Across the reviewed literature, we found that two predominant behavioral patterns are often reported in the context of both depredation and commensal interactions: potential attraction to sounds produced by gear haulback and the tendency of interacting whales to follow fishing vessels over long distances (Table 1). Killer whales may use acoustic cues that vessels produce during gear hauling to home in on fishing locations (Dahlheim, 1988; Fertl and Leatherwood, 1997; Visser, 2000; Thode et al., 2007). Some depredating odontocetes, such as sperm whales (Physeter macrocephalus), are known to cue in on propeller cavitation noise produced by fishing vessels during haul-backs (Thode et al., 2007). It is less clear what specific acoustic signals killer whales may use to detect fishing activity or vessels, or how they may vary across fisheries. However, our review suggests that sounds may serve as a common signal for killer whales to identify foraging opportunities associated with fishing activity. Once killer whales have located fishing vessels, they may continue to follow them over long distances, positioning themselves to exploit later feeding opportunities (Cieslak et al., 2021; Tixier et al., 2015c; Towers et al., 2019).

We also found differences between interaction types across gear types and fisheries (Figure 3). Commensal interactions were associated more often with gear aggregating large schools of fish, such as trawl and purse seine fisheries, which often result in the spillover of fish during hauling (Figure 3) (Luque et al., 2006; Mul et al., 2020). Killer whales also forage around fisheries that discard species that may be high-priority prey (Dahlheim et al., 2022). Additionally, some mammal-eating killer whales take advantage of commercial fisheries by pursuing species, such as pinnipeds, attracted to fishing activities. While potentially less common, this type of secondary foraging highlights the potential for fisheries harvest and management to have cascading effects on multiple predators.

In contrast, depredating killer whales were documented more frequently in association with longline fisheries (Figure 3), which target large fish with exposed, baited hooks. Fish immobilized by their capture on longline gear are vulnerable to depredation by killer whales, which may remove whole fish or leave behind just the heads or lips (Secchi and Vaske, 1998; Peterson et al., 2013; Passadore et al., 2015). Tunas, which can exceed 600 kg (NOAA, 2024), are particularly prone to depredation, especially in the tropics (Supplementary Table 1). Esteban et al. (2016b) estimated that a medium-sized pod of killer whales (n=14) would need to hunt at least 21–141 Atlantic bluefin tuna (Thunnus thynnus) per day if the fish ranged in size from 0.8-1.5 m. However, their energetic requirements could be met by as few as eight larger (≥ 2 m) tuna when depredating from local fisheries (Esteban et al., 2016b). The opportunity to intercept large, immobilized, and unprotected fish captured by fishing gear enables killer whales to feed at low energetic cost.

These findings illustrate the shared mechanisms that may facilitate killer whale interactions with fisheries, while also highlighting how interactions can manifest differently across gear types and fisheries.

There is often uncertainty regarding whether a depredated species constitutes a natural component of a killer whale’s diet or if it is consumed only (or primarily) due to facilitation by fisheries. This is especially true in regions where information on killer whale diets is poor, such as the tropics and subtropics. However, even in relatively well-studied areas, as research techniques have advanced, recent studies have found killer whales naturally forage on species previously only documented to be consumed through depredation, such as sablefish (Myers et al., 2024; Van Cise et al., 2024) and toothfish (Tixier et al., 2019). Sablefish, a commonly depredated species in the Bering Sea, Aleutian Islands, and Gulf of Alaska (Dahlheim, 1988; Peterson et al., 2013), was only recently confirmed as a natural prey species for resident killer whale populations in the North Pacific through fecal sample analysis (Myers et al., 2024; Van Cise et al., 2024). Consumption of sablefish may have been previously undetected through traditional surface prey sampling of prey remains. Similarly, though killer whales in the Crozet Islands have heavily depredated toothfish fisheries since the mid-1990s, it was not until 2019 that Tixier et al. (2019) showed killer whales from this population rely on medium-to-large toothfish as a natural part of their diet through the use of stable isotope mixing models and dietary reconstruction.

Killer whales often depredate selectively, even if multiple species are available in the fishing gear (Kock et al., 2006; Belonovich and Burkanov, 2012; Tixier et al., 2016). In New Zealand, for example, killer whales have been documented removing school sharks (Galeorhinus galeus) and blue-eyed trevalla while ignoring hāpuku (Polyprion oxygeneios) on the same longline (Visser, 2000). Similar selective depredation behavior has been reported from South Georgia (Purves et al., 2004; Gasco et al., 2015), the Crozet Islands (Tixier et al., 2010), the Sea of Okhotsk (Belonovich et al., 2021), the Bering Sea (Peterson et al., 2013), and Iceland (Samarra et al., 2018). Depredating killer whales can be sufficiently selective in their prey choices that the ratio of target catch to bycatch in the presence or absence of killer whales has been used to estimate catch lost to depredation (Gasco et al., 2015). Additionally, depredation of sharks by killer whales is often associated with the targeted removal of the liver and nearby organs through the pelvic girdle (Morrice, 2004; Silva et al., 2011; Passadore et al., 2015; Mucientes and Gonzalez-Pestana, 2020), a behavior that is also known from killer whales that naturally forage on sharks (Engelbrecht et al., 2019; Towner et al., 2022; Reeves et al., 2025). However, some studies have noted that killer whales removed normally neglected bycatch species when catch amounts of target species were low (Passadore et al., 2015; Charles et al., 2020), indicating some flexibility in choice.

Tixier et al. (2019) hypothesize that depredation may be more likely to develop in killer whale groups if the species captured in the fishing gear are already part of their natural diets. Forty-six percent of the fish species that killer whales were documented depredating from fisheries have also been identified as natural prey (Table 3). However, selectiveness may have developed or compounded over time with repeated exposure to prey sources more readily available through operational fishery interactions. For example, in the Gulf of Alaska, Chinook (O. tshawytscha), chum (O. keta), and coho (O. kisutch) salmon dominate resident killer whale diets in the summer, whereas sablefish make up a smaller proportion (Myers et al., 2024; Van Cise et al., 2024). However, sablefish constitute a high proportion of killer whale depredation records in the same region (Peterson and Hanselman, 2017). Similarly, in the Crozet Islands, killer whales may switch from natural predation of toothfish to depredation when fisheries facilitate access to aggregated toothfish (Tixier et al., 2019). When depredating, an individual killer whale can likely satisfy its daily energy requirements from depredated toothfish alone. However, annual contributions of depredated toothfish fulfill less than an estimated 10% of the Crozet Island killer whale population’s energetic requirements (Faure et al., 2021), as the fishery has a short season. Nevertheless, if killer whales are fulfilling a substantial portion of their caloric needs through depredation, even if only seasonally, trophic interactions within a local ecosystem may shift with the release of predation pressure from other prey species. Such potential ecosystem effects likely depend on seasonal fishing effort, targets, and killer whale foraging activities outside of interactions (Faure et al., 2021).

Killer whales may modify their diving behavior to facilitate exploitation of fisheries and can also exceed depths previously thought to be a limiting factor in interactions. In the northern and southern hemispheres, killer whales have been documented diving up to 480 m (Schorr et al., 2022) and 767 m (Reisinger et al., 2015), respectively, when not around fishing vessels, though most documented foraging dives for the species are under 200 m (Baird et al., 2005; Miller et al., 2010; Tennessen et al., 2019). Killer whale research efforts have typically been biased towards coastal regions, where study areas are often shallow (e.g., Baird et al., 2005). Consequently, initial efforts to study killer whale depredation of demersal longlines focused primarily on the haulback, the retrieval process when captured fish are brought to the surface (Dahlheim, 1988; Purves et al., 2004; Clark and Agnew, 2010; Werner et al., 2015).

More recent studies have demonstrated that killer whales can access greater depths at which these species occur and where demersal longline gear is deployed (Towers et al., 2019; Richard et al., 2019, 2022). For example, a tagged killer whale depredating toothfish longlines in South Georgia dove up to 1087 m, the deepest documented dive for this species (Towers et al., 2019). Towers et al. (2019) suggested that intra- and interspecific competition during fishery interactions likely drives this extreme diving behavior. In South Georgia, killer whales and sperm whales depredate longlines simultaneously and modify their dive depths and speeds to access toothfish during gear retrieval (Kock et al., 2006; Towers et al., 2019). The benefits of gaining first access to longlines, such as the opportunity to select the largest fish available, may outweigh the energetic and physiological costs of undertaking rapid and deep dives (Towers et al., 2019). Similarly, in the Bering Sea, killer whales foraging around trawl vessels were recorded close to fishing nets at approximately 400 m depth (Myers et al., 2025), a depth that exceeds most other dive records in the North Pacific (Baird et al., 2005; Miller et al., 2010; Tennessen et al., 2019).

Further, recent passive acoustic monitoring in the Crozet Island toothfish fishery revealed the presence of foraging killer whales from at least two different populations around set demersal longlines, suggesting that whales may detect and potentially depredate from demersal longlines before the retrieval process begins (Richard et al., 2022). Some killer whales in South Georgia may also depredate the longlines during the soak period (Towers et al., 2019). In addition, passive acoustic monitoring work from southeastern Australia’s blue-eyed trevalla fishery suggested that killer whales may remove fish from demersal longlines before gear retrieval (Cieslak et al., 2021). Monitoring of demersal longline depredation that relies on confirmation of killer whales at the surface during hauling and counting damaged fish (e.g., Peterson et al., 2014; Passadore et al., 2015) likely underestimates depredation rates and the total amount of fish lost if whales are depredating before gear retrieval.

Artificial wildlife provisioning can influence fecundity, offspring quality, and population trajectories of provisioned species (Griffin et al., 2022, 2023). These dynamics are particularly relevant to killer whales exploiting the predictable food sources fisheries provide. For example, in the Crozet Islands, adult female killer whales involved in depredation of the local toothfish fishery demonstrated a 4% increase in the probability of producing a calf the following year compared to non-depredating females (Tixier et al., 2015a). Additionally, Tixier et al. (2015a) found that depredating whales experienced higher survival rates than non-depredating individuals. Further, non-depredating matrilines have declined over the last few decades, possibly due to reduced reproduction and/or changes in natural prey availability (Tixier et al., 2015a, 2017).

While increased access to prey may boost reproductive output and overall fitness, depredation may lead to dependency upon fisheries for food. In the Strait of Gibraltar, a small subpopulation of killer whales is known to hunt Atlantic bluefin tuna through an endurance-exhaustion method, where individuals chase fish for over thirty minutes (Guinet et al., 2007). Increased demand and overfishing of bluefin tuna in the Eastern Atlantic and Mediterranean beginning in the 1960s led to a severe stock decline and reduced natural prey availability for the Gibraltar subpopulation of killer whales, which also depredates tuna from local drop-line fisheries (Esteban et al., 2016b; ICCAT, 2010). Esteban et al. (2016a) found that individuals interacting with the tuna fisheries exhibit higher survival and reduced reproductive intervals than non-interacting individuals (Esteban et al., 2016a). Additionally, a reduction in drop-line tuna harvest was associated with declining killer whale births, suggesting that the population relied on prey availability provided by the fishery (Esteban et al., 2016a). The bluefin tuna stock in this area has largely recovered (Bjørndal, 2023), though how stock recovery has impacted local killer whale depredation rates, survival, or reproduction has not been documented.

Sex biases have been detected in depredating odontocetes, such as Hawaiian false killer whales, where females interact more frequently with pelagic longlines than males (Baird et al., 2015). In 2023, all killer whales bycaught in the Bering Sea and Aleutian Islands fisheries for which sex was confirmed were adult females (NOAA Fisheries, 2023). Sex-associated differences in behavior may also be important in understanding the dynamics of fishery interactions with killer whales, especially as they relate to fecundity and mortality.

In some circumstances, fishers engaged in legal and illegal fishing operations may retaliate against killer whales. Retaliatory measures can include the use of guns, harpoons, explosives, or other projectiles to deter killer whales from accessing catch. Notably, all reports of retaliatory actions in the reviewed literature were associated with cases of depredation, rather than commensalism, though this should be interpreted cautiously, as many events likely go unreported. The loss of catch from fishing gear through depredation is more economically damaging to fisheries than commensal activities and thus may prompt direct action from some fishers, including harmful and injurious measures to repel killer whales from gear. This dynamic mirrors some human-wildlife conflicts in terrestrial environments—depredation of valuable livestock often results in retaliatory killings of large carnivores (Woodroffe et al., 2005; Kissui, 2008).

These sometimes lethal retaliatory tactics have been documented in fisheries in Alaska (Matkin et al., 2008; Fraker, 2013), Australia (Morrice, 2004), the Crozet Islands (Tixier et al., 2017), Colombia (Alvarez-León, 2002) Brazil and Uruguay (Rosa and Secchi, 2007), the Faroe Islands and Jan Mayen (Bloch and Lockyer, 1988), the Sea of Okhotsk (Kornev et al., 2014), the Strait of Gibraltar (De Stephanis et al., 2002), and parts of the equatorial Pacific and Indian Ocean basins (Sivasubramaniam, 1964) (Figure 4.). However, these documented cases likely underestimate the frequency of harmful retaliation due to insufficient reporting in many areas. Fishers have reported that explosives and gunfire may be ineffective in deterring killer whales because the whales returned after initially scattering (Kornev et al., 2014) or learned to stay out of range of projectiles while depredating (Bloch and Lockyer, 1988; Kornev et al., 2014). However, some researchers have noted that killer whales in areas of high depredation have displayed avoidance behaviors around vessels, which may suggest that past negative interactions potentially induced long-lasting behavioral responses (Dahlheim et al., 2022).

One of the most extreme cases of documented retaliation occurred from 1954–1956 in Iceland, when hundreds of killer whales were reportedly killed by the U.S. Navy in response to reports of damage to fishing gear (Jourdain et al., 2019). In Prince William Sound, Alaska, killer whales from the resident AB pod were subject to retaliatory shootings from fishers attempting to deter the whales from depredating sablefish catches (Matkin et al., 2008). Bullet wounds were documented on 13 killer whales from this pod from 1985–1986, and four of these individuals had died by 1987 (Matkin et al., 2008). Similarly, from 1996–2002, killer whales in the Crozet Islands were subject to fatal shootings and explosives intended to reduce their perceived impact on illegal toothfish fisheries; the deterrence efforts caused a 60% population decline (Poncelet et al., 2010; Tixier et al., 2017). Busson et al. (2019) found that these mortalities had a long-term impact on surviving individuals, including weakened social connections and reduced survival rates. Further, Auguin et al. (2024) detected behavioral heterogeneity across depredating killer whale social units in the Crozet Islands, which could suggest that the impacts of lethal retaliation may have been felt unevenly across the population. While illegal fishing in the Crozet Islands has been largely curtailed, there are still concerns that lethal deterrence in illegal, unreported, and unregulated fisheries may persist in neighboring regions as this population decline continued from 2005–2020 (Tixier et al., 2021b).

Killer whales are vulnerable to injury and mortality during fishery interactions. Entanglements and hooking of killer whales have been documented in longline fisheries in Alaska (Bolling et al., 2023; Dahlheim et al., 2022), the Gulf of Mexico (Barry et al., 2024), Australia (Bell et al., 2006), Brazil (Charles et al., 2020), New Zealand (Visser, 2000), the Indian Ocean (Sivasubramaniam, 1964), and the Faroe Islands (Bloch and Lockyer, 1988). Most documented cases of killer whale trawl entanglements have been reported from the Bering Sea, Aleutian Islands, and Gulf of Alaska (Perez, 2006; Bolling et al., 2023), with an additional record from New Zealand (Fertl and Leatherwood, 1997). These reports should be considered conservative estimates, as bycatch is likely underreported in many areas (Donoghue et al., 2003). Curiously, we found no reports of entanglement or incidental catch of killer whales off the Crozet Islands, where interaction rates are among the highest in the world and fisheries observer coverage is 100% (Tixier et al., 2017).

Reports of killer whale bycatch in gillnets are rare. However, a few instances have been reported from California and British Columbia (Carretta et al., 2023), eastern Canada (Lawson et al., 2007), and South Korea (Jin-gu, 2022). Reeves et al. (2013) found that at least 75% of odontocete species are impacted by gillnet bycatch (Reeves et al., 2013), and several species and populations are threatened with extinction due to gillnet entanglement (Read, 2008; Gray and Kennelly, 2018). Several factors may explain the limited number of reported killer whale entanglements in gillnets. Some gillnet fisheries have declined or ceased operations in certain areas of high killer whale abundance, such as off Washington state and California (Carretta et al., 2023). Elsewhere, a lack of spatial or temporal overlap with gillnet fishery operations may explain the low incidence of killer whale bycatch. Furthermore, acoustic deterrent devices are reported to have reduced overall cetacean bycatch in some drift gillnet fisheries (Barlow and Cameron, 2003). However, the recent increase in killer whale gillnet depredation in northern Japan may raise concerns about entanglement risks (Narayama, 2023; Mitani et al., 2024). Additionally, “cryptic” bycatch in gillnets, where an individual becomes entangled in the net but moves away before being observed or documented, may not be accounted for.

Whales depredating or foraging on discards from fisheries are likely to be at higher risk of bycatch because of their proximity to or immediate contact with fishing gear. Whales entangled or entrapped in gear that is soaked or towed for many hours, such as demersal longlines or non-pelagic trawl nets, may be less likely to survive. Only 21% of killer whales found entangled in trawl nets and longlines in Alaskan fisheries from 1991–2023 were released alive (Bolling et al., 2023; NOAA Fisheries, 2023). Most of these released whales had serious injuries and were determined to have a low chance of survival (Bolling et al., 2023).

However, in some bycatch situations, mortality and serious injury rates are low. For example, in northern Norway, killer whales are attracted to pelagic herring purse seine vessels and often approach during the hauling or pumping process (Similä, 2005; Mul et al., 2020). Despite frequent entrapments, nearly all killer whales are released from nets, and overall mortality is estimated to be less than one whale per year (Bjorge et al., 2023). Similar low mortality rates have been documented for cetacean species in other purse seine fisheries in the Atlantic and Indian Oceans (Escalle et al., 2015). Successful avoidance of fatal bycatch depends on multiple factors, including the extent to which whales interact with the fishing gear, fishers’ ability to promptly detect and respond to entrapped whales, and the ability of whales to reach the surface to breathe while entrapped.

Ship strikes are another risk for killer whales interacting with fisheries. Trawl fisheries tend to concentrate mammals near the stern where the net is being towed, increasing the chance of propeller strikes (Bonizzoni et al., 2022). In Alaska, at least ten killer whales were struck and killed by propellers on trawl vessels from 1998 through 2016 (Dahlheim et al., 2022). Some killer whales associated with these vessels display severe injuries caused by previous ship strikes, such as severed dorsal fins, suggesting that some individuals may continue to engage in high-risk, high-reward behaviors around fisheries despite prior negative experiences (Dahlheim et al., 2022).

Killer whales may be left with scars or injuries caused by interactions with net gear such as purse seines (Similä, 2005). Other depredating odontocetes sustain significant injuries during fishery interactions. For example, the insular Hawaiian Islands false killer whale population, known to interact frequently with pelagic longline fisheries, has a high rate of dorsal fin disfigurements caused by longlines and hooks (Baird and Gorgone, 2005). Analyses of dorsal fin disfigurations in killer whales are limited. However, research from Iceland suggests that a small percentage of killer whales have sustained superficial to moderate injuries through interactions with fishing gear (Lionnet, 2020).

When faced with high levels of depredation, fishers may attempt to reduce interactions by altering their fishing practices. Mitigation measures include moving to different fishing grounds, increasing distances between sets, changing gear length, changing hauling speed, or fishing in tandem with other vessels (Dahlheim, 1988; Guinet et al., 2015; Peterson and Carothers, 2013; Tixier et al., 2015c). These measures have variable efficacy rates and often come with their own costs. For example, because killer whales can pursue fishing vessels across large areas (300–1000 km; Cieslak et al., 2021; Tixier et al., 2015c; Towers et al., 2019), fishers must travel long distances to reduce the chance of being followed, which increases fishing time and associated costs. Fishers’ options may also be limited if fishing activity is constrained to specific areas.

While these measures are specifically aimed at reducing depredation, changing fishing practices may also prove useful for mitigating commensal interactions. While commensalism does not negatively affect fisheries as extensively as depredation, limiting commensal interactions may prevent depredation from developing by reducing the reinforcement of associations between fishing activity and foraging opportunities. Some fisheries may benefit from limiting discards of unwanted catch, bycatch, or offal in the presence of killer whales. However, discard retention within individual fisheries is often subject to capacities in vessel holds, quality of catch, and prevailing fisheries regulations (Suuronen and Gilman, 2020).

Management decisions can also influence killer whale interactions through spatiotemporal aspects of fisheries. For example, before 1995, halibut and sablefish longline fisheries in the Bering Sea and Gulf of Alaska were managed as open-access, derby-style fisheries, resulting in intense competition (Peterson and Carothers, 2013; Warpinski et al., 2016). Introducing individual fishing quotas reduced vessel numbers and extended fishing seasons, but also coincided with increased reports of killer whale depredation (Peterson and Carothers, 2013). The increase may be due to two factors: longer fishing seasons likely provided killer whales with more reliable feeding opportunities, while fewer vessels on the fishing grounds probably increased the chances of individual vessels being targeted by killer whales. For comparison, in the Crozet Islands, vessels fishing alone faced higher depredation levels than the average depredation levels experienced when multiple vessels fished near each other, suggesting a dilution or satiation effect (Tixier et al., 2015c).

Technological interventions aim to reduce or prevent depredation by rendering the catch inaccessible to whales or deterring whales from depredating—for example, by switching from unprotected gear, such as baited hooks, to protected gear, like pots or traps. Federal regulations for sablefish fisheries in the Bering Sea/Aleutian Islands region and the Gulf of Alaska were changed in 2008 and 2017, respectively, to permit the use of pot gear in place of hook-and-line gear to mitigate killer whale and sperm whale depredation (NOAA, 2008; 2016). In the Crozet Islands, switching to pot gear also proved effective against killer whale depredation (Guinet et al., 2015). Iceland’s fishers switched from longlines to trawl gear after killer whales significantly reduced catches of Greenland and Atlantic halibut in the 1970s, which largely eliminated killer whale depredation (Samarra et al., 2018). However, switching between gear types, such as from longlines to trawl, can be complicated by competing operational restraints and fishery management objectives, including complex bottom topography, vulnerable fish habitat, bycatch concerns, regulatory constraints, or economic considerations. Even when gear changes effectively reduce killer whale depredation, considerations such as vessel size, handling, costs, target catch rate, and adherence to relevant fishing regulations affect their uptake. For example, although pots reduce killer whale depredation in toothfish fisheries, they have not been adopted due to low CPUE, increased crab bycatch, biased catch of large female toothfish, and crew safety concerns (Guinet et al., 2015).

Alternatively, gear can be modified to obscure the catch from whales. For example, filamentous “umbrella” shrouding devices combined with shortened gangions resulted in a 68% reduction in killer whale depredation in blue-eyed trevalla longline fisheries (IPHC, 2022). Similarly, the “cachelotera” device, developed for Chilean toothfish fisheries, covers each hooked fish with a cone-shaped rigid net (Moreno et al., 2008; IPHC, 2022). Gear modifications also include bycatch excluder devices in fisheries where marine mammals may become entrapped in trawl nets. A gear modification to reduce the likelihood that killer whales will enter the trawl mouth is being investigated in deep-water flatfish trawl nets in the Bering Sea, with promising initial results (Myers et al., 2025).

Acoustic deterrent devices, which include pingers and acoustic harassment devices (AHDs), have been tested on odontocetes in a variety of fisheries and fish farming applications with mixed results (Dawson et al., 2013; Elmegaard et al., 2023; Kolipakam et al., 2022; López and Mariño, 2011; Palka et al., 2008). These devices are placed on or near fishing gear and emit sounds intended to alert cetaceans to the gear’s presence and/or discourage them from depredating or feeding around fishing operations (FAO, 2021). An AHD device designed specifically to deter killer whales, the OrcaSaver, was tested in the Crozet Islands toothfish fishery in 2011 (Tixier et al., 2015b). While killer whales initially departed when the device was activated, they demonstrated habituation (i.e., a reduced or nonexistent response) after fewer than ten exposures. Moreover, Tixier et al. (2015b) advised against using this device in longline fisheries due to the potential adverse effects of increased noise exposure on killer whales. Some scholars have also critiqued using these acoustic devices to keep whales away from fishing gear while simultaneously provisioning them (Lucas and Berggren, 2023).

Other potential techniques for deterring killer whales from interacting with fisheries include electric shocks, rubber bullets, bubble screens, noxious chemicals, and previously discussed injurious deterrents (Dahlheim, 1988). However, most of these methods are ineffective or untested, may raise ethical concerns, or may violate marine mammal protection statutes in some countries (Visser, 2000).

A major challenge for assessing operational fishery interactions with killer whales is underreporting and a lack of monitoring in many regions. Observer presence on vessels can be useful in documenting interactions. For example, in the Southern Ocean toothfish fishery, 100% observer coverage is required for all vessels fishing in waters managed through the Convention for the Conservation of Antarctic Living Marine Resources. This results in detailed data collection on interactions with killer whales (FAO, 2024). The deepwater flatfish trawl fishery in the Bering Sea and Aleutian Islands also operates with 100% observer coverage (every haul is observed). However, observer coverage can be uneven across fisheries (e.g., Somers et al., 2022), and in those with less than full coverage, fishing behavior may change when observers are present (Duarte and Cadrin, 2024).

Additionally, research efforts are unequally distributed across areas where fisheries interactions occur. The studies reviewed here showed a strong bias towards the Southern Ocean and North Pacific, with notable gaps in tropical and subtropical regions. The majority of the literature on killer whale depredation comes from studies conducted on toothfish fisheries in the Southern Ocean (e.g., Faure et al., 2021; Tixier et al., 2017, 2016), followed by research carried out in Alaska (Supplementary Table 1). Consequently, the patterns we present in this review may overrepresent certain gear types and fisheries while underrepresenting others. Additionally, this unequal coverage, which may stem from differences in research capacity and fisheries management structures, makes evaluating the status and trends of killer whale interactions in equatorial areas difficult.

Furthermore, depredation may be overrepresented in studies compared to behaviors like commensalism. Depredation can have both immediate and long-term consequences for fisheries (e.g., damaged gear, increased expenditures to avoid depredating animals, and decreased catches), likely resulting in increased attention from fishers, managers, and researchers. In contrast, commensal interactions, which do not impact fishery yields, may be less likely to attract notice or be formally reported. Literature on human-predator relations tends to emphasize negative outcomes (Pooley et al., 2016), and this bias may also be present in fishery interaction literature. For instance, behaviors like foraging on discards are intentionally excluded in some analyses of fishery interactions (Perez, 2006), which may reinforce emphasis on high-conflict behaviors like depredation. Managers may consider incorporating observations of other behaviors, such as foraging on discards, into monitoring to obtain a more robust understanding of all types of interactions and impacts to fisheries.

Another challenge in assessing interaction levels is that data from individual fisheries is often contained within RFMO reports and other gray literature and requires a high level of searching to collate.

Killer whale behavior and ecology are poorly understood in many world regions where fishery interactions occur, especially in the tropics. While some studies have described seasonal trends in fisheries interactions, few have examined possible driving factors. For instance, in southeastern Brazil, killer whale depredation of tuna and swordfish longlines occurred primarily between June and October (Secchi and Vaske, 1998). However, killer whale movements are largely unknown outside of that timeframe. In southern Australia, killer whales may naturally forage in areas where they also depredate blue-eyed trevalla fisheries (Cieslak et al., 2021), but their dietary habits outside of fisheries interactions remain unstudied.

Spatiotemporal closures have been proposed as a way to reduce contact between fishing operations and depredating marine mammals (Fader et al., 2021), but implementation requires a robust understanding of habitat use and movement patterns, and such data are lacking for many regions where killer whales depredate. Additionally, as fisheries can alter prey availability for marine mammals and may influence dependency on fisheries (Esteban et al., 2016a; Tixier et al., 2019), further ecological and distribution research on less well-studied killer whale populations would also support a better understanding of fishery interactions.

Details on killer whale behavior during fishery interactions are limited because individuals spend most of the time underwater when interacting with or around fishing gear. Thus, many aspects of these interactions remain unknown, such as how individuals access catch or become entangled. These knowledge gaps may reduce fishers’ and researchers’ ability to effectively prevent depredation and bycatch, and can also have implications for fish stock assessments and management. For example, research by Richard et al. (2022); Cieslak et al. (2021); Towers et al. (2019), and Tixier et al. (2019) in longline fisheries from the Southern Ocean and southern Australia demonstrated that killer whales are capable of diving to sufficient depths to access soaking demersal longlines and may actively depredate from them. However, it is unknown if demersal longline depredation in other areas is limited to when the gear is being hauled or if killer whales also depredate while it soaks.

Additionally, depredation behavior can vary across killer whale matrilines within a population, and some social groups engage in interactions more frequently than others (Tixier et al., 2015a, 2017; Auguin et al., 2024). Understanding social networks within populations may help explain how behaviors spread among individuals, especially in populations where interactions with fisheries are not widespread. Additional variables that may be relevant include competition with other depredating odontocetes, natural prey availability, foraging conditions, and overall population size.