Reproductive biology of the white marlin (Kajikia albida) in the southwestern and equatorial Atlantic Ocean

The present work describes the reproductive biology of the white marlin (Kajikia albida) caught in the southwestern and equatorial Atlantic Ocean. The gonads of 924 fish were collected by observers on board Brazilian tuna longliners, between November 2004 and December 2006. The spawning season was assessed by the monthly frequency distribution of distinct stages of maturity and monthly mean female gonadosomatic index GSI. Sixty-one percent (n = 656) of the fish examined were female, with a Lower Jaw Fork Length (LJFL) between 83 and 236 cm (mean = 155.5 ± 16.63). The 268 males had a LJFL between 90 and 220 cm (mean = 152.3 ± 34.62). Although the northeastern region of Brazil does not appear to be a significant spawning area for the species, the results suggest a higher reproductive activity in the third quarter of the year. Using a Bayesian logistic model approach, length at 50% maturity was estimated at 145.04 cm (credibility interval of 95%, 143.94–146.09 cm), for females, and at 140.03 cm (credibility interval of 95%, 137.28–142.52 cm), for males.     

Fish biodiversity of Saint Peter and Saint Paulʼs Archipelago,Mid-Atlantic Ridge,Brazil: new records and a species database

Saint Peter and Saint Paul's Archipelago (SPSPA), one of the smallest and most isolated island groups in the world, is situated on the Mid-Atlantic Ridge, between Brazil and the African continent. SPSPA has low species richness and high endemism; nonetheless, the diversity of fishes from deep habitats (>30 m depth) had not been previously studied in detail. Several expeditions conducted between 2009 and 2018 explored the shallow and deep reefs of SPSPA using scuba, closed-circuit rebreathers, manned submersibles, baited remote underwater stereo-videos (stereo-BRUV) and fishing between 0 and 1050 m depth. These expeditions yielded 41 new records of fishes for SPSPA: 9 in open waters, 9 in shallow waters (0–30 m), 8 in mesophotic ecosystems (30–150 m) and 15 in deeper reefs (>150 m). Combined with literature records of adult pelagic, shallow and deep-reef species, as well as larvae, the database of the fish biodiversity for SPSPA currently comprises 225 species (169 recorded as adult fishes and 79 as larvae, with 23 species found in both stages). Most of them (112) are pelagic, 86 are reef-associated species and 27 are deep-water specialists. Species accumulation curves show that the number of fish species has not yet reached an asymptote. Whereas the number of species recorded in SPSPA is similar to that in other oceanic islands in the Atlantic Ocean, the proportion of shorefishes is relatively lower, and the endemism level is the third highest in the Atlantic. Twenty-nine species are listed as threatened with extinction. Observations confirm the paucity of top predators on shallow rocky reefs of the island, despite the presence of several pelagic shark species around SPSPA. Because all of the endemic species are reef associated, it is argued that the new marine-protected areas created by the Brazilian government do not ensure the protection and recovery of SPSPA's biodiversity because they allow exploitation of the most vulnerable species around the archipelago itself. This study suggests a ban on reef fish exploitation inside an area delimited by the 1000 m isobath around the islands (where all known endemics are concentrated) as the main conservation strategy to be included in the SPSPA management plan being prepared by the Brazilian government.     

Diet composition of bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) caught on aggregated schools in the western equatorial Atlantic Ocean

The present study aims to characterize and compare the diet of bigeye and yellowfin tunas caught on aggregated schools in the western equatorial Atlantic Ocean. The samples were collected from January 2011 to June 2016. The tunas were measured on board and the stomachs were removed after evisceration. The stomachs were analyzed regarding their Index of Fullness and the importance of each prey in the diet was estimated by the Index of Relative Importance (IRI). The diet overlap was assessed by the Morisita‐Horn's Index, Non‐Metric Multidimensional Scale (NMDS), and Analysis of Similarity (ANOSIM). The feeding strategy was determined by the Costello's Diagram. The 195 bigeye and 212 yellowfin tunas ranged in fork length from 51 to 137 cm and 43 to 174 cm, respectively. The diet of bigeye tuna was composed of 10 families of fish, three cephalopod families, and four crustacean orders. The diet of yellowfin tuna was composed of 11 families of fish, three cephalopod families, and three crustacean orders. The yellowfin tuna seems to feed upon more abundant prey species near the surface like flying fish, which have the concentration enhanced by the light attractors on the boat, and occasionally on other prey from deeper habitats like lanternfish, squids, and pomfret. Bigeye tuna feed mainly at prey that commonly occurs in deeper habitats like squids, drift fish, lanternfish, and pomfret.     

Full-length L1CAM and not its Δ2Δ27 splice variant promotes metastasis through induction of gelatinase expression

Tumour-specific splicing is known to contribute to cancer progression. In the case of the L1 cell adhesion molecule (L1CAM), which is expressed in many human tumours and often linked to bad prognosis, alternative splicing results in a full-length form (FL-L1CAM) and a splice variant lacking exons 2 and 27 (SV-L1CAM). It has not been elucidated so far whether SV-L1CAM, classically considered as tumour-associated, or whether FL-L1CAM is the metastasis-promoting isoform. Here, we show that both variants were expressed in human ovarian carcinoma and that exposure of tumour cells to pro-metastatic factors led to an exclusive increase of FL-L1CAM expression. Selective overexpression of one isoform in different tumour cells revealed that only FL-L1CAM promoted experimental lung and/or liver metastasis in mice. In addition, metastasis formation upon up-regulation of FL-L1CAM correlated with increased invasive potential and elevated Matrix metalloproteinase (MMP)-2 and -9 expression and activity in vitro as well as enhanced gelatinolytic activity in vivo. In conclusion, we identified FL-L1CAM as the metastasis-promoting isoform, thereby exemplifying that high expression of a so-called tumour-associated variant, here SV-L1CAM, is not per se equivalent to a decisive role of this isoform in tumour progression.     

Reproduction in Bagre marinus (Ariidae) off Pernambuco, northeastern Brazil

Throughout 1997, the catches of artisanal gillnetters working off the coast of northeastern Brazil were sampled monthly for Bagre marinus (Mitchill 1815). Significantly more females (n = 207) than males (n = 82) were caught, although there was no significant difference in their size compositions (21–47 cm fork length, FL). All males sampled (21–40 cm FL) had developed gonads and were classified as sexually mature. According to macroscopic and microscopic examination of their reproductive tract, females were separated into four reproductive stages (immature, maturing, mature, and resting). Size at 50% sexual maturity for females was estimated to be 33 cm FL. A positive linear relationship was detected between the size of mature females and their fecundity (between 11 and 32 oocytes). Clear reproductive progress indicated a spawning period between March and May. We conclude that further fishery‐independent data are required to determine patterns of male abundances and distributions.     

Cookie‐cutter shark Isistius spp. predation upon different tuna species from the south‐western Atlantic Ocean

The predation of cookie‐cutter sharks Isistius spp. upon the early life stages of yellowfin tuna Thunnus albacares, skipjack tuna Katsuwonus pelamis and little tunny Euthynnus alletteratus are described. New evidence suggesting a connection between commercial fishing and predation by Isistius sp. is presented, with these sharks biting tunas hooked in surface waters during daylight. The healing patterns of the wounds made by the sharks are described in detail and, although such damage is known to negatively influence market price elsewhere, it is not the case on the south‐east Brazilian coast.     

Effects of the Pleistocene on the mitochondrial population genetic structure and demographic history of the silky shark (<Emphasis Type="Italic">Carcharhinus falciformis</Emphasis>) in the western Atlantic Ocean

The silky shark, Carcharhinus falciformis, is a large-bodied, oceanic-coastal, epipelagic species found worldwide in tropical and subtropical waters. Despite its commercial importance, concerns about overexploitation, and likely ecological significance of this shark as an upper trophic-level predator, understanding of its population dynamics remains unclear for large parts of its distribution. We investigated the genetic diversity, population structure and demographic history of the silky shark along the western Atlantic Ocean based on the use of 707 bp of the mitochondrial DNA control region (mtCR). A total of 211 silky sharks were sampled, originating from five areas along the western Atlantic Ocean. The mitochondrial sequences revealed 40 haplotypes, with overall haplotype and nucleotide diversities of 0.88 (± 0.012) and 0.005 (± 0.003), respectively. The overall population structure was significantly different among the five western Atlantic Ocean regions. Phylogenetic analysis of mtCR sequences from globally sourced silky shark samples revealed two lineages, comprising a western Atlantic lineage and western Atlantic—Indo-Pacific lineage that diverged during the Pleistocene Epoch. In general, tests for the demographic history of silky sharks supported a population expansion for both the global sample set and the two lineages. Although our results showed that silky sharks have high genetic diversity, the current high level of overexploitation of this species requires long-term, scientifically informed management efforts. We recommend that fishery management and conservation plans be done separately for the two western Atlantic matrilineal populations revealed here.     

Vulnerability to longline fisheries of three hammerhead shark Sphyrna species in the south‐western and equatorial Atlantic Ocean

Catch and effort data from 29 418 longline sets from Brazilian tuna longline vessels operating in the south‐western and equatorial Atlantic Ocean between 2004 and 2011 were analysed to investigate the distribution, catch rate and size of three species of hammerhead sharks (Sphyrna lewini, Sphyrna mokarran and Sphyrna zygaena). During that period, 6172 hammerhead sharks were caught. Among the elasmobranchs, the highest percentage of hammerhead sharks were caught in 2007, when they accounted for 3·90% of the group, while the lowest value of 0·40% was recorded in 2010. In general, the spatial distribution of the mean catch per unit effort (CPUE) by years and quarters showed a trend of higher catches near the equatorial region and in southern Brazil. The nominal mean CPUE was 0·12 Sphyrna spp. 1000⁻¹ hooks, with the highest value being recorded in 2007 (0·30 Sphyrna spp. 1000⁻¹ hooks). The standardized yearly CPUE estimated by a generalized linear model assuming a zero inflated negative binomial (ZINB) distribution were not much different from nominal values. Of the 205 sexed specimens, 117 were females and 88 were males, resulting in a sex ratio with a predominance of females (1·30:1·00), although not statistically significant. The total length of females ranged from 1200 to 2800 mm and of males from 1100 to 3100 mm. Juvenile hammerhead sharks represented 82 and 54% of the sexed female and male specimens, respectively.     

Vulnerability of the Oceanic Whitetip Shark to Pelagic Longline Fisheries

A combination of fisheries dependent and independent data was used to assess the vulnerability of the oceanic whitetip shark to pelagic longline fisheries. The Brazilian tuna longline fleet, operating in the equatorial and southwestern Atlantic, is used as a case study. Fisheries dependent data include information from logbooks (from 1999 to 2011) and on-board observers (2004 to 2010), totaling 65,277 pelagic longline sets. Fisheries independent data were obtained from 8 oceanic whitetip sharks tagged with pop-up satellite archival tags in the area where longline fleet operated. Deployment periods varied from 60 to 178 days between 2010 and 2012. Tagging and pop-up sites were relatively close to each other, although individuals tended to travel long distances before returning to the tagging area. Some degree of site fidelity was observed. High utilization hotspots of tagged sharks fell inside the area under strongest fishing pressure. Despite the small sample size, a positive correlation between tag recorded information and catch data was detected. All sharks exhibited a strong preference for the warm and shallow waters of the mixed layer, spending on average more than 70% of the time above the thermocline and 95% above 120 m. Results indicate that the removal of shallow hooks on longline gear might be an efficient mitigation measure to reduce the bycatch of this pelagic shark species. The work also highlights the potential of tagging experiments to provide essential information for the development of spatio-temporal management measures.