible Whale-Watching Guide for Aquatic Mammals in Colombia [17,21]. These recommendations advise approaching whales from behind and to the side, maintaining a minimum distance of 100 m, limiting encounters to a maximum duration of 30 min, ensuring that no more than three vessels engage with a group of whales at any given time, and keeping engines on throughout interactions [17].

Despite the numerous benefits derived from whale-watching, concerns remain regarding the negative effects of inadequate regulation and implementation of management practices on the behavior and health of targeted animals in the short, medium, and long term [18,22]. Multiple studies have examined behavioral changes in whales exposed to whale-watching vessels. Some of these studies have utilized private or research vessels as observation platforms [23,24,25,26,27,28,29,30], while others have employed commercial tourism vessels as platforms of opportunity. Although the latter approach is limited to detecting impacts occurring near the vessel [31], it nonetheless contributes to the sustainable development of the practice [16]. In Colombia, some studies have assessed these impacts [32,33,34,35,36], with most research focusing on Bahía Málaga.

Similarly, adherence to whale-watching recommendations has been researched [21,34,35]. Still, uncertainty persists regarding the behavior of humpback whales and the extent to which whale-watching guidelines are followed. This gap is particularly evident in areas such as the Gulf of Tribugá, located in Nuquí, Chocó, in the Colombian North Pacific, where whale-watching tourism has expanded significantly over the past decade [19]. In this region, the municipality of Nuquí plays a pivotal role in tourism logistics and expedition planning, serving as a departure point for vessels traveling north or south within the Gulf of Tribugá.

The need to evaluate the ecological and regulatory impacts of whale-watching activities in Colombia has been formally recognized since 2007 [37], and reaffirmed as a strategic priority in the National Action Plan for the Conservation of Colombia’s Aquatic Mammals 2022–2035 [13]. In response, this study investigates the degree of compliance with whale-watching regulations in the Gulf of Tribugá by analyzing vessel behavior and its influence on humpback whale responses. Specifically, we test three hypotheses: (1) that evasive responses increase with decreasing vessel distance, (2) that mother–calf pairs exhibit heightened sensitivity compared to other group types, and (3) that vessel operators frequently deviate from recommended practices, particularly in terms of approach distance, encounter duration, and vessel number per sighting. Surface-active behaviors are documented as supplementary indicators of behavioral state but are not central to the compliance analysis. Given the ecological, economic, and cultural significance of humpback whales in Colombia, the findings aim to support evidence-based conservation strategies and inform regulatory improvements for sustainable whale-watching in the region.

2. Materials and Methods

2.1. Study Area

The Gulf of Tribugá is part of the North Pacific Chocoan Coastal Environmental Unit (UAC-PNCh) and was designated as a marine protected area in 2015 under the Regional Integrated Management District of the Gulf of Tribugá-Cabo Corrientes. It has also been recognized as a Hope Spot and is included within the Tribugá-Cupica-Baudó Biosphere Reserve. As the largest gulf in Colombia [38], it spans 103,100 ha, extending from Utría National Natural Park in the north (6°11′ N, 77°09′ W) to Cabo Corrientes in the south (5°53′ N, 77°28′ W).

The area forms part of the Chocó Biogeographic Region, one of the most biodiverse in the world. It is characterized by high relative humidity (80–95%), frequent cloud cover, and an annual precipitation of approximately 10,000 mm, influenced by the Serranía del Baudó and the Intertropical Convergence Zone [39]. The mean annual air temperature is 28 °C, while the mean annual sea temperature is 20.5 °C, and oceanographic variables are periodically modulated by the El Niño-Southern Oscillation (ENSO). The width of the continental shelf ranges from 1 to 3 km and the turbidity in the study site is high, due to the confluence of multiple rivers [40].

The Gulf of Tribugá forms part of the humpback whale migratory corridor, with Utría National Natural Park and its southernmost boundary considered essential nursery areas for the species [39]. As stated previously, this population belongs to humpback whale Breeding Stock G, which feeds in the Antarctic Peninsula and along the coast of Chile, and breeds in southwestern Central America and northwestern South America [41]. The population abundance is estimated at roughly 11,785 individuals, with an average annual growth rate of 5% between 2006 and 2018 [41].

2.2. Data Collection

Data were collected between July and September 2023 as part of the “Responsible Whale and Dolphin Watching Research Project” and the “Community Science Program” of the R&E Ocean Community Conservation Foundation (https://www.facebook.com/reoceancom/ accessed on 19 February 2025). Observations were conducted by a single researcher aboard commercial whale-watching vessels operating in the study area. Vessels ranged from 7 to 9 m in length and were powered by one or two outboard engines rated between 40 and 90 horsepower. Variability in vessel type and engine power was not controlled for; therefore, interpretations of whale behavioral responses should be made with caution.

Sampling employed focal follows of humpback whale (Megaptera novaeangliae) groups, with continuous surface behavior recording throughout each encounter. Each focal follow was conducted by trained observers positioned on board the research vessels, who systematically recorded whale behavior, group composition, and vessel interactions using standardized protocols. Group composition was determined based on spatial proximity and behavioral synchrony among individuals [3,38]. Whales were categorized as adults (A) or calves (C). The adult nearest to a calf was presumed to be its mother (M), while additional accompanying adults were classified as escorts (E). Based on these criteria, four group types were defined: A (solitary adult), 2A (two or more adults), M+C (mother–calf pair), and M+C+≥1E (mother–calf pair with one or more escorts). For each encounter, the number of individuals and group type were recorded. Definitions of all variables are provided in Table S1.

Behavioral responses to vessel presence were documented when a whale-watching vessel approached a group within 100 m, initiating the focal follow. Observations concluded once the vessel exceeded 100 m from the group. Due to limited underwater visibility, only surface-active behaviors were recorded. Initial reactions to vessel approach were classified as neutral, evasive, or approach, based on changes in movement direction and spatial orientation between whales and vessels during the first five minutes post-encounter (modified from [3]).

In this study, evasive responses were defined strictly as changes in spatial positioning relative to the vessel. Behaviors such as prolonged dives, increased surfacing intervals, or long-distance underwater movement were not categorized as evasive, but rather as neutral. This classification was informed by previous studies employing consensus-based behavioral coding [3] and reflects the absence of baseline data on dive patterns prior to vessel encounters, which could otherwise introduce interpretive bias.

Additional surface-active behaviors were recorded throughout each observation period. Adult dive duration (in seconds) was calculated as the mean of up to three consecutive dives, defined as the interval between surfacing, within the first 15 min of each encounter. The frequency of five aerial displays—chin breach, tail breach, spin breach, lobtail, and flipper slap—was documented using standardized ethograms (adjusted from [42]). The identity of the performing individual (adult or calf) was noted. In groups with multiple adults, a single focal whale was selected for behavioral recording to maintain consistency.

Compliance with whale-watching regulations established by the Ministry of Environment and Sustainable Development (MADS) [17] was assessed using the following criteria: (1) approach maneuver, categorized as direct (frontal or rear) or indirect (lateral or angled); (2) initial distance between vessel and whale group at encounter onset (0–50 m, 50–100 m, ≥100 m); (3) number of vessels simultaneously present during the encounter (including the research vessel); (4) duration of the encounter (in minutes); and (5) engine status during the interaction (on or off). The duration of encounters involving other non-research vessels was not recorded. Vessel operators were not informed of the specific data being collected; instead, their engagement with researchers was framed as part of an environmental education and cetacean research initiative, without disclosing detailed study objectives.

2.3. Data Processing and Statistical Analysis

Data were categorized into five subsamples to facilitate analysis: (C-I) total number of encounters, (C-II) number of sampled days, (C-III) encountered group classes, (C-IV) whales’ initial reactions at the beginning of encounters, and (C-V) mean dive duration (Table S2). Figures and tables indicate the sample size (n) and the corresponding data category (C-I to C-V) used in each analysis. Descriptive statistics were applied to characterize humpback whale behavior during whale-watching encounters. Values are reported as mean ($\overline{x}$) and standard deviation (SD), or as median (M) and interquartile range (IQR), where applicable (n ≥ 4).

Behavioral variables were analyzed across four group classes: A (solitary adult), ≥2A (two or more adults), M+C (mother–calf pair), and M+C + ≥1E (mother–calf pair with one or more escorts), as group composition is considered an explanatory factor for behavioral variation [3]. The behavior rate was defined as the number of surface-active behaviors per minute per individual within each group class. Additionally, the relative frequency of encountered group types was standardized by the monthly number of encounters to account for temporal sampling variation.

To assess independence between behavioral responses and explanatory variables, pairwise comparisons were conducted. Behavioral responses included initial reaction, frequency of surface-active behaviors, and mean dive duration. These were tested against whale-watching compliance indicators—approach maneuver, encounter distance, engine status, and number of vessels present—as well as group class (A, ≥2A, M+C, and M+C+≥1E) (Table S3).

Assumptions of normality and homogeneity of variance were evaluated using the Shapiro–Wilk and Levene tests, respectively, with a significance level of α = 0.05. As the data did not meet parametric assumptions, non-parametric tests were applied. Chi-square (χ²) tests were used to examine independence among categorical variables, with test statistics compared against critical χ²₁ values to determine significance. Spearman’s rank correlation coefficient was employed to quantify associations between pairs of quantitative variables. Mann–Whitney U tests were used to compare medians of binomial variables, while Kruskal–Wallis tests assessed differences in medians across multiple groups. Post hoc analyses were performed using Dunn’s multiple comparison test with Bonferroni correction and Holm adjustment. All statistical analyses were conducted in RStudio© (version 2023.6.0.421), utilizing the car, nlme, dplyr, and PMCMRplus packages.

3. Results

Observations were conducted between 11 July and 26 September 2023 along the Gulf of Tribugá, spanning from Utría National Park in the north (06°00′36.7′′ N, 077°21′08.3′′ W) to La Roñosa in the south (05°35′6.22′′ N, 077°30′50.76′′ W) (Figure 1). Over the 43-day study period, 39.5% of encounters occurred north of Nuquí, while 60.5% occurred to the south. A total of 107 humpback whale sightings were recorded, with an effective sampling effort of 29 h and 43 min (excluding search time). Monthly effort was distributed as follows: July (16 encounters, 5.18 h), August (50 encounters, 10.62 h), and September (41 encounters, 13.92 h).

3.1. Whale Groups

A total of 236 humpback whales were observed, comprising 71 calves (C) and 165 adults, categorized as mothers (M), escorts (E), or solitary adults (A). The mean number of whales per encounter was 2.4 ± 1.2. Ninety-nine distinct groups were recorded, with calf-containing groups being most prevalent (

Table 1. Classes of humpback whale groups encountered during the 2023 breeding season in the Gulf of Tribugá. A = groups of one adult whale, ≥2A = groups of two or more adult whales, M+C = mother–calf pairs and M+C+≥1E = M+C pairs accompanied by one or more escorts. The category of data is C-III (see Table S2).

Whale Group Class	A	≥2A	M+C	M+C+≥1E
Group Class (n = 99)
	9.1%	20.2%	51.5%	19.2%
Group Classes Encountered Per Hour Per Month (n = 99)
July	0	1.16	1.16	0.77
August	0.6	0.80	2.30	0.80
September	0.23	0.46	1.68	0.54

). In July, M+C pairs and ≥2A groups were encountered at equal rates (1.16 groups/month). A and ≥2A groups were the least frequent across all months, while M+C and M+C+≥1E groups were most common in August.

3.2. Whale Behavior

Most whale groups (73.6%) exhibited a neutral response to vessel approach, while 22.2% responded evasively and 4.2% approached the vessel (

Table 2. Whale behavior during whale-watching encounters. A = groups of only one adult whale, ≥2A = groups formed by two or more adult whales, M+C = mother–calf pairs and M+C+≥1E = M+C groups accompanied by one or more escorts. $\overline{x}$ ± SD = mean ± standard deviation. The categories of data were C-I, IV and V (Table S2).

Whale Behavior Descriptors	Summary Statistics
Initial Reaction (N = 72; C-IV)
Evasive	22.2%
Neutral	73.6%
Approach	4.2%
Dive Duration in Seconds of Adults ($\overline{x}$ ± SD; n = 58; C-V)
All groups	104.54 ± 121.26
A	167.7 ± 204.71
≥2A	65.67 ± 41.79
M+C	109.03 ± 130.28
M+C+≥1E	125.14 ± 113.04
Rate of Surface-Active Behavior in each Month (n = 107; C-I)
July	0
August	4.34
September	6.21

). Initial reaction was independent of group class (χ²₆ = 3.25, p = 0.78) but significantly associated with initial encounter distance (χ²₄ = 10.39, p < 0.05). Evasive responses were more frequent at distances of 0–50 m (χ²₁ = 2.37, p > 0.05), though not statistically significant.

Mean dive duration did not differ significantly among group classes (Kruskal–Wallis: H₃ = 1.28, p = 0.73). Across all adult whales, mean dive time was 104.54 ± 121.26 s (Table 2). Although not a primary focus, resting behavior was opportunistically recorded in three encounters (2.8%), exclusively among M+C pairs.

Surface-active behavior occurred in 21.5% of encounters, with no aerial displays observed in July. These behaviors emerged in August and peaked in September. Lobtailing was the most frequent display, followed by spin breaching and chin breaching. Chin and tail breaching were observed only in groups containing calves. Calves exhibited the highest frequency of surface-active behaviors, particularly when accompanied by escorts (E) (Figure 2). Among adult-only groups, solitary adults (A) displayed the highest behavior rates.

3.3. Vessel Behavior

Approach maneuvers were indirect in 90.3% of encounters and direct in 9.7%. Vessels maintained a distance of 50–100 m in 50% of encounters, while 36.2% occurred within 50 m and 13.8% at ≥100 m. A single vessel was present in 57% of encounters, two vessels in 16.8%, three in 14%, and more than three in 12.2%. Median encounter duration was 15 min (IQR = 16 min; $\overline{x}$ ± SD = 16.98 ± 13.28 min). Half of the encounters lasted 8–24 min, with 25% exceeding 24 min. Engines remained on in approximately 75% of encounters and were turned off at least once in the remainder (

Table 3. Recommendations for approaching maneuver and encounter duration for whale-watching by the Responsible Whale-watching Guide of Aquatic Mammals in Colombia (MADS, 2017), with respective rates of adherence by tour operators that sailed from Nuquí obtained in this study.

Recommendations for Responsible Whale-Watching	Adherence Rate
Approach as slowly and progressively as possible, never make fast or sudden approaches	Not assessed in the present study
Approach from the rear at a 45° angle, using the posterior half of the animal as a reference. Never approach completely from the front or rear	90.29%
Never approach closer than 100 m to whales	13.83%
Vessels in the waiting zone (200 m from the targeted whale group) should keep a path parallel to the animals and should be positioned on only one side of the group	Not assessed in the present study
Leave an escape route for the animals	Not assessed in the present study
When staying 100–200 m from whales, maintain a constant trajectory and speeds should not exceed 5 kn or 9 km/h	Not assessed in the present study
If one individual or group approaches the vessel, keep the engine in neutral	Not assessed in the present study
Keep the engine on during whale-watching	78.00%
If the need to stop during an approaching maneuver arises, reduce speed gradually	Not assessed in the present study
If there is only one vessel present during an encounter, restrict the encounter duration to 30 min	$\overline{x}$ = 17.14 min Minimum = 0.17 min Maximum = 91 min
If there is more than one vessel, restrict the encounter duration to 15 min	$\overline{x}$ = 16.79 min Minimum = 1 min Maximum = 48 min
Restrict the number of vessels present during an encounter to no more than three for one individual or group	87.85%
Whale-watching should be performed by vessels in the order of their arrival	Not assessed in the present study

and

Table 4. Characterization of whale-watching vessel behavior with whales in the Gulf of Tribugá. $\overline{x}$ ± SD = mean ± standard deviation. All data are from C-I (see Table S2).

Vessel Behavior Descriptors	Summary Statistics
Approaching Maneuver (n = 103)
Direct	9.71%
Indirect	90.29%
Distance at the Beginning of the Encounters (n = 94)
0–50 m	36.17%
50–100 m	50%
≥100 m	13.83%
Number of Vessels Present During Encounters (n = 107)
One	57%
Two	16.8%
Three	14%
More than three vessels
Four	7.5%
Five	3.7%
Nine	1%
Duration of Encounters (min; n = 105; C-I)
Minimum	1
Maximum	91
Median	15
Interquartile range	16
Mode	15
$\overline{x}$ ± SD	16.98 ± 13.28
Engine’s Status (n = 100)
On (throughout encounter)	78%
Off (at least once during encounter)	22%

).

Group class was significantly associated with several vessel–whale interaction metrics. Initial distance and approach maneuver varied by group class (χ²₃ = 7.71, p > 0.05; χ²₆ = 18.19, p < 0.01). Vessels maintained distances ≥ 100 m more frequently from A groups (χ²₁ = 13.29, p < 0.05), while ≥2A groups were more often approached directly (χ²₁ = 3.73, p < 0.05). Encounter duration and vessel count also varied by group class (Kruskal–Wallis: H₃ = 10.6, p < 0.01; H₃ = 3.24, p < 0.05). Encounters with M+C+≥1E groups lasted longer (M = 22.5 min; IQR = 14.75–27 min) than those with A groups (M = 7 min; IQR = 4.75–10.5 min; p = 0.009; Figure 3A). The highest number of vessels was also recorded for M+C+≥1E groups (M = 3; IQR = 1–3.25), differing significantly from A groups (M = 1; IQR = 1–1; p < 0.05) and M+C pairs (M = 1; IQR = 1–2; p < 0.03; Figure 3B). The only encounter involving nine vessels occurred with an M+C+≥1E group.

Encounters involving surface-active behaviors lasted, on average, 4.44 min longer than those without such displays. However, the nine-vessel encounter did not involve surface-active behavior. These differences were not statistically significant (Mann–Whitney U: U = 1131, n = 105, p = 0.15; U = 969, n = 107, p = 0.98;

Table 5. Characterization of vessel behavior, according to the occurrence of surface-active behaviors. $\overline{x}$ ± SD = mean ± standard deviation. The category for data is C-I (see Table S2).

Encounters with Surface-Active behaviors		Encounters Without Surface-Active Behaviors
Duration of Encounters (min; n = 105)
$\overline{x}$ ± SD	19.94 ± 11.87	15.5 ± 13.72
Number of Vessels Present During Encounters (n = 107)
$\overline{x}$ ± SD	2.01 ± 1.74	1.82 ± 1.10
Maximum	9	5

).

4. Discussion

The high proportion of whale-watching encounters involving mother–calf (M+C) pairs (70.7%) suggests that the Gulf of Tribugá may serve as an important nursery area for humpback whales. This rate is comparable to that reported in Bahía Málaga (86%), a recognized breeding ground in the Colombian Pacific [34]. In contrast, Bahía Solano, Chocó, exhibits a lower proportion of M+C pairs (20%) and calf-containing groups (49.6%), likely reflecting its role as a migratory corridor for Stock G [43]. The increasing number of M+C pairs observed over time in this study aligns with the seasonal progression of the breeding period.

All four group classes exhibited predominantly neutral responses to vessel approaches. However, the absence of overt behavioral changes does not preclude disturbance, as physiological stress may precede visible reactions [44]. A tendency toward evasive behavior was noted when vessels approached within 0–50 m, differing from previous findings in the region where evasive responses were more frequent at 50–100 m [35]. These discrepancies may stem from methodological differences in defining “neutral” responses (see Methods). Additionally, sampling from whale-watching vessels may bias observations toward individuals tolerant of vessel proximity, potentially underestimating true rates of avoidance.

Mean dive durations for three group classes were shorter than those reported in the absence of vessels in Bahía Málaga [34], consistent with patterns observed in other breeding areas [22]. Although this study did not directly compare dive times between vessel-present and vessel-absent conditions, the findings suggest that whale-watching activity may influence short-term dive behavior in the Gulf of Tribugá, warranting further investigation.

The observation of resting M+C pairs during whale-watching encounters raises concern and requires further investigation. Adult humpback whales are particularly vulnerable during the breeding season, relying on stored energy reserves from polar feeding grounds [45]. Previous studies have shown that vessel presence reduces resting time in breeding areas [34,46,47,48]. Reduced rest may compromise maternal energy budgets and calf development, limiting nursing opportunities and increasing energetic costs associated with heightened activity [44,49,50]. These disruptions could ultimately affect reproductive success.

Surface-active behaviors were recorded in only 25% of encounters, with the highest frequency occurring in September, coinciding with the peak of the breeding season. Calves exhibited the highest rates of surface-active behavior, consistent with other studies in the Colombian Pacific. M+C+≥1E groups also displayed elevated frequencies of these behaviors and were encountered more often and by more vessels. This pattern aligns with previous reports from the southern extent of Stock G’s breeding range [51] and earlier studies in the Gulf of Tribugá [35].

Contrary to prior findings [35], flippering was not exclusive to adult-only groups in this study. While behavior rates were not explicitly analyzed in relation to vessel presence, previous research in the Colombian Pacific has yielded mixed results. Some studies suggest that surface-active behavior decreases in response to vessel disturbance [48], potentially reflecting transitions to evasive states such as traveling [46]. Others report increased activity, possibly as a communicative response to elevated noise levels [35,45].

The interpretation of surface-active behavior is context-dependent: newborn calves and juveniles are likely engaged in the acquisition, reinforcement, and refinement of motor and social skills critical for their development [52], while in adults, such behaviors may relate to courtship, group dynamics, or acoustic signaling [2,5]. Further research is needed to identify which natural behaviors are altered by tourism vessel presence and to assess the influence of environmental and social factors on behavioral variability [5]. Investigating physiological indicators and core behavioral states will be essential for understanding sub-lethal impacts.

Regarding compliance, tour operators in Nuquí adhered to four of five recommended whale-watching guidelines [17]. Compared to Bahía Málaga, where up to 14 vessels may observe a single group [19] and 51.6% of encounters involve 2–5 vessels [34], the Gulf of Tribugá exhibited lower vessel density, with a single vessel present in 57% of encounters and a maximum of nine vessels per group. Encounter durations were also shorter (16.98 ± 13.28 min), aligning with regulatory recommendations and remaining below durations reported in Bahía Málaga (29 ± 12.6 min in 2008 [34]; 42.8 ± 6.8 min in 2019 [18]). Even though observation durations in this study remained within the recommended thresholds, future studies need to account for cumulative exposure time, as prolonged or repeated interactions may lead to long-term impacts on whales.

Although the presence of a researcher may have influenced operator behavior, the imperfect adherence to guidelines suggests that operators acted as they typically would. This supports the validity of the compliance data. However, only a minority of vessels maintained the recommended ≥100 m distance from whales, mirroring patterns observed in Bahía Málaga [34]. The reasons for non-compliance with this specific guideline fall outside the scope of this study, but it is notable that some operators have failed to adhere even after receiving warnings. Prior research indicates that valuing whale-watching guidelines does not guarantee adherence [35]. Strengthening operator understanding of the ecological rationale behind these recommendations is essential for promoting sustainable whale-watching practices.

These findings underscore the need for governmental authorities to incorporate behavioral sensitivity thresholds into marine spatial planning and whale-watching regulations, particularly by enforcing temporal and spatial restrictions during breeding and nursing periods to reduce vessel-induced disturbances.

5. Conclusions

In summary, the findings of this study support all initial hypotheses. First, operator compliance with whale-watching guidelines was partial. Although most operators adhered to four out of five recommendations, maintaining the minimum 100 m distance was the least respected—mirroring patterns reported in other Colombian breeding grounds. Second, vessel proximity was associated with behavioral changes in humpback whales in the Gulf of Tribugá, particularly among mother–calf pairs. Alterations in dive duration and surface-active behaviors were observed, even in the absence of overt avoidance responses, suggesting subtle yet ecologically significant effects.

The study also demonstrated the utility of commercial tourism vessels as platforms of opportunity for behavioral monitoring, offering a cost-effective and scalable alternative to dedicated research vessels. Key management gaps were identified, prompting recommendations for proactive strategies, including the implementation of standardized monitoring tools, enhanced operator education, and targeted outreach programs to promote sustainable whale-watching practices in the region. Although most operators demonstrated general awareness of whale-watching guidelines, the consistent failure to maintain an appropriate distance highlights a gap between knowledge and practice. Notably, the presence of researchers onboard did not significantly alter operator behavior, suggesting that observed compliance levels reflect standard operating norms rather than observer-induced bias. Nevertheless, the results of this study contribute to public awareness and provide a scientific basis for refining whale-watching regulations to minimize disturbance. They also underscore the value of integrating commercial vessels into long-term monitoring programs, particularly in data-limited regions.

Furthermore, our findings reinforce the ecological importance of the Gulf of Tribugá as a potential nursery area for humpback whales, as evidenced by the high proportion of mother–calf pairs observed during whale-watching encounters. Behavioral observations indicate that vessel proximity may influence whale behavior, particularly among resting dyads, which are energetically constrained during the breeding season. The targeting of these vulnerable groups by tourism activities raises concerns about potential impacts on maternal investment and calf development.

To strengthen conservation outcomes, self-monitoring initiatives promoted by environmental and maritime authorities should be reinforced through the development of standardized evaluation frameworks. Given the vulnerability of breeding humpback whales and the increasing popularity of whale-watching in the Gulf of Tribugá, there is an urgent need to enhance regulatory enforcement, expand monitoring capacity, and invest in education and outreach. These measures are essential to ensure that whale-watching activities remain ecologically sustainable, safeguarding both humpback whale populations and the socioeconomic well-being of coastal communities. Proactive management is critical to prevent the intensification and unsustainable expansion of whale-watching operations—an issue already documented in other Colombian breeding areas.