Reproductive timing and putative mating behavior of the oceanic whitetip shark Carcharhinus longimanus in the eastern Bahamas

: Oceanic whitetip sharks Carcharhinus longimanus aggregate at Columbus Point, Cat Island, The Bahamas, in at least April and May. We show that signs of putative mating activity (i.e. bite wounds) on mature females, which dominate the aggregation, are exceedingly rare at that time, but may be more common in July. Male plasma testosterone concentrations also suggest that spermatogenesis occurs in April and May and copulation is underway or has just ended by July. We support these preliminary data with direct observations of putative precopulatory behavior made at Columbus Point in July 2019. Using 25 min of video footage from the event, we identify common shark mating behaviors such as echelon or parallel swimming, following, shielding, nosing, and biting. We also describe the ‘circle-back’, a newly observed behavior where the male orients to the trail of the female, possibly to investigate olfactory cues. Based on these 3 parallel lines of evidence, we hypothesize that mating could occur in the eastern Bahamas as early as May, but is probably concentrated in midsummer (i.e. July), and that Columbus Point, Cat Island, may be a mating habitat for the oceanic whitetip shark.


INTRODUCTION
Historical accounts and catch data from the 1950s and 1960s suggest that the oceanic whitetip shark Carcharhinus longimanus was once relatively common in tropical and sub-tropical pelagic oceanic habitats (Young & Carlson 2020). Commercial fishing has since reduced its global population by an estimated 98%, resulting in the oceanic whitetip shark being listed as Critically Endangered on The IUCN Red List of Threatened Species (Rigby et al. 2019) and being afforded some of the most comprehensive protections of any shark species globally (Young & Carlson 2020). An understanding of oceanic whitetip shark reproductive biology can contribute to the success of recovery efforts (Sims et al. 2000, Pratt & Carrier 2001, Young & Carlson 2020. Most of what is known about shark reproduction comes from post-mortem examinations (Whitney et al. 2004, Pratt et al. 2005) and the study of captive animals (Pratt & Carrier 2001), although a growing number of recent studies have presented data on shark reproductive ecology in situ using non-lethal approaches (e.g. Sulikowski et al. 2016, Hammerschlag et al. 2018. Circulating concentrations of the gonadal steroid hormone testosterone (T), for example, are often used to indicate reproductive stage and correlate well with seasonal spermatogenesis and copulation in male sharks. Generally, the highest T concentrations occur during mid-to late spermatogenesis and decline dramatically during and/or after copulation, although the exact timing of these changes can vary across species (Maruska & Gelsleichter 2011, Wyffels et al. 2020, Rangel et al. 2021. Less research has focused on shark reproductive behaviors, although an understanding of these behaviors can supplement information about reproductive traits (e.g. age at maturity, fecundity, reproductive periodicity) and inform conservation and management. Knowledge of when and where mating occurs, for example, can lead to the creation of time−area closures that protect critical habitats (e.g. Carrier & Pratt 1998).
Mating behaviors of wild, free-swimming sharks have rarely been observed (Bres 1993, Pratt & Carrier 2001, Whitney et al. 2004. Most in situ observations of mating behavior involve coastal species (see Pratt & Carrier 2001), including the reef-associated blacktip reef shark C. melanopterus (Johnson & Nelson 1978, McCauley et al. 2010, grey reef shark C. amblyrhynchos (Bres 1993), white-tipped reef shark Traenodon obesus (Johnson & Nelson 1978), and nurse shark Ginglymostoma cirratum (Klimley 1980, Pratt & Carrier 2001, Whitney et al. 2010, as well as the semi-oceanic scalloped hammerhead Sphyrna lewini (Klimley 1985, Salinas-De-León et al. 2017, silky shark C. falciformis (Clarke et al. 2013), and basking shark Cetorhinus maximus (Harvey-Clark et al. 1999, Sims et al. 2000, Wilson 2004, Gore et al. 2019. Some mating behaviors may occur universally across elasmobranch taxa. For ex ample, courtship is thought to begin when a female releases olfactory chemical cues or exhibits behavioral cues to signal that she is receptive (Pratt et al. 2005). Males then bite or hold the fins, body, or flank of the female in order to copulate using at least 1 clasper . This results in females having cuts and abrasions from the teeth of male sharks during the mating season (Pratt & Carrier 2001). For a thorough review of mating behaviors in elasmobranchs, see Pratt & Carrier (2001). Courtship and mating behaviors are largely undescribed in pelagic oceanic sharks.
Oceanic whitetip sharks exhibit site fidelity and seasonal residency at Columbus Point, southern Cat Island, The Bahamas (CI; within 20 km of 24°07' N, 75°17' W, Fig. 1; Howey-Jordan et al. 2013, Madigan et al. 2015. Abundant pelagic teleost prey (e.g. dolphinfish Coryphaena hippurus; Farrell et al. 2014) may motivate the April−May aggregation, which mostly consists of adult females, the majority of which are gravid (Howey-Jordan et al. 2013, Madigan et al. 2015. Males are less common, and juveniles are very rare (Madigan et al. 2015, V. Canabal pers. comm.), suggesting that parturition and possibly mating are unlikely to occur there in the winter (i.e. cold, dry season: November−April), although the aggregation has not been directly studied prior to April. In the summer (i.e. warm, wet season: May− October), some females leave CI and migrate to suspected mating or parturition areas in the Windward Passage, Straits of Florida, northern Lesser Antilles, or northern Bahamas (Castro 2011, Howey-Jordan et al. 2013, Ruiz-Abierno et al. 2021 and return to the eastern-central Bahamas by late summer or early winter (Howey-Jordan et al. 2013). Other adult females remain near CI for much or all of the summer (Howey-Jordan et al. 2013).
Here, we compare signs of oceanic whitetip shark mating activity and male plasma T concentrations between April−May and July in the eastern Bahamas and describe putative mating behaviors observed at CI in July. Based on these data, we evaluate whether oceanic whitetip sharks mate in the eastern Bahamas in the summer.

Sampling
We conducted annual expeditions to CI for 1 to 2 wk in April−May from 2011 to 2018. A dive charter company (Epic Diving; V. and D. Canabal) also provided sightings data from regular dives at CI every spring. We attracted sharks during daylight hours by placing little tunny Euthynnus alletteratus in crates down-current of the vessel and baiting for 4 to 8 h daily. In July 2019, we baited for 2 d at CI and 2 d off Mayaguana (within 5 km of 22°28' N, 73°09' W), which is about 280 km southeast of CI (Fig. 1). Shark capture and handling procedures were described by Howey-Jordan et al. (2013). We determined sex through the presence or absence of claspers and sexual maturity based on the degree of clasper calcification and rotation for males (Clark & von Schmidt 1965) and published size at maturity estimates for females (170−190 cm total length, TL; Seki et al. 1998, Lessa et al. 1999, Tambourgi et al. 2013.
As reported in past studies (e.g. Madigan et al. 2015, we collected various biological samples during shark workups. We drew blood via caudal venipuncture using sterile syringes and 16-gauge needles, then transferred samples to sterile vacuum tubes lined with acid citrate dextrose or lithium heparin anticoagulant before temporarily storing them on ice. We separated plasma with a centrifuge spun at 1500 × g and then stored it at −20°C until hormone analysis.

Hormone analysis
We measured plasma T concentrations using commercially available AccuLite chemiluminescent immuno assay kits (Monobind) following the methods recently described for the finetooth shark Carcharhi-nus isodon (Brown et al. 2020) and the bonnethead shark Sphyrna tiburo (Gonzalez De Acevedo et al. 2020). We measured chemiluminescence using the Synergy HT Multi-Mode Microplate Reader (BioTek Instruments) in luminescence mode. We validated each kit for use with oceanic whitetip shark plasma using parallelism to confirm that unknown analytes in serial dilutions of pooled samples (1/1 to 1/120) interacted with antibodies in a manner similar to that of assay standards. We used 'cold spikes' to determine percent recovery by adding a known amount of hormone standard to each pooled sample dilution and calculating recovery. We used results from validation tests to determine the ideal dilution of plasma to avoid matrix effects. Accordingly, we used a dilution factor of 1/50 for individual samples. We calculated hormone concentrations for each sample by multiplying by the dilution factor and correcting for procedural losses, which were determined by conducting 'cold spikes' on individual samples. Mean intra-assay variability was 4.9%. Mean inter-assay We grouped mature male plasma T concentrations by collection period and compared between periods using Student's t-test after confirming normality and homoscedasticity using the Shapiro-Wilk test and residual plots. Statistical significance was set at α = 0.05. We conducted all analyses in R Version 3.6.3 (R Core Team 2021).

Observations of putative mating behavior
We observed 2 oceanic whitetip sharks swimming synchronously beneath the boat on 16 July 2019 at CI. D. Brake, S. Williams, and W. Pavlo entered the water to film the sharks on snorkel and recorded video footage with a Red Epic-W in a Gates Underwater Housing at 8K resolution and 2 GoPro Hero 7 TM cameras in GoPro underwater housings at 2K resolution. One GoPro was attached to the Gates housing, and the other filmed separately.
One researcher analyzed 26 min 54 s of video by assigning a behavior (see Appendix of Pratt & Carrier 2001) to each animal for every second, comprising 15 min 39 s of continuous footage from one of the GoPro cameras and an additional 11 min 15 s of noncontinuous, non-overlapping video shot by the other cameras. This non-continuous footage was not collected in any specific manner (i.e. we did not film select behaviors) and was choppy because snorkelers switched between cameras, cleaned lenses, and entered and exited the water. The sharks were filmed by at least 1 camera nearly the entire time they were in sight. When multiple cameras were simultaneously recording, we cross-referenced behaviors between camera angles to ensure a comprehensive review. We watched the footage using VLC media player (VideoLAN Organization, version 3.0.7.1) and saved still images using the snapshot tool. We estimated shark TL in the field and compared those estimates to measured size differences of the 2 animals swimming side by side in video stills.
We observed up to 4 female oceanic whitetip sharks with bite wounds indicative of possible mating activity at CI. One observation occurred in May, and the other 3 occurred in July. On 17 May 2013, we captured a mature, 251 cm TL female (pregnancy status unknown) with puncture wounds, slashes, and multiple jaw imprints from its gills to its flank ( Fig. 2a−c). On 15 July 2019, we observed a female with bite wounds swimming near the boat, which may have been captured or re-sighted the following day, when we captured a mature, 224 cm TL, nongravid female with jaw imprints and punctures on its right flank (Fig. 2d). While we measured and collected samples from this female, 2 males approached it repeatedly, possibly showing interest in mating. We then observed a male and a different female engaged in putative mating behaviors nearby (detailed in Section 3.3). The female had multiple bite wounds: one along the right side below the trailing edge of the first dorsal fin from the upper jaw of a shark, another located 5−10 cm above the right gill slits, and finally a row of tooth cuts ~10 cm from the base of the right pectoral fin, which had evidence of bites along its length and trailing edge (Fig. 3).

Male plasma testosterone concentrations
We collected blood samples from 10 male oceanic whitetip sharks, comprising 6 mature males captured in April−May at CI and 4 males (3 mature, 1 immature) captured in July at CI (n = 2) and Mayaguana (n = 2). The plasma T concentration of the immature male was 15.8 ng ml −1 . The plasma T concentrations of the mature males ranged from 28.19 to 109.25 ng ml −1 (Table 1). Plasma T concentrations were significantly higher in mature males sampled in April−May than in those sampled in July (t = 2.48, df = 7, p = 0.04; Fig. 4).

Observations of putative mating behavior
On 16 July 2019, 2 oceanic whitetip sharks (1 male and 1 female) entered the chum slick and swam in unison under the boat at CI (24°07' N, 75°19' W). We immediately stopped baiting and did not see the sharks feed. The Beaufort Sea State was 2, underwater visibility was excellent (~30 m), and conditions were clear and sunny. Water depth was between 700 and 1000 m, and sea surface temperature was 26.9°C. The observation occurred between approximately 10:40 and 11:05 h. The sharks remained in the top 10 m of the water column. We estimated that the male was 200−225 cm TL and the female was 225−250 cm TL. Both animals were larger than the size at maturity, and the male had large claspers. The female had apparent bite wounds at the start of our observation (detailed in Section 3.1; Fig. 3). The male had no visible wounds. Early in the observation, another oceanic whitetip shark (sex undetermined) investigated the snorkelers, but it did not interact with other sharks and moved away from the immediate area after approximately 25 s.
The 15 min 39 s continuous video sequence (see Video S1 in the Supplement at www.int-res.com/articles/ suppl/n050p181_supp/ for highlights) began with the male and female 'echelon swimming' (Table 2) for 4 s, with the male mirroring the female's movements within 1 body length of and parallel to the female and its snout lined up to the female's flank between the trailing edge of the right pectoral and second dorsal fin (similar to 'parallel swimming'; Pratt & Carrier 2001). We observed echelon swimming more than any other behavior (~38% of total time observed for both the male and female; Fig. 5).
The male bit the female twice. Early in our observations, the male circled wide to intercept the female, crossed over the female's trail at roughly 1 body length behind its caudal fin, changed direction to follow the female ('circle-back'; Table 2, Fig. 6a), and approached to within 0.5 m below and behind the female's right pelvic fin ('following'; Table 2). The male accelerated and bit the female's right flank along the midline between the right pectoral and pelvic fin ('courtship bite'; Table 2). The female avoided the male by abruptly turning its longitudinal axis 30° away, lifting towards the surface, and rapidly accelerating ('direct avoidance'; Table 2). Simultaneously, the female angled its pectoral fins ventrally and shook its entire body vigorously. We saw no new injuries on the female.
Between bites, the male approached the female from below and behind the female's right posterior and rotated its dorsoventral axis at an oblique angle to the female so that its ventral surface was directed slightly towards the female ('rotating'; Table 2, Fig. 6d). The female mirrored the male's behavior by rotating slightly away from the male, demonstrating avoidance while echelon swimming ('shielding'; Table 2, Fig. 6d). Four seconds after beginning to shield, the female slowed and hung almost motionless at a 45° angle to the surface ('stalling'; while slowly turning 270° away from the male. After 4 s, the female resumed swimming in a circle for 48 s, continually angling away from the male while echelon swimming ('shielding'). Shortly after, the male circled back from an echelon position and followed the female for 8 s before returning to its previous position along the female's right flank. After echelon swimming for about 1 min, during which the female shielded, the male approached the female within 0.5 m of the female's right flank. The male bit the female below its midline just anterior to the pelvic fin. The female avoided the male as on the first occasion (Fig. 7). We saw no new marks on the female.
The male also exhibited variations of the 'circleback' behavior, which was the second most common male behavior after echelon swimming (Fig. 5). Repeatedly, the male caught up to the female until their snouts were nearly in line, turned 45° away from the female, swam towards the surface, and circled above and then behind the female, reaching nearly 3 body lengths of separation between itself and the female in a wide, high-arching circle-back (Fig. 6c). Often, the male then resumed the following behavior for a few seconds before echelon swimming or 'close swimming', where the pair swam asynchronously in the same direction (Table 2). During half of these circle-backs, the male left the female's side without crossing in front of the female ('rear circleback' ; Fig. 6a,c). During the other half, the male swam ahead and circled around the female, crossing in front of the female before approaching from

Shielding
Rotating away from the male while parallel swimming or swimming in Gordon (1993) Leaving a position alongside the female to loop behind the female, often initiated during parallel swimming. The circle-back can begin with the male turning away from the female or accelerating ahead before crossing in front of the female. The male may circle back at the same depth as the female or arch high above the female, but remains within 3 body lengths of the female. When the male crosses the female's trail, the male abruptly turns and follows the female, ultimately returning to a position that allows parallel swimming.
Close-swimming Swimming asynchronously in the same direction as the female and Gore et al. (2019) within 2 body lengths of the female.
Pratt & Carrier (2001) Echelon ( Following Swimming closely behind the female, often positioned slightly below Johnson & Nelson (1978), and behind the female's pelvic or caudal fins. Gordon (1993), Carrier et al. (1994) Nosing Approaching the female from behind and below the female until its Johnson & Nelson (1978), snout is just below the female's cloaca. Gordon (1993), Harvey-Clark et al. (1999), Pratt & Carrier (2001) Rotating Rotating its dorsoventral axis towards the female while parallel swimming.  Fig. 6b). Circle-backs dominated the last 5 min of the continuous sequence, during which the male exhibited the behavior 10 times, including 9 high-arching circle-backs. On 7 of those 9 occasions, the male crossed in front of the female. One of the male's passes brought it directly in front of the female at the same depth. All others took place 1−3 body lengths above and in front of the female. Both animals swam out of sight at the end of this sequence. The additional, non-continuous video footage showed similar behavior, but, notably, the male avoided the female on 3 occasions. On 1 occasion, the male crossed in front of the female until they were perpendicular, then it abruptly turned and accelerated away from the female as its right pectoral fin came in line with the female's snout. The female re sponded by avoiding contact. On 2 occasions, the female's flank came within 0.5 m of the male's snout while echelon swimming, and the female abruptly avoided the male by accelerating and turning away; the male did not attempt to bite in either instance and avoided the female's caudal fin as the female turned. We also observed the male briefly 'nosing' the female on one occasion (Table 2).

DISCUSSION
We inferred mating attempts from observations of bite wounds on adult female oceanic whitetip sharks, analyzed plasma T levels in males caught in April−May and July, and observed the first instance of putative mating behavior for this species in July. Our results suggest that some oceanic whitetip sharks mate in the summer near Columbus Point, Cat Island, The Bahamas.

Possible mating wounds
Male sharks presumably bite females to encourage cooperation during courtship, signal intent, stimulate ovulation, or stay in close contact during copulation (Springer 1967, Stevens 1974, Tricas & Le Feuvre 1985, Maruska et al. 1996, Pratt & Carrier 2001, Conrath & Musick 2012. We ob -served apparent mating wounds on females from the gill slits to the flank, including the pectoral fin base (Pratt & Carrier 2001), where mating wounds are also seen on other species (e.g. silky shark; Whitehead et al. 2022). We saw mating wounds on most females at CI in July (n = 2 of 3, or 3 of 4 depending on how many unique individuals were observed), but saw mating wounds on almost no females at CI in April−May (n = 1 of 127), suggesting that mating behavior does not generally occur in the weeks to months prior to our annual April−May expeditions. However, we have not sampled at CI in those months; thus, although we find it unlikely, it is possible that mating occasionally occurs at CI earlier in the year.

Male plasma T concentrations
Circulating T levels in male carcharhiniform sharks increase during sexual maturation (Rasmussen & Gruber 1993, Gelsleichter et al. 2002, then undergo cyclical patterns in relation to reproductive stage (Manire & Rasmussen 1997, Hoffmayer et al. 2010, Brown et al. 2020, Gonzalez De Acevedo et al. 2020). Generally, plasma T concentrations appear to be greatest in male carcha rhinids and sphyrnids during mid-to late spermatogenesis, then decline precipitously during and after the copulatory period, reaching their nadir during periods of reproductive inactivity (Manire & Rasmussen 1997, Hoffmayer et al. 2010, Brown et al. 2020, Gonzalez De Acevedo et al. 2020. It is noteworthy that peak plasma T concentrations in mature male sharks actively undergoing spermatogenesis can often be 5 to 10 times the levels observed in reproductively inactive mature males (Manire & Rasmussen 1997, Gelsleichter et al. 2002, Hoffmayer et al. 2010, Brown et al. 2020, Gonzalez De Acevedo et al. 2020, which generally have plasma T concentrations that are comparable to, if not indistinguishable from, those in immature males (Gelsleichter et al. 2002). For mature male oceanic whitetip sharks, plasma T concentrations suggest that spermatogenesis is occurring in April−May, when T concentrations are high (approximately 6fold greater than in the immature male), and that the copulatory period is underway or has just ended in July, when T concentrations are low. This is consistent with the declines generally reported in other male carcharhinids at that point in the reproductive cycle; mature male finetooth sharks, for example, had comparable declines in plasma T concentrations when mature females in the same population exhibited fresh mating wounds and the earliest signs of pregnancy (i.e. uterine eggs bearing blastodisc-stage embryos; Brown et al. 2020). At the very least, despite a low sample size, our data suggest that a change in reproductive activity occurs in some mature male oceanic whitetip sharks between April− May and July.

Observations of putative mating behavior
Mating behaviors are poorly described for pelagic sharks and documented for only a few obligateswimming species, some of which have been observed copulating (e.g. white shark Carcharodon carcharias, blacktip reef shark, silky shark, scalloped hammerhead; Johnson & Nelson 1978, Klimley 1985, Francis 1996, McCauley et al. 2010, Clarke et al. 2013, Salinas-De-León et al. 2017. Our observations, like those for basking sharks (Harvey-Clark et al. 1999, Sims et al. 2000, Wilson 2004, Gore et al. 2019, were limited to what we interpret to be pre-copulatory, pre-courtship, or courtship behaviors (Pratt & Carrier 2001), such as close-following, nosing, avoidance, and stalling.
Courtship in sharks and rays is likely initiated by a combination of olfactory and visual behavioral cues from receptive, mature females, although males sometimes initiate as well (Pratt et al. 2005). Females may secrete sex-attractant substances (i.e. pheromones) that signal to males a readiness to mate (Demski 1990, Kajiura et al. 2000, which could explain the 'following' and 'nosing' behaviors of the male oceanic whitetip shark (Myrberg & Gruber 1974, Johnson & Nelson 1978, Klimley 1980, Gordon 1993, Harvey-Clark et al. 1999, Pratt & Carrier 2001, Parsons et al. 2008. The male oceanic whitetip shark also engaged in variations of 'following', such as echelon swimming and close-swimming (Clark 1963, Klimley 1980, Carrier et al. 1994, Gore et al. 2019). Variations of 'following' have been observed in a mating context across multiple elasmobranch orders, in cluding Orectolobiformes (e.g. nurse shark, Klimley 1980, Carrier et al. 1994, Carcharhiniformes (e.g. lemon shark Negaprion brevirostris ;Clark 1963), Lamniformes (e.g. basking shark;Harvey-Clark et al. 1999, Wilson 2004, Sims et al. 2000, and Myliobatiformes (e.g. giant manta ray Manta birostris; Yano et al. 1999, McCallister et al. 2020. We identified a variation of following behavior where the male did a 'circle-back' to reposition himself behind the female, possibly to reorient to the female's attractive olfactory cues. This behavior resembled a 'turn-back' described in captive bonnethead sharks, where large males selectively turned back on large females as they passed (Myrberg & Gruber 1974). It also resembled the behaviors of great hammerheads Sphyrna mokarran and tiger sharks Galeocerdo cuvier at established shark feeding sites, where animals follow a scent trail towards fish carcasses presented by a feeder. Instead of remaining in the immediate vicinity of the carcasses, they may feed and then circle back to pick up the scent trail repeatedly (S. Williams pers. obs.). At times, the male oceanic whitetip shark passed in front of the female during circle-backs, which could be related to the male signaling its intent or perhaps displaying the claspers as its only obvious secondary sexual characteristic (Parsons et al. 2008). Following behaviors may also serve a social function in same-sex groups (Myrberg & Gruber 1974, Johnson & Nelson 1978, Bres 1993, Gallagher et al. 2014) and may increase foraging efficiency for filter feeders (Gore et al. 2019). Female sharks often avoid males, which may facilitate female choice or reflect the aggressive nature and associated energetic cost of mating that can result in serious injury or mortality (Pratt & Carrier 2001, Pratt et al. 2005, Daly-Engel et al. 2010. Female avoidance behavior can include shielding, arching, or rolling away from a male to limit access to the fins or cloaca (Pratt & Carrier 2001, Whitney et al. 2004, Conrath & Musick 2012. Here, the female avoided the male by shielding and, during male bite attempts, shaking vigorously to prevent the male from grasping its flank. The female's avoidance behaviors prevented copulation during our observations, but the presence of deeper lacerations consistent with mating wounds suggested that the female had recently been bitten with more force and possibly copulated. Although the female regularly avoided the male, it did demonstrate some 'acceptance' behaviors, such as parallel or echelon swimming and tolerance of the male's repeated approach (Pratt & Carrier 2001). The female also appeared to 'stall', which has been interpreted in sand tiger sharks Carcharias taurus as signaling a readiness to mate (Gordon 1993, Parsons et al. 2008. Receptive female sharks may also raise the caudal fin while a male is 'nosing' or 'close-following', as seen in blacktip reef sharks (Johnson & Nelson 1978), or flare or cup the pelvic fins to allow the male to bite and copulate, as seen in nurse sharks (Carrier et al. 1994, Pratt & Carrier 2001), but we did not observe these behaviors.

Conclusions
Based on these 3 lines of evidence (i.e. mating wounds, male plasma T concentrations, and observed precopulatory behaviors), and because most females in April−May at CI are gravid with what appear to be late-stage embryos (Madigan et al. 2015) developed during 9−12 mo of gestation (Backus et al. 1956, Bonfil et al. 2008, Tambourgi et al. 2013, we hypothesize that mating occurs in the summer in the eastern Bahamas. Limited satellite telemetry data support this hypothesis: nearly all female oceanic whitetip sharks tagged at CI in early May (n = 9) remain within the eastern-central Bahamas (~500 km area) for around 30 d posttagging (i.e. into June), with over half of all tagged animals remaining until July, and some remaining throughout the entire summer (Howey-Jordan et al. 2013). This leaves a sufficient window for oceanic whitetip sharks to mate as early as May through October, when mating may be triggered by rising sea surface temperatures in the region (Pratt & Carrier 2001, Gordon 1993. The timing of this proposed mating period aligns with previous research in the western North Atlantic Ocean (Backus et al. 1956, Ruiz-Abierno et al. 2021.
Additional observations and hormone data collected year-round are needed to comprehensively determine the seasonal use of CI by oceanic whitetip sharks and clarify the species' reproductive cycle. Studying the CI aggregation from June to October may provide more evidence of mating from apparent courtship scars or wounds, a shift in demographics towards more males and non-gravid females, or direct observations of copulation. Ultimately, CI may be an important foraging ground for oceanic whitetip sharks (Madigan et al. 2015), leading substantial numbers of this wide-ranging species to exhibit seasonal residency and site fidelity to this location (Howey-Jordan et al. 2013, Madigan et al. 2015. Abundant food resources may drive oceanic whitetip shark densities high enough to facilitate male− female interactions and mating, similar to dense zooplankton prey aggregating basking sharks in oceanic fronts, where courtship behaviors then occur (Sims et al. 2000). Other areas in the eastern Bahamas, such as sites where biophysical coupling (e.g. current−bathymetric interactions) leads to productivity hotspots (Hazen et al. 2013, Gove et al. 2016, may provide oceanic whitetip sharks with similar reproductive opportunities. Management efforts at the national, regional, and global levels present a multi-pronged framework for the recovery of the oceanic whitetip shark (Young & Carlson 2020). However, such management efforts may be compromised without an improved understanding of the species' reproductive ecology, including the timing and location of mating and parturition. We build on previous research documenting the importance of CI (Howey-Jordan et al. 2013, Madigan et al. 2015 to the oceanic whitetip shark in the western Atlantic Ocean (Camargo et al. 2016) by showing that CI may be a mating habitat in summer. This new understanding highlights the value of Bahamian shark conservation efforts, particularly the ban on longline fishing in 1993 and ban on shark fishing in 2011 (Fisheries Resources [Jurisdiction and Conservation] Act, Government of The Bahamas), in preventing shark fishing in potentially critical habitats prior to their recognition.