Blackfish as a conservation unit: A review of five Globicephalinae species with a focus on the Pacific

Adults of many free‐ranging delphinid species cannot be reliably sexed at sea. Sexually mature, known‐sex adult short‐finned pilot, pygmy killer, melon‐headed, and false killer whales were profiled from at‐sea photos to assess proportional fin and body dimorphism. Males of all four species had larger dorsal fins proportional to anterior body length. False killer whales showed no further dimorphism, while melon‐headed whales showed subtle dimorphism in dorsal fin overhang. Pygmy killer whales showed subtle dimorphism in lateral positioning of the top‐most point and overhang. Lastly, short‐finned pilot whales showed strong dimorphism in the leading edge, lateral positioning of the top‐most point, and height of the overhang. Generalized linear models showed strong predictive accuracy for pilot and false killer whales, and moderate accuracy for pygmy killer and melon‐headed whales. Results indicate that adult short‐finned pilot and false killer whales can be accurately sexed in the field or via morphometrics. Adult pygmy killer and melon‐headed whales have subtle sexual dimorphism that can be detected using morphometrics. The presence of dimorphism gives insight into potential reproductive strategies and social structure. Further analysis is needed to explore morphometric differences between inshore and pelagic populations of these species, as well as ontogenetic growth between life stages.

Melon-Headed Whale: Peponocephala electra

Odontocetes (toothed whales) are considered sentinel species in the marine environment because of their high trophic position, long life spans, and blubber that accumulates lipophilic contaminants. Cytochrome P4501A1 (CYP1A1) is a biomarker of exposure and molecular effects of certain persistent organic pollutants. Immunohistochemistry was used to visualize CYP1A1 expression in blubber biopsies collected by non-lethal sampling methods from 10 species of free-ranging Hawaiian odontocetes: short-finned pilot whale, melon-headed whale, pygmy killer whale, common bottlenose dolphin, rough-toothed dolphin, pantropical spotted dolphin, Blainville's beaked whale, Cuvier's beaked whale, sperm whale, and endangered main Hawaiian Islands insular false killer whale. Significantly higher levels of CYP1A1 were observed in false killer whales and rough-toothed dolphins compared to melon-headed whales, and in general, trophic position appears to influence CYP1A1 expression patterns in particular species groups. No significant differences in CYP1A1 were found based on age class or sex across all samples. However, within male false killer whales, juveniles expressed significantly higher levels of CYP1A1 when compared to adults. Total polychlorinated biphenyl (∑PCBs) concentrations in 84% of false killer whales exceeded proposed threshold levels for health effects, and ∑PCBs correlated with CYP1A1 expression. There was no significant relationship between PCB toxic equivalent quotient and CYP1A1 expression, suggesting that this response may be influenced by agonists other than the dioxin-like PCBs measured in this study. No significant differences were found for CYP1A1 expression among social clusters of false killer whales. This work provides a foundation for future health monitoring of the endangered stock of false killer whales and other Hawaiian odontocetes.

Cetaceans observed in Maldivian waters were recorded during the period August 1990 to June 2002, from both vessels-of-opportunity and dedicated cetacean-watching cruises. A total of 1,829 cetacean sightings were recorded during 535 days at sea (equivalent to 261 standardised days). There were 83 multispecies sightings, plus a further 58 sightings without associated effort data and 129 strandings were recorded by the author and others, making a total of 2,108 cetacean records. In all, 20 different species were positively identified from sightings. Spinner dolphins were the most abundant species seen, accounting for 35% of sightings and 53% of numbers. This species showed a clear diurnal pattern of behaviour, with many schools entering the atolls in the early morning, and leaving in the late afternoon. Spinner dolphins regularly occurred with pantropical spotted dolphins and both species associated with yellowfin tuna. Bryde’s whales also associated with yellowfin tuna and appeared to be most common in Maldivian waters during El Niño Southern Oscillation events. Blue whales were only recorded during November to April. Dwarf sperm whales were especially difficult to locate in rough weather but relatively common, making up one sixth of all sightings in flat-calm conditions. Melon-headed whales were particularly common in the south of the Maldives, but rare in the centre and north. Other species recorded were humpback whale, sperm whale, rough-toothed dolphin, Risso’s dolphin, bottlenose dolphin, striped dolphin, Fraser’s dolphin, pygmy killer whale, false killer whale, killer whale, short-finned pilot whale, Blainville’s beaked whale, Longman’s beaked whale and Cuvier’s beaked whale.

Information on cetaceans in the Indian Ocean Sanctuary and the South China Sea is summarised from a cruise carried out from 29 March to 17 April 1999. Ten species were positively identified: finless porpoise, pantropical spotted dolphin, spinner dolphin, sperm whale, melon-headed whale, pygmy killer whale, false killer whale, Cuvier’s beaked whale, Bryde’s whale and fin whale. Spotted dolphins, melon-headed and pygmy killer whales were sighted around the Island of Borneo and sightings of fin whales and a sperm whale west of the Balabac Strait suggest a possible migration route of these species between the South China Sea and the Sulu Sea. This is the first record of fin whales in the South China Sea.

The cetaceans of Ghana and the Gulf of Guinea have, until recently, remained unstudied. Periodical monitoring of artisanal fisheries for bycatches in seven Ghanaian artisanal fishing ports and landing sites over 1996-2004 has provided photographic and specimen evidence to validate occurrence of 18 species (17 odontocetes, 1 mysticete) in a tropical, predominantly pelagic cetacean fauna. At least nine species and subspecies had not previously been documented for Ghana (with asterisk), and four species are authenticated for the first time in the Gulf of Guinea (double asterisk), i.e. Tursiops truncatus, Stenella clymene, S. longirostris longirostris*, S. attenuata, S. frontalis, Delphinus capensis capensis*, Lagenodelphis hosei, Steno bredanensis, Grampus griseus, Peponocephala electra*, Feresa attenuata**, Globicephala macrorhynchus, Orcinus orca*, Pseudorca crassidens*, Kogia sima**, Physetermacrocephalus*, Ziphius cavirostris** and Megaptera novaeangliae . Also, the limited published information on distribution, natural history and conservation status is critically reviewed for each taxon. Indications are that most species encountered off Ghana may be widely distributed in the Gulf of Guinea, most notably the long-beaked common dolphin. The vulnerable Atlantic humpback dolphin, Sousa teuszii, remains unrecorded in Ghana and neighbouring nations despite apparently suitable coastal habitat. It is suggested that localized extinction may be blamed, possibly the result of accumulative bycatches and disturbance. A number of other cetacean species not yet encountered could occasionally occur in Ghana's waters, e.g. Balaenoptera brydei, Mesoplodon densirostris, Kogia breviceps, Stenella coeruleoalba and Delphinus delphis

In this assessment we incorporated published and unpublished information to delineate and score Biologically Important Areas (BIAs) for cetaceans in the Hawaiʻi region following standardized criteria. Twenty-six cetacean species have been documented in Hawaiʻi. Eleven odontocete species have distinct small populations resident to one or more island areas: rough-toothed dolphins, pantropical spotted dolphins, common bottlenose dolphins, spinner dolphins, short-finned pilot whales, false killer whales, pygmy killer whales, melon-headed whales, Blainville’s beaked whales, Cuvier’s beaked whales, and dwarf sperm whales. Eight species of mysticetes have been documented, although their occurrence and behavior are poorly understood, with the exception of breeding humpback whales and, more recently, common minke whales. Thirty-five BIAs were delineated or revised from the initial 2015 effort: 33 for small and resident odontocete populations and two for humpback whale reproductive areas. Hierarchical BIAs reflecting core areas of use or population-specific ranges were delineated for nine species. Reproductive watch list areas were designated for common minke whales in the main Hawaiian Islands (MHI) and humpback whales in the Northwestern Hawaiian Islands (NWHI); these areas did not meet the criteria for a BIA due to limited supporting information. All but three BIAs were in the MHI, reflecting the disparities in research effort between this region and the NWHI. Spatial extents of BIA boundaries ranged from 457 km2to 138,001 km2(median = 8,299 km2). Scores (range: 1-3) for Data Support and Boundary Certainty were moderate to high (mean = 2.40 and 2.43, respectively), while Intensity and Importance scores were slightly lower (mean = 1.94 and 1.89, respectively). Many of the Hawaiʻi species have been extensively studied over several decades; accordingly, this region ranks among the highest in terms of Data Support relative to other regions. BIAs presented here describe known ranges of small resident populations, intensities of use, and uncertainties in important areas for cetaceans in Hawaiʻi based on the best available data, and have also revealed knowledge gaps to guide future research efforts.

The study reports for the first time, the live sighting of the pygmy killer whale, Feresa attenuata Gray, 1857, from Indian waters adding valuable information on their limited records available from this region. The elusive nature of the species, along with its morphological similarities to the melon-headed whale (Peponocephala electra) and the false killer whale (Pseudorca crassidens), makes accurate identification challenging. Additionally, its predominantly nocturnal behaviour further contributes to the rarity of sightings worldwide. In the present study, a pod of 19 pygmy killer whales (F. attenuata) was sighted in the vicinity of Minicoy Island in the Lakshadweep Sea. This represents the first documented live encounter of the species in Indian waters, where previous records were limited to stranded individuals. The live observation of this rarely sighted delphinid provides valuable insights into its social interactions, behavioural patterns, and group dynamics.

The pygmy killer whale Feresa attenuata Gray, 1874 is one of the species usually known as 'black fish', which is easily mistaken for the false killer whale, Pseudorca crassidens (Owen 1846) and the melon-head whale, Peponocephala electra (Gray, 1846), especially in the field. Prior to 2002, there were very few data on this species in Venezuela and the only reports were based on craneometric studies of stranded animals in the western region. Five new reports on this species have been recorded since in the northeastern zone of the country, based on sightings or assistance of live-stranded animals. Detailed comparisons were made on specimens observed in the field for their corrected identification. These sightings and strandings of F. attenuata are the first reported for the Venezuelan northeast basin, thus increasing the number of reports of pygmy killer whales to seven in the country and extending their known distribution through the southern Caribbean Sea.

: A long-term assessment of odontocete populations throughout the main Hawaiian Islands has involved small-boat surveys using photo-identification, genetic sampling and satellite tagging, to address questions related to population structure and habitat use, among others. Prior to 2010 we had undertaken limited field operations off O'ahu (in 2002 and 2003), and off of Kaua'i (in 2003, 2005 and 2008). Navy training activities may take place throughout the Hawai'i Range Complex, however many of the training exercises are undertaken in the western main Hawaiian Islands, in particular at the Pacific Missile Range Facility (PMRF) off Kaua'i and Ni'ihau. As part of an effort to reduce uncertainty regarding the population structure, range, and abundance of odontocetes in the western main Hawaiian Islands, to help inform Navy impact assessments, we undertook small-boat based research efforts off O'ahu (in 2010) and off Kaua'i (in 2011 and 2012). These efforts utilized a variety of field methods to obtain data sets relevant to assessing these population characteristics, including photo-identification, collection of biopsy samples for genetic studies, and satellite tagging. Over the three years of the project surveys were undertaken on 66 days (406 hours), covering 6,559 km. Overall there were 191 odontocete sightings, 183 of which were identified to species. Off O ahu there were 30 sightings of 10 species, while off Kaua'i and Ni'ihau there were 153 sightings of eight species. One hundred and two biopsy samples were collected from seven different species for genetics and toxicology studies. Thirty satellite tags were deployed on five species: pygmy killer whales, false killer whales, bottlenose dolphins, rough-toothed dolphins, and short-finned pilot whales. For all five species, tag data indicate that there are island-associated populations.

The study of marine soundscapes is a growing field of research. Recording hardware is becoming more accessible; there are a number of off-the-shelf autonomous recorders that can be deployed for months at a time; software analysis tools exist as shareware; raw or preprocessed recordings are freely and publicly available. However, what is missing are catalogues of commonly recorded sounds. Sounds related to geophysical events (e.g. earthquakes) and weather (e.g. wind and precipitation), to human activities (e.g. ships) and to marine animals (e.g. crustaceans, fish and marine mammals) commonly occur. Marine mammals are distributed throughout Australia’s oceans and significantly contribute to the underwater soundscape. However, due to a lack of concurrent visual and passive acoustic observations, it is often not known which species produces which sounds. To aid in the analysis of Australian and Antarctic marine soundscape recordings, a literature review of the sounds made by marine mammals was undertaken. Frequency, duration and source level measurements are summarised and tabulated. In addition to the literature review, new marine mammal data are presented and include recordings from Australia of Omura’s whales (Balaenoptera omurai), dwarf sperm whales (Kogia sima), common dolphins (Delphinus delphis), short-finned pilot whales (Globicephala macrorhynchus), long-finned pilot whales (G. melas), Fraser’s dolphins (Lagenodelphis hosei), false killer whales (Pseudorca crassidens), striped dolphins (Stenella coeruleoalba) and spinner dolphins (S. longirostris), as well as the whistles and burst-pulse sounds of Australian pygmy killer whales (Feresa attenuata). To date, this is the most comprehensive acoustic summary for marine mammal species in Australian waters.

Melon-headed whale (Peponocephala electra) and Pygmy killer whale (Feresa attenuata) are very poorly known species and are often confused with each other. We examined in detail Figure 3 in MARIGO and GIFFONI (2010) who reported that two melon-headed whales were taken in a surface driftnet about 90 nm off Santos, Brazil. We concluded they were in fact pygmy killer whales and explain our reasoning. To aid in future identifications, we illustrate and describe some of the main differences between these two species of small cetaceans. The incident reported by MARIGO and GIFFONI (2010) might represent the 'tip of the iceberg' regarding the incidental catches of cetaceans by pelagic drift nets off Brazil. Offshore driftnetting operating along the south-southeastern coast of Brazil may threaten pygmy killer whales.

Despite recent advances in population genetic theory and empirical research, the extent of genetic differentiation among natural populations of animals remains difficult to predict. We reviewed studies of geographic variation in mitochondrial DNA in seabirds to test the importance of various factors in generating population genetic and phylogeographic structure. The extent of population genetic and phylogeographic structure varies extensively among species. Species fragmented by land or ice invariably exhibit population genetic structure and most also have phylogeographic structure. However, many populations (26 of 37) display genetic structure in the absence of land, suggesting that other barriers to gene flow exist. In these populations, the extent of genetic structure is best explained by nonbreeding distribution: almost all species with two or more population-specific nonbreeding areas (or seasons) have phylogeographic structure, and all species that are resident at or near breeding colonies year-round have population genetic structure. Geographic distance between colonies and foraging range appeared to have a weak influence on the extent of population genetic structure, but little evidence was found for an effect of colony dispersion or population bottlenecks. In two species (Galapagos petrel, Pterodroma phaeopygia, and Xantus's murrelet, Synthliboramphus hypoleucus), population genetic structure, and even phylogeographic structure, exist in the absence of any recognizable physical or nonphysical barrier, suggesting that other selective or behavioural processes such as philopatry may limit gene flow. Retained ancestral variation may be masking barriers to dispersal in some species, especially at high latitudes. Allopatric speciation undoubtedly occurs in this group, but reproductive isolation also appears to have evolved through founder-induced speciation, and there is strong evidence that parapatric and sympatric speciation occur. While many questions remain unanswered, results of the present review should aid conservation efforts by enabling managers to predict the extent of population differentiation in species that have not yet been studied using molecular markers, and, thus, enable the identification of management units and evolutionary significant units for conservation.

Odontocetes are key predators in marine food webs, but knowledge of their habitat use and trophic niche still needs to be improved. In this study, we used carbon (δ13C) and nitrogen (δ15N) stable isotopes to identify the trophic position, isotopic niche size, foraging habitat, and potential sex‐based differences in the dietary patterns of six odontocete species in the Madeira Archipelago: short‐beaked common dolphin (Delphinus delphis), Atlantic spotted dolphin (Stenella frontalis), common bottlenose dolphin (Tursiops truncatus), false killer whale (Pseudorca crassidens), short‐finned pilot whale (Globicephala macrorhynchus), and sperm whale (Physeter macrocephalus). Results delineated two distinct groups. The first (common dolphin, spotted dolphin, bottlenose dolphin) exhibited lower δ13C and δ15N values, lower trophic positions, and larger isotopic niches, indicating that these species are generalist predators and rely more on the pelagic food web. The second group (false killer whale, short‐finned pilot whale, sperm whale) displayed higher isotopic values and trophic positions, with smaller isotopic niches, relying more on shallow‐to‐deep mix food webs and displaying a more specialist diet. This distinction was further supported by comparisons with stable isotope values of potential prey species. However, for deep‐diving species such as short‐finned pilot whale and sperm whale, some prey species were not represented in the niche models due to lack of available samples. The isotopic niche overlap was highest for two pairs of species: spotted and bottlenose dolphin, probably related to their generalist diet and temporal co‐occurrence; false killer whale and short‐finned pilot whale, from which no interspecific competition is expected due to differing habitat preferences. No sex‐related differences were found in the five species analyzed for either isotope. This study characterizes the trophic ecology of several oceanic odontocetes in the Eastern North Atlantic and establishes a valuable baseline for future research. Understanding the trophic interactions of these species offers important insights into their ecological roles and the dynamics of the marine ecosystem they inhabit.

Small boat surveys were organized to study cetaceans of the Marquesas (9°S and 140°W) and the Society Islands (17°S and 150°W) in French Polynesia. Prospecting took place from 12–15 m sailboats, between 1996 and 2001 with systematic visual searching. Boats moved according to sea conditions, at a mean speed of 10 km/h. Effective effort of 4856 km in the Marquesas and 10,127 km in the Societies were logged. Relative abundance indices were processed for odontocetes using data obtained with Beaufort 4 or less. In the Marquesas, 153 on-effort sightings were obtained on 10 delphinids species including the spotted dolphin, spinner dolphin, bottlenose dolphin, melon-headed whale and rough-toothed dolphin. In the Societies, 153 sightings of 12 odontocetes included delphinids (spinner, rough-toothed and bottlenose dolphins, short-finned pilot and melon-headed whales, Fraser's dolphin, Risso's dolphin and pygmy killer whale) and two species of beaked whales, the sperm whale and dwarf sperm whale. Relative abundance indices were higher in the Marquesas than in the Societies both inshore (0.93 ind/km2against 0.36 ind/km2) and offshore (0.28 ind/km2against 0.14 ind/km2). Differences in remote-sensed primary production were equally important, the Marquesas waters featuring an annual average of 409 mgC.m−2 · day−1and the Societies of only 171 mgC · m−2 · day−1. The presence of a narrow shelf around the Marquesas also accounted for differences in odontocete populations, in particular the delphinids.