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Sociality of sperm whale off Ischia Island (Tyrrhenian Sea, Italy)
Abstract
The sperm whale ( Physeter macrocephalus ) is one of the eight species of cetaceans routinely encountered in the Mediterranean Sea; however, information on the social organization of sperm whales living in the basin remains scarce.
The social behaviour of sperm whales within female units, and groups of males are reported, made over an 11‐year period (2002–2012) in waters around the islands of Ischia and Ventotene (Tyrrhenian Sea, Italy), an area characterized by the presence of a submarine canyon system and a coastal marine protected area (‘Regno di Nettuno’ MPA).
Different types of aggregations were identified, consisting of social units and two arrangements of males (bachelor groups and clusters). Close clustering at the surface was recorded both for social units and bachelor groups, with evidence for long‐term relationships between females (as expected from other studies) and, surprisingly, also among some immature males.
Such long‐term associations between individuals in bachelor groups may allow immature males to benefit in several ways, including optimizing feeding efficiency.
Copyright © 2014 John Wiley & Sons, Ltd.
... To date, photo-ID studies of sperm whales have almost completely covered the western part of the Mediterranean Sea (i.e., Strait of Gibraltar, Alboran Sea, Balearic Islands, Gulf of Lyon, Ligurian Sea, and Tyrrhenian Sea) and the Hellenic Trench in the eastern part [5][6][7][8][9][10] (Figure 1). Based on these investigations, male sperm whales can be encountered in both the western [6,7,10,11] and eastern [8,12] Mediterranean basins. ...
... Based on these investigations, male sperm whales can be encountered in both the western [6,7,10,11] and eastern [8,12] Mediterranean basins. They can be found either as lone individuals or in small groups [8,9,12], called "bachelor groups", that can comprise immature and, sometimes, mature animals [13][14][15][16]. Concerning females, they are regularly encountered off the Balearic Islands [11,17,18] and in the Hellenic Trench [8]. ...
... Generally, the sampling efforts carried out in the Tyrrhenian basin are significantly lower than those applied in other areas, such as the Ligurian Sea and the Algero-Provençal basin [22]. Some data on sperm whales occurring in the Tyrrhenian Sea were already collected visually [11,17,23] and acoustically [22,[24][25][26][27], but long-term monitoring efforts and photo-ID results are available only for the Cuma Canyon area, located in the central-eastern part of the Tyrrhenian Sea, and the data are now a decade old [9]. The Mediterraneanisolated population of sperm whales [28][29][30] has been assessed regionally as "Endangered" by the IUCN (International Union for Conservation of Nature) [31]. ...
(1) While photo-identification has been used to study sperm whales worldwide, no long-term photo-id studies are available from the Southern Tyrrhenian Sea for the Mediterranean endangered population. (2) Here, sperm whale occurrence, group size, and the type of encounters were investigated around the Aeolian archipelago (Southern Italy) by photo-ID data collected between 2013 and 2024. Data were obtained through dedicated boat surveys and recreational sailors’ reports. (3) During 58 sighting events, 125 sperm whales were encountered, 60 of whom were photo-identified and cataloged. Of these, two sperm whales were found entangled. Only five individuals were re-sighted in later years or seasons. Encounters were more frequent in autumn, consisting mainly of solitary individuals (53.4%, n = 31) and aggregations of clustered, often not sexed, animals (23.5%, n = 8). Social units of females and calves were also encountered (8.6%, n = 5). (4) The low site fidelity and the group types encountered suggest that dispersed young males and social groups could use the area simultaneously. (4) Future matching of these data with databases from other surveyed areas, acoustic surveys, and enhanced analysis of age classes are crucial to better define the ecological role of the study area for the Mediterranean sperm whale population.
... In this area, solitary males, loose male aggregations, social units and small bachelor groups have been observed to coexist. Similarly, during nine years of surveys conducted off the Bay of Naples, Italy, Pace et al. (2014a) observed all the major types of groupings that have been identified elsewhere (female social groups, singleton males and bachelor groups), occurring in the same general study site. The same coexistence of age/sex classes is seen in the waters around the Balearic Islands (Pirotta et al., 2011). ...
... Nonetheless, repeated observations in the Mediterranean reveal a sympatry of solitary males and female groups, with no obvious reproductive purpose Pace et al., 2014a;Pirotta et al., 2011), that is not typically seen in other study sites (Whitehead, 2003). Such overlapping ranges could alter the way that different age/sex classes of sperm whales divide up ecological niches, and could in theory lead to increased competition for resources between female groups and solitary or very loosely associated juvenile males. ...
... Since large-scale surveys conducted over the entire eastern Mediterranean Basin indicate that the majority of the sperm whales concentrate along the Hellenic Trench (Boisseau et al., 2010;Lewis et al., 2007), the total number of sperm whales for the eastern Basin is very likely to be in the low hundreds. Nine years of photo-identification effort around the island of Ischia just outside the Bay of Naples in Italy has resulted in a catalogue of 60 individuals from a survey area approximately 8800 km 2 (Pace et al., 2014a), although the discovery curve showed no sign of a decreasing rate of new identifications, so this site may be part of a much larger home range for the western Basin population. Rendell et al. (2014) analysed 507 photoidentifications from across the northern part of the western Basin. ...
First observed in the classical era, a population of sperm whales (Physeter macrocephalus) persists to this day in the deep waters of the Mediterranean Sea. Genetic and observational evidence support the notion that this is an isolated population, separated from its Atlantic neighbours. These whales depend on mesopelagic squid for food, and appear to occupy a very similar ecological niche to sperm whales in the open oceans. Recent evidence proving that individuals can pass between the eastern and western deep water basins confirms that this is a single population, not isolated into western and eastern stocks. We lack robust information on their population status, but they could number in the hundreds rather than thousands, and current densities appear to be much lower than those reported in the 1950s, suggesting that we should be very concerned about the conservation status of this population. This makes it vitally important to address the serious threats posed by ship strikes and entanglement in fishing nets, especially driftnets, and to carefully monitor other potential sources of anthropogenic impact. A step change in funding to collect better data and a clear shift in policy priorities are needed if we are to be serious about conserving this population.
... Many population studies are consequently intended to estimate the abundance of a particular species, to understand the baseline conditions, assess its conservation status both at local and global scales, and evaluate population-level impacts associated with habitat modifications and natural/anthropogenic pressures [3]. These assessments may then assist conservation managers in the development of preservation actions targeted at the specific threats the population is facing [4][5][6][7][8] and in the evaluation, in terms of population size, of the efficacy of such measures [9]. ...
... The best model is the one that minimizes (7), but models with a QAICc difference (∆QAICc) of less than 2 provide the same inference. Finally, the superpopulation N, which considers well-marked (WM), fairly marked (FM), and unmarked (UM) dolphins (see Section 2.3), was calculated adjusting its estimates with the mark rate θ [67]:θ = n W M n W M + n FM + n UM (8) where n WM , n FM , and n UM are the number of WM, FM, and UM sampled individuals, respectively. We can subsequently useθ to correct the estimate of N aŝ ...
Simple Summary
Photo-identification is a non-invasive method of identifying individual animals from natural markings present on one or more parts of the body. The dorsal fin of a dolphin is the portion that contains individually distinctive marks and the most commonly visible when an animal surfaces to breathe. The camera captures an image of the dorsal fin whenever it is sighted and based on the number of times an image is captured, a statistical method called capture–recapture is used to estimate the site fidelity and the size of the population in a defined area. Here, we applied these methods to study the bottlenose dolphins (Tursiops truncatus) between 2017 and 2020 at the Tiber estuary (Mediterranean Sea, Rome, Italy), a polluted major river supplying organic material to the Capitoline (Roman) coastal area and nearby regions. We identified 347 unique individuals, with different patterns of residency (i.e., the tendency of dolphins to remain in, or return to, the study area): 42 were labeled resident, 73 part-time, and 232 transient. Estimating a total population size of 529 individuals and highlighting the presence of animals with a strong site-fidelity, this study suggests developing conservation plans for this vulnerable top-predator species not only focused on areas close to the Tiber River mouths but also extended to cover a broader scale of area.
Abstract
Periodic assessments of population status and trends to detect natural influences and human effects on coastal dolphin are often limited by lack of baseline information. Here, we investigated for the first time the site-fidelity patterns and estimated the population size of bottlenose dolphins (Tursiops truncatus) at the Tiber River estuary (central Mediterranean, Tyrrhenian Sea, Rome, Italy) between 2017 and 2020. We used photo-identification data and site-fidelity metrics to study the tendency of dolphins to remain in, or return to, the study area, and capture–recapture models to estimate the population abundance. In all, 347 unique individuals were identified. The hierarchical cluster analysis highlighted 3 clusters, labeled resident (individuals encountered at least five times, in three different months, over three distinct years; n = 42), part-time (individuals encountered at least on two occasions in a month, in at least two different years; n = 73), and transient (individuals encountered on more than one occasion, in more than 1 month, none of them in more than 1 year; n = 232), each characterized by site-fidelity metrics. Open POPAN modeling estimated a population size of 529 individuals (95% CI: 456–614), showing that the Capitoline (Roman) coastal area and nearby regions surrounding the Tiber River estuary represent an important, suitable habitat for bottlenose dolphins, despite their proximity to one of the major urban centers in the world (the city of Rome). Given the high number of individuals in the area and the presence of resident individuals with strong site fidelity, we suggest that conservation plans should not be focused only close to the Tiber River mouths but extended to cover a broader scale of area.
... It was concluded that large bachelor groups of males frequently split up and rejoin over a large area 2 , but the fidelity of their membership was doubtful. More recent research on sperm whales is equivocal, with some studies illustrating little apparent characteristics of social structure of males 6,10,11,32 , while another recent study even showed that immature males form long-term relationships 33 . A recent study on size and shape variations of the bony components of sperm whale cochleae suggested already that individuals might be affiliated to different bachelor pods 34 . ...
... However, witness reports indicated that the social cohesion within such male associations prevent animals from stranding or that they do not leave stranded individuals 3,4,42 . A recent study showed that immature males form long-term relationships occurring in tight surface groups that exhibit all types of surface behaviour seen within social units 33 . Our results from the 'January' and 'February' clusters imply likewise that sexually immature individuals in bachelor groups can form long-term associations. ...
Ecological and physiological factors lead to different contamination patterns in individual marine mammals. The objective of the present study was to assess whether variations in contamination profiles are indicative of social structures of young male sperm whales as they might reflect a variation in feeding preferences and/or in utilized feeding grounds. We used a total of 61 variables associated with organic compounds and trace element concentrations measured in muscle, liver, kidney and blubber gained from 24 sperm whales that stranded in the North Sea in January and February 2016. Combining contaminant and genetic data, there is evidence for at least two cohorts with different origin among these stranded sperm whales; one from the Canary Island region and one from the northern part of the Atlantic. While genetic data unravel relatedness and kinship, contamination data integrate over areas, where animals occured during their lifetime. Especially in long-lived animals with a large migratory potential, as sperm whales, contamination data may carry highly relevant information about aggregation through time and space.
... The high re-sighting rate deduced from photo-identification results (see Pace et al., 2014) suggests a high degree of site-fidelity both by social units and assemblages of immature males to the deep waters of the canyon of Cuma and shows the importance of the area through the years. Immature males in bachelor groups showed the largest re-sighting range (2004)(2005)(2006)(2007)(2008)(2009)(2010), with repeated identification of the same individuals over the course of years, indicating their tendency to return to or remain in the same area over time (rather than just passing through) (see Pace et al., 2014). ...
... The high re-sighting rate deduced from photo-identification results (see Pace et al., 2014) suggests a high degree of site-fidelity both by social units and assemblages of immature males to the deep waters of the canyon of Cuma and shows the importance of the area through the years. Immature males in bachelor groups showed the largest re-sighting range (2004)(2005)(2006)(2007)(2008)(2009)(2010), with repeated identification of the same individuals over the course of years, indicating their tendency to return to or remain in the same area over time (rather than just passing through) (see Pace et al., 2014). ...
Boat surveys aimed at studying sperm whales in the Tyrrhenian Sea were conducted between 2002 and 2011. During 768 daily surveys, a total effort of 32 602 km was achieved within an area of 8800 km ² resulting in 92 encounters with 229 sperm whale individuals.
Average encounter rates of sperm whales was 0.5 groups per 100 km ² , with a higher concentration in the vicinity of the submarine canyon of Cuma, confirming the importance for the species of this small hotspot in the Mediterranean Sea.
Encounter rates increased with increasing distance from the coast. It is possible that the intense boat traffic and anthropogenic disturbance in the area may be moving animals away from the coast leading to habitat loss.
The species–habitat relationship documented in this study has implications for conservation.
Copyright © 2014 John Wiley & Sons, Ltd.
... No social behaviour was observed, likely due to sea conditions. One whale was photographed and deemed an immature male based on its size and characteristic head shape (Maio et al., 2022;Pace et al., 2014;Whitehead, 2018) ...
Research in the western Mediterranean has shown that sperm ( Physeter macrocephalus ) and Cuvier's beaked whales ( Ziphius cavirostris ) are present as small, globally distinct populations that face numerous threats.
The eastern Mediterranean is not well studied, and few surveys have investigated the composition of cetacean communities. In this study, visual‐acoustic surveys were conducted off the coast of Israel during April–May 2022 to characterize the cetacean community.
Sperm whales (three encounters), Cuvier's beaked whales (one encounter), bottlenose dolphins (one encounter ( Tursiops truncatus )) and unidentified delphinids (17 encounters) were acoustically detected.
Sperm whales were foraging ~10 km off Haifa, at 370–1220 m deep and social vocalizations (codas) corresponded to the Mediterranean dialect. One immature male that was photographed is known from 12 previous encounters in the Ligurian Sea, indicating a west–east movement of approximately 2800 km.
Automated passive acoustic monitoring of narrow, relatively shallow areas such as the Sicily Channel could provide an opportunity to reduce mortality of individuals making long‐distance movements within Mediterranean basins. Israeli waters provide habitat for cetaceans, with two threatened subpopulations—sperm and Cuvier's beaked whales—that are negatively impacted by anthropogenic activities, including those that introduce underwater noise. More data are needed on densities of these deep‐water species, and an evaluation of the threats faced in the wider Levantine basin.
... Increased prey availability near river mouths is one of the possible drivers for the common bottlenose dolphin presence and abundance in the study site, which sustains a core nucleus of resident females with offspring [21]. However, anthropogenic disturbances and threats (vessel traffic, reduced prey availability caused by overfishing, plastic and chemical pollution, and habitat degradation, including noise) may impact distribution and individuals' interactions, thus altering the social structure and influencing how the population responds to changes to its environment [57][58][59][60][61]. Future investigations should address the structure of the relationships between individuals as it is an essential aspect affecting animals' responses to both human-related pressures and management actions [57,62]. ...
Simple Summary
Death-related behaviors have been often observed in cetaceans, frequently with a female caregiver (presumed mother) supporting a dead calf by carrying, lifting, or sinking it, generally accompanied by other escorting individuals. However, how cetaceans experience death and if their behavior could be compared to human grieving is still largely unknown, as well as their acoustic production in such contexts. This report describes two cases of an adult common bottlenose dolphin (Tursiops truncatus) supporting a dead newborn and associated acoustic behavior in the Tiber River estuary area (Rome, Mediterranean Sea, Italy). In both cases, a main supporter (putative mother) was observed interacting with the carcass of a newborn by lifting (case 1) and sinking it (case 2), always escorted by another adult individual. Several vocalizations were recorded, including a signature whistle (a tonal sound with a repeated, stereotyped, individual-specific frequency modulation pattern) in the first case, likely emitted by the putative mother to seek aid from other individuals. This result appears reasonable since bottlenose dolphins are a highly vocal species, that communicates mainly through acoustic signals. These observations confirm the occurrence of death-related supportive behavior in bottlenose dolphins and report a preliminary description of associated vocalizations, providing additional information on this largely unknown topic.
Abstract
Epimeletic behavior toward dead calves has been frequently reported in cetaceans, mostly with females (presumed mothers) showing supportive behaviors such as carrying, lifting, or sinking, often assisted by “escort” individuals. However, information on acoustic production in such contexts is scarce. This report describes two observations of epimeletic behavior toward dead newborns in bottlenose dolphins and associated acoustic production. Data were collected at the Tiber River estuary (Rome, Mediterranean Sea, Italy) with one hydrophone for passive acoustic monitoring and two digital cameras. In both cases, an individual (presumed mother) acting as the main supporter and directly interacting with the carcass by lifting it (case 1) or sinking it (case 2) was observed. Another adult individual (escort) was present in both encounters showing standing-by and excitement behaviors (case 1) and supportive behavior (case 2). In both encounters, whistles, pulsed sounds, and bray-call elements were recorded. The consistent vocal activity observed likely conveyed context-specific information. A signature whistle in the first encounter was also recorded, likely emitted by the putative mother as a distress call. This report confirms the occurrence of epimeletic behavior in bottlenose dolphins and reports a preliminary description of the acoustic production when a dead calf is involved, providing additional information on this largely unknown topic.
... In the last two years, 17 of the 21 sperm whales stranded in Italy were found along the Tyrrhenian Sea coast. This part of the Mediterranean basin is thought to be an important feeding/breeding ground for this species, where both mature/immature males and social units of mature females with their juveniles/calves are regularly encountered [19][20][21][22] as a result of the morphological aspects of the bathy-morphological setting, characterized by canyons and seamounts, which have already been positively related to the presence and distribution of the sperm whales [23,24]. The Aeolian Archipelago located in the Southern Tyrrhenian Sea (Sicily, Italy) is no exception [25]. ...
Illegal driftnetting causes each year several entanglements and deaths of sperm whales in different Mediterranean areas, primarily in the Tyrrhenian Sea. In summer 2020, during the June-July fishing season, two sperm whales were found entangled in illegal driftnets in the Aeolian Archipelago waters, Southern Italy. These two rare events were an exceptional chance to collect behavioural and acoustics data about entangled sperm whales. We analysed 1132 one-minute sets of breathing/behavioural data and 1575 minutes of acoustic recording, when the whales were found entangled, during the rescue operation, immediately after release, and in the days thereafter. The first whale was generally quiet showing a general status of debilitation/weakness, numerous skin lesions, and low breathing rate (0.31 (0.60)); it collaborated during rescue operations. On the contrary, the second whale showed a high level of agitation with a high breathing rate (1.48 (1.31)) during both the entanglement period and the net cutting operations, vigorously moving its fluke and pectoral fins, opening its mouth, sideway rolling or side fluking and frequently defecating. Acoustically, the first whale produced mainly single clicks in all phases except for two series of creaks during rescuing operations while the second whale produced a wide range of vocalizations (single clicks, likely either slow clicks or regular clicks, creaks, and codas). Our observations indicate that acoustics, respiratory and behavioural parameters may be useful to monitor the physical/physiological status of sperm whales during disentanglement operations.
... It is widely recognised that sperm whales travel through the whole western Mediterranean Sea, with movements and exchanges of males within the area 50,83 . Male sperm whales use the North-Western Mediterranean Sea especially in the summer months, while social units of females with calves and juveniles tend to remain in southern areas [84][85][86] . Foraging appears to be the predominant activity performed by sub-adult/adult males while they are at the higher latitudes 32,33,87,88 , with a strong relation with the continental slope area 30,40,41,89 . ...
Sperm whale trumpets are sounds only occasionally documented, with a well recognisable and stereotyped acoustic arrangement. This study investigated the acoustic features of the trumpets and the context in which these sounds were recorded, using acoustic data collected over 22 years, in the Pelagos Sanctuary area (North-Western Mediterranean Sea). Analysed trumpets (n = 230), recorded at the beginning of a dive after the whale fluke-up, comprised a series of acoustic units organized in short sequences. Acoustic parameters were derived for the entire trumpet and for each distinguishable unit in a trumpet. Overall, trumpet durations and their initial frequencies were higher in recordings collected when multiple whales were visually or acoustically detected in the observation area. The identity of 68 whales was assessed through photo-identification, with 29 individuals producing trumpets within and between years. The variability of the acoustic parameters appeared to be higher within the same individuals rather than between different individuals, suggesting an individual plasticity in composing and arranging units in a trumpet. Different click patterns were observed before and after the trumpets, with more complex sequences when (1) other whales were visually/ acoustically detected, and (2) individuals were in suitable foraging sites (i.e., canyon areas). Trumpets were commonly followed or preceded by click patterns suited for communication, such as codas and/ or slow clicks. Significant relations between the trumpet emission and the male-only long-range communication click pattern (i.e. slow clicks) emerged, supporting the hypothesis that a trumpet is a sound emitted by maturing/mature males in feeding grounds. This study provides the first evidence that trumpets were conserved in the sperm whale acoustic repertoire at the decadal timescale, persisting across years and individuals in the same area. This persistence may be functionally specific to foraging activities performed by males in a well-established feeding area. Marine mammals rely heavily on sounds as their primary means of communication and sensing their word; where acoustic cues serve a fundamental role in all exchanges between individuals, from social interactions to the coordination of group activities 1-3. Some of these sounds have been investigated quite extensively in several species such as sperm whale (Physeter macrocephalus), and their significance and diversity are relatively well-established. Sperm whales mostly produce a number of sharp onset, broadband, evenly spaced pulses of decaying amplitude known as 'clicks' , with different properties and repetition rates, and a bandwidth of 100 Hz-30 kHz 4-8. Clicks-generated by the massive sperm whale nasal complex-may be temporally arranged in different patterns , having both echolocation and communication functionality 4,7,8. Usual clicks and creaks 9,10 are produced at depth and appear to be used primarily in searching for food and targeting the prey, respectively 8. Codas, generally emitted at the surface, are stereotyped patterns of clicks thought to serve in social communication in both sexes 8,11. Slow clicks, which are heard in the presence of mature or maturing males 5,7,12 at depth and at the surface, seem to be related with the sperm whale mating system, as long-range communication for attracting females or in male-male competition 8. Long-range communication between males in foraging grounds has been also reported, suggesting that slow clicks functionality may vary depending on the behavioural context 12. Some additional defined click patterns of surface creaks 8 (i.e. coda-creaks 10), rapid/fast clicks, and chirrups 9,13) have also been described in the acoustic repertoire of the species, and are possibly used for scanning their social partners 8. Sperm whales are also able to produce non-click sounds 8. These include "squeals", with a possible communicative social function 13,14 , 'pips' 13 , "short trumpets" 13 and "trumpets" 9 .
... In this way, sperm whales would be able to capitalize on the food resources (cephalopods) available in both areas by shifting between different prey targets (Gannier et al., 2002). The lower sperm whale relative abundance in the northern part of the study area than in the southern part (Pontine Archipelago) also seems to be consistent with recent published results showing variable encounters in the north (Arcangeli et al., 2017) and regular occurrences near Ponza and Ventotene islands Pace, 2016;Pace et al., 2018;Pace, Miragliuolo, Mariani, Vivaldi, & Mussi, 2014). This is also in line with sperm whale strandings, all located in the southern part of the area where deep waters are closer to the coast. ...
1. Sources of data other than those derived from conventional research protocols may contribute valuable information to fill gaps in knowledge about cetacean occurrences and diversity in a given area and help address conservation issues.
2. The performance of a method to examine cetacean communities based on presence records systematically derived from shared photographs and videos posted by boaters and maritime operators on social media (e.g. YouTube and Facebook) combined with patchy distributed visual/acoustic data collected by researchers has been evaluated.
3. Records (N = 1,274) gathered over a 10-year period (2008-2017) have been used to obtain insights into species' presence and habitat selection in a scattered study area of the central Mediterranean Sea (Italy). The effectiveness of the method, practical and theoretical advantages, limitations, and challenges of using data originated from social media for research and conservation purposes are discussed.
4. Seven out of the eight cetacean species regularly residing in the Mediterranean have been reported in the area, with different relative densities. Maximum entropy modelling techniques have been applied to the datasets derived from (a) social media, (b) research surveys, and (c) the combination of the two, using six fixed variables as proxies for cetacean presence. Distance from the coast and depth emerged as the main variables predicting encounters, with specificities related to the ecology of the species.
5. The approach was reliable enough to obtain broad-scale, baseline information on cetacean communities in the region, on the basis of which initial conservation recommendations and future research programmes can be proposed.
6. With the increasing need for studying whale and dolphin population ecology coming from national/international directives, support from citizens to aid research may act as a practical, inexpensive solution to gathering extensive spatial-temporal data for regional‐scale monitoring and for the development of management
priorities.
Daniela Silvia Pace and Antonella Arcangeli are contributed equally to this article
... They met our definition (box 1) to be classified as a single social unit by 2009, even though at that point in their gradual merger the two social units were often seen apart (electronic supplementary material, table S4). This suggests that social unit members, as we have defined them, are not such constant companions as previously assumed, despite our definition of social units (based on [15]) being more stringent than or similar to what has been used in other studies [19,30,70,71]. Rather, it appears that, in some cases, sub-social unit social structures may exist but go undetected with the types of analyses currently used to define constant companions, which often rely on sparse data. ...
Sperm whales have a multi-level social structure based upon long-term, cooperative social units. What role kinship plays in structuring this society is poorly understood. We combined extensive association data (518 days, during 2005–2016) and genetic data (18 microsatellites and 346 bp mitochondrial DNA (mtDNA) control region sequences) for 65 individuals from 12 social units from the Eastern Caribbean to examine patterns of kinship and social behaviour. Social units were clearly matrilineally based, evidenced by greater relatedness within social units (mean r = 0.14) than between them (mean r = 0.00) and uniform mtDNA haplotypes within social units. Additionally, most individuals (82.5%) had a first-degree relative in their social unit, while we found no first-degree relatives between social units. Generally and within social units, individuals associated more with their closer relatives (matrix correlations: 0.18–0.25). However, excepting a highly related pair of social units that merged over the study period, associations between social units were not correlated with kinship (p > 0.1). These results are the first to robustly demonstrate kinship's contribution to social unit composition and association preferences, though they also reveal variability in association preferences that is unexplained by kinship. Comparisons with other matrilineal species highlight the range of possible matrilineal societies and how they can vary between and even within species.
... Juveniles were occasionally recorded in all seasons only in this sector where the only large group of six individuals was also detected. Except for that, the small group sizes recorded (1-3 individuals) were not consistent with the values documented for social units in known key areas (Frantzis, Alexiadou, & Gkikopoulou, 2014;Pace, Miragliuolo, Mariani, Vivaldi, & Mussi, 2014;Pirotta et al., 2011 supporting the hypothesis of a prevalent use of these latitudes for dispersal movement mostly by singletons or pair/small groups. ...
1. Cetaceans are key biological indicators of the status of marine waters and are protected under
an extensive legislative framework. Research about these highly dynamic species is challenging,
so seasonal cycles and patterns of distribution, especially in high sea areas, are still poorly
understood.
2. This study contributes to improving knowledge about cetacean occurrence in largely unexplored
areas of medium‐latitudes in the western Mediterranean Sea. Systematic surveys were
conducted along a trans‐regional transect over 3 years (October 2012 to September 2015)
allowing consistent data collection over almost 60 000 km of effort through all seasons.
3. Seasonal cetacean diversity wasinvestigated using a25km2 grid cell as a statistical unit to explore
patterns of abundance, distribution, and habitat use in three marine sectors (Sardinian–Balearic,
Bonifacio Strait, Tyrrhenian). All cetacean species regularly present in the Mediterranean basin
were detected, with highest occurrence in fin whale and striped dolphin, followed by bottlenose
dolphin and sperm whale.
4. The Sardinian–Balearic sector generally showed higher species richness and diversity than the
Tyrrhenian, where seasonal variations were more pronounced. The study suggested seasonal
movements, especially for fin whale and striped dolphin, in the Sardinian–Balearic sector with
peaks of occurrence during spring/summer and lower numbers during winter/autumn, and also
delivered interesting insights to rarer pelagic species.
5. The study identified areas/seasons in which the combined effect of high species diversity,
abundance, significance of hot spots and presence of juveniles require increasing conservation
effort. Results underline the important contribution of continuous monitoring in high sea areas
to the implementation of adaptive protection measures.
http://onlinelibrary.wiley.com/doi/10.1002/aqc.2758/full
Full text available at: https://rdcu.be/2rsa
In the Ligurian Sea, the northern part of the Western Mediterranean Sea, sperm whales (Physeter macrocephalus Linnaeus, 1758) are historically sighted as solitary individuals or loose aggregations of males, while social units are extremely occasional. On 21 August 2020, two different social units were recorded in this area with an estimate of 21 individuals in total (12 in the first and nine in the second). The Mediterranean sperm whale subpopulation is considered Endangered under the IUCN Red List and an understanding of its movements and social structure is lacking. These observations increase our knowledge on its conservation biology and possible threats.
Sociality and ecological drivers that can influence individual association patterns are infrequently considered in wildlife management, although they are essential aspects affecting animals’ responses to both human-related pressures and conservation strategies. In common bottlenose dolphins (Tursiops truncatus), sex-specific social dynamics and interactions with anthropogenic activities may affect grouping and induce changes in relationships between individuals. Out of a total of 347 individuals, we assessed the level of association among 68 bottlenose dolphins that have been sighted more than five times near the Roman coast (central Mediterranean Sea, Italy). The half-weight index (HWI) of dyadic associations, their network relations, and stability over time were investigated by using the SOCPROG software. Outcomes showed that females were more strongly associated than other individuals, with both preferred constant short-term associations and random long-term associations, possibly resulting in greater success in rearing young. Individuals interacting with the bottom trawl fishery showed weaker and short-term associations. Temporary disruption of individual associations during interaction with fishery and the relatively low number of females with calves participating in depredation seem to denote both the opportunistic nature of interactions with fishing vessels and the offspring-related protection strategy. The results show that the dolphins in this region maintain a complex but flexible social structure that varies with local biological requirements and is resilient to anthropogenic pressures.
The identification of significant habitats for highly mobile marine vertebrates is essential for their conservation. Evidence is often difficult to obtain for deep‐diving species such as sperm whales (Physeter macrocephalus), where standard visual survey methods are not sufficient to detect the species. Sperm whales rely on sound for most of their activities, so acoustics is a crucial tool to locate them in the environment and collect information about their daily life. We used a maximum entropy (MaxEnt) modeling approach to predict potential habitats for sperm whales during 2007–2015 in an area of the Mediterranean Sea (characterized by submarine canyon systems) where sperm whale singletons, social units of females and calves, and clusters with immature males, were regularly encountered in sympatry. Models to test species’ distribution and the potential differences between groups of varying composition and life stages were based on 3 independent variables (depth, slope, and Euclidean distance from the nearest coast) and a combination of presence‐only visual and acoustic data from boat‐based surveys. One variable (depth) was the strongest predictor in all encounters (pooled data) and clusters, whereas distance from coast and slope best predicted encounters with singletons and social units, respectively. The model predicted suitable locations in areas that were well‐known sperm whale habitat and in new regions of previously overlooked habitat, which possibly represent key areas for this endangered species in the Mediterranean. This study highlights that consideration should be taken regarding type of social aggregation when using modeling techniques for generating suitable habitat maps for conservation purposes. © 2018 The Wildlife Society.
This volume presents a sweeping picture of what we know about the natural history, biology, and ecology of whales in the broad context of the dynamics of ocean ecosystems. The book encompasses multiple points of view to consider the total ecological impact of industrial whaling on the world's oceans. Combining empirical research, ecological theory and modelling, and historical data, the chapters present perspectives from ecology, population biology, physiology, genetics, evolutionary history, ocean biogeography, economics, culture, and law, among other disciplines. Throughout, chapoters investigate how whaling fundamentally disrupted ocean ecosystems, examine the various roles whales play in food webs, and discuss the continuing ecological chain reactions to the depletion of these large animals. In addition to reviewing what is known of the current and historic whale populations, this book considers how this knowledge will bear on scientific approaches to conservation and whaling in the future and provocatively asks whether it is possible to restore ocean ecosystems to their pre-whaling condition.
Distribution of cetaceans has been investigated in the north-western coast of the island of Ischia, corresponding to the uppermost area of the submarine canyon of Cuma. This zone is an important habitat where a particular pelagic assemblage can be found. The constant presence of whales and dolphins, pelagic fishes and marine birds is related to the geological and ecological characteristics of the area. Every summer we can observe in the area large groups of common (Delphinus delphis), striped (Stenella coeruleoalba), bottlenose (Tursiops truncatus) and Risso's dolphins (Grampus griseus). Feeding and mating behaviours were observed in all species. Newborns were sighted in July and August. The area is also used as feeding ground by fin whales (Balaenoptera physalus), the commonest species in the canyon. The analysis of fin whales' faecal material has revealed the presence of crustacean exoskeleton belonging to the euphasiacean Meganyctiphanes norvegica, a key species in the pelagic trophic web. Interactions with fishery were recorded in the area with illuminated hand-lines for squids, surface long-lines, trawling nets, purse-seine nets, bottom gillnets and drift nets. The strong impact of the boats on cetaceans is becoming everyday routine especially in summertime: distress and disorientation, collisions and deaths by a propeller strike. Timely management measures to monitor illegal fisheries and protect cetaceans as well as other species from bycatch and collisions are clearly needed. A first step should be to include the studied area (at least the more coastal part of it) into the future perimeter of the marine protected area proposed by Italian Ministry of Environment in the Phlegrean islands (Ischia, Procida and Vivara).
Sperm whale social distribution was investigated in the Mediterranean Sea, using data collected during summer surveys from 1997 to 2002. Variations in the size of sperm whale schools/underwater aggregations were assessed using both visual and acoustic data. Individual body lengths were estimated acoustically, using the click inter-pulse intervals. Regional comparisons were undertaken, taking the 41° parallel as a north/south boundary. In the southern region, schools of up to seven sperm whales were sighted and calves were relatively frequent. The animals ranged between 8·6 m and 13·1 m long. In the northern region, school sizes were significantly smaller, with a maximum of three whales sighted at the surface. However, the acoustic survey showed that sperm whales form loose aggregations of up to five animals in certain areas. Whales detected in the north were 12·6 m long on average, and the body size range was relatively small. This summer survey demonstrated a segregation of males, in the north, from larger schools including calves, which seemed to be confined to the southern region.
This chapter examines some of the physical processes associated with the regions where life stages of Illex species have been identified. Various mechanisms, seen in other OSLR (Ocean Sciences in Relation to Living Resources) studies, for enrichment, concentrating food and paralarvae, transporting eggs and juveniles, and facilitating adult spawning migrations are hypothesized to be acting. In some cases these are substantiated by existing information and in others the additional evidence required is outlined. In general, the greatest variety of processes with the greatest stability is associated with the habitats of Illex argentinus, while Illex illecebrosus is dominated by a single powerful, but variable current system. Illex coindetii's habitats tend to support only weak and relatively unpredictable processes. These trends appear to be reflected in stock size and stability.
Intra-specific variation in social organization provides valuable insights into the selective forces driving social evolution. Sperm whales are distributed globally and live far from shore, thus obtaining large sample sizes on social organization in multiple areas is logistically challenging and few comparative studies exist. In order to address how ecological factors influence sociality, we investigated the social organization of sperm whales in the Gulf of California (GoC) using a long-term study (1998–2004) and compare our results to other published studies. Standard photo-identification and behavioural observation techniques were used. Group size was calculated from photographic mark–recaptures using a Petersen estimator. Social organization was investigated using SocProg 2.3. Mean typical group sizes in the GoC were similar to those in the Galápagos Islands, Chile and Seychelles (24.7, 24.8, 30.4 and 18 individuals respectively), but substantially larger than in the Sargasso Sea, Caribbean and northern Gulf of Mexico (12.0, 6.4 and 6.9 individuals respectively). Sperm whale social organization in the GoC best fitted a constant companion/casual acquaintance model, where permanent units sizes were 12.5 individuals and two units usually associated together to form a group. This structure is similar to the situation in the Galápagos Islands and Chile areas. However, groups were more stable in the GoC than in the South Pacific, as groups stayed together for periods of about 80 days versus about ten days in the Galápagos Islands and Chile. It is likely that differences in the social organization between the study areas in the Pacific and Atlantic Oceans were due to differences in predation pressure and/or food resources. We suggest that, site-specific ecological factors are likely to influence fundamental aspects of sperm whale social organization.
Sperm whale Physeter macrocephalus habitat preferences are still poorly understood in the Mediterranean, despite the population being classified as 'Endangered' by the IUCN. Techniques to make the best use of multiple data sources are important in improving this situation. This work provides a detailed evaluation of sperm whale distribution and habitat use around the Balearic Islands using a novel analytical framework that combines transect and follow data while accounting for any autocorrelation present. During dedicated research cruises (2003 to 2008), sperm whales were located by listening at regular intervals along a search track and subsequently followed acoustically. Sperm whales were encountered 56 times and followed for periods ranging from a few hours to 3 d. Logistic Generalized Additive Models were used to model the probability of whale presence across the study area as a function of environmental variables, and Generalized Estimating Equations were used to account for autocorrelation. The results suggest that sperm whales do not use the region uniformly and that topography plays a key role in shaping their distribution. Moreover, solitary individuals were found to use the habitat differently from groups. This segregation appeared to be driven by water temperature and might reflect different needs or intraspecific competition. By shedding light on sperm whale habitat preference in such a critical area, this study represents an important step towards the implementation of conservation measures for this population. © 2011 Inter-Research.
The distribution of sperm whales in the Mediterranean Sea was investigated over 4 consecutive years. Field surveys took place in 1997, 1998, 1999 and 2000 between June and August from a 12 m survey boat equipped with towed hydrophones. The boat cruised at a mean speed of 6 knots on zig-zag lines. The total transect length was 12 709 km, and 3903 acoustic stations were assigned along the transects to monitor the underwater acoustic environment for sperm whale clicks. The Mediterranean Sea was divided into 6 regions for data analysis: the Ligurian Sea, the Gulf of Lions, the southwestern basin, the Alboran Sea, the Tyrrhenian Sea and the Ionian Sea. Relative frequencies and relative abundances of sperm whales were calculated from both visual and acoustic data. Acoustically, the Gulf of Lions yielded the highest relative abundance, with an average of 2.15 × 10-2 whales heard km-1 effort. High abundance was also seen in the southwestern basin and the Ionian Sea (1.90 × 10-2 and 1.21 × 10-2 whales heard km-1 respectively). Visual results indicated high relative abundance in the southwestern basin, with 4.88 × 10-2 sperm whales sighted km-1 effort. Intermediate values were obtained in the Ligurian Sea, and there were few sightings in the Alboran and Tyrrhenian Seas. Most of the sightings south of the 41° parallel consisted of sperm whale groups, of 5 to 7 individuals. Analysis of sperm whale distribution with respect to bathymetry did not establish a significant preference for either continental-slope waters or the open sea. High biological productivity in the northwestern basin might explain high sperm whale relative abundance, noticeably in the Gulf of Lions.
We can examine the evolution of multilevel societies using comparative studies. Intraspecific omparisons are valuable because confounding factors are reduced. Female sperm whales live in multilevel societies. However, studies at several locations have found substantial and consistent differences in social structure between the eastern Pacific and North Atlantic Oceans, even though nuclear DNA shows no significant differentiation between the populations. In the Pacific, female sperm whales live in nearly permanent social units that typically contain about 11 females and immatures of multiple unrelated matrilines. These units form temporary groups with other units for periods of days, apparently exclusively with other units from the same cultural clan. Clans contain thousands of females, are not distinct in nuclear DNA, but are sympatric and have distinctive culturally determined vocalizations and movement patterns. In the North Atlantic social units rarely group with other units, and there is no evidence for sympatric cultural clans. Possible drivers of these contrasts include oceanographic differences, predation, the effects of whaling, and culture. We suggest that protection against predation by killer whales is the primary reason for grouping in the Pacific, and as killer whales do not seem such a threat in the Atlantic, social units there rarely form groups, and have not evolved the clans that primarily function to structure inter-unit interactions. This analysis highlighted several factors that may influence the evolution of multilevel societies, ranging from the attributes of resources, to predation, anthropogenic effects, culture, and even the cultures of other species.
Sperm whale residency and movements within the Mediterranean Sea were investigated using photo-identification data collected in summer over a 15 year period (1991–2005). Surveys were conducted from a 12 m motor sailing boat. Although dedicated to cetaceans, surveys did not solely focus on sperm whale photo-identification, so time to track and photograph all individuals forming a group was not always available. From good quality photographs, 44 individuals were identified in the western Mediterranean, including the Ligurian Sea, the Gulf of Lions and waters off the Balearics. Eleven identified whales were photographically re-captures. Within-year re-sightings occurred from 1 to 29 d apart, while five identified whales were re-sighted over several summer seasons, from 1 to 7 y apart. Four whales were seen in more than one year in the northern part of the basin, indicating site fidelity to this feeding area. The combination of photo-identification and acoustic data (size estimation from inter-pulse interval measurements) enabled us to demonstrate a north–south movement of some sexually mature males (around 13 m in length), feeding in the northern regions and joining groups of females off the Balearics for around 20 d. These displacements ranged over ~500 km, with travelling time of seven days or less.
Male sperm whales (Physeter macrocephalus) were the preferred target of the whaling industry between 1950 and 1985, but despite hundreds of thousands of kills, very little is known about their ecology. To partially redress this, we present data on residency, seasonal distribution, and diving behaviour of individually identified sperm whales off Kaikoura, South Island, New Zealand, gathered during 15 field seasons over 8 years. One hundred and thirty-six sperm whales were identified within the study area. A lack of statistically significant differences in the abundance of sperm whales between summer and winter, and among the 15 seasons of fieldwork, suggests an adequate food supply year-round. Significant differences in distribution between summer and winter suggest that off Kaikoura, male sperm whales may change their diet in response to fluctuations in prey biomass. Diving behaviour was also significantly different between summer and winter: sperm whales dived for longer, stayed longer at the surface, and travelled farther between consecutive fluke-ups in summer than in winter. Unlike female sperm whales, males at Kaikoura spent little time at the surface; they spent about 83% of their total time under water. This paper represent the most extensive non-invasive study of male sperm whales and provides new insights into their ecology.
Sperm whales (Physeter macrocephalus) are sexually dimorphic in several respects, including size, latitudinal distribution, and social structure. Females are known to have complex social structures, including long-term bonds, but the social structures of sexually mature or maturing males have received much less attention. Using data from aggregations of males off Norway, Nova Scotia, New Zealand, and the Galapagos Islands, we examined aggregation size, residence times within aggregations, clustering at the surface, and long-term bonds. Results were generally consistent among study areas. The aggregations found in each area contained around 10-30 males at any time, and were usually a few tens of kilometres across. Mean residence times within aggregations ranged from a few days to a few weeks. Close clustering at the surface was rare, but present at each site. There was no evidence for preferred companionship between individuals at any temporal scale in any of the study areas. The rarity of clustering and the apparent lack of long-term relationships amongst male sperm whales contrast strongly with results of studies on females, suggesting that both close spatial proximity at the surface and permanent bonds between individuals may be a consequence of the need for care of the young.
From 1991-2002 data on the presence and distribution of cetaceans in the Greek Seas have been systematically collated in a database (821 sightings and 715 strandings). Data originated from dedicated surveys, stranding reports, opportunistic sightings and published or unpublished photographic and video documents. Twelve cetacean species have been recorded. Seven of them are permanently present and commonly observed in one or more of the Greek Seas: striped dolphin, common bottlenose dolphin, short-beaked common dolphin, Cuvier's beaked whale, sperm whale, Risso's dolphin and fin whale. In addition, the harbour porpoise is present locally in the Thracian and northern Aegean Seas. The humpback whale, false killer whale and common minke whale are occasional Mediterranean species that were sighted or stranded infrequently; the Sowerby's beaked whale is an accidental species that was found floating dead only once. Five other species (white whale, Blainville's beaked whale, long-finned pilot whale, killer whale, blue whale) have been erroneously included in the Greek cetacean fauna in the past due to wrong assumptions, false identifications or lack of supporting evidence. The occasional occurrence of pilot and killer whales in the Greek Seas should still be regarded as unconfirmed. The distributional range, stranding numbers and sighting frequencies of sperm whales, Cuvier's beaked whales and short-beaked common dolphins in the Greek Seas indicate that their local 'sub-populations' are among the most important in the entire Mediterranean Sea. Harbour porpoises in the Thracian and northern Aegean Seas are important from a conservation perspective since this species does not inhabit any other part of the Mediterranean Sea.
We used individual-based stochastic models to examine how social structure influences the diversity of socially learned behaviour within a non-human population. For continuous behavioural variables we modelled three forms of dyadic social learning, averaging the behavioural value of the two individuals, random transfer of information from one individual to the other, and directional transfer from the individual with highest behavioural value to the other. Learning had potential error. We also examined the transfer of categorical behaviour between individuals with random directionality and two forms of error, the adoption of a randomly chosen existing behavioural category or the innovation of a new type of behaviour. In populations without social structuring the diversity of culturally transmitted behaviour increased with learning error and population size. When the populations were structured socially either by making individuals members of permanent social units or by giving them overlapping ranges, behavioural diversity increased with network modularity under all scenarios, although the proportional increase varied considerably between continuous and categorical behaviour, with transmission mechanism, and population size. Although functions of the form e(c)¹(m)⁻(c)² + (c)³(Log(N)) predicted the mean increase in diversity with modularity (m) and population size (N), behavioural diversity could be highly unpredictable both between simulations with the same set of parameters, and within runs. Errors in social learning and social structuring generally promote behavioural diversity. Consequently, social learning may be considered to produce culture in populations whose social structure is sufficiently modular.
In support of its acoustic risk mitigation policy, NATO SACLANT Undersea Research Centre (SACLANTCEN) is sponsoring a series of sea trials, entitled "Sirena" to collect a multiyear integrated oceanographic, biological, and hydrographic data set, the goal being to explain, based on these parameters, the distribution of marine mammals found in specific locations. By understanding how ocean dynamics affects the distribution and behavior of whales and the organisms forming the food web upon which the whales feed, it may be possible to conduct acoustic exercises in areas of low cetacean density. The first two Sirena multidisciplinary cruises were conducted in the Ligurian Sea in late summer time frame during 1999 and 2000. The focus of this analysis is to determine whether remotely sensed satellite data can indicate nutrient-rich regions in areas where the oceanography is known and to determine if these regions of higher productivity, coupled with knowledge of cetacean presence from all available sources, could be used as an indicator of marine mammal presence for acoustic risk mitigation purposes. For the two years of data examined, cooler sea-surface temperature data correlated with high levels of chlorophyll production as seen by remotely sensed images. This remotely sensed data correlated well with measured subsurface values of the same parameters. Coincident sightings of three species of marine mammals indicated that fin and sperm whales generally preferred the deep, nutrient-rich portion of the basin while Cuvier's beaked whales preferred a submarine canyon where there is a frontal influence, as indicated from satellite data and historical oceanography. This paper is intended as a contribution to the longer term objective of developing the means to accurately predict cetacean presence from physical oceanographic characteristics.
This study investigates the extent of the pollution of the Mediterranean Sea with respect to the four bordering EC countries - spain, France, Italy, and Greece. The environmental pressures and economic impacts are examined and the institutional/legal framework is described together with all the necessary environmental expenditures. The book is written in such a way that separate chapters are devoted to each of the four countries, after an initial section summarizing the major commonalities. These chapters are organized in parallel formats so that it is possible to examine the same topic country by country. Good references are provided for the reader who is not familiar with the subject of Mediterranean pollution. For specialists, the book provides a useful overview of adjacent fields other than their own speciality: for policymakers, the chapters provide sufficient foundations for decision-making: for the investment planner and banks, it provides budget and investment needs; and for the private sector, it gives an insight into the possibilities for corporate applications of environmental technologies. Four specialists - Prof. V. Silano (Italy), Dr. M. Vassilopoulos (Greece), Dr. L.A. Romafia (France), and Mr. A. Estevan (Spain- contributed sustantially by evaluating the necessary information from national documents on environmental policies and strategies. The book was developed on the basis of an integrated environmental study financed by the European Investment Bank, to which we would like to express our sincere thanks.
This unprecedented volume presents a sweeping picture of what we know about the natural history, biology, and ecology of whales in the broad context of the dynamics of ocean ecosystems. Innovative and comprehensive, the volume encompasses multiple points of view to consider the total ecological impact of industrial whaling on the world's oceans. Combining empirical research, ecological theory and modeling, and historical data, its chapters present perspectives from ecology, population biology, physiology, genetics, evolutionary history, ocean biogeography, economics, culture, and law, among other disiplines. Throughout, contributors investigate how whaling fundamentally disrupted ocean ecosystems, examine the various roles whales play in food webs, and discuss the continuing ecological chain reactions to the depletion of these large animals. In addition to reviewing what is known of the current and historic whale populations, Whales, Whaling, and Ocean Ecosystems considers how this knowledge will bear on scientific approaches to conservation and whaling in the future and provocatively asks whether it is possible to restore ocean ecosystems to their pre-whaling condition.
This chapter describes the ecology of the sperm whale, Physeter macrocephalus. It describes the trophic web surrounding the sperm whale with the goal of addressing three questions: How are sperm whale populations regulated? How do sperm whales affect other elements of the marine environment? How has sperm whaling affected marine ecosystems? In describing sperm whale ecology, it summarizes what people know of sperm whale prey, competitors, life history, and predators and tries to evaluate both the bottom-up (through competition for prey) and top-down (through predation by orcas) hypotheses for the natural regulation of populations. Whaling certainly affected sperm whale populations, and the chapter summarizes this huge enterprise and considers the potential effects of the killing of so many sperm whales on other elements of the ecosystem.
The cows with their young give from nothing up to 35 barrels, and seem to go in schools together, and we frequently see from twenty-five to fifty and sometimes one hundred or more in a school, with occasionally a large bull among them, and at times, though seldom, we find all sizes together. The male or bull whales seem to separate from the cows and calves when about the size of 35 barrels, as we seldom get them in the schools of the mother and its young to make more oil than that, and we find the young bulls in pods or schools beyond that size; we find them in what we call 40-barrel bulls, where they generally go in larger numbers than they do as they increase in size; we find them again in smaller schools of about the size of 50 barrels, and again about 60 barrels, where we sometimes see eight or ten together, and 70 barrels four or five, and beyond that one, two, and three....
Boat surveys aimed at studying sperm whales in the Tyrrhenian Sea were conducted between 2002 and 2011. During 768 daily surveys, a total effort of 32 602 km was achieved within an area of 8800 km ² resulting in 92 encounters with 229 sperm whale individuals.
Average encounter rates of sperm whales was 0.5 groups per 100 km ² , with a higher concentration in the vicinity of the submarine canyon of Cuma, confirming the importance for the species of this small hotspot in the Mediterranean Sea.
Encounter rates increased with increasing distance from the coast. It is possible that the intense boat traffic and anthropogenic disturbance in the area may be moving animals away from the coast leading to habitat loss.
The species–habitat relationship documented in this study has implications for conservation.
Copyright © 2014 John Wiley & Sons, Ltd.
Studies of mature male sperm whales (Physeter macrocephalus) were carried out on the Scotian Shelf during the summers of 1986, 1988, 1989, and 1990. Sperm whales were found principally along the edge of the Shelf, although there were some encounters in water less than 100 m deep. Within the Gully, a prominent submarine canyon, sperm whales showed a consistent pattern of distribution between years, distinct from that of northern bottlenose whales (Hyperoodon ampullatus). Some male sperm whales were individually identified in the Gully after periods of 2–47 days, and in one case, after 2 years. The male sperm whales showed little evidence of social organization and rarely performed aerial behaviour. However, their diving behaviour was similar to that observed from female sperm whales in the tropics. On one occasion a group of presumed female and immature sperm whales entered the Gully, attracting the attention of resident mature males.
Between February and April 1985 sperm whales (Physeter macrocephalus) were tracked visually and acoustically in the waters west of the Galapagos Islands. Individuals were identified and measured photographically. Using statistical criteria the female and immature whales encountered were clustered into 13 groups with closed membership during the study period. These groups had a median estimated population of 19.5 animals each, and associated with one another at different times. The groups showed no significant immigration into or emigration from the study area during the study. Seven large males were identified. These associated with each other and the groups of females and immatures for periods lasting approximately 6 h. Individual males were found with different groups of females and immatures at different times. A simple model suggests that a male employing a "searching" strategy should encounter more oestrous females than the traditionally accepted "harem" holder when the interval between encountering groups of females is less than the duration of the females' oestrus. Neither the groups of females nor the mature males appeared to possess territories or preferred ranges within the study area. The number of large males encountered was considerably less than that expected if all large males were present on the breeding grounds, suggesting that males may not breed every year.
A link is proposed between the processes that led to the evolution of large species of squid and the highly variable, cyclic recruitment seen in squid fisheries. Maximum growth requires maximal feeding and minimal routine metabolism at optimum temperatures, which decrease as squid grow. Topographically induced upwelling zones, inshore of western boundary currents, provide productive environments with appropriate temperatures for all life stages. Most squid are small and live in the tropics or subtropics; locomotor constraints prevent them from swimming long distances. Long annual migrations to spawn upstream in current systems require short-lived squids to maximize rates of growth. Therefore, such systems provide the opportunity and a powerful selective advantage for large size and rapid growth. Increased fecundity and cannibalism provide additional directional selection for large individuals. Current systems show food production peaks (blooms); paralarval release must match these to increase survival. Because squid are semelparous, disruption of delicately balanced lifecycles by physical events can virtually annihilate stocks. Recovery probably requires that populations of large squid "re-evolve" from smaller, more-stable tropical populations of small squid. This recovery phase may extend the "down-side" of abundance cycles. Studies of squid/current systems have focused on western boundary currents, but the Illex complex also associates with eastern boundaries. Such populations are generally smaller than in larger systems, supporting the hypothesis, but more detailed comparisons are required.
Strong social bonds are uncommon among male mammals. In many mammals, however, males form all-male groups, providing opportunities for male-male bonds to emerge. We examined association patterns of male African elephants, Loxodonta africana, in all-male groups and assessed the influence of age and genetic relatedness on these associations. We also examined the influence of age and genetic relatedness on the choice of sparring partners in male elephants. Males had many weak and random associations and few valuable relationships. Male associations were positively correlated with genetic relatedness, suggesting that kinship influences patterns of male associations. Male associations were negatively correlated with age disparity, and males were more likely to spar with other males closer in age to themselves. These results suggest that males associate with other males of similar age in part because sparring may facilitate the development and maintenance of motor and psychological responses to sudden and unexpected events that occur during play; this may help prepare males for male-male competition. We also found that older males had high centrality and strength in social networks, suggesting that older males influence the cohesion of male social groups. Consequently, the elimination of older males from elephant populations by poachers or trophy hunters could negatively affect social cohesion in male elephant groups. Finally, we found that age and genetic relatedness were not significantly correlated, suggesting that male associations based on age and relatedness did not overlap. These findings highlight the complexity of male social relationships in all-male groups.
In February 2002, France, Italy and Monaco agreed to establish an international sanctuary for Mediterranean marine mammals. The resulting Pelagos Sanctuary encompasses over 87500 km ² of the north‐western Mediterranean Sea, extending between south‐eastern France, Monaco, north‐western Italy and northern Sardinia, and surrounding Corsica and the Tuscan Archipelago.
The Pelagos Sanctuary illustrates how the tenets of Marine Protected Area (MPA) design can be reconciled with the dynamic nature of oceanic systems, because its spatial scale was defined by oceanographic and ecological considerations, specifically the location of the Ligurian permanent frontal system.
By expanding protective measures beyond national waters, the Pelagos Sanctuary also sets a precedent for the implementation of pelagic protected areas in the high seas. The Pelagos Sanctuary will contribute to the conservation of the Mediterranean Sea at two scales: (i) locally, by protecting important cetacean foraging and breeding grounds in the Ligurian Sea, and by providing ‘umbrella’ protection to other marine predators in this area; and (ii) regionally, by empowering other conservation measures, such as the Specially Protected Areas Protocol of the Barcelona Convention and the wider goals of the Agreement on the Conservation of Cetaceans of the Black and Mediterranean Seas (ACCOBAMS).
However, because few cetacean species are resident within the Sanctuary, their effective long‐term conservation will require large‐scale management and coordinated monitoring throughout the Mediterranean basin.
Copyright © 2007 John Wiley & Sons, Ltd.
Associations among female sperm whales, Physeter macrocephalus, and their dependent offspring, off the Galapagos Islands were studied between 1985 and 1989. The whales were found in groups containing about 23 individuals, with each individual having approximately 12 constant (over years) companions. These permanent units associated with one another for periods of 6.5 days, although the rate and duration of these associations seemed to vary between years, perhaps because of differences in the food supply. The principal function of the closed units may be care of the offspring, and units in the same general area may derive benefit from feeding in a coordinated manner.
Macrofaunal abundance, biomass, diversity and species assemblages within Scripps and La Jolla Submarine Canyons are compared with those on the nearby continental shelf and slope. Our primary objective was to examine the effect of detrital aggregates on infaunal communities within canyons. Two submarines, a remotely operated vehicle (ROV), and a Soutar box-corer were used to collect samples. Within the canyons, organic enrichment by macrophyte detritus was evident from canyon heads down to 550 m, and evidence of strong currents (coarse sediment) was found down to 700 m. Infaunal density and biomass were higher in the canyons than outside at all depths where comparative data were available (100–500 m). Infaunal assemblages in canyons were distinct from those at reference stations. Both the canyon and non-canyons samples showed community differentiation with depth. Species diversity was generally high, but decreased with depth outside of canyons and increased with depth within the canyons. Low diversity at shallow depths within the canyon is attributed to a combination of organic enrichment and physical disturbance. Submarine canyons are commonly found to contain distinct species assemblages or higher faunal densities and/or biomass than nearby non-canyon regions at similar depths. Canyons are regular features along most ocean margins and appear to be important as sites of enhanced secondary production, provide diverse habitats, and act as conduits of coastal detritus to the deep-sea.
The Gully, a submarine canyon off eastern Canada, was nominated as a pilot Marine Protected Area (MPA) in 1998, largely to safeguard the vulnerable population of northern bottlenose whales (Hyperoodon ampullatus) found there. The boundaries and ultimate management regime for the MPA for this area remain under review. We have estimated the energy consumption of bottlenose whales in the Gully based on the number of whales present at any time, their trophic level, the food requirements of each whale, and the rates of energy transfer between trophic levels. These calculations suggest that there must be a substantial spatial subsidy in the underlying foodweb of the submarine canyon to support the bottlenose whales using the Gully. A substantial area beyond the distribution of bottlenose whales in the area will therefore require protection. Conservation priorities to protect such subsidies will primarily involve additional protection at the level of the sea floor. Spatial subsidies are probably common in the marine environment, urging careful ecological analysis in the establishment of marine reserves and suggesting that conservation priorities need to take into account key ecological linkages and processes that are vital for sustaining species and habitats of concern.
During foraging dives, sperm whales (Physeter macrocephalus) produce long series of regular clicks at 0.5-2 s intervals interspersed with rapid-click buzzes called "creaks". Sound, depth and orientation recording Dtags were attached to 23 whales in the Ligurian Sea and Gulf of Mexico to test whether the behaviour of diving sperm whales supports the hypothesis that creaks are produced during prey capture. Sperm whales spent most of their bottom time within one or two depth bands, apparently feeding in vertically stratified prey layers. Creak rates were highest during the bottom phase: 99.8% of creaks were produced in the deepest 50% of dives, 57% in the deepest 15% of dives. Whales swam actively during the bottom phase, producing a mean of 12.5 depth inflections per dive. A mean of 32% of creaks produced during the bottom phase occurred within 10 s of an inflection (13x more than chance). Sperm whales actively altered their body orientation throughout the bottom phase with significantly increased rates of change during creaks, reflecting increased manoeuvring. Sperm whales increased their bottom foraging time when creak rates were higher. These results all strongly support the hypothesis that creaks are an echolocation signal adapted for foraging, analogous to terminal buzzes in taxonomically diverse echolocating species.
An unusually high concentration of blue whales,Balaenoptera musculus, fed on euphausiids that were concentrated in deep scattering layers and daytime surface swams in Monterey Bay, California, during the fall of 1986. Blue whales were closely associated with deep scattering layers that were elongated along the southeast edge of the Monterey Submarine Canyon throughout most of November 1986. These scattering layers contained euphausiids, primarily Thysanoessa spinifera, which accounted for 45.4% of the total biomass of zooplankton tows taken through deep scattering layers. Tows taken above or outside the layers consisted of only 4.0% euphausiids. The greatest concentrations of blue whales were observed in areas of thick scattering layers that contained high krill biomass. In addition, surface-lunging blue whales fed on daytime surface swarms of Thysanoessa spinifera near the head of Monterey Submarine Canyon on 11 and 12 November 1986. Surface tows taken in whale feeding areas were dominated by T. spinifera, which accounted for 64.4% of the total zooplankton biomass, while surface tows taken outside whale areas consisted of only 0.3% euphausiids. Euphausiid densities in surface swarms were slightly higher and more variable than in deep layers. Thysanoessa spinifera size frequency distributions showed that surface swarms may be similar to the deep layer in some areas, but they may contain larger, sexually mature individuals in other areas. Blue whale fecal samples confirmed that the whales were feeding on euphausiids. The disappearance of the blue whales from Monterey Bay was accompanied by a decline in krill biomass along the southeast edge of the submarine canyon. This coincided with the cessation of a prolonged upwelling period that persisted in Monterey Bay throughout November 1986.
Mature female sperm whales (Physeter macrocephalus) live in socially cohesive groups of 10-30, which include immature animals of both sexes, and within which there is communal care of the young. We examined kinship in such groups using analyses of microsatellite DNA, mitochondrial DNA sequence, and sex-linked markers on samples of sloughed skin collected noninvasively from animals in three groups off the coast of Ecuador. Social groups were defined through photographic identification of individuals. Each group contained about 26 members, mostly female (79%). Relatedness was greater within groups, as compared to between groups. Particular mitochondrial haplotypes were characteristic of groups, but all groups contained more than one haplotype. The data are generally consistent with each group being comprised of several matrillines from which males disperse at about the age of 6 years. There are indications of paternal relatedness among grouped individuals with different mitochondrial haplotypes, suggesting long-term associations between different matrilines.
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