Joint United States-Brazil Billfish Research in the Western South Atlantic

A joint research project between Brazilian and U.S. scientists was initiated in 2004 to investigate the interaction of istiophorid billfishes with pelagic longline fisheries in the western equatorial South Atlantic Ocean. This project incorporates two general themes (1) an investigation into several aspects of pelagic longline operations by comparing catch results between circle and “J” style hooks, time-of-capture with hook time recorders, and by direct monitoring of pelagic longline gear behavior, and (2) an additional evaluation of billfish trophic ecology using a combination of satellite tag technology and traditional analyses (e.g., gut contents and ageing). Data obtained from this research will provide additional data for the evaluation of habitat-based stock assessment modeling efforts for billfish and other pelagic fish species

Fishing Gear Modifications to Reduce Elasmobranch Mortality in Pelagic and Bottom Longline Fisheries Off Northeast Brazil

One of the biggest challenges of fisheries research is reducing the bycatch of unwanted species. The incidental fishing mortality of species with low reproductive rates, such as elasmobranchs (sharks, skates, and rays), is recognized as a key threat for their populations. In the present study, gear modifications related to the type of hook and position of the hook in the water column were tested to examine their effects on catch rates and mortality of elasmobranch species in both pelagic and coastal environments. Comparisons between circle (size 18/0, 0° offset) and J-style (size 9/0, 10° offset) hooks demonstrated that the circle hooks have a greater efficiency in reducing the mortality of most species caught, both in pelagic and coastal longline fisheries. Internal lodging of the hook was significantly less frequent for the individuals caught with circle hooks, which likely contributed to their higher survival rate at haulback. Additionally, circle hooks also increased the CPUE of elasmobranchs caught in the pelagic longline fishery, which was particularly evident for Carcharhinus falciformis and Prionace glauca. The position of the hook in the water column exhibited a strong influence on the species caught in the coastal bottom longline fishery. Suspending hooks in the middle of the water column reduced the bycatch of common demersal species, such as Carcharhinus acronotus, Ginglymostoma cirratum, and Dasyatis americana, while increasing the CPUE of potentially aggressive species, such as Galeocerdo cuvier and Carcharhinus leucas. The interaction of the type of hook utilized with its position in the water column appears to be an essential factor in the optimization of longline selectivity and minimization of bycatch mortality

Preliminary Results of Circle and J-Style Hook Comparisons in the Brazilian Pelagic Longline Fishery

Preliminary studies in western North Atlantic pelagic longline fisheries indicate that a change in terminal gear from J-style hooks to circle hooks may reduce bycatch mortality. However, such studies have not examined the impact of this change in the equatorial fishery. Catch composition, catch rates, hooking location, and condition at haulback were monitored during 26 sets in the commercial longline fishery operating in the western equatorial South Atlantic where circle (size 18/0, non-offset) and J-style (size 9/0 and 10/0, 10° offset) hooks were deployed in an alternating fashion. Catch rates for yellowfin tuna, swordfish, and a composite “all fishes” category were significantly (P \u3c 0.05) higher for circle hooks. Bigeye tuna, swordfish, sailfish, and yellowfin tuna were hooked significantly more often externally than internally. Yellowfin tuna were over eight times more likely to be hooked in the mouth with circle hooks than with J-style hooks. Bigeye tuna and sailfish showed significantly higher rates of survival at haulback with circle hooks. The results suggest that the use of size 18/0 non-offset circle hooks in the equatorial pelagic longline fishery may increase the survival of bycatch species at haulback with minimal detrimental effects on the catches of target species

Comparative Population Genetics and Evolutionary History of Two Commonly Misidentified Billfishes of Management and Conservation Concern

Background: Misidentifications between exploited species may lead to inaccuracies in population assessments, with potentially irreversible conservation ramifications if overexploitation of either species is occurring. A notable showcase is provided by the realization that the roundscale spearfish (Tetrapturus georgii), a recently validated species, has been historically misidentified as the morphologically very similar and severely overfished white marlin (Kajikia albida) (IUCN listing: Vulnerable). In effect, no information exists on the population status and evolutionary history of the enigmatic roundscale spearfish, a large, highly vagile and broadly distributed pelagic species. We provide the first population genetic evaluation of the roundscale spearfish, utilizing nuclear microsatellite and mitochondrial DNA sequence markers. Furthermore, we re-evaluated existing white marlin mitochondrial genetic data and present our findings in a comparative context to the roundscale spearfish. Results: Microsatellite and mitochondrial (control region) DNA markers provided mixed evidence for roundscale spearfish population differentiation between the western north and south Atlantic regions, depending on marker-statistical analysis combination used. Mitochondrial DNA analyses provided strong signals of historical population growth for both white marlin and roundscale spearfish, but higher genetic diversity and effective female population size (1.5-1.9X) for white marlin. Conclusions: The equivocal indications of roundscale spearfish population structure, combined with a smaller effective female population size compared to the white marlin, already a species of concern, suggests that a species-specific and precautionary management strategy recognizing two management units is prudent for this newly validated billfish

Regional movements of the tiger shark, Galeocerdo cuvier, off northeastern Brazil: inferences regarding shark attack hazard

An abnormally high shark attack rate verified off Recife could be related to migratory behavior of tiger sharks. This situation started after the construction of the Suape port to the south of Recife. A previous study suggested that attacking sharks could be following northward currents and that they were being attracted shoreward by approaching vessels. In this scenario, such northward movement pattern could imply a higher probability of sharks accessing the littoral area of Recife after leaving Suape. Pop-up satellite archival taus were deployed on five tiger sharks caught off Recife to assess their movement patterns off northeastern Brazil. All tags transmitted from northward latitudes after 7-74 days of freedom. The shorter, soak distance between deployment and pop-up locations ranged between 33-209 km and implied minimum average speeds of 0.02-0.98 km.h(-1). Both pop-up locations and depth data suggest that tiger shark movements were conducted mostly over the continental shelf. The smaller sharks moved to deeper waters within 24 hours after releasing, but they assumed a shallower (< 50 m) vertical distribution for most of the monitoring period. While presenting the first data on tiger shark movements in the South Atlantic, this study also adds new information for the reasoning of the high shark attack rate verified in this region,State Government of Pernambuco and Petrobras (Brazil); Fundacao para a Ciencia e Tecnologia (Portugal) [MCTES/FCT/SFRH/BD/37065/2007

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

Influences of type and orientation of bait on catches of swordfish (Xiphias gladius) and other species in an artisanal sub-surface longline fishery off northeastern Brazil

Two experiments were done to examine the relative effectiveness of squid and mackerel as bait for artisanal longliners operating off the northeast coast of Brazil. In experiment 1, compared to clusters of hooks baited with vertically orientated squid, those with vertically orientated mackerel (attached to hooks according to normal commercial operations) showed significantly more contact by fish and had less bait remaining at the end of each set, but retained significantly less total fish by weight and fewer swordfish. Significantly more swordfish swallowed hooks baited with vertically orientated squid, than those with vertically orientated mackerel and showed greater mortality. In experiment 2, clusters of hooks baited with horizontally orientated mackerel had significantly greater contact by fish and less bait remaining than those baited with vertically orientated squid. No other significant differences were detected between baits. Type of bait showed no significant effect on anatomical hook location and mortality for total catch (all species combined) and swordfish. The results are discussed in terms of possible factors influencing behaviour of fish during the hooking process and the importance of the visual stimuli of baits for subsurface longlines

Catches of Pelagic Sharks by Subsurface Longline Fisheries in the South Atlantic Ocean during the Last Century: A Review of Available Data with Emphasis on Uruguay and Brazil

Pelagic sharks are typically discarded as bycatch in subsurface longline fisheries in the South Atlantic Ocean. During the last 40 years of the 20th century, despite considerable fishing effort involving subsurface longline fleets from more than seven countries, there were few available data describing catch rates and relative abundances and distributions of the species caught. The majority of information came from small-scale longline fleets operating out of Brazil and Uruguay, where sharks historically have been landed and sold in local markets. This review shows that most of the large-scale temporal fluctuations in catch per unit of effort (numbers or weights of fish caught per 1,000 hooks per year) in these small-scale fisheries can be attributed to market-oriented factors (reflecting variabilities in consumer demand for various species) and the discovery of new fishing grounds. Toward the end of the century, gear-related changes also appear to have had an impact on catch rates. The lack of data precludes analyses of smaller-scale temporal and spatial trends in catches and relative abundances for nearly all species, except the blue shark (Prionace glauca). The available data indicate that such trends in the southwestern Atlantic Ocean can be largely attributed to movements associated with reproduction. We propose that the future effective management of pelagic sharks in the South Atlantic would be facilitated by implementation of more rigorous methods of obtaining information on catches and biological parameters for the key species, as well as an examination of the factors influencing gear selectivity

Global-Scale Genetic Population Structure and Diversity in the Oceanic Whitetip Shark, Carcharhinus longimanus

The oceanic whitetip, Carcharhinus longimanus, is a circumtropical, pelagic shark of high conservation concern (IUCN Red List: Critically Endangered in the W North and W Central Atlantic and Vulnerable globally). We present an updated assessment of the global population structure, genetic diversity, and demographic history of this shark based on analysis of two mitochondrial genome regions (whole control region and partial NADH dehydrogenase subunit 4 (ND4) gene) and nine nuclear microsatellite loci. No population differentiation was detected between the north and south Atlantic. However, significant structure was consistently detected between the Western Atlantic and Indo-Pacific Oceans across both mitochondrial and nuclear markers. This population structure was coupled with deep geographic mitochondrial haplotype mixing and evidence of contemporary migration between the Western Atlantic and Indo-Pacific Oceans. We theorize that semi-permeable thermal barriers are responsible for the differentiation between the Western Atlantic and Indo-Pacific. Additionally, a signal of matrilineal structure between the Indian and the Pacific Oceans was detected with AMOVA and pairwise analyses of the ND4 gene (pairwise ΦST = 0.051, P = 0.046; pairwise Jost\u27s D = 0.311, 95% CI = 0.020, 0.061). Relatively low mtDNA genetic diversity (concatenated mtCR-ND4: π = 0.32% ± 0.17%) compared to other globally distributed elasmobranch species raises concern for the future genetic health of these populations. Overall, despite the global distribution and high mobility of C. longimanus, significant population structure exists between the Western Atlantic and Indo-Pacific Oceans, and effective management strategies must take this into consideration

Effects of the Pleistocene on the Mitochondrial Population Genetic Structure and Demographic History of the Silky Shark (Carcharhinus falciformis) 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